Gundersen, Kjell¹, and Karen M. Orcutt²

¹Bigelow Laboratory for Ocean Sciences, McKown Point Rd., PO Box 475, West Boothbay Harbor, ME 04575, USA, Tel: 207-633-9619; Fax: 207-633-9661, E-mail: KGundersen@Bigelow.org and ²Darling Marine Center, 193 Clark’s Cove Rd, Walpole, ME 04573, USA

Seasonal patterns of Trichodesmium primary production at the Bermuda Atlantic Time-series Study (BATS) site

Primary production by the diazotrophic cyanobacteria Trichodesmium was investigated seasonally over a two-year period at the BATS site using ¹⁴C-bicarbonate. Colonies of Trichodesmium puffs and tufts were collected at monthly intervals in 1995 and 1996 and placed in a deck-board incubator with in situ sea surface temperature and light conditions. In contrast to N₂ fixation and N-doubling times, primary production and the corresponding C-doubling times showed a strong seasonal pattern.

Due to spatial scaling, the significance of primary production by Trichodesmium may have eluded the standard method of primary production performed in the BATS program. By accounting for the temporal and spatial abundance distribution of Trichodesmium colonies and trichomes, and a PI-curve developed locally, we were able to estimate the amount of C incorporated by the diazotrophs. Seasonal depth integrated estimates of Trichodesmium primary production are significant in surface waters in summer and the incorporation of C by the cyanobacteria is in the same order of magnitude as the observed draw-down of DIC at the BATS site.