Carbon is the building block of life and is transformed and exchanged within each sphere of the Earth’s system. The flow of carbon through ecosystems is of particular interest to the scientific community as the production of organic carbon through photosynthesis forms the fundamental base of energy production within most ecosystems, and its balance with subsequent respiration back to carbon dioxide ultimately determines whether ecosystems act as net sinks or sources of carbon to our atmosphere. Constraining the flow of carbon through ecosystems thus remains an important scientific priority.
The Greenland Ice Sheet is the largest permanent area of ice in the Northern Hemisphere and its vast surface is a uniquely microbe-dominated environment that contains diverse autotrophic (e.g. organic carbon producing) and heterotrophic (e.g. organic carbon consuming) communities. During summer melt seasons, the coincidence of liquid melt water, sunlight and nutrients allow substantial photoautotrophy on the ice surface, driving organic carbon accumulation and providing an energy source for associated heterotrophic communities.
Satellite image of the southwestern Greenland Ice Sheet showing the surface ice darkening caused by summer blooms of glacier algae (dark band down the centre of the image), which drive substantial photoautotrophy on the bare ice surface. Image from Williamson et al. (2020)
During the NERC funded Black and Bloom project (see www.blackandbloom.org) we recently demonstrated how a key group of supraglacial primary producers, Streptophyte glacier algae, dominate ablating ice surfaces of the Greenland Ice Sheet, forming widespread algal blooms each summer so large that they can be seen from space. We also showed how bacterial and fungal communities vary in association with these blooms, and the consequences of blooms for nutrient cycling and the darkening and melt of the ice surface itself.
Some of the Black and Bloom team take a well-earned break during helicopter transects across the Greenland Ice Sheet ablation zone to study glacier algal blooms in the summer of 2016.
Until now, however, these data have not been integrated to produce a robust empirical understanding of the carbon-cycling consequences of glacier algal blooms on the Greenland Ice Sheet, restricting our abilities to understand the importance of these blooms for the global carbon cycle or to project how they might change into the future.
Our supraglacial carbon cycling project aims to model how blooms of Streptophyte glacier algae develop across the entirety of the Greenland Ice Sheet, and to estimate their impacts to carbon cycling now and into the future.
We recently developed the first numerical model of glacier algal blooms on the Greenland Ice Sheet driven by physical data and under ridden by measurements of glacier algal physiology and spatiotemporal distribution that we made over the past few years.
Glacier algal bloom progression modeled for 2016 for sites across the southwestern Greenland Ice Sheet by Williamson et al. (2020)
For this project, we will apply our model ice sheet wide, verify outputs against new satellite tools recently developed by our collaborators that can directly monitor glacier algal blooms from space, and assess the spatiotemporal patterning in bloom progression and consequences for organic carbon accumulation. The next step will be to estimate the longevity of this carbon within the supraglacial system versus potential loss / consumption pathways. Finally, we will integrate data to produce a carbon budget for the Greenland Ice Sheet over the recent past and into the near future.
Watch this space for new project outputs and news…