Online Ph.D. Research Seminar - Shao-Min Chen

Shao-Min Chen
Ph.D. Candidate
Dalhousie University

Title: Tracking Arctic/Subarctic Export Productivity Variability Using Compound-Specific Isotope Analysis of Amino Acids

Arctic and Subarctic oceans have experienced dramatic reductions in sea ice extent as a result of climate change. The reduction in sea ice represents a loss of habitat for highly productive sympagic (ice-associated) algae, which are major contributors to Arctic/Subarctic primary production (up to 60%). Associated changes in density stratification and nutrient availability in seasonally ice-free waters have also affected the relative productivity and community composition of pelagic (water-column) algae. These changes in the physical environment in Arctic/Subarctic waters likely impact the timing, composition, and quality of export production supporting benthic food webs, as well as the efficiency of the biological CO2 pump. However, inaccessibility to Arctic/Subarctic habitats and lack of historical baselines have so far prevented a detailed understanding of these ecological changes in the context of ongoing climate change.
The overall goal of my thesis therefore is to develop a new proxy for characterizing changes in the composition of export productivity over climate-relevant timescales. My research leverages the interpretive power of compound-specific isotope analysis of amino acids (CSIA-AA). Amino acids represent the largest class of compounds in sinking and sedimented organic matter. Moreover, stable carbon (δ13C) and nitrogen (δ15N) isotopes in individual amino acids have opened up new ways to investigate biogeochemical and ecological processes in marine food webs.

My first project centers on amino acid δ13C and δ15N fingerprinting of natural sympagic and pelagic algae collected in the Northern Labrador Sea and Cambridge Bay. Significant difference in δ13C-AA and δ15N-AA patterns between sympagic and pelagic algae was observed and evidenced by multivariant analyses. These observations highlight the potential of CSIA-AA “fingerprints” to estimate sympagic algal contribution to export production and efficiency of benthic-pelagic coupling in polar marine environments.

My second project focuses on export productivity variability in sediment trap time series near Saglek Bank (Northern Labrador shelf). CSIA-AA revealed variability in baseline N sources, trophic fractionation, microbial degradation, and plankton community composition in the export production. The δ13C-EAA patterns indicate well preserved primary production and minimal contribution of microbial biomass in the export production. The δ15N-AA proxies suggest a relative dominance by zooplankton fecal pellets in the export production, indicating the importance of pelagic zooplankton to export productivity in this Subarctic region.

Finally, I will outline progress and plans for applying these new methods to characterizing the late Holocene changes in the composition of export productivity as recorded in sediment cores from Baffin Bay.

Overall, my research provides important new insights into the export productivity variability in the rapidly changing polar marine environment and demonstrates the potential of CSIA-AA as a novel proxy to complement other palaeoceanographic proxies.



Online via Zoom
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