MULTI-SENSOR, ECOSYSTEM-BASED APPROACHES FOR ESTIMATION OF PARTICULATE ORGANIC CARBON

Three members of this project team, currently funded under NASA OBB program will participate in the SABOR campaign, approaching the problem from the biogeochemical side of the story. The team will primarily be investigating whether polarized scattering measurements can help to constrain the nature of particles in the ocean, for example organic vs. inorganic material; and secondarily, does the presence of the certain phytoplankton species have an effect on polarization scattering measurements. The SABOR campaign permits these questions to be evaluated across a large set of measurement types, for example, do relationships observed from in situ polarized scattering measurements hold when extrapolated to measurements of in situ polarized reflectance, to ship-based above-water reflectance and lidar, all the way to airborne polarized reflectance and lidar measurements. The cruise track, covering waters ranging from the optically complex coastal waters (with four across-continental shelf transects), to the clear blue waters of the North Atlantic gyre offer a large enough range of oceanic systems to test the robustness of these relationships, potentially opening new avenues of study and discovering new applications for polarization measurements.

In addition to the primary focus on polarization and particle properties, other measurements and efforts made by the team and collaborators help to advance the NASA OBB mission:

·      Comparing of estimates of phytoplankton carbon using two different methods (OSU cell sorting approach and Bigelow flowcam/flow cytometry approach). Understanding methods of estimating phytoplankton biomass from optical measurements is of great interest to the OBB program, from the perspective of in situ measurements as well as development and validation of current (MODIS) and upcoming (PACE) satellite data products.

·      Collecting data on diel variability of optical and biogeochemical measurements during multiple 24-hour station experiments, covering complex waters of the Gulf of Maine as well as the blue waters of the gyre. This effort will help to highlight the mechanisms driving variability in these two systems (that is, the links between phytoplankton community, other particulate matter, and optical properties), and ultimately to identify optical measurements that would allow us to use the diel patterns in optical properties to improve the estimates of oceanic primary and net community productivity. Although current missions do not offer a possibility of resolving diel variability from space, measurements such as these are supportive of future geostationary type observations (for example, GEOCAPE).

·      Collecting size fractionated optical and biogeochemical measurements, with size fractions being analogous to phytoplankton size groups. Preliminary results from 2013 field work (presented on the recent Ocean Sciences Meeting in Hawaii) demonstrate that proxy algorithms used to convert optical measurements to biogeochemical quantities (such as Particulate Organic Carbon from backscattering coefficient) do not follow a simple linear models and are highly dependent on particle type (ecosystem type). This dataset, augmented by measurements collected by collaborators during SABOR, will be of great importance for the development and validation phytoplankton functional type and size group algorithms. 

Ivona Cetinić, PI, University of Maine Darling Marine Center, Walpole, ME

Mary Jane Perry, University of Maine Darling Marine Center, Walpole, ME

Nicole Poulton, Bigelow Laboratory for Ocean Sciences, East Boothbay, ME

Wayne Slade, Sequoia Scientific, Inc., Bellevue, WA