Deciphering the ecology of key diatom taxa to understand climate-induced changes in West Greenland lakes

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Across the Arctic, paleolimnological records provide some of the few key archives documenting rates of ecological change in this region over the Holocene. In particular, striking changes in communities of diatoms (a type of algae that responds rapidly to environmental change and leaves a fossil in lake sediments) have occurred over the last 150 years, with species generally associated with warmer conditions increasing at unprecedented rates in the sediment record. However, changes in diatom assemblages in lake sediments from west Greenland are different from those in the rest of the Arctic in that they are rich in these 'warmer' water diatoms throughout the Holocene. This difference has raised questions about what we can use diatoms to infer in the Arctic, and suggests the need to clarify the ecological traits of key diatom taxa in order to advance our understanding of drivers of change. Recent research in alpine regions reveals that key diatom species that are used as indicators of 20th century warming in both arctic and alpine lakes respond specifically to both climate-induced changes in energy (mixing depths) and mass inputs (nutrients) to lake ecosystems. This suggests that spatially- and temporally-variable interactions between climate-induced changes in the physical and chemical structure of lakes may drive diatom community changes, but this is currently untested in arctic lakes.This research will couple comparative lake sampling with both small- and large-scale experiments to provide key ecological information that will enable interpretation of climate- induced ecological changes from several existing diatom records from southwest Greenland. The objective of this project is to determine the effects of climate-driven changes in nutrients and water column stability on the relative abundances of key diatom taxa, and to apply that information to existing diatom records to determine climate-induced changes in these lake ecosystems. A suite of lakes will be sampled to determine the factors controlling the distributions of key diatom species. A small-scale experiment will be conducted to assess the importance of nutrients and incubation depth on the abundances of these key diatom species. A large-scale experiment (whole lake manipulation) will be conducted to assess the importance of thermal stratification on these diatoms, which will be tested by deepening the mixed layer of a lake that typically stratifies thermallyduring the summer. This large-scale experiment will be the first whole-lake ecosystem test of the importance of changing energy influx on the community structure of these arctic lakes.This project will provide support for a postdoctoral research associate at the Climate Change Institute at the University of Maine. The postdoctoral associate will gain valuable experience conducting arctic ecosystems research, mentoring undergraduate students, and working in a multidisciplinary institute focused on multiple aspects of climate change. This research will also involve two undergraduates over the course of the project. A distributed graduate seminar focused on climate change and high latitude and altitude lake ecosystems will be developed and taught in conjunction with ecologists from four countries. Data from this project will be made available through the NOAA paleoclimate database and website, and the Diatom Paleolimnology Data Cooperative website.