Funded Research - Project Profile: Lam, NSF-OCE 1829614



Project Title: Collaborative Research: Estimation of particle aggregation and disaggregation rates from the inversion of chemical tracer data


Project Lead: Phoebe J. Lam, Ocean Sciences Department, University of California Santa Cruz


NRA: N/A, project funded by NSF


Abstract:

Particle dynamics processes such as particle aggregation, disaggregation, and remineralization control the size distribution of marine particulate matter. Oceanic ecosystems that favor aggregation over disaggregation and remineralization are expected to produce large aggregates that can sink through the water column and therefore to have a strong and efficient biological pump. However, rates of (dis)aggregation are very difficult to observe and measure directly. In this project, particle aggregation, disaggregation, and remineralization rates will be estimated by applying inverse models to observations of size-fractionated lithogenic particles, particulate organic carbon (POC), and 234Th from the EXPORTS and GEOTRACES programs. Temporal and lateral variations in these rates will be documented from a variety of oceanic environments, ranging from oligotrophic to eutrophic, thereby testing our hypothesis that these rates vary significantly with tropic status and across the major biogeochemical provinces of the open ocean.

The key concept of this project derives from observations that we previously made of particulate titanium (pTi) in small (1-51μm) and large (>51μm) particles collected by in-situ filtration from the Saharan dust-influenced North Atlantic. The size-partitioning of Ti reflected a net aggregation of fine dust particles into large, dust-containing organic aggregates in the mixed layer, sinking of the aggregates, and a net disaggregation of the dust-containing large aggregates in the upper mesopelagic zone, which released the fine dust particles back to the small size fraction. Lithogenic particles thus act as an inert, passive tracer of particle dynamics, and the rates of particle aggregation, disaggregation, and sinking can be estimated from the best fit of a two-size class particle cycling model to the observed size-fractionated lithogenic particle data.

To accomplish our objectives, we will measure lithogenic particle concentrations in the size-fractionated particles collected by in-situ pumps and sediment traps during the EXPORTS program. In addition to our data generation effort, we will estimate bulk particle aggregation, disaggregation, and sinking rates in various oceanic environments based on the inversion of the observed lithogenic particle data from both EXPORTS and GEOTRACES programs. Furthermore, we will add size-fractionated POC and 234Th concentration data produced by colleagues to the size-class model in order to estimate POC remineralization rates and to compare the tracing of particle dynamics processes using lithogenic compared to surface-adsorbed chemical tracers. The results from the EXPORTS data will be also compared to the rich set of surface and mesopelagic measurements to be produced as part of EXPORTS.

Keywords: remineralization, aggregation, disaggregation, sinking rates, lithogenic particles, POC, Th, particle size fractionation, in-situ filtration, particle dynamics, inverse model



Project Lead(s):

  • Phoebe J. Lam, Ocean Sciences Department, University of California Santa Cruz


Co-Investigator(s):

  • Olivier Marchal, Geology & Geophysics, Woods Hole Oceanographic Institutions

  • Jong-Mi Lee, Ocean Sciences Department, University of California Santa Cruz


Post-Doc(s):


Student-Graduate(s):


Student-Undergraduate(s):


Collaborator(s):

  • all PIs in the EXPORTS program