During my postdoc at the University of British Columbia, I am investigating the cycling of the potent greenhouse gases methane (CH4) and nitrous oxide (N2O) in the Canadian Arctic. The rapid environmental changes occurring in the Arctic, which is warming at twice the rate of the rest of the world, have the potential to alter greenhouse gas emissions to the atmosphere, potentially creating significant climate feedbacks.
We are collecting measurements from coast guard icebreakers, conducting helicopter-based sampling of rivers in the Canadian Arctic Archipelago, and collecting a year-round time-series at the new Canadian High Arctic Research Station in Cambridge Bay, Nunavut.
Seasonality of CH4 emissions in Cambridge Bay, Nunavut
We are collecting year-round time-series of CH4 measurements in Cambridge Bay, Nunavut, in a river and estuary. We have demonstrated that extremely high CH4 concentrations occur in riverine and estuarine waters during the spring melt period (50 to 1000 times greater than the concentrations throughout the rest of the year), and that this CH4 is rapidly ventilated to the atmosphere when ice cover retreats. In 2018, we used a robotic kayak (the WHOI ChemYak) to obtain three-dimensional maps of CH4 and CO2 distributions during this dynamic melt period. A preprint on this work is available at EarthArXiv. An interview with my coauthor Dr. Anna Michel, one of the developers of the ChemYak is available from WHOI Oceanus.
Video of the ChemYak in Cambridge Bay, featuring my coauthors Victoria Preston and Kevin Manganini. Video by C. Manning
A multi-year record of greenhouse gas distributions across the North American Arctic Ocean
We are performing vertical profile measurements at repeat stations across the North American Arctic Ocean in collaboration with ArcticNet/Amundsen Science and Fisheries and Oceans Canada. The measurements from 2015-2018 allow us to observe interannual variability in gas distributions and predict how greenhouse gas cycling and emissions may change as the Arctic continues to warm. In particular, we observe strong interannual changes in CH4 and N2O distributions in the shallow Bering and Chukchi Seas associated with changes in water mass distributions. The image below shows where we collected samples in 2015-2017.
Nitrogen cycling and circulation in Baffin Bay investigated with isotopic measurements of N2, N2O, and NO3–
Abstract of upcoming presentation at the 2020 Ocean Sciences Meeting:
Baffin Bay is a marginal sea connecting Pacific waters traveling through the Arctic to the North Atlantic via the adjacent Labrador Sea. Pacific source waters entering Baffin Bay via the Canadian Arctic Archipelago have a fixed nitrogen (N) deficit as a result of denitrification, while the North Atlantic is a site of significant nitrogen fixation. Here we use isotopic and concentration measurements of NO3–, N2O, and N2 in Baffin Bay and surrounding waters to determine water mass origins and quantify fixed N sources and sinks. The long residence time of Baffin Bay Bottom Water allows distinctive geochemical signatures to accumulate. Excess N2O and N2 in basin deep waters, as well as a fixed N deficit (negative N*), indicate that sedimentary denitrification of organic matter is a significant fixed nitrogen sink within Baffin Bay. Isotopomeric measurements of N2O, which show strong enrichments in δ18O with depth, indicate that N2O derived from incomplete denitrification has diffused out of the sediments and into the water column. We quantify the excess N2 from denitrification using clumped isotope measurements (for the first time in an oceanic setting) and compare the results with N2/Ar-based estimates of excess N2 from denitrification. Isotopic measurements of NO3– suggest that the sedimentary denitrification is fueled by remineralization of organic matter produced in northern Baffin Bay, thereby regulating the nutrient inventories that are exchanged with adjacent oceanic regions. This study demonstrates that coupled isotopic measurements of multiple nitrogen species provide new insights into biogeochemical cycling and water mass circulation in a rapidly changing Arctic system.