Short-term variability of photosynthetic parameters and particulate and dissolved primary production in the Alboran Sea (SW Mediterranean)

Abstract

15 pages, 11 figures, 4 tablesThe short-term variability of photosynthesis-irradiance ( P -E) relationships and inte- grated primary production at 3 stations (Stns A, B, C in a coastal-offshore gradient) located across the Western Alboran Sea Gyre (SW Mediterranean) were investigated during a High Frequency Flux Experiment (1 to 16 May 1998). Photosynthetic production of total, particulate and dissolved organic carbon (TOC, POC and DOC respectively) was considered separatedly in 34 experiments. Photosynthetic parameters were calculated for TOC and POC data. For POC measurements, maximum photo- synthetic rate (P Bm POC) and the initial slope of the P-E curve (α) varied between 0.59 and 6.25 mg C (mg chl a) –1 h –1 and 0.0023 and 0.0182 mg C (mg chla)–1 h–1 (μmol photons m–2 s –1) –1, respectively, and were significantly correlated, showing a similar decrease with depth. No photoinhibition was detected at any depth and the light saturation parameter ( E k ) was on average 251 μmol photons m –2 s –1, suggesting that phytoplankton assemblages were acclimated to high irradiance levels in the whole area. Percent extracellular release (PER) obtained for each experimental irradiance (PER E = DOC/ [POC+DOC]) showed an inverse relationship with irradiance when data from all the P-E experiments were pooled. A light-saturated chl a-normalized DOC production rate ( P Bm DOC) was calculated as P Bm TOC – P Bm POC, and PERm values calculated as P Bm DOC /P Bm TOC tended to increase with depth. Integrated particulate and total primary production varied considerably (23- and 35-fold, respectively), but tended to decrease along a coastal-offshore gradient. During the cruise, a subsurface phytoplankton bloom was advected into Stn A, increasing primary production rates up to 1 g C m–2 d–1. Average particulate primary production was 632 mg C m–2 d–1 at Stn A, 388 mg C m–2 d–1 at Stn B and 330 mg C m–2 d –1 at Stn C, with dissolved primary production ranging from 4 to 44% of total values. Integrated primary production was significantly correlated with surface chl a but not with integrated chla. This finding has implications for the estimation of regional primary production based on remote sensing of near-surface pigments. Altogether, the results confirmed that the high hydrodynamism of the Alboran Sea was associated with marked biological variability and episodic high primary production eventsPeer reviewe