%0 Generic
%A Ruckelshausen, Mario
%C Heidelberg, Deutschland
%D 2013
%F heidok:15362
%R 10.11588/heidok.00015362
%T Cold-water corals: A paleoceanographic archive; Tracing past ocean circulation changes in the  mid-depth subtropical western South Atlantic off  Brazil for the last 40 ka BP  
%U https://archiv.ub.uni-heidelberg.de/volltextserver/15362/
%X Marine radiocarbon reconstructions from different intermediate depths reveal large depletions exceeding several thousand 14C years compared to the contemporaneous atmosphere during the last termination. It is suggested that very old waters from a radiocarbon-deficient abyssal reservoir previously well isolated from the atmosphere during the last glacial maximum was mixed back to the upper ocean and atmosphere during the deglaciation thereby raising atmospheric CO2. In pursuing the idea of a hypothesized isolated reservoir, measurements on sub-fossilized cold-water corals from intermediate depths off Brazil are performed. Coupled 230Th/U and 14C dates allow reconstruction of the ∆14C history of the ambient seawater for the past ∼40 ka BP. It becomes apparent that large depletions in the radiocarbon content of these depths are not a phenomenon restricted to the last termination. Injection of very old waters appear during the mid-Holocene and glacial period before the onset of the last termination with depletions comparable to other studies. Local hydrocarbon seepage activity as a possible source of 14C-dead carbon can be precluded as indicated by stable isotope measurements. Interestingly, 14C activity decrease apparently following in part the decay curve one would expect for a closed system pointing to an isolated and continuously ageing water mass, which bathed the corals. εNd isotopic composition indicate no significant changes of the water mass composition for the deeper coral sites for the last 37 ka BP supporting the assumption of a southern origin of the water also at times of large depletions in 14C. For the shallower corals, however, εNd exhibits large variations. It is suggested that local boundary exchange processes have altered the original Nd isotopic signature in these depths.