scholarly journals Deglacial variability of Antarctic Intermediate Water penetration into the North Atlantic from authigenic neodymium isotope ratios

2012 ◽  
Vol 27 (3) ◽  
pp. n/a-n/a ◽  
Author(s):  
Ruifang C. Xie ◽  
Franco Marcantonio ◽  
Matthew W. Schmidt
Keyword(s):  
North Atlantic ◽  
Isotope Ratios ◽  
Intermediate Water ◽  
Water Penetration ◽  
Antarctic Intermediate Water ◽  
The North ◽  
The North Atlantic

Transport of heat, CO 2 and O 2 by the Atlantic’s thermohaline circulation

1995 ◽  
Vol 348 (1324) ◽  
pp. 133-142 ◽  
Keyword(s):  
North Atlantic ◽  
Deep Water ◽  
Thermohaline Circulation ◽  
North Atlantic Deep Water ◽  
Return Flow ◽  
Intermediate Water ◽  
Biological Processes ◽  
Antarctic Intermediate Water ◽  
The North ◽  
The North Atlantic

We estimate transport of heat, CO 2 and O 2 by the Atlantic’s thermohaline circulation using an approach based on differences in the chemical and physical characteristics of North Atlantic Deep Water (NADW), Antarctic Intermediate Water (AAIW), and the northward return flow across the equator. The characteristics of the return-flow waters are constrained by imposing conservation of phosphate in the North Atlantic as a whole. Based on a total equatorial return flow of 13 x 10 6 m 3 s -1 , we find that the Atlantic north of the equator is a source of 7.7 ± 1.4 x 10 14 W to the atmosphere, a sink of 0.51 ± 0.21 x 10 14 mol of O 2 , and preindustrially was a sink of 0.33 ± 0.15 x 10 14 mol of CO 2 . Uptake of O 2 and CO 2 by the North Atlantic is driven mainly by thermal, as opposed to biological processes.

scholarly journals Transport and storage of anthropogenic C in the North Atlantic Subpolar Ocean

2018 ◽  
Vol 15 (14) ◽  
pp. 4661-4682 ◽  
Author(s):  
Virginie Racapé ◽  
Patricia Zunino ◽  
Herlé Mercier ◽  
Pascale Lherminier ◽  
Laurent Bopp ◽  
...  
Keyword(s):  
Interannual Variability ◽  
North Atlantic ◽  
General Circulation ◽  
Meridional Overturning Circulation ◽  
Intermediate Water ◽  
Data Set ◽  
The North ◽  
Storage Rate ◽  
The North Atlantic ◽  
And Storage

Abstract. The North Atlantic Ocean is a major sink region for atmospheric CO2 and contributes to the storage of anthropogenic carbon (Cant). While there is general agreement that the intensity of the meridional overturning circulation (MOC) modulates uptake, transport and storage of Cant in the North Atlantic Subpolar Ocean, processes controlling their recent variability and evolution over the 21st century remain uncertain. This study investigates the relationship between transport, air–sea flux and storage rate of Cant in the North Atlantic Subpolar Ocean over the past 53 years. Its relies on the combined analysis of a multiannual in situ data set and outputs from a global biogeochemical ocean general circulation model (NEMO–PISCES) at 1∕2∘ spatial resolution forced by an atmospheric reanalysis. Despite an underestimation of Cant transport and an overestimation of anthropogenic air–sea CO2 flux in the model, the interannual variability of the regional Cant storage rate and its driving processes were well simulated by the model. Analysis of the multi-decadal simulation revealed that the MOC intensity variability was the major driver of the Cant transport variability at 25 and 36∘ N, but not at OVIDE. At the subpolar OVIDE section, the interannual variability of Cant transport was controlled by the accumulation of Cant in the MOC upper limb. At multi-decadal timescales, long-term changes in the North Atlantic storage rate of Cant were driven by the increase in air–sea fluxes of anthropogenic CO2. North Atlantic Central Water played a key role for storing Cant in the upper layer of the subtropical region and for supplying Cant to Intermediate Water and North Atlantic Deep Water. The transfer of Cant from surface to deep waters occurred mainly north of the OVIDE section. Most of the Cant transferred to the deep ocean was stored in the subpolar region, while the remainder was exported to the subtropical gyre within the lower MOC.

