Impact of recently upwelled water on productivity investigated using in situ and incubation-based methods in Monterey Bay

Author Posting. © American Geophysical Union, 2017. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 122 (2017): 1901–1926, doi:10.1002/2016JC012306.Photosynthetic conversion of inline image to organic carbon and the transport of this carbon from the surface to the deep ocean is an important regulator of atmospheric inline image. To understand the controls on carbon fluxes in a productive region impacted by upwelling, we measured biological productivity via multiple methods during a cruise in Monterey Bay, California. We quantified net community production and gross primary production from measurements of inline image/Ar and inline image triple isotopes ( inline image), respectively. We simultaneously conducted incubations measuring the uptake of 14C, inline image, and inline image, and nitrification, and deployed sediment traps. At the start of the cruise (Phase 1) the carbon cycle was at steady state and the estimated net community production was 35(10) and 35(8) mmol C m−2 d−1 from inline image/Ar and 15N incubations, respectively, a remarkably good agreement. During Phase 1, net primary production was 96(27) mmol C m−2 d−1 from C uptake, and gross primary production was 209(17) mmol C m−2 d−1 from inline image. Later in the cruise (Phase 2), recently upwelled water with higher nutrient concentrations entered the study area, causing 14C and inline image uptake to increase substantially. Continuous inline image/Ar measurements revealed submesoscale variability in water mass structure and likely productivity in Phase 2 that was not evident from the incubations. These data demonstrate that inline image/Ar and inline image incubation-based NCP estimates can give equivalent results in an N-limited, coastal system, when the nonsteady state inline image fluxes are negligible or can be quantified.Funding for this work was provided by NSF awards OCE-1060840 to R.H.R. Stanley, OCE-1129644 to D.P. Nicholson, OCE-1357042 to F.P. Chavez, NASA award NNX14AI06G to M.R. Fewings, the David and Lucile Packard Foundation through their generous annual donation to the Monterey Bay Aquarium Research Institute, an Ocean Ventures Fund award from the WHOI Academic Programs Office to CC Manning, and graduate scholarships from NSERC and CMOS to CC Manning.2017-09-1