Previous research

Master's thesis: Seasonal and interannual variation in phytoplankton assemblages in a near-shore Antarctic sea-ice environment

Polar regions are especially vulnerable to climate change, and sea ice along the western Antarctic Peninsula has declined significantly in recent decades. My thesis documented changes in phytoplankton assemblages in a near-shore Antarctic environment, to assess the impacts of subtle changes in sea ice cover on the composition of these algal communities. Ryder Bay, near the British Rothera base, is considered representative of the conditions in Marguerite Bay and the greater western Antarctic Peninsula region as a whole. Over the summer growing season, all phytoplankton taxa were observed at high temporal resolution, in conjunction with the Rothera Oceanographic Time Series (RaTS) routine sampling regime.

Prior to this study, algal speciation data were limited to single samples taken during austral summer that showed diatoms (glass-walled, single celled algae) as the main taxon. We confirm that phytoplankton biomass is dominated throughout the growing season by large diatoms, with occasional, but significant contributions from small diatoms, dinoflagellates, and prymnesiophytes.

Additional samples from two previous austral summers allowed interannual comparison of diatom assemblages. These analyses revealed significant species richness and interannual variability between dominant species. First season samples were dominated by a succession of five main species groups. In contrast, the second season quickly came to be dominated by Proboscia inermis, which eventually comprised over 90% of the diatom biomass. This is the first report of such an extensive bloom of this species, a diatom only rarely seen in the sediment record and usually considered to indicate the presence of relatively warm, low-nutrient waters. While nutrients were relatively low, these data show that southward incursion of warmer waters is not a requirement for high abundance of this species.

Sediment trap analysis traced the sinking of diatom assemblages. Many of the dominant species from the surface were either absent from, or poorly represented in the traps. This may reflect the fragility of the fastest growing species groups and highlights a considerable discrepancy between sediment trap and surface water assemblages. The need to better understand this offset is crucial to our ability to reconstruct past environments from sediment samples; current methods linking sediment assemblages to conditions favouring similar surface communities will be flawed if the assemblage is heavily modified as it sinks.

Surface water conditions were relatively stratified across all three seasons. Phytoplankton biomass proxies indicate that high melt water inputs, from sea ice and glaciers, lead to high algal biomass in this region. Melt water inputs were greatest in the second season, resulting in the lowest degree of upwelled nutrient injection, but concentrating algae near the surface. Thus, despite the high biomass of the Proboscia bloom at the surface, carbon export was actually lowest during the second season, showing that single measurements of surface productivity are insufficient to estimate export potential. Our data also imply that increased melt water inputs due to warming do not necessarily increase carbon export in near-shore areas, an important discovery towards understanding how continued climate change will affect carbon cycling.

Bachelor's thesis: Copper requirements in coastal and oceanic diatoms

Click here for a .pdf version of “The effects of Cu and Fe availability on the growth and Cu : C ratios of marine diatoms.”

However, in several major areas of the open ocean (~30%), photosynthetic biomass is limited by low levels of iron. Iron is supplied to oceanic regions in the dust that blows off of the continents (called aeolian inputs). Three major areas of the ocean are considered iron-limited, where nutrient concentrations stay high because there is not enough iron available for the plankton to use all the nutrients up. These are the red and green areas in the map, where nitrate (a main phytoplankton nutrient) is high. Thus, these regions are called High-Nutrient, Low-Chlorophyll (or HNLC) regions. However, when iron is added to the water - either naturally by dust or by people for experimental reasons - the phytoplankton bloom, which shows that diatoms do in fact live in these regions, although their growth is very slow. This is similar to the way deserts appear lifeless, but bloom after the rain.