149 Sentences With "thermohaline circulation"

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Data-transmitting devices confirmed the pollution is flowing toward the pole via the "thermohaline circulation," a current that's known as the global ocean conveyer belt.
This particular part of the ocean is important in the thermohaline circulation, a deepwater global current dictated by differences in temperature and salinity around the world.
These currents are propelled by a phenomenon called thermohaline circulation that depends, as its name suggests, on the salinity and temperature of seawater, and thus its density.
This current is also referred to as a global conveyor belt or global thermohaline circulation, carrying heat and oxygen from the bottom of the world to the far north, and back again.
A summary of the path of the thermohaline circulation. Blue paths represent deep-water currents, while red paths represent surface currents. Thermohaline circulation Thermohaline circulation (THC) is a part of the large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes. The adjective thermohaline derives from thermo- referring to temperature and ' referring to salt content, factors which together determine the density of sea water.
Thermohaline circulation or Oceanic conveyor belt illustrated Another possibility is that there was a slowing of thermohaline circulation. The circulation could have been interrupted by the introduction of a large amount of fresh water into the North Atlantic, possibly caused by a period of warming before the Little Ice Age known as the Medieval Warm Period. There is some concern that a shutdown of thermohaline circulation could happen again as a result of the present warming period.
Surface heat and freshwater fluxes create global density gradients that drive the thermohaline circulation part of large-scale ocean circulation. It plays an important role in supplying heat to the polar regions, and thus in sea ice regulation. Changes in the thermohaline circulation are thought to have significant impacts on Earth's energy budget. In so far as the thermohaline circulation governs the rate at which deep waters reach the surface, it may also significantly influence atmospheric carbon dioxide concentrations.
Diagram of the major ocean currents, showing the Antarctic Circumpolar Current (ACC). In addition to the global thermohaline circulation, the ACC strongly influences regional and global climate. Global thermohaline circulation strongly influences regional and global climate. Blue paths represent deep-water currents, while red paths represent surface currents.
Due to global warming and increased glacier melt, thermohaline circulation patterns may be altered by increasing amounts of freshwater released into oceans and, therefore, changing ocean salinity. Thermohaline circulation is responsible for bringing up cold, nutrient-rich water from the depths of the ocean, a process known as upwelling.
The modern thermohaline circulation is thus more controlled by density contrasts due to thermal differences, whereas during the LGM the oceans were more than twice as sensitive to differences in salinity rather than temperature. In this way, the thermohaline circulation can be considered to have been less "thermo" and more "haline".
Contourite deposition is active in many locations throughout the world, but particularly in areas affected by the thermohaline circulation.
For a discussion of the possibilities of changes to the thermohaline circulation under global warming, see shutdown of thermohaline circulation. The Antarctic Circumpolar Current encircles that continent, influencing the area's climate and connecting currents in several oceans. One of the most dramatic forms of weather occurs over the oceans: tropical cyclones (also called "typhoons" and "hurricanes" depending upon where the system forms).
First, the outburst from Lake Agassiz during the Preboreal Oscillation flooded into the Arctic, instead of the North Atlantic Ocean as during the Younger Dryas. Also, as the period leading up to the Preboreal Oscillation was interstadial to interglacial, the thermohaline circulation would have been more stable than during the Younger Dryas. Finally, the North Atlantic thermohaline circulation was not being pre-conditioned preceding the Preboreal Oscillation, as meltwater from Lake Agassiz was not being routed to the Gulf of Mexico.
For example, alterations to ocean processes such as thermohaline circulation play a key role in redistributing heat in the world's oceans. Understanding internal variability helped scientists to attribute recent climate change to greenhouse gases.
Greene, C.H., et al. (2008) Arctic Climate Change and Its Impacts on the Ecology of the North Atlantic. Ecology 89, S24–S38Hátún, H., et al. (2005) Influence of the Atlantic subpolar gyre on the thermohaline circulation.
Small increases in freshwater fluxes have been shown to reduce the thermohaline circulation and in some cases could halt the production of North Atlantic Deep Water all together. One particular model allowed for a flux of 1 Sv of freshwater into high latitudes of the Atlantic Ocean for a period of 10 years, which resulted in a sudden drop of sea surface temperatures and a weaker thermohaline circulation. It was nearly 200 years before the ocean system returned to normal in this case. Another modeling study by the same research group indicated that if just 0.1 Sv of freshwater was added to high North Atlantic Ocean latitudes, sea surface temperatures could drop by as much as 6 °C in less than 100 years, also weakening the thermohaline circulation, albeit less so than with higher freshwater fluxes.
A schematic of modern thermohaline circulation. Tens of millions of years ago, continental-plate movement formed a land-free gap around Antarctica, allowing the formation of the ACC, which keeps warm waters away from Antarctica. The oceanic aspects of climate variability can generate variability on centennial timescales due to the ocean having hundreds of times more mass than in the atmosphere, and thus very high thermal inertia. For example, alterations to ocean processes such as thermohaline circulation play a key role in redistributing heat in the world's oceans.
It has been suggested that a shutdown of the Atlantic thermohaline circulation may result in relative cooling of the North Atlantic region by up to 8C in certain locations. Recent research suggests that this process is not currently underway.
Bower investigates ocean circulation, including thermohaline circulation (the so-called ocean conveyor belt), using research floats. She also goes on research cruises to retrieve the floats. Bower's research covers the Arctic Ocean and Gulf of Mexico, among other locations.
The ACC carries up to 150 Sverdrups (150 million cubic meters per second), equivalent to 150 times the volume of water flowing in all the world's rivers. The ACC and the global thermohaline circulation strongly influence regional and global climate as well as underwater biodiversity. Another factor that contributes to the climate of the subantarctic region, though to a much lesser extent than the thermohaline circulation, is the formation of Antarctic Bottom Water (ABW) by halothermal dynamics. The halothermal circulation is that portion of the global ocean circulation that is driven by global density gradients created by surface heat and evaporation.
Direct estimates of the strength of the thermohaline circulation have been made at 26.5°N in the North Atlantic since 2004 by the UK-US RAPID programme. By combining direct estimates of ocean transport using current meters and subsea cable measurements with estimates of the geostrophic current from temperature and salinity measurements, the RAPID programme provides continuous, full-depth, basinwide estimates of the thermohaline circulation or, more accurately, the meridional overturning circulation. The deep water masses that participate in the MOC have chemical, temperature and isotopic ratio signatures and can be traced, their flow rate calculated, and their age determined. These include 231Pa / 230Th ratios.
The thermohaline circulation plays an important role in supplying heat to the polar regions, and thus in regulating the amount of sea ice in these regions, although poleward heat transport outside the tropics is considerably larger in the atmosphere than in the ocean. Changes in the thermohaline circulation are thought to have significant impacts on the Earth's radiation budget. Large influxes of low-density meltwater from Lake Agassiz and deglaciation in North America are thought to have led to a shifting of deep water formation and subsidence in the extreme North Atlantic and caused the climate period in Europe known as the Younger Dryas.
Density-driven thermohaline circulation Energy for the ocean circulation (and for the atmospheric circulation) comes from solar radiation and gravitational energy from the sun and moon.Munk, W. and Wunsch, C., 1998: Abyssal recipes II: energetics of tidal and wind mixing. Deep-Sea Research Part I, 45, pp. 1977-- 2010.
The high surface salinity in the Atlantic, on which the Atlantic thermohaline circulation is dependent, is maintained by two processes: the Agulhas Leakage/Rings, which brings salty Indian Ocean waters into the South Atlantic, and the "Atmospheric Bridge", which evaporates subtropical Atlantic waters and exports it to the Pacific.
The Gulf Stream proper is a western-intensified current, driven largely by wind stress. (see also Rahmstorf.) The North Atlantic Drift, in contrast, is largely driven by thermohaline circulation. In 1958, oceanographer Henry Stommel noted that "very little water from the Gulf of Mexico is actually in the stream".Henry Stommel. (1958).
This realigned the thermohaline circulation in the Atlantic, increasing heat transport into the Arctic, which melted the polar ice accumulation and reduced other continental ice sheets. The release of water raised sea levels again, restoring the ingress of colder water from the Pacific with an accompanying shift to northern hemisphere ice accumulation.
