Sentinel-1 monitors growing crack in Larsen-C

Sentinel-1 monitors growing crack in Larsen-C

Radar mission Sentinel-1 continues to monitor the growing crack in Antarctica’s Larsen-C ice shelf, which is expected to produce a massive iceberg

Two Sentinel-1 radar images from 7 and 14 April 2017 have been combined to reveal the growing crack in Antarctica’s Larsen-C ice shelf.

CPOM scientist Dr Anna Hogg said: “We can measure the iceberg crack propagation much more accurately when using the precise surface deformation information from an interferogram like this, rather than the amplitude – or black and white – image alone where the crack may not always be visible.”

Credit: Contains modified Copernicus Sentinel data (2017), processed by A. Hogg/CPOM/Priestley Centre, CC BY-SA 3.0 IGO Description

When the ice shelf calves this iceberg it will be one of the largest ever recorded – but exactly how long this will take is difficult to predict. The sensitivity of ice shelves to climate change has already been observed on the neighbouring Larsen-A and Larsen-B ice shelves, both of which collapsed catastrophically in 1995 and 2002 respectively.

These ice shelves are important because they act as buttresses, holding back the grounded ice that flows towards the sea, and contributes to present day sea level rise.

The Copernicus Sentinel-1 two-satellite constellation is indispensable for discovering and monitoring events like these because it delivers radar images every six days, even when Antarctica is shrouded in darkness for several months of the year.

CPOM is continuing to analyse Sentinel-1 data, distributing maps of ice velocity for key outlet glaciers of the Antarctic and Greenland ice sheets in near real time. The velocity maps are produced by tracking moving features in synthetic aperture radar data acquired by Sentinel-1.

Phytoplankton blooms under Arctic sea ice

In 2011, researchers observed a massive bloom of phytoplankton growing under Arctic sea ice – conditions that should have been far too dark for anything requiring photosynthesis to survive.

Dark areas of Arctic sea ice show where conditions have become suitable for algae and phytoplankton underneath the ice. Credit: NASA

Using mathematical modelling, researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) found that thinning Arctic sea ice may be responsible for these blooms and that the conditions that cause phytoplankton blooms have become more common. This has the potential to cause significant disruption in the Arctic food chain.

The research, published in Science Advances, involved CPOM scientists David Schroeder, Daniela Flocco and Danny Feltham from the University of Reading.

Phytoplankton shouldn’t be able to grow under the ice because ice reflects most sunlight light back into space, blocking it from reaching the water below.

But over the past decades, Arctic ice has gotten darker and thinner due to warming temperatures, allowing more and more sunlight to penetrate to the water beneath. Large, dark pools of water on the surface of the ice, known as melt ponds, have increased, lowering the reflectivity of the ice. The ice that remains frozen is thin and getting thinner.

The big question was how much sunlight gets transmitted through the sea ice, both as a function of thickness, which has been decreasing, and the melt pond percentage, which has been increasing.

Chris Horvat, first author of the paper and graduate student in applied mathematics at SEAS explained: “What we found was that we went from a state where there wasn’t any potential for plankton blooms to massive regions of the Arctic being susceptible to these types of growth.”

The team’s mathematical modeling found that while the melt ponds contribute to conditions friendly to blooms, the biggest culprit is ice thickness.

Twenty years ago, only about 3 to 4% of Arctic sea ice was thin enough to allow large colonies of plankton to bloom underneath. Today, the researchers found that nearly 30% of the ice-covered Arctic Ocean permits sub-ice blooms in summer months.

Horvat added: “All of a sudden, our entire idea about how this ecosystem works is different. 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.”

Dr Schroeder summarised:  “This study demonstrates that improving the sea ice model leads to a step forward in our understanding of how the Arctic is responding to climate change.”

The researchers hope their model will be helpful for planning future expeditions to observe these blooms and measuring the impact this shift will have on ecosystems.

Read the full paper: Horvat et al. (2017) The frequency and extent of sub-ice phytoplankton blooms in the Arctic OceanScience Advances, 3, 3, 2375-2548.

Further information can be found on the Harvard and Reading University websites, as well as via extensive media coverage.