Variations in Synechococcus cell quotas of phosphorus, sulfur, manganese, iron, nickel, and zinc within mesoscale eddies in the Sargasso Sea

Abstract

The quotas of P, S, Mn, Fe, Ni, and Zn in individual Synechococcus cells collected from the surface and deep chlorophyll maximum (DCM) layer of three mesoscale eddies in the Sargasso Sea were measured using synchrotron X‐ray fluorescence microscopy. Cells in a mode‐water eddy had significantly higher P (57 ± 10 amol) and Mn (28 ± 7 zmol) cell quotas than cells collected from a cyclone (22 ±2 amol and 10 ± 1 zmol, respectively) or anticyclone (25 ± 3 amol and 18 ± 3 zmol, respectively). Conversely, Ni and Zn quotas were significantly higher in the cells from the anticyclone (92 ± 19 and 561 ± 150 zmol, respectively) than in cells from the cyclonic (25 ± 4 and 35 ± 7 zmol, respectively) or mode‐water (30 ± 9 and 21 ± 8 zmol, respectively) eddies. These changes may reflect biochemical responses (e.g., production of urease and alkaline phosphatase) to gradients in inorganic N and P supplies. Cellular quotas of Fe (111 ± 17 zmol in the cyclone) and S (52 ± 6 amol in the cyclone) did not vary significantly among eddies despite two‐ to threefold higher dissolved and particulate Fe concentrations in the anticylone. Cells collected from 10‐m depth contained approximately 80% more Ni and S than cells collected from the DCM, potentially reflecting cell responses to heightened oxidative stress. Depthrelated trends varied by eddy for the other elements. Cellular P and Zn varied significantly during repeated samplings of the cyclone, with quotas of both elements dropping as bulk chlorophyll biomass in the DCM increased. These data demonstrate the dynamic responses of phytoplankton elemental composition to physical and chemical environmental gradients.