An explainer and a FAQ: phytoplankton blooms underneath sea ice.

Our paper: The frequency and extent of sub-ice phytoplankton blooms in the Arctic Ocean has recently been published in the journal Science Advances. 

Ice-covered regions were long thought to be ecological deserts, as sea ice is a strong reflector of solar radiation. Yet in 2011, scientists observed a massive bloom of phytoplankton underneath the sea ice in July in the Chukchi Sea, with chlorophyll concentrations among the highest ever observed in the world's oceans. 

We use mathematical modeling and observations to conclude that thinning of the Arctic sea ice may have led to a dramatic change in the under-ice ecology: massive blooms of photosynthetic critters known as phytoplankton now have sufficient sunlight to grow and bloom in the summer months, before the retreat of the ice edge. 

The proportion of the Arctic Ocean in July, from about 1980 to the present, in which sufficient light reaches under the sea ice to permit a bloom.

FAQ

What does this mean for Arctic ecology? 
At present, observations of under-ice algae and phytoplankton in the Arctic are hard to come by, but are being made more and more as this new type of bloom has come to scientific attention. The shift from a September ice-edge bloom to a July-August under-ice bloom in certain regions may mean that the food web has undergone a dramatic shift it may not be adapted to. 

What does this mean for Carbon uptake in the Arctic?
This is unclear. If the blooms occur in addition to those as the sea ice retreats, it is conceivable that more carbon is being taken up in the Arctic than previously though. However if now there is still only one annual bloom or period of phytoplankton growth, but it just occurs several months earlier, the impact on carbon fixation may be small. We need more observations to know!!! 

How certain are we that melt ponds are the reason for these blooms?
This is an area of debate. Melt ponds were likely responsible for the sunlight needed in the 2011 bloom observed by Arrigo and colleagues. However a similar under-ice bloom was observed during the 2015 N-ICE mission, in a region with snow-covered, unmelted ice. Here, it is thought that the presence of leads, or long cracks in the sea ice allowed for sufficient light penetration and blooming. 

Where can I find out more about these events?
Under-ice blooms have been observed by the Arrigo group (in the Chukchi Sea) and during the N-ICE expedition (around Svalbard), and potentially others!