A groundbreaking study conducted by an international research team led by geochemist Dr. Torben Struve from the University of Oldenburg has unveiled a surprising and complex climate feedback mechanism linked to the West Antarctic Ice Sheet (WAIS). Published recently in the prestigious journal Nature Geoscience, the study draws upon sediment core analysis from the Pacific sector of the Southern Ocean, revealing that carbon uptake in this critical oceanic region is intricately controlled not simply by iron supply but by the bioavailability of iron minerals sourced from the melting WAIS. This discovery challenges existing paradigms and has profound implications for predicting future climate trajectories under ongoing global warming.
The sediment core, drilled in 2001 from nearly 5,000 meters depth at 62 degrees south and 116 degrees west, contains continuous deposits dating back approximately 500,000 years, covering four glacial cycles. The site lies south of the Antarctic Polar Front, between South America and New Zealand, a region essential for global carbon cycling. By investigating trace elements and microfossil assemblages within these sediments, Dr. Struve and his collaborators reconstructed variations in ice sheet dynamics and marine productivity across climatic transitions spanning multiple interglacial and glacial periods.
Central to their investigation was iron, a micronutrient critical to marine phytoplankton growth. In typical Southern Ocean settings, iron often limits photosynthesis, and dust-borne iron fertilization during glacial times has been linked to enhanced carbon sequestration, contributing to global cooling. Surprisingly, this study demonstrated that the Pacific sector south of the Antarctic Polar Front experienced elevated iron inputs during warm interglacial periods, precisely when the WAIS underwent significant retreat. Contrary to expectations, this increased iron delivery did not translate into elevated marine algae productivity or carbon uptake.
The researchers attribute this counterintuitive decoupling to the chemical nature of the iron delivered by icebergs melting in this region. The sediment composition and particle size distribution indicated that iron was transported primarily by icebergs calving from the West Antarctic Ice Sheet as it disintegrated. Importantly, detailed geochemical analyses revealed that the iron in these sediments was in a highly weathered and less bioavailable form, limiting its effectiveness as a nutrient for phytoplankton growth. The bioavailability of iron, rather than its sheer abundance, emerged as the controlling factor influencing primary productivity in this ocean sector.
This nuanced understanding is particularly significant because the WAIS, characterized by large portions of ice grounded below sea level, is widely considered one of the most vulnerable ice sheets to 21st-century warming. Paleoclimate evidence suggests that during the last interglacial period roughly 130,000 years ago—when global temperatures were comparable to today—the WAIS retreated substantially, generating a profusion of icebergs laden with weathered sediments. These iceberg-transported minerals, rich in iron but chemically inert to biological uptake, suppressed phytoplankton productivity despite the high iron flux, thus reducing the ocean’s capacity to sequester atmospheric CO₂.
In light of these findings, the traditional narrative—that enhanced iron fertilization from ice sheet retreat or increased dust deposition would inevitably amplify Southern Ocean carbon drawdown—is considerably more complex. “We were surprised to find that iron input does not always stimulate phytoplankton growth,” explains Dr. Frank Lamy, paleoclimatologist at the Alfred Wegener Institute and co-author. “Our data show that the chemical speciation and weathering state of iron-bearing minerals must be taken into account to understand their ecological role.”
This research not only elucidates critical feedbacks operating during past climate warmings but also raises important concerns about future climate change. As anthropogenic warming proceeds, ongoing thinning and potential further retreat of the WAIS could increase the delivery of similarly weathered iron minerals to the Southern Ocean. Contrary to expectations, such processes might suppress rather than enhance biological carbon uptake in these waters, weakening one of the planet’s vital natural mechanisms for absorbing CO₂ from the atmosphere.
The implications extend to global climate models, which currently struggle to replicate fine-scale biogeochemical feedbacks involving iron bioavailability and phytoplankton response. These models often treat iron inputs simplistically, failing to account for mineralogical differences in iron sources. Incorporating realistic iron chemistry linked to ice sheet erosion and sediment transport will be essential for improving climate projections, especially in polar and subpolar marine systems.
Moreover, this study contributes to the broader understanding of ice sheet sensitivity and responses to climate variability. The WAIS’s role as a dynamic source of iron and other micronutrients connects cryospheric changes directly to marine ecosystem functioning and carbon cycling. Decoding these links is crucial for interpreting sedimentary records and predicting future environmental shifts.
Looking forward, Dr. Struve emphasizes the need for expanded research. “Our findings suggest exciting new avenues involving the chemical characterization of iron in multiple sediment cores, coupled with high-resolution palaeoceanographic reconstructions,” he notes. Such investigations will refine the mechanistic insights gained from the Pacific sector and explore how widespread this phenomenon is across other Southern Ocean regions influenced by ice sheet dynamics.
Overall, this compelling research highlights the importance of integrating geology, chemistry, and biology to unravel climate feedback processes under changing Earth conditions. The story of the West Antarctic Ice Sheet’s retreat and its paradoxical suppression of marine carbon uptake is a testament to the intricate and sometimes counterintuitive pathways through which Earth’s climate system operates.
Subject of Research: Not applicable
Article Title: South Pacific carbon uptake controlled by West Antarctic Ice Sheet dynamics
News Publication Date: 2-Feb-2026
Web References:
DOI: 10.1038/s41561-025-01911-0
Image Credits: Johann P. Klages / Alfred Wegener Institut
Keywords: West Antarctic Ice Sheet, Southern Ocean, iron bioavailability, climate feedback, marine phytoplankton, sediment core analysis, carbon uptake, interglacial period, global warming, icebergs, geochemistry, palaeoclimate
