Narrow bands of ocean covering just over one-third of the world's seas are responsible for absorbing nearly three-quarters of the carbon dioxide that oceans pull from the atmosphere, new research shows.
The PhD study published in Nature Climate Change reveals ocean fronts play a far larger role in regulating Earth's carbon cycle than previously understood.
Ocean fronts are boundaries where different water masses collide, creating turbulent zones rich in marine life. These areas cover 36% of the global ocean but account for 72% of total ocean carbon dioxide uptake, absorbing about 1.8 billion tonnes of carbon each year.
"This is the first time we've been able to quantify the disproportionate role that ocean fronts play in absorbing atmospheric carbon dioxide on a global scale, and it has major implications for climate modelling," said lead author Dr Kai Yang, who completed the research during his PhD at the University of Tasmania's Institute for Marine and Antarctic Studies (IMAS), and is now a postdoctoral researcher at Xiamen University in China.
"If computer models don't accurately represent these dynamic ocean zones, scientists may be miscalculating how much carbon dioxide the oceans can absorb in coming decades."
The IMAS-led study team analysed more than two decades of satellite data from 2003 to 2024, tracking where ocean fronts occur globally and how they're changing.
"We can now directly link changes in frontal activity to changes in both phytoplankton biomass and ocean carbon dioxide uptake," IMAS oceanographer and co-author, Dr Amelie Meyer said.
While ocean fronts can be found everywhere, they are most common in mid to high latitudes, particularly where major currents like the Gulf Stream and Kuroshio Current flow, and throughout the Southern Ocean.
"In these zones, different water masses collide, driving both downwelling and upwelling, which brings deep, nutrient-rich water to the surface," Dr Meyer said.
"This nutrient surge fuels enormous blooms of phytoplankton, and these microscopic plants absorb carbon dioxide as they photosynthesise. And when they die, they sink, carrying carbon into the deep ocean where it can remain locked away for centuries."
The study found phytoplankton concentrations were 1.8 times higher in key frontal zones compared with the global average. But these critical carbon-absorbing zones are shifting.
"Over the past 22 years, frontal activity has intensified in some regions, particularly between 40 and 60 degrees latitude in both hemispheres. In other areas, mainly closer to the equator, fronts have weakened," Dr Yang said.
The pattern suggests some ocean front groups are moving poleward, consistent with observations that major ocean currents are shifting toward Earth's poles as the climate changes.
"Where fronts are intensifying, carbon dioxide uptake is strengthening at twice the global average rate. Where they're declining, carbon absorption is weakening," Dr Yang said.
"Current climate models struggle to represent the fine-scale dynamics of ocean fronts because their resolution is often too coarse to capture these relatively narrow zones."
The world's oceans have absorbed about 26% of human carbon emissions between 2013 and 2022, slowing the pace of climate change. But whether oceans can maintain this capacity as they warm remains a critical unknown.
"The oceans play an indispensable role in regulating Earth's climate," Dr Meyer said. "This research helps us understand where that regulation is happening most intensively and how it might change."
The study team included researchers from the University of Tasmania's Institute for Marine and Antarctic Studies, the Australian Research Council Centre of Excellence for Climate Extremes, Xiamen University in China, and the Australian Maritime College.
Banner image credit: Matt Hardy | Unsplash
