An international team of researchers, including a glaciologist at Newcastle University, UK, has discovered remarkably well-preserved glacial landforms buried almost 1 km beneath the North Sea.
The team used sound wave, known as seismic, data to reveal Ice Age landforms buried beneath almost 1 km of mud in the North Sea. The results, reported in the journal Science Advances, suggest that the landforms were produced about 1 million years ago, when an ice sheet centred over Norway extended towards the British Isles.
This is important because the timing of this ice advance corresponds to a period of global cooling called the Mid-Pleistocene Transition.
Glacial landforms reveal how past ice sheets responded to changes in climate, which can help to make better predictions about how today's ice sheets will respond to climate warming. A challenge is that glacial landforms are often buried beneath thick layers of sediment, preventing their identification.
Dr Christine Batchelor, Senior Lecturer in Physical Geography, Newcastle University, played a key role in the research by helping to map and interpret the landforms. "To fully understand the linkages between ice sheets and climate, we need to study how past ice sheets responded to long-term changes in climate," said Dr Batchelor. "Using modern seismic data, our results suggests that ice sheets in northwest Europe expanded significantly in response to climate cooling about 1 million years ago."
Dr Dag Ottesen from the Geological Survey of Norway, the paper's lead author, said: "This study was made possible by the availability of 3D seismic data from the North Sea, which allowed us to examine the buried landforms in striking detail."
3D seismic technology was developed to assess sediment suitability to host oil and gas or renewable infrastructures. However, this same data can be used to study buried landforms produced by glacial processes.
The mapped landscape includes streamlined features that were carved beneath the former ice sheet and ridges that record the imprint of the ice sheet as it started to retreat. Despite their ancient age, the landforms have striking resemblance to similar features produced by ice sheets much more recently.
The buried landforms provide new knowledge about the mechanisms by which ice sheets retreat. In order for such subdued landforms to remain unmodified, the former ice sheet must have retreated rapidly by lift-off and floatation of its frontal margin.
In addition to glacial landforms, the researchers also found elongated furrows incised into the former seabed, which they interpreted to have been produced by strong ocean currents. These landforms are even more deeply buried than the glacial landforms, showing that they were produced prior to the advance of the ice sheet.
"With our high-resolution data, we can see that the shape and size of the furrows is consistent with an origin as ocean current furrows," said Dr Ottesen. "This differs from previous interpretations of these features as glacial landforms, re-writing our understanding of North Sea glacial history."
By providing a new level of detail about the buried landforms, the findings shed light into the evolution of the North Sea in our recent geological past. The study shows that the North Sea was characterised by strong ocean currents prior to about 1 million years ago, after which it became more directly influenced by ice sheets.
The research team acknowledge that a limitation of the study is a lack of data about the precise age of the landforms.
"A wealth of seismic data are now available for the North Sea", said Dr Batchelor. "The next step is to acquire long sediment cores that can allow researchers to better understand the timing of glacial events."
Other co-authors are Helge Løseth at Equinor ASA, Trondheim and Harald Brunstad at Aker BP ASA, Trondheim.
