Bolboforma from Leg 105, Labrador Sea and Baffin Bay, and the Chronostratigraphy of Bolboforma in the North Atlantic

Subsurface nitrate in the Labrador Sea (NW Atlantic) and Baffin Bay is provided by North Pacific water flowing through Bering Strait and the Canadian Arctic as well as by advection from the North Atlantic. Both these nitrate sources are distinct in their isotopic signature (&#948;15N), owing to benthic denitrification on the Bering, Chukchi and east Siberian shelves and nitrogen fixation in the North Atlantic, respectively. Accordingly, water column profiles of &#948;15N(nitrate) collected off Greenland in the eastern Labrador Sea show low &#948;15N(nitrate), which mixes with more 15N-enriched nitrate flowing through Baffin Bay into the northern Labrador Sea. The Labrador Current carries this mixture southward along the western Labrador Sea, toward Newfoundland. The &#948;15N of surface sediments in the Labrador Sea closely mirrors these water column signals, suggesting that sediments can be used to trace changes in both the source signature of Atlantic versus Pacific-derived nitrate as well as in the admixture of the two source waters.Two downcore sedimentary &#948;15N records from the NE and NW Labrador Sea coast both show high &#948;15N values of ca. 7&#8240; during the early Holocene (9-7 kyrs BP). In the NE Labrador Sea, this is followed by a long-term decrease toward &#948;15N of ca. 4.5&#8240; at the core top, in contrast to a much more subtle decrease in the NW Labrador Sea (surface sediment &#948;15N of ca. 6.5&#8240;). The decreasing &#948;15N values along the eastern Labrador Sea are consistent with a Holocene increase in nitrogen fixation in the North Atlantic or an increasing advection of isotopically light nitrate. In turn, an increasing admixture of North-Pacific-derived nitrate, or intensified denitrification on the Bering Shelf would be required to explain the much subdued Holocene &#948;15N decrease in the NW Labrador Sea.

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Low - Level Aeromagnetic Profiles Over the Labrador Sea, Baffin Bay, and Across the North Atlantic Ocean

10.4095/106616 ◽

1967 ◽

Author(s):

M E Bower ◽

P J Hood ◽

P Sawatzky

Keyword(s):

Atlantic Ocean ◽

North Atlantic ◽

North Atlantic Ocean ◽

Labrador Sea ◽

Baffin Bay ◽

Low Level ◽

The North ◽

The North Atlantic

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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).

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The Metasomatized Mantle beneath the North Atlantic Craton: Insights from Peridotite Xenoliths of the Chidliak Kimberlite Province (NE Canada)

Journal of Petrology ◽

10.1093/petrology/egz061 ◽

2019 ◽

Vol 60 (10) ◽

pp. 1991-2024 ◽

Cited By ~ 1

Author(s):

M G Kopylova ◽

E Tso ◽

F Ma ◽

J Liu ◽

D G Pearson

Keyword(s):

