GEOTRACES: Multi-tracer investigation of the effect of climate change on nutrient and carbon cycles in the Arctic Ocean

• Main Authors: Francois, Roger, A. Mucci, C. Holmden, D. Varela, J. Cullen, K. Orians, M. Maldonado, P. Tortell, R. Rivkin
• Format: Dataset
• Language: English
• Published: Canadian Cryospheric Information Network 2016
• Subjects: Arctic Ocean; Beaufort Sea; Carbon fluxes; Climate change; Ice thickness; Mackenzie Shelf; Marine ecology; Nutrient cycling; Sea ice; Trace elements; International Polar Year-Multi-tracer investigation of the effect of climate change on nutrient and carbon cycles in the Arctic ocean; Arctic; Mackenzie River; Canada; ArcticNet; canada basin; International Polar Year; Mackenzie river; Phytoplankton
• Online Access: https://dx.doi.org/10.5443/11458; https://www.polardata.ca/pdcsearch/?doi_id=11458

Our sampling program took place from August 27, 2009 through September 12, 2009. It was part of Leg 3a of the 2009 CCGS Amundsen Expedition in the Arctic Ocean (ArcticNet 0903). Sampling started in the Mackenzie River delta and continued into the Beaufort Sea (Shelf, slope and deep Canada Basin). Various measurements (temperature, salinity, nutrients, alkalinity, pH, primary production, bacterial production) and sampling (seawater, marine particles) were conducted at 10 stations. Underway measurements (temperature, salinity, trace gases) and sampling (marine particles) were also conducted along the cruise track. Sampling tools on stations were the ship's CTD/rosette (ArcticNet), a Trace-Metal CTD/rosette system (UVic / UBC) and large volume in-situ pumps (UBC). We conducted measurements and collected samples to document a suite of key physical (temperature, salinity, ice cover, light penetration), chemical (nutrients, trace metals, trace gases, radioisotopes, stable isotopes) and biological (phytoplankton and microbial assemblages, primary and microbial productivity, trace metal phytoplankton quotas) parameters in relation to proximity to the Mackenzie River delta, seafloor bathymetry and ice cover to elucidate the processes influencing phytoplankton growth and carbon cycling in the Arctic Ocean. In particular, we collected samples to study the processes which supply and remove trace metals, nutrients and carbon to and from the upper ocean, and conducted ship-board experiments to study how biological productivity is affected by various chemical and physical conditions. Through a combination of on-board measurements, experiments and subsequent laboratory analysis, our research program aims at: (i) documenting the pathways of addition, removal and cycling of key trace elements which act as biological micronutrients or tracers of carbon and nutrient cycles in the Arctic Ocean; (ii) elucidating the potential effects of changing ice cover and river discharge on productivity, carbon sequestration and trace gas emission in the Arctic Ocean; (iii) developing chemical tracers to establish a historical sedimentary record of Arctic Ocean productivity in relation to long term natural climate change. : Purpose: Significant environmental changes are under way in the Arctic, in particular, a large reduction in sea ice extent and thickness, as well as increasing river discharge. Primary production in the Arctic Ocean is highly seasonal and highest on the shelf and at the receding ice edge. As the summer ice cover shrinks and river input increases, the physical and biogeochemical processes that control both the productivity and the structure of the marine ecosystems it supports are bound to be affected. Yet, our limited understanding of the factors that control the supply and cycling of organic carbon and essential nutrients in Arctic waters prevents us from predicting the longer term consequences of such changes. A better understanding of carbon and nutrient cycling, and their evolution in response to changes in ice cover and river discharge is clearly important to better predict the impact of climate change on the socio-economic sustainability of northern Canadians communities, the carbon sequestration capacity of the Arctic Ocean, and the oceanic sources/sinks of climatologically active gases (CO2, CH4, N2O, DMS). To this end, our proposal aims to: (i) elucidate the mode of addition, removal and cycling of key trace elements which act as micronutrients (Fe, Cu, Zn, Cd) or tracers of sources or processes (Al, Ba, Ga, Mn, Cr, Th, Pa) impacting the carbon and nutrient cycles in the Beaufort Sea and Canada Basin; (ii) use this information to elucidate the effect of climate change on the productivity, carbon sequestration and trace gas emission in the Arctic Ocean; (iii) develop geochemical tracers (alkenone, delta 53C, uranium isotopes, 231Pa/230Th) that will provide a sedimentary record yielding insight into the past evolution of these processes in relation to past climate changes. This project is a contribution to an emerging international program called "GEOTRACES" whose goals are to document the processes that control the oceanic distribution of trace elements and their isotopes (chemical elements found at very low concentration in seawater) and establish their role as regulators or recorders of processes that affect the structure and productivity of marine ecosystems, the dispersion of contaminants in the ocean, the level of greenhouse gases in the atmosphere, and global climate. : Summary: Trace elements are chemicals that occur at very low concentrations, but play a role in the carbon cycle, marine ecosystems, and contaminant and climate processes of the oceans. This project is looking at the distribution and processes relating to trace elements in the Arctic Ocean. Specifically, how trace elements interact with changes in temperature, sea-ice cover, fresh water discharge, marine ecosystem structure and carbon sequestration capacity of the Arctic Ocean are being studied. Trace elements of interest include metals, such as iron and copper, as well as chemicals related to carbon and nutrient cycles, greenhouse gases and atmosphere-ocean interactions.