Faculty Opinions recommendation of Distribution and activity of Bacteria and Archaea in the deep water masses of 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).

Download Full-text

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.

Download Full-text

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.

Download Full-text

Viral infection of prokaryotic plankton during early formation of the North Atlantic Deep Water

Aquatic Microbial Ecology ◽

10.3354/ame01934 ◽

2020 ◽

Vol 84 ◽

pp. 175-189

Author(s):

MG Weinbauer ◽

C Griebler ◽

HM van Aken ◽

GJ Herndl

Keyword(s):

Viral Infection ◽

North Atlantic ◽

Deep Water ◽

North Atlantic Deep Water ◽

Water Masses ◽

Life Strategy ◽

Viral Abundance ◽

The North ◽

Early Formation ◽

The North Atlantic

Viral abundance was assessed in different water masses of the NW Atlantic, and the development of viral abundance, lytic viral infection and lysogeny was followed for the first ca. 5000 km (corresponding to ca. 50 yr in the oceanic conveyor belt) of the western branch of the North Atlantic Deep Water (NADW). Viral abundance was significantly higher in the 100 m layer than in the NADW (2400-2700 m depth) and the Denmark Strait Overflow Water (2400-3600 m depth). The virus-to-prokaryote ratio (VPR) increased with depth, ranging from 32-43 for different water masses of the bathypelagic ocean, thus corroborating the enigma of high viral abundance in the dark ocean. The O2-minimum layer (250-600 m) also showed high viral abundance and VPRs. Viral abundance, a viral subgroup and VPRs decreased in a non-linear form with distance from the NADW origin. Viral production (range: 0.2-2.4 × 107 viruses l-1) and the fraction of lytically infected cells (range: 1-22%) decreased with increasing distance from the formation site of the NADW. Conservative estimations of virus-mediated mortality of prokaryotes in the NADW averaged 20 ± 12%. The fraction of the prokaryotic community with lysogens (i.e. harboring a functional viral DNA) in the NADW averaged 21 ± 14%. Hence, we conclude that (1) viral abundance and subgroups differ between water masses, (2) virus-mediated mortality of prokaryotes as well as lysogeny are significant in the dark ocean and (3) the lysogenic life strategy became more important than the lytic life style during the early formation of the NADW.

Download Full-text

Trends of anthropogenic CO2 storage in North Atlantic water masses

Biogeosciences ◽

10.5194/bg-7-1789-2010 ◽

2010 ◽

Vol 7 (5) ◽

pp. 1789-1807 ◽

Cited By ~ 38

Author(s):

F. F. Pérez ◽

M. Vázquez-Rodríguez ◽

H. Mercier ◽

A. Velo ◽

P. Lherminier ◽

...

Keyword(s):

North Atlantic ◽

Deep Water ◽

Atlantic Water ◽

Average Concentration ◽

Rate Of Change ◽

Point Of View ◽

Water Masses ◽

Meridional Overturning Circulation ◽

The North ◽

The North Atlantic

Abstract. A high-quality inorganic carbon system database, spanning over three decades (1981–2006) and comprising of 13 cruises, has allowed the applying of the φC°T method and coming up with estimates of the anthropogenic CO2 (Cant) stored in the main water masses of the North Atlantic. In the studied region, strong convective processes convey surface properties, like Cant, into deeper ocean layers and grants this region an added oceanographic interest from the point of view of air-sea CO2 exchanges. Generally, a tendency for decreasing Cant storage rates towards the deep layers has been observed. In the Iberian Basin, the North Atlantic Deep Water has low Cant concentrations and negligible storage rates, while the North Atlantic Central Water in the upper layers shows the largest Cant values and the largest annual increase of its average concentration (1.13 ± 0.14 μmol kg−1 yr−1). This unmatched rate of change in the Cant concentration of the warm upper limb of the Meridional Overturning Circulation decreases towards the Irminger basin (0.68 ± 0.06 μmol kg−1 yr−1) due to the lowering of the buffering capacity. The mid and deep waters in the Irminger Sea show rather similar Cant concentration rates of increase (between 0.33 and 0.45 μmol kg−1 yr−1), whereas in the Iceland basin these layers seem to have been less affected by Cant. Overall, the Cant storage rates in the North Atlantic subpolar gyre during the first half of the 1990s, when a high North Atlantic Oscillation (NAO) phase was dominant, are ~48% higher than during the 1997–2006 low NAO phase that followed. This result suggests that a net decrease in the strength of the North Atlantic sink of atmospheric CO2 has taken place during the present decade. The changes in deep-water ventilation are the main driving processes causing this weakening of the North Atlantic CO2 sink.

