The biological pump in the Costa Rica Dome: an open-ocean upwelling system with high new production and low export.
The Costa Rica Dome is a picophytoplankton-dominated, open-ocean upwelling system in the Eastern Tropical Pacific that overlies the ocean's largest oxygen minimum zone. To investigate the efficiency of the biological pump in this unique area, we used shallow (90-150 m) drifting sediment traps and234Th:238U deficiency measurements to determine export fluxes of carbon, nitrogen and phosphorus in sinking particles. Simultaneous measurements of nitrate uptake and shallow water nitrification allowed us to assess the equilibrium balance of new and export production over a monthly timescale. Whilef-ratios (new:total production) were reasonably high (0.36 ± 0.12, mean ± standard deviation), export efficiencies were considerably lower. Sediment traps suggestede-ratios (export/14C-primary production) at 90-100 m ranging from 0.053 to 0.067. ThE-ratios (234Th disequilibrium-derived export) ranged from 0.038 to 0.088. C:N and N:P stoichiometries of sinking material were both greater than canonical (Redfield) ratios or measured C:N of suspended particulates, and they increased with depth, suggesting that both nitrogen and phosphorus were preferentially remineralized from sinking particles. Our results are consistent with an ecosystem in which mesozooplankton play a major role in energy transfer to higher trophic levels but are relatively inefficient in mediating vertical carbon flux to depth, leading to an imbalance between new production and sinking flux.
Department of Earth, Ocean, and Atmospheric Science , Florida State University , Tallahassee, FL 32306 , USA.
Michael R
MR
Stukel
Marine Science Program and Department of Earth and Ocean Sciences , University of South Carolina , Columbia, SC 29208 , USA.
Claudia R
CR
Benitez-Nelson
Scripps Institution of Oceanography, University of California at San Diego, La Jolla, CA 92037, USA; National Institute of Water and Atmospheric Research (NIWA), 301 Evans Bay Parade, Hataitai 6021, Wellington, New Zealand.
Moira
M
Décima
Scripps Institution of Oceanography , University of California at San Diego , La Jolla, CA 92037 , USA.
Andrew G
AG
Taylor
Woods Hole Oceanographic Institution , Woods Hole, MA 02543 , USA.
Carolyn
C
Buchwald
Scripps Institution of Oceanography , University of California at San Diego , La Jolla, CA 92037 , USA.
Michael R
MR
Landry
Eastern Tropical Pacific; biogeochemistry; carbon flux; nutrients; plankton