Quay¹, Paul D., Nicolas Gruber² and Holger Brix²

¹University of Washington, Seattle, WA, Tel: 206-685-8061 (-3351 FAX), E-mail: pdquay@u.washington.edu and ²University of California, Los Angeles, CA

¹³C/¹²C of Dissolved Inorganic Carbon: a means to close the carbon budgets at ALOHA and BATS

Measurements of the seasonal cycle in the concentration and ¹³C/¹²C of dissolved inorganic carbon (DIC) in the surface layer at ALOHA and BATS have been used to close the surface layer DIC budget at these time-series sites. The approach relies on constructing simultaneous budgets for DIC and d¹³C. At ALOHA and BATS, there is a summertime enrichment in the d¹³C of the DIC of 0.1 and 0.2 ‰, respectively, and a concurrent DIC decrease of 14 and 30 μmol kg^–1, respectively. These seasonal trends are the result primarily of net community production ocuring at rates of ~7±2 mmol C m^-2 d^-1 at both sites. Notably, these rates are similar despite the seasonal cycle in the DIC and d¹³C being twice as strong at BATS than at ALOHA. The different magnitude of summertime DIC and d¹³C change observed at BATS and ALOHA depends on differences in the magnitudes of air-sea CO₂ gas exchange, vertical mixing and mixed layer depth. At ALOHA, the major DIC input over the year results from vertical mixing at the base of the surface layer. At BATS, in contrast, the major DIC sources are entrainment, horizontal advection and the uptake of atmospheric CO₂.