Estimation of new production in the tropical Pacific

A synthesis of field data from nine cruises and 121 stations in the tropica l Pacific (15 degreesN-16 degreesS by 135 degreesW-167 degreesE) was used t o develop a statistical model relating areal new production rates (based on (NO3)-N-15 uptake incubations) to other measured biological and chemical w ater properties. The large dynamic range off ratios (new to primary product ion) measured in the region (0.01-0.46, with a mean of 0.16 +/- 0.08) could not be described by any simple function of any of the more than three doze n measured variables tested. Thus the commonly used approach of extrapolati ng new production using mean f ratios is likely to lead to large uncertaint ies when used in the tropical Pacific. An alternative approach is examined in which new production is estimated directly by multiple linear regression (MLR) of measured properties. Nearly 80% of variability in new production could be explained with a MLR of four variables together (rates of primary production (or chlorophyll inventories), inventories of ammonium and nitrat e, and temperature) better than any single variable alone or any other comb ination of variables. Each of these variables exhibited effective linearity with respect to new production for this data set, and the robustness of th is MLR method to predict new production for other data sets was confirmed b y cross validation. These results thus provide a robust, simple tool to ext end new production estimates to locations and times where it is not measure d directly, using ship-based measurements and potentially remotely sensed d ata from moorings and satellites.