PAST CLIMATE VARIABILITY FROM SOUTHERN GREENLAND LAKE SEDIMENTS: EXPLORING THE POTENTIAL OF SEDIMENTARY LIPID BIOMARKERS COMBINED WITH NOVEL HYPERSPECTRAL IMAGING TECHNIQUES

The Arctic is warming rapidly and there are concerns about Greenland’s climate. To put the current warming into context, previous warm periods need to be investigated. Chronologically well-constrained and high-resolution climate reconstructions from lakes help elucidate Greenland's past climate variability.

Lacustrine branched glycerol dialkyl glycerol tetraethers (brGDGTs) are useful biomarkers for reconstructing past temperature. However, the temporal resolution of brGDGTs is limited by the sample size required to obtain adequate material for analysis and the large amount of time needed for sample preparation. Recent advances in spectral imaging techniques (VIS-RS, spatial resolution: 2mm) reported a successful proxy-to-proxy (PtP) calibration between a high-resolution spectral index (RABD_660:670) and a low-resolution biomarker index (U^K₃₇) in lake sediments from W Greenland. Thus, spectral imaging techniques, which are relatively quick, increased the temporal resolution of the quantitative temperature reconstruction by an order of magnitude (von Gunten et al., 2012). Here, we explore the potential of a PtP between a hyperspectral imaging index (HSI, RABD_590:730, spatial resolution of 70µm, reflecting green-pigments and paleo productivity) and brGDGT-derived temperatures, from Lakes Igaliku and 578 from S Greenland. We also investigate hypolimnetic oxygen variations with the HSI index RABD_790:900 (bacteriopheophytin).

Both lakes reveal a rapid productivity increase during the 20^th century, while Lake 578 also records increased productivity from ~1000 - 400 cal. yrs BP. This stands in contrast to our evidence of a decreasing temperature trend (from brGDGTs) and likely reflects changes in local land use (sheep farming in recent years and during the Norse settlement period). The HSI index RABD_790:900 of Lake 578 shows rather anoxic conditions in the mid-Holocene indicating a thermally stratified water column. We suggest this was either caused by extended lake-ice cover or a different prevailing wind-pattern. The downcore brGDGT-temperature reconstruction (in progress), in addition to other algal biomarkers, will improve our understanding of the environmental and human factors causing changes in primary productivity and hypolimnetic oxygen variations in southern Greenland lakes.