HOT GOLDEN ANNIVERSARY SCIENCE SYMPOSIUM, November 1993

Inorganic Carbon Assimilation at Station ALOHA: Possible Evidence of a Change in Carbon Fluxes

R. M. Leteller

Light and dark inorganic carbon uptake estimated at Staion ALOHA (22 45'N, 158W) using the H₁₄CO₃^- method indicates a significant change of carbon fluxes in the euphoric zone (0-200 m) during the first 4 years of the HOT program (1989-1992). While autotrophic carbon assimilation (light uptake) increases significantly in the first 45 m of the water column during 1991 and 1992, microheterotrophic assimilation (dark uptake) decreases on average 40%.

These changes appear to be correlated with a decrease of nutrient input from the base of the euphotic zone and to an increase in the N:P ratio of particulate matter. Although it is generally accepted that under nutrient limiting conditions heteratrophic bacteria have an advantage over phytoplankton, my data base suggests that during 1991-1992 microheterotrophic activity is reduced by 50% with respect to photosynthesis.