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

2018 ◽  
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.

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

2018 ◽  
Vol 15 (7) ◽  
pp. 2075-2090 ◽  
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.

scholarly journals Millennial-scale variations of sedimentary oxygenation in the western subtropical North Pacific and its links to the North Atlantic climate

2019 ◽  
Author(s):  
Jianjun Zou ◽  
Xuefa Shi ◽  
Aimei Zhu ◽  
Selvaraj Kandasamy ◽  
Xun Gong ◽  
...  
Keyword(s):  
North Atlantic ◽  
Deep Water ◽  
North Pacific ◽  
Co2 Concentration ◽  
Meridional Overturning Circulation ◽  
Atmospheric Co2 ◽  
Intermediate Water ◽  
The North ◽  
The North Atlantic ◽  
Millennial Scale

Abstract. Lower glacial atmospheric CO2 concentrations have been attributed to carbon sequestration in deep oceans. However, potential roles of voluminous subtropical North Pacific in modulating atmospheric CO2 levels on millennial timescale are poorly constrained. Further, an increase in respired CO2 concentration in the glacial deep ocean due to biological pump generally is coeval with less oxygenation in the subsurface layer. This link thus offers a chance to visit oceanic ventilation and the coeval export productivity based on redox-controlled sedimentary geochemical parameters. Here we investigate a suite of sediment geochemical proxies to understand the sedimentary oxygenation variations in the subtropical North Pacific (core CSH1) over the last 50 thousand years (ka). Our results suggest that sedimentary oxygenation at mid-depths of the subtropical North Pacific intensifies during the episodes of late glacial (50–25 ka), Last Glacial Maximum (LGM) and also the interval after 8.5 ka, especially pronounced for the North Atlantic millennial-scale abrupt cold events of the Younger Dryas, Heinrich Stadial (HS) 1 and 2. On the other hand, oxygen-depleted seawater is found during the Bölling-Alleröd (B/A) and Preboreal. Our findings of enhanced sedimentary oxygenation in the subtropical North Pacific is aligned with intensified formation of North Pacific Intermediate Water (NPIW) during cold spells, while the ameliorated sedimentary oxygenation seems to be linked with the intensified Kuroshio Current since 8.5 ka. In our results, diminished sedimentary oxygenation during the B/A indicates an enhanced CO2 sequestration at mid-depth waters, along with slight increase in atmospheric CO2 concentration. Mechanistically, we speculate that these millennial-scale changes were linked to the strength of North Atlantic Deep Water, leading to intensification of NPIW formation and enhanced abyss flushing during deglacial cold and warm intervals, respectively. Enhanced formation of NPIW seem to be driven by the perturbation of sea ice formation and sea surface salinity oscillation in high latitude North Pacific through atmospheric and oceanic teleconnection. During the B/A, decreased sedimentary oxygenation likely resulted from an upward penetration of aged deep water into the intermediate-depth in the North Pacific, corresponding to a resumption of Atlantic Meridional Overturning Circulation.

scholarly journals Mediterranean Outflow Water variability during the Early Pleistocene climate transition

2017 ◽  
Author(s):  
Stefanie Kaboth ◽  
Patrick Grunert ◽  
Lucas J. Lourens
Keyword(s):  
North Atlantic ◽  
Early Pleistocene ◽  
Time Interval ◽  
Intermediate Water ◽  
Mediterranean Outflow Water ◽  
The North ◽  
Pleistocene Climate ◽  
Mediterranean Outflow ◽  
The North Atlantic ◽  
Climate Transition

