Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Data Files
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

All 234Th measurements made during this study. Measurements were made at the San Pedro Ocean Time-series (SPOT) station (33 33'N, 118 24'W). Data are also published in Table A1 in the following publication:
Haskell, W. Z., et al. 2016. An organic carbon budget for coastal Southern California determined by estimates of vertical nutrient flux, net community production and export. Deep-Sea Research I, 116, 49-76. doi:10.1016/j.dsr.2016.07.003

See complete methodology in Haskell et al. (2016). In summary:
This study is part of an effort aimed at characterizing the biological response to upwelling at SPOT on 21 cruises between January 2013 and June 2014; the Upwelling Regime In-Situ Ecosystem Efficiency (Up.R.I.S.E.E.) study.

Thorium-234: Vertical profiles from the surface to 200 m were collected for thorium via Niskin/CTD on every cruise. Ten liters were collected at eight depths, chosen based on the fluorescence profile observed during the CTD's descent. A 229Th spike of known activity was added to the samples as they were being transferred from Niskins into 10 L or 20 L polycarbonate carboys (to an activity ~0.9 dpm/L) and allowed to equilibrate for at least 24 h. The recovery yield of 229Th in each sample was used in all calculations of 234Th to correct for methodological efficiency. The samples were coprecipitated with MnO2 using the technique originally developed by Rutgers van der Loeff and Moore (1999) and detailed in Haskell et al. (2013). Samples were filtered onto a 0.45 um Pall Supor Membrane filter (142 mm). The filters were dried at room temperature, placed in a plastic test tube, and placed in an Ortec low background gamma detector (intrinsic germanium, well-type, 150cc active volume). 234Th has readily identifiable gamma peaks at 63.2 keV (branching ratio ~4%) and 92.4+92.8 keV (branching ratio ~5.5%). All reported activities of 234Th have been calculated using the sum of these two peaks. Each sample was counted until counting uncertainty was below 8%. Counts were corrected for 234Th decay, ingrowth from 238U between collection and filtration, and production from co-precipitated 238U, which was measured by re-counting multiple samples from each profile six months after collection (45 half-lives). Standardization was done using a solution of known 238U activity.

BCO-DMO Processing:
-modified parameter names to conform with BCO-DMO naming conventions;
-formatted date to yyyy-mm-dd;
-replaced "-" and blanks (missing data) with "nd";
-added site name, lat, and lon from information on metadata form.

The marine biological pump is one of the primary pathways via which anthropogenic carbon dioxide may be sequestered from the atmosphere and exported to the deep ocean as organic carbon. While the link between nutrient supply and high primary productivity in upwelling regions is well established, factors controlling the organic carbon export efficiency of upwelling ecosystems are not well known. Scientists from the University of Southern California and Pomona College plan to determine the factors that control the rates and magnitudes of two components of biological production, Net Community Production (NCP) and Gross Primary Production (GPP), as well as particulate organic carbon export efficiency, at the San Pedro Ocean Time Series, a coastal site in the California Borderland during periods of minimal and high upwelling velocity over a 2-year span. At this site, past and ongoing observations of hydrography and carbon rain will provide an historical context for interpreting results and mechanisms at work.

Rates of NCP and GPP will be quantified at different upwelling intensity, using dissolved oxygen to argon (O2/Ar) ratios and the oxygen triple isotope composition of dissolved oxygen (O2). The export of organic carbon will be established using 234Th (thorium) profiles in the water column, coupled with floating sediment trap deployments, and the development of a carbon isotope balance for the water column. Upwelling will be characterized using non-steady state budgets for atmospheric 7Be (beryllium) input and its depth-integrated decay, as well as estimating rates based on remote measurements of wind stress curl and budgets for dissolved inorganic carbon and silicon. Application of the O2/Ar ratio and the oxygen triple isotope approach will require depth-integrated profiles of these tracers to evaluate the impact of upwelling on mixed layer inputs and use of non-steady state models during seasonal transitions in upwelling. The comprehensive data set to be obtained should provide insights into the organic carbon export efficiency under variable upwelling regimes and help to relate the satellite-based measurements of chlorophyll to the organic carbon export of these highly productive ecosystems.

Broader Impacts: One graduate and one undergraduate student from the University of Southern California and two undergraduate students from Pomona College would be supported and trained as part of this project.