Surface exposure geochronology using cosmogenic nuclides : applications in Antarctic glacial geology

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, and the Woods Hole Oceanographic Institution, 1994.Vita.Includes bibliographical references (leaves 224-227).by Edward Jeremy Brook.Ph.D

Atmospheric CO₂ and climate from 65 to 30 ka B.P.

Using new and existing ice core CO₂ data from 65 ∼ 30 ka a new chronology for CO₂ is established and synchronized with Greenland ice core records to study how high latitude climate change and the carbon cycle were linked during the last glacial period. Atmospheric CO₂ rose several thousand years before abrupt warming in Greenland associated with Dansgaard-Oeschger events, 8, 12, 14, 17, four large warm events that follow Heinrich events. The CO₂ rise terminated at the onset of Greenland warming for each of these events. Atmospheric CO₂ is strongly correlated with the Antarctic isotopic temperature proxy with an average time lag of 720 ± 370 yr (mean ± 1σ) during the time interval studied. The new data and chronology should provide a better target for models attempting to explain CO₂ variability and abrupt climate change

CO(2) Diffusion in Polar Ice: Observations from Naturally Formed CO(2) Spikes in the Siple Dome (Antarctica) Ice Core

One common assumption in interpreting ice-core CO(2) records is that diffusion in the ice does not affect the concentration profile. However, this assumption remains untested because the extremely small CO(2) diffusion coefficient in ice has not been accurately determined in the laboratory. In this study we take advantage of high levels of CO(2) associated with refrozen layers in an ice core from Siple Dome, Antarctica, to study CO(2) diffusion rates. We use noble gases (Xe/Ar and Kr/Ar), electrical conductivity and Ca(2+) ion concentrations to show that substantial CO(2) diffusion may occur in ice on timescales of thousands of years. We estimate the permeation coefficient for CO(2) in ice is similar to 4 x 10(-21) mol m(-1) s(-1) Pa(-1) at -23 degrees C in the top 287 m (corresponding to 2.74 kyr). Smoothing of the CO(2) record by diffusion at this depth/age is one or two orders of magnitude smaller than the smoothing in the firn. However, simulations for depths of similar to 930-950m (similar to 60-70 kyr) indicate that smoothing of the CO(2) record by diffusion in deep ice is comparable to smoothing in the firn. Other types of diffusion (e.g. via liquid in ice grain boundaries or veins) may also be important but their influence has not been quantified

Impact of the Ocean’s Overturning Circulation on Atmospheric CO2

A coupled climate-carbon cycle model and ice core CO2 data from the last glacial period are used to explore the impact of changes in ocean circulation on atmospheric CO2 concentrations on millennial time scales. In the model, stronger wind driven circulation increases atmospheric CO2. Changes in the buoyancy driven deep overturning in the Atlantic affect atmospheric CO2 only indirectly through their effect on Southern Ocean stratification. In simulations with an abrupt and complete shutdown of the Atlantic overturning, stratification in the Southern Ocean decreases due to salinification of surface waters and freshening of the deep sea. Deeper mixed layers and steeper isopycnals lead to outgassing of CO2 in the Southern Ocean and hence gradually increasing atmospheric CO2 concentrations on a multi-millennial time scale. The rise in CO2 terminates at the time of rapid resumption of deep water formation and warming in the North Atlantic, and CO2 levels subsequently gradually decrease. These model responses and a strong correlation between simulated atmospheric CO2 and Antarctic surface air temperatures with little or no time lag are consistent with newly synchronized ice core data from the last ice age. Sensitivity experiments reveal that the amplitude of the response of atmospheric CO2 is sensitive to the model background climatic state and decreases in a colder climate owing to smaller changes in the overturning.Keywords: modeling, atmospheric CO2, Southern Ocean, climate dynamics, ocean circulatio

Gases in ice cores

Air trapped in glacial ice offers a means of reconstructing variations in the concentrations of atmospheric gases over time scales ranging from anthropogenic (last 200 yr) to glacial/interglacial (hundreds of thousands of years). In this paper, we review the glaciological processes by which air is trapped in the ice and discuss processes that fractionate gases in ice cores relative to the contemporaneous atmosphere. We then summarize concentration–time records for CO₂ and CH₄ over the last 200 yr. Finally, we summarize concentration–time records for CO₂ and CH₄ during the last two glacial–interglacial cycles, and their relation to records of global climate change.This is the publisher’s final pdf. The published article is copyrighted by the National Academy of Sciences of the United States of America and can be found at: http://www.pnas.org

Response of atmospheric CO₂ to the abrupt cooling event 8200 years ago

Atmospheric CO₂ records for the centennial scale cooling event 8200 years ago (8.2 ka event) may help us understand climate-carbon cycle feedbacks under interglacial conditions, which are important for understanding future climate, but existing records do not provide enough detail. Here we present a new CO₂ record from the Siple Dome ice core, Antarctica, that covers 7.4–9.0 ka with 8 to 16 year resolution. We observe a small, about 1–2 ppm, increase of atmospheric CO₂ during the 8.2 ka event. The increase is not significant when compared to other centennial variations in the Holocene that are not linked to large temperature changes. Our results do not agree with leaf stomata records that suggest a CO₂ decrease of up to ~25 ppm and imply that the sensitivity of atmospheric CO₂ to the primarily Northern Hemisphere cooling of the 8.2 ka event was limited.Keywords: Carbon cycle, Carbon dioxide, 8.2 ka event, Abrupt climate chang