North Atlantic ◽

Thermal State ◽

Mineral Chemistry ◽

Mantle Metasomatism ◽

Labrador Sea ◽

The North ◽

Rock Types ◽

History Of ◽

The North Atlantic ◽

North Atlantic Craton

Abstract We studied the petrography, mineralogy, thermobarometry and whole-rock chemistry of 120 peridotite and pyroxenite xenoliths collected from the 156–138 Ma Chidliak kimberlite province (Southern Baffin Island). Xenoliths from pipes CH-1, -6, -7 and -44 are divided into two garnet-bearing series, dunites–harzburgites–lherzolites and wehrlites–olivine pyroxenites. Both series show widely varying textures, from coarse to sheared, and textures of late formation of garnet and clinopyroxene. Some samples from the lherzolite series may contain spinel, whereas wehrlites may contain ilmenite. In CH-6, rare coarse samples of the lherzolite and wehrlite series were derived from P = 2·8 to 5·6 GPa, whereas predominant sheared and coarse samples of the lherzolite series coexist at P = 5·6–7·5 GPa. Kimberlites CH-1, -7, -44 sample mainly the deeper mantle, at P = 5·0–7·5 GPa, represented by coarse and sheared lherzolite and wehrlite series. The bulk of the pressure–temperature arrays defines a thermal state compatible with 35–39 mW m–2 surface heat flow, but a significant thermal disequilibrium was evident in the large isobaric thermal scatter, especially at depth, and in the low thermal gradients uncharacteristic of conduction. The whole-rock Si and Mg contents of the Chidliak xenoliths and their mineral chemistry reflect initial high levels of melt depletion typical of cratonic mantle and subsequent refertilization in Ca and Al. Unlike the more orthopyroxene-rich mantle of many other cratons, the Chidliak mantle is rich (∼83 vol%) in forsteritic olivine. We assign this to silicate–carbonate metasomatism, which triggered wehrlitization of the mantle. The Chidliak mantle resembles the Greenlandic part of the North Atlantic Craton, suggesting the former contiguous nature of their lithosphere before subsequent rifting into separate continental fragments. Another, more recent type of mantle metasomatism, which affected the Chidliak mantle, is characterized by elevated Ti in pyroxenes and garnet typical of all rock types from CH-1, -7 and -44. These metasomatic samples are largely absent from the CH-6 xenolith suite. The Ti imprint is most intense in xenoliths derived from depths equivalent to 5·5–6·5 GPa where it is associated with higher strain, the presence of sheared samples of the lherzolite series and higher temperatures varying isobarically by up to 200 °C. The horizontal scale of the thermal-metasomatic imprint is more ambiguous and could be as regional as tens of kilometers or as local as <1 km. The time-scale of this metasomatism relates to a conductive length-scale and could be as short as <1 Myr, shortly predating kimberlite formation. A complex protracted metasomatic history of the North Atlantic Craton reconstructed from Chidliak xenoliths matches emplacement patterns of deep CO2-rich and Ti-rich magmatism around the Labrador Sea prior to the craton rifting. The metasomatism may have played a pivotal role in thinning the North Atlantic Craton lithosphere adjacent to the Labrador Sea from ∼240 km in the Jurassic to ∼65 km in the Paleogene.

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The recent AMOC variability in the Subpolar Gyre: results across the OVIDE section

10.5194/egusphere-egu2020-19663 ◽

2020 ◽

Author(s):

Pascale Lherminier ◽

Herlé Mercier ◽

Fiz F. Perez ◽

Marcos Fontela

Keyword(s):

North Atlantic ◽

Lower Limb ◽

Deep Convection ◽

Labrador Sea ◽

Subpolar Gyre ◽

North Atlantic Current ◽

The North ◽

Subarctic Front ◽

The North Atlantic ◽

Atlantic Current

According to the subpolar AMOC index built from ARGO and altimetry, the AMOC amplitude across the OVIDE section (from Greenland to Portugal) was similar to that of the mid-1990s between 2014 and 2017, i.e. 4-5 Sv above the level of the 2000s. It then returned to average values in 2018. The same index computed independently from the biennial summer cruises over 2002-2018 confirms this statement. Interestingly, despite the concomitant cold and fresh anomaly in the subpolar Atlantic, the heat flux across OVIDE remains correlated with the AMOC amplitude. This can be explained by the paths taken by the North Atlantic Current and the transport anomalies in the subarctic front. In 2014, the OVIDE section was complemented by a section from Greenland to Newfoundland (GA01), showing how the water of the lower limb of the AMOC was densified by deep convection in the Labrador Sea. The spatial patterns of volume, heat, salt and oxygen transport anomalies after 2014 will be discussed at the light of the 2000s average.

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Dissolved iron in the North Atlantic Ocean and Labrador Sea along the GEOVIDE section (GEOTRACES section GA01)

10.5194/bg-2018-147 ◽

2018 ◽

Cited By ~ 10

Author(s):

Manon Tonnard ◽

Hélène Planquette ◽

Andrew R. Bowie ◽

Pier van der Merwe ◽

Morgane Gallinari ◽

...

