Using reconstructed Irminger Water changes within the past three decades to connect the West Greenland shelf to the production of Labrador Sea Water

The Arctic ◽

Labrador Sea ◽

The West ◽

West Greenland ◽

The Past ◽

Local Water ◽

In this study we analyze the exchange processes between the West Greenland shelf and the Labrador Sea. This region is affected by warm and saline waters originating from the subtropical North Atlantic, as well as cold and fresh waters from the Arctic and the Greenland Ice Sheet. Heat and freshwater both impact the local formation of Labrador Sea Water (LSW) that itself is a major contributor to the Atlantic Meridional Overturning Circulation.We use the ARMOR3D large-scale hydrographic data set from the Copernicus Marine Environmental Monitoring Service (CMEMS) and validate it with ship-based measurements in the period between 1993 to 2018. By extracting cross-shelf sections from ARMOR3D for various locations around Greenland, we reconstruct time series of local water masses like the Irminger Water (IW) for the past three decades. Previous studies from the West Greenland shelf have shown that IW properties are locally anti-correlated to changes in LSW. We analyze the interannual and decadal variability of these IW time series and compare them towards hydrographic changes observed in the interior Labrador Sea.Since ARMOR3D allows us to investigate interannual and decadal changes along cross-shelf sections, the goal of this study is to unravel the complex connection between changes in the shelf regions around Greenland and the interior Labrador Sea, especially the local water mass production.

How Does Labrador Sea Water Enter the Deep Western Boundary Current?

Journal of Physical Oceanography ◽

10.1175/2007jpo3807.1 ◽

2008 ◽

Vol 38 (5) ◽

pp. 968-983 ◽

Cited By ~ 18

Author(s):

Jaime B. Palter ◽

M. Susan Lozier ◽

Kara L. Lavender

Keyword(s):

Heat Flux ◽

Water Mass ◽

Sea Water ◽

Western Boundary Current ◽

Labrador Sea ◽

Western Boundary ◽

Boundary Current ◽

Deep Western Boundary Current ◽

Abstract Labrador Sea Water (LSW), a dense water mass formed by convection in the subpolar North Atlantic, is an important constituent of the meridional overturning circulation. Understanding how the water mass enters the deep western boundary current (DWBC), one of the primary pathways by which it exits the subpolar gyre, can shed light on the continuity between climate conditions in the formation region and their downstream signal. Using the trajectories of (profiling) autonomous Lagrangian circulation explorer [(P)ALACE] floats, operating between 1996 and 2002, three processes are evaluated for their role in the entry of Labrador Sea Water in the DWBC: 1) LSW is formed directly in the DWBC, 2) eddies flux LSW laterally from the interior Labrador Sea to the DWBC, and 3) a horizontally divergent mean flow advects LSW from the interior to the DWBC. A comparison of the heat flux associated with each of these three mechanisms suggests that all three contribute to the transformation of the boundary current as it transits the Labrador Sea. The formation of LSW directly in the DWBC and the eddy heat flux between the interior Labrador Sea and the DWBC may play leading roles in setting the interannual variability of the exported water mass.

Origin and Composition of Seasonal Labrador Sea Freshwater

Journal of Physical Oceanography ◽

10.1175/jpo3065.1 ◽

2007 ◽

Vol 37 (6) ◽

pp. 1445-1454 ◽

Cited By ~ 44

Author(s):

Sunke Schmidt ◽

Uwe Send

Keyword(s):

Time Scales ◽

Late Summer ◽

The Arctic ◽

Labrador Sea ◽

The West ◽

East Greenland ◽

West Greenland ◽

Boundary Currents ◽

East Greenland Current ◽

West Greenland Current

Abstract The depth of winter convection in the central Labrador Sea is strongly influenced by the prevailing stratification in late summer. For this late summer stratification salinity is as important as temperature, and in the upper water layers salinity even dominates. To analyze the source of the spring and summer freshening in the central region, seasonal freshwater cycles have been constructed for the interior Labrador Sea, the West Greenland Current, and the Labrador Current. It is shown that none of the local freshwater sources is responsible for the spring–summer freshening in the interior, which appears to occur in two separate events in April to May and July to September. Comparing the timing and volume estimates of the seasonal freshwater cycles of the boundary currents with the central Labrador Sea helps in understanding the origin of the interior freshwater signals. The first smaller pulse cannot be attributed clearly to either of the boundary currents. The second one is about three times stronger and supplies 60% of the seasonal summer freshwater. Transport estimates and calculated mixing properties provide evidence that its source is the West Greenland Current. The finding implies a connection also on interannual time scales between Labrador Sea surface salinity and freshwater sources in the West Greenland Current and farther upstream in the East Greenland Current. The freshwater input from the West Greenland Current thus also is the likely pathway for the known modulation of Labrador Sea Water mass formation by freshwater export from the Arctic (via the East Greenland Current), which implies some predictability on longer time scales.

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 ◽

Subtropical Gyre ◽

Global Ocean ◽

Labrador Sea ◽

Deep Water Formation ◽

Water Formation ◽

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.

