Stanford University

*** Ph.D. Thesis/ Oral Defense ***

Primary producers in the changing polar oceans 

Stephanie Lim

Monday, June 2,  9:00 AM

Mitchell Earth Sciences - Hartley Conference Room

Zoom link

Department of Earth System Science

Advisor: Dr. Kevin Arrigo

Abstract: Microalgal primary producers play a key role in biogeochemical cycling and form the base of the marine food web. Climate change is drastically altering the environmental conditions that control the distribution, timing, and magnitude of algal blooms. This is particularly evident in the polar oceans, which are undergoing some of the most severe and rapid change in the world. This dissertation investigates the recent impacts of climate change on primary producers in the Arctic and Southern Oceans. Chapters 1 and 2 assess the effects of dramatic sea ice loss on sea ice algal habitat over 34 years in the Arctic and 16 years in the Antarctic, respectively. I combined circumpolar remote sensing datasets, a radiative transfer model, and a sea ice growth model to estimate sea ice suitability as algal habitat. Chapter 3 uses field-based observations to examine the nutrient dynamics supporting a massive harmful algal bloom in 2022 in the Pacific Arctic Ocean, where reports of the toxic dinoflagellate Alexandrium catenella are becoming increasingly frequent. To understand how A. catenella thrives in low-nutrient conditions, I measured uptake rates of four nitrogen substrates by the bulk phytoplankton community and single cells. Overall, this dissertation documents the current status of two primary producer groups in the polar oceans and improves predictions of their future responses to continued climate change. Whether it is a mid-century “inflection point” that marks the impending decline of Arctic ice algae or the likely persistence of harmful algal blooms in the Pacific Arctic Ocean given favorable nutrient conditions, this work traces potential futures for polar marine ecosystems.