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Oceanography Seminar

August 29, 3:00pm - 4:15pm
Mānoa Campus, MSB 100

Cecelia Hannides
Postdoctoral Researcher
UH Department of Geology & Geophysics

"Midwater zooplankton and suspended particle dynamics: A stable isotope perspective"

Abstract: Carbon flux to the deep ocean is limited in part by particle cycling and biological activity in the mesopelagic zone. Midwater zooplankton are thought to play an important role in these dynamics, but very little is known about their activity at depth. One promising approach for investigating these processes is stable isotope analysis. In several regions of the world’s oceans zooplankton become significantly 15N enriched with depth. Here I use compound-specific stable isotope analysis (CSIA) to demonstrate that this enrichment is driven in part by change in the N isotope composition (15N value) of food resources at the base of zooplankton food web. At the same time CSIA indicates a shift in trophic structure, with potentially more carnivorous zooplankton in the mesopelagic zone. Linkages between zooplankton and a potential food resource, suspended particles, are also explored using CSIA. The results indicate that this organic matter pool is not a significant zooplankton food resource at depth, and instead 62 – 88% of the N sustaining midwater zooplankton is ‘surface derived’, obtained through consumption of sinking particles, carnivory of vertical migrants, or direct feeding in surface waters at night. Finally, CSIA is used to further explore the dynamics of suspended particles in midwaters. Results indicate isotope fractionation associated with heterotrophic degradation, rather than a change in ‘trophic status’ or N source, is the main mechanism driving 15N enrichment in this organic matter size class with depth.

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Oceanography, Mānoa Campus

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