Concentrations and uptake of neutral monosaccharides along 140 degrees W in the equatorial Pacific: Contribution of glucose to heterotrophic bacterial activity and the DOM flux

We examined concentrations and uptake of dissolved neutral monosaccharides (DNMS) in order to determine the contribution of DNMS to heterotrophic bacterial production and to the flux of dissolved organic matter (DOM) in the equatorial Pacific. DNMS concentrations were greater during El Nino-affected months of February-April 1992 than during August-October 1992; in contrast, glucose turnover was the opposite-turnover was faster in August-October than in February-April. The variation in sugar concentrations and turnover probably resulted from El Nino-induced changes in primary production; as El Nino waned primary production increased, which appeared to stimulate bacterial activity, especially glucose turnover, that in turn forced down DNMS concentrations. In all months, however, DNMS concentrations were low, especially compared with total dissolved organic carbon concentrations (<1%) Glucose was the dominant neutral monosaccharide and alone supported 15-47% of bacterial production. Other monosaccharides apparently did not support much bacterial growth; concentrations of other sugars were low, as probably was turnover. Respiration of glucose (30-50% of uptake) and mannose (60-90%) was relatively high, suggesting that DNMS supported a large fraction of bacterial respiration as well as biomass production. These results point to the importance of DNMS and glucose in particular in supporting bacterial growth and in contributing to the flux of labile DOM.