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

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.

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

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.

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

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

<p><span>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 </span><span>to assess whether hydrographic conditions in the LC </span><span>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. </span></p>

scholarly journals Breaking the Linkage Between Labrador Sea Water Production and Its Advective Export to the Subtropical Gyre

2016 ◽  
Vol 46 (7) ◽  
pp. 2169-2182 ◽  
Author(s):  
Sijia Zou ◽  
M. Susan Lozier
Keyword(s):  
Deep Water ◽  
Sea Water ◽  
Water Masses ◽  
Meridional Overturning Circulation ◽  
Subtropical Gyre ◽  
Global Ocean ◽  
Labrador Sea ◽  
Deep Water Formation ◽  
Water Formation ◽  
Labrador Sea Water

AbstractDeep water formation in the northern North Atlantic has been of long-standing interest because the resultant water masses, along with those that flow over the Greenland–Scotland Ridge, constitute the lower limb of the Atlantic meridional overturning circulation (AMOC), which carries these cold, deep waters southward to the subtropical region and beyond. It has long been assumed that an increase in deep water formation would result in a larger southward export of newly formed deep water masses. However, recent observations of Lagrangian floats have raised questions about this linkage. Motivated by these observations, the relationship between convective activity in the Labrador Sea and the export of newly formed Labrador Sea Water (LSW), the shallowest component of the deep AMOC, to the subtropics is explored. This study uses simulated Lagrangian pathways of synthetic floats produced with output from a global ocean–sea ice model. It is shown that substantial recirculation of newly formed LSW in the subpolar gyre leads to a relatively small fraction of this water exported to the subtropical gyre: 40 years after release, only 46% of the floats are able to reach the subtropics. Furthermore, waters produced from any one particular convection event are not collectively and contemporaneously exported to the subtropical gyre, such that the waters that are exported to the subtropical gyre have a wide distribution in age.

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

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

<p>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 ‘Arctic Amplification’. 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.</p>

Assessing the stability of the AMOC during past warm climates

2021 ◽  
Author(s):  
Megan Murphy O' Connor ◽  
Christophe Colin ◽  
Audrey Morley
Keyword(s):  
North Atlantic ◽  
Deep Water ◽  
Meridional Overturning Circulation ◽  
Labrador Sea ◽  
Deep Water Formation ◽  
Nordic Seas ◽  
Water Formation ◽  
Rockall Trough ◽  
Eastern North Atlantic ◽  
Warm Climates

<p>There is emergent evidence that abrupt shifts of the Atlantic Meridional Overturning Circulation (AMOC) have occurred during interglacial periods, with recent observations and model simulations showing that we may have over-estimated its stability during warm climates. In this study, we present a multi-proxy reconstruction of deep-water characteristics from the Rockall Trough in the Eastern North Atlantic to assess the variability of Nordic seas and Labrador Sea deep-water formation during past interglacial periods MIS 1, 5, 11, and 19. To test the warm climate stability hypothesis and to constrain the variability of deep-water formation for past warm climates, we performed geochemical analysis on planktic (Nd isotopes) and benthic foraminifera (δ<sup>18</sup>O and δ<sup>13</sup>C) along with sedimentological analysis. This approach allows us to reconstruct paleocurrent flow strength, as well as the origin and contribution of different water masses to one of the deep-water components of the AMOC in the Rockall Trough. We found that deep-water properties varied considerably during each of our chosen periods. For example during the Holocene εNd variability is smaller (1.8 per mil) when compared to variability during MIS 19 (3.3 per mil), an interglacial that experienced very similar orbital boundary conditions. Our results confirm that deep-water variability in the eastern North Atlantic basin was more variable in previous interglacial periods when compared to our current Holocene and provide new insight into the relative contribution of Nordic Seas Deep Water and Labrador Sea Water in the Rockall trough.</p>

Neoglacial Ice Advance and Sediment Provenance Changes in Southwest Greenland and its Marginal Seas Traced by Radiogenic Isotopes

