Late Quaternary changes in surface water and deep water masses of the Nordic Seas and north-eastern North Atlantic: a review

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.

The silicon stable isotope distribution along the GEOVIDE section (GEOTRACES GA-01) of the North Atlantic Ocean

Biogeosciences ◽

10.5194/bg-15-5663-2018 ◽

2018 ◽

Vol 15 (18) ◽

pp. 5663-5676 ◽

Cited By ~ 3

Author(s):

Jill N. Sutton ◽

Gregory F. de Souza ◽

Maribel I. García-Ibáñez ◽

Christina L. De La Rocha

Keyword(s):

Stable Isotope ◽

Atlantic Ocean ◽

North Atlantic ◽

Deep Water ◽

North Atlantic Ocean ◽

Water Masses ◽

Labrador Sea ◽

The North ◽

The North Atlantic ◽

Eastern North Atlantic

Abstract. The stable isotope composition of dissolved silicon in seawater (δ30SiDSi) was examined at 10 stations along the GEOVIDE section (GEOTRACES GA-01), spanning the North Atlantic Ocean (40–60∘ N) and Labrador Sea. Variations in δ30SiDSi below 500 m were closely tied to the distribution of water masses. Higher δ30SiDSi values are associated with intermediate and deep water masses of northern Atlantic or Arctic Ocean origin, whilst lower δ30SiDSi values are associated with DSi-rich waters sourced ultimately from the Southern Ocean. Correspondingly, the lowest δ30SiDSi values were observed in the deep and abyssal eastern North Atlantic, where dense southern-sourced waters dominate. The extent to which the spreading of water masses influences the δ30SiDSi distribution is marked clearly by Labrador Sea Water (LSW), whose high δ30SiDSi signature is visible not only within its region of formation within the Labrador and Irminger seas, but also throughout the mid-depth western and eastern North Atlantic Ocean. Both δ30SiDSi and hydrographic parameters document the circulation of LSW into the eastern North Atlantic, where it overlies southern-sourced Lower Deep Water. The GEOVIDE δ30SiDSi distribution thus provides a clear view of the direct interaction between subpolar/polar water masses of northern and southern origin, and allow examination of the extent to which these far-field signals influence the local δ30SiDSi distribution.

Northward advection of Atlantic water in the eastern Nordic Seas over the last 3000 yr

Climate of the Past ◽

10.5194/cp-9-1505-2013 ◽

2013 ◽

Vol 9 (4) ◽

pp. 1505-1518 ◽

Cited By ~ 29

Author(s):

C. V. Dylmer ◽

J. Giraudeau ◽

F. Eynaud ◽

K. Husum ◽

A. De Vernal

Keyword(s):

Surface Water ◽

North Atlantic ◽

Barents Sea ◽

Water Masses ◽

Ice Age ◽

The Arctic ◽

Fram Strait ◽

Nordic Seas ◽

The North ◽

The North Atlantic

Abstract. Three marine sediment cores distributed along the Norwegian (MD95-2011), Barents Sea (JM09-KA11-GC), and Svalbard (HH11-134-BC) continental margins have been investigated in order to reconstruct changes in the poleward flow of Atlantic waters (AW) and in the nature of upper surface water masses within the eastern Nordic Seas over the last 3000 yr. These reconstructions are based on a limited set of coccolith proxies: the abundance ratio between Emiliania huxleyi and Coccolithus pelagicus, an index of Atlantic vs. Polar/Arctic surface water masses; and Gephyrocapsa muellerae, a drifted coccolith species from the temperate North Atlantic, whose abundance changes are related to variations in the strength of the North Atlantic Current. The entire investigated area, from 66 to 77° N, was affected by an overall increase in AW flow from 3000 cal yr BP (before present) to the present. The long-term modulation of westerlies' strength and location, which are essentially driven by the dominant mode of the North Atlantic Oscillation (NAO), is thought to explain the observed dynamics of poleward AW flow. The same mechanism also reconciles the recorded opposite zonal shifts in the location of the Arctic front between the area off western Norway and the western Barents Sea–eastern Fram Strait region. The Little Ice Age (LIA) was governed by deteriorating conditions, with Arctic/Polar waters dominating in the surface off western Svalbard and western Barents Sea, possibly associated with both severe sea ice conditions and a strongly reduced AW strength. A sudden short pulse of resumed high WSC (West Spitsbergen Current) flow interrupted this cold spell in eastern Fram Strait from 330 to 410 cal yr BP. Our dataset not only confirms the high amplitude warming of surface waters at the turn of the 19th century off western Svalbard, it also shows that such a warming was primarily induced by an excess flow of AW which stands as unprecedented over the last 3000 yr.

