[Eoas-seminar] Oceanography Thesis Defense - Taylor Shropshire - April 17, 11am - 327OSB

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Wed Apr 10 09:01:24 EDT 2019


Major Professor: Mike Stukel and Eric Chassignet


Zooplankton play an important role in global biogeochemistry and their secondary production supports valuable fisheries of the world's oceans. Coupled physical-biogeochemical models (PBMs) provide a unique oceanographic research tool for studying zooplankton on basin and global scales since zooplankton cannot currently be estimated using remote sensing techniques. However, evaluating the accuracy of zooplankton abundance estimates from PBMs has been a major challenge as a result of sparse ship-based observations. Consequently, zooplankton dynamics have been under studied and under validated in PBMs. In this study, we configure a PBM for the Gulf of Mexico (GoM) and validate simulated zooplankton fields against an extensive combination of in situ biomass and rate measurements. We find that spatial variability in mesozooplankton biomass observed in a multi-decadal database for the northern GoM is well resolved by the model with a statistically significant (p < 0.05) correlation of 0.74. In terms of community composition, the model estimates that large zooplankton (LZ) and predatory zooplankton (PZ) functional groups makes up approximately 40% and 60% of the simulated mesozooplankton biomass respectively, which is further supported by ship-based measurements. Model results of LZ dietary composition suggests that herbivory is the dominate feeding pathway whereas PZ dietary composition is largely carnivorous. Dietary composition is found to be less binary in the oligotrophic GoM where LZ and PZ feed on a combination of phytoplankton and zooplankton. We hypothesize that already low mesozooplankton biomass in the oligotrophic Gulf (~0.04 mmol N m-3) may become further reduced in the future with important impacts on food availability for higher planktivorous trophic levels such as pelagic larval fish. Such reductions could be expected from increases in thermal stratification as a result of a warming ocean and ensuing increases in bottom-up ecosystem limitation.

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