However, even if net accumulation of biomass continues for a very long time (and produces very deep soils), the rate of accumulation is going to be steady at best — it is certainly not going to increase as the forest matures. (realclimate.org)
Although recent models predict that a small net accumulation of carbon will occur in Arctic tundra during the present century (low confidence), higher methane emissions responding to the thawing of permafrost and an overall increase in wetlands will enhance radiative forcing (medium confidence). (ipcc.ch)
In fact, according to [Moelg and Hardy, 2004] precipitation aids net accumulation much more through the albedo affect, which reduces ablation, than through the mass added directly by snowfall. (geosci.uchicago.edu)