Global Environ Chang 11, 261–269 Ecosystem services affected by dry land degradation usually include low biomass productivity, thus reducing provisioning and supporting services for agriculture and water cycling. Polar regions have been the focus on research examining the impacts of climate warming. Regime shifts in polar regions include the melting of the Greenland ice sheet and the possible collapse of the thermohaline circulation system. While the melting of the Greenland ice sheet is driven by global warming and threatens worldwide coastlines with an increase of sea level, the collapse of the thermohaline circulation is driven by the increase of fresh water in the North Atlantic which in turn weakens the density driven water transport between the tropics and polar areas.
That is to say, North Atlantic Deep Water formation could have periodically completely ceased, and the thermohaline circulation could have shut down. Basically, the thermohaline circulation refers to the circulation resulting from differences in ocean temperature and salinity. For example, a large portion of deep water is created in the Arctic as surface water adjacent to glaciers that is more dense than surrounding water (because it is influenced by recent cold melt water, cooled by evaporation from surface winds, and is saline) sinks to the deep ocean. However, if a large enough quantity of this water becomes less saline, deep ocean formation would be primarily through thermal differences, which tend to be less dominant than with the added effects of salinity.
Lake Agassiz did not exist long before the Younger Dryas cold period, so changes in the thermohaline circulation and climate before then would have probably been caused by re-routing of other North American drainage basins, possibly coupled with an influx of icebergs. However, the Younger Dryas cold period has been linked to flood water diversion from Lake Agassiz. Water that normally flowed through the Mississippi River to the Gulf of Mexico was re-routed into the Great Lakes and the St. Lawrence River about 12.8 ka calendar years ago. There is uncertainty as to whether this change was enough to trigger the Younger Dryas, but the runoff through the Mississippi River could have pre-conditioned the thermohaline circulation prior to the cold period and outburst.
A summary of the path of the thermohaline circulation. Blue paths represent deep-water currents, while red paths represent surface currents. Using rudimentary observation techniques, the circulation of the surface ocean can be determined. In the Atlantic basin, surface waters flow from the south towards the north in general, while also creating gyres in the northern and southern Atlantic.
Other climate determinants are more dynamic: the thermohaline circulation of the ocean leads to a 5 °C (9 °F) warming of the northern Atlantic Ocean compared to other ocean basins.Stefan Rahmstorf The Thermohaline Ocean Circulation: A Brief Fact Sheet. Retrieved on 2008-05-02. Other ocean currents redistribute heat between land and water on a more regional scale.
The closure of the seaway led to an increased poleward salt and heat transport, strengthening the North Atlantic thermohaline circulation 2.95–2.82 million years ago, in turn increasing moisture supply to Arctic latitudes, contributing to both Arctic continental glaciation and sea ice formation, and eventually—with the orbitally paced extension of Gelasian ice sheets—the Quaternary ice age.
A combination is also possible, e.g., sudden loss of albedo in the Arctic Ocean as sea ice melts, followed by more gradual thermal expansion of the water. Climate variability can also occur due to internal processes. Internal unforced processes often involve changes in the distribution of energy in the ocean and atmosphere, for instance, changes in the thermohaline circulation.
Deep ocean currents are driven by density and temperature gradients. This thermohaline circulation is also known as the ocean's conveyor belt. These currents, sometimes called submarine rivers, flow deep below the surface of the ocean and are hidden from immediate detection. Where significant vertical movement of ocean currents is observed, this is known as upwelling and downwelling.
The Macelwane Medal is presented to young scientists who has made significant contributions in the realm of geophysical sciences. Clement was nominated for this award because of her research in tropical atmospheric and ocean dynamics. In conducting this research, she focused on how the atmosphere and ocean interact with both orbital changes and the thermohaline circulation system.
When nutrients from the benthos cannot travel up into the photic zone, phytoplankton may be limited by nutrient availability. Lower primary production also leads to lower net productivity in waters. A large-scale circulation of horizontally stratified water masses, called the thermohaline circulation, occurs in the ocean. The entire circulation pattern takes around 2,000 years to complete.
Physical characteristics like weak thermohaline circulation in the North Pacific and the fact that it is mostly blocked by land in the north, also help facilitate this circulation. As depth increases, these gyres in the North Pacific grow smaller and weaker, and the high pressure at the center of the Subtropical Gyre will migrate poleward and westward.
Additionally, it has been found from a separate study that a freshwater flux of 0.53 Sv into the North Atlantic Ocean in the absence of an existing thermohaline circulation could reduce North Atlantic Deep Water production by 95% in about a century. Large fluxes such as this are capable of cooling the oceans and climate on a large scale. If freshwater fluxes into the Northern Atlantic Ocean were stopped once the North Atlantic Deep Water production had completely ceased, production did not begin again. The above modeling studies suggest that even if the fluxes during the major outburst events of Lake Agassiz occurred over longer time periods, thus being weaker in magnitude, they still would have possibly been sufficient to trigger a change in thermohaline circulation and climate change.
This feedback loop can become so strong that irreversible melting occurs. Marine ice sheet instability could trigger a tipping point in West Antarctica. Crossing either of these tipping points leads to accelerated global sea level rise. When fresh water gets released as a consequence of Greenland melting, a threshold may be crossed which leads to disruption of the thermohaline circulation.
The Weddell Sea is an important area of deep water mass formation through cabbeling, the main driving force of the thermohaline circulation. Deepwater masses are also formed through cabbeling in the North Atlantic and are caused by differences in temperature and salinity of the water. In the Weddell sea, this is brought about mainly by brine exclusion and wind cooling.
Global warming could, via a shutdown of the thermohaline circulation, trigger cooling in the North Atlantic, Europe, and North America.Shutdown Of Circulation Pattern Could Be Disastrous, Researchers Say, 20 December 2004, ScienceDaily This would particularly affect areas such as the British Isles, France and the Nordic countries, which are warmed by the North Atlantic drift. Major consequences, apart from regional cooling, could also include an increase in major floods and storms, a collapse of plankton stocks, warming or rainfall changes in the tropics or Alaska and Antarctica, more frequent and intense El Niño events due to associated shutdowns of the Kuroshio, Leeuwin, and East Australian Currents that are connected to the same thermohaline circulation as the Gulf Stream, or an oceanic anoxic event — oxygen () below surface levels of the stagnant oceans becomes completely depleted – a probable cause of past mass extinction events.
All reduced their seasonal predictions in early August, but even the revised predictions were too high. The lack of activity was primarily caused by an unexpected significant weakening of the Atlantic Ocean thermohaline circulation between winter and spring. This resulted in continuation of the spring weather pattern over the Atlantic Ocean, with strong vertical wind shear, mid-level moisture, and atmospheric stability, which suppressed tropical cyclogenesis.
Large amounts of carbon are exchanged each year between the ocean and the atmosphere. A major controlling factor in oceanic- atmospheric carbon exchange is thermohaline circulation. In regions of ocean upwelling, carbon-rich water from the deep ocean comes to the surface and releases carbon into the atmosphere as carbon dioxide. Large amounts of carbon dioxide are dissolved in cold water in higher latitudes.
Instead ocean deep water is formed in polar regions where cold salty waters sink in fairly restricted areas. This is the beginning of the thermohaline circulation. Oceanic currents are largely driven by the surface wind stress; hence the large-scale atmospheric circulation is important to understanding the ocean circulation. The Hadley circulation leads to Easterly winds in the tropics and Westerlies in mid-latitudes.
Additionally, changes in the ocean's thermohaline circulation (specifically slowing)Bryden, H. L., Longworth, H. R. and Cunningham, S. A. (2005). Slowing of the Atlantic meridional overturning circulation at 25° N. Nature, 438, 655-657. may act to decrease transport of dissolved CO2 into the deep ocean. However, the magnitude of these processes is still uncertain, preventing good long-term estimates of the fate of the solubility pump.
The thermohaline circulation transports heat northward which is important for temperature regulation in the Atlantic region. Risks for a complete shutdown are low to moderate under the Paris agreement levels of warming. Other examples of possible large scale tipping elements are a shift in El Niño–Southern Oscillation. After crossing a tipping point, the warm phase (El Niño) would start to occur more often.
Stratified waters, in combination with slow vertical mixing, are essential to maintaining euxinic conditions. Stratification occurs when two or more water masses with different densities occupy the same basin. While the less dense surface water can exchange gas with the oxygen-rich atmosphere, the denser bottom waters maintain low oxygen content. In the modern oceans, thermohaline circulation and upwelling prevent the oceans from maintaining anoxic bottom waters.
This array was deployed in March 2004 to continuously monitor the MOC and ocean heat transport that are primarily associated with the Thermohaline Circulation across the basin at 26°N. The RAPID-MOCHA array is planned to be continued through 2014 to provide a decade or longer continuous time series.Johns WE, Baringer MO, Beal LM, et al. 2011. Continuous, array-based estimates of Atlantic Ocean heat transport at 26.5°N.
