ASLO/TOS/AGU Ocean Sciences Meeting, Honolulu, HI, February 2006.

Inter-annual to decadal variability in soluble reactive phosphorus concentration in the North Pacific Subtropical Gyre

R. M. Letelier¹, A. White¹, D. M. Karl², M. J. Church², J. Christian³

¹College of Oceanic and Atmospheric Sciences, Oregon State University, 104 COAS Admin. Bldg., Corvalis, OR 97331-5503

²Department of Oceanography, University of Hawaii, 1000 Pope Road, Honolulu, HI 96822

³Canadian Centre for Modelling and Analysis, University of Victoria, PO Box 1700 STN CSC, Victoria, BC V8W 2Y2

Historical biogeochemical records from studies in the oligotrophic North Pacific subtropical gyre provide evidence of pelagic ecosystem responses to changes in climate patterns. For example, we observe an increase in primary productivity and photoautotrophic prokaryotes and a decrease in the upper water soluble reactive phosphorus (SRP) concentration that coincide with the start of the last warm phase of the Pacific Decadal Oscillation (PDO). More recently, monthly records from the Hawaii Ocean Time-series (HOT) program covering the past 15 years have confirmed a significant and puzzling inverse correlation between warm PDO indices and SRP concentrations, but not nitrate, in the euphotic zone. In addition, these records suggest that summer blooms by nitrogen fixers under well stratified conditions contribute significantly to the SRP depletion. In this presentation we will discuss possible physical and biological mechanisms responsible for the inter-annual to decadal variability observed in phosphorus concentration and their potential effects on pelagic elemental fluxes in the North Pacific subtropical gyre.