Upper-ocean-to-atmosphere radiocarbon offsets imply fast deglacial carbon dioxide release by Kathryn A. Rose et al., Nature 466 (2010)

Nature, 466, 1093-1097 (26 August 2010); doi: 10.1038/nature09288

Upper-ocean-to-atmosphere radiocarbon offsets imply fast deglacial carbon dioxide release

Kathryn A. Rose^1,7,8, Elisabeth L. Sikes^2,8, Thomas P. Guilderson^3,4, Phil Shane⁵, Tessa M. Hill¹, Rainer Zahn⁶ & Howard J. Spero¹

1. Department of Geology, University of California, Davis, California 95616, USA
2. Institute of Marine and Coastal Sciences, Rutgers University, 71 Dudley Road, New Brunswick, New Jersey 08901, USA
3. Lawrence Livermore National Laboratory, Livermore, California 94550, USA
4. Institute of Marine Sciences, University of California, Santa Cruz, California 95064, USA
5. School of Environment, University of Auckland, Auckland 1142, New Zealand
6. Institució Catalana de Recerca i Estudis Avançats, ICREA, Universitat Autònoma de Barcelona, Institut de Ciència i Tecnologia Ambientals, Departmento de Geologia, 08193 Bellaterra, Spain
7. Present address: Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02540, USA.
8. These authors contributed equally to this work.

Abstract

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Abstract

Radiocarbon in the atmosphere is regulated largely by ocean circulation, which controls the sequestration of carbon dioxide (CO₂) in the deep sea through atmosphere–ocean carbon exchange. During the last glaciation, lower atmospheric CO₂levels were accompanied by increased atmospheric radiocarbon concentrations that have been attributed to greater storage of CO₂in a poorly ventilated abyssal ocean^1, 2. The end of the ice age was marked by a rapid increase in atmospheric CO₂concentrations² that coincided with reduced ¹⁴C/¹²C ratios (Δ¹⁴C) in the atmosphere³, suggesting the release of very ‘old’ (¹⁴C-depleted) CO₂ from the deep ocean to the atmosphere³. Here we present radiocarbon records of surface and intermediate-depth waters from two sediment cores in the southwest Pacific and Southern oceans. We find a steady 170 per mil decrease in Δ¹⁴C that precedes and roughly equals in magnitude the decrease in the atmospheric radiocarbon signal during the early stages of the glacial–interglacial climatic transition. The atmospheric decrease in the radiocarbon signal coincides with regionally intensified upwelling and marine biological productivity⁴, suggesting that CO₂released by means of deep water upwelling in the Southern Ocean lost most of its original depleted-¹⁴C imprint as a result of exchange and isotopic equilibration with the atmosphere. Our data imply that the deglacial ¹⁴C depletion previously identified in the eastern tropical North Pacific⁵ must have involved contributions from sources other than the previously suggested carbon release by way of a deep Southern Ocean pathway⁵, and may reflect the expanded influence of the ¹⁴C-depleted North Pacific carbon reservoir across this interval. Accordingly, shallow water masses advecting north across the South Pacific in the early deglaciation had little or no residual ¹⁴C-depleted signals owing to degassing of CO₂ and biological uptake in the Southern Ocean.

*Correspondence e-mail: sikes@marine.rutgers.edu

Link:  http://www.nature.com/nature/journal/v466/n7310/full/nature09288.html