2020 ◽  
Author(s):  
Lina Madaj ◽  
Claude Hillaire-Marcel ◽  
Friedrich Lucassen ◽  
Simone Kasemann
Keyword(s):  
Marine Sediments ◽  
Deep Water ◽  
Radiogenic Isotopes ◽  
Labrador Sea ◽  
Coastal Current ◽  
Deep Water Formation ◽  
The West ◽  
The Holocene ◽  
Water Formation ◽  
Southwest Greenland

<p>Marine sediments from the West Greenland margin represent high-resolution archives of Holocene climate history, past ice sheet dynamics, changes in meltwater discharge and coastal current intensities. We investigate potential changes of sediment provenances using strontium (Sr) and neodymium (Nd) radiogenic isotopes as tracers for the origin and pathways of the silicate detrital fraction in marine sediments. Meltwater discharge and coastal currents are the most important transport pathways for detrital sediments into (northeast) Labrador Sea, which is an important pathway for freshwater from the Arctic Ocean and meltwater from the Greenland Ice Sheet to enter the North Atlantic, where deep water formation takes place. Variations in freshwater supply into Labrador Sea may influence deep water formation and therefore further circulation and climate patterns on a global scale.</p><p>The marine sediment record collected in Nuuk Trough, southwest Greenland, displays uniform isotopic compositions throughout most of the Holocene, indicating well mixed detrital material from local sources through meltwater discharge and distal sources transported via the West Greenland Current. From around 4 ka BP to present the composition of Nd isotopes reveals a steep (εNd: -29 to -35) and the Sr isotope composition a slight (<sup>87</sup>Sr/<sup>86</sup>Sr: 0.723 to 0.728) but pronounced shift. This time interval coincides with the transition into the Neoglacial time period [1], which is characterized by a significant drop in atmospheric temperatures [2], and the onset of the modern Labrador Sea circulation pattern (e.g. [3]). We suggest that the shift in Nd and Sr isotopes indicates a change towards less distal and more local sediment sources, possibly caused by enhanced erosion of the local bedrock during Neoglacial ice advance [4], along with a decrease in meltwater discharge [5] and coastal current strength, leading to a sediment delivery shift.</p><p>[1] Funder & Fredskild (1989) Quaternary geology of Canada and Greenland, 775–783. [2] Seidenkrantz et al. (2007) The Holocene 17, 387-401. [3] Fagel et al. (2004) Paleoceanography 19, PA3002. [4] Funder et al. (2011) Developments in Quaternary Sciences 15, 699-713, (and references therein). [5] Møller et al. (2006) The Holocene 16, 685-695.</p>

Absence of deep-water formation in the Labrador Sea during the last interglacial period

Nature ◽  
2001 ◽  
Vol 410 (6832) ◽  
pp. 1073-1077 ◽  
Author(s):  
C. Hillaire-Marcel ◽  
A. de Vernal ◽  
G. Bilodeau ◽  
A. J. Weaver
Keyword(s):  
Deep Water ◽  
Labrador Sea ◽  
Interglacial Period ◽  
Deep Water Formation ◽  
Last Interglacial ◽  
Last Interglacial Period ◽  
Water Formation

scholarly journals An examination of the role of particles in oceanic mercury cycling

2016 ◽  
Vol 374 (2081) ◽  
pp. 20150297 ◽  
Author(s):  
Carl H. Lamborg ◽  
Chad R. Hammerschmidt ◽  
Katlin L. Bowman
Keyword(s):  
Deep Water ◽  
Oceanic Water ◽  
Deep Water Formation ◽  
Mercury Cycling ◽  
Trace Element Chemistry ◽  
Sinking Particles ◽  
Water Formation ◽  
Climatic Impacts ◽  
Using Data

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’.

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

Ocean Science ◽  
2014 ◽  
Vol 10 (2) ◽  
pp. 227-241 ◽  
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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