The seasonal progression of rates of productivity and export from the North Pacific NASA EXPORTS field study as observed by autonomous assets

David P Nicholson, Woods Hole Oceanographic Institution, Department of Marine Chemistry and Geochemistry, Woods Hole, MA, United States, Eric A D'Asaro, Applied Physics Lab, Univ of Washington, Seattle, WA, United States, Andrea J Fassbender, Monterey Bay Aquarium Research Institute, Moss Landing, United States, Craig Lee, Univ Washington, Seattle, WA, United States, Melissa Omand, University of Rhode Island, Graduate School of Oceanography, Narragansett, RI, United States, Mary Jane Perry, University of Maine, Orono, ME, United States and Andrew F Thompson, California Institute of Technology, Pasadena, United States
Abstract:
Ocean biology plays an important role in the Earth's carbon cycle. While most of the organic material produced by phytoplankton in the sunlit surface waters of the oceans is eaten and recycled in the surface waters, a small amount sinks to the deep ocean in what is called the "biological carbon pump." Here, we highlight recent results from the NASA EXPORTS study to quantify ocean productivity and carbon fluxes. During the 2018 process study near Station Papa in the Northeast Pacific autonomous assets were deployed to extend ship-based studies from a month-long occupation by the R/V Revelle and R/V Ride. A Lagrangian profiling float, Seaglider and two biogeochemical Argo floats were deployed as part of the NASA EXPORTS from July through December 2018. Observations from Ocean Observatories Initiative (OOI) and Pacific Marine Environmental Laboratory (PMEL) gliders and moorings supplemented EXPORTS observations. During the study period the Seaglider tracked the trajectory of the Lagrangian float, profiling the upper 1000 m and quantified the temporal evolution of biogeochemical properties. We present preliminary interpretation from the suite of biogeochemical sensors on these platforms. Net community production (NCP) was quantified from oxygen mass balance and gross primary production (GPP) from diel oxygen changes. After the ship-based cruises concluded, the autonomous platforms documented a fall bloom characterized by elevated rates of GPP at the same time as NCP was reduced. Optical backscatter and chlorophyll fluorescence sensors quantified seasonal changes in particulate organic carbon and sinking fluxes. Trends in oxygen also were used to quantify respiratory demand in the mesopelagic. This study illustrates the value of coordinated ship-based and autonomous platform investigations in quantitatively resolving carbon uptake and export in the ocean.