Melting iceberg monitored up close by underwater robotic gliders

In a world-first, researchers have ventured remarkably close to one of the planet’s largest icebergs, gathering data that reveals how melting ice reshapes the surrounding waters and marine ecosystems of the Southern Ocean. Their findings, published recently in Nature Geoscience, shed new light on the iceberg’s environmental reach.

Back in February 2021, a team from the British Antarctic Survey (BAS) and the National Oceanography Centre (NOC) launched robotic gliders from the research vessel RRS James Cook, just 23 kilometres from the colossal iceberg A-68a near South Georgia in the sub-Antarctic. The mission marked a bold step into largely uncharted waters – both literally and scientifically.

Gathering data on icebergs is notoriously difficult. Large-scale movements of giant icebergs can be tracked with satellites, but ships will not get close as smaller scale movements are currently unpredictable. This means the data needed by researchers to develop accurate models – critical for predicting future climate change – is often missing.

Winter Water

The gliders collected data on the ocean’s salinity and temperature, along with chlorophyll (a proxy for productivity) and optical backscatter, which measures the particles suspended in the water.

The unique measurements revealed that as the iceberg melts from beneath – a process called basal melting – a layer of water called ‘Winter Water’ (formed in the Austral summer when warmer waters cap cooler winter waters below) is ‘eroded’. This band of cold water, only present in this time period, provides a barrier between surface and deeper waters, restricting nutrients from reaching subsurface layers.

By eroding this barrier, nutrient-rich deep waters can rise towards the surface, along with mineral-rich particles, such as iron and silica, from the melting iceberg. These nutrients play a key role in stimulating primary productivity creating food for the charismatic animals that live in the Southern Ocean.

Since the A-68a calved in 2021, several more megabergs have made their way towards South Georgia. Most notable of these is A-23a, which grounded on the island’s continental shelf earlier this year. Researchers on the RRS Sir David Attenborough recently collected samples from the iceberg as they transited past as part of the BIOPOLE 2 science mission which will be analysed back in the UK.

Read the full article, complete with expert insights, here.