UC San Diego

The Western Antarctic Peninsula (WAP) is rapidly changing due to climate forcing in recent decades. These changes manifest as an overall increase in ocean and air temperatures (with some regional cooling), retreating glaciers, and increases in precipitation associated with shifts in atmospheric circulation. As these changes continue and intensify, meteoric water input to the coastal ocean is expected to increase. Continued monitoring of these changes can help us better understand their impacts. The physical effects of glacial melting on sea level has been extensively studied in the past. However, the impact of glacial meltwater on phytoplankton community composition remains largely elusive. Due to the critical role of primary producers in the Antarctic food web and their significance to local biogeochemical cycle and ecosystem dynamics, the immediate ramification of meltwater input on these communities need to be better understood.

In order to accomplish such task, robust datasets are required that can encompass both long-term temporal scale and broad geographic extent. Coincidentally, these datasets exist in the Western Antarctic Peninsula region. Two oceanographic expeditions (FjordEco) were conducted in an Antarctic fjord (Andvord Bay) in November to December 2015 and April to May 2016. This dataset provides insights on nearshore water properties and how they impact phytoplankton community. Over the Peninsula shelf, a multi-decadal time series was curated and collected by the Palmer Long-Term Ecological Research (LTER) program. The LTER database has extensive spatial and temporal coverage which make it suitable for understanding the impact of environmental variables on phytoplankton over the continental shelf.

This dissertation contains three main chapters. In Chapter 2, I aim to understand the spatial and temporal distribution of glacial meltwater in Andvord Bay and characterize their optical features in order to develop a method for quantifying meltwater fraction based on water column optics. The fjord severs as an end-member and thus an extreme in various environmental and biological gradients. Hence, the ecological connectivity between the fjord and the shelf has significant implications to the entire Antarctic ecosystem. In Chapter 3, I will investigate the phytoplankton community composition within Andvord Bay and understand how environmental conditions, particularly meltwater, impact this community. The data from this chapter will be utilized to train a machine learning model; techniques developed in this chapter will be applied to the broader coastal ocean over the WAP continental shelf in Chapter 4. I hope this dissertation can improve our understanding of how environmental variables influence phytoplankton community in the WAP, as well as contextualize the physical impacts of climate forcing in the perspective of Antarctic ecosystems.