Browning, T. J., Bouman, H. A., Moore, C. M., Schlosser, Christian , Tarran, G. A., Woodward, E. M. S. and Henderson, G. M. (2014) Nutrient regimes control phytoplankton ecophysiology in the South Atlantic. Biogeosciences (BG), 11 (2). pp. 463-479. DOI 10.5194/bg-11-463-2014.

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Abstract

Fast Repetition Rate fluorometry (FRRf) measurements
of phytoplankton photophysiology from an acrossbasin
South Atlantic cruise (as part of the GEOTRACES
programme) characterised two dominant ecophysiological
regimes which were interpreted on the basis of nutrient limitation.
South of the South Subtropical Convergence (SSTC)
in the northern sub-Antarctic sector of the Antarctic Circumpolar
Current (ACC) in the Eastern Atlantic Basin, waters
are characterised by elevated chlorophyll concentrations, a
dominance by larger phytoplankton cells, and low apparent
photochemical efficiency (Fv / Fm). Shipboard 24 h iron
(Fe) addition incubation experiments confirmed that Fe stress
was primarily responsible for the low Fv / Fm, with Fe addition
to these waters, either within the artificial bottle additions
or naturally occurring downstream enrichment from
Gough Island, significantly increasing Fv / Fm values. To the
north of the SSTC at the southern boundary of the South
Atlantic Gyre, phytoplankton are characterised by high values
of Fv / Fm which, coupled with the low macronutrient
concentrations and increased presence of picocyanobacteria,
are interpreted as conditions of Fe replete, balanced
macronutrient-limited growth. Spatial correlation was found
between Fv / Fm and Fe:nitrate ratios, supporting the suggestion
that the relative supply ratios of these two nutrients
can control patterns of limitation and consequently the ecophysiology
of phytoplankton in subtropical gyre and ACC
regimes.

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