Interdisciplinary Seminar: Chad Lloyd & Yun Chang

The UNC-CH Department of Earth, Marine, and Environmental Sciences presents the interdisciplinary seminars of graduate students Chad Lloyd & Yun Chang. This event will be held on  Monday October 18th, at 12:20 pm. The seminars are held both in person in room G201 of Murray Hall and online via Zoom ID 935 3703 8099.

Chad Lloyd’s Seminar Title: Using ancient DNA to reconstruct past ecosystems: Investigating past fish populations

Chad Lloyd’s Abstract: The rise in global human population has resulted in increased exploitation of resources, including fish. This increased pressure on resource access has led to the decline of fish populations, and in many cases a collapse of fisheries. Advances in DNA sequencing have led to using ancient DNA to uncover past ecosystems. Understanding past ecosystems could allow us to better manage our current resources. The high degree of physiochemical degradation of DNA in both the water column and sediments makes it difficult to recover and analyze ancient environmental DNA; however, using excavated fish bones from water-logged and free-draining archaeological sites, researchers were able to predict the origins of these ancient DNA samples by comparing them with DNA taken from modern-day fish populations. In this presentation, I will discuss how genome-wide variation as well as the frequency distribution of inverted loci on four different chromosomes was used to map where the ancient remains of fish likely originated. This analysis revealed that ancient samples, which were excavated in areas throughout Europe, showed most similarity to modern-day samples collected in the North East Arctic and near the Lofoten Archipelago in Norway, suggesting that this area has participated in international trade since the Viking Age. This method also has implications for modern-day studies, most notably using loci inversion to map changes in fish migration patterns, and potentially using variation in gene sequences to predict which species can better adapt to environmental changes.

Yun Chang’s Seminar Title: The influence of global warming on deep convection and phytoplankton bloom initiation in the North Atlantic

Yun Chang’s Abstract: Phytoplankton blooms in the North Atlantic support Earth’s productive fisheries and play a crucial role in the air-sea exchange of carbon-dioxide. The timing of the bloom initiation has significant impact on zooplankton development and larval fish survival. By synthesizing literature in biological and physical oceanography, in this talk I will address how deep convection controls phytoplankton bloom initiation, and how global warming influences these two processes. Specifically, phytoplankton bloom initiation in the North Atlantic can be explained by the dilution recoupling hypothesis, in which mixed layer depth and zooplankton grazing are the tightly linked: adeeper mixed layer reduces grazing by diluting zooplankton, favoring phytoplankton survival. Because deep convection determines the thickness of the mixed layer, it directly impacts phytoplankton biomass. Finally, global warming melts ice near the North Atlantic and the resulting fresh water overflow and warmer air reduce water density on the ocean surface, increasing stratification in the upper ocean. Consequently, the increased stratification weakens deep convection and the mixed layer becomes shallower. This trend is confirmed by both observations and numerical simulations, and most likely will continue in the future. The predicted future impact for phytoplankton is that a shallower mixed layer will result in increased grazing, a decline in phytoplankton biomass, and delay in bloom initiation. Moreover, these predicted changes in phytoplankton dynamics are expected to negatively impact fisheries that are dependent on phytoplankton for food, and may reduce export of carbon from the atmosphere into the ocean.