The role of climate change in regulating Arctic permafrost peatland hydrological and vegetation change over the last millennium

Abstract

Climate warming has inevitable impacts on the vegetation and hydrological dynamics of high-latitude permafrost peatlands. These impacts in turn determine the role of these peatlands in the global biogeochemical cycle. Here, we used six active layer peat cores from four permafrost peatlands in Northeast European Russia and Finnish Lapland to investigate permafrost peatland dynamics over the last millennium. Testate amoeba and plant macrofossils were used as proxies for hydrological and vegetation changes. Our results show that during the Medieval Climate Anomaly (MCA), Russian sites experienced short-term permafrost thawing and this induced alternating dry-wet habitat changes eventually followed by desiccation. During the Little Ice Age (LIA) both sites generally supported dryhummock habitats, at least partly driven by permafrost aggradation. However, proxy data suggest that occasionally, MCA habitat conditions were drier than during the LIA, implying that evapotranspiration may create important additional eco-hydrological feedback mechanisms under warm conditions. All sites showed a tendency towards dry conditions as inferred from both proxies starting either from ca. 100 years ago or in the past few decades after slight permafrost thawing, suggesting that recent warming has stimulated surface desiccation rather than deeper permafrost thawing. This study shows links between two important controls over hydrology and vegetation changes in high-latitude peatlands: direct temperature-induced surface layer response and deeper permafrost layer-related dynamics. These data provide important backgrounds for predictions of Arctic permafrost peatlands and related feedback mechanisms. Our results highlight the importance of increased evapotranspiration and thus provide an additional perspective to understanding of peatland-climate feedback mechanisms.

Inconsistent Response of Arctic Permafrost Peatland Carbon Accumulation to Warm Climate Phases

“…But we also recorded some comparable features to previous studies. For example, in Russia the MCA warming resulted in permafrost thawing and the consequent establishment of moist fen‐type communities (Ind4; Zhang et al, ), which correspond to previous European Russian studies (e.g., Routh et al, ). However, these moist communities were subsequently replaced by shrubs and dry conditions, which were supported by testate amoeba reconstructions.…”

“…During the MCA, permafrost thawing and subsequent desiccation were recorded in our study sites (Zhang et al, ). In some parts of our sites, post–Little Ice Age (LIA) warming since 1850 CE has caused permafrost thawing and triggered Sphagnum establishment, while a stronger recent warming has started to desiccate the peat surface (Zhang et al, ). The peat plateaus both at Seida and Indico are elevated a few meters from the surrounding mineral soil, and the vegetation is dominated by shrub‐lichen‐moss communities, such as Betula nana , Rhododendron tomentosum , Empetrum nigrum , Polytrichum strictum , Sphagnum fuscum , S. lindbergii , and sedges of Eriophorum spp.…”

“…The estimated rate of permafrost loss may be approximately 4.0 million square kilometers per 1° warming (Chadburn et al, ), and permafrost landscapes are likely to get wetter (Oberman, ; Romanovsky et al, ) or drier (Zhang et al, ) in the future depending on microtopographical features. Interlinked changes in temperature and moisture conditions may trigger shifts in vegetation composition (e.g., Zhang et al, ) and consequently cause significant changes in C accumulation patterns (Charman et al, ; Treat et al, ). Moreover, permafrost thaw may expose substantial quantities of old stored organic C to decomposition (Jones et al, ; O'Donnell et al, ).…”

Pathways for Ecological Change in Canadian High Arctic Wetlands Under Rapid Twentieth Century Warming

“…The apparent increase in wetness is likely as a result of increased catchment thaw under warming conditions—a process that has been observed in other Arctic and alpine regions (Fontana et al, ; Woo & Young, ). The increase in dry indicator testate amoeba taxa may represent increasingly dry conditions toward the end of the growing season as a result of increased evapotranspiration over a longer and warmer summer (Oechel et al, ; Woo & Young, ; Zhang, Piilo, et al, ). This increased variability in hydrological conditions from ~ ad 1950 is further supported by the presence of the hummock mosses T. nitens (30%–50%) and Aulacomnium palustre (<5%).…”

“…Arctic wetlands exemplify the complexity of landscapes underlain by permafrost and typically occur in three locales: on ground affected by ice wedge formations (polygon mires), on previously glaciated terrain with favorable topographic depressions (known as patchy wetlands), and in coastal zones of isostatic uplift (coastal wetlands; Glenn & Woo, ; Woo & Young, ). Across Arctic wetlands, warming has been linked to greater plant biomass (Hill & Henry, ), vegetation composition changes and desiccation (Woo & Young, , ; Zhang, Piilo, et al, ). Ice wedge polygon mires specifically are complex and dynamic systems (de Klerk et al, ; Fritz et al, ), and degradation in response to recent warming has led to changes in vegetation and drainage (Fraser et al, ; Jorgenson et al, ; Liljedahl et al, ; Perreault et al, ).…”