50 years ago, researchers discovered a leak in Earth’s oceans

Oceans may be shrinking — Science News, March 10, 1973

The oceans of the world may be gradually shrinking, leaking slowly away into the Earth’s mantle…. Although the oceans are constantly being slowly augmented by water carried up from Earth’s interior by volcanic activity … some process such as sea-floor spreading seems to be letting the water seep away more rapidly than it is replaced.

Update

Scientists traced the ocean’s leak to subduction zones, areas where tectonic plates collide and the heavier of the two sinks into the mantle. It’s still unclear how much water has cycled between the deep ocean and mantle through the ages. A 2019 analysis suggests that sea levels have dropped by an average of up to 130 meters over the last 230 million years, in part due to Pangea’s breakup creating new subduction zones. Meanwhile, molten rock that bubbles up from the mantle as continents drift apart may “rain” water back into the ocean, scientists reported in 2022. But since Earth’s mantle can hold more water as it cools (SN: 6/13/14), the oceans’ mass might shrink by 20 percent every billion years.

Citations

D. Andrault and N. Bolfan-Casanova. Mantle rain toward the Earth's surface: A model for the internal cycle of water. Physics of the Earth and Planetary Interiors. Vol. 322, January 2022. doi: 10.1016/j.pepi.2021.106815.

K.S. Karlsen, C.P. Conrad and V. Magni. Deep Water Cycling and Sea Level Change Since the Breakup of Pangea. Geochemistry, Geophysics, Geosystems. Vol. 20, June 2019, p. 2919. doi: 10.1029/2019GC008232.

A remotely operated vehicle in the western Pacific explores the Mariana Trench, the deepest oceanic trench in the world. Earth’s surface and mantle exchange water through such trenches, but the mantle may be taking on more water than it’s giving back, resulting in the ocean slowly shrinking over millions to billions of years.

NOAA Office of Ocean Exploration and Research

Ocean exploration is a dynamic and exciting field. New discoveries and explorations, advances in technology, and important findings in deep-ocean science happen every day. The items on this page capture some of the big news in ocean exploration, not just at NOAA, but around the field. The stories posted represent just a snapshot and the list here is not intended to be all encompassing; posting of links does not constitute specific endorsement of a story or news outlet. Check back regularly to stay on top of the ever-changing world of deep-ocean exploration or visit the archive for past stories.

Most of the plastic that enters our oceans in unaccounted for. While large, charismatic macroplastics float on or just beneath the surface, making for dramatic scenes of vast swaths of garbage littering the sea, the bulk of the plastic in the ocean exists as tiny particles of degraded plastics that sink to the bottom, enter food chains, and accumulate not just in the ecosystem, but within the tissue of marine animals.

Most of the plastic that enters our oceans in unaccounted for. While large, charismatic macroplastics float on or just beneath the surface, making for dramatic scenes of vast swaths of garbage littering the sea, the bulk of the plastic in the ocean exists as tiny particles of degraded plastics that sink to the bottom, enter food chains, and accumulate not just in the ecosystem, but within the tissue of marine animals.

The deep sea is a hotspot for microplastic accumulation. While we are just beginning to understand how microplastics accumulate in deep ocean sediments, precious few studies have investigated microplastic accumulation within organisms at vents and seeps.

Microplastic sink that cannot be ignored in chemosynthetic organisms

Microplastics are now ubiquitous in the world’s oceans. Though they have been found in the tissues of shallow water species and isolated from deep-sea sediment, only a few studies have investigated the extent to which microplastics have accumulated in the tissues of deep sea macrofauna, especially those associated with hydrothermal vents and methane seeps. These ecosystems are not only deep, dark, and diverse, but rely on chemosynthesis for primary production.

If you’ve been following along with my adventures across social media, you may have seen that I recently inherited a massive collection of biological specimens from the deep sea. In addition to all the samples from my PhD work, I now have an archive that covers hydrothermal vents and methane seeps around the world collected over the last 20 years. This unique archive of biological samples provides a once-in-a-generation opportunity to establish a baseline for microplastic accumulation in hydrothermal vent and methane seep species.