Western Boundary Currents (WBCs) such as the Gulf Stream are regions of intense air-sea exchange and some of the strongest CO2 uptake in the world ocean. Yet basic questions persist about the mechanisms governing this uptake, partly because of the difficulty of making sustained measurement in these dynamic regions. This project will demonstrate that Saildrone, a fast-moving (3-5 knots), high-endurance (over 3 months) autonomous surface platform that measures lower atmosphere and surface ocean properties, can provide a much-needed, novel WBC observing strategy. With the integration of a state-of-the-art CO2 sensor designed for autonomous use by NOAA's Pacific Marine Environment Lab (PMEL), Saildrone could provide as a potentially transformative solution to observing air-sea fluxes across the remote and chronically-undersampled WBCs of the Southern Hemisphere. Thus, the proposed work is an important step toward closing the global ocean carbon budget. The project will also include some outreach to the general public. The principal investigator is working with the University of Rhode Island Office of Marine Programs to coordinate a public event to coincide with the recovery of the Saildrone in Newport. She also plans to visit a local elementary school to do a map-reading exercise with a bilingual second grade, in which they pick a Saildrone waypoint and track its progress toward it.
The main goal of this study is to use Saildrone to measure wintertime surface heat and CO2 fluxes across the Gulf Stream. Because of the short space and time scales characterizing their variability, WBCs present tremendous observing challenges that are not addressed with Argo float measurements. A state-of-the-art, self-calibrating CO2 sensor developed by PMEL has collected climate-quality data for hundreds of days on moored buoys, was recently adapted for use on the Saildrone, and preliminary missions show that it is capable of collecting climate quality pCO2 data (accurate to < 2 micro atm) aboard the platform. The principal investigator of this project recently won the Saildrone award to sail a 30-day mission across the Gulf Stream in winter 2019. This RAPID project funds the urgent task of preparing and integrating the Autonomous Surface Vehicle CO2 sensor system (ASVCO2) in time for the deployment. The Saildrone mission can reveal, for the first time, the importance of CO2 uptake along the Lagrangian pathway of the Gulf Stream relative to uptake during mode water formation. The Gulf Stream is also an ideal region to test the capability of the Saildrone platform as a WBC air-sea flux observing strategy, as there are nearby observing assets that will provide independent data for calibration and validation and a recent wintertime ship-based flux survey to provide valuable data for comparison.
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.