Labrador Sea Water Formation Rate and Its Impact on the Local Meridional Overturning Circulation

Journal of Geophysical Research Oceans ◽

10.1029/2019jc015065 ◽

2019 ◽

Vol 124 (8) ◽

pp. 5654-5670 ◽

Cited By ~ 4

Author(s):

Charlène Feucher ◽

Yarisbel Garcia‐Quintana ◽

Igor Yashayaev ◽

Xianmin Hu ◽

Paul G. Myers

Keyword(s):

Sea Water ◽

Formation Rate ◽

Labrador Sea ◽

Overturning Circulation ◽

Water Formation ◽

Meridional Overturning ◽

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

Ventilation variability of Labrador Sea Water and its impact on oxygen and anthropogenic carbon: a review

10.1098/rsta.2016.0321 ◽

2017 ◽

Vol 375 (2102) ◽

pp. 20160321 ◽

Cited By ~ 10

Author(s):

Monika Rhein ◽

Reiner Steinfeldt ◽

Dagmar Kieke ◽

Ilaria Stendardo ◽

Igor Yashayaev

Keyword(s):

Time Scales ◽

North Atlantic ◽

Sea Water ◽

Labrador Sea ◽

Southern Boundary ◽

Rate Of Increase ◽

Anthropogenic Carbon ◽

Warming World ◽

Ventilation of Labrador Sea Water (LSW) receives ample attention because of its potential relation to the strength of the Atlantic Meridional Overturning Circulation (AMOC). Here, we provide an overview of the changes of LSW from observations in the Labrador Sea and from the southern boundary of the subpolar gyre at 47° N. A strong winter-time atmospheric cooling over the Labrador Sea led to intense and deep convection, producing a thick and dense LSW layer as, for instance, in the early to mid-1990s. The weaker convection in the following years mostly ventilated less dense LSW vintages and also reduced the supply of oxygen. As a further consequence, the rate of uptake of anthropogenic carbon by LSW decreased between the two time periods 1996–1999 and 2007–2010 in the western subpolar North Atlantic. In the eastern basins, the rate of increase in anthropogenic carbon became greater due to the delayed advection of LSW that was ventilated in previous years. Starting in winter 2013/2014 and prevailing at least into winter 2015/2016, production of denser and more voluminous LSW resumed. Increasing oxygen signals have already been found in the western boundary current at 47° N. On decadal and shorter time scales, anomalous cold atmospheric conditions over the Labrador Sea lead to an intensification of convection. On multi-decadal time scales, the ‘cold blob’ in the subpolar North Atlantic projected by climate models in the next 100 years is linked to a weaker AMOC and weaker convection (and thus deoxygenation) in the Labrador Sea. This article is part of the themed issue ‘Ocean ventilation and deoxygenation in a warming world’.

Local and Downstream Relationships between Labrador Sea Water Volume and North Atlantic Meridional Overturning Circulation Variability

Journal of Climate ◽

10.1175/jcli-d-18-0735.1 ◽

2019 ◽

Vol 32 (13) ◽

pp. 3883-3898 ◽

Cited By ~ 11

Author(s):

Feili Li ◽

M. Susan Lozier ◽

Gokhan Danabasoglu ◽

Naomi P. Holliday ◽

Young-Oh Kwon ◽

...

Keyword(s):

Time Scales ◽

North Atlantic ◽

Sea Water ◽

Atlantic Meridional Overturning Circulation ◽

Global Ocean ◽

Labrador Sea ◽

Overturning Circulation ◽

Meridional Overturning ◽

Abstract While it has generally been understood that the production of Labrador Sea Water (LSW) impacts the Atlantic meridional overturning circulation (MOC), this relationship has not been explored extensively or validated against observations. To explore this relationship, a suite of global ocean–sea ice models forced by the same interannually varying atmospheric dataset, varying in resolution from non-eddy-permitting to eddy-permitting (1°–1/4°), is analyzed to investigate the local and downstream relationships between LSW formation and the MOC on interannual to decadal time scales. While all models display a strong relationship between changes in the LSW volume and the MOC in the Labrador Sea, this relationship degrades considerably downstream of the Labrador Sea. In particular, there is no consistent pattern among the models in the North Atlantic subtropical basin over interannual to decadal time scales. Furthermore, the strong response of the MOC in the Labrador Sea to LSW volume changes in that basin may be biased by the overproduction of LSW in many models compared to observations. This analysis shows that changes in LSW volume in the Labrador Sea cannot be clearly and consistently linked to a coherent MOC response across latitudes over interannual to decadal time scales in ocean hindcast simulations of the last half century. Similarly, no coherent relationships are identified between the MOC and the Labrador Sea mixed layer depth or the density of newly formed LSW across latitudes or across models over interannual to decadal time scales.

