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.


Organic Carbon Cycling in Antarctic Lakes

Lakes in the McMurdo Dry Valley of Antarctica are permanently covered by 3-6m of ice that overlies 20-85 m water columns. These closed-basin lakes have strong, permanent chemoclines and receive <5% of ambient light in summer (no light in the polar winter). Phytoplankton photosynthesis produces 2000-10,000 kg C yr-1. Streams deliver allocthonous organic matter (OM) when cyanobacterial mats that grow on steam margins are flushed into the lakes during high flows. OM loss rates from sinking and grazing are presumed to be low. Decomposition rates are not well constrained but are also likely low (<0.1% per day) due to low temperatures (~-5°C). To determine if decomposition is a significant OM sink, I will assess microbial mineralization rates at several depths in Lakes Fryxell and Bonney by measuring the rate of 14C-CO2 released from 14C-labeled autochthonous and allocthonous OM sources.

Many aspects of Dry Valley lake ecosystems are predicted to change under a warming climate, including thinning lake ice cover and elevated stream flow. These processes will increase in situ production and stream OM inputs. To predict how lake ecosystem functioning will be affected, it is important to better constrain carbon loss mechanisms, including microbial decomposition.

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. (Harris et al. 2017).

Quantifying terrestrial subsidies to Arctic lagoon food webs

My M.S. research at UT Austin focused on ecological and hydrological observations of hypersaline lagoons in the eastern Alaskan Beaufort Sea. I determined salinity and temperature regimes in coastal lagoons and their relation to source waters (precipitation, sea ice melt, and marine water) using stable oxygen isotopes and salinity as tracers (Harris et al. 2017). I also worked with bayesian stable isotope mixing models to quantify the assimilation of terrestrially-derived carbon by nearshore consumers– from invertebrates, to fish, to polar bears using stable isotope mixing models. (Harris et al. 2018).

Poster: Dunton, K.H., Schonberg, S.V., Harris, C.M., Bonsell, C., Iken, K., Bluhm, B.A. 2016. Trophic relationships and infaunal community structure of the Beaufort Sea Shelf. ASLO Meeting.