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GLOBAL BIOGEOCHEMICAL CYCLES, VOL. 18, GB2007, doi:10.1029/2003GB002162, 2004

Planktonic foraminiferal δ¹³C records from Southern Ocean sediment traps: New estimates of the oceanic Suess effect

Alexandra L. King

Institute of Antarctic and Southern Ocean Studies, University of Tasmania, Hobart, Tasmania, Australia

William R. Howard

Antarctic Cooperative Research Centre, University of Tasmania, Hobart, Tasmania, Australia

Abstract

The carbon isotopic composition is measured for three species of planktonic foraminifera (Globigerina bulloides, Globorotalia inflata and Neogloboquadrina pachyderma (s.)) from Southern Ocean sediment traps. The sediment traps represent the annual flux of foraminifera in Subtropical to Polar Frontal environments from the western Pacific/Southern Australia sector. Comparison between the seasonal δ¹³C composition of the foraminifera and estimated δ¹³C of dissolved inorganic carbon (DIC) allows disequilibrium effects to be determined. Disequilibrium exhibits a latitudinal trend, with greatest offsets from equilibrium at lower latitudes. This effect causes a north to south increase in foraminiferal δ¹³C, while the δ¹³C_DIC displays a decrease across these latitudes. Disequilibrium in G. bulloides can be accounted for by changes in temperature. The relationship between disequilibrium and temperature which we derive in this field study is consistent with the laboratory relationship of Bemis et al. [2000] . Corrected δ¹³C for G. bulloides is closely correlated to seasonal changes in nutrients at each site, indicating the utility of G. bulloides δ¹³C as a nutrient tracer in Southern Ocean environments. Comparison between flux-weighted sediment trap values and nearby core tops indicates a modern depletion in δ¹³C, which we attribute to the oceanic Suess effect. The imprint of this effect on the foraminiferal isotopes provides further evidence for the equilibration between surface waters and the atmosphere in the Subantarctic Zone.

Received 29 September 2003; accepted 9 March 2004; published 20 May 2004.

Keywords: carbon isotopes; Southern Ocean; sediment traps; planktonic foraminifera disequilibrium; seasonal variability.

Index Terms: 4267 Oceanography: General: Paleoceanography; 4806 Oceanography: Biological and Chemical: Carbon cycling; 4808 Oceanography: Biological and Chemical: Chemical tracers; 4870 Oceanography: Biological and Chemical: Stable isotopes.

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Citation: King, A. L., and W. R. Howard (2004), Planktonic foraminiferal δ¹³C records from Southern Ocean sediment traps: New estimates of the oceanic Suess effect, Global Biogeochem. Cycles, 18, GB2007, doi:10.1029/2003GB002162.

Copyright 2004 by the American Geophysical Union.