A major change in North Atlantic deep water circulation during the Early Pleistocene transition 1.6 million years ago

Climate of the Past Discussions ◽

10.5194/cpd-9-6495-2013 ◽

2013 ◽

Vol 9 (6) ◽

pp. 6495-6513 ◽

Cited By ~ 1

Author(s):

N. Khélifi ◽

M. Frank

Keyword(s):

North Atlantic ◽

Deep Water ◽

Late Quaternary ◽

Major Change ◽

Water Circulation ◽

Water Masses ◽

Early Pleistocene ◽

Global Ocean ◽

Northeast Atlantic ◽

Water Depths

Abstract. The global ocean-climate system has been highly sensitive to the formation and advection of deep water in the North Atlantic but its evolution over the Pliocene–Pleistocene global cooling is not fully understood. In particular, changes in the sources and mixing of prevailing deep waters are not well constrained. Here we present new records of the bottom-water radiogenic neodymium isotope (&varepsilon;Nd) variability obtained from three DSDP/ODP sites at water depths between 2100 and 5000 m in the Northeast Atlantic to reconstruct changes in deep water circulation over the past 4 million years. Prior to 1.6 million years ago (Ma), we find &varepsilon;Nd values primarily oscillating between −9 and −11 at all sites, consistent with enhanced vertical mixing of water masses. At 1.6 Ma, the &varepsilon;Nd signatures synchronously shifted to less radiogenic values around −12 at different water depths and water mass signatures gradually became more distinct. Since then values and amplitudes of "glacial/interglacial" &varepsilon;Nd oscillations have been similar to the Late Quaternary at each site. This change 1.6 Ma reflects a major reorganization of deep water circulation in the Northeast Atlantic towards a more stratified water column with distinct water masses accompanying the enhanced response of climate to the Earth's obliquity forcing during the Early Pleistocene transition.

Northward advection of Atlantic water in the eastern Nordic Seas over the last 3000 yr: a coccolith investigation of volume transport and surface water changes

Climate of the Past Discussions ◽

10.5194/cpd-9-1259-2013 ◽

2013 ◽

Vol 9 (2) ◽

pp. 1259-1295 ◽

Cited By ~ 1

Author(s):

C. V. Dylmer ◽

J. Giraudeau ◽

F. Eynaud ◽

K. Husum ◽

A. De Vernal

Keyword(s):

Surface Water ◽

North Atlantic ◽

Barents Sea ◽

Volume Transport ◽

Volume Flow ◽

Water Masses ◽

Fram Strait ◽

Nordic Seas ◽

The North ◽

The North Atlantic

Abstract. Three marine sediment cores distributed along the Norwegian (MD95-2011), Barents Sea (JM09-KA11-GC), and Svalbard (HH11-134-BC) continental margins have been investigated in order to reconstruct changes in the poleward flow of Atlantic Waters (AW) and in the nature of upper surface water masses within the eastern Nordic Seas over the last 3000 yr. These reconstructions are based on a limited set of coccolith proxies: the abundance ratio between Emiliania huxleyi and Coccolithus pelagicus, an index of Atlantic vs. Polar-Arctic surface water masses; and Gephyrocapsa muellerae, a drifted coccolith species from the temperate North Atlantic, whose abundance changes are related to variations in the volume transport of the North Atlantic Current and its northernmost extension (the West Spitsbergen Current – WSC) off western Svalbard. The entire investigated area, from 66 to 77° N, was affected by an overall increase in volume flow of AW from 3000 cal yr BP to Present. The long-term modulation of westerlies strength and location which are essentially driven by the dominant mode of the North Atlantic Oscillation (NAO), is thought to explain the observed dynamics of poleward AW flow. The same mechanism also reconciles the recorded opposite zonal shifts in the location of the Arctic Front between the area off western Norway and the Barents Sea-eastern Fram Strait region. The Little Ice Age was governed by deteriorating conditions, with Arctic/Polar waters dominating in the surface off western Svalbard and western Barents Sea, possibly associated with both severe sea-ice conditions and a strongly reduced AW volume flow. A sudden short pulse of resumed high WSC flow interrupted this cold spell in eastern Fram Strait from 330 to 410 cal yr BP, with a a magnitude only surpassed by the one which characterizes the Modern Period. Our dataset not only confirms the high amplitude warming of surface waters at the turn of the 19th century off western Svalbard, it also shows that such a warming was primarily induced by an excess volume flow of AW which stands as unprecedented over the last 3000 yr.

