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Seltzer, AM, Buizert C, Baggenstos D, Brook EJ, Ahn J, Yang JW, Severinghaus JP.  2017.  Does delta O-18 of O-2 record meridional shifts in tropical rainfall? Climate of the Past. 13:1323-1338.   10.5194/cp-13-1323-2017   AbstractWebsite

Marine sediments, speleothems, paleo-lake elevations, and ice core methane and delta O-18 of O-2 (delta O-18(atm)) records provide ample evidence for repeated abrupt meridional shifts in tropical rainfall belts throughout the last glacial cycle. To improve understanding of the impact of abrupt events on the global terrestrial biosphere, we present composite records of delta O-18(atm) and inferred changes in fractionation by the global terrestrial biosphere (Delta epsilon(LAND)) from discrete gas measurements in the WAIS Divide (WD) and Siple Dome (SD) Antarctic ice cores. On the common WD timescale, it is evident that maxima in Delta epsilon(LAND) are synchronous with or shortly follow small-amplitude WD CH4 peaks that occur within Heinrich stadials 1, 2, 4, and 5 - periods of low atmospheric CH4 concentrations. These local CH4 maxima have been suggested as markers of abrupt climate responses to Heinrich events. Based on our analysis of the modern seasonal cycle of gross primary productivity (GPP)-weighted delta(OatmO)-O-18 of terrestrial precipitation (the source water for atmospheric O-2 production), we propose a simple mechanism by which Delta epsilon(LAND) tracks the centroid latitude of terrestrial oxygen production. As intense rainfall and oxygen production migrate northward, Delta epsilon(LAND) should decrease due to the underlying meridional gradient in rainfall delta O-18. A southward shift should increase Delta epsilon(LAND). Monsoon intensity also influences delta O-18 of precipitation, and although we cannot determine the relative contributions of the two mechanisms, both act in the same direction. Therefore, we suggest that abrupt increases in Delta epsilon(LAND) unambiguously imply a southward shift of tropical rainfall. The exact magnitude of this shift, however, remains under-constrained by Delta epsilon(LAND).

Fischer, H, Severinghaus J, Brook E, Wolff E, Albert M, Alemany O, Arthern R, Bentley C, Blankenship D, Chappellaz J, Creyts T, Dahl-Jensen D, Dinn M, Frezzotti M, Fujita S, Gallee H, Hindmarsh R, Hudspeth D, Jugie G, Kawamura K, Lipenkov V, Miller H, Mulvaney R, Parrenin F, Pattyn F, Ritz C, Schwander J, Steinhage D, van Ommen T, Wilhelms F.  2013.  Where to find 1.5 million yr old ice for the IPICS "Oldest-Ice" ice core. Climate of the Past. 9:2489-2505.   10.5194/cp-9-2489-2013   AbstractWebsite

The recovery of a 1.5 million yr long ice core from Antarctica represents a keystone of our understanding of Quaternary climate, the progression of glaciation over this time period and the role of greenhouse gas cycles in this progression. Here we tackle the question of where such ice may still be found in the Antarctic ice sheet. We can show that such old ice is most likely to exist in the plateau area of the East Antarctic ice sheet (EAIS) without stratigraphic disturbance and should be able to be recovered after careful pre-site selection studies. Based on a simple ice and heat flow model and glaciological observations, we conclude that positions in the vicinity of major domes and saddle position on the East Antarctic Plateau will most likely have such old ice in store and represent the best study areas for dedicated reconnaissance studies in the near future. In contrast to previous ice core drill site selections, however, we strongly suggest significantly reduced ice thickness to avoid bottom melting. For example for the geothermal heat flux and accumulation conditions at Dome C, an ice thickness lower than but close to about 2500m would be required to find 1.5 Myr old ice (i.e., more than 700m less than at the current EPICA Dome C drill site). Within this constraint, the resolution of an Oldest-Ice record and the distance of such old ice to the bedrock should be maximized to avoid ice flow disturbances, for example, by finding locations with minimum geothermal heat flux. As the geothermal heat flux is largely unknown for the EAIS, this parameter has to be carefully determined beforehand. In addition, detailed bedrock topography and ice flow history has to be reconstructed for candidates of an Oldest-Ice ice coring site. Finally, we argue strongly for rapid access drilling before any full, deep ice coring activity commences to bring datable samples to the surface and to allow an age check of the oldest ice.

Severinghaus, JP, Beaudette R, Headly MA, Taylor K, Brook EJ.  2009.  Oxygen-18 of O2 Records the Impact of Abrupt Climate Change on the Terrestrial Biosphere. Science. 324:1431-1434.   10.1126/science.1169473   AbstractWebsite

Photosynthesis and respiration occur widely on Earth's surface, and the O-18/O-16 ratio of the oxygen produced and consumed varies with climatic conditions. As a consequence, the history of climate is reflected in the deviation of the O-18/O-16 of air (delta O-18(atm)) from seawater delta O-18 (known as the Dole effect). We report variations in delta O-18(atm) over the past 60,000 years related to Heinrich and Dansgaard-Oeschger events, two modes of abrupt climate change observed during the last ice age. Correlations with cave records support the hypothesis that the Dole effect is primarily governed by the strength of the Asian and North African monsoons and confirm that widespread changes in low-latitude terrestrial rainfall accompanied abrupt climate change. The rapid delta O-18(atm) changes can also be used to synchronize ice records by providing global time markers.