An examination of the role of particles in oceanic mercury cycling

Recent models of global mercury (Hg) cycling have identified the downward flux of sinking particles in the ocean as a prominent Hg removal process from the ocean. At least one of these models estimates the amount of anthropogenic Hg in the ocean to be about 400 Mmol, with deep water formation and sinking fluxes representing the largest vectors by which pollutant Hg is able to penetrate the ocean interior. Using data from recent cruises to the Atlantic, we examined the dissolved and particulate partitioning of Hg in the oceanic water column as a cross-check on the hypothesis that sinking particle fluxes are important. Interestingly, these new data suggest particle-dissolved partitioning ( K d ) that is approximately 20× greater than previous estimates, which thereby challenges certain assumptions about the scavenging and active partitioning of Hg in the ocean used in earlier models. For example, the new particle data suggest that regenerative scavenging is the most likely mechanism by which the association of Hg and particles occurs. This article is part of the themed issue ‘Biological and climatic impacts of ocean trace element chemistry’.

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Influence of Nordic Seas dynamics on the Atlantic Water propagation and its impacts on sea ice concentration.

10.5194/egusphere-egu21-14798 ◽

2021 ◽

Author(s):

Sourav Chatterjee ◽

Roshin P Raj ◽

Laurent Bertino ◽

Nuncio Murukesh

Keyword(s):

Sea Ice ◽

Deep Water ◽

Atlantic Water ◽

The Arctic ◽

Deep Water Formation ◽

Sea Ice Concentration ◽

Nordic Seas ◽

Ice Concentration ◽

Water Formation

Enhanced intrusion of warm and saline Atlantic Water (AW) to the Arctic Ocean (AO) in recent years has drawn wide interest of the scientific community owing to its potential role in &#8216;Arctic Amplification&#8217;. Not only the AW has warmed over the last few decades , but its transfer efficiency have also undergone significant modifications due to changes in atmosphere and ocean dynamics at regional to large scales. The Nordic Seas (NS), in this regard, play a vital role as the major exchange of polar and sub-polar waters takes place in this region. Further, the AW and its significant modification on its way to AO via the Nordic Seas has large scale implications on e.g., deep water formation, air-sea heat fluxes. Previous studies have suggested that a change in the sub-polar gyre dynamics in the North Atlantic controls the AW anomalies that enter the NS and eventually end up in the AO. However, the role of NS dynamics in resulting in the modifications of these AW anomalies are not well studied. Here in this study, we show that the Nordic Seas are not only a passive conduit of AW anomalies but the ocean circulations in the Nordic Seas, particularly the Greenland Sea Gyre (GSG) circulation can significantly change the AW characteristics between the entry and exit point of AW in the NS. Further, it is shown that the change in GSG circulation can modify the AW heat distribution in the Nordic Seas and can potentially influence the sea ice concentration therein. Projected enhanced atmospheric forcing in the NS in a warming Arctic scenario and the warming trend of the AW can amplify the role of NS circulation in AW propagation and its impact on sea ice, freshwater budget and deep water formation.

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Surface and subsurface Labrador Shelf water mass conditions during the last 6000 years

Climate of the Past ◽

10.5194/cp-16-1127-2020 ◽

2020 ◽

Vol 16 (4) ◽

pp. 1127-1143

Author(s):

Annalena A. Lochte ◽

Ralph Schneider ◽

Markus Kienast ◽

Janne Repschläger ◽

Thomas Blanz ◽

...

Keyword(s):

