Analysis of the microfossil content of sediment cores discloses that a subpolar species connected to Atlantic water spread widely into the Arctic Ocean during the Last Interglacial. This suggests that there was no ice in the Arctic during these summers. The results have been released in Nature Geoscience.
Photograph taken in the marginal ice zone of the Arctic Ocean from the Swedish icebreaker Oden, summer 2021. Image Credit: Flor Vermassen
An essential part of the Earth’s system, Arctic Sea ice, is melting quickly due to global warming. Within this century, it is predicted that summer sea ice will completely disappear. Researchers have looked to analogs from the geological past to gain a deeper understanding of the dynamics of the climate in a world without Arctic sea ice.
The Last Interglacial, between 129,000 and 115,000 years BP, is an interesting period to study because it is the last time in Earth’s history when global average temperatures were similar or perhaps higher than currently and sea levels were considerably higher, up to +6 to +9 m.
Flor Vermassen, Postdoctoral Researcher, Stockholm University
However, the amount of sea ice during this time has been heavily debated, and there is no consensus; as a result, knowledge of this time and scientists’ ability to simulate it in climate models are both constrained.
To address this, a group of marine geology scientists from the Department of Marine Geological Sciences at Stockholm University examined the microfossil content of numerous sediment cores from sites that lie directly beneath the thickest portions of the present-day Arctic ice pack.
They looked at the variation in planktonic foraminifera abundance and composition in these cores, a kind of free-floating, unicellular zooplankton that is sensitive to changes in oceanographic and environmental conditions.
The high relative abundance of the typically subpolar, Atlantic-water species Turborotalita quinqueloba discovered by the researchers provides evidence of the species’ extensive range expansion into the central Arctic Ocean. T. quinqueloba’s ecological preference for primarily ice-free, seasonally productive waters, typically found in the Atlantic Ocean, leads one to believe that it was adapting to conditions that had spread to the central Arctic Ocean.
The Arctic Ocean has undergone changes collectively known as “Atlantification” which are equivalent to the absence of summer sea ice and the increased influence of Atlantic currents in the Arctic domain during the Last Interglacial.
The finding that the Arctic Ocean was seasonally ice-free during the Last Interglacial is worrying because this period would have been only around 1.5 °C above pre-industrial levels, comparable to the targets of the Paris Agreement. Yet the global sea level is estimated to have been several meters higher than at present.
Flor Vermassen, Postdoctoral Researcher, Stockholm University
Thus, if the goals of the Paris Agreement are not exceeded, the researchers suggest that the most recent and possibly most pertinent geological epoch for studying a seasonally ice-free Arctic Ocean is the Last Interglacial.
To fully comprehend the physical conditions and environment of this unfamiliar Arctic during the Last Interglacial, additional quantitative proxy reconstructions of sea-surface temperature and other water mass parameters are needed, along with targeted climate and oceanographic model studies of the same period.
Flor Vermassen, Postdoctoral Researcher, Stockholm University
Journal Reference:
Vermassen, F., et al. (2023). A seasonally ice-free Arctic Ocean during the Last Interglacial. Nature Geoscience. doi.org/10.1038/s41561-023-01227-x.