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

2016 ◽  
Author(s):  
Pearse J. Buchanan ◽  
Richard J. Matear ◽  
Andrew Lenton ◽  
Steven J. Phipps ◽  
Zanna Chase ◽  
...  
Keyword(s):  
Southern Hemisphere ◽  
Last Glacial Maximum ◽  
Northern Hemisphere ◽  
Deep Ocean ◽  
Atmospheric Co2 ◽  
Biogeochemical Processes ◽  
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 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 (Northern Hemisphere: 105 %; Southern Hemisphere: 225 %) and maximum (Northern Hemisphere: 145 %; Southern Hemisphere: 120 %) sea ice cover broadly consistent with proxy reconstructions. Within the ocean, a significant reorganisation of the large-scale circulation and biogeochemical fields occurs. The LGM simulation stores an additional 322  Pg C in the deep ocean relative to the Pre-Industrial (PI) simulation, particularly due to a strengthening in Antarctic Bottom Water circulation. However, 839 Pg C is lost from the upper ocean via equilibration with a lower atmospheric CO2 concentration, causing a net loss of 517 Pg C relative to the PI simulation. The LGM deep ocean also experiences an oxygenation (> 100 mmol O2 m−3) and deepening of the aragonite saturation depth (> 2000 m deeper) at odds with proxy reconstructions. Hence, physical changes cannot in isolation produce plausible biogeochemistry nor the required drawdown of atmospheric CO2 of 80–100 ppm at the LGM. 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 in the glacial oceanic reservoir can be increased (326 Pg C) to a level that is sufficient to explain the reduction in atmospheric and terrestrial carbon at the LGM (520 ± 00 Pg C). These modifications also go some way to reconcile simulated export production, aragonite saturation state and oxygen fields with those that have been reconstructed by proxy measurements, thereby implicating changes in ocean biogeochemistry as an essential driver of the climate system.

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.

scholarly journals Quantifying the effect of vegetation dynamics on the climate of the Last Glacial Maximum

2005 ◽  
Vol 1 (1) ◽  
pp. 1-7 ◽  
Author(s):  
A. Jahn ◽  
M. Claussen ◽  
A. Ganopolski ◽  
V. Brovkin
Keyword(s):  
Last Glacial Maximum ◽  
Vegetation Dynamics ◽  
Ice Sheets ◽  
Atmospheric Co2 ◽  
Radiative Effect ◽  
Temperature Changes ◽  
Last Glacial ◽  
Atmospheric Co2 Concentrations ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract. The importance of the biogeophysical atmosphere-vegetation feedback in comparison with the radiative effect of lower atmospheric CO2 concentrations and the presence of ice sheets at the last glacial maximum (LGM) is investigated with the climate system model CLIMBER-2. Equilibrium experiments reveal that most of the global cooling at the LGM (-5.1°C) relative to (natural) present-day conditions is caused by the introduction of ice sheets into the model (-3.0°C), followed by the effect of lower atmospheric CO2 levels at the LGM (-1.5°C), while a synergy between these two factors appears to be very small on global average. The biogeophysical effects of changes in vegetation cover are found to cool the global LGM climate by 0.6°C. The latter are most pronounced in the northern high latitudes, where the taiga-tundra feedback causes annually averaged temperature changes of up to -2.0°C, while the radiative effect of lower atmospheric CO2 in this region only produces a cooling of 1.5°C. Hence, in this region, the temperature changes caused by vegetation dynamics at the LGM exceed the cooling due to lower atmospheric CO2 concentrations.

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

scholarly journals Influence of dynamic vegetation on climate change and terrestrial carbon storage in the Last Glacial Maximum

