Using Sea Level to Determine the Strength, Structure and Variability of the Cape Horn Current.

The Cape Horn Current (CHC) is one of the components of the Antarctic Circumpolar Current system that enables it to fulfill its crucial role as a conduit between ocean basins. Despite this, to‐date there have been very few measurements of CHC strength and none continuous in time or space. Here, we use a combination of ocean models, one free‐running and one data‐assimilating, and satellite altimetry (1993–2021) to estimate the time‐dependent strength of the CHC at 10 transects along its length. We find the time‐mean CHC transport increases from 0.4 ± 0.5 Sv near 49°S to 5.3 ± 2.2 Sv at Cape Horn, with peak‐to‐peak interannual fluctuations of 0.8–3.4 Sv. Although, theoretically, increased run‐off from a wasting Patagonian Ice‐field would strengthen its flow, the CHC appears quite stable over the last 29 years, with little evidence of a coherent, long‐term increase or decrease in the strength of the current. Plain Language Summary: By connecting the Pacific, Atlantic and Indian Oceans, the Antarctic Circumpolar Current system plays a crucial role in shaping Earth's climate. One component of this current system is the Cape Horn Current (CHC) which flows south about 150 km off the coast of Chile, before entering the South Atlantic through Drake Passage. The CHC is especially important as it carries relatively freshwater, nutrients, marine larvae, and pollutants from the South Pacific and into the South Atlantic, home to globally‐important fisheries and sensitive ecosystems. However, we still do not have a continuous record of the CHC strength and how it may be changing as Earth warms. In this study, we develop a method that uses numerical models of the ocean together with satellite observations of sea level to estimate the strength of the CHC over the last 29 years. We find the CHC increases in strength from 400 thousand m3 s−1 in its early stages to more than 5 million m3 s−1 as it rounds Cape Horn. From 1993 to 2021, the CHC appears quite stable, with little evidence of a long‐term increase or decrease in the strength of the current. Key Points: The Cape Horn Current (CHC) contributes to the overall Antarctic Circumpolar Current system's role as a conduit between ocean basinsObservationally‐based timeseries of CHC strength along its length are provided for the first timeCHC strength ranges from 0.4 Sv at 49°S to 5.3 Sv at Cape Horn and is stable over recent decades [ABSTRACT FROM AUTHOR]