Intensification of the Atlantic Deep Circulation by the Canadian Archipelago Throughflow

Abstract Low-salinity water export through the Canadian Archipelago is one of the main components of the freshwater budget in the Arctic Ocean. Nevertheless, the Canadian Archipelago is closed in most global ocean models. How it is that deep-water formation at high latitudes of the Northern Hemisphere depends on the opening and closing of the Canadian Archipelago is investigated. An ice–ocean coupled model, whose horizontal resolution is 1°, is used without restoring surface salinity to observed data. When the Canadian Archipelago is open, the Atlantic deep circulation strengthens by 21%. This enhancement is caused by intensification of deep-water formation in the northern North Atlantic Ocean. Surface salinity in these regions is affected by the East Greenland Current, which flows from the Fram Strait and increases its salinity when the Canadian Archipelago is opened. The low-salinity flow through the Canadian Archipelago affects surface salinity only in the western part of the Labrador Sea. A cyclonic circulation in the Labrador Sea plays an important role in limiting the direct impact of the Canadian Archipelago throughflow. Consequently, the deep-water formation there is intensified and the Atlantic deep circulation is strengthened. Thus, it is suggested that the Canadian Archipelago throughflow does not weaken the Atlantic deep circulation by the freshening of the Labrador Sea but strengthens it by the salinity increase in the Fram Strait.

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

Journal of Physical Oceanography ◽

10.1175/jpo-d-15-0210.1 ◽

2016 ◽

Vol 46 (7) ◽

pp. 2169-2182 ◽

Cited By ~ 23

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.

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Arctic–North Atlantic Interactions and Multidecadal Variability of the Meridional Overturning Circulation

Journal of Climate ◽

10.1175/jcli3462.1 ◽

2005 ◽

Vol 18 (19) ◽

pp. 4013-4031 ◽

Cited By ~ 190

Author(s):

Johann H. Jungclaus ◽

Helmuth Haak ◽

Mojib Latif ◽

Uwe Mikolajewicz

Keyword(s):

North Atlantic ◽

Deep Water ◽

Ocean Model ◽

Meridional Overturning Circulation ◽

The Arctic ◽

Deep Water Formation ◽

Overturning Circulation ◽

Multidecadal Variability ◽

Water Formation ◽

Meridional Overturning

Abstract Analyses of a 500-yr control integration with the non-flux-adjusted coupled atmosphere–sea ice–ocean model ECHAM5/Max-Planck-Institute Ocean Model (MPI-OM) show pronounced multidecadal fluctuations of the Atlantic overturning circulation and the associated meridional heat transport. The period of the oscillations is about 70–80 yr. The low-frequency variability of the meridional overturning circulation (MOC) contributes substantially to sea surface temperature and sea ice fluctuations in the North Atlantic. The strength of the overturning circulation is related to the convective activity in the deep-water formation regions, most notably the Labrador Sea, and the time-varying control on the freshwater export from the Arctic to the convection sites modulates the overturning circulation. The variability is sustained by an interplay between the storage and release of freshwater from the central Arctic and circulation changes in the Nordic Seas that are caused by variations in the Atlantic heat and salt transport. The relatively high resolution in the deep-water formation region and the Arctic Ocean suggests that a better representation of convective and frontal processes not only leads to an improvement in the mean state but also introduces new mechanisms determining multidecadal variability in large-scale ocean circulation.

