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Lal, D, Charles C.  2007.  Deconvolution of the atmospheric radiocarbon record in the last 50,000 years. Earth and Planetary Science Letters. 258:550-560.   10.1016/j.epsl.2007.04.016   AbstractWebsite

Here we identify the principal causes of changes in the atmospheric Delta(14)C record by removing the influence of two discrete large changes in the geomagnetic field between 45 and 30 kyr. The marked transitions in the Delta(14)C record during this period can be interpreted as being the result of either "zero magnetic field" for periods of the order of 6500 y and 600 y at similar to 40 kyr and 32 kyr B.P, respectively, or for longer durations if the field was non-zero for appreciable time during the event. Once the effect of these events has been removed, the residual Delta(14)C record shows a plateau with nearly constant value at similar to 300 parts per thousand during 28-17 kyr B.P, followed by a sharp decrease in Delta(14)C between 17 kyr B.P. and the present, to a Delta(14)C value of similar to 0 parts per thousand. Estimated global paleomagnetic fields derived from paleointensity measurements in deep sea sediments (SINT-800, NAPIS-75 and Sumatra Basin) can only explain a maximum of 50% of this residual Delta(14)C record during 30-0 kyr B.P. We propose that the remainder must have resulted from changes in oceanic circulation leading to isolation of >= 20% of oceanic radiocarbon inventory from large scale mixing with the atmosphere during 28-17 kyr B.P. Subsequent inclusion of this carbon may be responsible in part for the decrease between 17 kyr B.P. to the present, to a Delta(14)C value of similar to 0 parts per thousand. We also note that the deconvoluted Delta(14)C record during the past 15,000 y B.P. seems to be primarily influenced by the changes in the atmospheric CO(2) concentrations. These possibilities have been discussed in previous works, but our results here point to a seemingly cyclical change in carbon exchange that was initiated prior to the Last Glacial Maximum. (c) 2007 Elsevier B.V. All rights reserved.

Mortyn, PG, Charles CD, Ninnemann US, Ludwig K, Hodell DA.  2003.  Deep sea sedimentary analogs for the Vostok ice core. Geochemistry Geophysics Geosystems. 4   10.1029/2002gc000475   AbstractWebsite

Many applications of the Vostok ice core depend critically on the ability to make stratigraphic ties to marine records in the adjacent Southern Ocean. Here we present oxygen isotopic records from high accumulation rate sites in the South Atlantic sector of the Southern Ocean, collected for the purpose of complementing the recently extended deltaD record from the Vostok ice core. The combination of several planktonic foraminiferal delta(18)O records from northern subantarctic piston cores demonstrates that all of the millennial-scale oscillations expressed in the Vostok ice core over the last 60 ky are also present in marine records. The observations also support the assumption that the millennial-scale oscillations common to both marine and ice archives are synchronous, thus providing a rationale for extending the marine-ice core comparison through the last 400,000 years, making use of a marine drilled core (ODP Site 1089). By aligning the phase of these common abrupt events, we anchor the Vostok chronology to an orbitally tuned marine sediment chronology-a refinement that allows examination of a variety of paleoclimatological issues such as the relationship between deep ocean variability and Antarctic polar climate. For example, this exercise suggests that, over at least the 4 major deglaciation events, the primary (orbital scale) changes in the chemistry and, most likely, the temperature of the deep Southern ocean were synchronous with changes in atmospheric pCO(2) and polar air temperatures. We also find that the deuterium excess in the ice core resembles marine (foraminiferal) delta(13)C records and that the deuterium excess is synchronous with an "anomalous'' foraminiferal delta(18)O signal ( the residual between normalized versions of Vostok deltaD and foraminiferal delta(18)O). These observations demand a tight link between the Vostok isotopic record and the air-sea interaction of the subantarctic zone.