Determination of δ18O of Seawater in the Deep Ocean during the Last Glacial Maximum

1993 ◽  
Vol 8 (1) ◽  
pp. 1-6 ◽  
Author(s):  
D. P. Schrag ◽  
D. J. DePaolo
Keyword(s):  
Last Glacial Maximum ◽  
Deep Ocean ◽  
Glacial Maximum ◽  
Last Glacial ◽  
The Last Glacial Maximum ◽  
The Last Glacial

scholarly journals Deep ocean nutrients during the Last Glacial Maximum deduced from sponge silicon isotopic compositions

2010 ◽  
Vol 292 (3-4) ◽  
pp. 290-300 ◽  
Author(s):  
Katharine R. Hendry ◽  
R. Bastian Georg ◽  
Rosalind E.M. Rickaby ◽  
Laura F. Robinson ◽  
Alex N. Halliday
Keyword(s):  
Last Glacial Maximum ◽  
Deep Ocean ◽  
Glacial Maximum ◽  
Last Glacial ◽  
Isotopic Compositions ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Northern Sourced Water dominated the Atlantic Ocean during the Last Glacial Maximum

2020 ◽  
Author(s):  
Frerk Pöppelmeier ◽  
Patrick Blaser ◽  
Marcus Gutjahr ◽  
Samuel Jaccard ◽  
Martin Frank ◽  
...  
Keyword(s):  
Carbon Storage ◽  
Last Glacial Maximum ◽  
Water Mass ◽  
Stable Carbon Isotope ◽  
Deep Ocean ◽  
Glacial Maximum ◽  
Ice Age ◽  
Last Glacial ◽  
The Last Glacial Maximum ◽  
The Last Glacial

<p>Increased carbon sequestration in the ocean subsurface is commonly assumed to have been one of the main causes responsible for lower glacial atmospheric CO<sub>2</sub> concentrations. This carbon must have been stored away from the atmosphere for thousands of years, yet the water mass structure accommodating such increased carbon storage continues to be debated. Here we present new sediment derived bottom water neodymium isotope data that allow fingerprinting of water masses and their mixtures and provide a more complete picture of the Atlantic overturning circulation geometry during the Last Glacial Maximums. These results suggest that the vertical and meridional structure of the Atlantic deep water mass distribution only experienced minor changes since the last ice age. In particular, we find no compelling evidence supporting glacial southern sourced water substantially expanding to shallower depths and farther into the northern hemisphere than today, which has been inferred from stable carbon isotope reconstructions. We argue that depleted δ<sup>13</sup>C values observed in the deep Northwest Atlantic do not necessarily indicate the presence of southern sourced water. Instead, these values may represent a northern sourced water mass with lower than modern preformed δ<sup>13</sup>C values that were further modified downstream by increased sequestration of remineralized carbon, facilitated by a more sluggish glacial deep circulation. If proven to be correct, the glacial water mass structure inferred from Nd isotopes has profound implications on our understanding of the deep ocean carbon storage during the Last Glacial Maximum.</p>

scholarly journals Oxygen stable isotopes during the Last Glacial Maximum climate: perspectives from data–model (<i>i</i>LOVECLIM) comparison

2014 ◽  
Vol 10 (6) ◽  
pp. 1939-1955 ◽  
Author(s):  
T. Caley ◽  
D. M. Roche ◽  
C. Waelbroeck ◽  
E. Michel
Keyword(s):  
Last Glacial Maximum ◽  
Data Model ◽  
Model Comparison ◽  
Greenland Ice Sheet ◽  
Deep Ocean ◽  
Glacial Maximum ◽  
Last Glacial ◽  
The North ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract. We use the fully coupled atmosphere–ocean three-dimensional model of intermediate complexity iLOVECLIM to simulate the climate and oxygen stable isotopic signal during the Last Glacial Maximum (LGM, 21 000 years). By using a model that is able to explicitly simulate the sensor (δ18O), results can be directly compared with data from climatic archives in the different realms. Our results indicate that iLOVECLIM reproduces well the main feature of the LGM climate in the atmospheric and oceanic components. The annual mean δ18O in precipitation shows more depleted values in the northern and southern high latitudes during the LGM. The model reproduces very well the spatial gradient observed in ice core records over the Greenland ice sheet. We observe a general pattern toward more enriched values for continental calcite δ18O in the model at the LGM, in agreement with speleothem data. This can be explained by both a general atmospheric cooling in the tropical and subtropical regions and a reduction in precipitation as confirmed by reconstruction derived from pollens and plant macrofossils. Data–model comparison for sea surface temperature indicates that iLOVECLIM is capable to satisfyingly simulate the change in oceanic surface conditions between the LGM and present. Our data–model comparison for calcite δ18O allows investigating the large discrepancies with respect to glacial temperatures recorded by different microfossil proxies in the North Atlantic region. The results argue for a strong mean annual cooling in the area south of Iceland and Greenland between the LGM and present (> 6 °C), supporting the foraminifera transfer function reconstruction but in disagreement with alkenones and dinocyst reconstructions. The data–model comparison also reveals that large positive calcite δ18O anomaly in the Southern Ocean may be explained by an important cooling, although the driver of this pattern is unclear. We deduce a large positive δ18Osw anomaly for the north Indian Ocean that contrasts with a large negative δ18Osw anomaly in the China Sea between the LGM and the present. This pattern may be linked to changes in the hydrological cycle over these regions. Our simulation of the deep ocean suggests that changes in δ18Osw between the LGM and the present are not spatially homogeneous. This is supported by reconstructions derived from pore fluids in deep-sea sediments. The model underestimates the deep ocean cooling thus biasing the comparison with benthic calcite δ18O data. Nonetheless, our data–model comparison supports a heterogeneous cooling of a few degrees (2–4 °C) in the LGM Ocean.

