IDENTIFYING SOURCES AND TRANSFORMATION OF PARTICULATE ORGANIC MATTER IN THE NORTH ATLANTIC SPRING BLOOM USING ISOTOPES, AMINO ACIDS, AND CARBOHYDRATES

In May 2021, the EXPORTS (EXport Processes in the Ocean from RemoTe Sensing) program sampled a declining phytoplankton bloom in the North Atlantic. To understand the overall biogeochemical impact of particle flux during the bloom, including episodic flux of aggregates, questions remain about the chemical composition, sources, and degradative transformation of particulate organic matter (POM). We measured the concentrations of carbohydrate monomers and the concentrations, nitrogen isotope ratios, and carbon isotope ratios of individual amino acids in sinking and suspended particles collected from the surface to mid-mesopelagic (30-500 m) depths and over time during the bloom decline. In the euphotic zone, patterns in the nitrogen isotope ratios of amino acids indicated that POM derived predominantly from primary producers, with nitrogen sources varying across size fractions, and carbon isotopic fingerprints of essential amino acids identified major phytoplankton clades contributing to particle size fractions. Patterns in the nitrogen isotope ratios of amino acids confirm that phytoplankton-derived material persisted into the mesopelagic, but with significant overprinting by microbial degradation. Carbohydrate composition shifted from glucose-dominated in the euphotic zone to more amino-containing and acidic carbohydrates in the mesopelagic, which are components associated with the formation of sinking algal aggregates. We discuss how the observed POM composition may affect the export and dietary potential of sinking particles across the sampling period.

Presentation Preference: Either

Primary Presenter: Elizabeth Yanuskiewicz, University of Miami (eay10@miami.edu)

Authors:

Elizabeth Yanuskiewicz, University of Miami  (eay10@miami.edu)

Connor Shea, University of Hawai'i at Manoa  (chshea@hawaii.edu)

Lillian Henderson, University of Miami  (lillianhenderson05@gmail.com)

Chance English, University of California Santa Barbara  (cje@ucsb.edu)

Craig Carlson, University of California Santa Barbara  (craig_carlson@ucsb.edu)

Brian Popp, University of Hawai'i at Manoa  (popp@hawaii.edu)

Hilary Close, University of Miami  (hclose@miami.edu)