With the retreat of ice sheets during the transition from the last glacial period to the current interglacial, massive amounts of old organic material were released and found their way into the ocean. The material stemmed e.g. from oil shale, a type of rock containing substantial organic material, which was left behind as finely ground “glacial meal” by melting glaciers, was exposed to the atmosphere, and ultimately transported out to ocean, rapidly oxidising during the process. As our planet warmed after the last glacial, the release of old carbonaceous material from the land has raised the atmospheric CO2 concentration by as much as 12 ppm. These findings were just released by researchers from the Alfred Wegener Institute in the journal Nature Communications.
![[Translate to English:] AWI - Massenspektrometer C14-Labor](/fileadmin/_processed_/4/b/csm_20161124_C14_Labor_039_AWI_2acf17d439.jpg "Carbon dating MICADAS C14 laboratory")
As the climate continues to warm, in the Arctic larger and larger amounts of fossil organic material are being released into the ocean, because the erosion of the Arctic’s coasts continues to accelerate. In addition to thawing permafrost soils, experts from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) have now discovered a further source of fossil carbon: types of rock containing kerogen, like oil shale. In the form of finely ground glacial meal, they are released by melting glaciers and partly transported to the ocean; moreover, they can oxidise very quickly.
The team of researchers analysed a nearly six-metre-long sediment core – collected at a water depth of ca. 1,200 metres offshore of the Mackenzie River Delta of northern Canada that encompasses the past 14,000 years. As such, this sediment archive reflects the transition from the last glacial period (roughly 20,000 years ago) to the current interglacial, which began ca. 10,000 years ago. “The data from this sediment archive indicate that the oxidative release of CO2 from organic-rich rock during the transition from the last ice age to today’s interglacial played a significant, previously overlooked role,” says Dr Gesine Mollenhauer, one of the study’s authors. The AWI geochemist heads the MICADAS 14 C laboratory (MIniCArbonDAtingSystem), where the analyses took place.
“During the last glacial, the catchment area of the Mackenzie River was glaciated, which means we can’t expect to find any organic-rich thawing permafrost soils as a source there,” Mollenhauer explains. Such soil can only be found on the coasts to the west of the Mackenzie. With the aid of radiocarbon techniques, AWI Ph.D. candidate Junjie Wu, Gesine Mollenhauer and their colleagues have now confirmed the existence of multiple phases in which large amounts of old organic material reached the ocean. “These occurred not only during sea-level-rise maxima ca. 14,000 and 11,000 years ago, but also during a flooding event from the Mackenzie ca. 13,000 years ago. That tells us that an inland source must have also contributed.” Using a carbon-cycle model, the team estimated how this release affected the atmospheric CO2 concentration. Their findings show that the release of old organic material from the land increased the atmospheric CO2 concentration by up to 12 ppm, while simultaneously decreasing its 14C signature by ca. 12 ‰ .
The new study will make it possible to predict which additional greenhouse-gas emissions can be expected from thawing in permafrost regions and melting in ice-covered regions. “In a time marked by rapid ice-sheet decline in Greenland and West Antarctica, there could be the risk of an additional, previously overlooked greenhouse-gas-releasing process,” says Gesine Mollenhauer with regard to the study’s outcomes.
Original publication:
Junjie Wu, Gesine Mollenhauer, Ruediger Stein, Peter Köhler, Jens Hefter, Kirsten Fahl, Hendrik Grotheer, Bingbing Wie, Seung-Il Nam: Deglacial release of petrogenic and perma- frost carbon from the Canadian Arctic impacting the carbon cycle, Nature Communications (2022). DOI: https://doi.org/10.1038/s41467-022-34725-4