New research indicates that rising ocean temperatures may benefit Nitrosopumilus maritimus, a microbe essential for marine nutrient cycles. This archaea adapts by using iron more efficiently in warmer, nutrient-poor conditions, potentially sustaining ocean productivity. The findings, published in the Proceedings of the National Academy of Sciences, suggest these microbes could play a larger role in ocean chemistry amid climate change.
Rising ocean temperatures, influenced by marine heat waves and broader climate change, are penetrating deep waters, potentially disrupting marine chemical and biological systems. However, a study led by University of Illinois Urbana-Champaign microbiology professor Wei Qin and University of Southern California global change biology professor David Hutchins reveals that Nitrosopumilus maritimus, a key ammonia-oxidizing archaea, can adapt to these changes.
These microbes constitute about 30% of marine microbial plankton and are vital for the ocean's nitrogen cycle. They oxidize ammonia, converting nitrogen into forms that regulate the growth of plankton at the base of the marine food chain, thereby supporting biodiversity.
"Ocean-warming effects may extend to depths of 1,000 meters or more," Qin stated. "We used to think that deeper waters were mostly insulated from surface warming, but now it is becoming clear that deep-sea warming can change how these abundant archaea use iron -- a metal they depend on heavily -- potentially affecting trace metal availability in the deep ocean."
In controlled experiments, the team exposed pure cultures of the microbe to varying temperatures and iron levels, avoiding contamination. Results showed that under iron-limited conditions and higher temperatures, Nitrosopumilus maritimus required less iron and utilized it more efficiently, adjusting its metabolism accordingly.
Coupled with global ocean biogeochemical modeling by University of Liverpool's Alessandro Tagliabue, the findings indicate that deep-ocean archaeal communities may maintain or enhance their contributions to nitrogen cycling and primary production in iron-limited regions as the climate warms.
To validate these results, Qin and Hutchins will co-lead an expedition this summer aboard the research vessel Sikuliaq. Starting from Seattle, the voyage will head to the Gulf of Alaska, the subtropical gyre, and Honolulu, Hawaii, involving 20 researchers to study natural archaeal populations and interactions between temperature, metal availability, and microbial activity.
The research received support from the National Science Foundation, Simons Foundation, National Natural Science Foundation of China, University of Illinois Urbana-Champaign, and the University of Oklahoma. It appears in the Proceedings of the National Academy of Sciences (2026; 123 (10); DOI: 10.1073/pnas.2531032123).