2013 ◽  
Vol 9 (4) ◽  
pp. 1571-1587 ◽  
Author(s):  
R. O'ishi ◽  
A. Abe-Ouchi
Keyword(s):  
Carbon Storage ◽  
Last Glacial Maximum ◽  
Glacial Maximum ◽  
Atmospheric Co2 ◽  
Terrestrial Carbon ◽  
Dynamic Global Vegetation Model ◽  
Vegetation Feedback ◽  
Last Glacial ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract. When the climate is reconstructed from paleoevidence, it shows that the Last Glacial Maximum (LGM, ca. 21 000 yr ago) is cold and dry compared to the present-day. Reconstruction also shows that compared to today, the vegetation of the LGM is less active and the distribution of vegetation was drastically different, due to cold temperature, dryness, and a lower level of atmospheric CO2 concentration (185 ppm compared to a preindustrial level of 285 ppm). In the present paper, we investigate the influence of vegetation change on the climate of the LGM by using a coupled atmosphere-ocean-vegetation general circulation model (AOVGCM, the MIROC-LPJ). The MIROC-LPJ is different from earlier studies in the introduction of a bias correction method in individual running GCM experiments. We examined four GCM experiments (LGM and preindustrial, with and without vegetation feedback) and quantified the strength of the vegetation feedback during the LGM. The result shows that global-averaged cooling during the LGM is amplified by +13.5 % due to the introduction of vegetation feedback. This is mainly caused by the increase of land surface albedo due to the expansion of tundra in northern high latitudes and the desertification in northern middle latitudes around 30° N to 60° N. We also investigated how this change in climate affected the total terrestrial carbon storage by using offline Lund-Potsdam-Jena dynamic global vegetation model (LPJ-DGVM). Our result shows that the total terrestrial carbon storage was reduced by 597 PgC during the LGM, which corresponds to the emission of 282 ppm atmospheric CO2. In the LGM experiments, the global carbon distribution is generally the same whether the vegetation feedback to the atmosphere is included or not. However, the inclusion of vegetation feedback causes substantial terrestrial carbon storage change, especially in explaining the lowering of atmospheric CO2 during the LGM.

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>

Southern Hemisphere westerly wind changes during the Last Glacial Maximum: paleo-data synthesis

2013 ◽  
Vol 68 ◽  
pp. 76-95 ◽  
Author(s):  
K.E. Kohfeld ◽  
R.M. Graham ◽  
A.M. de Boer ◽  
L.C. Sime ◽  
E.W. Wolff ◽  
...  
Keyword(s):  
Southern Hemisphere ◽  
Last Glacial Maximum ◽  
Glacial Maximum ◽  
Westerly Wind ◽  
Data Synthesis ◽  
Last Glacial ◽  
The Last Glacial Maximum ◽  
The Last Glacial

scholarly journals A three-dimensional climate—ice-sheet model applied to the Last Glacial Maximum

1997 ◽  
Vol 25 ◽  
pp. 333-339 ◽  
Author(s):  
Philippe Huybrechts ◽  
Stephen T’siobbel
Keyword(s):  
Last Glacial Maximum ◽  
Northern Hemisphere ◽  
Climate Model ◽  
Three Dimensional ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Glacial Maximum ◽  
Last Glacial ◽  
The Last Glacial Maximum ◽  
The Last Glacial

A quasi-three-dimensional (3-D) climate model (Sellers, 1983) was used to simulate the climate of the Last Glacial Maximum (LGM) in order to provide climatic input for the modelling of the Northern Hemisphere ice sheets. The climate model is basically a coarse-gridded general circulation (GCM) with simplified dynamics, and was subject to appropriate boundary conditions for ice-sheet elevation, atmospheric CO2concentration and orbital parameters. When compared with the present-daysimulation, the simulated climate at the Last Glacial Maximum is characterized by a global annual cooling of 3.5°C and a reduction in global annualprecipitation of 7.5%, which agrees well with results from other, more complex GCMs. Also the patterns of temperature change compare fairly with mostother GCM results, except for a smaller cooling over the North Atlantic and the larger cooling predicted for the summer rather than for the winter over Eurasia.The climate model is able to simulate changes in Northern Hemisphere tropospheric circulation, yielding enhanced westerlies in the vicinity of the Laurentide and Eurasian ice sheets. However, the simulated precipitation patterns are less convincing, and show a distinct mean precipitation increase over the Laurentide ice sheet. Nevertheless, when using the mean-monthly fields of LGM minus present-day anomalies of temperature and precipitation rate to drive a three-dimensional thermomechanical ice-sheet model, it was demonstrated that within realistic bounds of the ice-flow and mass-balance parameters, veryreasonable reconstructions of the Last Glacial Maximum ice sheets could be obtained.

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