Hidden ocean feedback loop could accelerate climate change
URochester scientists identify how warming oceans may trigger increased methane emissions, adding a key insight for current climate models.
The world’s oceans may be quietly amplifying climate change in ways scientists are only beginning to understand.
In a new study published in the journal Proceedings of the National Academy of Sciences, University of Rochester scientists—including Thomas Weber, an associate professor in the Department of Earth and Environmental Sciences, and graduate student Shengyu Wang and postdoctoral research associate Hairong Xu in Weber’s lab—uncovered a key mechanism behind methane production in the open ocean. Their research indicates that this mechanism could intensify as the planet warms, providing an alarming feedback loop for global warming.
Methane is a powerful greenhouse gas, and for decades scientists have puzzled over a paradox: surface ocean waters consistently release methane into the atmosphere, even though surface water is rich in oxygen. Traditionally, methane production has been associated with oxygen-free environments, such as wetlands or deep sediments.
Weber’s team set out to solve this puzzle using a global dataset and computer modeling. Their findings point to a specific microbial process that is responsible for methane production in the ocean environment: certain bacteria generate methane as a byproduct when they break down organic compounds, but they only do this when the nutrient phosphate is scarce.
“This means that phosphate scarcity is the primary control knob for methane production and emissions in the open ocean,” Weber says.
The findings reframe how scientists understand methane production in the ocean. Rather than being a rare or unusual process, methane production in oxygen-rich environments may be widespread in regions where phosphate is limited.
But the study extends further than explaining marine methane production in the present—it also offers a troubling glimpse into the future.
“Climate change is warming the ocean from the top down, increasing the density difference between surface and deep waters,” Weber says. “This is expected to slow the vertical mixing that carries nutrients like phosphate up from depth.”
According to the team’s model, with less vertical mixing, surface waters could become increasingly nutrient-starved, creating ideal conditions for methane-producing microbes to thrive.
The result, Weber warns, would be more methane released from the ocean into the atmosphere. Because methane is such a potent greenhouse gas, this creates the potential for a harmful feedback loop: warming oceans lead to more methane emissions, which in turn drive further warming.
The findings highlight how even processes occurring at the microscopic level in the ocean can have global consequences.
Crucially, this feedback is not currently included in major climate projection models. As researchers continue to refine climate models, incorporating feedbacks such as this may be essential for accurately predicting the pace and scale of future climate change.
“Our work will help fill a key gap in climate predictions, which often overlook interactions between the changing environment and natural greenhouse gas sources to the atmosphere,” Weber says.
Journal
Proceedings of the National Academy of Sciences
Article Title
Phosphate scarcity governs methane production in the global open ocean
Systematic understanding of typical characteristics and driving factors of oxygen minimum zone (OMZ) from the perspective of global change
image:
Driving factors of OMZ in the context of global change.
view moreCredit: ©Science China Press
This study is led by Dr. Ma Jun and Dr. Song Jinming from Institute of Oceanology, Chinese Academy of Sciences. Focusing on the research of OMZ, the research team clarified that the DO threshold range of OMZ in the global ocean is 20-100 μmol L-1. They pointed out the differences in the horizontal and vertical distributions of OMZ in different sea areas, expounded that the continuous consumption of DO in the ocean interior and the restriction of water exchange caused by ocean stratification are the two core mechanisms for the formation of OMZ, and analyzed that two positive-feedback regulation methods, namely the increase in microbial oxygen consumption and the increase in oxygen consumption by anaerobic metabolites, are the maintenance mechanisms for the hypoxic state of OMZ.
In the context of global change, the OMZ is evolving rapidly. The researchers indicated that its expansion can usually be attributed to two core controls: the temperature and the ocean circulation. On the one hand, rising temperature provides direct impetus for the expansion of OMZ by reducing the solubility of O2, increasing the rates of organic matter respiration and remineralization, and enhancing the stratification of the upper ocean. On the other hand, global change alters the intensity, structure, and spatial distribution patterns of ocean circulations represented by thermohaline circulation, wind-driven circulation, and upwelling, significantly influencing the formation, maintenance, and transmission of hypoxic waters. In addition, wind stress, mesoscale vortex, and freshwater flux can also further regulate the structure and evolution process of OMZ.
The researchers suggested that in the future, attention should be paid to establishing OMZ gradient thresholds and classification criteria that conform to the laws of deoxygenation, improving the systematic understanding of the spatio-temporal changes of OMZ, and continuously strengthening in-depth research on OMZ in sea areas such as the Western Pacific Ocean, which has a relatively weak OMZ intensity and is greatly affected by global change. This will help to better understand the evolution process of global ocean hypoxia and deoxygenation, providing scientific support for formulating future-oriented sustainable development strategies.
Journal
Science China Earth Sciences
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