A new study from UC San Diego's Scripps Institution of Oceanography suggests that climate change-driven glacial retreat could decrease essential micronutrients in meltwater, impacting marine ecosystems.
The receding glaciers of Alaska hold a significant, yet troubling revelation according to new research led by scientists at UC San Diego's Scripps Institution of Oceanography. Their findings indicate that as glaciers shrink due to climate change, they could deliver fewer vital nutrients to marine ecosystems, with potentially extensive ecological consequences.
The researchers examined meltwater from two Alaskan glaciers - one stable and one rapidly retreating - and discovered that the retreating glacier's meltwater contained notably lower amounts of bioavailable iron and manganese, which are critical nutrients for ocean life.
Published in the journal Nature Communications, this study could reshape our understanding of glacial influences on ocean health.
"If we can duplicate these findings elsewhere, the impacts go beyond our scientific understanding of glaciers," co-author Sarah Aarons, a geochemist at Scripps, said in a news release. "This could impact the productivity of really significant marine ecosystems, which could have long term implications for the health of major fisheries.
Glaciers grind rock into fine sediment that enters ocean water through glacial melt, acting as a crucial source of micronutrients, especially in high-latitude regions like Alaska and Antarctica. These nutrients, especially iron and manganese, are essential for phytoplankton growth, forming the foundation of most marine food webs and playing a key role in controlling atmospheric carbon dioxide levels.
The study's focus was on two glaciers on Alaska's Kenai Peninsula.
The stable Aialik Glacier produced meltwater with higher concentrations of bioavailable iron (18%) and manganese (26%). In contrast, meltwater from the retreating Northwestern Glacier had considerably lower concentrations of these nutrients at 13% and 14-15%, respectively.
This disparity is attributed to longer water-rock interaction times in retreating glaciers, which enhance chemical weathering and reduce the nutrient bioavailability.
"The longer you have water in contact with rock or sediments, the more chemical breakdown or weathering takes place," Aarons added. "So a retreating glacier might be sending more sediment to the ocean but with lower concentrations of bioavailable nutrients like iron because more weathering is occurring."
These findings raise concerns about the broader implications for global marine ecosystems, particularly in nutrient-limited regions such as the Gulf of Alaska. The reduction in essential nutrients resulting from glacial retreat could alter the productivity of these waters and disrupt the food chains they support.
"We see very clear geochemical differences between these two glacier systems that we link to their state of retreat," added lead author Kiefer Forsch, who conducted the study as a postdoctoral fellow at Scripps and is now at the University of Southern California. "However, this is a snapshot of two glaciers in one region. Understanding whether these patterns hold across glaciers elsewhere in the world with different bedrock types and stages of retreat will require more research."
This study highlights the significant ecological consequences of climate change-induced glacial retreat, emphasizing the importance of ongoing research and government support.
"This research would not have been possible without funding from the National Science Foundation and cooperation with the National Park Service," Aarons added. "Funding from NSF allows us to understand how this landscape is responding to a warming planet, and has a direct impact upon the many people who subsist on these lands and visit these glacial fjords for their abundant and diverse wildlife."
As glaciers worldwide continue to lose ice, the researchers call for further studies to assess whether similar patterns hold in other regions. Such insights are crucial for predicting ecosystem responses to continued glacier retreat and formulating strategies to mitigate the impacts on marine biodiversity and fisheries.
The study included contributions from Angel Ruacho of the U.S. Environmental Protection Agency, who conducted the research as a postdoctoral fellow at the University of Washington.