Ancient Icebergs Reveal What’s Coming

A study by Utrecht University researchers has solved a decades-old Antarctic mystery, revealing that massive icebergs were navigating the Southern Ocean millions of years earlier than previously thought – a discovery with profound implications for our understanding of climate change today.

The research, published in February in the journal Climate of the Past, used sophisticated computer modeling to demonstrate that Antarctica was already calving substantial icebergs 37 million years ago, challenging long-held assumptions that the continent’s massive ice sheet only formed around 34 million years ago.

Lead researcher Mark Elbertsen, working with oceanographer Erik van Sebille and earth scientist Peter Bijl, traced the mysterious journey of ancient ice-rafted debris (IRD) discovered at Ocean Drilling Program (ODP) Site 696 on the South Orkney Microcontinent, a location that sits squarely in what scientists call “Iceberg Alley.”

“The simulated trajectories suggest icebergs released along the coasts from Palmer Land to Dronning Maud Land can potentially deposit IRD at ODP Site 696,” the researchers note in their paper. Through meticulous analysis, they determined that the regions “offshore the Filchner Ice Shelf and Dronning Maud Land are the most likely source locations” for the ancient Antarctic material.

The scientific mystery began in 2017 when researchers found Antarctic debris near South Orkney dated to 37 million years ago – about 3 million years before Antarctica was thought to have developed its large ice sheet. This discovery raised fundamental questions about whether Antarctica had significant ice during the warmer late Eocene period and how icebergs could possibly survive the journey through the warm ocean conditions of that era.

Massive Icebergs Required

The Utrecht team’s modeling revealed that only substantial icebergs could have made the journey from Antarctica to the South Orkney Microcontinent during the late Eocene. Their calculations showed icebergs needed to be “on the order of at least 100 Mt or several tens of metres in thickness to survive the flow path.”

“Although this mass is at the larger end of the present-day range of common iceberg masses around Antarctica, the minimum estimates are not unfeasible,” the researchers concluded.

The study incorporated sophisticated melt rate calculations to determine how quickly these ancient icebergs would deteriorate in the warm Eocene waters. “The late Eocene iceberg melt rates are significantly higher than those found nowadays,” the researchers found, with total melt rates reaching almost 25 meters per day – dramatically higher than present-day rates.

Despite these intense melt rates, the team’s models confirmed that larger icebergs could indeed survive long enough to reach the South Orkney Microcontinent, depositing their rocky cargo as evidence of their journey.

Climate Implications Beyond History

This revelation isn’t merely academic. Understanding ancient iceberg patterns provides crucial context for what’s happening today as climate change accelerates ice loss around Antarctica.

“If climate change continues at its current pace, the Southern Ocean will soon face more and larger icebergs than in the past,” the researchers warn. Their findings help establish historical patterns that can inform predictions about how meltwater might affect ocean currents and carbon absorption in the coming decades.

The study also demonstrates that Antarctica received sufficient snowfall during the late Eocene to support substantial ice cap growth and iceberg production before the major cooling event that caused the continent’s complete freeze-over.

The research team is now expanding their investigation through the EMBRACER climate research program, focusing on periods in recent geological history that saw high rates of iceberg calving during transitions from ice ages to interglacial periods.

Modern-Day Parallel

In a striking parallel to their historical research, the scientists point to current events – the massive iceberg A23a that broke off from the Filchner ice sheet in 1986, remained grounded for decades, and recently began drifting toward South Georgia island.

Like the ancient icebergs they studied, A23a carries important ecological consequences. Scientists are monitoring it closely as it approaches South Georgia, an important breeding ground for penguins, seals, and albatrosses. While a direct collision could disrupt wildlife access to breeding grounds, the iceberg is more likely to run aground on the shallow waters surrounding the island or be guided around it by ocean currents.

The Utrecht University study provides valuable historical context for such events, suggesting that what we’re witnessing today has precedents stretching back millions of years – though now occurring in a rapidly warming world where such events may become increasingly common.

As researchers Bijl and van Sebille continue their collaboration, their work promises to shed light on how the increasing volumes of meltwater entering the Southern Ocean might influence deep ocean currents and the ocean’s carbon absorption capacity – critical factors in our planet’s climate future.