Recent Projects

 

Export Production Measured Using 234Th and Sediment Traps in the Eastern Tropical South Pacific

(in collaboration with William M. Berelson, Maria G. Prokopenko, Doug E. Hammond, Laurence Y. Yeung, Douglas G. Capone)

Abstract: During February 2010 and April 2011, 234Th profiles were measured from the surface to 300m in the Eastern Tropical South Pacific, in a region bounded by 10°S - 20°S and 80°W - 100°W.  Horizontal transport of 234Th was determined using geostrophic current vectors and found to be negligible, thus only vertical transport should be significant.  Depth-integrated Thorium deficiencies (DITD) and measured ratios of particulate organic carbon (POC) to 234Th obtained from sediment trap samples were used in a steady state, one-dimensional model to determine POC export from the upper ocean. In 2010, 234Th flux ranged from 800 +/- 180 to 3120 +/- 260 dpm/m2-d, and DITD calculated POC export flux at 200m ranged from 2.27 +/- 0.5 to 12.9 +/- 1.1 mmolC/m2-d.  At each location, drifting sediment traps were deployed for 23-65 hours at 200m to measure 234Th and POC flux directly. The flux of 234Th into the traps ranged from 48 +/- 3 to 747 +/- 12 dpm/m2-d, which was very low compared to the flux calculated using the Thorium deficiency (DITD).  However, at two stations, the integrated deficiency and trap results agreed to 47% and 76%.  The trap-measured flux of POC was also much lower, ranging between 0.19 +/- 0.1 and 2.27 +/- 1.1 mmolC/m2-d. Net community production (in the mixed layer only), calculated from O2 supersaturation and estimates of piston velocity at each station, was found to predict an upper limit for POC fluxes between 0.0 to 9.5 mmolC/m2-d in 2010. All three estimates of POC export may suffer biases and artifacts, and certainly a 24-hour trap deployment may not be representative of export integrated over the time-scale of the 234Th tracer or of oxygen production and gas exchange.  Other possible explanations for the observed differences include: grazing of zooplankton swimmers on trap material, the vertical transport by swimmers past the trap depth, remineralization of POC and 234Th above the trap depth, and non-steady-state conditions.




Haskell, W.Z.II, W.M. Berelson, D.E. Hammond, D.G Capone. (2013) Particle sinking dynamics and POC        

        fluxes in the Eastern Tropical South Pacific based on 234Th and sediment trap deployments. Deep-

        Sea Res. I, 81, pp.1-13.

Upwelling Velocities and Eddy Diffusivity from 7Be Measurements Used to Calculate Vertical Nutrient Fluxes in the Eastern Tropical South Pacific

(in collaboration with David Kadko and Doug E. Hammond)

Abstract: Five 7Be profiles, measured in an area bounded by 10°S-20°S and 80°W-100°W, were used to determine upwelling velocity (wH) and vertical diffusivity (Kz). A positive correlation between wH and 14C primary production rate and a negative correlation between the inventories of 7Be and phosphate were observed. We interpret this as the influence of deeper, nutrient-rich, 7Be-poor water brought up by upwelling. Excluding two stations that appear to be influenced by non-steady state dynamics or horizontal transport, upwelling velocities were estimated to be 0 to 1.0 m d-1 and Kz values ranged from 0.4 to 2.6 cm2 s-1. From these parameters, NO3- fluxes into the euphotic zone were assessed and ranged from 0.15 to 2.9 mmol m-2 d-1. Using these values, we estimate 1.0 to 19 mmolC m-2 d-1 of new production in the ETSP. New production based on 7Be-derived transport parameters agree with carbon export estimates using a 234Th balance, sediment traps and O2/Ar supersaturation for stations along 20°S, but are higher than export estimates at 10°S, 100°W.




Haskell, W.Z.II, D. Kadko, D.E. Hammond, M.G. Prokopenko, W.M. Berelson, A.N. Knapp, D.G.  

        Capone. Upwelling velocities and eddy diffusivity from 7Be measurements used to compare vertical    

        nutrient fluxes to export POC flux calculated from 234Th, sediment traps, and O2/Ar supersaturation

        in the Eastern Tropical South Pacific. Mar. Chem. (in press)






















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(14C Production from D. Capone and M. Tiahlo - pers. comm.)

ETSP-I cruise track (NOAA, 2010)

Use of Triple Oxygen Isotopes, O2/Ar, and 7Be to Esimate Upwelling Velocity and Ecosystem Export Efficiency in the Southern California Bight

(in collaboration with Maria G. Prokopenko and Doug E. Hammond)


(in progress)


Project Site:

earth.usc.edu/files/UpRISEE



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This research has been funded by: National Science Foundation, International Association of Geochemistry, USC Earth Sciences Teaching Assistantships, and the Sonosky Foundation.