The density of the water below the newly formed ice increases due to the brine rejection. Saltier water can also become colder without freezing. The dense waters that form in the Arctic are called North Atlantic Deep Waters (NADW), while the Antarctic Bottom Water (AABW) forms in the southern hemisphere. These two areas of brine rejection play an important role in the thermohaline circulation of all of earth's oceans.
BOINC has stopped distributing classic models in favour of sulfur cycle models. A more user friendly BOINC client and website called GridRepublic, which supports climateprediction and other BOINC projects, was released in beta in 2006. A thermohaline circulation slowdown experiment was launched in May 2004 under the classic framework to coincide with the film The Day After Tomorrow. This program can still be run but is no longer downloadable.
Among other things, Wyrtki is known for his work on understanding and forecasting El Nino. He established a tidal gauge network, gave an explanation for the Pacific oxygen minimum zone under the thermocline, and discovered the ocean current jet that now bears his name, the "Wyrtki Jet". "Klaus Wyrtki" The International Association for the Physical Sciences of the Oceans. He is also known for his work on thermohaline circulation.
Euxinic conditions have nearly vanished from Earth's open-ocean environments, but a few small scale examples still exist today. Many of these locations share common biogeochemical characteristics. For example, low rates of overturning and vertical mixing of the total water column is common in euxinic bodies of water. Small surface area to depth ratios allow multiple stable layers to form while limiting wind- driven overturning and thermohaline circulation.
2005 Tropical Eastern North Pacific Hurricane Outlook. . Retrieved May 2, 2006. Tropical cyclones also help maintain the global heat balance by moving warm, moist tropical air to the middle latitudes and polar regions, and by regulating the thermohaline circulation through upwelling. The storm surge and winds of hurricanes may be destructive to human-made structures, but they also stir up the waters of coastal estuaries, which are typically important fish breeding locales.
Annual snow cover has decreased, sea ice is declining and widespread melting of glaciers is underway. Thermal expansion and glacial retreat cause sea levels to increase. Retreat of ice mass may impact various geological processes as well, such as volcanism and earthquakes. Increased temperatures and other human interference with the climate system can lead to tipping points to be crossed such as the collapse of the thermohaline circulation or the Amazon rainforest.
It is thought that these outflow events, leading to the drawdown of Lake Agassiz, could have lasted as little as a few months to a few years. The implication of this is that the rate of outflow would have been extremely high, especially in comparison to values that have been found to be necessary for disruptions of the thermohaline circulation (~1 Sv over ten years, or 0.1 Sv over about a century).
On their journey, the water masses transport both energy (in the form of heat) and matter (solids, dissolved substances and gases) around the globe. As such, the state of the circulation has a large impact on the climate of the Earth. The thermohaline circulation is sometimes called the ocean conveyor belt, the great ocean conveyor, or the global conveyor belt. On occasion, it is imprecisely used to refer to the meridional overturning circulation, MOC.
The North Pacific subtropical fronts are occupied by wind driven submesoscale subduction. Due to the constant thermohaline circulation fronts, cold air flows near the surface and bottom of the ocean. There are alternating fluxes throughout the year, that is influenced by jet streams which causes temperatures in these areas to differ.Hosegood, P. J., M. C. Gregg, and M. H. Alford (2013), Wind-driven submesoscale subduction at the north Pacific subtropical front, J. Geophys. Res.
The sea ice cycle is also an important source of dense (saline) "bottom water". When sea water freezes it leaves most of its salt content behind. The remaining surface water, made dense by the extra salinity, sinks and produces dense water masses such as North Atlantic Deep Water. This production of dense water is essential in maintaining the thermohaline circulation, and the accurate representation of these processes is important in climate modelling.
Thermohaline circulation determines the relative ages of the water in these basins. Because organic material, such as fecal pellets from copepods, sink from the surface waters into deeper water, deep water masses tend to accumulate dissolved carbon dioxide as they age. The oldest water masses have the highest concentrations of and therefore the shallowest CCD. The CCD is relatively shallow in high latitudes with the exception of the North Atlantic and regions of Southern Ocean where downwelling occurs.
Though partially retired, Bryden remains active at the University of Southampton in both research and the wider scientific community. A particular focus of Bryden's research is the large-scale thermohaline circulation of the ocean, in particular its role in transporting heat. A decline in the strength of the Atlantic Meridional Overturning Circulation (AMOC) caused by global warming has been hypothesised, and Bryden and colleagues have studied this via the RAPID array that crosses the Atlantic at 26.5°N.
Downwelling is the process of accumulation and sinking of higher density material beneath lower density material, such as cold or saline water beneath warmer or fresher water or cold air beneath warm air. It is the sinking limb of a convection cell. Upwelling is the opposite process and together these two forces are responsible in the oceans for the thermohaline circulation. The sinking of cold lithosphere at subduction zones is another example of downwelling in plate tectonics.
Monsoons, seasonal changes in wind and precipitation that occur mostly in the tropics, form due to the fact that land masses heat up more easily than the ocean. The temperature difference induces a pressure difference between land and ocean, driving a steady wind. Ocean water that has more salt has a higher density and differences in density play an important role in ocean circulation. The thermohaline circulation transports heat from the tropics to the polar regions.
There is some speculation that global warming could, via a shutdown or slowdown of the thermohaline circulation, trigger localized cooling in the North Atlantic and lead to cooling, or lesser warming, in that region. This would affect in particular areas like Scandinavia and Britain that are warmed by the North Atlantic drift. The chances of this near-term collapse of the circulation, which was fictionally portrayed in the 2004 film Day After Tomorrow, are unclear. Lenton et al.
Sulfur aerosols, especially stratospheric sulfur aerosols have a significant effect on climate. One source of such aerosols is the sulfur cycle, where plankton release gases such as DMS which eventually becomes oxidised to sulfur dioxide in the atmosphere. Disruption to the oceans as a result of ocean acidification or disruptions to the thermohaline circulation may result in disruption of the sulfur cycle, thus reducing its cooling effect on the planet through the creation of stratospheric sulfur aerosols.
Extensive mixing therefore takes place between the ocean basins, reducing differences between them and making the Earth's oceans a global system. The water in these circuits transport both energy (in the form of heat) and mass (dissolved solids and gases) around the globe. As such, the state of the circulation has a large impact on the climate of the Earth. The thermohaline circulation is sometimes called the ocean conveyor belt, the great ocean conveyor, or the global conveyor belt.
The cold blob visible on NASA's global mean temperatures for 2015, the warmest year on record (since 1880) – colors indicate temperature anomalies (NASA/NOAA; 20 January 2016). The cold blob in the North Atlantic (also called the North Atlantic warming hole) describes a cold temperature anomaly of ocean surface waters, affecting the Atlantic Meridional Overturning Circulation (AMOC) which is part of the thermohaline circulation, possibly related to global warming-induced melting of the Greenland ice sheet.
See Thermohaline Circulation. The term halothermal circulation refers to the part of the large-scale ocean circulation that is driven by global density gradients created by surface heat and evaporation. The adjective halothermal derives from halo- referring to salt content and -thermal referring to temperature, factors which together determine the density of sea water. Halothermal circulation is driven primarily by salinity changes and secondarily by temperature changes (as opposed to the thermohaline mode in modern oceans).
In addition, it is thought that extensive salinity stratification can lead to a reduction in the meridional overturning circulation (MOC) through the slowing of thermohaline circulation. Increased stratification means that there is effectively a barrier to subduction of parcels of water; isopycnals effectively do not outcrop at the surface and are parallel to the surface. The ocean, in this case, can be described as "less ventilated", and this has been implicated in the slowing down of the MOC.
The North Atlantic Deep Water is considered to be one of several possible tipping points in the climate system. North Atlantic Deep Water (NADW) is a deep water mass formed in the North Atlantic Ocean. Thermohaline circulation (properly described as meridional overturning circulation) of the world's oceans involves the flow of warm surface waters from the southern hemisphere into the North Atlantic. Water flowing northward becomes modified through evaporation and mixing with other water masses, leading to increased salinity.
Ocean currents are another important factor in determining climate, particularly the major underwater thermohaline circulation which distributes heat energy from the equatorial oceans to the polar regions. These currents help to moderate the differences in temperature between winter and summer in the temperate zones. Also, without the redistributions of heat energy by the ocean currents and atmosphere, the tropics would be much hotter, and the polar regions much colder. Lightning Weather can have both beneficial and harmful effects.
