The California Current Ecosystem Long-Term Ecological Research (CCE LTER) program is designed to build upon the outstanding 60+ year CalCOFI time-series. Its goal is to elucidate the underlying mechanisms driving interannual variability in plankton and fish populations off the coast of Southern California. At the same time, it has served as a platform for many projects investigating the interactions between the atmosphere, ocean, and biota.

 

I have been involved in the CCE LTER program since its inception in 2005, and have been responsible for vertical carbon flux measurements on each CCE Process cruise. In the process, I have developed a field sampling program that involves both drifting VERTEX-style sediment trap deployments and 234Th:238U deficiency measurements as independent assessments of carbon export rates. Depending on the questions being addressed on any particular cruise, I have also extended my sampling plans to include phytoplankton sinking rates, 15NO3- uptake new production measurements, and microscopic enumeration of sediment trap contents.

 

On cruises from 2006-2008, I was focused on the role of mesozooplankton in carbon export. I developed a simple trophic model to predict mesozooplankton fecal production, which corresponded very well (both in magnitude and variability) to contemporaneous particulate carbon export measurements. I also sorted through sediment trap contents and found that fecal pellets were often a dominant component of the export during high flux periods, but were less important in oligotrophic periods and regions. Using results from MOCNESS tows made by my collaborators, I also found that mesozooplankton active transport was responsible for on average an additional 19% of the passive flux which would not be assessed by typical carbon export measurements.

 

In our most recent funding cycle, the CCE focus has been on mesoscale features (fronts and eddies) that are potential sites of upwelling and downwelling. These regions may play a disproportionate role in biological production as different water parcels mix and nutrients are brought to the surface and they also have important biogeochemical roles as sites where mesozooplankton may aggregate or particles may be advected beneath the euphotic zone. To determine carbon flux across the front, I have taken vertical sections of thorium during rapid frontal crossings on the cruise. Our results show that these fronts, which are common in the California Current System, play important roles in vertical carbon flux through increased sinking particle flux and subduction of particles along sloping isopycnals.