Iceland's Ice Sheet Repeatedly Reshaped North Atlantic Seawater Chemistry, Study Finds

The growth and retreat of Iceland's ice sheet over the past 230,000 years repeatedly changed the seawater chemistry of the North Atlantic, driven by the interaction between the island's volcanic rock and its ice, according to scientists at the Institute of Environmental Physics at Heidelberg University. The findings, based on sediment cores from the Rockall Plateau in the northeastern Atlantic, are published in the journal Science Advances.

The researchers analyzed the isotopic composition of neodymium, a rare-earth element, in seawater — a method commonly used to reconstruct past ocean circulation. It relies on the idea that the chemical "fingerprint" of a large water mass stays largely constant over time. As the Icelandic ice sheet advanced during a glacial period and ground through the island's basaltic bedrock, it produced fine, reactive rock dust that dissolved into the North Atlantic, releasing neodymium with a distinct isotopic signature.

Analysis of the ODP Site 982 sediment core showed that the North Atlantic's upper water masses were consistently more radiogenic — enriched in that distinct signature — during glacial maximums than during warm interglacial periods, and that these shifts closely tracked the volume of the Icelandic ice sheet. "The isotopic signal followed the rhythm of the ice ages almost step by step," said researcher Antao Xu, suggesting the Icelandic ice sheet itself was the driving force behind these repeated changes.

A computer model built by the team showed the changes were not linear but peaked during periods of rapid glaciation. The researchers say the ice sheet likely also regulated the supply of micronutrients such as iron to the ocean, which could have affected marine life and the carbon cycle during past ice ages. "Ice sheet systems at high latitudes play a crucial role in regulating ocean chemistry," said Norbert Frank, who led the research, adding that the fixed "fingerprints" long assumed for reconstructing past ocean circulation may not hold during North Atlantic glacial periods.