Water exchanges between de Northern Argentinean Shelf and the open ocean on interannual timescales: remote influences

Abstract

The present study addresses the importance of the water exchanges between the Northern Argentinean Shelf and the open ocean at interannual timescales. Based on the ocean reanalysis ORAP5.0 data set the main objective of this work is to identify which mechanisms drivers these exchanges and also estimate the interchanges of waters across the shelf-break. In order to estimate the interchanges in the region we compute the velocity field normal to shelf-break and perform an empirical orthogonal function analysis to unveil potential modes of variability. A leading mode that explains the largest percentage of variance is found. This mode presents a dipole structure associated to increments and decrements in the shelf water exportation in the Argentinian and southern Brazilian shelves. Wavelet analysis of the principal component associated to the mode suggest that power concentrates in 2, 4 and 10-years periods. These timescales coincide with those of the latitude of separation of the Brazil Current timeseries, which is suggested to modulate the mode. Statistical analysis techniques are employed to strengthen confidence in the proposed hypothesis linking the mode to the potential driver. Satellite chlorophyll-a maps are explored to evaluate potential implications of the mode on biology. This independent data set is employed to further validate the results derived from the ocean reanalysis at 2-years timescales. At these timescales the chlorophyll-a concentration field exhibits positive and negative interannual anomalies close to the shelf-break and in the neighboring open ocean that are consistent with the circulation patterns characteristics of biennial modulations.