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

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 bymore » 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 (~2m), (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« less

Authors:

Parazoo, Nicholas C. ;

• Search DOE PAGES for author "Parazoo, Nicholas C."
• Search DOE PAGES for ORCID "0000-0002-4424-7780"

Koven, Charles D. ;

• Search DOE PAGES for author "Koven, Charles D."
• Search DOE PAGES for ORCID "0000-0002-3367-0065"

Lawrence, David M. ;

• Search DOE PAGES for author "Lawrence, David M."
• Search DOE PAGES for ORCID "0000-0002-2968-3023"

Romanovsky, Vladimir ;

• Search DOE PAGES for author "Romanovsky, Vladimir"
• Search DOE PAGES for ORCID "0000-0002-9515-2087"

Miller, Charles E.

Publication Date:

Fri Jan 12 00:00:00 EST 2018

Research Org.:

Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Biological and Environmental Research (BER)

OSTI Identifier:

1459718

Alternate Identifier(s):

OSTI ID: 1435105

Grant/Contract Number:  

FC03-97ER62402/A0101; AC02-05CH11231

Resource Type:

Published Article

Journal Name:

The Cryosphere (Online)

Additional Journal Information:

Journal Name: The Cryosphere (Online) Journal Volume: 12 Journal Issue: 1; Journal ID: ISSN 1994-0424

Publisher:

Copernicus Publications, EGU

Country of Publication:

Germany

Language:

English

Subject:

54 ENVIRONMENTAL SCIENCES