A major change in North Atlantic deep water circulation 1.6 million years ago

Climate of the Past ◽

10.5194/cp-10-1441-2014 ◽

2014 ◽

Vol 10 (4) ◽

pp. 1441-1451 ◽

Cited By ~ 9

Author(s):

N. Khélifi ◽

M. Frank

Keyword(s):

Deep Water ◽

Late Quaternary ◽

Sediment Cores ◽

Major Change ◽

Water Masses ◽

Meridional Overturning Circulation ◽

Global Ocean ◽

Overturning Circulation ◽

Nordic Seas ◽

Northeast Atlantic

Abstract. The global ocean–climate system has been highly sensitive to the formation and advection of deep overflow water from the Nordic Seas as integral part of the Atlantic Meridional Overturning Circulation (AMOC) but its evolution over the Pliocene–Pleistocene global cooling is not fully understood. In particular, changes in the sources and mixing of prevailing deep waters that were involved in driving overturning throughout the Pliocene–Pleistocene climate transitions are not well constrained. Here we investigate the evolution of a substantial deep southward return overflow of the AMOC over the last 4 million years. We present new records of the bottom-water radiogenic neodymium isotope (&varepsilon;Nd) variability obtained from three sediment cores (DSDP site 610 and ODP sites 980/981 and 900) at water depths between 2170 and 5050 m in the northeast Atlantic. We find that prior to the onset of major Northern Hemisphere glaciation (NHG) ∼3 million years ago (Ma), &varepsilon;Nd values primarily oscillated between −9 and −11 at all sites, consistent with enhanced vertical mixing and weak stratification of the water masses during the warmer-than-today Pliocene period. From 2.7 Ma to ∼2.0 Ma, the &varepsilon;Nd signatures of the water masses gradually became more distinct, which documents a significant advection of Nordic Seas overflow deep water coincident with the intensification of NHG. Most markedly, however, at ∼1.6 Ma the interglacial &varepsilon;Nd signatures at sites 610 (2420 m water depth (w.d.)) and 980/981 (2170 m w.d.) synchronously and permanently shifted by 2 to 3 &varepsilon;Nd units to less radiogenic values, respectively. Since then the difference between glacial and interglacial &varepsilon;Nd values has been similar to the Late Quaternary at each site. A decrease of ∼2&varepsilon;Nd units at 1.6 Ma was also recorded for the deepest water masses by site 900 (∼5050 m w.d.), which thereafter, however, evolved to more radiogenic values again until the present. This major &varepsilon;Nd change across the 1.6 Ma transition reflects a significant reorganization of the overturning circulation in the northeast Atlantic paving the way for the more stratified water column with distinct water masses prevailing thereafter.

Late Quaternary palaeo-oceanography of the Denmark Strait overflow pathway, South-East Greenland margin

Geology of Greenland Survey Bulletin ◽

10.34194/ggu-bulletin.v180.6514 ◽

1998 ◽

Vol 180 ◽

pp. 163-167

Author(s):

Antoon Kuijpers ◽

Jørn Bo Jensen ◽

Simon R . Troelstra ◽

And shipboard scientific party of RV Professor Logachev and RV Dana

Keyword(s):