Download Full-text

Distribution and activity of Bacteria and Archaea in the deep water masses of the North Atlantic

Limnology and Oceanography ◽

10.4319/lo.2006.51.5.2131 ◽

2006 ◽

Vol 51 (5) ◽

pp. 2131-2144 ◽

Cited By ~ 81

Author(s):

Eva Teira ◽

Philippe Lebaron ◽

Hendrik van Aken ◽

Gerhard J. Herndl

Keyword(s):

North Atlantic ◽

Deep Water ◽

Water Masses ◽

The North ◽

The North Atlantic

Download Full-text

Trends of anthropogenic CO2 storage in North Atlantic water masses

Biogeosciences Discussions ◽

10.5194/bgd-7-165-2010 ◽

2010 ◽

Vol 7 (1) ◽

pp. 165-202

Author(s):

F. F. Pérez ◽

M. Vázquez-Rodríguez ◽

H. Mercier ◽

A. Velo ◽

P. Lherminier ◽

...

Keyword(s):

North Atlantic ◽

Deep Water ◽

Atlantic Water ◽

Water Masses ◽

Meridional Overturning Circulation ◽

Oscillation Phase ◽

Study Region ◽

The North ◽

Deep Waters ◽

The North Atlantic

Abstract. A high-quality inorganic carbon system database spanning over three decades (1981–2006) and comprising 13 cruises has allowed applying the φCT° method and coming up with accurate estimates of the anthropogenic CO2 (Cant) stored in the main water masses of the North Atlantic. In the studied region, strong convective processes convey surface properties, like Cant, into deeper ocean layers and confer this region an added oceanographic interest from the point of view of air-sea CO2 exchanges. Commonly, a tendency for decreasing Cant storage rates towards the deep layers has been observed. In the Iberian Basin, the deep waters (North Atlantic Deep Water) have low Cant values and negligible Cant storage rates, while the North Atlantic Central Water in the upper layers shows the largest Cant concentrations and capacity to increase its storage on a yearly basis (1.13±0.14 μmol kg−1 yr−1). This unmatched Cant storage capacity of the warm upper limb of the Meridional Overturning Circulation weakens towards the Irminger basin (0.68±0.06 μmol kg−1 yr−1) due to the lowering of the buffering capacity. The mid and deep waters in the Irminger Sea show rather homogeneous Cant storage rates (between 0.33 and 0.45 μmol kg−1 yr−1), whereas in the Iceland basin these layers seem to have been less affected by Cant. The Cant storage rates in the study region during the 1991–1997 high NAO (North Atlantic Oscillation) phase are ~48% higher than during the 1997–2006 low NAO phase that followed. This result suggests that a net decrease in the strength of the North Atlantic sink of atmospheric CO2has taken place during the present decade. The changes in deep-water ventilation together with a detrimental renewal of the main water masses are likely the main driving processes causing this weakening of the North Atlantic CO2sink.

Download Full-text

Change in the North Atlantic circulation associated with the mid-Pleistocene transition

Climate of the Past ◽

10.5194/cp-14-1639-2018 ◽

2018 ◽

Vol 14 (11) ◽

pp. 1639-1651 ◽

Cited By ~ 3

Author(s):

Gloria M. Martin-Garcia ◽

Francisco J. Sierro ◽

José A. Flores ◽

Fátima Abrantes

Keyword(s):

North Atlantic ◽

Major Change ◽

Water Masses ◽

Meridional Overturning Circulation ◽

The Arctic ◽

North Atlantic Current ◽

The North ◽

Oceanic Fronts ◽

Surface Circulation ◽

The North Atlantic

Abstract. The southwestern Iberian margin is highly sensitive to changes in the distribution of North Atlantic currents and to the position of oceanic fronts. In this work, the evolution of oceanographic parameters from 812 to 530 ka (MIS20–MIS14) is studied based on the analysis of planktonic foraminifer assemblages from site IODP-U1385 (37∘34.285′ N, 10∘7.562′ W; 2585 m b.s.l.). By comparing the obtained results with published records from other North Atlantic sites between 41 and 55∘ N, basin-wide paleoceanographic conditions are reconstructed. Variations of assemblages dwelling in different water masses indicate a major change in the general North Atlantic circulation during MIS16, coinciding with the definite establishment of the 100 ky cyclicity associated with the mid-Pleistocene transition. At the surface, this change consisted in the redistribution of water masses, with the subsequent thermal variation, and occurred linked to the northwestward migration of the Arctic Front (AF), and the increase in the North Atlantic Deep Water (NADW) formation with respect to previous glacials. During glacials prior to MIS16, the NADW formation was very weak, which drastically slowed down the surface circulation; the AF was at a southerly position and the North Atlantic Current (NAC) diverted southeastwards, developing steep south–north, and east–west, thermal gradients and blocking the arrival of warm water, with associated moisture, to high latitudes. During MIS16, the increase in the meridional overturning circulation, in combination with the northwestward AF shift, allowed the arrival of the NAC to subpolar latitudes, multiplying the moisture availability for ice-sheet growth, which could have worked as a positive feedback to prolong the glacials towards 100 ky cycles.

Download Full-text