Anthropocene climate warming enhances autochthonous carbon cycling in an upland Arctic lake, Disko Island, West Greenland

Mark A. Stevenson,Xianyu Huang,George E. A. Swann,Suzanne McGowan,Erika Whiteford,Joseph J. Bailey,Emma J. Pearson,Melanie J. Leng,Vivienne J. Jones

doi:10.5194/bg-18-2465-2021

Abstract

Abstract. The Arctic is rapidly changing, disrupting biogeochemical cycles and the processing, delivery and sedimentation of carbon (C), in linked terrestrial–aquatic systems. In this investigation, we coupled a hydrogeomorphic assessment of catchment soils, sediments and plants with a recent lake sediment sequence to understand the source and quality of organic carbon present in three Arctic upland lake catchments on Disko Island, located just south of the low–high Arctic transition zone. This varied permafrost landscape has exposed soils with less vegetation cover at higher altitudes, and lakes received varying amounts of glacial meltwater inputs. We provide improved isotope and biomarker source identifications for palaeolimnological studies in high-latitude regions, where terrestrial vegetation is at or close to its northerly and altitudinal range limit. The poorly developed catchment soils lead to lake waters with low dissolved organic carbon (DOC) concentrations (≤1.5 mg L−1). Sedimentary carbon/nitrogen (C/N) ratios, the C isotope composition of organic matter (δ13Corg) and biomarker ratios (n-alkanes, n-alkanols, n-alkanoic acids and sterols) showed that sedimentary organic matter (OM) in these lakes is mostly derived from aquatic sources (algae and macrophytes). We used a 210Pb-dated sediment core to determine how carbon cycling in a lake–catchment system (Disko 2) had changed over recent centuries. Recent warming since the end of the Little Ice Age (LIA∼1860 CE), which accelerated after ca. 1950, led to melt of glacier ice and permafrost, releasing nutrients and DOC to the lake and stimulating pronounced aquatic algal production, as shown by a >10-fold increase in β-carotene, indicative of a major regime shift. We also demonstrate that recent increases in catchment terrestrial vegetation cover contributed to the autochthonous response. Our findings highlight that in Arctic lakes with sparsely developed catchment vegetation and soils, recent Anthropocene warming results in pronounced changes to in-lake C processing and the deposition of more reactive, predominately autochthonous C, when compared with extensively vegetated low-Arctic systems.

Highlights

The carbon (C) stored and cycled in permafrost, soils and lake sediments of Arctic landscapes is a vital component of the terrestrial C budget (Hugelius et al, 2014; Anderson et al, 2019), but Arctic ecosystems are changing rapidly (Saros et al, 2019)
This paper investigates the organic geochemistry of organic matter (OM) in the catchments and lake sediments on Disko Island to identify how terrestrial and aquatic δ13Corg biomarkers (C/N ratios and δ13Corg/δ13CFAMEs, chlorophyll and carotenoid pigments) can be interpreted as palaeoenvironmental proxies in this sparsely vegetated Arctic region
Our study demonstrates that Arctic lakes in catchments with limited vegetation and located at the transition between the low- and high-Arctic can respond rapidly to recent warming throughout the Anthropocene

Summary

Introduction

The carbon (C) stored and cycled in permafrost, soils and lake sediments of Arctic landscapes is a vital component of the terrestrial C budget (Hugelius et al, 2014; Anderson et al, 2019), but Arctic ecosystems are changing rapidly (Saros et al, 2019). Climate warming in Arctic regions (Smol and Douglas, 2007) can change the ecosystem structure of catchments and lakes with probable implications for landscape-scale C cycling (Anderson et al, 2018). “Arctic greening”, where warmer temperatures have enhanced terrestrial vegetation growth (Arndt et al, 2019), or “Arctic browning”, where changing climate regimes such as drought and winter warming can reduce vegetation productivity (Phoenix and Bjerke, 2016), has the potential to alter primary production in lakes (McGowan et al, 2018), with associated implications for C cycling. Characterised by the presence (low Arctic) or absence (high Arctic) of vegetation, warming may push marginal ecosystems into different ecological states (Corell et al, 2013)

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