The research project proposed here is focused on three overarching hypotheses regarding export fluxes from the upper ocean:
Hypothesis #1: Ratios of bulk photic layer plankton properties (e.g., phytoplankton:total particulate carbon ratio, phytoplankton division:accumulation ratio, community composition ratios, etc) can improve estimates of export compared to any single property alone.
Hypothesis #2: For a given combination of bulk properties, variability in the export fraction can be related to details of plankton community composition. Hypothesis #3: Key bulk and compositional properties of the upper ocean regulating the export fraction can be directly linked to optical properties retrievable from remote sensing.
This project addresses EXPORTS Science Question 1 (SQ1): How do upper ocean ecosystem characteristics determine the vertical transfer of organic matter from the well-lit surface ocean? Our study will evaluate how plankton community properties govern organic matter export and thus is particularly relevant to Subquestion 1a of SQ1. Our characterizations of plankton communities will also contribute critical information for addressing Subquestion 1b and 1c of SQ1. While EXPORTS Science Question 2 (SQ2) is primarily focused on vertical organic matter transfer below the photic zone, our project will contribute significantly to Subquestions 2b and 2d of SQ2, as these two Subquestions address linkages between photic layer community properties (which we will measure) and processes occurring at depth. With respect to EXPORTS Program Elements, our project primarily contributes to (1) ‘Phytoplankton and Microbes’, (2) ‘Zooplankton’, and (3) ‘Optics’, but will also make contributions to Elements (4) ‘Export’ and (5) ‘Bulk Biogeochemical Stocks’. We are requesting support for direct participation in the EXPORTS field campaigns and will provide a diverse array of measurements characterizing: (1) phytoplankton biomass (i.e., carbon stocks), composition, physiology, and productivity, (2) zooplankton stocks, composition, and grazing rates, and (3) continuous surface layer and station-specific water-column optical properties. For each of these properties, we are proposing multiple measurement approaches to provide a quantitative measure of uncertainty. We envision our suite of measurements to contribute significantly to supporting other independent EXPORTS field teams by providing key information on the ‘first steps’ of export - i.e., plankton community composition, production, and distribution within the photic layer. We envision our science investigation to contribute significantly to answering the overall questions of the EXPORTS program. We are proposing a 3 year project.