Stratospheric Ozone Depletion - The Changing Arctic Environment: The Arctic Messenger - page 116

to the dynamics between sub-Arctic birch trees and caterpillars of the autumn moth, espe-
cially in combination with climate warming. The moth compensates for the reduced size
and nutritive value of birch trees exposed to higher UV by eating up to three times as much
as normal. This causes significant forest damage. The situation is exacerbated by winter
climate warming, which is increasing the overwinter survival of moth eggs. There is very
little information relating to trophic impacts on larger herbivores.
The first limiting factor on the impact of UV radiation on aquatic life is how far it can
penetrate below the surface. In clear oceanic and lake waters, UV-B can penetrate tens of
metres, but in cloudy waters, it can be almost entirely absorbed in the upper centimetres.
This roughly corresponds with the upper mixed-layer euphotic zone, within which photo-
synthetic phytoplankton are responsible for most oceanic and much lake primary produc-
tion. The UNEP 2010 ozone assessment showed that phytoplankton, fish eggs and larvae,
zooplankton and other animals from higher trophic levels that inhabit the euphotic mixed
layer can be adversely impacted by UV radiation. For example, UV radiation penetrates
well into the euphotic zone in the Gulf of Maine, a key nursery area for the embryos and
larvae of the Atlantic cod. In experimental studies, significant mortality of cod embryos
and a significant decrease in the length of young cod occurred following exposure to UV
radiation equivalent to the 10-metre depth level in the Gulf of Maine. This represented a
level of UV exposure that is common in many fish-spawning areas.
Calcium carbonate efficiently absorbs UV radiation. In the climate chapter, we will
spend some time looking at how increased levels of carbon dioxide in the atmosphere are
leading to acidification of the oceans. At the same time, we will see how increasing acidity
makes it difficult for many marine organisms to incorporate calcium carbonate into their
shells and other skeletal structures. For example, in experimental studies, Gao and col-
leagues found that increased acidity depressed calcification rates in the marine coccolitho-
phore Emiliania huxleyi . This resulted in a thinning of the calcium carbonate-containing
scales (coccoliths) that surround the organism. Therefore, the effectiveness of the cocco-
liths to protect the organism from UV radiation is diminished. This could be a signific-
ant finding. Planktonic coccolithophores are responsible for much of the photosynthetic