Keeling has studied Antarctic ice and glacial with Britton B. Stephens, modeling concentrations of atmospheric during both glacial and interglacial periods. With Stephens and others, Keeling hypothesizes about oceanographic processes that may have stabilized and destabilized the oceans over time, in particular about possible thermostatic effects of Antarctic ice. He studies Thermohaline circulation and circulation patterns in the Southern Ocean to better understand oceanic warming. Keeling is also involved in monitoring of local emissions over Los Angeles, including methane.
Marshall holds degrees in physics and atmospheric science from Imperial College, London, where he was a faculty member in the Physics Department. Marshall joined MIT in 1991, and has worked there ever since. Marshall studies the circulation of the ocean, its coupling to the atmosphere and the role of the oceans in climate. Specific research interests include ocean convection and thermohaline circulation, ocean gyres and circumpolar currents, geophysical fluid dynamics, climate dynamics and numerical modeling of ocean and atmosphere.
Based on the about 150-year instrumental record a quasi-periodicity of about 70 years, with a few distinct warmer phases between ca. 1930–1965 and after 1995, and cool between 1900–1930 and 1965–1995 has been identified. In models, AMO-like variability is associated with small changes in the North Atlantic branch of the Thermohaline Circulation. However, historical oceanic observations are not sufficient to associate the derived AMO index to present-day circulation anomalies.
The factors that change OMZs are the amount of oceanic primary production resulting in increased respiration at greater depths, changes in the oxygen supply due to poor ventilation, and amount of oxygen supplied through thermohaline circulation. From recent observations, it is evident that the extent of OMZs has expanded in tropical oceans during the past half century. Vertical expansion of tropical OMZs has reduced the area between the OMZ and surface where oxygen is used by many organisms.
Further afield, some tropical records report a cooling, based on cores drilled into an ancient coral reef in Indonesia. The event also caused a global CO2 decline of about 25 ppm over about 300 years. However, dating and interpretation of other tropical sites are more ambiguous than the North Atlantic sites. In addition, climate modeling work shows that the amount of meltwater and the pathway of meltwater are both important in perturbing the North Atlantic thermohaline circulation.
The film The Day After Tomorrow exaggerates a scenario related to the AMOC shutdown. Kim Stanley Robinson's science-fiction novel Fifty Degrees Below, a volume in his Science in the Capital series, depicts a shutdown of thermohaline circulation & mankind's efforts to counteract it by adding great quantities of salt to the ocean. In Ian Douglas' Star Corpsman novels, an AMOC shutdown triggered an early glacial maximum, covering most of Canada and northern Europe in ice sheet by the mid-22nd century.
Tropical cyclones can also cause a cool wake, due to turbulent mixing of the upper of the ocean. SST changes diurnally, like the air above it, but to a lesser degree. There is less SST variation on breezy days than on calm days. In addition, ocean currents such as the Atlantic Multidecadal Oscillation (AMO), can effect SST's on multi- decadal time scales, a major impact results from the global thermohaline circulation, which affects average SST significantly throughout most of the world's oceans.
Three explorers are again embarking on a two-month trek across the Arctic sea ice, gathering information that is vital for scientists to understand the impact of ice cover reduction on ocean acidification. This trek ended in May 2010 when the explorers reached the North Pole. Catlin Arctic Survey 2011 focused on thermohaline circulation, which are powerful ocean currents that circulate warm and cold water around the world's oceans. These currents have a major impact on Earth's climate and weather patterns.
Uranium is well mixed in the ocean, and its decay produces 231Pa and 230Th at a constant activity ratio (0.093). The decay products are rapidly removed by adsorption on settling particles, but not at equal rates. 231Pa has a residence equivalent to the residence time of deep water in the Atlantic basin (around 1000 yrs) but 230Th is removed more rapidly (centuries). Thermohaline circulation effectively exports 231Pa from the Atlantic into the Southern Ocean, while most of the 230Th remains in Atlantic sediments.
This lower-density air then rises and is replaced by cooler, higher-density air. The result is atmospheric circulation that drives the weather and climate through redistribution of thermal energy. The primary atmospheric circulation bands consist of the trade winds in the equatorial region below 30° latitude and the westerlies in the mid-latitudes between 30° and 60°. Ocean currents are also important factors in determining climate, particularly the thermohaline circulation that distributes thermal energy from the equatorial oceans to the polar regions.
Oceans contain the greatest quantity of actively cycled carbon in the world and are second only to the lithosphere in the amount of carbon they store. The oceans' surface layer holds large amounts of dissolved organic carbon that is exchanged rapidly with the atmosphere. The deep layer's concentration of dissolved inorganic carbon is about 15 percent higher than that of the surface layer and it remains there for much longer periods of time. Thermohaline circulation exchanges carbon between these two layers.
This work, based on laboratory studies, predated the discovery of such boundary currents, and remains one of the great triumphs of theoretical physical oceanography. Stommel also developed early models of the thermohaline circulation which suggested that it might have more than one stable state. In addition to his work on large-scale ocean currents, Stommel did research on a variety of problems in oceanography and meteorology. These include work on the classification of estuaries, estimates of turbulent diffusion, and studies of the impact of volcanoes on climate.
The lake briefly returned during the Younger Dryas and eventually desiccated during the Holocene. Wind-driven erosion has excavated depressions in the former lakebed that are in part filled with playas. The lake is only one of several pluvial lakes in southwestern North America that developed during the late Pleistocene. Their formation has been variously attributed to decreased temperatures during the ice age and increased precipitation; a shutdown of the thermohaline circulation and the Laurentide Ice Sheet altered atmospheric circulation patterns and increased precipitation in the region.
The Gulf Stream is a major surface current, primarily driven by thermohaline circulation that originates in the Gulf of Mexico and then flows through the Straits of Florida into the North Atlantic. In essence, it is a river within an ocean, and, like a river, it can and does carry floating objects. It has a maximum surface velocity of about . A small plane making a water landing or a boat having engine trouble can be carried away from its reported position by the current.
What was the exact effect of drainage on the formation of North Atlantic Deep water, the thermohaline circulation, and climate? There are two proposed scenarios for the final drawdown of Lake Agassiz, so which one, if either, is right? The above are just some of the challenges faced when attempting to reconstruct events in Earth's history. Though it is a difficult field of study, advancements in the understanding of proxies for, and indicators of, certain environmental parameters in the geologic record are constantly being made.
This denser salt water sinks by convection and the replacing seawater is subject to the same process. This produces essentially freshwater ice at −1.9 °C on the surface. The increased density of the sea water beneath the forming ice causes it to sink towards the bottom. On a large scale, the process of brine rejection and sinking cold salty water results in ocean currents forming to transport such water away from the Poles, leading to a global system of currents called the thermohaline circulation.
The amount of sea ice passing through the Fram Strait varies from year to year and affects the global climate through its influence on thermohaline circulation. The warming in the Fram Strait region has likely amplified Arctic shrinkage, and serves as a positive feedback mechanism for transporting more internal energy to the Arctic Ocean. In the past century, the sea surface temperature at Fram Strait has on average warmed roughly 1.9 °C (3.5 °F), and is 1.4 °C (2.5 °F) warmer than during the Medieval Warm Period.
Animation of the thermohaline circulation. The later part of this animation shows the Antarctic Circumpolar Current The Antarctic Circumpolar Current (ACC) is an ocean current that flows clockwise (as seen from the South Pole) from west to east around Antarctica. An alternative name for the ACC is the West Wind Drift. The ACC is the dominant circulation feature of the Southern Ocean and has a mean transport estimated at 100-150 Sverdrups (Sv, million m³/s), or possibly even higher, making it the largest ocean current.
Upwelling of deep water under the sea ice brings substantial amounts of nutrients. As the ice melts, the melt water provides stability and the critical depth is well below the mixing depth, which allows for a positive net primary production. As the sea ice recedes epontic algae dominate the first phase of the bloom, and a strong bloom dominate by diatoms follows the ice melt south. Another phytoplankton bloom occurs more to the north near the Antarctic convergence, here nutrients are present from thermohaline circulation.
In oceanographic studies the Greenland Sea is considered part of the Nordic Seas, along with the Norwegian Sea. The Nordic Seas are the main connection between the Arctic and Atlantic oceans and, as such, could be of great significance in a possible shutdown of thermohaline circulation. In oceanography the Arctic Ocean and Nordic Seas are often referred to collectively as the "Arctic Mediterranean Sea", a marginal sea of the Atlantic. The sea has Arctic climate with regular northern winds and temperatures rarely rising above .
