Deep water circulation in the Arabian Sea during the last glacial cycle: Implications for paleo-redox condition, carbon sink and atmospheric CO2 variability

Abstract. A 2.5-dimensional climate model of intermediate complexity, CLIMBER-2, fully coupled with the GREMLINS 3-D thermo-mechanical ice sheet model is used to simulate the evolution of major Northern Hemisphere ice sheets during the last glacial-interglacial cycle and to investigate the ice sheets responses to both insolation and atmospheric CO2 concentration. This model reproduces the main phases of advance and retreat of Northern Hemisphere ice sheets during the last glacial cycle, although the amplitude of these variations is less pronounced than those based on sea level reconstructions. At the last glacial maximum, the simulated ice volume is 52.5×1015 m3 and the spatial distribution of both the American and Eurasian ice complexes is in reasonable agreement with observations, with the exception of the marine parts of these former ice sheets. A set of sensitivity studies has also been performed to assess the sensitivity of the Northern Hemisphere ice sheets to both insolation and atmospheric CO2. Our results suggest that the decrease of summer insolation is the main factor responsible for the early build up of the North American ice sheet around 120 kyr BP, in agreement with benthic foraminifera δ18O signals. In contrast, low insolation and low atmospheric CO2 concentration are both necessary to trigger a long-lasting glaciation over Eurasia.

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Climatology of the Eastern Arabian Sea during the last glacial Cycle reconstructed from paired measurement of foraminiferal δ18O and Mg/Ca

Quaternary Research ◽

10.1016/j.yqres.2010.02.002 ◽

2010 ◽

Vol 73 (3) ◽

pp. 535-540 ◽

Cited By ~ 29

Author(s):

V.K. Banakar ◽

B.S. Mahesh ◽

G. Burr ◽

A.R. Chodankar

Keyword(s):

Time Series ◽

Arabian Sea ◽

Sea Surface ◽

Sea Surface Salinity ◽

Glacial Cycle ◽

Surface Salinity ◽

Last Glacial ◽

Sst Cooling ◽

Eastern Arabian Sea ◽

The Last Glacial

Paired measurements of Mg/Ca and δ18O of Globigerenoides sacculifer from an Eastern Arabian Sea (EAS) sediment core indicate that sea-surface temperature (SST) varied within 2°C and sea-surface salinity within 2 psu during the last 100 ka. SST was coldest (∽ 27°C) during Marine Isotope Stage (MIS) 4 and 2. Sea-surface salinity was highest (∽ 37.5 psu) during most of the last glacial period (∽ 60–18 ka), concurrent with increased δ18O G.sacculifer and C/N ratios of organic matter and indicative of sustained intense winter monsoons. SST time series are influenced by both Greenland and Antarctic climates. However, the sea-surface salinity time series and the deglacial warming in the SST record (beginning at ∽18 ka) compare well with the LR04 benthic δ18O-stack and Antarctic temperatures. This suggests a teleconnection between the climate in the Southern Hemisphere and the EAS. Therefore, the last 100-ka variability in EAS climatology appears to have evolved in response to a combination of global climatic forcings and regional monsoons. The most intense summer monsoons within the Holocene occurred at ∽8 ka and are marked by SST cooling of ∽ 1°C, sea-surface salinity decrease of 0.5 psu, and δ18O G.sacculifer decrease of 0.2‰.

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Glacial CO<sub>2</sub> cycle as a succession of key physical and biogeochemical processes

Climate of the Past Discussions ◽

10.5194/cpd-7-1767-2011 ◽

2011 ◽

Vol 7 (3) ◽

pp. 1767-1795 ◽

Cited By ~ 2

Author(s):

V. Brovkin ◽

A. Ganopolski ◽

D. Archer ◽

G. Munhoven

Keyword(s):

Radiative Forcing ◽

Marine Biology ◽

Deep Ocean ◽

Co2 Concentration ◽

Atmospheric Co2 ◽

Glacial Cycle ◽

Minimum Concentration ◽

Carbon Cycle Model ◽

Last Glacial ◽

The Last Glacial

Abstract. During glacial-interglacial cycles, atmospheric CO2 concentration varied by about 100 ppmv in amplitude. While testing mechanisms that had led to the low glacial CO2 level could be done in equilibrium model experiments, an ultimate goal is to explain CO2 changes in transient simulations through the complete glacial-interglacial cycle. A computationally efficient Earth System model of intermediate complexity CLIMBER-2 is used to simulate global biogeochemistry over the last glacial cycle (126 kyr). The physical core of the model (atmosphere, ocean, land and ice sheets) is driven by orbital changes and reconstructed radiative forcing from greenhouses gases, ice, and aeolian dust. The carbon cycle model is able to reproduce the main features of the CO2 changes: a 50 ppmv CO2 drop during glacial inception, a minimum concentration at the last glacial maximum by 80 ppmv lower than the Holocene value, and an abrupt 60 ppmv CO2 rise during the deglaciation. The model deep ocean δ13C also resembles reconstructions from deep-sea cores. The main drivers of atmospheric CO2 evolve with time: changes in sea surface temperatures and in the volume of bottom water of southern origin controls atmospheric CO2 during the glacial inception and deglaciation, while changes in carbonate chemistry and marine biology are dominant during the first and second parts of the glacial cycle, respectively. These feedback mechanisms could also significantly impact the ultimate climate response to the anthropogenic perturbation.

