Marine photosynthetic performance forcing and periodicity for the Bermuda Atlantic Time Series, 1989-1995
We use the first seven years of the Bermuda Atlantic Time Series (BATS) core data set (1989-1995) to examine periodicity of and correlations between potential forcing and photosynthetic performance (P(b)opt). This analysis, which focuses on seasonal to annual time scales, points to a strong annual periodicity for many of the parameters investigated, with weaker annual P(b)opt variability. As has been previously demonstrated for primary production at the BATS location, shorter time scale variability induced by mesoscale events (e.g. fronts, eddies) is likely driving the majority of variability in P(b)opt. Of the parameters examined, chlorophyll, temperature and mixing depth demonstrate the strongest correlations with P(b)opt. Decomposition of the temperature signal into principal components further suggests that physical mixing is correlated with P(b)opt, whereas the true thermal level is less important. Macronutrients and grazing indices are uncorrelated with P(b)opt. Because only chlorophyll and mixing depth (of the parameters investigated) are strongly correlated with P(b)opt, we suggest that light history was the dominant forcing variable at the time scales examined for P(b)opt at the BATS location for 1989-1995. However, when vertical mixing is minimal, other factors, which are equally or more important in forcing P(b)opt and ultimately integrated primary production, are likely acting at scales that may not be readily discernible with the BATS sampling scheme. These results are discussed in the context of a mixing-photoadaptation rate constant model that functionally describes P(b)opt-mixing depth relationships and shows a great deal of consistency with observations. (C) 2000 Elsevier Science Ltd.
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