The thermohaline circulation affects the climate in the Norwegian Sea, and the regional climate can significantly deviate from average. There is also a difference of about 10 °C between the sea and the coastline. Temperatures rose between 1920 and 1960,Gerold Wefer, Frank Lamy, Fauzi Mantoura Marine Science Frontiers for Europe, Springer, 2003 , pp. 32–35 and the frequency of storms decreased in this period. The storminess was relatively high between 1880 and 1910, decreased significantly in 1910–1960, and then recovered to the original level.
Frank Vanderwal, having spent a year at the National Science Foundation (NSF) in Washington, D.C., is impatient with what he sees as its passivity and its reluctance to demand serious political change in the face of severe climate change. He keeps an eye on environmental triggers such as climate change in the Arctic and thermohaline circulation. Though he likes his colleague, Anna Quibler, and much of her work, he misses his hometown, San Diego. An athletic man, he frequently goes climbing and canyoneering when he can.
The Antarctic Circumpolar Current could then flow through it, isolating Antarctica from warm waters and triggering the formation of its huge ice sheets. The Isthmus of Panama developed at a convergent plate margin about 2.6 million years ago, and further separated oceanic circulation, closing the last strait, outside the polar regions, that had connected the Pacific and Atlantic Oceans.EO Newsroom: New Images – Panama: Isthmus that Changed the World This increased poleward salt and heat transport, strengthening the North Atlantic thermohaline circulation, which supplied enough moisture to arctic latitudes to create the northern glaciation.
These events could have been triggered by an extended shutdown of the thermohaline circulation, which caused Arctic sea ice to expand and Antarctic sea ice to contract, causing a southward migration of the Intertropical Convergence Zone. The forcing by the Laurentide Ice Sheet was important for the Mystery Interval lake level changes as well. The highstand between 16,100 and 14,500 years ago has been christened the "Big Wet". There ware two more highstands 14,000 - 12,500 years ago, followed by desiccation 12,000 or 14,000 years ago when the lake declined over the course of a millennium.
Topographic map of the Nordic Seas and subpolar basins with schematic circulation of surface currents (solid curves) and deep currents (dashed curves) that form a portion of the Atlantic meridional overturning circulation. Colors of curves indicate approximate temperatures. The Atlantic meridional overturning circulation (AMOC) is the zonally-integrated component of surface and deep currents in the Atlantic Ocean. It is characterized by a northward flow of warm, salty water in the upper layers of the Atlantic, and a southward flow of colder, deep waters that are part of the thermohaline circulation.
This is also known as 'haline forcing' (net high latitude freshwater gain and low latitude evaporation). This warmer, fresher water from the Pacific flows up through the South Atlantic to Greenland, where it cools off and undergoes evaporative cooling and sinks to the ocean floor, providing a continuous thermohaline circulation.United Nations Environment Programme / GRID-Arendal, 2006, . Potential Impact of Climate Change Hence, a recent and popular name for the thermohaline circulation, emphasizing the vertical nature and pole-to-pole character of this kind of ocean circulation, is the meridional overturning circulation.
Deep ocean currents are currently being researched using a fleet of underwater robots called Argo. The thermohaline circulation is a part of the large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes. The adjective thermohaline derives from thermo- referring to temperature and ' referring to salt content, factors which together determine the density of sea water. Wind-driven surface currents (such as the Gulf Stream) travel polewards from the equatorial Atlantic Ocean, cooling en route, and eventually sinking at high latitudes (forming North Atlantic Deep Water).
Although this is now thought unlikely in the near future, it has also been suggested that there could be a shutdown of thermohaline circulation, similar to that which is believed to have driven the Younger Dryas, an abrupt climate change event. There is also potentially a possibility of a more general disruption of ocean circulation, which may lead to an ocean anoxic event; these are believed to be much more common in the distant past. It is unclear whether the appropriate pre-conditions for such an event exist today.
This ice floats on the surface, and the salt that is "frozen out" adds to the salinity and density of the sea water just below it, in a process known as brine rejection. This denser salt water sinks by convection. This produces essentially freshwater ice at −1.9 °C on the surface. On a large scale, the process of brine rejection and sinking cold salty water results in ocean currents forming to transport such water away from the Poles, leading to a global system of currents called the thermohaline circulation.
This map shows the general location and direction of the warm surface (red) and cold deep water (blue) currents of the thermohaline circulation. Salinity is represented by color in units of the Practical Salinity Scale. Low values (blue) are less saline, while high values (orange) are more saline. The Atlantic Meridional Overturning Circulation (AMOC), an important component of the Earth's climate system, is a northward flow of warm, salty water in the upper layers of the Atlantic and a southward flow of colder water in the deep Atlantic.
This exportation of freshwater helps control the thermohaline circulation and the global climate. Flow rates of taiga rivers are variable and "flashy" due to the presence of a permafrost that keeps water from percolating deep into the soil. Due to global warming, flow rates have increased as more of the permafrost melts every year. In addition to "flashy" flow levels, the permafrost in the taiga allows dissolved inorganic nitrogen and organic carbon levels in the water to be higher while calcium, magnesium, sulfate, and hydrogen bicarbonate levels are shown to be much lower.
The Weddell Sea is one of few locations in the World Ocean where deep and bottom water masses are formed to contribute to the global thermohaline circulation. The characteristics of exported water masses result from complex interactions between surface forcing, significantly modified by sea ice processes, ocean dynamics at the continental shelf break, and slope and sub-ice shelf water mass transformation. Circulation in the western Weddell Sea is dominated by a northward flowing current. This northward current is the western section of a primarily wind-driven, cyclonic gyre called the Weddell Gyre.
L'Anse aux Meadows, Newfoundland, today, with a reconstruction of a Viking settlement. In Chesapeake Bay (now Maryland and Virginia in the United States), researchers found large temperature excursions (changes from the mean temperature of that time) during the Medieval Warm Period (about 950–1250) and the Little Ice Age (about 1400–1700, with cold periods persisting into the early 20th century), possibly related to changes in the strength of North Atlantic thermohaline circulation. Sediments in Piermont Marsh of the lower Hudson Valley show a dry Medieval Warm period from 800 to 1300.
Ocean krill, a cornerstone species, prefer cold water and are the primary food source for aquatic mammals such as the blue whale. Alterations to the ocean currents, due to increased freshwater inputs from glacier melt, and the potential alterations to thermohaline circulation of the worlds oceans, may affect existing fisheries upon which humans depend as well. The white lemuroid possum, only found in the Daintree mountain forests of northern Queensland, may be the first mammal species to be driven extinct by global warming in Australia. In 2008, the white possum has not been seen in over three years.
Bottom current flow in the Gulf of Cadiz Thermohaline circulation is the principal driving force of deepwater bottom- currents. The term refers to the movement of water over large distances as a consequence of global oceanic density gradients. This circulation commonly travels at velocities between 2 – 20 cm/s. Note that at this velocity range, considering the general shape of the Shields diagram still holds in these conditions, a flow will only be able to continue transporting finer sediment that is already in suspension but will not be able to erode the same sized sediment once it is deposited.
A northwards branch of the Gulf Stream, the North Atlantic Drift, is part of the thermohaline circulation (THC), transporting warmth further north to the North Atlantic, where its effect in warming the atmosphere contributes to warming Europe. The evaporation of ocean water in the North Atlantic increases the salinity of the water as well as cooling it, both actions increasing the density of water at the surface. Formation of sea ice further increases the salinity and density, because salt is ejected into the ocean when sea ice forms. This dense water then sinks and the circulation stream continues in a southerly direction.
The 8.2 ka event, an abrupt cold spell recorded as a negative excursion in the record lasting 400 years, is the most prominent climatic event occurring in the Holocene epoch, and may have marked a resurgence of ice cover. It has been suggested that this event was caused by the final drainage of Lake Agassiz, which had been confined by the glaciers, disrupting the thermohaline circulation of the Atlantic. Subsequent research, however, suggested that the discharge was probably superimposed upon a longer episode of cooler climate lasting up to 600 years and observed that the extent of the area affected was unclear.
December 1997 chart of ocean surface temperature anomaly [°C] during the last strong El Niño The interaction of ocean circulation, which serves as a type of heat pump, and biological effects such as the concentration of carbon dioxide can result in global climate changes on a time scale of decades. Known climate oscillations resulting from these interactions, include the Pacific decadal oscillation, North Atlantic oscillation, and Arctic oscillation. The oceanic process of thermohaline circulation is a significant component of heat redistribution across the globe, and changes in this circulation can have major impacts upon the climate.
