Evidence that an ice-free Arctic Ocean allowed ancient CO2 and methane emissions

Speleothems like these form fastest when the permafrost has thawed. Image: By James St John, via Wikimedia Commons

As the world warms, more greenhouse gas will enter the atmosphere. Researchers now think an ice-free Arctic Ocean explains how and why.

by Tim Radford, Climate News Network, January 10, 2020

LONDON – Deep in a cave in Siberia, Israeli, Russian and British scientists have identified evidence of periodic losses of carbon from the permafrost. And the unexpected link is not simply with peak periods of bygone global warming, but with an ice-free Arctic Ocean. The escape into the atmosphere of prodigious volumes of methane and carbon dioxide from the thawing soils is in step not with average planetary temperature rise, but with long periods when the Arctic Ocean is free of ice every summer.

Fact one: about one quarter of land in the northern hemisphere is now, and has been for much of the last half million years, permanently frozen, and with it about twice as much atmospheric carbon – in the form of peat and preserved vegetation – as there exists freely in the planetary atmosphere.

Fact two: in the most recent decades, sea ice has been both thinning and dwindling rapidly, and the polar ocean could by 2050 become almost entirely ice-free in the summer months. “This discovery about the behaviour of the permafrost suggests that the expected loss of Arctic sea ice will accelerate melting of the permafrost presently found across much of Siberia” And this twist in the tale of a rapidly-warming Arctic is preserved in stalagmite formations in a cave deep beneath the rim of the Arctic Circle in Siberia.

The chronology of stalagmite and stalactite development can be established precisely by the pattern of uranium and lead isotope deposits in formations, built up imperceptibly by the steady drip of water from, and through, the soils far above. That is, the speleothems – a geologist’s catch-all word for both stalactite and stalagmite – form fastest when the permafrost has thawed. And unexpectedly, the periods of thaw did not match the peaks of interglacial warming during the last 1.35 million years. They did however coincide with periods when the Arctic was ice-free in the summer.

“This discovery about the behaviour of the permafrost suggests that the expected loss of Arctic sea ice in the future will accelerate melting of the permafrost presently found across much of Siberia,” said Gideon Henderson of the University of Oxford, and one of the authors of a new study in the journal Nature.

The argument goes like this: if there is no sea ice then more heat and moisture is delivered from the ocean to the atmosphere, with warmer air flowing over Siberia, and therefore more autumn snowfall. A blanket of snow insulates the soil beneath from the extreme winter cold, so ground temperatures go up, to unsettle the permafrost and start a thaw that leads to accelerated plant decay and ever-increasing escape of carbon dioxide and methane that would otherwise have been frozen into the permafrost. So the stalagmites endure as evidence of these warmer soils and survive as a direct link to periods of ice-free ocean.

“If these processes continue during modern climate change, future loss of summer Arctic sea ice will accelerate the thawing of Siberian permafrost,” the scientists say. 

https://climatenewsnetwork.net/ice-free-arctic-ocean-allowed-ancient-carbon-leaks/

Detecting the permafrost carbon feedback: talik formation and increased cold-season respiration as precursors to sink-to-source transitions

The Cryosphere, 12(1) (2018) 123–144

Detecting the permafrost carbon feedback: Talik formation and increased cold-season respiration as precursors to sink-to-source transitions

Nicholas C. Parazoo1, Charles D. Koven2, David M. Lawrence3, Vladimir Romanovsky4, and Charles E. Miller1
1Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, 91109, USA
2Lawrence Berkeley National Laboratory, Berkeley, CA, USA
3National Center for Atmospheric Research, Boulder, CO, USA
4Geophysical Institute UAF, Fairbanks, AK, 99775, USA

Received: 31 Aug 2017; discussion started: 18 Sep 2017
Revised: 20 Nov 2017; accepted: 29 Nov 2017; published: 12 Jan 2018

