High Resolution Underway Air-Sea Observations in Drake Passage for Climate Science

The Antarctic Circumpolar Current (ACC) is the largest current on the planet, flowing west to east around Antarctica, forming a barrier that separates warmer waters to the north from colder waters to the south. Ocean eddies (like atmospheric storms) break through the ACC barrier, transferring heat across the ACC towards Antarctica. When warmer ocean waters intrude onto the Antarctic continental shelves, they contribute to glacial melt and ice shelf retreat. Over the past several decades, the Southern Ocean has warmed and winds have increased due to climate change. Somewhat surprisingly the ACC, though pushed by faster winds, has not accelerated; a faster current would present a stronger barrier to heat transfer. Instead, ocean eddies have increased. These eddies are concentrated at 6-7 "hot spots". Drake Passage is one of these hot spots. As the narrowest land gap on the entire circumpolar path of the ACC, Drake Passsage is an ideal monitoring spot. However, it is also one of the windiest and roughest stretches of water on the globe. The only ship that crosses Drake Passage year-round is the USAP supply vessel for Palmer Station, making it a unique platform to monitor the currents and temperature with a minimum of personnel and resources. The Drake Passage time series of upper ocean currents and temperature is now in its 24th year. The upper ocean temperature measurements have found significant warming in Drake Passage. The upper ocean current measurements have confirmed that the ACC has remained steady on average but have also revealed a complicated filamented current structure. Combining temperature and current measurements has provided a better understanding of heat transfer across the ACC by eddies. The time series has also provided valuable ground-truth for satellite measurements and for numerical model predictions looking at the entire ACC. Our studies are focused on examining low-frequency variability - seasonal, interannual, and decadal - in order to provide baselines from which to evaluate and interpret physical and biogeochemical changes occurring in the Southern Ocean.