Publications

Export 6 results:
Sort by: Author [ Title  (Asc)] Type Year
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z   [Show ALL]
C
Bauska, TK, Baggenstos D, Brook EJ, Mix AC, Marcott SA, Petrenko VV, Schaefer H, Severinghaus JP, Lee JE.  2016.  Carbon isotopes characterize rapid changes in atmospheric carbon dioxide during the last deglaciation. Proceedings of the National Academy of Sciences of the United States of America. 113:3465-3470.   10.1073/pnas.1513868113   AbstractWebsite

An understanding of the mechanisms that control CO2 change during glacial-interglacial cycles remains elusive. Here we help to constrain changing sources with a high-precision, high-resolution deglacial record of the stable isotopic composition of carbon in CO2 (delta C-13-CO2) in air extracted from ice samples from Taylor Glacier, Antarctica. During the initial rise in atmospheric CO2 from 17.6 to 15.5 ka, these data demarcate a decrease in delta C-13-CO2, likely due to a weakened oceanic biological pump. From 15.5 to 11.5 ka, the continued atmospheric CO2 rise of 40 ppm is associated with small changes in delta C-13-CO2, consistent with a nearly equal contribution from a further weakening of the biological pump and rising ocean temperature. These two trends, related to marine sources, are punctuated at 16.3 and 12.9 ka with abrupt, century-scale perturbations in delta C-13-CO2 that suggest rapid oxidation of organic land carbon or enhanced air-sea gas exchange in the Southern Ocean. Additional century-scale increases in atmospheric CO2 coincident with increases in atmospheric CH4 and Northern Hemisphere temperature at the onset of the Bolling (14.6-14.3 ka) and Holocene (11.6-11.4 ka) intervals are associated with small changes in delta C-13-CO2, suggesting a combination of sources that included rising surface ocean temperature.

Bauska, TK, Brook EJ, Marcott SA, Baggenstos D, Shackleton S, Severinghaus JP, Petrenko VV.  2018.  Controls on millennial-scale atmospheric CO2 variability during the last glacial period. Geophysical Research Letters. 45:7731-7740.   10.1029/2018gl077881   AbstractWebsite

Changes in atmospheric CO2 on millennial-to-centennial timescales are key components of past climate variability during the last glacial and deglacial periods (70-10 ka), yet the sources and mechanisms responsible for the CO2 fluctuations remain largely obscure. Here we report the C-13/C-12 ratio of atmospheric CO2 during a key interval of the last glacial period at submillennial resolution, with coeval histories of atmospheric CO2, CH4, and N2O concentrations. The carbon isotope data suggest that the millennial-scale CO2 variability in Marine Isotope Stage 3 is driven largely by changes in the organic carbon cycle, most likely by sequestration of respired carbon in the deep ocean. Centennial-scale CO2 variations, distinguished by carbon isotope signatures, are associated with both abrupt hydrological change in the tropics (e.g., Heinrich events) and rapid increases in Northern Hemisphere temperature (Dansgaard-Oeschger events). These events can be linked to modes of variability during the last deglaciation, thus suggesting that drivers of millennial and centennial CO2 variability during both periods are intimately linked to abrupt climate variability. Plain Language Summary Ice cores provide unique records of variations in atmospheric CO2 prior to the instrumental era. While it is clear that changes in atmospheric CO2 played a significant role in driving past climate change, it is unclear what in turn drove changes in atmospheric CO2. Here we investigate enigmatic changes in atmospheric CO2 levels during an interval of the last glacial period (similar to 50,000 to 35,000 years ago) that are associated with abrupt changes in polar climate. To determine the sources and sinks for atmospheric CO2, we measured the stable isotopes of carbon in CO2 and found that the primary source of carbon to the atmosphere was an organic carbon reservoir. Most likely, this carbon was sourced from a deep ocean reservoir that waxed and waned following changes in either the productivity of the surface ocean or stratification of the deep ocean. We also found that atmospheric CO2 can change on the centennial timescale during abrupt climate transitions in the Northern Hemisphere. This observation adds to a growing body of evidence that abrupt changes in atmospheric CO2 are an important component of past carbon cycle variability.

E
Baggenstos, D, Haberli M, Schmitt J, Shackleton SA, Birner B, Severinghaus JP, Kellerhals T, Fischer H.  2019.  Earth's radiative imbalance from the Last Glacial Maximum to the present. Proceedings of the National Academy of Sciences of the United States of America. 116:14881-14886.   10.1073/pnas.1905447116   AbstractWebsite

The energy imbalance at the top of the atmosphere determines the temporal evolution of the global climate, and vice versa changes in the climate system can alter the planetary energy fluxes. This interplay is fundamental to our understanding of Earth's heat budget and the climate system. However, even today, the direct measurement of global radiative fluxes is difficult, such that most assessments are based on changes in the total energy content of the climate system. We apply the same approach to estimate the long-term evolution of Earth's radiative imbalance in the past. New measurements of noble gas-derived mean ocean temperature from the European Project for Ice Coring in Antarctica Dome C ice core covering the last 40,000 y, combined with recent results from the West Antarctic Ice Sheet Divide ice core and the sea-level record, allow us to quantitatively reconstruct the history of the climate system energy budget. The temporal derivative of this quantity must be equal to the planetary radiative imbalance. During the deglaciation, a positive imbalance of typically +0.2 W.m(-2) is maintained for similar to 10,000 y, however, with two distinct peaks that reach up to 0.4 Wm(-2) during times of substantially reduced Atlantic Meridional Overturning Circulation. We conclude that these peaks are related to net changes in ocean heat uptake, likely due to rapid changes in North Atlantic deep-water formation and their impact on the global radiative balance, while changes in cloud coverage, albeit uncertain, may also factor into the picture.

