Fossilized plankton study gives long-term hope for oxygen depleted oceans
University of Southampton
image:
Scanning electron image of fossilised planktonic foraminifera.
view moreCredit: Anya Hess
Key findings
- Arabian Sea was better oxygenated 16 million years ago than it is today, despite warmer climate conditions.
- Monsoons, ocean circulation, and ocean gateways play an important role, adding complexity as we try to predict future ocean oxygenation.
- In the very long-term, future sea oxygenation may improve, with unknown consequences for marine biology.
A new study suggests the world’s oxygen depleted seas may have a chance of returning to higher oxygen concentrations in the centuries to come, despite our increasingly warming climate.
Researchers at the University of Southampton (UK) and Rutgers University (USA) examined fossilised plankton from the Arabian Sea and found that despite dramatic global warming 16 million years ago, oxygen levels were higher than today. The sea only became truly oxygen deficient four million years later, as the climate cooled.
In addition, the team revealed the region, off the west coast of India, behaved differently than a similar low-oxygen area in the Pacific, suggesting other local systems, such as strong winds, ocean currents, and outflow from marginal seas may have delayed the process.
The scientists’ findings are published in the Nature journal Communications Earth & Environment.
“Oxygen dissolved in our oceans is essential for sustaining marine life, promoting greater biodiversity and stronger ecosystems. However, over the past 50 years, two percent of oxygen in the seas worldwide has been lost each decade as global temperatures rise,” explains co-lead author, Dr Alexandra Auderset of the University of Southampton and formerly of Max Planck Institute of Chemistry, Mainz.
She adds: “The Miocene Climatic Optimum (MCO), a period approximately 17 to 14 million years ago, had similar temperatures and atmospheric conditions to those we predict will occur after 2100. We have taken a snapshot of sea oxygenation during the MCO to help understand how things might develop a-hundred years or more from now.”
The scientists examined tiny fossilised plankton called foraminifera (forams) extracted from core samples provided by the Ocean Drilling Program (ODP). The remains of these creatures hold important chemical information that can indicate oxygen concentrations in sea water over millions of years.
The researchers found that an Oxygen Minimum Zone (OMZ) existed in the Arabian Sea, with oxygen levels below about 100 micromol per kilogram of water, from the early Miocene (19 million years ago) to around 12 million years ago.
However, the oxygen levels at this time were not so low as to trigger a process where nitrogen is expelled from the water and into the atmosphere – a state that is observed nowadays in the Arabian Sea. Rather, this process was delayed and did not occur until later, after the 12 million year mark and beyond.
“Today parts of the Arabian sea are ‘suboxic’, supporting only limited marine life due to minimal oxygenation. This same region during the MCO, under similar climatic conditions, was hypoxic – so comparatively moderate oxygen content, supporting a wider range of organisms,” says Dr. Auderset.
Co-lead-author, Dr Anya Hess of George Mason University, and formerly of Rutgers University and Woods Hole Oceanographic Institution, adds: “The MCO is the closest comparison we have to climate warming beyond 2100 under a high-emissions scenario. One of our previous studies shows the eastern tropical Pacific was actually well oxygenated during this period, in contrast to the deoxygenation trend we see today.
“The Arabian Sea was also better oxygenated during the MCO, but not as much as the Pacific, with moderate oxygenation and an eventual decline that lagged behind the Pacific by about 2 million years.”
Dr Auderset concludes: “Our results suggest that ocean oxygen loss, already underway today, is strongly shaped by local oceanography. Global models that focus solely on climate warming, risk not capturing the regional factors that may either amplify or counteract those more general trends.
“Our research shows ocean response to climate warming is complex, and this means that we will need to be ready to adapt to changing ocean conditions.”