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North Atlantic deep water formation and AMOC in CMIP5 models

Ocean Science ◽

10.5194/os-13-609-2017 ◽

2017 ◽

Vol 13 (4) ◽

pp. 609-622 ◽

Cited By ~ 26

Author(s):

Céline Heuzé

Keyword(s):

Sea Ice ◽

Ocean Circulation ◽

North Atlantic ◽

Deep Water ◽

Deep Convection ◽

The Arctic ◽

Subpolar Gyre ◽

Deep Water Formation ◽

Nordic Seas ◽

Water Formation

Abstract. Deep water formation in climate models is indicative of their ability to simulate future ocean circulation, carbon and heat uptake, and sea level rise. Present-day temperature, salinity, sea ice concentration and ocean transport in the North Atlantic subpolar gyre and Nordic Seas from 23 CMIP5 (Climate Model Intercomparison Project, phase 5) models are compared with observations to assess the biases, causes and consequences of North Atlantic deep convection in models. The majority of models convect too deep, over too large an area, too often and too far south. Deep convection occurs at the sea ice edge and is most realistic in models with accurate sea ice extent, mostly those using the CICE model. Half of the models convect in response to local cooling or salinification of the surface waters; only a third have a dynamic relationship between freshwater coming from the Arctic and deep convection. The models with the most intense deep convection have the warmest deep waters, due to a redistribution of heat through the water column. For the majority of models, the variability of the Atlantic Meridional Overturning Circulation (AMOC) is explained by the volumes of deep water produced in the subpolar gyre and Nordic Seas up to 2 years before. In turn, models with the strongest AMOC have the largest heat export to the Arctic. Understanding the dynamical drivers of deep convection and AMOC in models is hence key to realistically forecasting Arctic oceanic warming and its consequences for the global ocean circulation, cryosphere and marine life.

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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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Assessing the stability of the AMOC during past warm climates

10.5194/egusphere-egu21-15298 ◽

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

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 (&#948;18O and &#948;13C) 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 &#949;Nd 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.

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The global ocean circulation on a retrograde rotating earth

Climate of the Past ◽

10.5194/cp-7-487-2011 ◽

2011 ◽

Vol 7 (2) ◽

pp. 487-499 ◽

Cited By ~ 3

Author(s):

V. Kamphuis ◽

S. E. Huisman ◽

H. A. Dijkstra

Keyword(s):

Ocean Circulation ◽

Deep Water ◽

North Pacific ◽

Global Ocean ◽

Freshwater Flux ◽

Deep Water Formation ◽

The North ◽

Water Formation ◽

Global Ocean Circulation ◽

The North Pacific

Abstract. To understand the three-dimensional ocean circulation patterns that have occurred in past continental geometries, it is crucial to study the role of the present-day continental geometry and surface (wind stress and buoyancy) forcing on the present-day global ocean circulation. This circulation, often referred to as the Conveyor state, is characterised by an Atlantic Meridional Overturning Circulation (MOC) with a deep water formation at northern latitudes and the absence of such a deep water formation in the North Pacific. This MOC asymmetry is often attributed to the difference in surface freshwater flux: the Atlantic as a whole is a basin with net evaporation, while the Pacific receives net precipitation. This issue is revisited in this paper by considering the global ocean circulation on a retrograde rotating earth, computing an equilibrium state of the coupled atmosphere-ocean-land surface-sea ice model CCSM3. The Atlantic-Pacific asymmetry in surface freshwater flux is indeed reversed, but the ocean circulation pattern is not an Inverse Conveyor state (with deep water formation in the North Pacific) as there is relatively weak but intermittently strong deep water formation in the North Atlantic. Using a fully-implicit, global ocean-only model the stability properties of the Atlantic MOC on a retrograde rotating earth are also investigated, showing a similar regime of multiple equilibria as in the present-day case. These results indicate that the present-day asymmetry in surface freshwater flux is not the most important factor setting the Atlantic-Pacific salinity difference and, thereby, the asymmetry in the global MOC.

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

10.5194/egusphere-egu2020-786 ◽

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

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.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 (&#949;Nd: -29 to -35) and the Sr isotope composition a slight (87Sr/86Sr: 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.[1] Funder & Fredskild (1989) Quaternary geology of Canada and Greenland, 775&#8211;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] M&#248;ller et al. (2006) The Holocene 16, 685-695.

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

Nature ◽

10.1038/35074059 ◽

2001 ◽

Vol 410 (6832) ◽

pp. 1073-1077 ◽

Cited By ~ 170

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

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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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