Glacial water mass geometry and the distribution of δ13C of ΣCO2 in the western Atlantic Ocean -: art. no. PA1017

Oxygen and carbon isotopic data were produced on the benthic foraminiferal taxa Cibicidoides and Planulina from 25 new piston cores, gravity cores, and multicores from the Brazil margin. The cores span water depths from about 400 to 3000 m and intersect the major water masses in this region. These new data fill a critical gap in the South Atlantic Ocean and provide the motivation for updating the classic glacial western Atlantic delta C-13 transect of Duplessy et al. ( 1988). The distribution of delta C-13 of Sigma CO2 requires the presence of three distinct water masses in the glacial Atlantic Ocean: a shallow (similar to 1000 m), southern source water mass with an end-member d(13)C value of about 0.3-0.5% VPDB, a middepth (similar to 1500 m), northern source water mass with an end-member value of about 1.5%(0) and a deep (> 2000 m), southern source water with an end-member value of less than -0.2%, and perhaps as low as the -0.9%(0) values observed in the South Atlantic sector of the Southern Ocean (Ninnemann and Charles, 2002). The origins of the water masses are supported by the meridional gradients in benthic foraminiferal delta O-18. A revised glacial section of deep water delta C-13 documents the positions and gradients among these end-member intermediate and deep water masses. The large property gradients in the presence of strong vertical mixing can only be maintained by a vigorous overturning circulation.