The area of sea ice during the winter is greater than large terrestrial biomes such as grasslands and deserts and can cover up to 40% of the Southern Ocean (Lizotte 2001). Hence the sea ice (or pack ice) is an important area of study and will be the main focus of this blog.
Pack ice sampling methods and some basic information on this habitat is shown in the following link, a video from the University of Alaska Fairbanks: Sea ice survey techniques and basic information.
Productivity in the oceans comes mainly from unicellular algae in the form of diatoms (Figure 1), however several other organisms can contribute to the overall biomass, such as macroalgae, photosynthetic dinoflagellates and nanoflagellates, chrysophytes and cyanobacteria (Thomas 2004). The relative importance of these other species is becoming increasingly greater as more is learned about this unique ecosystem (Garibotti et al. 2005)
Within the ice, the algae have the highest productivity in the lowest section where the temperature and salinity remain the most constant; however algae inhabit the brine channels between the ice lattices and the melt pools on the ice surface. The best studied of these algal forms is the diatom, with over 200 Arctic species and 100 Antarctic species identified (Thomas 2004).
The in-ice average total algal biomass for the Antarctic of 133mg chlorophyll a m-2 is greater than the average of 88mg chlorophyll a m-2 for the Arctic. The increase in the concentration at the Antarctic is due to the increase in biomass due to platelet ice. Greater species richness is found in the Antarctic than the arctic; this is likely to be due to the greater area of the southern ocean and its isolation from life from other oceans (Thomas 2004).
Outside of the ice, ice edge blooms of microalgae can develop in the surface waters in boreal and austral late spring and summer when the ice is melting. These blooms tend to be inoculated by the species dominating within the ice and are major sites of primary production, lasting several weeks and spreading hundreds of kilometres (Lizotte 2001).
Primary productivity by algae is the basis for most sea ice communities and helps support a large range of higher vertebrate and invertebrate species, bacteria and viruses (Lizotte 2001, Hashihama et al. 2010). Understanding the processes that determine algal growth will help us understand the ecosystem as a whole.
It is important to understand this extreme environment as we move forward into a period of climatic uncertainty, as some models on the impacts of climate change use the pack ice environment as a carbon sink, whilst others as a source. The impact of loss of ice on this system is poorly understood and until the ecological pathways in this habitat are understood, climate change modelling is likely to be inaccurate (Arrigo et al. 2010).