In this month’s Ocean Brief, we take a look at reducing whale shark injuries, changes to the Atlantic Meridional Overturning Circulation, and Antarctica’s once-hidden canyons.
A reason for hope
Whale sharks in West Papua face preventable injuries
Credit: Klaus Stiefel/Flickr (CC BY-NC 2.0)
Whale sharks are the largest fish in the sea - but they’re also among the most endangered. Globally, numbers have dropped by more than half in the past 75 years. The threats are many, such as fishing, entanglement in fishing gear, and the degradation and loss of critical habitat.
One area whale sharks like to congregate is the Bird's Head Seascape off Indonesian West Papua. A new study from Edy Setyawan (Elasmobranch Institute Indonesia) and colleagues has found that many whale sharks spotted by the researchers and citizen scientists in this area have scars and injuries caused by people. Most injuries are minor abrasions from rubbing against fishing platforms called bagans, or from contact with boats. As whale shark tourism grows in the area, so too does the risk of injury.
Fortunately, the researchers say these changes may be preventable. They recommend removing sharp edges from nets and outriggers that can injure the whale sharks. They also stress that boats near bagans (whale sharks are often spotted near bagans, so that is where the tourism boats go) should follow established whale shark tourism codes of conduct.
Why it matters: This study shows local threats to whale sharks in the Bird's Head Seascape are preventable. With simple fixes, communities can both safeguard these iconic animals while strengthening whale shark tourism as a sustainable livelihood.
Read the paper Insights into the population demographics and residency patterns of photo-identified whale sharks Rhincodon typus in the Bird’s Head Seascape, Indonesia (open access)
Something to work on
Atlantic current system (AMOC) could shut down after 2100
Map of the Nordic Seas and subpolar basins with currents that form part of the AMOC. Solid lines represent currents at/near the sea surface and dashed lines deep currents. Credit R. Curry, WHOI/Science/USGCRP (CC BY 3.0)
The Atlantic Meridional Overturning Circulation (AMOC) - the vast system of ocean currents that includes the Gulf Stream - acts like a giant conveyor belt, carrying warm water north and cold water south. This system helps keep Europe's climate mild and influences weather patterns worldwide. A new study led by Sybren Drijfhout (Royal Netherlands Meteorological Institute) suggests this vital current system could completely shut down after 2100 if we continue with high emissions. Even with moderate emission cuts, the models show worrying signs of slowdown.
The breakdown starts in key northern seas (Labrador, Irminger, and Nordic) where cold surface water normally sinks deep in winter. But as the planet warms, surface waters stay warmer and lighter, so they don't sink as easily. This disrupts the ocean's natural mixing and weakens the entire current system, creating a downward spiral that becomes harder to reverse.
The research team used advanced climate models running far into the future (to 2300-2500) and found that all high-emission scenarios led to a complete shutdown. Worryingly, scientists are already seeing signs of weakening in these northern regions. Once a critical threshold is crossed — possibly within decades — the collapse becomes unstoppable. A shutdown could take 50–100 years, reducing heat transport to a fraction of today’s levels.
Why it matters: If this ocean conveyor belt shuts down, northwestern Europe would face much harsher summers and winters, tropical rain patterns would shift dramatically, and ice sheets would melt faster. The models might even underestimate how quickly this could happen since they don't fully account for melting ice in Greenland. Rapidly cutting emissions is our only chance to avoid crossing this dangerous point of no return.
Read the paper Shutdown of northern Atlantic overturning after 2100 following deep mixing collapse in CMIP6 projections (open access)
Something we learned
Antarctica’s submarine canyons mapped in unprecedented detail
Luigi peak 1.415 m, Sierra DuFief, Wiencke Island. Credit: Georges Nijs (CC BY 2.0)
Scientists have produced the most detailed catalogue yet of Antarctic canyons, using new high-resolution bathymetric (seabed) data from the International Bathymetric Chart of the Southern Ocean. Their work identified 332 canyon networks - five times more than earlier studies! Some plunge more than 4,000 metres into the depths. This discovery is particularly significant given that only ~27% of Earth's seafloor has been mapped in high resolution, suggesting many more canyons likely remain undiscovered globally.
The study from Riccardo Arosio (University College Cork) and David Amblàs (Universitat de Barcelona) reveals striking differences between East and West Antarctica. In the east, there are sprawling, branching canyons with U-shaped profiles. In contrast, western canyons are shorter and steeper, with V-shaped profiles. These findings add weight to evidence that the East Antarctic Ice Sheet is older and more persistent than its western counterpart.
But submarine canyons are more than geological curiosities. They transport sediments, channel nutrients, and act as pathways connecting shallow and deep waters. Critically, they influence how warm and cold waters move, potentially influencing melting of floating ice shelves, ocean circulation, and sea-level rise.
Why it matters: Understanding Antarctic canyons improves our ability to predict how ice, ocean, and climate interact. By integrating these canyons into climate models, researchers can improve predictions of ice loss, ocean circulation shifts, and sea-level rise, helping coastal communities prepare for the future.
Read the paper The geomorphometry of Antarctic submarine canyons (open access)