Deeper snow increases the net soil organic carbon accrual rate in moist acidic tussock tundra:²¹⁰Pb evidence from Arctic Alaska

Abstract

The net change in the carbon inventory of arctic tundra remains uncertain as global warming leads to shifts in arctic water and carbon cycles. To better understand the response of arctic tundra carbon to changes in winter precipitation amount, we investigated soil depth profiles of carbon concentration and radionuclide activities (7 Be, 137 Cs, 210 Pb, and 241 Am) in the active layer of a twenty-two-year winter snow depth manipulation experiment in moist acidic tussock tundra at Toolik Lake, Alaska. Depth correlations of cumulative carbon dry mass (g cm −2) vs. unsupported 210 Pb activity (mBq g −1) were examined using a modified constant rate of supply (CRS) model. Results were best fit by two-slope CRS models indicating an apparent step temporal increase in the accumulation rate of soil organic carbon. Most of the best-fit model chronologies indicated that the increase in carbon accumulation rate apparently began and persisted after snow fence construction in 1994. The inhomogeneous nature of permafrost soils and their relatively low net carbon accumulation rates make it challenging to establish robust chronologic records. Nonetheless, the data obtained in this study support a decadal-scale increase in net soil organic carbon accumulation rate in the active layer of arctic moist acidic tussock tundra under conditions of increased winter precipitation.

More Snow Accelerates Legacy Carbon Emissions From Arctic Permafrost

“…A younger soil age at the organic‐mineral interface (at 25–40 cm below the surface, Figure 1) indicates greater inputs of modern carbon (CO 2 assimilated by photosynthesis since 1950), presumably from the rhizosphere. This modern carbon input is consistent with our observations of greater GPP (Figure 2a–2c) and with earlier work that reported two to three times greater carbon accumulation rates in the topsoil (2.8 ± 0.2 to 4.6 ± 0.3 mg cm −2 yr −1 , 0–15 cm depth) (DeFranco et al., 2020). In summary, more snow triggered soil thaw, compaction, and subsidence, which together with greater plant activity, greatly increased the amount of carbon and nitrogen in the active layer.…”

“…), lichens, and mosses. To simulate forecasted increases in Arctic snow, a 2.8 m‐tall, 60 m‐wide wooden snow fence was installed perpendicular to the prevailing wind direction in 1994 that accumulates a tapered snowdrift on its leeward (north) side (DeFranco et al., 2020). This study was conducted about 30 m from the fence (intermediate zone).…”