Cuffey, KM, Conway H, Gades AM, Hallet B, Lorrain R, Severinghaus JP, Steig EJ, Vaughn B, White JWC.  2000.  Entrainment at cold glacier beds. Geology. 28:351-354.   10.1130/0091-7613(2000)028<0351:eacgb>2.3.co;2   AbstractWebsite

Here we present measurements of the gas content and isotopic composition of debris-rich basal layers of a polar glacier, Meserve Glacier, Antarctica, which has a basal temperature of -17 degrees C. These measurements show that debris entrainment has occurred without alteration of the glacial ice, and provide the most direct evidence to date that active entrainment occurs at the beds of cold glaciers, without bulk freezing of water. Entrainment at subfreezing temperatures may have formed the U-shaped trough containing Meserve Glacier. In addition to possibly allowing some cold-based glaciers to be important geomorphic agents, entrainment at subfreezing temperatures provides a general mechanism for formation of the dirty basal layers of polar glaciers and ice sheets, which are theologically distinct and can limit the time span of ice-core analyses. Furthermore, accumulating evidence suggests that geomorphologists should abandon the assumption that cold-based glaciers do not slide and abrade their beds.

F
Severinghaus, JP, Battle MO.  2006.  Fractionation of gases in polar lee during bubble close-off: New constraints from firn air Ne, Kr and Xe observations. Earth and Planetary Science Letters. 244:474-500.   10.1016/j.epsl.2006.01.032   AbstractWebsite

Gas ratios in air withdrawn from polar firn (snowpack) show systematic enrichments of Ne/N(2), O(2)/N(2) and Ar/N(2), in the firn-ice transition region where bubbles are closing off. Air from the bubbles in polar ice is correspondingly depleted in these ratios, after accounting for gravitational effects. Gas in the bubbles becomes fractionated during the process of bubble close-off and fractionation may continue as ice cores are stored prior to analysis. We present results from firn air studies at South Pole and Siple Dome, Antarctica, which add Ne, Kr and Xe measurements to the suite of observations. Ne, O(2) and Ar appear to be preferentially excluded from the shrinking and occluding bubbles, and these gases therefore accumulate in the residual firn air, creating a progressive enrichment with time (and depth) in firn air. Early sealing of gases by thin horizontal impermeable layers into a nondiffusive zone or "lock-in zone" greatly enhances this enrichment. A simple model of the bubble close-off fractionation and lock-in zone enrichment fits the data adequately. The model presumes that fractionation is caused by selective permeation of gas through the ice lattice from slightly overpressured bubbles. The effect appears to be size-dependent, because Ne, 02 and Ar have smaller effective molecular diameters than N(2), and fractionation increases strongly with decreasing size. Ne is fractionated 34 2 times more than 0, in South Pole firn air and reaches an enrichment of 90 parts per thousand in the deepest sample. The large atoms Kr and Xe do not appear to be fractionated by this process, despite the large size difference between the two gases, suggesting a threshold atomic diameter of similar to 3.6 angstrom above which the probability becomes very small that the gas will escape from the bubble. These findings have implications for ice core and firn air studies that use gas ratios to infer paleotemperature, chronology and past atmospheric composition. (c) 2006 Elsevier B.V.. All rights reserved.

M
Orsi, AJ, Cornuelle BD, Severinghaus JP.  2014.  Magnitude and temporal evolution of Dansgaard-Oeschger event 8 abrupt temperature change inferred from nitrogen and argon isotopes in GISP2 ice using a new least-squares inversion. Earth and Planetary Science Letters. 395:81-90.   10.1016/j.epsl.2014.03.030   AbstractWebsite

Polar temperature is often inferred from water isotopes in ice cores. However, non-temperature effects on 3180 are important during the abrupt events of the last glacial period, such as changes in the seasonality of precipitation, the northward movement of the storm track, and the increase in accumulation. These effects complicate the interpretation of 8180 as a temperature proxy. Here, we present an independent surface temperature reconstruction, which allows us to test the relationship between delta O-18(ice) and temperature, during Dansgaard-Oeschger event 8, 38.2 thousand yrs ago using new delta N-15 and delta Ar-40 data from the GISP2 ice core in Greenland. This temperature reconstruction relies on a new inversion of inert gas isotope data using generalized least-squares, and includes a robust uncertainty estimation. We find that both temperature and delta O-18 increased in two steps of 20 and 140 yrs, with an overall amplitude of 11.80 +/- 1.8 degrees C between the stadial and interstadial centennial-mean temperature. The coefficient alpha = d delta O-18/dT changes with each time-segment, which shows that non-temperature sources of fractionation have a significant contribution to the delta O-18 signal. When measured on century-averaged values, we find that alpha = d delta O-18/dT = 0.32 +/- 0.06%(0)/degrees C, which is similar to the glacial/Holocene value of 0.328%(o)/degrees C. (C) 2014 Elsevier B.V. All rights reserved.