Expansion rate and geometry of floating vegetation mats on the margins of thermokarst lakes, northern Seward Peninsula, Alaska, USA

Abstract

Investigations on the northern Seward Peninsula in Alaska identified zones of recent (<50years) permafrost collapse that led to the formation of floating vegetation mats along thermokarst lake margins. The occurrence of floating vegetation mat features indicates rapid degradation of near-surface permafrost and lake expansion. This paper reports on the recent expansion of these collapse features and their geometry is determined using geophysical and remote sensing measurements. The vegetation mats were observed to have an average thickness of 0.57m and petrophysical modeling indicated that gas content of 1.5-5% enabled floatation above the lake surface. Furthermore, geophysical investigation provides evidence that the mats form by thaw and subsidence of the underlying permafrost rather than terrestrialization. The temperature of the water below a vegetation mat was observed to remain above freezing late in the winter. Analysis of satellite and aerial imagery indicates that these features have expanded at maximum rates of 1-2myr -1 over a 56year period. Including the spatial coverage of floating 'thermokarst mats' increases estimates of lake area by as much as 4% in some lakes.

Peat accumulation in drained thermokarst lake basins in continuous, ice‐rich permafrost, northern Seward Peninsula, Alaska

“…Despite the overestimation of C stocks in some of the thinner peat deposits, the estimate for the surface peat C stocks is conservative, since neither method adequately captures the oldest and thickest peat deposits. In addition, these estimates do not include peat that forms on lakes in the form of floating mats, which occupy a significant proportion of many arctic lakes [ Parsekian et al , 2011]. Our estimate of 6.6 Tg (1.7 × 10 10 g km −2 ) of surface peat C in the drained lake basins of the northern Seward Peninsula study area falls within the range of organic C estimates for the 0–30 cm (1 × 10 10 g km −2 ) and 0–100 cm (2.6 × 10 10 g km −2 ) depths in northern circumboreal soils [ Tarnocai et al , 2009], suggesting that the MNF‐ and NDVI‐based extrapolations realistically estimate the total amount of peat organic C.…”

Using the deuterium isotope composition of permafrost meltwater to constrain thermokarst lake contributions to atmospheric CH4 during the last deglaciation

“…We multiplied lake area A by CH 4 emission rates representative of first‐generation (160 ± 19.3 mg CH 4 m −2 yr −1 ), later generation (63.1 ± 11.4 mg CH 4 m −2 yr −1 ), and non‐yedoma thermokarst lakes (18.7 ± 2.0 mg CH 4 m −2 yr −1 ) (Walter Anthony et al, submitted manuscript, 2011) in order to estimate regional thermokarst lake CH 4 emissions over time. The CH 4 emission values are conservative in that they do not account for additional CH 4 emissions associated with littoral vegetation and floating mats, which are common features of many later generation thermokarst lakes [ Jones et al , 2011; Parsekian et al , 2011].…”

Long-term dynamics of a palsa in the sporadic permafrost zone of northwestern Quebec (Canada)

“…In fact, several palsas appeared in the discontinuous permafrost zone in northern regions of Russia, Scandinavia, and Canada during the Neoglacial, including the period of the Little Ice Age (LIA; ϳ1650-1850 A.D.) (e.g., Zoltai 1993Zoltai , 1995Vardy et al 1997Vardy et al , 1998Jasinski et al 1998;Peteet et al 1998;Blyakharchuk and Sulerzhitsky 1999;Oksanen et al 2001;Väliranta et al 2003;Oksanen 2005Oksanen , 2006Bhiry et al 2007;Jaworski and Niewiarowski 2012;Hunt et al 2013). Climate warming that began at the end of the 19th century then resulted in a degradation of peatland permafrost in a number of these regions, and the formation of thermokarst ponds (e.g., Sollid and Sörbel 1998;Zuidhoff and Kolstrup 2000;Payette et al 2004;Arlen-Pouliot and Bhiry 2005;Vallée andPayette 2007, Bauer andVitt 2011;Parsekian et al 2011;Jones et al 2013;Fillion et al 2014).…”