scholarly journals Constraining the Last Glacial Maximum climate by data-model (<i>i</i>LOVECLIM) comparison using oxygen stable isotopes

2014 ◽  
Vol 10 (1) ◽  
pp. 105-148 ◽  
Author(s):  
T. Caley ◽  
D. M. Roche ◽  
C. Waelbroeck ◽  
E. Michel
Keyword(s):  
Last Glacial Maximum ◽  
Data Model ◽  
Model Comparison ◽  
Greenland Ice Sheet ◽  
Deep Ocean ◽  
Glacial Maximum ◽  
Last Glacial ◽  
The North ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract. We use the fully coupled atmosphere-ocean three-dimensional model of intermediate complexity iLOVECLIM to simulate the climate and oxygen stable isotopic signal during the Last Glacial Maximum (LGM, 21 000 yr). By using a model that is able to explicitly simulate the sensor (δ18O), results can be directly compared with data from climatic archives in the different realms. Our results indicate that iLOVECLIM reproduces well the main feature of the LGM climate in the atmospheric and oceanic components. The annual mean δ18O in precipitation shows more depleted values in the northern and southern high latitudes during the LGM. The model reproduces very well the spatial gradient observed in ice core records over the Greenland ice-sheet. We observe a general pattern toward more enriched values for continental calcite δ18O in the model at the LGM, in agreement with speleothem data. This can be explained by both a general atmospheric cooling in the tropical and subtropical regions and a reduction in precipitation as confirmed by reconstruction derived from pollens and plant macrofossils. Data-model comparison for sea surface temperature indicates that iLOVECLIM is capable to satisfyingly simulate the change in oceanic surface conditions between the LGM and present. Our data-model comparison for calcite δ18O allows investigating the large discrepancies with respect to glacial temperatures recorded by different microfossil proxies in the North Atlantic region. The results argue for a trong mean annual cooling between the LGM and present (> 6°C), supporting the foraminifera transfer function reconstruction but in disagreement with alkenones and dinocyst reconstructions. The data-model comparison also reveals that large positive calcite δ18O anomaly in the Southern Ocean may be explained by an important cooling, although the driver of this pattern is unclear. We deduce a large positive δ18Osw anomaly for the north Indian Ocean that contrasts with a large negative δ18Osw anomaly in the China Sea between the LGM and present. This pattern may be linked to changes in the hydrological cycle over these regions. Our simulation of the deep ocean suggests that changes in δ18Osw between the LGM and present are not spatially homogenous. This is supported by reconstructions derived from pore fluids in deep-sea sediments. The model underestimates the deep ocean cooling thus biasing the comparison with benthic calcite δ18O data. Nonetheless, our data-model comparison support a heterogeneous cooling of few degrees (2–4°C) in the LGM Ocean.

