Drivers of phytoplankton dynamics, and corresponding impacts on biogeochemistry, along the West Antarctic Peninsula

The West Antarctic Peninsula (WAP) has experienced rapid warming and melting since the mid-20th century. While there is evidence that these environmental drivers are altering the WAP marine food web, there is uncertainty regarding the mechanisms of these changes, and how they will impact the regional carbon cycle. In this dissertation, I examine the drivers of variability in phytoplankton dynamics along the WAP, with a primary focus on diatoms and cryptophytes (the two major phytoplankton groups), and how this variability impacts regional biogeochemistry. In Chapter 2 (Enhanced oceanic CO2 uptake along the rapidly changing West Antarctic Peninsula), I use a 25-year dataset to examine the coupling between upper ocean stability, phytoplankton dynamics, and oceanic CO2 uptake along the WAP. I demonstrate that greater upper ocean stability drives increased phytoplankton biomass, resulting in greater oceanic CO2 uptake. Diatom assemblages achieve higher biomass and oceanic CO2 uptake than cryptophyte assemblages. Over the past 25 years, in response to changes in sea ice dynamics, there have been significant positive trends in upper ocean stability, phytoplankton biomass, and oceanic CO2 uptake along the WAP. In Chapter 3 (Low diversity of a key phytoplankton group along the West Antarctic Peninsula), I use a phylogenetic placement approach with a 5-year dataset of DNA sequences to characterize WAP cryptophyte diversity and its drivers to a high taxonomic resolution. I demonstrate that there are just two major WAP cryptophyte taxa that consistently comprise nearly 100% of the cryptophyte community. Variability in the proportion of these two taxa is associated with changes in oceanographic conditions, including temperature, salinity, nutrients, and phytoplankton dynamics. These variables are all predicted to be altered with continued environmental change along the WAP. In Chapter 4 (Meltwater chemistry of a receding West Antarctic Peninsula glacier), I characterize the chemical composition and discharge dynamics of two WAP glacial meltwater streams. While different in their physical characteristics, I demonstrate that both streams have a similar composition of stable oxygen isotopes of water, which is important for determining regional oceanic freshwater budgets. Additionally, relative to coastal seawater, both streams have high concentrations of trace metals (including iron and copper), and low concentrations of silicate. These high glacial meltwater trace metal concentrations could be important for structuring coastal phytoplankton communities along the WAP.Ph.D.Includes bibliographical reference