Atmospheric CO2 and Climate on Millennial Time Scales During the Last Glacial Period (original) (raw)
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Nature, 2000
Twenty years ago, measurements on ice cores showed that the concentration of carbon dioxide in the atmosphere was lower during ice ages than it is today. As yet, there is no broadly accepted explanation for this difference. Current investigations focus on the ocean's 'biological pump', the sequestration of carbon in the ocean interior by the rain of organic carbon out of the surface ocean, and its effect on the burial of calcium carbonate in marine sediments. Some researchers surmise that the whole-ocean reservoir of algal nutrients was larger during glacial times, strengthening the biological pump at low latitudes, where these nutrients are currently limiting. Others propose that the biological pump was more efficient during glacial times because of more complete utilization of nutrients at high latitudes, where much of the nutrient supply currently goes unused. We present a version of the latter hypothesis that focuses on the open ocean surrounding Antarctica, involvin...
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Recent progress in the reconstruction of atmospheric CO 2 records from Antarctic ice cores has allowed for the documentation of natural CO 2 variations on orbital time scales over the last up to 800,000 years and for the resolution of millennial CO 2 variations during the last glacial cycle in unprecedented detail. This has shown that atmospheric CO 2 varied within natural bounds of approximately 170-300 ppmv but never reached recent CO 2 concentrations caused by anthropogenic CO 2 emissions. In addition, the natural atmospheric CO 2 concentrations show an extraordinary correlation with Southern Ocean climate changes, pointing to a significant (direct or indirect) influence of climatic and environmental changes in the Southern Ocean region on atmospheric CO 2 concentrations.
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We present a new high-resolution record of atmospheric CO2 from the Siple Dome ice core, Antarctica over the early Holocene (11.7-7.4 ka) that quantifies natural CO2 variability on millennial timescales under interglacial climate conditions. Atmospheric CO2 decreased by ~10 ppm between 11.3 and 7.3 ka. The decrease was punctuated by local minima at 11.1, 10.1, 9.1 and 8.3 ka with amplitude of 2-6 ppm. These variations correlate with proxies for solar forcing and local climate in the South East Atlantic polar front, East Equatorial Pacific and North Atlantic. These relationships suggest that weak solar forcing changes might have impacted CO2 by changing CO2 outgassing from the Southern Ocean and the East Equatorial Pacific and terrestrial carbon storage in the Northern Hemisphere over the early Holocene.
Global Biogeochemical Cycles, 2012
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The influence of Antarctic sea ice on glacial–interglacial CO2 variations
Nature, 2000
The robust observation of an 80 ppm drop in atmospheric CO 2 during glacial times is without a satisfactory explanation. There is growing evidence that ocean models previously used to investigate this problem significantly overestimate the amount of deep water upwelling at low latitudes. Here we use a box model that has no low-latitude deep-water upwelling to investigate the linkages between glacialinterglacial temperature and atmospheric CO 2 variations. This model allows us to explore the possibility that atmospheric CO 2 responds to temperature through effects on air-sea gas exchange resulting from variations in Antarctic sea ice. Operating from the simple assumptions that deep waters only significantly outcrop south of 55°S, and that sea ice covered most of this region during glacial times, our model reproduces 67 ppm of the observed glacial-interglacial CO 2 difference. Unlike other mechanisms put forward to explain this difference, our model is consistent with estimates of glacial deep O 2 concentrations, Antarctic surface δ 13 C ratios, and lysocline depths, and also with estimates of the timing of events during deglaciation.
Global warming preceded by increasing carbon dioxide concentrations during the last deglaciation
Nature, 2012
The covariation of carbon dioxide (CO(2)) concentration and temperature in Antarctic ice-core records suggests a close link between CO(2) and climate during the Pleistocene ice ages. The role and relative importance of CO(2) in producing these climate changes remains unclear, however, in part because the ice-core deuterium record reflects local rather than global temperature. Here we construct a record of global surface temperature from 80 proxy records and show that temperature is correlated with and generally lags CO(2) during the last (that is, the most recent) deglaciation. Differences between the respective temperature changes of the Northern Hemisphere and Southern Hemisphere parallel variations in the strength of the Atlantic meridional overturning circulation recorded in marine sediments. These observations, together with transient global climate model simulations, support the conclusion that an antiphased hemispheric temperature response to ocean circulation changes superim...
The role of Southern Ocean mixing and upwelling in glacial-interglacial atmospheric CO2 change
Tellus B: Chemical and Physical Meteorology, 2006
Decreased ventilation of the Southern Ocean in glacial time is implicated in most explanations of lower glacial atmospheric CO 2. Today, the deep (>2000 m) ocean south of the Polar Front is rapidly ventilated from below, with the interaction of deep currents with topography driving high mixing rates well up into the water column. We show from a buoyancy budget that mixing rates are high in all the deep waters of the Southern Ocean. Between the surface and ∼2000 m depth, water is upwelled by a residual meridional overturning that is directly linked to buoyancy fluxes through the ocean surface. Combined with the rapid deep mixing, this upwelling serves to return deep water to the surface on a short time scale. We propose two new mechanisms by which, in glacial time, the deep Southern Ocean may have been more isolated from the surface. Firstly, the deep ocean appears to have been more stratified because of denser bottom water resulting from intense sea ice formation near Antarctica. The greater stratification would have slowed the deep mixing. Secondly, subzero atmospheric temperatures may have meant that the present-day buoyancy flux from the atmosphere to the ocean surface was reduced or reversed. This in turn would have reduced or eliminated the upwelling (contrary to a common assumption, upwelling is not solely a function of the wind stress but is coupled to the air-sea buoyancy flux too). The observed very close link between Antarctic temperatures and atmospheric CO 2 could then be explained as a natural consequence of the connection between the air-sea buoyancy flux and upwelling in the Southern Ocean, if slower ventilation of the Southern Ocean led to lower atmospheric CO 2. Here we use a box model, similar to those of previous authors, to show that weaker mixing and reduced upwelling in the Southern Ocean can explain the low glacial atmospheric CO 2 in such a formulation.
Journal of Quaternary Science, 2002
A recent high-resolution record of Late-glacial CO 2 change from Dome Concordia in Antarctica reveals a trend of increasing CO 2 across the Younger Dryas stadial (GS-1). These results are in good agreement with previous Antarctic ice-core records. However, they contrast markedly with a proxy CO 2 record based on the stomatal approach to CO 2 reconstruction, which records a ca. 70 ppm mean CO 2 decline at the onset of GS-1. To address these apparent discrepancies we tested the validity of the stomatal-based CO 2 reconstructions from Kråkenes by obtaining further proxy CO 2 records based on a similar approach using fossil leaves from two independent lakes in Atlantic Canada. Our Late-glacial CO 2 reconstructions reveal an abrupt ca. 77 ppm decrease in atmospheric CO 2 at the onset of the Younger Dryas stadial, which lagged climatic cooling by ca. 130 yr. Furthermore, the trends recorded in the most accurate high-resolution ice-core record of CO 2 , from Dome Concordia, can be reproduced from our stomatal-based CO 2 records, when time-averaged by the mean age distribution of air contained within Dome Concordia ice (200 to 550 yr). If correct, our results indicate an abrupt drawdown of atmospheric CO 2 within two centuries at the onset of GS-1, suggesting that some re-evaluation of the behaviour of atmospheric CO 2 sinks and sources during times of rapid climatic change, such as the Late-glacial, may be required.