Within 2 weeks the Mertz Iceberg rotated about the point of impact with B9-B and lay parallel with the coastline.European Space Agency Envisat radar images The iceberg drifted westwards after the collision and in April 2010 hit a submerged peak which caused it to break into two pieces.Australian Antarctic Division News updateLatest National Ice Center pictures The flow of icebergs from the calved glacier tongue has reduced the effectiveness of the polynya west of Mertz Glacier that acted as one of Antarctica's major areas for the formation of dense Antarctic Bottom Water. The calving could affect future thermohaline circulation around Antarctica.
Tropical cyclones also help maintain the global heat balance by moving warm, moist tropical air to the middle latitudes and polar regions, and by regulating the thermohaline circulation through upwelling. The storm surge and winds of hurricanes may be destructive to human-made structures, but they also stir up the waters of coastal estuaries, which are typically important fish breeding locales. Tropical cyclone destruction spurs redevelopment, greatly increasing local property values. When hurricanes surge upon shore from the ocean, salt is introduced to many freshwater areas and raises the salinity levels too high for some habitats to withstand.
The Medieval Warm Period from 950 to 1250 occurred mostly in the Northern Hemisphere, causing warmer summers in many areas; the high temperatures would only be surpassed by the global warming of the 20th/21st centuries. It has been hypothesized that the warmer temperatures allowed the Norse to colonize Greenland, due to ice-free waters. Outside of Europe there is evidence of warming conditions, including higher temperatures in China and major North American droughts which adversely affected numerous cultures. After 1250, glaciers began to expand in Greenland, affecting its thermohaline circulation, and cooling the entire North Atlantic.
Once the flood ceased, the AMOC would recover and the Younger Dryas would stop in less than 100 years. Therefore, continuous freshwater input was necessary to maintain a weak AMOC for more than 1000 years. Recent study proposed that the snowfall could be a source of continuous freshwater resulting in a prolonged weakened state of the AMOC. An alternative theory suggests instead that the jet stream shifted northward in response to the changing topographic forcing of the melting North American ice sheet, which brought more rain to the North Atlantic, which freshened the ocean surface enough to slow the thermohaline circulation.
Together with the water currents, they break up the floating ice sheets and mix various water layers both laterally and along the depth. The progressively colder waters of North Atlantic Current sink in the Arctic Ocean, returning south in the form of cold East Greenland Current, an important part of the Atlantic conveyor belt, which flows along the western part of the sea. Along the eastern part flows the warm Spitsbergen Current, a part of Gulf Stream. Mixtures of cold, freshwater ice melt and the warm, salty Spitsbergen Current may experience cabbeling, which might contribute to thermohaline circulation.
Driven by the global thermohaline circulation, the North Atlantic Current is part of the wind-driven Gulf Stream, which goes further east and north from the North American coast across the Atlantic and into the Arctic Ocean. The North Atlantic Current, together with the Gulf Stream, have a long-lived reputation for having a considerable warming influence on European climate. However, the principal cause for differences in winter climate between North America and Europe seems to be winds rather than ocean currents (although the currents do exert influence at very high latitudes by preventing the formation of sea ice).
If the high latitude waters are below , they will be dense enough to sink; as they are cool, oxygen is highly soluble in their waters, and the deep ocean will be oxygenated. If high latitude waters are warmer than , their density is too low for them to sink below the cooler deep waters. Therefore, thermohaline circulation can only be driven by salt-increased density, which tends to form in warm waters where evaporation is high. This warm water can dissolve less oxygen, and is produced in smaller quantities, producing a sluggish circulation with little deep water oxygen.
Full article: Solubility pump Dissociation of carbon dioxide following Henry's Law The oceans store the largest pool of reactive carbon on the planet as DIC, which is introduced as a result of the dissolution of atmospheric carbon dioxide into seawater – the solubility pump. Aqueous CO2, carbonic acid, bicarbonate ion, and carbonate ion concentrations comprise dissolved inorganic carbon (DIC). DIC circulates throughout the whole ocean by Thermohaline circulation, which facilitates the tremendous DIC storage capacity of the ocean. The below chemical equations show the reactions that CO2 undergoes after it enters the ocean and transforms into its aqueous form.
Ocean Thermal Energy Conversion (OTEC) uses the ocean thermal gradient between cooler deep and warmer shallow or surface seawaters to run a heat engine and produce useful work, usually in the form of electricity. OTEC can operate with a very high capacity factor and so can operate in base load mode. The denser cold water masses, formed by ocean surface water interaction with cold atmosphere in quite specific areas of the North Atlantic and the Southern Ocean, sink into the deep sea basins and spread in entire deep ocean by the thermohaline circulation. Upwelling of cold water from the deep ocean is replenished by the downwelling of cold surface sea water.
The Oyashio water is freshened in the Okhotsk Sea and transported to the North Pacific subtropical gyre by thermohaline circulation. Some studies have found that Gulf of Alaska Intermediate Water additionally contributes to the subpolar waters on the eastern side of the gyre. The density of the NPIW in the MWR, about 26.6 – 26.9 σθ, is slightly higher than the apparent later winter surface density of the subpolar water. The low salinity and high oxygen at the density of the NPIW are attained in the subpolar gyre, through vertical diffusion in the open North Pacific and direct ventilation in the Okhotsk Sea as a result of sea ice formation.
Natural convection has attracted a great deal of attention from researchers because of its presence both in nature and engineering applications. In nature, convection cells formed from air raising above sunlight-warmed land or water are a major feature of all weather systems. Convection is also seen in the rising plume of hot air from fire, plate tectonics, oceanic currents (thermohaline circulation) and sea-wind formation (where upward convection is also modified by Coriolis forces). In engineering applications, convection is commonly visualized in the formation of microstructures during the cooling of molten metals, and fluid flows around shrouded heat-dissipation fins, and solar ponds.
Driven by the density gradients this sets up the main driving force behind deep ocean currents like the deep western boundary current (DWBC). The thermohaline circulation is mainly driven by the formation of deep water masses in the North Atlantic and the Southern Ocean caused by differences in temperature and salinity of the water. The great quantities of dense water sinking at high latitudes must be offset by equal quantities of water rising elsewhere. Note that cold water in polar zones sink relatively rapidly over a small area, while warm water in temperate and tropical zones rise more gradually across a much larger area.
In order to gain an idea of the effect that large freshwater fluxes into the ocean would have on global ocean circulation, numerical modeling is needed. Of particular importance to the cases of freshwater fluxes from Lake Agassiz are the locations of their entry into the ocean and the rapidity at which they entered. The likely outcome is that the fluxes themselves, combined with the effect of the re-direction of the Agassiz Baseline flow, had an appreciable impact on ocean circulation and consequently climate. Some simulations of North Atlantic Deep Water formation confirm that the oceans and the thermohaline circulation are affected by these fluxes.
Variable salinity in water and variable water content in air masses are frequent causes of convection in the oceans and atmosphere which do not involve heat, or else involve additional compositional density factors other than the density changes from thermal expansion (see thermohaline circulation). Similarly, variable composition within the Earth's interior which has not yet achieved maximal stability and minimal energy (in other words, with densest parts deepest) continues to cause a fraction of the convection of fluid rock and molten metal within the Earth's interior (see below). Gravitational convection, like natural thermal convection, also requires a g-force environment in order to occur.
It has also been hypothesized that the Clovis culture had its decline in the wake of the Younger Dryas cold phase. This "cold shock", lasting roughly 1500 years, affected many parts of the world, including North America. This appears to have been triggered by a vast amount of meltwater – possibly from Lake Agassiz – emptying into the North Atlantic, disrupting the thermohaline circulation. The Younger Dryas impact hypothesis, or Clovis comet hypothesis, originally proposed that a large air burst or earth impact of a comet or comets from outer space initiated the Younger Dryas cold period about 12,900 BP calibrated (10,900 14C uncalibrated) years ago.
Reduced glacial runoff can lead to insufficient stream flow to allow these species to thrive. Alterations to the ocean currents, due to increased freshwater inputs from glacier melt, and the potential alterations to thermohaline circulation of the World Ocean, may affect existing fisheries upon which humans depend as well. One major concern is the increased risk of Glacial Lake Outburst Floods (GLOF), which have in the past had great effect on lives and property. Glacier meltwater left behind by the retreating glacier is often held back by moraines that can be unstable and have been known to collapse if breached or displaced by earthquakes, landslides or avalanches.
