HOT-75 COMMEMORATIVE SCIENCE SYMPOSIUM

Secular Changes in Inorganic Carbon Parameters at HOT and BATS

Christopher Winn

School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, HI 96822

Time-series carbon measurements at both of the time-series stations display secular changes. At HOT, after empirical corrections for the influence of salinity and temperature, dissolved inorganic carbon (DIC) in the upper reaches of the water column displays an interannual increase of approximately 1 µmol kg^-1 yr^-1. This increase has been interpreted as the response of the ocean to changes in atmospheric pCO₂. The observed 1 µmol kg^-1 yr^-1 interannual trend is consistent with simple models that predict this rate of oceanic increase in response to rising atmospheric CO₂ inventories. Interestingly, there is a residual pattern in the empirically corrected DIC time-series that can be interpreted as evidence for a significant advective signal at Station ALOHA.

The BATS DIC time-series data show remarkable similarity to the HOT time-series data. When the same empirical temperature and salinity corrections used for the HOT DIC time-series were applied to the surface ocean DIC time-series at BATS, a secular increase at BATS was observed that was almost identical to that observed at HOT. In addition, the BATS time-series displays a residual pattern that is remarkably similar to that observed at HOT. Although this residual pattern cannot unequivocally be interpreted to be a consequence of advective influences, it suggests that similar processes control the upper ocean carbon balance at HOT and BATS.

We also compare carbon inventories at HOT and BATS integrated over the upper 250 m, as well as the alkalinity time-series at both locations. These comparisons also show considerable similarities at both locations.