The possibility that life a kilometer below the ocean’s surface may be subtly restructuring itself in reaction to a crisis it did not cause is almost unsettling. No panic, no headlines. Time, iron, and chemistry alone. And, it seems, not as long as anyone had anticipated.
The marine science community is paying close attention to a recent study that was published in the Proceedings of the National Academy of Sciences, and for good reason. Researchers have discovered that the microscopic organism Nitrosopumilus maritimus, which is a member of the archaea group, seems to be modifying its metabolism to cope with warmer, iron-poor environments with a level of efficiency that wasn’t previously anticipated. The results are posing subtle but important queries regarding the speed at which biological systems can react to environmental stress and the potential implications for the oceans as a whole.
David Hutchins from the University of Southern California and Wei Qin, a microbiology professor at the University of Illinois Urbana-Champaign, spearheaded the study. In order to distinguish serious deep-sea research from noise, their team took extra precautions to prevent trace metal contamination while conducting meticulously controlled experiments that exposed pure cultures of N. maritimus to various temperature and iron combinations. They discovered that under iron-limited conditions, the microbes did not suffer as temperatures rose. They adjusted. They made better use of what little iron they had and required less of it. That is not insignificant. In actuality, that metabolic pivot is pretty amazing.
It’s important to take a moment to recognize the original purpose of these organisms. About 30% of marine microbial plankton is composed of Nitrosopumilus maritimus and its close relatives. They transform nitrogen into chemical forms that control plankton growth throughout the water column by oxidizing ammonia. The foundation of the whole marine food chain is made up of plankton. Therefore, when scientists refer to these microbes as “important,” they mean it in the most fundamental sense possible—the kind of significance that doesn’t become public until something goes wrong.
Deep ocean waters were thought to be largely shielded from surface-level warming for many years. That presumption is eroding. According to Qin, “Ocean-warming effects may extend to depths of 1,000 meters or more,” because deep-sea warming can change the way these archaea interact with iron, which could change the availability of trace metals throughout entire ocean regions. The direction of concern is obvious, but the implications are not yet fully mapped.
The picture became even more intriguing when Alessandro Tagliabue of the University of Liverpool combined the experimental results with global ocean biogeochemical modeling. According to the models, deep-ocean archaeal communities may expand their role in nitrogen cycling and primary production support across iron-limited regions, rather than merely holding their ground in a warming climate. It’s still unclear if that will occur as the models predict, and until field data supports it, it’s probably best to retain some skepticism.
It’s possible that field data will arrive sooner than anticipated. Qin and Hutchins will co-lead an expedition later this summer on the research ship Sikuliaq, which will depart from Seattle, pass through the Gulf of Alaska, descend to the subtropical gyre, and make a stop in Honolulu. They will be joined by twenty more researchers who will study natural archaeal populations in actual ocean conditions instead of controlled laboratory cultures. Finding out whether what occurred in the lab is also occurring in the water is the simple objective.
In all of this, it’s difficult to avoid feeling a certain tension. Contrary to all reasonable expectations, the news from the deep ocean is somewhat encouraging: these microbes appear to be surviving and may even be gaining traction in conditions that should, according to conventional wisdom, be destabilizing. However, the overall narrative remains unchanged. The margin of error in marine ecosystems is smaller than most people realize, and the ocean is warming more quickly and deeply than previously predicted by models. Evolution might proceed more quickly than previously thought. The question of whether it’s fast enough is quite different.