Ends
Notes to editors
- The paper ‘Contrasting evolution of the Arabian Sea and Pacific Ocean oxygen minimum zones during the Miocene’ is published in the journal Communications Earth & Environment: https://www.nature.com/articles/s43247-025-03112-4
- For interview or further info contact Peter Franklin, Media Manager, University of Southampton. press@soton.ac.uk +44 23 8059 3212
- Download images here: https://safesend.soton.ac.uk/pickup?claimID=MPwt2BeKMrpdqqe4&claimPasscode=ptdNzvynfPSYQvHj&emailAddr=259933
- More about Ocean and Earth Science at the University of Southampton can be found here: https://www.southampton.ac.uk/about/faculties-schools-departments/school-of-ocean-and-earth-science
- The University of Southampton drives original thinking, turns knowledge into action and impact, and creates solutions to the world’s challenges. We are among the top 100 institutions globally (QS World University Rankings 2026). Our academics are leaders in their fields, forging links with high-profile international businesses and organisations, and inspiring a 25,000-strong community of exceptional students, from over 135 countries worldwide. Through our high-quality education, the University helps students on a journey of discovery to realise their potential and join our global network of over 300,000 alumni. www.southampton.ac.uk
- For more about Rutgers University visit: https://www.rutgers.edu/
Alexandra Auderset and Alfredo Martinez-Garcia in laboratory at Max Planck Institute for Chemistry.
Credit
Simone Moretti
Graphic showing modern (top) and MCO (bottom) oxygenation.
Credit
University of Southampton
Journal
Communications Earth & Environment
Method of Research
Computational simulation/modeling
Subject of Research
Not applicable
Article Title
Contrasting evolution of the Arabian Sea and Pacific Ocean oxygen minimum zones during the Miocene
Article Publication Date
26-Jan-2026
Key drivers of recurrent extinction in the Triassic
New study in Geology links massive undersea volcanism to repeated marine extinctions
Contributed by Kea Giles, Managing Editor, Geology
Boulder, Colo., USA: Mass extinctions are extremely catastrophic events on Earth. Throughout Earth’s evolutionary history, numerous mass extinctions have occurred, with five major mass extinctions being particularly representative. These extinctions have reshaped the course of life’s evolution on Earth. In addition to the five major mass extinctions, many frequent, lower-order extinctions have also taken place on Earth, such as the Norian–Rhaetian Extinction during the Triassic. Regarding the triggering mechanisms of extinctions, the five major events have been relatively well studied. However, the triggering mechanisms of the frequent lower-order extinctions remain unclear.
In their new study titled “Marine large igneous provinces: Key drivers of Triassic recurrent extinction” and published last week in Geology, Jian-Jun Fan and colleagues present a detailed analysis of oceanic island, seamount, and plateau remnants in the Tibetan Plateau that trace the evolution of Meso- and Neo-Tethys, incorporating new and published data. During the Triassic, three major episodes of marine large igneous provinces (LIPs) formed at 250–248, 233–231, and 210–208 million years ago. By integrating geological records of these LIP episodes with Triassic geological datasets, Fan and colleagues demonstrate a correlation between marine LIPs and at least four extinctions in marine biota, driven by the resultant anoxic-euxinic events. Marine LIPs account for half of the extinctions with an identifiable geological trigger during the Triassic. This indicates that marine LIPs are a key driver of Triassic extinctions.
Marine LIP eruptions on Earth are frequent; however, evidence of ancient marine LIPs is likely significantly reduced by subduction during ocean basin closure. The authors note that “this destruction renders such records difficult to identify and, even when identified, challenging to interpret and date precisely,” and therefore hypothesize that orogenic belts (i.e., remnants of vanished ancient ocean basins) contain many unidentified “ghost” marine LIPs, and these marine LIP eruptions likely constitute a key driver of other Phanerozoic extinctions that were previously under-recognized in Earth system models.
Geology: https://doi.org/10.1130/G53406.1
About the Geological Society of America
The Geological Society of America (GSA) is a global professional society with more than 17,000 members across over 100 countries. As a leading voice for the geosciences, GSA advances the understanding of Earth's dynamic processes and fosters collaboration among scientists, educators, and policymakers. GSA publishes Geology, the top-ranked geoscience journal, along with a diverse portfolio of scholarly journals, books, and conference proceedings—several of which rank among Amazon's top 100 best-selling geology titles.
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Journal
Geology
Article Title
Marine large igneous provinces: Key drivers of Triassic recurrent extinction
Article Publication Date
20-Jan-2026
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