engleski

A 55-Year Time Series Station for Primary Production in the Adriatic Sea: Data Correction, Extraction of Photosynthesis Parameters and Regime Shifts

In 1962, a series of in situ primary production measurements began in the Adriatic Sea, at a station near the island of Vis. To this day, over 55 years of monthly measurements through the photic zone have been accumulated, including close to 3000 production measurements at different depths. The measurements are conducted over a six-hour period around noon, and the average production rate extrapolated linearly over daylength to calculate daily production. Here, a non-linear primary production model is used to correct these estimates for potential overestimation of daily production due to linear extrapolation. The assimilation numbers are recovered from the measured production profiles and subsequently used to model production at depth. Using the recovered parameters the model explained 87\% of variability in measured normalized production at depth. The model is then used to calculate daily production at depth and it is observed to give on average 20% lower daily production at depth than the estimates based on linear extrapolation. Subsequently, watercolumn production is calculated and here the model predicted on average 26% lower watercolumn production. With the recovered parameters and the known magnitude of the overestimation, the time series of watercolumn production is then re-established with the non-linearly corrected data. During this 55 year period, distinct regimes are observed, which are classified with a regime shift detection method. It is then demonstrated how the recovered parameters can be used in a remote sensing application. A seasonal cycle of the recovered assimilation number is constructed along with the seasonal cycle of remotely sensed chlorophyll. The two are then used to model the seasonal cycle of watercolumn production. An upper and a lower bound on the seasonal cycle of watercolumn production based on remotely sensed chlorophyll data are then presented. Measured watercolumn production was found to be well within the range of remotely sensed estimates. With this work, the utility of in situ measurements as a means of providing information on the assimilation number is presented and its application as a reference for remote sensing models highlighted.

primary production ; photosynthesis parameters ; production model ; time-series ; regime shift ; Adriatic Sea ;

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