Impacts of Parameterizing Estuary Mixing on the Large-Scale Circulations in the Community Earth System Model

Abstract

Abstract Riverine outflow between the land surface/cryosphere and the ocean undergoes intricate physical and biogeochemical transformations in estuaries before it finally merges with oceanic waters. To enhance our understanding of these transformations, estuary box models (EBMs) are being incorporated into comprehensive Earth system models. These models aim to refine our knowledge of both physical and biogeochemical processes. In our study, we conducted simulations using the Community Earth System Model, version 2, both with and without the inclusion of an EBM that was jointly developed by the University of Connecticut and the National Center for Atmospheric Research and by default included in the climate model. The objective was to examine the influence of these modifications on global climate patterns. We performed these simulations under fixed atmospheric and runoff conditions, using a standalone version of the ocean/sea ice components of the model. Additionally, we conducted a fully coupled Earth system model simulation at a 2° atmosphere and 1° ocean resolution. The implementation of the EBM into the ocean component of the model resulted in regional variations and noticeable improvements in the salinity distribution on the Siberian shelves and at the Amazon outflow. Interestingly, our findings revealed that the tropical Atlantic Ocean plays a significant role in controlling the global salinity distribution. Due to the tropical Atlantic circulation, which redirects thermocline water southward while allowing surface waters to continue northward, the improved vertical mixing in the EBM leads to an accumulation of salt in the North Atlantic and a freshening of other ocean basins. This shift subsequently results in an intensification of the Atlantic meridional overturning circulation and a northward shift of tropical precipitation patterns. Significance Statement This research investigates the impact of riverine outflow interactions with ocean waters on global climate dynamics. Implementing an enhanced representation of river runoff within a global climate model reveals that the tropical Atlantic region is pivotal in regulating the salinity distribution across the world’s oceans. This dynamic leads to an increased salt concentration in the North Atlantic and extends its influence to other ocean basins. The resulting shifts in salinity have profound consequences, as they alter rainfall patterns in the tropics. The insights gained from this study contribute to the advancement of climate projections, offering society a valuable tool to anticipate and adapt to the impending effects of climate change more effectively.