SURFACE SEAWATER DISTRIBUTIONS OF INORGANIC CARBON AND NUTRIENTS AROUND THE GALAPAGOS-ISLANDS - RESULTS FROM THE PLUMEX EXPERIMENT USING AUTOMATED CHEMICAL MAPPING

During the second leg (PlumEx) of the 1993 IRONEX cruise, the partial pressure of CO2 and the concentrations of nitrate and silicate in the surface waters around the Galapagos Islands were continuously measured using automated underway systems. Based on salinity-versus constituen t mixing diagrams, physical mixing processes dominate the pCO(2) and n utrient distributions upstream of the Galapagos Islands. Downstream of the islands, slight removal of nitrate and CO2 can be discerned becau se of the high resolution of the underway measurements. The high spati al resolution of the underway measurements allowed evaluation of fine features such as sharp fluorescence peaks on the ''warm'' side of fron tal boundaries. In the waters immediately adjacent to Fernandina and I sabela islands (Bolivar channel), dramatic drawdown of pCO(2) and nutr ients was measured, coincident with the highest measured levels of iro n (3 nM) and chlorophyll ( > 13 mu g l(-1)) (Martin et al., 1994). The nearly constant alkalinity of the waters was combined with the measur ed pCO(2) to calculate total carbon dioxide in the waters. Based on mi xing diagrams, the ratio of Delta TCO2 to Delta NO3- was found to be h ighly variable, ranging from approximately 6.4 to > 10 in the waters n ear Isabela Island. The ratio of Delta TCO2 to Delta NO3- is approxima tely 8.5 in the waters west of the Galapagos where slight removal of n itrate and TCO2 occurs. In these waters, the physical process of mixin g and CO2 degassing due to warming of the water becomes significant re lative to the biological uptake and the ratio is driven higher. (C) 19 98 Elsevier Science Ltd. All rights reserved.