Reconstruct paleoclimate at the Norse Settlements of Greenland
Norse settlers developed the Eastern Settlement on southern Greenland in 985 CE, and the last documented evidence for their presence there was in the early 15th century. Climate change is often cited as the reason for settlement failure, however this explanation rests on poorly constrained paleoclimate records.
In this project, I used modern samples (soils, plants, settling particulate matters in water column, etc.) and lake sediment cores to validate, improve, and apply a relatively new paleothermometer (branched glycerol dialkyl glycerol tetraethers: brGDGTs) to reconstruct past temperature in southern Greenland. I also explored sedimentary leaf wax hydrogen isotopes to investigate the hydrological cycle over the past 2000 years from southern Greenland. The overall goal is to disentangle the climate-human-environment interactions in this region.
In this project, I used modern samples (soils, plants, settling particulate matters in water column, etc.) and lake sediment cores to validate, improve, and apply a relatively new paleothermometer (branched glycerol dialkyl glycerol tetraethers: brGDGTs) to reconstruct past temperature in southern Greenland. I also explored sedimentary leaf wax hydrogen isotopes to investigate the hydrological cycle over the past 2000 years from southern Greenland. The overall goal is to disentangle the climate-human-environment interactions in this region.
Improve the application of brGDGTs in Lake 578
brGDGTs are abundant in lake sediments and can potentially be used as proxies for evaluating past environmental conditions. Back to 2016 when this project was initiated, there was no lacustrine brGDGTs-temperature calibration. To validate and calibration this proxy in Arctic settings, we conducte a 3-year sediment trap experiment in Lake 578, a dimictic lake located in southern Greenland. We examine brGDGTs in a sediment core, surface sediments, catchment soils, and settling particulate matter (SPM). We find that the MBT′<sub>5ME</sub> (methylation of branched tetraethers) of Lake 578 SPM is strongly correlated with summer water temperature, thus we provide the first lake water temperature-brGDGT calibration of the MBT′<sub>5ME</sub> index. We also observe a significant cooling trend in the uppermost 7 cm, but this result is unrealistic because it conflicts with the instrumental temperature record from this region. The anomalous ‘‘core-top cooling” phenomenon, which is noted in numerous other published lacustrine brGDGT records, highlights the need for further studies of brGDGTs in modern and recent lake sediments.
B. Zhao, I. S. Castañeda, R. S. Bradley, J. M. Salacup, G. A. de Wet, W. C. Daniels, T. Schneider, Development of an in situ branched GDGT calibration in Lake 578, southern Greenland. Org. Geochem. 152, 104168 (2021). https://doi.org/10.1016/j.orggeochem.2020.104168
brGDGTs are abundant in lake sediments and can potentially be used as proxies for evaluating past environmental conditions. Back to 2016 when this project was initiated, there was no lacustrine brGDGTs-temperature calibration. To validate and calibration this proxy in Arctic settings, we conducte a 3-year sediment trap experiment in Lake 578, a dimictic lake located in southern Greenland. We examine brGDGTs in a sediment core, surface sediments, catchment soils, and settling particulate matter (SPM). We find that the MBT′<sub>5ME</sub> (methylation of branched tetraethers) of Lake 578 SPM is strongly correlated with summer water temperature, thus we provide the first lake water temperature-brGDGT calibration of the MBT′<sub>5ME</sub> index. We also observe a significant cooling trend in the uppermost 7 cm, but this result is unrealistic because it conflicts with the instrumental temperature record from this region. The anomalous ‘‘core-top cooling” phenomenon, which is noted in numerous other published lacustrine brGDGT records, highlights the need for further studies of brGDGTs in modern and recent lake sediments.
B. Zhao, I. S. Castañeda, R. S. Bradley, J. M. Salacup, G. A. de Wet, W. C. Daniels, T. Schneider, Development of an in situ branched GDGT calibration in Lake 578, southern Greenland. Org. Geochem. 152, 104168 (2021). https://doi.org/10.1016/j.orggeochem.2020.104168
Temperature and hydroclimate reconstructions from southern Greenland during the late Holocene
We reconstruct the temperature and hydroclimate history using brGDGTs and leaf wax hydrogen isotopes from Lake 578, situated in the Eastern Settlement with Norse ruins within the catchment. Our preliminary results show that increasingly dry conditions played a more important role in undermining the viability of the Eastern Settlement than minor temperature changes.
Stay tuned!
We reconstruct the temperature and hydroclimate history using brGDGTs and leaf wax hydrogen isotopes from Lake 578, situated in the Eastern Settlement with Norse ruins within the catchment. Our preliminary results show that increasingly dry conditions played a more important role in undermining the viability of the Eastern Settlement than minor temperature changes.
Stay tuned!