North Atlantic ◽

Deep Water ◽

Deep Convection ◽

Conveyor Belt ◽

Water Masses ◽

Labrador Sea ◽

Greenland Sea ◽

The North ◽

Denmark Strait ◽

The North Atlantic

Direct interaction between the atmosphere and the deep ocean basins takes place today only in the Southern Ocean near the Antarctic continent and in the northern extremity of the North Atlantic Ocean, notably in the Norwegian–Greenland Sea and Labrador Sea. Cooling and evaporation cause surface waters in the latter region to become dense and sink. At depth, further mixing occurs with Arctic water masses from adjacent polar shelves. Export of these water masses from the Norwegian–Greenland Sea (Norwegian Sea Overflow Water) to the North Atlantic basin occurs via two major gateways, the Denmark Strait system and the Faeroe– Shetland Channel and Faeroe Bank Channel system (e.g. Dickson et al. 1990; Fig.1). Deep convection in the Labrador Sea produces intermediate waters (Labrador Sea Water), which spreads across the North Atlantic. Deep waters thus formed in the North Atlantic (North Atlantic Deep Water) constitute an essential component of a global ‘conveyor’ belt extending from the North Atlantic via the Southern and Indian Oceans to the Pacific. Water masses return as a (warm) surface water flow. In the North Atlantic this is the Gulf Stream and the relatively warm and saline North Atlantic Current. Numerous palaeo-oceanographic studies have indicated that climatic changes in the North Atlantic region are closely related to changes in surface circulation and in the production of North Atlantic Deep Water. Abrupt shut-down of the ocean-overturning and subsequently of the conveyor belt is believed to represent a potential explanation for rapid climate deterioration at high latitudes, such as those that caused the Quaternary ice ages. Here it should be noted, that significant changes in deep convection in Greenland waters have also recently occurred. While in the Greenland Sea deep water formation over the last decade has drastically decreased, a strong increase of deep convection has simultaneously been observed in the Labrador Sea (Sy et al. 1997).

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.

Deep water circulation patterns in the Atlantic during MISs 12-11

10.5194/egusphere-egu2020-20750 ◽

2020 ◽

Author(s):

Jasmin M. Link ◽

Norbert Frank

Keyword(s):

North Atlantic ◽

Deep Water ◽

Glacial Maximum ◽

Water Circulation ◽

Water Masses ◽

Overturning Circulation ◽

The Past ◽

The North ◽

Circulation Patterns ◽

The North Atlantic

Glacial Termination V is one of the most extreme glacial-interglacial transitions of the past 800 ka [1]. However, the changes in orbital forcing from Marine Isotope Stage (MIS) 12 to 11 are comparatively weak. In addition, MIS 11c is exceptionally distinct compared to other interglacials with for example a longer duration [2] and a higher-than-present sea level [3] despite a relative low incoming insolation. Therefore, the term &#8220;MIS 11 paradox&#8221; was coined [4]. However, only little is known about the Atlantic overturning circulation during this time interval [e.g. 5,6].Here, we present Atlantic-wide deep water circulation patterns spanning the glacial maximum of MIS 12, Termination V, and MIS 11. Therefore, sediment cores throughout the Atlantic were analyzed regarding their Nd isotopic composition of authigenic coatings to reconstruct the provenance of the prevailing bottom water masses.During the glacial maximum of MIS 12, the deep Atlantic Ocean was bathed with a higher amount of southern sourced water compared to the following interglacial. Termination V is represented by a sharp transition in the high-accumulating sites from the North Atlantic with a switch to northern sourced water masses. MIS 11 is characterized through an active deep water formation in the North Atlantic with active overflows from the Nordic Seas, only disrupted by a short deterioration. A strong export of northern sourced water masses to the South Atlantic points to an overall strong overturning circulation.&#160;[1] Lang and Wolff 2011, Climate of the Past 7: 361-380.[2] Candy et al. 2014, Earth-Science Reviews 128: 18-51.[3] Dutton et al. 2015, Science 349: aaa4019.[4] Berger and Wefer 2003, Geophysical Monograph 137: 41-60.[5] Dickson et al. 2009, Nature Geoscience 2: 428-433.[6] V&#225;zquez Riveiros et al. 2013, EPSL 371-372: 258-268.

Diets of four deep-water scaphopod species (Mollusca) in the North Atlantic and the Nordic Seas

Marine Biology ◽

10.1007/s00227-003-1046-3 ◽

2003 ◽

Vol 142 (6) ◽

pp. 1103-1112 ◽

Cited By ~ 7

Author(s):

G. Gudmundsson ◽

K. Engelstad ◽

G. Steiner ◽

J. Svavarsson

Keyword(s):

North Atlantic ◽

Deep Water ◽

Nordic Seas ◽

The North ◽

The North Atlantic