Structure, variability, and dynamics of the West Greenland Boundary Current System

10.1575/1912/27886 ◽

2022 ◽

Author(s):

◽

Astrid Pacini

Keyword(s):

Current System ◽

Labrador Sea ◽

Small Scale ◽

Western Boundary ◽

Coastal Current ◽

Boundary Current ◽

The West ◽

West Greenland ◽

Atlantic Origin

The ventilation of intermediate waters in the Labrador Sea has important implications for the strength of the Atlantic Meridional Overturning Circulation. Boundary current-interior interactions regulate the exchange of properties between the slope and the basin, which in turn regulates the magnitude of interior convection and the export of ventilated waters from the subpolar gyre. This thesis characterizes theWest Greenland Boundary Current System near Cape Farewell across a range of spatio-temporal scales. The boundary current system is composed of three velocity cores: (1) the West Greenland Coastal Current (WGCC), transporting Greenland and Arctic meltwaters on the shelf; (2) the West Greenland Current (WGC), which advects warm, saline Atlantic-origin water at depth, meltwaters at the surface, and newly-ventilated Labrador Sea Water (LSW); and (3) the Deep Western Boundary Current, which carries dense overflow waters ventilated in the Nordic Seas. The seasonal presence of the LSW and Atlantic-origin water are dictated by air-sea buoyancy forcing, while the seasonality of the WGCC is governed by remote wind forcing and the propagation of coastally trapped waves from East Greenland. Using mooring data and hydrographic surveys, we demonstrate mid-depth intensified cyclones generated at Denmark Strait are found offshore of the WGC and enhance the overflow water transport at synoptic timescales. Using mooring, hydrographic, and satellite data, we demonstrate that the WGC undergoes extensive meandering due to baroclinic instability that is enhanced in winter due to LSW formation adjacent to the current. This leads to the production of small-scale, anticyclonic eddies that can account for the entirety of wintertime heat loss within the Labrador Sea. The meanders are shown to trigger the formation of Irminger Rings downstream. Using mooring, hydrographic, atmospheric, and Lagrangian data, and a mixing model, we find that strong atmospheric storms known as forward tip jets cause upwelling at the shelfbreak that triggers offshore export of freshwater. This freshwater flux can explain the observed lack of ventilation in the eastern Labrador Sea. Together, this thesis documents previously unobserved interannual, seasonal, and synoptic-scale variability and dynamics within the West Greenland boundary current system that must be accounted for in future modeling.

Topographic and Glaciological Controls on Holocene Ice-Sheet Margin Dynamics. Central West Greenland

Annals of Glaciology ◽

10.3189/s0260305500008806 ◽

1990 ◽

Vol 14 ◽

pp. 307-310 ◽

Cited By ~ 11

Author(s):

C.R. Warren ◽

N.R.J. Hulton

Keyword(s):

Ice Sheet ◽

Greenland Ice Sheet ◽

Glacial Maximum ◽

Warm Climate ◽

Short Term ◽

The West ◽

West Greenland ◽

The Past

The retreat of the West Greenland ice sheet from its Sisimiut (Wisconsinan) glacial maximum, was punctuated by a series of Stillstands or small readvances that formed numerous moraines. These landforms have been interpreted in the past as the result of short-term, regional falls in ablation-season temperatures. However, mapping of the geomorphological evidence south of Ilulissat (Jakobshavn) suggests that retreat behaviour was not primarily governed by climate, and therefore that the former ice margins are not palaeoclimatically significant. During warm climate ice-sheet wastage, the successive quasi-stable positions adopted by the ice margin were largely governed by topography. The retreat of the inherently unstable calving glaciers was arrested only at topographically-determined locations where stability could be achieved.

The History of the Labrador Sea Water: Production, Spreading, Transformation and Loss

Arctic–Subarctic Ocean Fluxes ◽

10.1007/978-1-4020-6774-7_25 ◽

2008 ◽

pp. 569-612 ◽

Cited By ~ 18

Author(s):

Igor Yashayaev ◽

N. Penny Holliday ◽

Manfred Bersch ◽

Hendrik M. van Aken

Keyword(s):

Sea Water ◽

Labrador Sea ◽

Water Production ◽

History Of ◽

Detecting changes in Labrador Sea Water through a water mass analysis of BATS data

Ocean Science Discussions ◽

10.5194/osd-2-417-2005 ◽

2005 ◽

Vol 2 (4) ◽

pp. 417-435 ◽

Cited By ~ 1

Author(s):

A. Henry-Edwards ◽

M. Tomczak

Keyword(s):

Water Mass ◽

Sea Water ◽

Source Region ◽

Labrador Sea ◽

Sargasso Sea ◽

Mass Analysis ◽

Data Set ◽

Water Mass Analysis ◽

Quadratic Programming Method ◽

Abstract. A new water mass analysis technique is used to analyse the BATS oceanographic data set in the Sargasso Sea of 1988-1998 for changes in Labrador Sea Water (LSW) properties. The technique is based on a sequential quadratic programming method and requires careful definition of constraints to produce reliable results. Variations in LSW temperature and salinity observed in the Labrador Sea are used to define the constraints. It is shown that to minimize the residuals while matching the observed temperature and salinity changes in the source region the nitrate concentration in the Labrador Sea has to be allowed to vary as well. It is concluded that during the period of investigation nitrate underwent significant variations in the Labrador Sea.