Keyword(s):

Atlantic Ocean ◽

North Atlantic ◽

Sea Water ◽

North Atlantic Ocean ◽

Deep Convection ◽

Labrador Sea ◽

Intermediate Water ◽

The North ◽

Irminger Sea ◽

The North Atlantic

Abstract. Dissolved Fe (DFe) samples from the GEOVIDE voyage (GEOTRACES GA01, May–June 2014) in the North Atlantic Ocean were analysed using a SeaFAST-picoTM coupled to an Element XR HR-ICP-MS and provided interesting insights on the Fe sources in this area. Overall, DFe concentrations ranged from 0.09 ± 0.01 nmol L−1 to 7.8 ± 0.5 nmol L−1. Elevated DFe concentrations were observed above the Iberian, Greenland and Newfoundland Margins likely due to riverine inputs from the Tagus River, meteoric water inputs and sedimentary inputs. Air-sea interactions were suspected to be responsible for the increase in DFe concentrations within subsurface waters of the Irminger Sea due to deep convection occurring the previous winter, that provided iron-to-nitrate ratios sufficient to sustain phytoplankton growth. Increasing DFe concentrations along the flow path of the Labrador Sea Water were attributed to sedimentary inputs from the Newfoundland Margin. Bottom waters from the Irminger Sea displayed high DFe concentrations likely due to the dissolution of Fe-rich particles from the Denmark Strait Overflow Water and the Polar Intermediate Water. Finally, the nepheloid layers were found to act as either a source or a sink of DFe depending on the nature of particles.

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Identification and quantification of the North Atlantic Deep Water pathways

10.5194/egusphere-egu21-10358 ◽

2021 ◽

Author(s):

Philippe Miron ◽

Maria J. Olascoaga ◽

Francisco J. Beron-Vera ◽

Kimberly L. Drouin ◽

M. Susan Lozier

Keyword(s):

North Atlantic ◽

Deep Water ◽

Sea Water ◽

Lower Layer ◽

North Atlantic Deep Water ◽

Meridional Overturning Circulation ◽

Labrador Sea ◽

Western Boundary ◽

The North ◽

The North Atlantic

The North Atlantic Deep Water (NADW) flows equatorward along the Deep Western Boundary Current (DWBC) as well as interior pathways and is a critical part of the Atlantic Meridional Overturning Circulation. Its upper layer, the Labrador Sea Water (LSW), is formed by open-ocean deep convection in the Labrador and Irminger Seas while its lower layers, the Iceland&#8211;Scotland Overflow Water (ISOW) and the Denmark Strait Overflow Water (DSOW), are formed north of the Greenland&#8211;Iceland&#8211;Scotland Ridge.In recent years, more than two hundred acoustically-tracked subsurface floats have been deployed in the deep waters of the North Atlantic. &#160;Studies to date have highlighted water mass pathways from launch locations, but due to limited float trajectory lengths, these studies have been unable to identify pathways connecting &#160;remote regions.This work presents a framework to explore deep water pathways from their respective sources in the North Atlantic using Markov Chain (MC) modeling and Transition Path Theory (TPT). Using observational trajectories released as part of OSNAP and the Argo projects, we constructed two MCs that approximate the lower and upper layers of the NADW Lagrangian dynamics. The reactive NADW pathways&#8212;directly connecting NADW sources with a target at 53&#176;N&#8212;are obtained from these MCs using TPT.Preliminary results show that twenty percent more pathways of the upper layer(LSW) reach the ocean interior compared to &#160;the lower layer (ISOW, DSOW), which mostly flows along the DWBC in the subpolar North Atlantic. Also identified are the Labrador Sea recirculation pathways to the Irminger Sea and the direct connections from the Reykjanes Ridge to the eastern flank of the Mid&#8211;Atlantic Ridge, both previously observed. Furthermore, we quantified the eastern spread of the LSW to the area surrounding the Charlie&#8211;Gibbs Fracture Zone and compared it with previous analysis. Finally, the residence time of the upper and lower layers are assessed and compared to previous observations.

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Water mass distributions and transports for the 2014 GEOVIDE cruise in the North Atlantic

Biogeosciences ◽

10.5194/bg-15-2075-2018 ◽

2018 ◽

Vol 15 (7) ◽

pp. 2075-2090 ◽

Cited By ~ 21

Author(s):

Maribel I. García-Ibáñez ◽

Fiz F. Pérez ◽

Pascale Lherminier ◽

Patricia Zunino ◽

Herlé Mercier ◽

...

