Background and Rationale
Photo: NASA
Arctic sea ice is naturally variable; however, the current question is whether the observed changes in both multi-year and annual sea ice are a result of anthropogenic climate change (Fisher et al 2006). Sea ice can influence and be influenced by changes in global climate, as ice is closely linked to the circulation of warm and cool ocean currents. Past changes in sea ice therefore may provide useful insight into past climate regimes. Proxies such as microfossils, geochemical tracers and sedimentation have been widely used in reconstructing past arctic sea ice cover (de Vernal et al 2001). This study attempts to establish the relationship between diatoms and sea ice concentrations in Baffin Bay, Davis Strait and Labrador Sea, which will make it possible to make inferences from diatom sediment composition on sea ice extent. The results of this study will determine whether diatoms (unicellular, photosynthetic, siliceous microorganisms) are a viable proxy for sea ice concentrations in Baffin Bay, Davis Strait and Labrador Sea. Because diatoms are the most ubiquitous and abundant microorganisms in the arctic, it is important to add diatoms in the multi-proxy effort to determine past sea ice changes in the Baffin Bay, Davis Strait, Labrador Sea region. While diatoms have been widely used to reconstruct sea ice cover in the Southern Ocean (Taylor and McMinn, 2001; Gersonde et al 2005), northern North Atlantic Ocean (Justwan and Koc, 2008), and North Pacific Ocean (Katsuki and Takahashi, 2005), with the exception of preliminary studies undertaken by Williams (1986, 1990), there has been very little marine diatom research carried out in the eastern Canadian Arctic. The existing data on the Baffin Bay-Davis Strait area are limited to the research undertaken by Williams (1986, 1990).
Study Area
Besides the anthropic effects of sea ice change (on such industries as fishing, shipping and hunting), annual sea ice in Baffin Bay-Labrador Sea region is of crucial importance to ocean-atmosphere interactions. Sea ice in the area of study is very important because there is a complex relationship between the annual sea ice in the area and thermohaline circulation. Figure 1 depicts the role played by annual ("newly formed ice") sea ice in the formation of dense saline water. When sea ice forms, brine is excluded, salinifying the underlying water mass. When sea ice melts it is relatively fresh and will cause a freshening of the underlying ocean. This plays a large role in the formation of currents in Baffin Bay. Figure 2 shows the cold, fresh Baffin Current (cold and fresh due to the melting of sea ice) and the relatively warm West Greenland Current. Determining past sea ice concentrations can provide insight into the circulation regimes of the time, allowing researchers to compare past conditions to the present.
Figure 1. Depiction of the formation of a cold dense water mass linked to the formation of sea ice (Photo: Jayne Doucette, WHOI)
Figure 2. Map depicting the major currents in and around Baffin Bay, Davis Strait and Labrador Sea (Photo: AMAP)
Diatoms and Sea Ice - The Connection
Fig 3. SEM of sea ice diatom
Diatoms (Bacillariophyceae) are unicellular, photosynthetic algae found in all aquatic environments. The outer shell (or frustule; two overlapping valves similar to two sides of a Petri dish) of a diatom is composed of silica. The siliceous frustrule of a diatom is marked with distinguishing features, such as pores, processes, and striae. Diatoms are useful in numerous environmental applications because of their resistant siliceous frustules. Paleoecologists use preserved frustrules as a proxy for numerous conditions, such as temperature, salinity, and productivity in lakes, rivers, coastal regions and oceans over time. The high diversity of diatoms allows for such analysis, since each particular condition may have a very specific diatom species assemblage. Paleoecologists are able to determine sea ice conditions based on the autecology of species assemblages of diatoms and other microorganisms. More specifically, there is a certain community of microorganisms associated with arctic sea ice that has been termed sympagic communities (Horner, 1992).The preservation of diatom fossils in the Baffin Bay, Davis Strait, Labrador Sea area has been questioned in the past due to low nutrient levels and dissolved silica in the Northwest Atlantic waters and sediments (Gersonde, 1985). Therefore the first goal in this study is to determine whether diatoms are preserved in such quantities to be used in this particular analysis.
Specific diatom assemblages live in specific ecological niches. Sea ice retreat has been tracked by the presence of an assemblage that is associated with what is called the marginal ice zone (MIZ; von Quillfeldt, 2000; Justwan and Koc, 2008). The MIZ marks the area where open ocean begins to affect ice extent, which experiences the replacement of sea ice algal assemblages with polar open water algal assemblages (Horner, 1985). Light and temperature are often optimal in the MIZ, and sometimes upwelling occurs, which leads to the MIZ producing open water algal blooms (high productivity). Other factors inherently related to sea ice also play a large role in species composition, including salinity (influenced by meltwater and runoff), stratification, and ice condition (i.e., fast ice versus pack ice). In general, in the winter, the most abundant diatom species will be those that are adapted to living within the brine channels of sea ice (high salinity, low light etc.). When spring rolls around, there is an increase in melting of snow and ice, therefore a change in environmental conditions. Diatoms that are adapted to living in the "Marginal Ice Zone" will now dominate.
Specific diatom assemblages live in specific ecological niches. Sea ice retreat has been tracked by the presence of an assemblage that is associated with what is called the marginal ice zone (MIZ; von Quillfeldt, 2000; Justwan and Koc, 2008). The MIZ marks the area where open ocean begins to affect ice extent, which experiences the replacement of sea ice algal assemblages with polar open water algal assemblages (Horner, 1985). Light and temperature are often optimal in the MIZ, and sometimes upwelling occurs, which leads to the MIZ producing open water algal blooms (high productivity). Other factors inherently related to sea ice also play a large role in species composition, including salinity (influenced by meltwater and runoff), stratification, and ice condition (i.e., fast ice versus pack ice). In general, in the winter, the most abundant diatom species will be those that are adapted to living within the brine channels of sea ice (high salinity, low light etc.). When spring rolls around, there is an increase in melting of snow and ice, therefore a change in environmental conditions. Diatoms that are adapted to living in the "Marginal Ice Zone" will now dominate.
Fig 4: Simplified diagram of seasonal diatom assemblage shifts. Shift from sea ice assemblages to marginal ice zone (MIZ) assemblages in the early spring, from MIZ assemblages to more complex, open ocean assemblages in summer. Seasonality is variable.
Research Objectives
- Analyze surface sediment samples of Baffin Bay, Davis Strait and Labrador Sea to determine whether or not diatom frustules are preserved, indicating whether or not diatoms can be considered for use as a proxy for sea ice.
- Characterize the diatom community present in surface sediments of study areas, determining assemblage differences between sites.
- Compare diatom assemblages to sea ice concentration data to determine the relationship between diatoms and sea ice regimes in Baffin Bay, Davis Strait and Labrador Sea.
Expected Results
I expect to find that more known "sea ice diatom" species will be found in the higher latitudes, where there are higher sea ice concentration for a longer time each year. I expect to find differences in diatom assemblages based on latitude and on differences in monthly sea ice concentration, especially the between months of maximum and minimum sea ice concentrations.
