Reconstructions of atmospheric Delta C-14 for the deglacial period reveal a 190 +/- 10%. drop between 17.5 and 14.5 kyr before present, during the 'mystery interval'. While it appears that the major contributor must be the mixing between an isolated low radiocarbon abyssal reservoir and the remainder of the ocean, a combination of C-14 measurements on coexisting benthic and planktic foraminifera shells and C-13/C-12 measurements on benthic foraminifera make it difficult to identify a sufficiently large volume for this reservoir. An alternative scenario, based on higher C-14 production rates between about 38 and 18 kyr ago, would escape the need for a large, isolated reservoir prior to the mystery interval but instead would call for a better ventilated ocean afterwards. The addition of (14) C-deficient sedimentary carbon appears not to be an important contributor. While the unlikely explanation that the half-life of C-14 is 15% greater than the accepted value (5730 yr) would eliminate the steady decrease in the C-14/C over the last 40 kyr, it would not explain the steep drop which occurred between 17.5 and 14.5 kyr. (c) 2007 Elsevier B.V. All rights reserved.
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