Eye in the sky watching Arctic blooms

By Martin Leggett - 07 Mar 2011 16:44:0 GMT
Eye in the sky watching Arctic blooms

Image Provided by the SeaWiFS Project, NASA/Goddard Space Flight Center, and ORBIMAGE

Every spring, as Arctic sea-ice retreats with rising temperatures, large swathes of the sea are re-exposed to the sun, and so blossom into life. Vast blooms of phytoplankton take advantage of the nutrient-rich sun-lit waters, starting off a cascade of life up the entire length of the Arctic food chain.

These blooms are not only important to fish populations, they also trigger a 'carbon sink' response, which feeds back into the wider carbon cycle. In order to get a better grasp of the effects of these yearly 'bloomings', scientists are now taking advantage of satellite technology to track their progress.

Phytoplankton are tiny microscopic plant-like organisms, that photosynthesize - in the process absorbing CO2, so removing carbon from the atmosphere. They thrive in the warm, oxygenated waters left behind as the sea-ice melts. This upper layer persists on top of the ocean as the melt-waters make it less salty, and so lighter, than the cold dense waters beneath.

Scientists have long known of the existence of blooms, monitoring them from cruises in various locations in the Arctic Ocean. But now real-time, region-wide information is at the hands of scientists from UK-based National Oceanography Center

They are using color data from NASA's SeaWiFs satellite to map out the extent and progress of the blooms - taking advantage of the color changes caused by the blooms themselves. As the phytoplankton concentrations build up, the satellite picks up the higher levels of green caused by the photosynthesis pigment - chlorophyll.

Combining a decade's worth of these data, with sea-ice mapping from the US National Snow and Ice Data Center (NSDIC), has allowed the team to map the evolution of the blooms, season by season. What they have found is that the blooms extend in bands, 12 to 60 miles wide, across the edge of the Arctic ice-cap. They usually follow the ice as it retreats - though sometimes holding position - and can persist for months on end, peaking closest to the ice edge.

The information gathered helps to tease out the implications of sea-ice loss, due to climate change, on the wider marine productivity of the Arctic. One of the team, Dr Andrew Yool, explained ''It is quite possible that ongoing climate change will lead to ice-free summers in the Arctic within the next few decades. As the melt season becomes longer, ice-edge blooms may propagate over larger distances, stripping out surface nutrients as they go.''

The team doesn't yet know whether this effect will lead to a boon for sea-life - or a loss. That depends on overall effect of sea-ice loss on ''complex factors affecting ocean stratification and mixing, and thus the availability of nutrients in sunlit surface waters.'' As with much Arctic science, keeping up with the implications of global warming is very much a process of playing catch-up - to the rapid-changes that are already being felt there.