Award: OPP-1951090

Sinking particles transport organic carbon fixed by phytoplankton (algae) into the deep ocean, thus leading to a net transport of carbon dioxide into the ocean interior where it can be stored for decades to millennia. Changes in this biological carbon pump as a result of ocean warming are thus a potentially important feedback in the global carbon cycle. Quantifying these changes is challenging, however, because carbon export is highly variable in space and time, driven by multiple different ecological and biogeochemical processes that create and transform sinking particles, and requires extensive dedicated ship time for typical sediment trap collection of sinking particles. In this project we utilized a chemical proxy approach (238U-234Th disequilibrium) to measure carbon export on annual cruises of the Palmer LTER program along the Western Antarctic Peninsula. This region is an excellent laboratory for studying ocean responses to climate warming, because the region is warming rapidly and the Palmer LTER cruises provide a cost effective sampling platform. We measured carbon export at typically ~20 stations per cruise, which when combined with previous results, allow us to create a time-series of carbon export across the region from 2009 2020. Our results showed that the region is surprisingly inefficient at exporting phytoplankton production as sinking particles. On average the ratio of sinking carbon export to net photosynthesis was only 5%, with no major differences on average between the northern and southern regions of the domain or between the coastal or offshore stations. Across the time-series we observed substantial variability in carbon export flux. For instance, average sinking carbon flux in 2010 was more than double that in 2019. While we did observe a decrease in export flux over the course of the time series, it was not statistically significant and we caution that it was largely driven by the anomalously high export during 2010 and anomalously low export in 2019. We also note that the highest export year (2012) was also a year of early sea ice retreat. Without the two anomalous years of 2012 and 2019, no trend would be evident in the data. We also observed substantial differences in spatial patterns of export between years, with some years (e.g., 2013) having much higher carbon export near the coast and other years (e.g., 2012) exhibiting highest export offshore. Our results set the stage for greater understanding of the oceans ability to absorb anthropogenic carbon dioxide. The finding that carbon export was similar in the northern and southern regions of the domain, despite an expected shift in phytoplankton populations suggests that the regional biological carbon pump is relatively resilient to sea-ice driven community shifts. This supposition is further supported by a lack of a statistical correlation between carbon export and the proportion of diatoms in the phytoplankton community. More research will be needed to determine whether these patterns are robust and indicate that the areally integrated biological carbon pump across the Western Antarctic Peninsula will increase as sea ice melt continues and more ocean habitat opens. This project also supported the research of three Ph.D. students, two of whom gained first-hand experience working in Antarctic ecosystems. Results from this project were incorporated into a week-long, immersive biological oceanography course developed for high school students in Illinois. Last Modified: 09/28/2024 Submitted by: MichaelRStukel