Coupling of nitrate, carbon and heat in warm waters of the western equatorial Pacific: Consequences for estimating new production and air -sea exchange of carbon dioxide

Recent studies indicate that the western equatorial Pacific Warm Pool may play an important role in interannual and decadal climate variation, global new production, and global atmosphere CO2 concentration. In this study, I compared the rates of new production and air-sea exchange of CO 2 in the western equatorial Pacific Warm Pool during normal conditions (December 1995/January 1996 and January 1997), during a moderate El Nino event (November/December 1994), and during the strongest El Nino event (December 1997/January 1998) in recent history. As an aid for interpreting and understanding of these processes I used both direct measurements and a box model.;Direct measurements of the rate of nitrate uptake (new production) along the equator (from 145°E to 165°W) show that interannual variations in new production in the western and central equatorial Pacific correlate well with the change of the nutricline depth during the eastward expansion of the Warm Pool depending strongly upon the severity of the El Nino event. The analysis of nitrate, carbon, and heat balances in the western equatorial Pacific indicates that---in non-El Nino conditions---vertical turbulent diffusion is primarily responsible for both the loss of heat and the supply of nitrate and inorganic carbon to the euphotic zone.;Based on this conclusion on the importance of vertical processes, I developed a box model that allows estimation of the rates of new production and air-sea CO2 exchange in the Warm Pool from the net surface heat flux, elemental ratios, and the C:N ratio of the organic matter sinking from the euphotic zone. The model predictions agree qualitatively with the direct measurements. The model may provide a means for estimating the rates of new production and air-sea CO2 exchange over the large areas of equatorial Pacific using the remotely-sensed data. The results of this study may also be useful in further understanding of the role of the western equatorial Pacific in biogeochemical cycles and climate variations, and for assessment of this part of the ocean for future fisheries demands.