Marine sediments as archives of past climate and recent anthropogenic changes

Dust aerosols play a direct role in Earth's energy balance by scattering as well as absorbing radiation. Mineral dust and its associated nutrients also fertilize ecosystems and thus influence climate indirectly via photosynthesis and carbon uptake. However, large gaps exist in our understanding of the global dust cycle, in part due to the severe lack of direct observations of dust deposition in present and past environments. Mineral dust and its effect on radiative forcing and future climate have been identified as critical areas of research by the Intergovernmental Panel on Climate Change (IPCC). The first objective of this proposal is to investigate how much dust was deposited where, at what time, and from which sources, and whether changes in dust deposition caused changes in phytoplankton productivity and carbon removal from the upper ocean-atmosphere system. We combine measurements of a novel radioisotope tracer (232Th) with other geochemical proxies in marine sediment cores to generate new paleo records of dust deposition and organic carbon fluxes in the global ocean. The results are compared to simulations of state-of-the-art coupled climate models, such as the Community Climate System Model (CCSM), which are used in climate change scenarios by the ICPP and provide time slice as well as transient targets for hindcasting studies of the dust cycle. Research related to this objective generates critical new knowledge on the dust and carbon cycles in the undisturbed atmosphere-ocean system of the past, which is a recognized pre-requisite for the accurate prediction of future climate conditions.

In addition to recording past environmental conditions, marine sediments act increasingly as a sink for pollutants from human activities, especially in coastal areas. Using highly similar geochemical tools as above, the second objective of this research program is to investigate metal fluxes in coastal sediments near finfish aquaculture operations. Canadian aquaculture production has expanded fourfold since the 1990's, reaching ~187,000 tonnes worth $967 million in 2015. However, aquaculture related activities appear to cause increased accumulation of harmful metals, such Cu and Zn, in underlying sediments. We will analyze metal fluxes in coastal sites that are proximal and distal to finfish aquaculture operations and compare observed levels with baseline values (pre-Anthropocene, pre-industrial). We will test whether metal concentrations exceed Probable Effect Levels (PEL) identified by the Canadian Council of Ministers of the Environment. If so, we will investigate whether there is a risk of metal re-mobilization back into the water column. Research related to objective 2 generates new insight that will advance our understanding of environmental sustainability in coastal areas and contribute to sustainable resource extraction in Canada.