ASLO/TOS Ocean Research Conference, Honolulu, HI, February 2004, p. 29.

Regionalization of the Hawaii Ocean Time-series (HOT) observations

T. Clemente¹, K. Björkman¹, E. Dafner¹, L. Fujieki¹, N. Jachowski¹, D. Sadler¹, G. Corno², R. Letelier², M. Church³, J. Zehr³, D. Karl¹

¹University of Hawaii, Honolulu, USA

²Oregon State Un iversity, Corvallis, USA

³University of California, Santa Cruz

The HOT program has made monthly measurements for 15 years at Station ALOHA (22 45N, 158 W). Data from this Eulerian ocean observatory have been supplemented by several transects of opportunity aimed at detecting spatial variations of key biogeochemical properties, including nutrients (N, P, Si) chlorophyll, DIC/alkalinity/pH, dissolved and particulate organic matter pico- and nanoplankton biomass and activity, nitrogenase gene espression, and bio-optics characteristics to name a few. The most recent HOT transects, from Hawaii to Alaska and return (April and October 2003, respectively), show a comparative analysis of relevant biogeochemical properties across the gyre and its northern boundary. For example P begins to accumulate (>0.2 umol P/l) in the surface waters at about 34N; this boundary also marks the switch from surface water phototroph dominance by Prochorococcus in the south, to Synechococcus and eukaryotic phytoplanaton in the north. While heterotrophic bacteria are more abundant in the north (>1 x 10⁶/ml vs. 5 x 10⁵/ml), bacterial production (leucine incorporation) is greater in the south. These and other patterns in habitat and microbial community structure provide invaluable insights into ecosystem processes and function.