A weaker Atlantic Meridional Overturning Circulation at the Last Glacial Maximum led to a greater deep ocean carbon content

2020 ◽  
Author(s):  
Laurie Menviel ◽  
Paul Spence ◽  
Luke Skinner ◽  
Kazuyo Tachikawa ◽  
Tobias Friedrich ◽  
...  
Keyword(s):  
Last Glacial Maximum ◽  
North Atlantic ◽  
Deep Ocean ◽  
Glacial Maximum ◽  
Last Glacial ◽  
The North ◽  
The North Atlantic ◽  
Ocean Carbon ◽  
The Last Glacial Maximum ◽  
The Last Glacial

&lt;p&gt;While paleoproxy records and modelling studies consistently suggest that North Atlantic&amp;#160; Deep Water (NADW) was shallower at the Last Glacial Maximum (LGM) than during pre-industrial times, its strength is still subject to debate partly due to different signals across the North Atlantic. Here, using a series of LGM experiments performed with a carbon isotopes enabled Earth system model, we show that proxy records are consistent with a shallower and weaker NADW. A significant equatorward advance of sea-ice over the Labrador Sea and the Nordic Seas shifts the NADW convection sites to the south of the Norwegian Sea. While the deep western boundary current in the Northwest Atlantic weakens with NADW, a change in density gradients strengthens the deep southward flow in the Northeast Atlantic. A shoaling and weakening of NADW further allow penetration of Antarctic Bottom Water in the North Atlantic despite its transport being reduced. This resultant globally weaker oceanic circulation leads to an increase in deep ocean carbon of ~500 GtC, thus significantly contributing to the lower LGM atmospheric CO&lt;sub&gt;2&lt;/sub&gt; concentration.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

Forcing of the deep ocean circulation in simulations of the Last Glacial Maximum

2002 ◽  
Vol 17 (2) ◽  
pp. 5-1-5-15 ◽  
Author(s):  
A. Schmittner ◽  
K. J. Meissner ◽  
M. Eby ◽  
A. J. Weaver
Keyword(s):  
Last Glacial Maximum ◽  
Ocean Circulation ◽  
Deep Ocean ◽  
Glacial Maximum ◽  
Last Glacial ◽  
Deep Ocean Circulation ◽  
The Last Glacial Maximum ◽  
The Last Glacial

scholarly journals The simulated climate of the Last Glacial Maximum and insights into the global marine carbon cycle

2016 ◽  
Vol 12 (12) ◽  
pp. 2271-2295 ◽  
Author(s):  
Pearse J. Buchanan ◽  
Richard J. Matear ◽  
Andrew Lenton ◽  
Steven J. Phipps ◽  
Zanna Chase ◽  
...  
Keyword(s):  
Last Glacial Maximum ◽  
Deep Ocean ◽  
Glacial Maximum ◽  
Biological Pump ◽  
Biogeochemical Processes ◽  
Export Production ◽  
Last Glacial ◽  
Proxy Reconstructions ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract. The ocean's ability to store large quantities of carbon, combined with the millennial longevity over which this reservoir is overturned, has implicated the ocean as a key driver of glacial–interglacial climates. However, the combination of processes that cause an accumulation of carbon within the ocean during glacial periods is still under debate. Here we present simulations of the Last Glacial Maximum (LGM) using the CSIRO Mk3L-COAL (Carbon–Ocean–Atmosphere–Land) earth system model to test the contribution of physical and biogeochemical processes to ocean carbon storage. For the LGM simulation, we find a significant global cooling of the surface ocean (3.2 °C) and the expansion of both minimum and maximum sea ice cover broadly consistent with proxy reconstructions. The glacial ocean stores an additional 267 Pg C in the deep ocean relative to the pre-industrial (PI) simulation due to stronger Antarctic Bottom Water formation. However, 889 Pg C is lost from the upper ocean via equilibration with a lower atmospheric CO2 concentration and a global decrease in export production, causing a net loss of carbon relative to the PI ocean. The LGM deep ocean also experiences an oxygenation ( >  100 mmol O2 m−3) and deepening of the calcite saturation horizon (exceeds the ocean bottom) at odds with proxy reconstructions. With modifications to key biogeochemical processes, which include an increased export of organic matter due to a simulated release from iron limitation, a deepening of remineralisation and decreased inorganic carbon export driven by cooler temperatures, we find that the carbon content of the glacial ocean can be sufficiently increased (317 Pg C) to explain the reduction in atmospheric and terrestrial carbon at the LGM (194 ± 2 and 330 ± 400 Pg C, respectively). Assuming an LGM–PI difference of 95 ppm pCO2, we find that 55 ppm can be attributed to the biological pump, 28 ppm to circulation changes and the remaining 12 ppm to solubility. The biogeochemical modifications also improve model–proxy agreement in export production, carbonate chemistry and dissolved oxygen fields. Thus, we find strong evidence that variations in the oceanic biological pump exert a primary control on the climate.

Sign in / Sign up

Export Citation Format

Share Document