Annual cyclicity in export efficiency in the inner Southern California Bight

Abstract

The balance of marine autotrophy and heterotrophy regulates the ocean's ability to serve as a CO2 sink, as organic material produced by autotrophs sinks into the ocean interior to drive the biological pump. Marine ecosystems over the continental margins, especially coastal upwelling regions, account for a disproportionate amount of carbon export; thus, even small fluctuations in export in these regions can have a large impact on the global carbon cycle. In this study, we estimated the rate of gross oxygen production (GOP), stoichiometrically related to gross primary production, by combining measurements of the triple isotope composition of dissolved oxygen with estimates of vertical advection, eddy diffusion, and air‐sea gas exchange in a one‐dimensional two‐box nonsteady state model of the euphotic zone. Net oxygen production (NOP) estimates based on O2/Ar were then combined with GOP to estimate the NOP/GOP ratio, or potential export efficiency, out of the euphotic zone at the San Pedro Ocean Time‐series during an 18 month period between January 2013 and June 2014. GOP estimates ranged from 161 ± 44 to 477 ± 155 mmol m−2 d−1 during this period, peaking in May each year, and NOP/GOP ratios ranged from 0.05 ± 0.10 to 0.65 ± 0.28. The highest export efficiency occurred in late February/early March, following the onset of spring upwelling, declining as the upwelling season continued. This study demonstrates that export efficiency changes through time in this temperate coastal upwelling region on a repeated annual cycle, and the magnitude of export efficiency suggests efficient photosynthetic energy conversion by phytoplankton in spring.

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

“…Haskell et al [2016b] found mixed layer NCP to be 10(15) mmol C m 22 d 21 in inshore California waters near Los Angeles during October 2013, lower than NCP during our study. GPP was 230(37) mmol C m 22 d 21 during the same time period [Haskell et al, 2017], which is similar to GPP during our study. Johnson [2010].…”

Accurate Estimation of Net Community Production From O2/Ar Measurements

“…However, upwelling of low oxygen water at the coast violates the assumption that only net biological production and air-sea gas exchange affect the surface layer O 2 /Ar mass balance. Strong upwelling in coastal and equatorial regions can create waters undersaturated in O 2 /Ar (Haskell et al, 2017;Ianson et al, 2009;Tortell, 2005;Tortell et al, 2012), leading past studies to discard O 2 /Ar data within upwelling zones (Hendricks et al, 2004;Kaiser et al, 2005;Stanley et al, 2010). Jonsson et al (2013) used biogeochemical ocean circulation models to assess the O 2 /Ar derived NCP bias due to vertical exchange of oxygen across the base of the Southern Ocean mixed layer.…”

Net Community Production in a Productive Coastal Ocean From an Autonomous Buoyancy‐Driven Glider

“…Piston velocity at the sea surface and vertical diffusive mixing are estimated using a wind speed-based approach (Figure 9, middle row) that calculates these rates daily, using a weighting procedure of the wind speed over the previous 15 days. The top row in Figure 9 presents NOP calculated from our box model of glider-measured oxygen concentration through time and piston velocity with black lines for both velocities reported by Haskell, Prokopenko, Hammond, et al (2016) and Haskell et al (2017), whereas the orange line uses Bakun Upwelling Index-based velocities. The ticks on the x axis mark the first of each month.…”

“…The ticks on the x axis mark the first of each month. Black square symbols (and gray lines) are NOP rates (and uncertainties) reported by Haskell, Prokopenko, Hammond, et al (2016) and Haskell et al (2017). The middle row shows piston velocity (PV; black) and eddy diffusivity (K z ) at the mixed layer depth (dashed green) and euphotic depth (solid green) used in the NOP estimates in the top row, all calculated daily using a 15-day weighting procedure (Reuer et al, 2007).…”

“…The middle row shows piston velocity (PV; black) and eddy diffusivity (K z ) at the mixed layer depth (dashed green) and euphotic depth (solid green) used in the NOP estimates in the top row, all calculated daily using a 15-day weighting procedure (Reuer et al, 2007). The bottom row presents 7 Be-based upwelling velocity (w; blue) reported by Haskell, Prokopenko, Hammond, et al (2016) and Haskell et al (2017) and Bakun Upwelling…”