Abstract
Warmer temperatures and elevated atmospheric CO2 concentrations over the last several decades have been credited with increasing vegetation activity
and photosynthetic uptake of CO2 from the atmosphere in the high
northern latitude ecosystems: the boreal forest and arctic tundra. At the
same time, soils in the region have been warming, permafrost is melting, fire
frequency and severity are increasing, and some regions of the boreal forest
are showing signs of stress due to drought or insect disturbance. The recent
trends in net carbon balance of these ecosystems, across heterogeneous
disturbance patterns, and the future implications of these changes are
unclear. Here, we examine CO2 fluxes from northern boreal and tundra
regions from 1985 to 2012, estimated from two atmospheric inversions (RIGC and Jena).
Both used measured atmospheric CO2 concentrations and wind fields from
interannually variable climate reanalysis. In the arctic zone, the latitude
region above 60° N excluding Europe
(10° W–63° E), neither inversion finds a significant long-term
trend in annual CO2 balance. The boreal zone, the latitude region from
approximately 50–60° N, again excluding Europe,
showed a trend of 8–11 Tg C yr−2 over the common period of validity
from 1986 to 2006, resulting in an annual CO2 sink in 2006 that was
170–230 Tg C yr−1 larger than in 1986. This trend appears to
continue through 2012 in the Jena inversion as well. In both latitudinal
zones, the seasonal amplitude of monthly CO2 fluxes increased due to
increased uptake in summer, and in the arctic zone also due to increased
fall CO2 release. These findings suggest that the boreal zone has been
maintaining and likely increasing CO2 sink strength over this period,
despite browning trends in some regions and changes in fire frequency and land
use. Meanwhile, the arctic zone shows that increased summer CO2 uptake,
consistent with strong greening trends, is offset by increased fall CO2 release, resulting in a net neutral trend in annual fluxes. The inversion
fluxes from the arctic and boreal zones covering the permafrost regions
showed no indication of a large-scale positive climate–carbon feedback caused
by warming temperatures on high northern latitude terrestrial CO2 fluxes from 1985 to 2012.
Citation
ID:
229615
Ref Key:
welp2016atmosphericincreasing