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climate and geology

Editorial: Deep Carbon Science

by D. Cardace et al., Nov 12, 2020 in Front.Earth.Sci.

Editorial on the Research Topic
Deep Carbon Science

Our understanding of the slow, deep carbon cycle, key to Earth’s habitability is examined here. Because the carbon cycle links Earth’s reservoirs on nano- to mega-scales, we must integrate geological, physical, chemical, biological, and mathematical methods to understand objects and processes so small and yet so vast. Here, we profile current research in the physical chemistry of carbon in natural and model systems, processes ongoing in the deepest portions of planets, and observations of carbon utilization by the deep biosphere. The relationships between the carbon cycle and planetary habitability are undeniable, forming a conceptual anchor to all work in deep carbon science.

Carbon minerals respond to changing pressures, temperatures, and geochemical conditions. The geologic record preserves evidence of transitional periods at the submicroscopic to regional landscape scales, and demonstrates interplay between carbon-bearing phases and the biosphere. In a new review, Morrison et al. (2020) cast a retrospective look through deep time and call for emerging approaches to clarify the coevolution of the biosphere and geosphere.

Critical to transformations of Earth’s carbon inventory over time are indomitable tectonics – which influence Earth’s surface environment, weathering, metamorphism, magmatism, and volcanism. The slow, deep (endogenous) carbon cycle refines and re-distributes carbon within Earth. In fact, over the 200-million-year-long time scale, important tectonic controls on carbon cycling emerge (Wong et al., 2019). Wong et al. (2019) document the spatiotemporal evolution of fluxes inferred from plate tectonic reconstructions, and highlight CO2 fluxes from continental rift settings post-Pangea. The volcanic flux of CO2 has been successfully reconstructed by direct study of CO2 flux through lakes and adjacent soils (Hughes et al., 2019), an important and often overlooked CO2 valve linking lithosphere, atmosphere, and hydrosphere. From perspectives rooted deeper in the tectonic system, the important roles that serpentinites play in the carbon cycle are evaluated in two senses: 1) serpentinite as a carbon vector to the deep mantle (Merdith et al., 2019), and 2) serpentine mud volcanoes as sites of carbon mobilization through organic acid release (Eickenbusch et al., 2019), in a Mariana Trench case study.

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Atmospheric rivers help create massive holes in Antarctic sea ice

by Rutgers University, Nov 15, 2020 in WUWT

Warm, moist rivers of air in Antarctica play a key role in creating massive holes in sea ice in the Weddell Sea and may influence ocean conditions around the vast continent as well as climate change, according to Rutgers co-authored research.

Scientists studied the role of long, intense plumes of warm, moist air – known as atmospheric rivers – in creating enormous openings in sea ice. They focused on the Weddell Sea region of the Southern Ocean near Antarctica, where these sea ice holes (called polynyas) infrequently develop during the winter. A large hole in this area was first observed in 1973 and a hole developed again in the late winter and early spring of 2017.

IMAGE: A BAND OF CLOUDS IN AN ATMOSPHERIC RIVER EXTENDING FROM SOUTH AMERICA TO THE ANTARCTIC SEA ICE ZONE ON SEPT. 16, 2017. view more CREDIT: NASA

In the first study of its kind, published in the journal Science Advances, scientists found that repeated strong atmospheric rivers during late August through mid-September 2017 played a crucial role in forming the sea ice hole. These rivers brought warm, moist air from the coast of South America to the polar environment, warming the sea ice surface and making it vulnerable to melting.

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Possible 1,000-kilometer-long river running deep below Greenland’s ice sheet

by  Hokkaido University, Nov 12, 2020 in EurekaAlert

Computational models suggest that melting water originating in the deep interior of Greenland could flow the entire length of a subglacial valley and exit at Petermann Fjord, along the northern coast of the island. Updating ice sheet models with this open valley could provide additional insight for future climate change predictions.

IMAGE: THE SUGGESTED VALLEY AND POSSIBLE RIVER FLOWING FROM THE DEEP INTERIOR OF GREENLAND TO PETERMANN FJORD DEEP BELOW GREENLAND’S ICE SHEET (500 METERS BELOW SEA LEVEL). (CHRISTOPHER CHAMBERS ET AL,… view more 

CREDIT: CHRISTOPHER CHAMBERS ET AL, THE CRYOSPHERE, NOVEMBER 12, 2020.

Radar surveys have previously mapped Greenland’s bedrock buried beneath two to three thousand meters of ice. Mathematical models were used to fill in the gaps in survey data and infer bedrock depths. The surveys revealed the long valley, but suggested it was segmented, preventing water from flowing freely through it. However, the peaks breaking the valley into segments only show up in areas where the mathematical modelling was used to fill in missing data, so could not be real.

Christopher Chambers and Ralf Greve, scientists at Hokkaido University’s Institute of Low Temperature Science, wanted to explore what might happen if the valley is open and melting increases at an area deep in Greenland’s interior known for melting. Collaborating with researchers at the University of Oslo, they ran numerous simulations to compare water dynamics in northern Greenland with and without valley segmentation.

The results, recently published in The Cryosphere, show a dramatic change in how water melting at the base of the ice sheet would flow, if the valley is indeed open. A distinct subglacial watercourse runs all the way from the melting site to Petermann Fjord, which is located more than 1,000 kilometers away on the northern coast of Greenland. The watercourse only appears when valley segmentation is removed; there are no other major changes to the landscape or water dynamics.

“The results are consistent with a long subglacial river,” Chambers says, “but considerable uncertainty remains. For example, we don’t know how much water, if any, is available to flow along the valley, and if it does indeed exit at Petermann Fjord or is refrozen, or escapes the valley, along the way.”

If water is flowing, the model suggests it could traverse the whole length of the valley because the valley is relatively flat, similar to a riverbed. This suggests no parts of the ice sheet form a physical blockade. The simulations also suggested that there was more water flow towards the fjord with a level valley base set at 500 meters below sea level than when set at 100 meters below. In addition, when melting is increased only in the deep interior at a known region of basal melting, the simulated discharge is increased down the entire length of the valley only when the valley is unblocked. This suggests that a quite finely tuned relationship between the valley form and overlying ice can allow a very long down-valley water pathway to develop.

“Additional radar surveys are needed to confirm the simulations are accurate,” says Greve, who has been developing the model used in the study, called Simulation Code for Polythermal Ice Sheets (SICOPOLIS). “This could introduce a fundamentally different hydrological system for the Greenland ice sheet. The correct simulation of such a long subglacial hydrological system could be important for accurate future ice sheet simulations under a changing climate.”