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

During the last interglacial period, global temperatures were ~2°C warmer than at present and sea level was 6 to 8 meters higher. Southern Ocean sediments reveal a spike in authigenic uranium 127,000 years ago, within the last interglacial, reflecting decreased oxygenation of deep water by Antarctic Bottom Water (AABW). Unlike ice age reductions in AABW, the interglacial stagnation event appears decoupled from open ocean conditions and may have resulted from coastal freshening due to mass loss from the Antarctic ice sheet. AABW reduction coincided with increased North Atlantic Deep Water (NADW) formation, and the subsequent reinvigoration in AABW coincided with reduced NADW formation. Thus, alternation of deep water formation between the Antarctic and the North Atlantic, believed to characterize ice ages, apparently also occurs in warm climates.

Download Full-text

Variability in surface and deep water conditions in the nordic seas during the last interglacial period

Quaternary Science Reviews ◽

10.1016/s0277-3791(98)00038-9 ◽

1998 ◽

Vol 17 (9-10) ◽

pp. 963-985 ◽

Cited By ~ 65

Author(s):

Torben Fronval ◽

Eystein Jansen ◽

Haflidi Haflidason ◽

Hans Petter Sejrup

Keyword(s):

Deep Water ◽

Interglacial Period ◽

Last Interglacial ◽

Nordic Seas ◽

Last Interglacial Period ◽

Water Conditions

Download Full-text

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.

Download Full-text

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.

Download Full-text

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.

Download Full-text

Surface and deep-water hydrography on Gardar Drift (Iceland Basin) during the last interglacial period

Earth and Planetary Science Letters ◽

10.1016/j.epsl.2009.08.040 ◽

2009 ◽

Vol 288 (1-2) ◽

pp. 10-19 ◽

Cited By ~ 48

Author(s):

David A. Hodell ◽

Emily Kay Minth ◽

Jason H. Curtis ◽

I. Nicholas McCave ◽

Ian R. Hall ◽

...

Keyword(s):

Deep Water ◽

Interglacial Period ◽

Last Interglacial ◽

Iceland Basin ◽

Last Interglacial Period

Download Full-text

Intensification of the Atlantic Deep Circulation by the Canadian Archipelago Throughflow

Journal of Physical Oceanography ◽

10.1175/jpo2709.1 ◽

2005 ◽

Vol 35 (5) ◽

pp. 775-789 ◽

Cited By ~ 22

Author(s):

Yoshiki Komuro ◽

Hiroyasu Hasumi

Keyword(s):

Deep Water ◽

The Arctic ◽

Global Ocean ◽

Labrador Sea ◽

Fram Strait ◽

Deep Water Formation ◽

Surface Salinity ◽

Deep Circulation ◽

Low Salinity ◽

Water Formation

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.

Download Full-text

Sensitivity of biogenic carbon export to ocean climate in the Labrador Sea, a deep-water formation region

Global Biogeochemical Cycles ◽

10.1029/2002gb001969 ◽

2003 ◽

Vol 17 (4) ◽

pp. n/a-n/a ◽

Cited By ~ 1

Author(s):

Ru Cheng Tian ◽

Alain F. Vézina ◽

Don Deibel ◽

Richard B. Rivkin

Keyword(s):

Deep Water ◽

Labrador Sea ◽

Deep Water Formation ◽

Carbon Export ◽

Formation Region ◽

Ocean Climate ◽

Biogenic Carbon ◽

Water Formation

Download Full-text

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.

Download Full-text