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Special Session 3: Size matters or not, particles export in marine environments |
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Degradative status, microbial influence, and export potential of small size classes of particulate organic matter in open ocean water columns
Tuesday 10th @ 0945-1010
Room 4
Hilary G. Close* , RSMAS, University of Miami
Cassie A. Ka'apu-Lyons, University of Hawaii
Kalina C. Grabb, Woods Hole Oceanographic Institution
Blaire P. Umhau, University of South Carolina
Claudia R. Benitez-Nelson, University of South Carolina
Kristen Gloeckler, University of Hawaii
Cecelia C.S. Hannides, University of Hawaii
Jeffrey C. Drazen, University of Hawaii
Brian N. Popp, University of Hawaii
Presenter Email: hclose@rsmas.miami.edu
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| Current climate trends are likely to cause major ecological shifts in the world¡¯s oceans. The effects of such ecosystem change on the marine carbon cycle are under debate, largely due to uncertainties in the relative contribution of microbial versus higher food web processes to the biological pump. Stable isotope ratios hold promise as long-lived tracers of the fate of diverse biomass in the ocean: variations in ¦Ä13C and ¦Ä15N values can reflect a range of autotrophic and heterotrophic metabolisms. However, these distinctions may be obscured in the larger pool of marine organic matter due to particle dynamics and isotope effects associated with microbial degradation.
Compound-specific isotope analysis (CSIA) of organic constituents with different degradation potential (e.g., lipids and amino acids) is allowing us to distinguish the importance of microbial biomass and degradative processes across the particle size spectrum in the water column. Here we present CSIA results of size-fractionated particulate organic matter (POM) from diverse regimes in the Pacific Ocean. We identify compound-specific isotopic patterns relating to the proportion of POM composed of partially-hydrolyzed detrital material, autotrophic versus heterotrophic biomass, and accumulated bacterial biomass resistant to degradation. These proportions vary across particle size classes (submicron/¡±X-POM¡±, slowly settling/¡±suspended¡±, large/¡±sinking¡±) as well as depth in the water column, with bacterial biomass most dominant in X-POM and at mesopelagic depths.
Through collaborative efforts we have begun to pair these CSIA findings with 234Th-based measurements of carbon flux, as well as identification of dietary sources for zooplankton and micronekton, from surface to upper bathypelagic depths. We postulate a history of biological inputs, particle dynamics interactions, and degradation of small versus large particles, suggesting that small particles and microbial biomass may represent seasonally-important contributors to both carbon export and higher food web diets.
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