Proceedings of the 2nd International Symposium CO₂ in the Oceans, Tsukuba, January 1999, CGER-I037-'99, CGER/NIES

The biological carbon pump in the subtropical Pacific Ocean: Nutrient limitations and CO₂ fluxes

Steven Emerson¹ and David Karl²

¹School of Oceanography, University of Washington, Seattle, WA 98195

²School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, Hawaii 96822

Recent estimates of the rate of carbon export at the subtropical Pacific Ocean time-series site near Hawaii (the Hawaii Ocean Time series, HOT) indicate that the biological pump in this area is within a factor of two of traditional high-productivity regions. The carbon flux from the euphotic zone in this location determined by measuring organic carbon fluxes, DIC/Dl¹³C mass balance, and oxygen mass balance are within 50 % of each other, which is roughly the error of each of the measurements. If this carbon export rate is typical of the world's subtropical oceans, then these regions may account for up to 50 % of the global marine biological pump [Emerson et al, 1997].

A long-standing problem in the subtropical oceans is the method by which nutrients enter the euphotic zone in sufficient quantities to support this relatively high productivity [Hayward, 1987]. Karl et al. [1997] and Micheals et al. [1996] working at the Pacific and Atlantic JGOFS time-series sites demonstrated that up to 50 % of the nitrogen required for photosynthesis in the subtropical oceans is supplied from the atmosphere by nitrogen fixation. High N:P ratios (20-30) in the particulate and dissolved organic matter at HOT suggests that productivity at this location presently occurs at a phosphorus deficit with respect to the Redfield ratio. Karl et al. [1997] suggests that the rate of photosynthesis at HOT is presently limited by the availability of phosphorus, but the source of phosphorus has not been identified.