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Calcium carbonate corrosiveness in the South Atlantic during the Last Glacial Maximum as inferred from changes in the preservation of Globigerina bulloides: A proxy to determine deep-water circulation patterns?

Marine Geology ◽

10.1016/s0025-3227(03)00372-4 ◽

2004 ◽

Vol 204 (1-2) ◽

pp. 43-57 ◽

Cited By ~ 28

Author(s):

A.N.A Volbers ◽

R Henrich

Keyword(s):

Calcium Carbonate ◽

Last Glacial Maximum ◽

Deep Water ◽

Glacial Maximum ◽

Water Circulation ◽

Last Glacial ◽

Globigerina Bulloides ◽

Circulation Patterns ◽

The Last Glacial Maximum ◽

The Last Glacial

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Rapid bottom-water circulation changes during the last glacial cycle in the coastal low-latitude NE Atlantic

Quaternary Research ◽

10.1016/j.yqres.2013.11.004 ◽

2014 ◽

Vol 81 (2) ◽

pp. 330-338 ◽

Cited By ~ 7

Author(s):

David Gallego-Torres ◽

Oscar E. Romero ◽

Francisca Martínez-Ruiz ◽

Jung-Hyun Kim ◽

Barbara Donner ◽

...

Keyword(s):

High Resolution ◽

Deep Water ◽

Bottom Water ◽

Meridional Overturning Circulation ◽

Last Deglaciation ◽

Glacial Cycle ◽

Last Glacial ◽

Deep Waters ◽

High Resolution Reconstruction ◽

The Last Glacial

AbstractPrevious paleoceanographic studies along the NW African margin focused on the dynamics of surface and intermediate waters, whereas little attention has been devoted to deep-water masses. Currently, these deep waters consist mainly of North Atlantic Deep Waters as part of the Atlantic Meridional Overturning Circulation (AMOC). However, this configuration was altered during periods of AMOC collapse. We present a high-resolution reconstruction of bottom-water ventilation and current evolution off Mauritania from the last glacial maximum into the early Holocene. Applying redox proxies (Mo, U and Mn) measured on sediments from off Mauritania, we describe changes in deep-water oxygenation and we infer the evolution of deep-water conditions during millennial-scale climate/oceanographic events in the area. The second half of Heinrich Event 1 and the Younger Dryas were recognized as periods of reduced ventilation, coinciding with events of AMOC reduction. We propose that these weakening circulation events induced deficient deep-water oxygenation in the Mauritanian upwelling region, which together with increased productivity promoted reducing conditions and enhanced organic-matter preservation. This is the first time the effect of AMOC collapse in the area is described at high resolution, broadening the knowledge on basin-wide oceanographic changes associated with rapid climate variability during the last deglaciation.

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Glacial CO<sub>2</sub> cycle as a succession of key physical and biogeochemical processes

Climate of the Past ◽

10.5194/cp-8-251-2012 ◽

2012 ◽

Vol 8 (1) ◽

pp. 251-264 ◽

Cited By ~ 66

Author(s):

V. Brovkin ◽

A. Ganopolski ◽

D. Archer ◽

G. Munhoven

Keyword(s):

Radiative Forcing ◽

Marine Biology ◽

Deep Ocean ◽

Co2 Concentration ◽

Atmospheric Co2 ◽

Glacial Cycle ◽

Minimum Concentration ◽

Carbon Cycle Model ◽

Last Glacial ◽

The Last Glacial

Abstract. During glacial-interglacial cycles, atmospheric CO2 concentration varied by about 100 ppmv in amplitude. While testing mechanisms that have led to the low glacial CO2 level could be done in equilibrium model experiments, an ultimate goal is to explain CO2 changes in transient simulations through the complete glacial-interglacial cycle. The computationally efficient Earth System model of intermediate complexity CLIMBER-2 is used to simulate global biogeochemistry over the last glacial cycle (126 kyr). The physical core of the model (atmosphere, ocean, land and ice sheets) is driven by orbital changes and reconstructed radiative forcing from greenhouses gases, ice, and aeolian dust. The carbon cycle model is able to reproduce the main features of the CO2 changes: a 50 ppmv CO2 drop during glacial inception, a minimum concentration at the last glacial maximum 80 ppmv lower than the Holocene value, and an abrupt 60 ppmv CO2 rise during the deglaciation. The model deep ocean δ13C also resembles reconstructions from deep-sea cores. The main drivers of atmospheric CO2 evolve in time: changes in sea surface temperatures and in the volume of bottom water of southern origin control atmospheric CO2 during the glacial inception and deglaciation; changes in carbonate chemistry and marine biology are dominant during the first and second parts of the glacial cycle, respectively. These feedback mechanisms could also significantly impact the ultimate climate response to the anthropogenic perturbation.

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