James J. McCarthy1, John L. Nevins1
1Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts, 02138
Tóm tắt
Profound changes in concentrations of phytoplankton biomass and rates of primary production in warm‐core Gulf Stream rings can occur, apparently in response to nutrient enrichment, within a few months after a ring separates from the Gulf Stream.In Ring 81‐D at 3 months of age the dependence on NO3− was 2½–3 times as high as in the northern Sargasso Sea and in Ring 79‐E shortly after formation. The NO3− gradient at the base of the mixed layer in the new Ring 79‐E was 0.09 µmol kg−1 m−1, whereas that for the older Ring 81‐D was 0.30. The increase in proximity of NO3− to the mixed layer may be a general phenomenon associated with the aging process of warm‐core rings. The increase in this gradient enhances the potential for episodic bursts of production in warm‐core rings in response to turbulent mixing at the base of the mixed layer.Following an interaction with the Gulf Stream and a gale force storm, the mixed layer of Ring 81‐D cooled and its NO3− content increased. In response to increased availability of NO3−, both the rate of phytoplankton utilization of NO3− and the rate of primary production increased. Integrated rates for NO3− uptake in the mixed layer increased sevenfold (from 28 to 195 µmol m−2 h−1).
