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Soil organic layer: Implications for Arctic present-day climate and future
climate changes
Annette Rinke 1) , Peter Kuhry 2) and Klaus Dethloff 1)
1) Alfred Wegener Institute for Polar and Marine Research, Potsdam, Germany; Annette.Rinke@awi.de;
2) University of Stockholm, Department of Physical Geography and Quaternary Geology, Stockholm, Sweden
1. Introduction
A top layer of organic material is a dominant feature of
northern forest and tundra soils, and plays a prominent role
in ground temperature and moisture regimes because of its
distinct thermal and hydraulic properties.
Previous modelling studies have focussed on the impact of
organic soil on the ground temperature and moisture, and
surface energy fluxes (Lawrence and Slater, 2008).
However, it is important to indicate that changes in ground
heat flux necessarily affect turbulent heat fluxes which have
consequences for the regional Arctic climate. In this study,
we investigate these potentially critical feedbacks on Arctic
climate, and its impact on Arctic climate change estimates.
2. Simulations
The regional climate model HIRHAM is applied on a pan-
Arctic domain. It has been improved by coupling it to the
sophisticated land-surface model LSM from NCAR (Bonan,
1996; Saha et al., 2006). Further, moss, lichen and peat have
been included as additional texture types. Their thermal and
hydraulic parameters have been specified according to
Beringer et al. (2001). The top organic layer has been
prescribed according to land surface type. For the main
types it is as follows: non-wood tundra, 0–10 cm peat; forest
tundra, 0–10 cm moss and 10–30 cm peat; forests, 0–10 cm
moss/lichen. In deeper layers, the original mineral ground
texture has been kept.
The following HIRHAM simulations have been performed:
(i) For present-day climate, the model has been run over 21
years (1979–1999), driven by ERA40 analyses. The first 11
years are devoted to spin-up the deep ground conditions in
order to obtain a balanced ground-atmosphere system. The
remaining 10 years (1990–1999) have been analyzed.
(ii) For future climate change, the model has been run over
1980-1999 and 2080-2099, driven by ECHAM5/MPI-OM
20C control and A1B emission scenario data. The difference
between both periods quantifies the simulated change by the
end of the 21 st century.
To investigate the implications of a top organic layer the
differences between the runs without any organic layer and
the runs including such a layer have been analyzed for both
present-day and future climate.
3. Results
The inclusion of a top organic layer modifies not only the
ground thermal and hydrological regimes, but also
dynamically feeds back into the atmosphere (Rinke et al.,
2008).
The low thermal conductivity and high heat capacity of the
top organic layer cause an effective insulation of the
underlying ground, contributing there to slightly warmer
ground temperatures in winter and much cooler conditions
in summer. The strongest response is simulated for summer.
It reduces the ground temperatures by 0.5°C to 8°C. It is
shown that the ground temperature changes vary strongly
from region to region due to the specific climatological and
hydrological conditions. The addition of the top organic
layer has also effects on the energy exchange from and to
the surface. The most important calculated response is the
increased latent heat flux in summer due to a strong
increase in ground evaporation which causes a significant
2m air temperature decrease. Furthermore, the dynamical
response due to the turbulent heat flux changes affects the
large-scale atmospheric circulation. The regional mean sea
level pressure (SLP) changes over land are directly
thermally driven: An increase of SLP over those land
regions characterized by an air temperature cooling is
calculated. Furthermore, a remote SLP response over the
Arctic Ocean appears. In winter, the SLP is reduced over
the Barents- and Kara Seas which is an improvement
compared to observations.
Based on the GCM-driven simulations, the uncertainty of
the future climate change signal in 2m air temperature and
atmospheric circulation concerning the set-up of the land
surface model LSM is presently being quantified.
Acknowledgment. This research was supported by the
6th EU Framework Programme (CARBO-North project)
and the Bert Bolin Climate Research Centre of Stockholm
University.
References
Beringer, J., A.H. Lynch, F.S. Chapin III, M. Mack, G.B.
Bonan, The representation of Arctic soils in the Land
Surface Model (LSM): The importance of mosses, J.
Clim., 14, 3324-3335, 2001
Bonan, G.B., A land surface model for ecological,
hydrological and atmospheric studies: Technical
description and user guide, Tech. Rep. NCAR/TN-
417+STR, Boulder, USA, 1996
Lawrence, D.M., A.G. Slater, Incorporating organic soil
into a global climate model, Clim. Dyn., 30, 145 –
160, 2008
Rinke, A., P. Kuhry, K. Dethloff, Importance of soil
organic layer for Arctic climate: A sensitivity study
with an RCM, Geophys. Res. Lett., 35, L13709, 2008
Saha, S.K., A. Rinke, K. Dethloff, P. Kuhry, Influence of a
complex land surface scheme on Arctic climate
simulations, J. Geophys. Res., 111, D22104, 2006