Pelagic Environment Team

The pelagic environment team will measure chemical parameters of the water column to characterize the physical and biogeochemical dynamics that interact with the local pelagic and benthic habitats. More specifically, we are interested in capturing the spatial and temporal variability of the Oxygen Minimum Zone (OMZ) in the San Diego continental margin. 

A recent study shows that the upper-boundary of the OMZ has shoaled by up to 90m in the Southern California Bight (Bograd et al., 2008). However, detailed spatial and temporal variability of the OMZ and water column in the San Diego continental margin has yet to be assessed in spite of a few reports on scales (Frieder et al., 2012) and relevance to interannual climate event (Nam et al., 2011) and upwelling relaxation (Send and Nam, 2012) of dissolved oxygen and pH in San Diegan water.

There are two main objectives for this team:

  • Quantify the spatial and temporal variability of the OMZ in the San Diego continental margin. Spatial measurements from this expedition will be combined with time series data from the Del Mar Mooring to determine which processes are most responsible for the variability of biogeochemical parameters.
  • Test prototype autonomous pH and dissolved inorganic carbon (DIC) sensors for profiling float applications and collect basic data for further development of pH and DIC sensors for both moving and fixed platforms.

Water samples will be collected and analyzed from various depths between ~1000m and the surface at 28 key locations around the San Diego continental margin. The seawater will be analyzed for dissolved oxygen, pH, DIC, calcium, particulate organic carbon (POC), and various nutrients. The pH and DIC from water samples will be compared to the measurements from the prototype sensors to assess their performance. Continuous measurements of surface pH, DIC, and oxygen as well as meteorological variables and current profiles will be made throughout the expedition.



Photo: Map of the stations where water samples will be collected. The transect lines cover shallow stations (~30m) to deeper stations (~1000m), as we hope to capture upwelling events that bring low oxygen waters to the surface.



Photo: System to continuously measure surface dissolved inorganic carbon (DIC). 
Photo credit: Phil Bresnahan.



Photo: A third generation buoy off the coast of Del Mar. Various meterological, and physical/chemical oceanographic data are telemetered via satellite to provide real time data. Photo credit: http://mooring.ucsd.edu/projects/delmar/img/dm_buoy04.jpg



Citations:

Bograd SJ, Castro CG, Di Lorenzo E, et al. (2008). Oxygen declines and the shoaling of the hypoxic boundary in the California Current. Geophys Res Lett 35, L12607

Frieder, C. A., S. H. Nam, T. R. Martz, and L. A. Levin (2012). High temporal and spatial variability of dissolved oxygen and pH in a nearshore California kelp forest, Biogeosciences Discuss, 9, 4099-4132, doi:10.5194/bgd-9-4099-2012.

Send, U. and S. Nam (2012). Relaxation from Upwelling: the effect on dissolved oxygen on the continental shelf, J. Geophys. Res. - Ocean, 117, C04024, doi:10.1029/2011JC007517.

Nam, S., H.-J. Kim, and U. Send (2011). Amplification of hypoxic and acidic events by La Niña conditions on the continental shelf off California, Geophys. Res. Lett., 38, L22602, doi:10.1029/2011GL049549.

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