24.000 years ago, the greenhouse gas methane started seeping from the Arctic Ocean floor northwest of Svalbard. And it is seeping still. New PhD thesis from CAGE sheds light on this event using minuscule time capsules.
Text: Maja Sojtaric
They are called foraminifera and are some of the most prolific creatures on the planet.
“Foraminifera are single-celled animals that float in the water column and live at the seafloor. They build shells from calcite, which are often well preserved in seafloor sediments after the foraminifera die and sink to the ocean bottom.” says PhD Andrea Schneider. She recently successfully defended her thesis, “Diagenetically altered benthic foraminifera reveal paleo-methane seepage.” at UiT The Arctic University of Norway.
Altered by methane through thousands of years
Methane release alters the tiny shells of “forams” and leaves a distinctive isotopic signature that can be examined my scientists. Isotopic signatures can be used to date past events of methane release, as well as their duration.
“When methane is released from the seafloor, a different type of calcite encrusts those left-over foraminifera shells. I investigated changes in calcite composition of the foraminifera shells over time looking especially for those affected by methane release.” says Schneider.
Foraminifera shells in Schneider’s studies were retrieved from the sediment cores from the ocean floor at Vestnesa Ridge north west of Svalbard. This investigation uncovered that periods of past methane release likely started occurring as the massive ice sheet over Svalbard-Barents Ice Sheet began retreating some 24 000 years ago. This release is still happening to this day.
Powerful greenhouse gas
Methane is a powerful greenhouse gas that contributes to climate warming. Large amounts of methane are stored in seafloor sediments as gas hydrate, and as these melt the gas is released into the water column. But little is known about this methane release: when did it first start and how long has the methane been seeping; why was it released; can periods of methane release be linked to regional environmental change.
Perhaps the most important question of all is: how and where can we find records of this past and present methane seepage?
“In my thesis I aim to illuminate these questions and contribute to knowledge needed to assert whether periods of methane release can be linked to regional environmental change.”
This helps scientists understand whether methane release from the seafloor is a recent phenomenon, or if it is a natural process that has been persisting over thousands of years.
“This research contributes to our knowledge of climate change and can inform models used for predictions of future climate change.” Schneider concludes.