Abstract

Thaw and release of permafrost carbon (C) due to climate change is likely to offset increased vegetation C uptake in northern high-latitude (NHL) terrestrial ecosystems. Models project that this permafrost C feedback may act as a slow leak, in which case detection and attribution of the feedback may be difficult. The formation of talik, a subsurface layer of perennially thawed soil, can accelerate permafrost degradation and soil respiration, ultimately shifting the C balance of permafrost-affected ecosystems from long-term C sinks to long-term C sources. It is imperative to understand and characterize mechanistic links between talik, permafrost thaw, and respiration of deep soil C to detect and quantify the permafrost C feedback. Here, we use the Community Land Model (CLM) version 4.5, a permafrost and biogeochemistry model, in comparison to long-term deep borehole data along North American and Siberian transects, to investigate thaw-driven C sources in NHL ( >  55° N) from 2000 to 2300. Widespread talik at depth is projected across most of the NHL permafrost region (14 million km2) by 2300, 6.2 million km2 of which is projected to become a long-term C source, emitting 10 Pg C by 2100, 50 Pg C by 2200, and 120 Pg C by 2300, with few signs of slowing. Roughly half of the projected C source region is in predominantly warm sub-Arctic permafrost following talik onset. This region emits only 20 Pg C by 2300, but the CLM4.5 estimate may be biased low by not accounting for deep C in yedoma. Accelerated decomposition of deep soil C following talik onset shifts the ecosystem C balance away from surface dominant processes (photosynthesis and litter respiration), but sink-to-source transition dates are delayed by 20–200 years by high ecosystem productivity, such that talik peaks early ( ∼  2050s, although borehole data suggest sooner) and C source transition peaks late ( ∼  2150–2200). The remaining C source region in cold northern Arctic permafrost, which shifts to a net source early (late 21st century), emits 5 times more C (95 Pg C) by 2300, and prior to talik formation due to the high decomposition rates of shallow, young C in organic-rich soils coupled with low productivity. Our results provide important clues signaling imminent talik onset and C source transition, including (1) late cold-season (January–February) soil warming at depth ( ∼  2 m), (2) increasing cold-season emissions (November–April), and (3) enhanced respiration of deep, old C in warm permafrost and young, shallow C in organic-rich cold permafrost soils. Our results suggest a mosaic of processes that govern carbon source-to-sink transitions at high latitudes and emphasize the urgency of monitoring soil thermal profiles, organic C age and content, cold-season CO2 emissions, and atmospheric 14CO2 as key indicators of the permafrost C feedback.

Citation: Parazoo, N. C., Koven, C. D., Lawrence, D. M., Romanovsky, V., and Miller, C. E., Detecting the permafrost carbon feedback: Talik formation and increased cold-season respiration as precursors to sink-to-source transitions, The Cryosphere, 12, 123-144, https://doi.org/10.5194/tc-12-123-2018, 2018.

USGS Projects Large Loss of Alaska Permafrost by 2100 (and it won't stop there!)

Using statistically modeled maps drawn from satellite data and other sources, U.S. Geological Survey scientists have projected that the near-surface permafrost that presently underlies 38% of boreal and arctic Alaska would be reduced by 16-24% by the end of the 21st Century under widely accepted climate scenarios.

from the USGS, November 30, 2015

Using statistically modeled maps drawn from satellite data and other sources, U.S. Geological Survey scientists have projected that the near-surface permafrost that presently underlies 38% of boreal and arctic Alaska would be reduced by 16-24% by the end of the 21st century under widely accepted climate scenarios. Permafrost declines are more likely in central Alaska than northern Alaska. 

Northern latitude tundra and boreal forests are experiencing an accelerated warming trend that is greater than in other parts of the world. This warming trend degrades permafrost, defined as ground that stays below freezing for at least two consecutive years. Some of the adverse impacts of melting permafrost are changing pathways of ground and surface water, interruptions of regional transportation, and the release to the atmosphere of previously stored carbon. 

“A warming climate is affecting the Arctic in the most complex ways,” said Virginia Burkett, USGS Associate Director for Climate and Land Use Change. “Understanding the current distribution of permafrost and estimating where it is likely to disappear are key factors in predicting the future responses of northern ecosystems to climate change.” 

In addition to developing maps of near-surface permafrost distributions, the researchers developed maps of maximum thaw depth, or active-layer depth, and provided uncertainty estimates. Future permafrost distribution probabilities, based on future climate scenarios produced by the Intergovernmental Panel on Climate Change (IPCC), were also estimated by the USGS scientists. Widely used IPCC climate scenarios anticipate varied levels of climate mitigation action by the global community. 

These future projections of permafrost distribution, however, did not include other possible future disturbances in the future, such as wildland fires. In general, the results support concerns about permafrost carbon becoming available to decomposition and greenhouse gas emission. 

[Below, be sure to check out the size of the blue area in the north.]

The research has been published in Remote Sensing of Environment. The current near-surface permafrost map is available via ScienceBase.

Current probability of near-surface permafrost in Alaska. Future scenarios.

Funky music video (I kid you not!): Debris flow from a retrogressive thaw slump

https://www.youtube.com/watch?v=FSdb-T_9f-I