Most of the already formed ice continued floating south, driven by the wind, so a cold open water surface was exposed on which new ice formed as frazil ice and pancake ice in the rough seas, producing a giant tongue shape. The salt rejected back into the ocean from this ice formation caused the surface water to become denser and sink, sometimes to great depths ( or more), making this one of the few regions of the ocean where winter convection occurred, which helped drive the entire worldwide system of surface and deep currents known as the thermohaline circulation. Since the 1990s, the Odden ice tongue rarely develops.
Ocean models make use of a branch of physics, geophysical fluid dynamics, that describes the large-scale flow of fluids such as seawater. The global conveyor belt shown in blue with warmer surface currents in red Surface currents only affect the top few hundred metres (yards) of the sea, but there are also large-scale flows in the ocean depths caused by the movement of deep water masses. A main deep ocean current flows through all the world's oceans and is known as the thermohaline circulation or global conveyor belt. This movement is slow and is driven by differences in density of the water caused by variations in salinity and temperature.
Carbon enters the ocean as atmospheric carbon dioxide dissolves in the surface layers and is converted into carbonic acid, carbonate, and bicarbonate: :CO2 (gas) CO2 (aq) :CO2 (aq) \+ H2O H2CO3 :H2CO3 HCO3− \+ H+ :HCO3− CO32− \+ H+ It can also enter through rivers as dissolved organic carbon and is converted by photosynthetic organisms into organic carbon. This can either be exchanged throughout the food chain or precipitated into the deeper, more carbon rich layers as dead soft tissue or in shells and bones as calcium carbonate. It circulates in this layer for long periods of time before either being deposited as sediment or being returned to surface waters through thermohaline circulation.
Export flux is defined as the sedimentation out of the surface layer (at approximately 100 m depth) and sequestration flux is the sedimentation out of the mesopelagic zone (at approximately 1000 m depth). A portion of the POC is respired back to CO2 in the oceanic water column at depth, mostly by heterotrophic microbes and zooplankton, thus maintaining a vertical gradient in concentration of dissolved inorganic carbon (DIC). This deep-ocean DIC returns to the atmosphere on millennial timescales through thermohaline circulation. Between 1% and 40% of the primary production is exported out of the euphotic zone, which attenuates exponentially towards the base of the mesopelagic zone and only about 1% of the surface production reaches the sea floor.
In reality, it is understood that this value is variable, so freshwater fluxes into the open ocean and their effect on thermohaline circulation, ocean circulations, and global climate would vary as well. Considering the enormity of Lake Agassiz, changes in the make-up of its shores (beaches, cliffs), or strandlines, could result in very massive outflows. These changes were often sudden, causing thousands of cubic kilometers of water to exit via the newly created outflow channels, eventually making its way to the open ocean through one of four major routes. These routes have been identified to be the Mississippi River Valley, the St. Lawrence River Valley, the Mackenzie River Valley, and the Hudson Strait (Fig. 2).
The increasing eastward momentum imparted by the winds causes water parcels to drift outward from the axis of the Earth's rotation (in other words, northward) as a result of the Coriolis force. This northward Ekman transport is balanced by a southward, pressure-driven flow below the depths of the major ridge systems. Some theories connect these flows directly, implying that there is significant upwelling of dense deep waters within the Southern Ocean, transformation of these waters into light surface waters, and a transformation of waters in the opposite direction to the north. Such theories link the magnitude of the Circumpolar Current with the global thermohaline circulation, particularly the properties of the North Atlantic.
NADW and its formation is essential to the Atlantic Meridional Overturning Circulation (AMOC), which is responsible for transporting large amounts of water, heat, salt, carbon, nutrients and other substances from the Tropical Atlantic to the Mid and High Latitude Atlantic. In the conveyor belt model of thermohaline circulation of the world's oceans, the sinking of NADW pulls the waters of the North Atlantic drift northward. However, this is almost certainly an oversimplification of the actual relationship between NADW formation and the strength of the Gulf Stream/North Atlantic drift. NADW has a temperature of 2-4 °C with a salinity of 34.9-35.0 psu found at a depth between 1500 and 4000m.
The importance of internal tides and internal waves in general relates to their breaking, energy dissipation, and mixing of the deep ocean. If there were no mixing in the ocean, the deep ocean would be a cold stagnant pool with a thin warm surface layer. While the meridional overturning circulation (also referred to as the thermohaline circulation) redistributes about 2 PW of heat from the tropics to polar regions, the energy source for this flow is the interior mixing which is comparatively much smaller- about 2 TW. Sandstrom (1908) showed a fluid which is both heated and cooled at its surface cannot develop a deep overturning circulation. Most global models have incorporated uniform mixing throughout the ocean because they do not include or resolve internal tidal flows.
Thermohaline circulation Oceanography (compound of the Greek words ὠκεανός meaning "ocean" and γράφω meaning "write"), also known as oceanology, is the study of the physical and biological aspects of the ocean. It is an important Earth science, which covers a wide range of topics, including ecosystem dynamics; ocean currents, waves, and geophysical fluid dynamics; plate tectonics and the geology of the sea floor; and fluxes of various chemical substances and physical properties within the ocean and across its boundaries. These diverse topics reflect multiple disciplines that oceanographers blend to further knowledge of the world ocean and understanding of processes within: astronomy, biology, chemistry, climatology, geography, geology, hydrology, meteorology and physics. Paleoceanography studies the history of the oceans in the geologic past.
The origin of modern circulation of cold, deep water -- known as the "Big Flush" -- is associated with Early Eocene () geological events; tectonism that resulted in the opening of the north-east Atlantic and fracture zones that developed in the subsiding Rio Grande Rise, which allowed cold water from the Antarctic Weddell Sea to flow northward into the North Atlantic. , the generation of cold bottom water in the Antarctic resulted in the formation of psychrospheric fauna, which today live in temperatures below , in the Atlantic and Tethys. This global distribution suggests that the Rio Grande Rise had been breached by this time, allowing cold, dense water to move north-south through a corridor enhancing the transition from a latitudinal thermospheric circulation to a meridional thermohaline circulation.
Because of the relatively long residence time of the ocean's thermohaline circulation, carbon transported as marine snow into the deep ocean by the biological pump can remain out of contact with the atmosphere for more than 1000 years. That is, when the marine snow is finally decomposed to inorganic nutrients and dissolved carbon dioxide, these are effectively isolated from the surface ocean for relatively long time-scales related to ocean circulation. Consequently, enhancing the quantity of marine snow that reaches the deep ocean is the basis of several geoengineering schemes to enhance carbon sequestration by the ocean. Ocean nourishment and iron fertilisation seek to boost the production of organic material in the surface ocean, with a concomitant rise in marine snow reaching the deep ocean.
However, the accuracy of this date is uncertain, as several radiocarbon plateaus exist around this time. The extinction does not coincide with the end of the last ice age, but does coincide with a minor yet severe climatic reversal that lasted for about 1,000-1,250 years, the Younger Dryas (GS1—Greenland Stadial 1), characterized by glacial readvances and severe cooling globally, a brief interlude in the continuing warming subsequent to the termination of the last major ice age (GS2), thought to have been due to a shutdown of the thermohaline circulation in the ocean due to huge influxes of cold fresh water from the preceding sustained glacial melting during the warmer Interstadial (GI1—Greenland Interstadial 1: ca. 16,000–11,450 14C years B.P.).
The rate and total content of oxygen loss varies by region, with the North Pacific emerging as a particular hotspot of deoxygenation due to the increased amount of time since its deep waters were last ventilated (see thermohaline circulation) and related high apparent oxygen utilization (AOU) (. Estimates of total oxygen loss in the global ocean range from 119 to 680 T mol decade−1 since the 1950s. These estimates represent 2% of the global ocean oxygen inventory. Modeling efforts show that global ocean oxygen loss rates will continue to accelerate up to 125 T mol year−1 by 2100 due to persistent warming, a reduction in ventilation of deeper waters, increased biological oxygen demand, and the associated expansion and shoaling of OMZs.
The event may have been caused by a large meltwater pulse from the final collapse of the Laurentide Ice Sheet of northeastern North America, most likely when the glacial lakes Ojibway and Agassiz suddenly drained into the North Atlantic Ocean. The same type of action produced the Missoula floods that created the Channeled scablands of the Columbia River basin. The meltwater pulse may have affected the North Atlantic thermohaline circulation, reducing northward heat transport in the Atlantic and causing significant North Atlantic cooling. Estimates of the cooling vary and depend somewhat on the interpretation of the proxy data, but drops of around have been reported. In Greenland, the event started at 8175 BP, and the cooling was 3.3 °C (decadal average) in less than 20 years.
