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

Abstract

AbstractPhotosynthetic conversion of to organic carbon and the transport of this carbon from the surface to the deep ocean is an important regulator of atmospheric . 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 /Ar and triple isotopes ( ), respectively. We simultaneously conducted incubations measuring the uptake of 14C, , and , 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 /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 . Later in the cruise (Phase 2), recently upwelled water with higher nutrient concentrations entered the study area, causing 14C and uptake to increase substantially. Continuous /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 /Ar and incubation‐based NCP estimates can give equivalent results in an N‐limited, coastal system, when the nonsteady state fluxes are negligible or can be quantified.