Echoes of the Ice Age: Giant Icebergs in the North Sea

Newly discovered marks on the seafloor reveal that massive icebergs once drifted off the coast of the U.K.The scrape-marks show where the underside of these bergs dragged across the floor of the North Sea some 18,000 to 20,000 years ago, according to scientists at the British Antarctic Survey (BAS).

This is the first clear evidence that monster blocks of ice roamed in this area, less than 90 miles off the British coast, and offers valuable insights into how Antarctica’s frozen landscape could change as the continent warms up.

Marine geophysicist Dr. James Kirkham from the BAS described the icebergs that caused the deep grooves as enormous flat-topped, or ‘tabular’ icebergs. He added, Conservatively, they measured five to perhaps a few tens of kilometers in width—comparable to the area of a medium-sized U.K. city such as Cambridge or Norwich—and could be a couple of hundred meters thick.

unearthing the Past: How the Discovery Was Made

The plough-marks, preserved in the sediments buried beneath the present-day seafloor, date back to the last ice age, a period when an ice sheet covering much of the British and Irish Isles retreated due to a warming climate.

They were first spotted in seismic survey data that was used to locate sites for oil and gas drilling platforms in the Witch Ground Basin, situated between Scotland and Norway. Single grooves made by small bergs have been detected here before, but the hundreds of meters wide Witch Ground tramlines prove that mammoth flat-topped icebergs were also present.

Ice shelves and Tabular Icebergs: A Vital Connection

Tabular bergs are discharged from ice shelves,the floating fronts of glaciers that have flowed off the land into the ocean. Researchers infer that the British and Irish ice sheet also had these structures. Dr. Kelly Hogan, a marine geophysicist at BAS and co-author of the new study published in the journal Nature Communications, explains how this provides historical clues.

We can actually document the catastrophic collapse of these ice shelves at the end of the last ice age using our data, because around 18,000 years ago we detect a shift in the type of iceberg plough-mark recorded in seafloor sediments, from giant tabular bergs—produced by the normal calving lifecycle of ice shelves—to much more numerous and smaller icebergs as the ice shelves disintegrated.
Dr. Kelly Hogan, British antarctic Survey

Implications for Antarctica: Lessons from the North Sea

Ice shelves are critically important for ice sheet stability, BAS explains. They buttress and hold back glacial ice, which would otherwise drain much faster into the ocean. The regular breakaway of tabular bergs at the leading edge of shelves, occurring sometimes only every few decades, helps to maintain the glaciers behind them in a steady state.

Seventy-five percent of Antarctica is surrounded by these buoyant platforms. But it’s unclear how the frozen continent will shift as human-caused climate change bites.

A significant example of ice shelf breakdown is what happened to the Larsen B ice shelf. In 2002, rising air temperatures melted parts of the ice shelf’s surface, sending meltwater trickling thru the platform and shattering the ice into countless small bergs in the space of one week.

After the ice shelf disintegrated, the glaciers previously held back behind it sped up to several times their former speed, accelerating their contribution to sea-level rise.

The ancient North Sea plough-marks suggest this phenomenon occurred on a much larger scale when the British and Irish ice sheet was shrinking rapidly by 650 to 980 feet per year at its edges.

A remaining mystery is whether this speedy withdrawal was triggered by the collapse of its ice shelves or if the fragmentation was a symptom of ice sheet mass losses that were already underway. But better dating of the sediments might provide the answer.

It’s an captivating question that goes to the heart of how ice shelves influence the modern Antarctic Ice Sheet. If we observe a similar transition from large tabular icebergs to smaller icebergs,it could indicate the continent is about to experience significant and rapid mass loss.
Dr. Rob Larter, BAS co-author

FAQ: Icebergs in the North Sea

• When did these icebergs exist in the North Sea?

  These icebergs were present in the North Sea between 18,000 and 20,000 years ago, during the last ice age.

• How big were these icebergs?

  The icebergs were enormous, flat-topped tabular icebergs, measuring five to a few tens of kilometers in width and up to a couple of hundred meters thick.

• Why is this discovery important?

  This discovery provides insights into the behavior of ice sheets and their potential impact on future sea-level rise, particularly in the context of a warming climate.

• Where were these marks discovered?

  The marks were discovered in the Witch Ground Basin, situated between scotland and Norway, using seismic survey data.