The Geochemical Ocean Sections Study (GEOSECS) was a global survey of the three-dimensional distributions of chemical, isotopic, and radiochemical tracers in the ocean. A key objective was to investigate the deep thermohaline circulation of the ocean, using chemical tracers, including radiotracers, to establish the pathways taken by this. Expeditions undertaken during GEOSECS took place in the Atlantic Ocean from July 1972 to May 1973, in the Pacific Ocean from August 1973 to June 1974, and in the Indian Ocean from December 1977 to March 1978. Measurements included those of physical oceanographic quantities such as temperature, salinity, pressure and density, chemical / biological quantities such as total inorganic carbon, alkalinity, nitrate, phosphate, silicic acid, oxygen and apparent oxygen utilisation (AOU), and radiochemical / isotopic quantities such as carbon-13, carbon-14 and tritium.
Following Le Chatelier's principle, the chemical equilibrium of the Earth's carbon cycle will shift in response to anthropogenic CO2 emissions. The primary driver of this is the ocean, which absorbs anthropogenic CO2 via the so-called solubility pump. At present this accounts for only about one third of the current emissions, but ultimately most (~75%) of the CO2 emitted by human activities will dissolve in the ocean over a period of centuries: "A better approximation of the lifetime of fossil fuel CO2 for public discussion might be 300 years, plus 25% that lasts forever". However, the rate at which the ocean will take it up in the future is less certain, and will be affected by stratification induced by warming and, potentially, changes in the ocean's thermohaline circulation.
Plants transpire water from depths lower than 1 meter in many places and satellites like SMOS can only provide moisture content down to a few centimeters, but using repeated measurements in a day, the satellite can extrapolate soil moisture. The SMOS team of ESA hope to work with farmers around the world, including the United States Department of Agriculture to use as ground-based calibration for models determining soil moisture, as it may help to better understand crop yields over wide regions.How Dry We Are: European Space Agency To Test Earth's Soil Moisture Via Satellite-Science News, Science Daily Ocean salinity is crucial to the understanding of the role of the ocean in climate through the global water cycle. Salinity in combination with temperature determine ocean circulation by defining its density and hence thermohaline circulation.
One of the greatest influences on the climate of the UK is the Atlantic Ocean and especially the Gulf Stream, which carries warm water up from lower latitudes and modifies the high latitude air masses that pass across the UK. This thermohaline circulation has a powerful moderating and warming effect on the country's climate. This warm water current warms the climate to such a great extent that if the current did not exist then temperatures in winter would be about lower than they are today and similar to eastern Russia or Canada near the same latitude. The current allows England to have vineyards at the same latitude that Canada has polar bears. These warm ocean currents also bring substantial amounts of humidity which contributes to the notoriously wet climate that western parts of the UK experience.
CICE () is a computer model that simulates the growth, melt and movement of sea ice. It has been integrated into many coupled climate system models as well as global ocean and weather forecasting models and is often used as a tool in Arctic and Southern Ocean research. CICE development began in the mid-1990s by the United States Department of Energy (DOE), and it is currently maintained and developed by a group of institutions in North America and Europe known as the CICE Consortium. Its widespread use in earth system science in part owes to the importance of sea ice in determining Earth's planetary albedo, the strength of the global thermohaline circulation in the world's oceans, and in providing surface boundary conditions for atmospheric circulation models, since sea ice occupies a significant proportion (4-6%) of earth's surface.
In particular, one hypothesis links polar amplification to extreme weather by changing the polar jet stream. However, a 2013 study noted that extreme events in particular associated with sea ice and snow cover decline have not yet been observed for long enough to distinguish natural climate variability from impacts related to recent climate change. Studies published in 2017 and 2018 identified stalling patterns of rossby waves, in the northern hemisphere jet stream, to have caused almost stationary extreme weather events, such as the 2018 European heatwave, the 2003 European heat wave, 2010 Russian heat wave, 2010 Pakistan floods - these events have been linked to global warming, the rapid heating of the Arctic. According to a 2009 study the Atlantic Multi-decadal Oscillation (AMO) is highly correlated with changes in Arctic temperature, suggesting that the Atlantic Ocean thermohaline circulation is linked to temperature variability in the Arctic on a multi-decadal time scale.
Changes in climate indicators that show global warming The projected effects for the environment and for civilization are numerous and varied. The main effect is an increasing global average temperature. the average surface temperature could increase by a further by the end of the century.. This causes a variety of secondary effects, namely, changes in patterns of precipitation, rising sea levels, altered patterns of agriculture, increased extreme weather events, the expansion of the range of tropical diseases, and the opening of new marine trade routes; that without taking into account the social effects of climate change as inequity, pollution and diseases, environmental injustice and poverty. Potential effects include sea level rise of between 1990 and 2100, repercussions to agriculture, possible slowing of the thermohaline circulation, reductions in the ozone layer, increased intensity and frequency of extreme weather events, lowering of ocean pH, and the spread of tropical diseases such as malaria and dengue fever.
Possible causes supported by strong evidence appear to describe a sequence of catastrophes, each worse than the last: the Siberian Traps eruptions were bad enough alone, but because they occurred near coal beds and the continental shelf, they also triggered very large releases of carbon dioxide and methane. The resultant global warming may have caused perhaps the most severe anoxic event in the oceans' history: according to this theory, the oceans became so anoxic, anaerobic sulfur-reducing organisms dominated the chemistry of the oceans and caused massive emissions of toxic hydrogen sulfide. However, there may be some weak links in this chain of events: the changes in the 13C/12C ratio expected to result from a massive release of methane do not match the patterns seen throughout the early Triassic; and the types of oceanic thermohaline circulation that may have existed at the end of the Permian are not likely to have supported deep-sea anoxia.
If the wind patterns shift into a cyclonic circulation due to the residence of a low pressure system (rising air induced by warmer ocean temperatures a greater volume of open Arctic Ocean water), this will cause the circulation of the Beaufort Gyre to reverse and flow counter-clockwise. If this occurs, the Coriolis force would bend the flow out and away from the center of the gyre and, instead of the formation of a rising water dome, a depression would form and upwelling of the warmer water from the Atlantic ocean would occur. Oceanographer Andrey Proshutinsky has theorized that if the winds and the gyre's circulation were to weaken, high volumes of freshwater could leak out of the eastern part of the Arctic Ocean into the Northern Atlantic Ocean, impacting the Thermohaline Circulation and thus climate. Due to seasonal sea ice formation, the Beaufort Gyre is difficult to access and thus study in the Northern Hemisphere winter months; the lack of sunlight in these months forces the use of artificial light.. Expanded Academic ASAP. Web.
The first forecast for the year was issued by CSU on December 11, who anticipated that one of four different scenarios could occur. The scenario considered most likely was that Atlantic multidecadal oscillation (AMO) and thermohaline circulation (THC) would be stronger, but effects from El Niño would remain, resulting in a slightly above average season. The next most likely scenario was that both the AMO and THC would strengthen and the El Niño effects would cease to exist, causing a well above average season. In the other two scenarios, which were given the same probability of occurrence, the AMO and THC would weaken and the effects of El Niño would either disappear or some would remain, resulting in either a near average or well below average season. TSR subsequently issued their first outlook for the 2016 season during December 16, 2015 and predicted that activity would be about 20% below the 1950–2015 average, or about 15% below the 2005–2015 average. Specifically they thought that there would be 13 tropical storms, 5 hurricanes, 2 major hurricanes and an ACE index of 79 units.
Subscribers to the newsgroup took up the challenge and, despite Hyde's protests, raised the $100. Hyde's review on Google Groups criticized the film's depiction of weather which stopped at national borders; it was "to climate science as Frankenstein is to heart transplant surgery". Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research, an expert on thermohaline circulation and its effect on climate, said after a talk with scriptwriter Jeffrey Nachmanoff at the film's Berlin preview: > Clearly this is a disaster movie and not a scientific documentary, [and] the > film makers have taken a lot of artistic license. But the film presents an > opportunity to explain that some of the basic background is right: humans > are indeed increasingly changing the climate and this is quite a dangerous > experiment, including some risk of abrupt and unforeseen changes ... Luckily > it is extremely unlikely that we will see major ocean circulation changes in > the next couple of decades (I'd be just as surprised as Jack Hall if they > did occur); at least most scientists think this will only become a more > serious risk towards the end of the century.

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