Satellite gravimetry in studies of permafrost thawing and permafrost vegetation productivity
V. I. Kharuk1,2,3, A. S. Golyukov1,2,3, M. L. Dvinskaya1,3, S.T. Im1,2,3,4, I. A. Petrov1,2,3, E. G. Shvetsov1,3
1Krasnoyarsk Science Centre of the Siberian Branch of Russian Academy of Science, V. N. Sukachev Institute of Forest, Krasnoyarsk, Russia
2Tomsk State University, Tomsk, Russia
3Siberian Federal University, Krasnoyarsk, Russia
4Reshetnev Siberian State University of Science and Technology, Krasnoyarsk, Russia
Keywords: permafrost thawing, forest-tundra, GRACE, gravimetry, permafrost zone, northern larch forests, forest-tundra productivity
Abstract
Changes in the soil hydrothermal regime caused by the permafrost layer melting, represent the most important environmental factor in the dynamics of vegetation cover in the permafrost zone. The impact of soil melting on the growth index (GI) of larch ( Larix spp.) and on the gross and net primary productivity (GPP, NPP) of vegetation in the Arctic region of Central Siberia (open woodlands, tundra and forest-tundra) was studied. The following hypotheses were tested: (1) gravimetric data make it possible to estimate the water mass dynamics in soils; (2) thawing of frozen soils stimulates the growth of woody plants and the productivity of vegetation. The work used dendrochronology methods, field data, satellite gravimetry (GRACE survey) and GPP (Terra/MODIS survey). Analysis of gravimetry data revealed a significant long-term trend in water mass decreasing in soils of the permafrost zone (R2 = 0.68). The amount of water released during melting is estimated at 6.4 ± 2.3 kg/m-2 per year. A close connection was found between larch GI and GPP with moisture anomalies in soils (r = - 0.7 and r = - 0.9, respectively). The increasing temperature of the root layer and the moisture deficiency in water vapor also have a positive effect on the GI of larch and the vegetation GPP value in general (r = 0.6 and r = 0.6…0.9, respectively). It was found that pyrogenic carbon losses are significantly (by two orders of magnitude) lower than the NPP value. In conditions of waterlogging of soils, typical for the Arctic, climate warming is accompanied by an improvement in the hydrothermal regime of vegetation growth, promotes an increase in vegetation productivity and the permafrost zone maintains the status of a carbon sink area.
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