Biodiversity in the cryosphere

As one of Earth's major biomes, the Cryosphere (taken from the Greek 'krios' meaning cold, frost or ice) is extremely important to consider when trying to understand global biodiversity. The Cryosphere encompasses those parts of the world which are frozen including, ice sheets, glaciers, frozen rivers, lakes, sea ice, permafrost and ice shelves. Today, I am focusing on the importance of sea ice to Arctic biodiversity after being fascinated by the paper published from Post et al (2013) introduced to me by my global environmental change lecture on the 6th December. With it being published only a few months ago, I decided to read the full paper and became instantly intrigued by polar biodiversity.

Sea ice compromises unique ecosystems in, on and under the ice. This habitat is critical for many species including vertebrates, diatoms, also terrestrial productivity and aquatic diversity. With 80% of the tundra in the Arctic lying within 100km of an sea ice covered ocean, Arctic ice loss driven from amplification Arctic warming is vital for ecological dynamics in this area (Post et al. 2013). Arctic amplification is the melting of ice due to a positive feedback albedo system. Ice has a high albedo therefore reflecting sunlight keeping the poles cool. However through ice melt, more of the Arctic ocean becomes exposed and due to oceans being darker they have a much lower albedo. This means they absorb heat warming the oceans and the atmosphere. As the oceans absorb heat, they also have to release this increased heat to enable the sea ice to form for the next year. Due to this feedback, the more ice loss the longer it takes for oceans to release the heat it has absorbed and therefore sea ice formation gets delayed. This can have affects for semi-aquatic species such as polar bears which use the sea ice for reproduction ground and for resting during long migration routes.

With anthropogenic warming Arctic sea ice extent has slowly been declining.

Source. A) Graph showing the declining annual minimum Arctic sea ice extent from 1979 to 2012. Although,  there is seasonal variability the overarching trend is a decline. B/C) Two maps showing the percentage concentration loss of sea ice with the scale bar showing -5% to 5% change. B is from 1979-1999 and C from 2000 -2011. 


The trend seen in the maps is showing percentage loss, especially around the edges of the sea ice, due to warming oceans.

The direct effects of Arctic sea ice loss

1. Primary producers depend on the sea ice habitat, underpinning the whole Arctic marine food web.

- With the loss of sea ice, this is a loss of habitat for algae and phytoplankton.  The timing of the algae bloom which is ultimately driven by light penetrating the ice when it is thin enough, is vital for the reproduction of zooplankton grazers. Disruption of this timing due to accelerated ice melt has created mismatches for zooplankton production timing and the consumers up the food chain.
- Earlier phytoplankton blooms can shorten the length for primary productivity consequently affecting the zooplankton production and the Arctic cod species that feed on them (Post et al. 2013).

2. With ice melt comes increasing freshness of the Arctic ocean.
- This reduces the nutrient availability for phytoplankton which limits their productivity despite increased solar penetration through ice thinning.

3. As previously touched upon, vertebrate species such as polar bears require sea ice for reproduction and resting and therefore they are directly implicated by sea ice thinning. One species also effected is the ringed seal (Gohring, 2012). More than two thirds of the Arctic has been estimated to have insufficient snow cover for ringed seals to reproduce challenging their whole survival. A ringed seal is currently under consideration for the threatened species list due to the way it builds caves to rear its offspring in snow drifts on sea ice (NOAA, 2013).  (Hezel et al. 2012) estimated that snow drifts must be at least 20cm deep to support the caves. As sea ice disappears, there is no where for the snow to pile up, ultimately declining the area where the seals can reproduce. What is also worrying is that with earlier snow melt year on year, the caves will melt also much earlier, leaving the young vulnerable to the outside conditions and predators.

Next week, I will be continuing the polar theme by exploring the indirect impacts of sea ice loss in the Arctic so keep those eyes peeled. Only two weeks till christmas!!

Score Board Update: Anthropocene 4 - 2 Biodiversity.