The Dark Zone of Greenland

Greenland is the world鈥檚 largest 鈥渘on-continental鈥� island, and about 80听per cent听of this island is covered by the Greenland Ice Sheet. In recent years, however, the melting of this ice sheet has听accelerated, leading to an increased contribution to听rising听sea levels.听

A portion of听this听increased听melting can be attributed to the presence of dark algae on the ice sheet surface. Contrary to white, reflective ice, the dark听pigmentation听of听these听algae absorbs听sunlight and warms听the surrounding听ice, causing melting.听Climate change is causing Arctic summers to become warmer and longer than in the past. These longer summers allow for increased ice algal growth, and the resulting algal blooms are causing increased darkening and melting.听听

As a听geomicrobiologist,听Jenine听McCutcheon, a professor in the Earth and Environmental Sciences department at the University of 蓝莓视频,听has been studying Greenland鈥檚 glacier听algae in an effort to uncover their changing annual patterns. This research, done during her postdoctoral fellowship at the University of Leeds,听was published听January 25th in Nature Communications.听

鈥淲hat we鈥檙e trying听to do is to better understand how algal blooms form, why they form where they do and is there a way to predict how they鈥檒l form in future melt seasons,鈥澨齭ays听McCutcheon. 鈥淥ne season to the next,听algal blooms may change and vary in intensity, making them difficult to model year-to-year.鈥澨�

>听Professor听Jenine听McCutcheon听sampling snow and ice on the Greenland Ice Sheet.听
> Photo: Andrew听Tedstone, PhD听

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Understanding algal bloom development is important because these blooms darken the ice sheet surface, causing it to melt more quickly than ice that is free of glacier algae. Ice sheet darkening by glacier algae is just one reason听why听surface melting of the Greenland Ice Sheet has accelerated in recent decades. Since the Greenland Ice Sheet contains enough water to raise sea level by over听seven meters, it is crucial to understand all of the processes that impact melting in order to predict how melting will proceed in the years to come.听

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Behind the research

The study focused on听five听different locations along听a large band听on the Western edge听of the Greenland Ice Sheet known as the 鈥淒ark Zone鈥� due to its听low albedo (a measure of听the amount of听solar听radiation听reflected听by听a听surface).听The ice surface in this zone is made dark by听impurities such as algal cells, mineral dust, and black carbon (particles produced by fossil fuel combustion). Algal blooms are the primary cause of听the听darkening听observed听in this region.听听

dark zone pictured

>听Aerial photo of the Greenland Ice Sheet鈥檚 Dark Zone.
>听听Photo:听Professor听Jenine听McCutcheon听

In order to determine where听glacier听algae get听their听nutrients, the team measured the photosynthesis rate of听glacier听algae听in the presence of the different nutrients.听They听found that听there was a distinct improvement when听the algae听were provided with phosphorus.听The team concluded that the algal blooms听in this region听were regulated and limited by the presence of phosphorus.听

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Upon finding this, they analyzed听the surface听dust present in the Dark Zone around听the听algal blooms, and found听the mineral听hydroxylapatite.听Hydroxylapatite听contains听the听bio-available听phosphorus听needed to nourish the algae, and听likely听facilitates the development of glacier algal blooms by supplying phosphorus to the听ice听surface habitat.听

The reliance of algae on this mineral dust then creates a positive feedback loop, wherein听the more algae that bloom, the greater the ice sheet melting.听As听more ice melts, mineral听dust frozen in the ice听becomes听exposed, thus听providing more nutrients to help听the听glacier听algae grow. However, more studies are needed to quantify this feedback loop and measure its extent.听

鈥淭he findings of this study will impact how听we听predict where the blooms will happen in the future,鈥� McCutcheon听says.听鈥淲e鈥檙e working to be able to model these algal blooms and match them with satellite data to听get a better understanding of the overall impact of these algal blooms on ice sheet albedo reduction and resulting melting.鈥澨�

This research was done through an international collaboration by researchers from the United Kingdom, Germany, Belgium,听Canada,听and Denmark, and was funded by the UK Natural Environmental Research Council Consortium Grant.听