In:
Climate of the Past, Copernicus GmbH, Vol. 14, No. 12 ( 2018-12-18), p. 2011-2036
Abstract:
Abstract. We have developed a
new module to calculate soil organic carbon (SOC) accumulation in perennially
frozen ground in the land surface model JSBACH. Running this offline version
of MPI-ESM we have modelled long-term permafrost carbon accumulation and
release from the Last Glacial Maximum (LGM) to the pre-industrial (PI) age.
Our simulated near-surface PI permafrost extent of
16.9 × 106 km2 is close to observational estimates.
Glacial boundary conditions, especially ice sheet coverage, result in
profoundly different spatial patterns of glacial permafrost extent. Deglacial
warming leads to large-scale changes in soil temperatures, manifested in
permafrost disappearance in southerly regions, and permafrost aggregation in
formerly glaciated grid cells. In contrast to the large spatial shift in
simulated permafrost occurrence, we infer an only moderate increase in total
LGM permafrost area (18.3 × 106 km2) – together with
pronounced changes in the depth of seasonal thaw. Earlier empirical
reconstructions suggest a larger spread of permafrost towards more southerly
regions under glacial conditions, but with a highly uncertain extent of
non-continuous permafrost. Compared to a control simulation without describing the transport of SOC into perennially
frozen ground, the implementation of our newly developed module for simulating permafrost
SOC accumulation leads to a doubling of simulated LGM permafrost SOC storage (amounting
to a total of ∼ 150 PgC). Despite LGM temperatures favouring a larger permafrost
extent, simulated cold glacial temperatures – together with low precipitation and low
CO2 levels – limit vegetation productivity and therefore prevent a larger
glacial SOC build-up in our model. Changes in physical and biogeochemical boundary
conditions during deglacial warming lead to an increase in mineral SOC storage towards
the Holocene (168 PgC at PI), which is below observational estimates (575 PgC in
continuous and discontinuous permafrost). Additional model experiments clarified the
sensitivity of simulated SOC storage to model parameters, affecting long-term soil carbon
respiration rates and simulated ALDs. Rather than a steady increase in carbon release
from the LGM to PI as a consequence of deglacial permafrost degradation, our results
suggest alternating phases of soil carbon accumulation and loss as an effect of dynamic
changes in permafrost extent, ALDs, soil litter input, and heterotrophic respiration.
Type of Medium:
Online Resource
ISSN:
1814-9332
DOI:
10.5194/cp-14-2011-2018
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2018
detail.hit.zdb_id:
2217985-9
Permalink