Deep Water ◽

Late Holocene ◽

Thermohaline Circulation ◽

Sea Water ◽

Labrador Sea ◽

Circulation System ◽

Deep Water Formation ◽

Holocene Thermal Maximum ◽

Water Formation

Abstract. The Labrador Sea is important for the modern global thermohaline circulation system through the formation of intermediate Labrador Sea Water (LSW) that has been hypothesized to stabilize the modern mode of North Atlantic deep-water circulation. The rate of LSW formation is controlled by the amount of winter heat loss to the atmosphere, the expanse of freshwater in the convection region and the inflow of saline waters from the Atlantic. The Labrador Sea, today, receives freshwater through the East and West Greenland currents (EGC, WGC) and the Labrador Current (LC). Several studies have suggested the WGC to be the main supplier of freshwater to the Labrador Sea, but the role of the southward flowing LC in Labrador Sea convection is still debated. At the same time, many paleoceanographic reconstructions from the Labrador Shelf focussed on late deglacial to early Holocene meltwater run-off from the Laurentide Ice Sheet (LIS), whereas little information exists about LC variability since the final melting of the LIS about 7000 years ago. In order to enable better assessment of the role of the LC in deep-water formation and its importance for Holocene climate variability in Atlantic Canada, this study presents high-resolution middle to late Holocene records of sea surface and bottom water temperatures, freshening, and sea ice cover on the Labrador Shelf during the last 6000 years. Our records reveal that the LC underwent three major oceanographic phases from the mid- to late Holocene. From 6.2 to 5.6 ka, the LC experienced a cold episode that was followed by warmer conditions between 5.6 and 2.1 ka, possibly associated with the late Holocene thermal maximum. While surface waters on the Labrador Shelf cooled gradually after 3 ka in response to the neoglaciation, Labrador Shelf subsurface or bottom waters show a shift to warmer temperatures after 2.1 ka. Although such an inverse stratification by cooling of surface and warming of subsurface waters on the Labrador Shelf would suggest a diminished convection during the last 2 millennia compared to the mid-Holocene, it remains difficult to assess whether hydrographic conditions in the LC have had a significant impact on Labrador Sea deep-water formation.

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The role of subpolar deep water formation and Nordic Seas overflows in simulated multidecadal variability of the Atlantic meridional overturning circulation

Ocean Science ◽

10.5194/os-10-227-2014 ◽

2014 ◽

Vol 10 (2) ◽

pp. 227-241 ◽

Cited By ~ 19

Author(s):

K. Lohmann ◽

J. H. Jungclaus ◽

D. Matei ◽

J. Mignot ◽

M. Menary ◽

...

Keyword(s):

Deep Water ◽

Atlantic Meridional Overturning Circulation ◽

Meridional Overturning Circulation ◽

Deep Water Formation ◽

Multidecadal Variability ◽

Nordic Seas ◽

Denmark Strait ◽

Water Formation ◽

Meridional Overturning

Abstract. We investigate the respective role of variations in subpolar deep water formation and Nordic Seas overflows for the decadal to multidecadal variability of the Atlantic meridional overturning circulation (AMOC). This is partly done by analysing long (order of 1000 years) control simulations with five coupled climate models. For all models, the maximum influence of variations in subpolar deep water formation is found at about 45° N, while the maximum influence of variations in Nordic Seas overflows is rather found at 55 to 60° N. Regarding the two overflow branches, the influence of variations in the Denmark Strait overflow is, for all models, substantially larger than that of variations in the overflow across the Iceland–Scotland Ridge. The latter might, however, be underestimated, as the models in general do not realistically simulate the flow path of the Iceland–Scotland overflow water south of the Iceland–Scotland Ridge. The influence of variations in subpolar deep water formation is, on multimodel average, larger than that of variations in the Denmark Strait overflow. This is true both at 45° N, where the maximum standard deviation of decadal to multidecadal AMOC variability is located for all but one model, and at the more classical latitude of 30° N. At 30° N, variations in subpolar deep water formation and Denmark Strait overflow explain, on multimodel average, about half and one-third respectively of the decadal to multidecadal AMOC variance. Apart from analysing multimodel control simulations, we have performed sensitivity experiments with one of the models, in which we suppress the variability of either subpolar deep water formation or Nordic Seas overflows. The sensitivity experiments indicate that variations in subpolar deep water formation and Nordic Seas overflows are not completely independent. We further conclude from these experiments that the decadal to multidecadal AMOC variability north of about 50° N is mainly related to variations in Nordic Seas overflows. At 45° N and south of this latitude, variations in both subpolar deep water formation and Nordic Seas overflows contribute to the AMOC variability, with neither of the processes being very dominant compared to the other.

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The Role of Polar Deep Water Formation in Global Climate Change

Annual Review of Earth and Planetary Sciences ◽

10.1146/annurev.ea.21.050193.001303 ◽

1993 ◽

Vol 21 (1) ◽

pp. 227-254 ◽

Cited By ~ 11

Author(s):

W W Hay

Keyword(s):

Climate Change ◽

Deep Water ◽

Global Climate Change ◽

Global Climate ◽

Deep Water Formation ◽

Water Formation

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The Role of North Atlantic Deep Water Formation in an OGCM’s Ventilation and Thermohaline Circulation*

Journal of Physical Oceanography ◽

10.1175/1520-0485(1998)028<1759:tronad>2.0.co;2 ◽

1998 ◽

Vol 28 (9) ◽

pp. 1759-1785 ◽

Cited By ~ 25

Author(s):

Paul J. Goodman

Keyword(s):

North Atlantic ◽

Deep Water ◽

Thermohaline Circulation ◽

North Atlantic Deep Water ◽

Deep Water Formation ◽

Water Formation

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The role of subpolar deep water formation and Nordic Seas overflows in simulated multidecadal variability of the Atlantic overturning

Ocean Science Discussions ◽

10.5194/osd-10-1895-2013 ◽

2013 ◽

Vol 10 (5) ◽

pp. 1895-1931

Author(s):

K. Lohmann ◽

J. H. Jungclaus ◽

D. Matei ◽

J. Mignot ◽

M. Menary ◽

...