Abstract. Gaining insights into the evolution of Mediterranean Outflow Water (MOW) during the Early Pleistocene climate transition has been so far hampered by the lack of available paleoclimatic archives. Here we present the first benthic foraminifera stable oxygen and carbon isotope records and grain-size data from IODP Expedition 339 Site U1389 presently located within the upper core of the MOW in the Gulf of Cadiz for the time interval between 2.6 and 1.8 Ma. A comparison with an intermediate water mass record from the Mediterranean Sea strongly suggest an active MOW supplying Site U1389 on glacial-interglacial timescales during the Early Pleistocene. We also find indication that the increasing presence of MOW in the Gulf of Cadiz during the investigated time interval aligns with the progressive northward protrusion of Mediterranean sourced intermediate water masses into the North Atlantic, possibly modulating the intensification of the North Atlantic Meridional Overturning Circulation at the same time. Additionally, our results suggest that MOW flow strength was already governed by precession and semi-precession cyclicity during the Early Pleistocene against the background of glacial-interglacial variability dominated by the obliquity cycle of Earth`s inclination axis.

Glacial-to-interglacial variations in the deep water at the Bermuda Rise inferred from a Nd isotope record covering the last million years

2020 ◽  
Author(s):  
Maria Jaume-Seguí ◽  
Joohee Kim ◽  
Karla P. Knudson ◽  
Maayan Yehudai ◽  
Steven L. Goldstein ◽  
...  
Keyword(s):  
North Atlantic ◽  
Deep Water ◽  
Isotope Ratios ◽  
Nepheloid Layer ◽  
Nd Isotope ◽  
Isotope Signature ◽  
The North ◽  
The North Atlantic ◽  
Gyre System ◽  
Bermuda Rise

<p>The formation of North Atlantic Deep Water (NADW) in the North Atlantic is an important modulator of the climate system, as it drives the global termohaline circulation, responsible for the distribution of heat, salts and nutrients across the oceans. ODP Site 1063 (4584 m), on the deep Bermuda Rise, is located in the mixing zone between NADW and Antarctic Bottom Water (AABW) and appears to be a good location to study how ocean circulation and climate interconnect. Here we present a new record based on Nd isotope ratios that covers ~1 Ma at that Site. Our data shows Nd isotope ratios during parts of interglacials that are much lower than present day NADW. These results are coherent with recent published studies on the last interglacial–glacial cycle that show that the deep North Atlantic Nd isotope ratios are also lower than NADW during the early interglacial. However, Nd isotope values from the shallower DSDP Site 607 (3427 m), within the core of NADW, have remained similar to modern NADW during interglacials over the same time interval. Site 607 is thought to represent the deep North Atlantic, as shown by an Atlantic meriodional transect that displays Nd isotopes ratios for glacial and interglacial maxima over the last ~1 Ma. We suggest that Nd isotope ratios at Site 1063 do not fully represent the North Atlantic endmember of the AMOC during interglacials, but regional or local processes. However, glacial values at Site 1063 fitting those of Site 607 suggest that Nd isotope ratios represent, indeed, water mass mixing during glacial periods. The low Nd-isotope ratios in the deep Bermuda Rise during interglacials would be the result of particle-seawater exchange derived from the arrival of freshly ground, poorly weathered bedrock from the Canadian shield to the North Atlantic during major ice sheet retreats, such as deglaciations as well as stadial-to-interstadial transitions. Consequently, a deep, regionally constrained layer of seawater is tagged with this extreme Nd isotope signature that is not representative of the AMOC. We suggest that a benthic nepheloid layer, whose development is driven by a deep-recirculating gyre system regulated by the interaction between the northward flowing Gulf Stream and the southward flowing deep western boundary current, facilitates the periodical masking of the deep Atlantic Nd isotope signature at Site 1063. The intermittence of the masking allows for a speculation on how the deep-recirculating gyre system might have changed over the last ~1 Ma glacial-to-interglacial cycles.</p>

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