Seasonal and Interannual Variability in the Distribution and Removal of Terrigenous Dissolved Organic Carbon in the Amazon River Plume

The Amazon River is a large source of terrigenous dissolved organic carbon (tDOC) to the Atlantic Ocean. The fate of this tDOC in the ocean remains unclear despite its importance to the global carbon cycle. Here, we used two decades of satellite ocean color to describe variability in tDOC in the Amazon River plume. Our analyses showed that tDOC distribution has a distinct seasonal pattern, reaching northwest toward the Caribbean during high discharge periods, and moving eastward entrained in the North Brazil Current retroflection during low discharge periods. Elevated tDOC content extended beyond the shelfbreak in all months of the year, suggesting that cross-shelf carbon transport occurs year-round. Maximum variability was found at the plume core, where seasonality accounted for 40% of the total variance, while interannual variability accounted for 15% of the variance. Our results revealed a seasonal pattern in tDOC removal over the shelf with increased consumption in May when river discharge is high. Anomalies in tDOC removal over the shelf with respect to the seasonal cycle were significantly correlated with anomalies in tDOC concentration offshore of the shelfbreak with a lag of 30–40 days, so that anomalously high inshore tDOC removal was associated with anomalously low tDOC content offshore. This suggests that variability in the offshore transport of tDOC in the Amazon River plume is modulated by interannual changes in tDOC removal over the shelf.