Project: Constraining Upper-Ocean Carbon Export with Biogeochemical Profiling Floats

OCE-1756932 Start Date: 2018-03-01
OCE-2032754 Start Date: 2020-05-28

NSF abstract:
A goal in chemical oceanography is to advance our understanding of the global carbon cycle, specifically to quantify the transfer of carbon from the surface ocean to depth through the sinking of particles produced by marine organisms. Yet, modern global estimates of this process (commonly called carbon export) differ by over 100%. These estimates are often derived from regional relationships between ocean measurements and satellite observations that are then applied globally. Persistent differences between the satellite and field-based estimates of carbon export have been found throughout the ocean, suggesting that improvements are needed. This project will determine whether profiling floats equipped with chemical sensors can be used to estimate the export of carbon in the ocean. Floats will be deployed at Ocean Station Papa, but the approach is scalable in nature and could be used to validate and improve the satellite algorithms used for global carbon export determinations. The project will support a female, early career scientist and a postdoc, as well as facilitate international collaboration with Canadian scientists. Additionally, the results may assist the National Aeronautics and Space Administration (NASA) EXPORTS campaign as well as other satellite carbon export development efforts.

Modern global estimates of the biological pump differ by over 100% (~5 to >12 Pg C yr-1) making it challenging to determine the role of marine biogeochemical (BGC) cycling in modern climate and climate variability. Global carbon export estimates are often derived from regional empirical relationships between field and satellite observations that are then applied globally. Persistent discrepancies between unique satellite algorithms and unique geochemical approaches suggest that accurately quantifying the biological pump remains a fundamental research goal. This project will assess the capability of using BGC profiling floats to estimate the export of distinct biogenic carbon pools (dissolved and particulate organic carbon, and particulate inorganic carbon). By using BGC floats to close multiple upper ocean tracer budgets this project will address two known issues common to other geochemical approaches: assumptions about (1) dissolved organic carbon cycling and (2) the integration depth used for annual carbon export assessments. The method will be tested at Ocean Station Papa, but is scalable in nature and could be used to develop a carbon export database suitable for the validation and training of satellite algorithms required for global carbon export determinations. Results from the floats will be compared to satellite carbon export algorithm estimates over the 5-year float lifetimes. Ten years of existing BGC data from profiling floats and a mooring in the region will also be used to provide further context about interannual variability.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.