Résumé
In this paper, we investigate the influences of different environmental parameters on branched glycerol dialkyl glycerol tetraethers (brGDGTs) distributions from soils and wetland from the semi-arid to arid altitudinal transect from the Republic of Armenia. Large variation between elevation across this mountainous region means changes in temperature, precipitation, and vegetation occur in short distances making it an ideal location for understanding these influences on brGDGT communities. In addition to the traditional measured environmental markers (i.e. temperature and precipitation) we also utilize remote sensing data from Google Earth Engine (i.e. Sentinel, Landsat, TerraClimate, etc.) to calculate vegetation indices (i.e. NDVI, EVI) and classify land-use characteristics (i.e. agriculture, pastoral, and industrial land-use) to evaluate if vegetation and human landscape change influences this distribution. We find, similar to previous studies (i.e. Dugerdil et al., 2021), that temperature and moisture/aridity influence the distribution of brGDGTs in our soils. Also, similar to Guo et al. (2021) we also note the influence of temperature and aridity on methylation of both the 5 and 6 brGDGTs which may impact temperature reconstructions based on the MBT5'me index alone. And finally, we find that changes in brGDGTs occur between areas of dense grassland vegetation and more open desert vegetation which may be linked to precipitation controls and effective moisture on vegetation along with human land clearing. However, these soil samples differ from those in wetland and peat contexts suggesting differences in environmental controls. This is the first step in a larger project aiming to create calibrations in the semi-arid and arid S. Caucasus while exploring the expansion of the biomarker into new areas of investigation including the archaeological record. Dugerdil, Lucas, et al. "Climate reconstructions based on GDGT and pollen surface datasets from Mongolia and Baikal area: calibrations and applicability to extremely cold-dry environments over the Late Holocene." Climate of the Past17.3 (2021): 1199-1226. Guo, Jingjing, et al. "Soil pH and aridity influence distributions of branched tetraether lipids in grassland soils along an aridity transect." Organic Geochemistry (2021): 104347.