Keyword(s):

Deep Water ◽

Climate Models ◽

Meridional Overturning Circulation ◽

Deep Water Formation ◽

Multidecadal Variability ◽

Nordic Seas ◽

Model Average ◽

Denmark Strait ◽

Water Formation

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Surface and subsurface Labrador Shelf water mass conditions during the last 6,000 years

10.5194/cp-2019-100 ◽

2019 ◽

Author(s):

Annalena A. Lochte ◽

Ralph Schneider ◽

Janne Repschläger ◽

Markus Kienast ◽

Thomas Blanz ◽

...

Keyword(s):

Deep Water ◽

Late Holocene ◽

Thermohaline Circulation ◽

Sea Water ◽

Labrador Sea ◽

Circulation System ◽

Deep Water Formation ◽

Holocene Thermal Maximum ◽

Water Formation

Abstract. The Labrador Sea is important for the modern global thermohaline circulation system through the formation of intermediate Labrador Sea Water (LSW) that has been hypothesized to stabilize the modern mode of North Atlantic deep-water circulation. The rate of LSW formation is controlled by the amount of winter heat loss to the atmosphere, the expanse of freshwater in the convection region and the inflow of saline waters from the Atlantic. The Labrador Sea, today, receives freshwater through the East and West Greenland Currents (EGC, WGC) and the Labrador Current (LC). Several studies have suggested the WGC to be the main supplier of freshwater to the Labrador Sea, but the role of the southward flowing LC in Labrador Sea convection is still debated. At the same time, many paleoceanographic reconstructions from the Labrador Shelf focussed on late Deglacial to early Holocene meltwater run-off from the Laurentide Ice Sheet (LIS), whereas little information exists about LC variability since the final melting of the LIS about 7,000 years ago. In order to enable better assessment of the role of the LC in deep-water formation and its importance for Holocene climate variability in Atlantic Canada, this study presents high-resolution middle to late Holocene records of sea surface and bottom water temperatures, freshening and sea ice cover on the Labrador Shelf during the last 6,000 years. Our records reveal that the LC underwent three major oceanographic phases from the Mid- to Late Holocene. From 6.2 to 5.6 ka BP, the LC experienced a cold episode that was followed by warmer conditions between 5.6 and 2.1 ka BP, possibly associated with the late Holocene Thermal Maximum. Although surface waters on the Labrador Shelf cooled gradually after 3 ka BP in response to the Neoglaciation, Labrador Shelf subsurface/bottom waters show a shift to warmer temperatures after 2.1 ka BP. Although such an inverse stratification by cooling of surface and warming of subsurface waters on the Labrador Shelf would suggest a diminished convection during the last two millennia compared to the mid-Holocene, it remains difficult to assess whether hydrographic conditions in the LC have had a significant impact on Labrador Sea deep-water formation.

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Surface and subsurface Labrador Shelf water mass conditions during the last 6,000 years

10.5194/egusphere-egu2020-3160 ◽

2020 ◽

Author(s):

Annalena Lochte ◽

Ralph Schneider ◽

Janne Repschläger ◽

Markus Kienast ◽

Thomas Blanz ◽

...

Keyword(s):

