SEASONAL-VARIATION OF CO2 AND NUTRIENTS IN THE HIGH-LATITUDE SURFACE OCEANS - A COMPARATIVE-STUDY

Seasonal data for pCO2 and the concentrations of CO2 and nutrients in high-latitude surface oceans obtained by the Lamont-Doherty CO2 group and Marine Research Institute, Reykjavik, are presented and analyzed. The seasonal progression and relationships between these properties ar e described, and their inter-ocean variation is compared. Spring phyto plankton blooms in the surface water of the North Atlantic Ocean and I celand Sea caused a precipitous reduction of surface water pCO2 and th e concentrations of CO2 and nutrients within two weeks, and proceeded until the nutrient salts were exhausted. This type of seasonal behavio r is limited to the high-latitude (north of approximately 40-degrees-N ) North Atlantic Ocean and adjoining seas. In contrast, seasonal chang es in CO2 and nutrients were more gradual in the North Pacific and the nutrients were only partially consumed in the surface waters of the s ubarctic North Pacific Ocean and Southern Ocean. The magnitude of seas onal changes in nutrient concentrations in the North Pacific and South ern Oceans was similar to that observed in the North Atlantic and adjo ining seas. In the subpolar and polar waters of the North and South At lantic and North Pacific Oceans, PCO2 and the concentrations of CO2 an d nutrients were much higher during winter than summer. During winter, the high latitude areas of the North Atlantic, North Pacific, and Wed dell Sea were sources for atmospheric CO2; during summer, they became CO2 sinks. This is attributed to the upwelling of deep waters rich in CO2 and nutrients during winter, and the intense photosynthesis occurr ing in strongly stratified upper layers during summer. On the other ha nd, subtropical waters were a CO2 source in summer and a sink in winte r. Since these waters were depleted of nutrients and could only sustai n low levels of primary production, the seasonal variation of pCO2 in subtropical waters and the CO2 sink/source condition were governed pri marily by temperature. An intense CO2 sink zone was found along the co nfluence of the subtropical and subpolar waters (or the subtropical co nvergence). Its formation is attributed to the combined effects of coo ling in subtropical waters and photosynthetic drawdown of CO2 in subpo lar waters.