Sediment core from the Northeast Atlantic, drilled in 1995 aboard the research vessel JOIDES Resolution. | Bathymetry: ETOPO 2022, NOAA National Centers for Environmental Information. Core photograph: Ocean Drilling Program, Hole 162-982A, Core 4H
Image Credit: International Ocean Discovery Program
Scientific Frontline: Extended "At a Glance" Summary: Icelandic Ice Sheet Dynamics and Seawater Chemistry
The Core Concept: The growth and retreat of the Icelandic ice sheet over the past 230,000 years caused significant fluctuations in the seawater chemistry of the North Atlantic, specifically altering the isotopic composition of neodymium.
Key Distinction/Mechanism: As the ice sheet advanced during glacial periods, it ground through Icelandic basalt, creating highly reactive rock dust that dissolved in the ocean. This released neodymium with a distinct radiogenic signature, demonstrating that the chemical "fingerprints" of large water masses are not constant, contrary to previous central assumptions in oceanographic reconstruction.
Major Frameworks/Components:
- Isotopic Analysis: Examination of the ratio of neodymium isotopes (143Nd and 144Nd) in deep-sea sediment to trace the origin of dissolved rare-earth elements.
- Box Modeling: Development of a computational model to reproduce the sediment data, revealing that chemical changes peaked during rapid glaciation.
- Cryosphere-Ocean Interaction: The mechanism by which advancing ice creates rock dust that alters ocean chemistry and regulates micronutrient influx.
Branch of Science: Environmental Physics, Paleoceanography, Geochemistry, Glaciology.
Future Application: The research necessitates a reevaluation of models used to reconstruct past ocean circulation, as they can no longer rely on the assumption of fixed isotopic fingerprints in the North Atlantic during glacial periods.
Why It Matters: This study reveals a critical, previously underestimated link between ice sheet dynamics (the cryosphere), continental weathering, and ocean chemistry, suggesting that glacial grinding also regulated essential micronutrients like iron, impacting marine life and the global carbon cycle during ice ages.
Environmental physicists reveal fluctuations over the past 230,000 years based on the isotopic composition of deep-sea sediment samples
Over the past 230,000 years, the growth and retreat of the Icelandic ice sheet have led to major changes in the seawater chemistry of the North Atlantic, caused by the interaction between volcanism and ice in Iceland. Scientists at the Institute of Environmental Physics at Heidelberg University have demonstrated this using sediment cores from the northeastern Atlantic—the Rockall Plateau. The researchers analyzed the isotopic composition of the rare-earth element neodymium in these drill cores. According to their findings, the isotopic signal fluctuated significantly over the course of glacial and interglacial periods, following the "rhythm" of the ice ages, as shown by the studies led by Professor Norbert Frank.
The isotopic composition of neodymium (Nd) in seawater is one of the most commonly used tools for reconstructing how ocean circulation has changed in the recent geological past. The method is based on the central assumption that the chemical "fingerprints" characteristic of the composition of large water masses have remained largely constant over time. Research by the Heidelberg scientists now suggests that this fixed isotopic composition did not apply to the North Atlantic during glacial periods. Their analyses of deep-sea sediments from the Rockall Plateau show that the chemistry of North Atlantic seawater changed repeatedly and significantly. The researchers attribute these changes to volcanic material from Iceland.
Their investigations are based on the fact that different types of continental rock exhibit different isotopic signatures. The ratio of the specific isotopes 143Nd and 144Nd of neodymium dissolved in seawater reflects the rocks from which the rare-earth element was extracted. As the ice sheet in Iceland advanced during a glacial period and carved its way through the Icelandic basaltic bedrock, it produced large quantities of fine, highly reactive rock dust. This material was released into the surrounding North Atlantic Ocean, where it dissolved and released neodymium with a distinct radiogenic signature—enriched in 143Nd. Analysis of neodymium isotopes from the ODP Site 982 sediment core on the Rockall Plateau shows that the upper water masses of the North Atlantic were consistently much more radiogenic during glacial maxima than during the warm interglacial periods, and that these fluctuations correlated closely with the volume of the Icelandic ice sheet.
The Heidelberg scientists developed a box model that allowed them to reproduce their analyses of the deep-sea sediment samples. According to the model, the changes in seawater chemistry resulting from volcanic input were not strictly linear but rather responses to the dynamics of the ice in Iceland—they peaked during periods of rapid glaciation. "The isotopic signal followed the rhythm of the ice ages almost step by step," says Dr. Antao Xu. "This suggests that the Icelandic ice sheets themselves were the driving forces behind the repeated reshaping of the North Atlantic's seawater chemistry over the past 230,000 years." The research findings also show that the ice sheet regulated the influx of micronutrients, such as iron. This likely had an impact on marine life and the carbon cycle during the ice ages, according to Dr. Xu, who is a member of the Physics of Environmental Archives research group led by Professor Frank.
"The results of our research underscore that ice sheet systems at high latitudes play a crucial role in regulating ocean chemistry," emphasizes Professor Frank. According to the scientist, the findings have far-reaching implications. "They urge caution regarding the assumption that there are fixed isotopic fingerprints that can be used to reconstruct past ocean circulation. Furthermore, they reveal a previously underestimated connection between the cryosphere, continental weathering, and ocean chemistry."
Funding: German Research Foundation
Published in journal: Science Advances
Title: Ice-sheet dynamics drive glacial-interglacial shifts in North Atlantic seawater neodymium isotopes
Authors: Antao Xu, Kira Just, Alexander M. Piotrowski, Jonathan Stohl, and Norbert Frank
Source/Credit: Universität Heidelberg
Edited by: Scientific Frontline
Reference Number: es082026_01