Site selection for ocean alkalinity enhancement informed by passive tracer simulations

Abstract

Abstract Ocean alkalinity enhancement is a marine-based carbon dioxide removal strategy that involves adding alkaline material to the surface ocean to boost carbon uptake and storage. The physical circulation of ocean water exerts fundamental control on the dilution, spreading, and retention of alkaline materials, influencing carbon removal effectiveness, environmental impacts, and monitoring feasibility. Here we evaluate potential sites and timing for ocean alkalinity enhancement on the U.S. Northeast Shelf by conducting passive tracer simulations from 2009 to 2017. Monthly dye release experiments across ten locations were analyzed by quantifying dye evolution metrics such as surface spread, lateral movement, upper-ocean concentration, and gas transfer velocity. A site selection index was developed to assess site and time suitability for tracer dispersal for ocean alkalinity enhancement. Results showed strong seasonality, with optimal conditions in summer and less favorable conditions in winter. Among the tested locations, Wilkinson Basin emerged as the most favorable tracer release site due to its larger spreading area, higher tracer concentrations, and longer decay time. These findings inform a future field experiment in the region and offer a scalable framework for guiding future research on ocean alkalinity enhancement in other regions based on physical characteristics of tracer evolution.