Diel variability of glycolate in the eastern tropical Atlantic Ocean

The concentration of dissolved glycolate in sea water was measured by high performance liquid chromatography in the eastern tropical Atlantic Ocean during the Eumeli 4 oceanographic cruise in June 1992. Diurnal concentrations of glycolate reached 74 kg 1−1 1−1 in mesotrophic waters and 17 μg 1−1 1 in oligotrophic waters. At midday total dissolved glycolate exceeded 1 g of carbon per m2 of ocean, decreasing strongly during the night (less than 0.1 g of carbon per m2). At the three stations studied, glycolate carbon difference between night and day in the water column was of the same order as the daily primary production estimated by incorporation of 14C02. Disappearance of this compound at night suggested a rapid consumption by heterotrophic organisms. These data suggest that glycolate excretion by phytoplankton may be important, and possibly influenced by ambient nutrient concentrations. Further, with glycolate representing up to 50% of daily productivity, our estimates of the total biological reduction of C02 need to be re-examined.