Polygonal tundra geomorphological change in response to warming alters future CO₂ and CH₄ flux on the Barrow Peninsula

Abstract

The landscape of the Barrow Peninsula in northern Alaska is thought to have formed over centuries to millennia, and is now dominated by ice-wedge polygonal tundra that spans drained thaw-lake basins and interstitial tundra. In nearby tundra regions, studies have identified a rapid increase in thermokarst formation (i.e., pits) over recent decades in response to climate warming, facilitating changes in polygonal tundra geomorphology. We assessed the future impact of 100 years of tundra geomorphic change on peak growing season carbon exchange in response to: (i) landscape succession associated with the thaw-lake cycle; and (ii) low, moderate, and extreme scenarios of thermokarst pit formation (10%, 30%, and 50%) reported for Alaskan arctic tundra sites. We developed a 30 × 30 m resolution tundra geomorphology map (overall accuracy:75%; Kappa:0.69) for our ~1800 km² study area composed of ten classes; drained slope, high center polygon, flat-center polygon, low center polygon, coalescent low center polygon, polygon trough, meadow, ponds, rivers, and lakes, to determine their spatial distribution across the Barrow Peninsula. Land-atmosphere CO2 and CH4 flux data were collected for the summers of 2006-2010 at eighty-two sites near Barrow, across the mapped classes. The developed geomorphic map was used for the regional assessment of carbon flux. Results indicate (i) at present during peak growing season on the Barrow Peninsula, CO2 uptake occurs at -902.3 10(6) gC-CO2 day(-1) (uncertainty using 95% CI is between -438.3 and -1366 10(6) gC-CO2 day(-1)) and CH4 flux at 28.9 10(6) gC-CH4 day(-1) (uncertainty using 95% CI is between 12.9 and 44.9 10(6) gC-CH4 day(-1)), (ii) one century of future landscape change associated with the thaw-lake cycle only slightly alter CO2 and CH4 exchange, while (iii) moderate increases in thermokarst pits would strengthen both CO2 uptake (-166.9 10(6) gC-CO2 day(-1)) and CH4 flux (2.8 10(6) gC-CH4 day(-1)) with geomorphic change from low to high center polygons, cumulatively resulting in an estimated negative feedback to warming during peak growing season.

PeRL: a circum-Arctic Permafrost Region Pond and Lake database

“…Ground surveys of waterbody surface area were available for only a few study sites. Accuracy ranged between 89 % for object-oriented mapping of multispectral imagery (Lara et al, 2015), 93 % for object-oriented mapping of panchromatic imagery (Andresen and Lougheed, 2015), and more than 95 % for a supervised maximum-likelihood classification of multispectral aerial images (Muster et al, 2012). Errors in the classification may be largely due to commission errors: i.e., the spectral signal is misinterpreted as water where in reality it may be land surface.…”

“…Due to their small surface areas and shallow depths, ponds are especially prone to change; various studies reported ponds drying out or increasing in abundance due to new thermokarst or the drainage of large lakes (Jones et al, 2011;Andresen and Lougheed, 2015;Liljedahl et al, 2016). Such changes in surface inundation may significantly alter regional water, energy, and carbon fluxes (Watts et al, 2014;Lara et al, 2015). Both the monitoring and modeling of pond and lake development are therefore crucial to better understand the trajectories of Arctic land cover dynamics in relation to climate and environmental change.…”

Thermo-erosion gullies boost the transition from wet to mesic tundra vegetation

“…The presence of Carex aquatilis, Eriophorum scheuchzeri and Dupontia fisheri characterizes well the typical vegeta- tion of Arctic wetlands (Jorgenson et al, 2013;Sandvik and Odland, 2014;Lara et al, 2015) whilst that of Arctagrostis latifolia, Luzula and Salix spp. are common features of Arctic mesic environments (Audet et al, 2007;Sjögersten et al, 2008).…”

“…There is evidence for a strong vegetation control on methane emission from wetlands (Olefeldt et al, 2013;Lara et al, 2015;McEwing et al, 2015;Tveit et al, 2015). In wet polygonal tundra of Northern Siberia, Kutzbach et al (2004) found for instance that dense Carex aquatilis stands emitted more methane than sites with low Carex densities.…”

Impacts of temperature and soil characteristics on methane production and oxidation in Arctic polygonal tundra

“…The large uncertainty associated with this estimation is due to the spatial and temporal 15 complexity of the Arctic ecosystem. The unique polygonal ground in Arctic coastal plain tundra creates natural gradients in hydrology, snow pack depth and density, and soil organic carbon storage that control CH 4 fluxes Lara et al, 2015). Thermal contraction processes create cracks in the tundra soil, which can fill with water that freezes to produce massive ground ice (French, 2007).…”