River plumes are important parts of the land–ocean matter fluxes and provide the key stage of transformation of river discharge and river-borne matter in the sea. However, both the plume-sea mixing budget and the ultimate fate of continental discharge in the open sea remain poorly understood. In this study, we analyze the GLORYS12 ocean reanalysis data to assess structure and variability of the 10 largest river plumes in the World Ocean. We quantify the interrelated characteristics of plume-sea interaction, namely, (1) response of a river plume to variability of river discharge, (2) residence time of river water in a river plume, (3) mixing intensity at plume-sea frontal zone. Based on these characteristics, we distinguish three different types of large river plumes in relation to their horizontal advection and vertical mixing with ambient seawater. The opposite ends of this classification are illustrated by the Amazon plume, which is shallow and occupies wide area due to reduced vertical mixing, and the Changjiang and St. Lawrence plumes, which have deep penetration, albeit small area due to strong vertical mixing near the river mouths. Our results aim to contribute to our understanding of how river discharge merges with and alters ambient shelf and ocean waters. It provides new insights into the spreading and mixing patterns of river plumes formed by diverse river systems.
Konik et al. (Fri,) studied this question.