Lake 578: Holocene-length multiproxy (temperature, productivity, anoxia) reconstructions; 2019-2024

Global warming particularly impacts terrestrial and aquatic ecosystems in the Arctic. To constrain the sensitivity of Arctic lakes and make meaningful predictions about future change under global warming, we need to examine their response to previous warm phases, such as those throughout the Holocene. Lake sediments from Greenland’s deglaciated area offer valuable archives to investigate past climate variability and associated lake changes.
Here, we applied hyperspectral imaging and lipid biomarker thermometry to a Holocene-length sediment record from Lake 578 in the Eastern Settlement of the Norse (61.08° North (N), 45.62° West (W); ~170 meters (m) above sea level (asl)) to investigate the local temperature, productivity, and anoxia histories. We calibrated branched glycerol dialkyl glycerol tetraethers (brGDGTs) with summer mean water temperatures (SMWT) using a site-specific calibration and analyzed pigment fluxes based on hyperspectral imaging. Notably, the anoxia reconstructions were corroborated with two independent proxies (GDGT-0/Crenarchaeol and bacterio pheophytins). We investigated the lake's environmental history and identified periods of significant change by employing generalized additive models (GAMs).
Our results reveal significant environmental transitions in Lake 578 due to both natural climate shifts and anthropogenic impacts. During the early Holocene, low SMWT and productivity coupled with high anoxia suggested prolonged ice cover and inverted thermal stratification. In contrast, the mid-Holocene experienced higher SMWT and productivity, indicating reduced ice cover. The Holocene Thermal Maximum (7.5 – 4.5 thousand years before present (ka BP)) aligned with regional reconstructions. After 3ka BP, we observed a Neoglacial cooling phase characterized by increased anoxia and reduced temperatures due to enhanced stratification. At around 1.0 ka BP, Lake 578 saw a surge in productivity and anoxia, which we attribute to land use and lake damming by the Norse. Despite a post-Norse decrease in productivity and anoxia, the lake never recovered to its pre-Norse state. Modern sheep farming intensified productivity to high levels in recent decades. While early Holocene anoxia was due to natural cold temperature stratification induced by extended ice cover, anoxia during the Norse period was anthropogenically caused.
This research underscores the value of integrating lipid biomarkers with hyperspectral imaging for detailed reconstructions of changes within Arctic lakes. It provides crucial insights for anticipating the ecologic and climatic resilience of Arctic lakes to ongoing global warming and anthropogenic influence.
This dataset was published in QSR: Schneider et al. (2024) "Tracing Holocene Temperatures and Human Impact in a Greenlandic Lake: Novel Insights from Hyperspectral Imaging and Lipid Biomarkers"