DEEP-SEA RESEARCH II: SPECIAL VOLUME

Ecological nitrogen-to-phosphorus stoichiometry at station ALOHA

David M. Karl¹, Karin M. Björkman¹, John E. Dore², Lance A. Fujieki¹, Dale V. Hebel¹, Terrence Houlihan¹, Ricardo M. Letelier³, Luis M. Tupas¹

¹Department of Oceanography, School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, HI 96822, USA

²Aquasearch Inc., 73-4460 Queen Kaahumanu Hwy., Suite 110, Kailua-Kona, HI 96740, USA

³College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331-5503, USA

The elemental stoichiometry of dissolved and particulate matter in the sea, especially the nitrogen-to-phosphorus ratio, is an important parameter for studies of the nutrient control of plankton growth and for modeling biogeochemical processes, including carbon sequestration. Nitrogen (N) and phosphorus (P) pools have been measured on approximately monthly intervals for a 9-yr period at a deep-ocean station in the North Pacific subtropical gyre (Sta. ALOHA; 22 45'N, 158W). These data sets reveal complex interactions between N and P pools, and several unexpected secular trends. Models based on steady-state assumptions will not capture these temporal variations, especially the apparently rapid response of the microbial assemblages to stochastic nutrient intrusion events and the time-varying (seasonal, interannual and decadal scale) changes in dissolved matter N: P ratios. Based on an analysis of these data, we hypothesize that the gyre is presently in a period of net fixed N sequestration and P control of plankton rate processes.