Annual cyclicity in export efficiency in the inner Southern California Bight

• Published in: Global biogeochemical cycles Vol. 31; no. 2; pp. 357 - 376
• Main Authors: Haskell, William Z., Prokopenko, Maria G., Hammond, Douglas E., Stanley, Rachel H. R., Sandwith, Zoe O.
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01-02-2017
• Subjects: Advection; Algae; Annual variations; Autotrophs; Autotrophy; Biogeochemistry; Carbon cycle; Carbon dioxide; Coastal upwelling; Coastal zone; Continental margins; Dissolved oxygen; Dye dispersion; Ecosystems; Eddy diffusion; Efficiency; Energy conversion; Energy conversion efficiency; Estimates; Euphotic zone; export efficiency; Exports; Gas exchange; gross oxygen production (GOP); Heterotrophy; Isotope composition; Isotopes; Marine; Marine biology; Marine ecosystems; Ocean circulation; Oceans; Oxygen; Oxygen production; Photosynthesis; Phytoplankton; Primary production; Ratios; Regions; Southern California Bight; Spring; Temperature (air-sea); triple oxygen isotopes; Turbulent diffusion; Upwelling; Vertical advection; Vortices; INE, USA, California, Southern California Bight; INE, USA, California, San Pedro
• ISSN: 0886-6236; 1944-9224
• DOI: 10.1002/2016GB005561

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.
Key Points
We incorporate upwelling into a NSS model of the isotopes of dissolved oxygen
We estimate NOP and GOP over 18 months with approximately biweekly resolution
Export efficiency cycles annually in a temperate coastal upwelling region