“It’s an unassuming rock, greenish in colour, and just over 4cm in its longest dimension. And yet this little piece of sandstone holds important clues to all our futures.”
So opens a BBC story, “Climate change: A small green rock's warning about our future,” that features a discovery by Colorado College Professor of Geology Christine Siddoway, presented last week at the European Geosciences Union General Assembly. Usually held in Vienna, Austria, this year’s vEGU21 meeting was convened online because of COVID restrictions.
Siddoway presented in the session The Antarctic Ice Sheet: past, present and future contributions towards global sea level. Her abstract caught the attention of the EGU media team, who invited Siddoway to speak in the Scientific sleuthing: geoforensics & fingerprinting press conference on April 26. The event provided an opportunity for journalists to learn about some of the latest detection techniques that geoscientists use to trace geological materials to their point of origin on Earth, or in geological time.
As the EGU press team describes it, Siddoway seeks to “trace the source of cobbles dropped by icebergs in the Amundsen Sea — and explain how these clues offer new information regarding the previous extent of the West Antarctic Ice Sheet.” Sediment cores were recovered from Amundsen Sea by the drill ship JOIDES Resolution in 2019, far off the coast of West Antarctica.
Siddoway’s discovery centered upon one unassuming rock — a dropstone, or piece of ice-rafted debris, recovered from the ocean mud. Icebergs “floated” the piece of green sandstone away from Antarctica. The stone melted out, and dropped 2.5 miles to the seabed.
Using the latest “geo-fingerprinting” techniques, Siddoway and collaborators determined that the green sandstone came from the Ellsworth Mountains, the tallest range in Antarctica, surrounded in all directions by the massive Antarctic Ice Sheet. The range lies some 1,300 kilometers away from where the rock was found.
How could the rock travel from the inland high peaks out to the deep sea?
The answer is that the impermanent ice sheet must have melted away, leaving an open “inner passage” swept by ocean currents, which carried icebergs seaward. The scenario is being investigated by International Ocean Discovery Program Expedition 379, which Siddoway joined in 2019. Read more about Siddoway’s Antarctica research and grants. Siddoway has been named one of Colorado College’s Faces of Innovation.