Deep Water ◽

Late Holocene ◽

Thermohaline Circulation ◽

Sea Water ◽

Labrador Sea ◽

Circulation System ◽

Deep Water Formation ◽

The North ◽

Water Formation

The Labrador Sea is important for the modern global thermohaline circulation system through the formation of intermediate Labrador Sea Water (LSW) that has been hypothesized to stabilize the modern mode of North Atlantic deep-water circulation. The rate of LSW formation is controlled by the amount of winter heat loss to the atmosphere, the expanse of freshwater in the convection region and the inflow of saline waters from the Atlantic. The Labrador Sea, today, receives freshwater through the East and West Greenland Currents (EGC, WGC) and the Labrador Current (LC). Several studies have suggested the WGC to be the main supplier of freshwater to the Labrador Sea, but the role of the southward flowing LC in Labrador Sea convection is still debated. At the same time, many paleoceanographic reconstructions from the Labrador Shelf focussed on late Deglacial to early Holocene meltwater run-off from the Laurentide Ice Sheet (LIS), whereas little information exists about LC variability since the final melting of the LIS about 7,000 years ago. In order to enable better assessment of the role of the LC in deep-water formation and its importance for Holocene climate variability in Atlantic Canada, this study presents high-resolution middle to late Holocene records of sea surface and bottom water temperatures, freshening and sea ice cover on the Labrador Shelf during the last 6,000 years. Our records reveal that the LC underwent three major oceanographic phases from the Mid- to Late Holocene. From 6.2 to 5.6 ka BP, the LC experienced a cold episode that was followed by warmer conditions between 5.6 and 2.1 ka BP, possibly associated with the late Holocene Thermal Maximum. Although surface waters on the Labrador Shelf cooled gradually after 3 ka BP in response to the Neoglaciation, Labrador Shelf subsurface/bottom waters show a shift to warmer temperatures after 2.1 ka BP. Although such an inverse stratification by cooling of surface and warming of subsurface waters on the Labrador Shelf would suggest a diminished convection during the last two millennia compared to the mid-Holocene, it remains difficult to assess whether hydrographic conditions in the LC have had a significant impact on Labrador Sea deep-water formation. This study was conducted within the HOSST research school with the aim to improve our understanding of the critical processes involved in the North Altantic thermohaline circulation, which is particularly important in light of current climate change.&#160;

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Revisiting the Role of Convective Deep Water Formation in Northern Baltic Sea Bottom Water Renewal

Journal of Geophysical Research Oceans ◽

10.1029/2020jc016114 ◽

2020 ◽

Vol 125 (10) ◽

Author(s):

Céline Giesse ◽

H. E. Markus Meier ◽

Thomas Neumann ◽

Matthias Moros

Keyword(s):

Baltic Sea ◽

Deep Water ◽

Bottom Water ◽

Deep Water Formation ◽

Water Renewal ◽

Sea Bottom ◽

Water Formation

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Localization of Deep Water Formation: Role of Atmospheric Moisture Transport and Geometrical Constraints on Ocean Circulation

Journal of Climate ◽

10.1175/2009jcli3197.1 ◽

2010 ◽

Vol 23 (6) ◽

pp. 1456-1476 ◽

Cited By ~ 61

Author(s):

David Ferreira ◽

John Marshall ◽

Jean-Michel Campin

Keyword(s):

Ocean Circulation ◽

Deep Water ◽

Atmospheric Precipitation ◽

North Pole ◽

Present Climate ◽

Deep Water Formation ◽

The North ◽

Water Formation ◽

Small Basin

Abstract A series of coupled atmosphere–ocean–ice aquaplanet experiments is described in which topological constraints on ocean circulation are introduced to study the role of ocean circulation on the mean climate of the coupled system. It is imagined that the earth is completely covered by an ocean of uniform depth except for the presence or absence of narrow barriers that extend from the bottom of the ocean to the sea surface. The following four configurations are described: Aqua (no land), Ridge (one barrier extends from pole to pole), Drake (one barrier extends from the North Pole to 35°S), and DDrake (two such barriers are set 90° apart and join at the North Pole, separating the ocean into a large basin and a small basin, connected to the south). On moving from Aqua to Ridge to Drake to DDrake, the energy transports in the equilibrium solutions become increasingly “realistic,” culminating in DDrake, which has an uncanny resemblance to the present climate. Remarkably, the zonal-average climates of Drake and DDrake are strikingly similar, exhibiting almost identical heat and freshwater transports, and meridional overturning circulations. However, Drake and DDrake differ dramatically in their regional climates. The small and large basins of DDrake exhibit distinctive Atlantic-like and Pacific-like characteristics, respectively: the small basin is warmer, saltier, and denser at the surface than the large basin, and is the main site of deep water formation with a deep overturning circulation and strong northward ocean heat transport. A sensitivity experiment with DDrake demonstrates that the salinity contrast between the two basins, and hence the localization of deep convection, results from a deficit of precipitation, rather than an excess of evaporation, over the small basin. It is argued that the width of the small basin relative to the zonal fetch of atmospheric precipitation is the key to understanding this salinity contrast. Finally, it is argued that many gross features of the present climate are consequences of two topological asymmetries that have profound effects on ocean circulation: a meridional asymmetry (circumpolar flow in the Southern Hemisphere; blocked flow in the Northern Hemisphere) and a zonal asymmetry (a small basin and a large basin).

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