Skating on thin ice..?

It seems we can expect the Arctic to go green in future years - but that won't be good news for species threatened by Climate Change.
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Science, like a cat on a hot tin roof, doesn’t stand still. Should it ever stand still it will wither and die. To avoid this fate, it needs to keep moving. Moving for science means advancing knowledge by continuing to ask questions and building upon what has gone before. In that way it helps to define and refine our view of the world. Although this is not the place for a long essay about the Scientific Method and how science works, insight into the gradual, bit-by- bit, progress of science can be illustrated by a look back into the Cuttings’ archives.

massive congregations of greenish phytoplankton swirl in the dark water around Gotland
In the style of Van Gogh’s painting Starry Night, massive congregations of greenish phytoplankton swirl in the dark water around Gotland, a Swedish island in the Baltic Sea. Phytoplankton are microscopic marine plants that form the first link in nearly all ocean food chains. Population explosions, or blooms, of phytoplankton, like the one shown here, occur when deep currents bring nutrients up to sunlit surface waters, fueling the growth and reproduction of these tiny plants. Image: USGS/NASA/Landsat 7 / Wikipedia

Almost five and a half years ago we reported on an oceanic algal bloom that occurred not in the open sea – where it might be expected – but beneath Arctic sea ice. That was a bizarre phenomenon since the commonly held view was that light conditions under the ice would be too low to support such an event. Nevertheless, happen it did. Although the reasons for this bloom were uncertain, Kevin Arrigo et al. did suggest that it may partly be due to thinner ice in the region (which would let through more light than thicker ice) and the presence of so-called melt pondspuddles of melted ice – on top of the ice that permitted the ice beneath them to transmit four times more light than snow-free ice. Subsequent modelling of the process predicted that those ice and melt conditions could increase growth of shade-adapted Arctic phytoplankton and increase NPP (net primary productivity) of the area in the way observed in nature.

Now, Christopher Horvat et al. have taken that modelling approach further and confirmed the contribution of melt ponds to a more bloom-favourable light environment beneath the ice. But they also point out that the contribution of thinner ice to the phenomenon is more important than melt ponds. And noting the prevalence of thinner ice in the Arctic [I wonder what might have caused that..?] over the past 30 years – and therefore the possibility of more extensive sub-ice blooms – they raise a note of caution about our ideas of the ecology of this area because the ‘foundation of the Arctic food web is now growing at a different time and in places that are less accessible to animals that need oxygen’ (presumably they here have in mind air-breathing mammals such as whales and seals that would find it harder to get oxygen beneath ice rather than in open water)’.

They also remind us that light isn’t the only abiotic factor needed for a bloom to develop, as the role of nutrients also needs to be taken account of in more comprehensive models.* So, corroboration for the original work of Arrigo et al., but there remain more questions to answer, more investigations to be undertaken, more science to do. Like money (apparently), science never sleeps.

* They also point out the difficulties in detecting and monitoring sub-ice blooms because satellite-based approaches – used to monitor chlorophyll levels on land, in freshwaters and the oceans to give an estimate of photosynthesis, hence NPP – can’t detect chlorophyll through the ice. This probably partly explains why sub-ice blooms are likely to have been under-reported and their contribution to ocean ecology under-appreciated.

References

Arrigo, K. R., Perovich, D. K., Pickart, R. S., Brown, Z. W., van Dijken, G. L., Lowry, K. E., … Swift, J. H. (2012). Massive Phytoplankton Blooms Under Arctic Sea Ice. Science, 336(6087), 1408–1408. https://doi.org/10.1126/science.1215065

Palmer, M. A., Saenz, B. T., & Arrigo, K. R. (2014). Impacts of sea ice retreat, thinning, and melt-pond proliferation on the summer phytoplankton bloom in the Chukchi Sea, Arctic Ocean. Deep Sea Research Part II: Topical Studies in Oceanography, 105, 85–104. https://doi.org/10.1016/j.dsr2.2014.03.016

Horvat, C., Jones, D. R., Iams, S., Schroeder, D., Flocco, D., & Feltham, D. (2017). The frequency and extent of sub-ice phytoplankton blooms in the Arctic Ocean. Science Advances, 3(3), e1601191. https://doi.org/10.1126/sciadv.1601191


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