Drivers and implications of the recent increase in surface silicate-to-nitrate availability in the southern Drake Passage

Natalie M Freeman, Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, United States, David R Munro, National Oceanic and Atmospheric Administration, Global Monitoring Laboratory, Boulder, United States, Janet Sprintall, Univ California San Diego, La Jolla, United States; Scripps Institution of Oceanography, La Jolla, United States, Matthew R Mazloff, Scripps Institution of Oceanography, UC San Diego, La Jolla, CA, United States and Sarah G Purkey, Scripps Institution of Oceanography, University of California San Diego, San Diego, United States
The Drake Passage Time-series (DPT) is the longest year-round biogeochemical data set in the historically under-sampled Southern Ocean. Discrete surface water samples have been collected across the many fronts and jets of the Antarctic Circumpolar Current flowing through the Drake Passage since 2004, providing sufficient spatiotemporal coverage to resolve seasonal and annual cycling of key biogeochemical tracers such as nitrate and silicate in this bell-weather region. Recent shifts in atmospheric forcing coupled with dramatic changes in sea and land ice along the Antarctic peninsula have imprinted on the region’s physical and biogeochemical processes. Here, we utilize a combination of seasonally-distributed in situ observations from the year-round DPT, Argo, and Scripps High Resolution XBT programs, annual summer sampling from the Palmer Long-Term Ecological Research (LTER), and a suite of satellite and reanalysis products to (1) better understand physical and biogeochemical co-variability on seasonal to interannual timescales over the last 15 years and (2) diagnose the physical and biological drivers of the recent observed increase in silicate-to-nitrate availability in the southern Drake Passage. Our study highlights the combined use of long-term, coordinated in situ sampling and the importance of maintaining these efforts into the future. A robust and sustained ship-based observational network in the Drake Passage is key to characterizing seasonal to decadal variability, constraining and improving models, and for understanding how anthropogenic change is influencing the physical and biogeochemical state of the Southern Ocean.