Keyword(s):

North Atlantic ◽

Water Mass ◽

Water Levels ◽

Water Masses ◽

Meridional Overturning Circulation ◽

Labrador Sea ◽

Intermediate Water ◽

North East ◽

The North ◽

The North Atlantic

Abstract. We present the distribution of water masses along the GEOTRACES-GA01 section during the GEOVIDE cruise, which crossed the subpolar North Atlantic Ocean and the Labrador Sea in the summer of 2014. The water mass structure resulting from an extended optimum multiparameter (eOMP) analysis provides the framework for interpreting the observed distributions of trace elements and their isotopes. Central Waters and Subpolar Mode Waters (SPMW) dominated the upper part of the GEOTRACES-GA01 section. At intermediate depths, the dominant water mass was Labrador Sea Water, while the deep parts of the section were filled by Iceland–Scotland Overflow Water (ISOW) and North-East Atlantic Deep Water. We also evaluate the water mass volume transports across the 2014 OVIDE line (Portugal to Greenland section) by combining the water mass fractions resulting from the eOMP analysis with the absolute geostrophic velocity field estimated through a box inverse model. This allowed us to assess the relative contribution of each water mass to the transport across the section. Finally, we discuss the changes in the distribution and transport of water masses between the 2014 OVIDE line and the 2002–2010 mean state. At the upper and intermediate water levels, colder end-members of the water masses replaced the warmer ones in 2014 with respect to 2002–2010, in agreement with the long-term cooling of the North Atlantic Subpolar Gyre that started in the mid-2000s. Below 2000 dbar, ISOW increased its contribution in 2014 with respect to 2002–2010, with the increase being consistent with other estimates of ISOW transports along 58–59° N. We also observed an increase in SPMW in the East Greenland Irminger Current in 2014 with respect to 2002–2010, which supports the recent deep convection events in the Irminger Sea. From the assessment of the relative water mass contribution to the Atlantic Meridional Overturning Circulation (AMOC) across the OVIDE line, we conclude that the larger AMOC intensity in 2014 compared to the 2002–2010 mean was related to both the increase in the northward transport of Central Waters in the AMOC upper limb and to the increase in the southward flow of Irminger Basin SPMW and ISOW in the AMOC lower limb.

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Impact of Labrador Sea Convection on the North Atlantic Meridional Overturning Circulation

Journal of Physical Oceanography ◽

10.1175/jpo3178.1 ◽

2007 ◽

Vol 37 (9) ◽

pp. 2207-2227 ◽

Cited By ~ 99

Author(s):

Robert S. Pickart ◽

Michael A. Spall

Keyword(s):

North Atlantic ◽

World Ocean ◽

Atlantic Meridional Overturning Circulation ◽

Meridional Overturning Circulation ◽

Labrador Sea ◽

Overturning Circulation ◽

The North ◽

Meridional Overturning ◽

The North Atlantic ◽

Density Space

Abstract The overturning and horizontal circulations of the Labrador Sea are deduced from a composite vertical section across the basin. The data come from the late-spring/early-summer occupations of the World Ocean Circulation Experiment (WOCE) AR7W line, during the years 1990–97. This time period was chosen because it corresponded to intense wintertime convection—the deepest and densest in the historical record—suggesting that the North Atlantic meridional overturning circulation (MOC) would be maximally impacted. The composite geostrophic velocity section was referenced using a mean lateral velocity profile from float data and then subsequently adjusted to balance mass. The analysis was done in depth space to determine the net sinking that results from convection and in density space to determine the diapycnal mass flux (i.e., the transformation of light water to Labrador Sea Water). The mean overturning cell is calculated to be 1 Sv (1 Sv ≡ 106 m3 s−1), as compared with a horizontal gyre of 18 Sv. The total water mass transformation is 2 Sv. These values are consistent with recent modeling results. The diagnosed heat flux of 37.6 TW is found to result predominantly from the horizontal circulation, both in depth space and density space. These results suggest that the North Atlantic MOC is not largely impacted by deep convection in the Labrador Sea.

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