DECONVOLVING PROPORTIONAL CONTRIBUTIONS TO THE FLUX OF MARINE SINKING ORGANIC PARTICLES AT THREE SITES OFF EASTERN CANADA USING COMPOUND SPECIFIC NITROGEN ISOTOPE ANALYSIS

Constraining the mechanisms and rates of particulate organic matter (POM) export and carbon sequestration is a fundamental concern in marine biogeochemistry. Compound-specific nitrogen isotope analysis of amino acids (d¹⁵N-AA) is a potentially powerful way to disentangle the proportional contributions of different source materials to the downward flux of POM, particularly when particle disaggregation and degradation processes can render visual identification difficult. We compiled new and previously published d¹⁵N-AA and associated geochemical data from long-term (9 – 12 months) sediment traps deployed off Eastern Canada (Gulf of Maine, St Lawrence Estuary, and Labrador Sea), which together span gradients in proximity to land (1 – 175 km) and trap depth (130 – 915 m). Fluxes of particulate organic carbon and nitrogen decreased exponentially with depth, as expected. However, d¹⁵N-AA based indices of trophic position and microbial resynthesis varied little, which implies common origins and excellent preservation of d¹⁵N-AA signatures in the POM during export and sinking. Mixing model analysis of the d¹⁵N-data revealed a dominance of zooplankton fecal pellets (>70%) relative to phytoplankton (<15%) or other sources contributing to the sinking POM at all sites. Results are in broad agreement with other recent sediment trap d¹⁵N-AA investigations from sites in the Pacific Ocean and support the idea, based on visual analysis of sediment trap particles and biogeochemical models, that fecal pellets are the dominant form of POM export in many ocean regions.

Primary Presenter: Owen Sherwood, Dalhousie University (owen.sherwood@dal.ca)

Authors:

Shao-Min Chen, Dalhousie University  (shaomin.chen@dal.ca)

Nina Golombek, Dalhousie University  (nina.golombek@dal.ca)

Hannah Sharpe, University of New Brunswick  (hsharpe@unb.ca)

Cynthia Pilskaln, University of Massachusetts Dartmouth  (cpilskaln@umassd.edu)

David Cote, Northwest Atlantic Fisheries Centre, Fisheries and Oceans Canada  (David.Cote@dfo-mpo.gc.ca)

Audrey Limoges, University of New Brunswick  (alimoges@unb.ca)