Upwelling and Chl‐a spatiotemporal variability along the Galician coast: dependence on circulation weather types

Abstract

ABSTRACTThe eastern boundaries of the world's oceans are among the most productive marine regions owing to the wind induced coastal upwelling. In this context, changes in coastal upwelling influence chlorophyll‐a (Chl‐a) concentration along the Northwest (NW) Iberian Peninsula (IP) coast. This work aimed to evaluate and quantify the influence of meteorological conditions defined by circulation weather types (CWTs) on upwelling and Chl‐a variability along the Galician coast. A seasonal (April–September and October–March) characterization of satellite wind‐derived upwelling index (UI) and Chl‐a concentration was performed dividing the Galician coast into three domains: western (North–south orientation), intermediate (Northeast‐Southwest orientation) and northern (West–east orientation) segments. Results revealed that UI and Chl‐a concentrations were different among the three coastal segments and seasons. The most favourable upwelling conditions and high Chl‐a levels occurred during April–September at western coast. During October–March, high‐primary production also occurred and therefore a correlation analysis was performed during winter between Chl‐a, UI and discharges of the main rivers. Chl‐a and discharges were strongly correlated (0.52 for Minho and 0.31 for Nalon), suggesting that Chl‐a during this period was related to signal contamination due to river discharge. The probability that Chl‐a or UI exceeded a certain value, given the occurrence of a specified CWT was computed. Results showed that along the western coastal segment the strongest relations between CWTs, upwelling and Chl‐a concentration were obtained during April–September when N and NE occurred, with probabilities higher than 70% for UI and 30% for Chl‐a. During winter only the NW type had statistically significant probabilities for UI (50%) and Chl‐a (30%). For the intermediate coastal segment during October–March (April–September), when E type occurred, high probabilities of upwelling and Chl‐a were observed [100% (66), 50% (25), respectively]. Finally, at the northern coastal segment, Chl‐a probability was highest (40–50%) under the S weather type for both seasons.