I study ecology and biogeochemistry in polar environments. Broadly, I work to understand how climate warming and its associated effects on the cryosphere affect carbon cycling and ecological dynamics in aquatic and marine environments. I use biogeochemical tools, such as stable isotope analysis, to answer ecological questions and better understand past and present environments.
Microbially-mediated carbon cycling in permanently ice-covered Antarctic lakes
Antarctica is warming. This causes many changes to lake conditions in the Dry Valleys of Antarctica. Glacial melt and stream flow are increasing, which raises the water level of closed-basin, ice-covered lakes. Warming also thins the permanent ice-cover of these lakes, allowing more light to reach the water column. This increase in light and habitatable space increases phytoplankton carbon fixation, but we don’t know what effects these changes will have on carbon loss rates. Therefore, I propose to study carbon loss rates in two Dry Valley Lakes: Lake Bonney and Lake Fryxell. Specifically, my proposed work will assess decomposition rates by bacterioplankton in the lake water columns and the potential for microbial mat biomass to be advected from lake moats to the surrounding soils.
Poster: Carolynn Harris. 2019. Lift-off mats may transfer organic matter from lakes to desert soils in the McMurdo Dry Valleys, Antarctica. Montana State Graduate Research Colloquium, Bozeman MT. *Best Student Poster
Poster: Carolynn Harris, A. Chiuchiolo, J. Priscu. 2018. Microbial decomposition of photosynthetic carbon in the water column of ice-covered Antarctic Lakes. LTER All Scientists Meeting. Pacific Grove CA.
Limpet shells provide evidence for climatic and anthropogenic impacts on coastal ecosystems in subarctic Shetland
Zooarchaeological faunal remains are commonly examined to investigate harvesting behavior. We determined limpet (Patella vulgata) shell size and shape, and estimated shell age from several middens at the Late Norse Sandwick South Site, Unst, Shetland, UK, whose strata represent distinct occupational phases (Phase 1: AD 1100–1200, Phase 2: AD 1200–1250, Phase 3: AD 1250–1350). Our goal was to determine if the many limpets found there could provide insight into Norse harvesting behavior and/or climatic impacts on coastal ecosystems. Shell length, conicity, and modeled age all declined between Phases 1 and 2, suggesting intensive, size-selective harvesting of limpets and a shift to harvesting lower in the intertidal zone between phases. Length and conicity varied in Phases 2 and 3 and no major changes seem to have occurred over these periods, indicating that harvesting maintained the limpet population at an impacted level throughout the later phases. The conicity decline between Phases 1 and 2 may also have been caused by increased storminess that accompanied the onset of the Little Ice Age.
Ecology & hydrology of hypersaline lagoons in the Eastern Alaskan Beaufort Sea
Shallow estuarine lagoons characterize >70 % of the eastern Alaskan Beaufort Sea coastline and, like temperate and tropical lagoons, support diverse and productive biological communities. These lagoons experience large variations in temperature (−2 to 14 °C) and salinity (0 to >45) throughout the year. Unlike lower latitude coastal systems, transitions between seasons are physically extreme and event-driven. On Arctic coastlines, a brief summer open-water period is followed by a 9-month ice-covered period that concludes with a late-spring sea ice breakup and intense freshwater run-off. From 2011 to 2014, we examined interannual variations in water column physical structure (temperature, salinity, and δ18O) in five lagoons that differ with respect to their degree of exchange with adjacent marine waters and magnitude of freshwater inputs. Temperature, salinity, and source water composition (calculated using a salinity and δ18O mixing model) were variable in space and time. During sea ice breakup in June, water column δ18O and salinity measurements showed that low salinity waters originated from meteoric inputs (50–80 %; which include river inputs and direct precipitation) and sea ice melt (18–51 %). Following breakup, polar marine waters became prevalent within a mixed water column over the summer open-water period within all five lagoons (26–63 %). At the peak of ice-cover extent and thickness in April, marine water sources dominated (75–87 %) and hypersaline conditions developed in some lagoons. Seasonal runoff dynamics and differences in lagoon geomorphology (i.e., connectivity to the Beaufort Sea) are considered key potential drivers of observed salinity and source water variations.
Lagoons are a prominent feature of Arctic coastlines, support diverse benthic foodwebs, and provide vital feeding grounds for fish, migratory birds, and marine mammals. Across the Arctic, loading of terrestrial/ freshwater-derived organic carbon (CT) from watershed runoff and coastal erosion is predicted to increase with global warming, and may subsidize marine organic carbon as an energy source. To assess the importance of CT, we analyzed the trophic links and carbon assimilation pathways of twenty genera in five trophic guilds (suspension and filter feeders (Su/FF), surface and subsurface deposit feeders (Ss/De), epibenthic omnivorous invertebrates (Ep/Om), omnivorous fishes (Fish), and mammalian carnivores (Mam/Carn) as well as end-member organic matter (OM) sources. Because end-members had distinct carbon and nitrogen isotopic ratios, we employed a Bayesian stable isotope mixing model (simmr) to determine the contributions of CT, shelf OM, and marine microphytobenthos, to the diets of resident fauna. Ss/De and Ep/Om mainly assimilated marine-derived OM end-members. Su/FF, Fish, and beluga whales derived large portions of their diet from CT (N40%). We conclude that (1) coastal food webs are characterized by a high degree of omnivory and plasticity, (2) CT is an important OM subsidy to food webs, and (3) omnivorous fish transfer CT from lower to upper trophic levels.