The Biological Carbon Pump in the Anthropocene

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The three main objectives of my DG proposal are central components to my larger goal to understand the Biological Carbon Pump (BCP), so that we may (a) evaluate its role in the distribution of pollutants and (b) determine how the ability of the ocean to sequester carbon may change. Since the industrial revolution the ocean has taken up 25-30% of anthropogenic carbon, yet it is unclear whether the ocean will continue to take up carbon as atmospheric pCO2 is increasing. Objective 1: Determine the strength of the gravitational settling particle flux pathway of the BCP in the North-West Atlantic: Although the Labrador Sea plays a central role in the global carbon cycle, as well as in the exchange of oxygen and CO2 between the surface and deep ocean, our knowledge of the role and variability of gravitational particle sinking and the loss rate of this flux with depths, is extremely limited for this region. Careful analysis of samples from moored, time-series sediment traps will provide information on seasonal variability of flux type and strength and of flux attenuation. Nutritional value of sinking matter, which provides the food source for organisms at depths will be investigated. Severe changes in nutritional value would impact food webs, including commercially valuable fish. Objective 2: Identify response patterns of phytoplankton to multiple stressors, e.g. shifts in temperature, light and carbonate chemistry. Recent research efforts have revealed that the response of phytoplankton to several simultaneous stressors is not additive, but complex, requiring targeted experiments to investigate interactive responses affecting growth, aggregation and sedimentation. Commonly only a single stressor and only the growth phase of phytoplankton are investigated. As phytoplankton primary production provides the maximum theoretical flux potential, changes in productivity, aggregation and sedimentation will drive shifts in the functioning of the BCP, and the potential for the ocean to sequester CO2. Loss of ice has the potential to alter sedimentation patterns, as ice algae and their exudates cause sinking ice edge blooms. These mechanisms will be investigated experimentally. Objective 3: Characterize the role of aggregation for the transport and fate of micro-plastics. Initial experiments show that small plastic particles may be incorporated into rapidly sinking aggregates, transporting them to the seafloor where benthic organisms and those feeding on them are exposed. As plastics are less dense than seawater, this pathway is unexpected and largely unexplored. A combination of detailed aggregation experiments and analysis of sinking material collected in sediment traps, will yield sedimentation patterns of plastic, and give insights to mechanisms driving their flux. Understanding these distribution pathways is a prerequisite for the mitigation and clean up of plastic pollution in the ocean, which Canada has pledged to in the "strategy on zero plastic waste".