The cloudy, sediment-laden meltwater from glaciers, a crucial source of nutrients for ocean life, may become less nutritious as climate change causes many glaciers to shrink and retreat, a new study warns. Conducted by scientists at UC San Diego’s Scripps Institution of Oceanography, the study reveals that meltwater from a rapidly retreating Alaskan glacier contains significantly lower concentrations of bioavailable iron and manganese compared to a nearby stable glacier.
Published in Nature Communications and funded by the National Science Foundation (NSF), the research highlights the potential impact of climate change-driven glacial retreat on the nutrient supply to the ocean. These metals, essential micronutrients for phytoplankton, are scarce in many parts of the ocean, including the highly productive Gulf of Alaska.
Understanding the Impact of Glacial Retreat
As glaciers grind across bedrock, the pulverized rock and sediment they create flow into the ocean via glacial runoff. This sediment is a vital source of trace metal micronutrients like iron and manganese for coastal marine ecosystems in high-latitude regions such as Alaska, Antarctica, and Greenland. These nutrients fuel phytoplankton growth, forming the base of the marine food web and absorbing significant amounts of carbon dioxide.
The study’s lead author, Kiefer Forsch, a postdoctoral fellow at Scripps, alongside co-author Sarah Aarons, a geochemist at Scripps, traveled to two adjacent fjords on Alaska’s Kenai Peninsula in May 2022. Each fjord contained a glacier: the stable Aialik Glacier and the retreating Northwestern Glacier, which has retreated approximately 15 kilometers since 1950. This proximity allowed the researchers to isolate the influence of glacial retreat on nutrient content.
Key Findings and Chemical Analysis
The team collected samples from both glaciers and analyzed their chemical composition, focusing on metals like manganese and iron, as well as phosphorus, another key nutrient. The analysis aimed to determine whether these elements were present in bioavailable forms that marine organisms could readily absorb and utilize.
“The stable Aialik Glacier produced sediments where approximately 18% of iron and 26% of manganese existed in bioavailable forms. In contrast, Northwestern Glacier’s sediments contained lower fractions of bioavailable iron (13%) and manganese (14-15%).”
The retreating glacier’s sediments showed signs of extensive chemical weathering and depletion of reactive metals, suggesting that prolonged interactions between water and rock transform these metals into less bioavailable states.
Broader Implications for Marine Ecosystems
The findings suggest that as glaciers retreat inland, meltwater and sediments take longer to reach the ocean, providing more opportunities for chemical interactions that reduce nutrient availability. This could have significant implications for marine ecosystems, particularly in regions like the Gulf of Alaska and the Southern Ocean, where iron is a scarce nutrient.
“If we can duplicate these findings elsewhere, the impacts go beyond our scientific understanding of glaciers,” said Aarons. “This could impact the productivity of really significant marine ecosystems, which could have long-term implications for the health of major fisheries.”
Most ocean-terminating glaciers worldwide are losing ice as climate change progresses. If the patterns observed in these Alaskan fjords are consistent across other glaciers, the implications for global marine ecosystems could be profound.
Future Research and Global Context
While the study provides a snapshot of two glaciers in one region, understanding whether these patterns hold across glaciers worldwide with different bedrock types and stages of retreat will require further research. Aarons emphasized the importance of government support, noting that the NSF funding was crucial for this research.
“This research would not have been possible without funding from the National Science Foundation and cooperation with the National Park Service,” said Aarons.
The researchers propose that future work should analyze meltwater sediment from multiple glacier systems at different stages of retreat to clarify whether the results from these two Alaskan fjords can inform predictions about ecosystem responses to continued glacier retreat globally.
In addition to Aarons and Forsch, Angel Ruacho of the US Environmental Protection Agency co-authored the study. Ruacho conducted the research while completing a postdoctoral fellowship at the University of Washington, further highlighting the collaborative effort behind these critical findings.
