Spatio-temporal patterns in the north-western Mediterranean from MERIS derived chlorophyll a concentration

Ana Gordoa,Xenia Illas,Zoila Velásques,Antonio Cruzado

doi:10.3989/scimar.2008.72n4757

Ana Gordoa, Xenia Illas + Show 2 more

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https://doi.org/10.3989/scimar.2008.72n4757

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Journal: Scientia Marina	Publication Date: Oct 29, 2008
Citations: 37	License type: cc-by

Affiliation: Spanish National Research Council

Abstract

We address the major surface signatures of chlorophyll a in the Catalan Sea within the context of the dynamics of the north-western Mediterranean basin. Monthly composites from MERIS measurements and CHL products for Case 1 waters were analysed from June 2002 to June 2005. Composite images of variability were used to identify surface dynamics. The results showed that coastal and open sea waters were separated by a belt of low variability, a permanent oligotrophic belt that is noticeable with respect to the bloom conditions of the surrounding areas. The width of this Catalan Oligotrophic Belt (COB) located along the continental slope, varied between 17 and 30 km and became blurred in the southernmost area. The chlorophyll a temporal pattern over the shelf showed an almost steady increase from September to March. A similar behaviour but with lower concentrations was observed in oceanic waters. Both temporal patterns showed a disruption during January and/or February that coincided with the well known deep water formation event in the Gulf of Lions. In 2004, the convection was weaker and the offshore temporal trend was not disrupted; however, the opposite was observed in 2005. The spatial chlorophyll a distribution of oceanic waters presented a clear north-south decreasing trend, while the coastal distribution did not show any latitudinal patterns but rather peaks in the areas enriched by river runoff. The observed seasonality was similar to the one published from SeaWiFS data and slightly different from the seasonality shown by CZCS data. Nevertheless, we did not discard the possibility that some of the observed seasonal differences could be a true temporal shift in chlorophyll a production.

Highlights

The north-western Mediterranean basin (Fig. 1) is formed by the northern part of the Algero-Provençal basin, and includes the Gulf of Lions, the Ligurian Sea and the Catalan Sea
SUMMARY: We address the major surface signatures of chlorophyll a in the Catalan Sea within the context of the dynamics of the north-western Mediterranean basin
Medium Resolution Imaging Spectrometer (MERIS), an ocean colour sensor developed by the European Space Agency (ESA), is part of the ENVISAT platform launched in March 2002 (Rast et al, 1999)

Summary

INTRODUCTION

The north-western Mediterranean basin (Fig. 1) is formed by the northern part of the Algero-Provençal basin, and includes the Gulf of Lions, the Ligurian Sea and the Catalan Sea. Mesoscale changes in physical and biological coupling showed high chlorophyll a values over the shelf in association with continental waters These were limited by the salinity front, which exhibited high variability in offshore locations in a short period of time, even reversing the inshore-offshore salinity and chlorophyll gradients (Masó et al, 1998). The scope of the present study is to provide a basis for understanding the biological response to the complex hydrography of the north-western Mediterranean Sea. The specific objective is to identify and describe the major spatial and temporal patterns of sea surface chlorophyll a derived from the Medium Resolution Imaging Spectrometer (MERIS) in the region, and pay particular attention to the frontal system between shelf and open sea waters in the Catalan Sea (Fig. 1)

DATA AND METHODS

RESULTS AND DISCUSSION

Mean Coastal Mean Oceanic

CONCLUSION

January February March April