Abstract
Abstract. A novel proxy for continental mean annual air temperature (MAAT) and soil pH, the MBT/CBT-paleothermometer, is based on the temperature (T) and pH-dependent distribution of specific bacterial membrane lipids (branched glycerol dialkyl glycerol tetraethers – GDGTs) in soil organic matter. Here, we tested the applicability of the MBT/CBT-paleothermometer to sediments from Lake Cadagno, a high Alpine lake in southern Switzerland with a small catchment of 2.4 km2. We analysed the distribution of bacterial GDGTs in catchment soils and in a radiocarbon-dated sediment core from the centre of the lake, covering the past 11 000 yr. The distribution of bacterial GDGTs in the catchment soils is very similar to that in the lake's surface sediments, indicating a common origin of the lipids. Consequently, their transfer from the soils into the sediment record seems undisturbed, probably without any significant alteration of their distribution through in situ production in the lake itself or early diagenesis of branched GDGTs. The MBT/CBT-inferred MAAT estimates from soils and surface sediments are in good agreement with instrumental values for the Lake Cadagno region (~0.5 °C). Moreover, downcore MBT/CBT-derived MAAT estimates match in timing and magnitude other proxy-based T reconstructions from nearby locations for the last two millennia. Major climate anomalies recorded by the MBT/CBT-paleothermometer are, for instance, the Little Ice Age (~14th to 19th century) and the Medieval Warm Period (MWP, ~9th to 14th century). Together, our observations indicate the quantitative applicability of the MBT/CBT-paleothermometer to Lake Cadagno sediments. In addition to the MWP, our lacustrine paleo T record indicates Holocene warm phases at about 3, 5, 7 and 11 kyr before present, which agrees in timing with other records from both the Alps and the sub-polar North-East Atlantic Ocean. The good temporal match of the warm periods determined for the central Alpine region with north-west European winter precipitation strength implies a strong and far-reaching influence of the North Atlantic Oscillation on continental European T variations during the Holocene.
Highlights
The assessment of climate variations in Earth’s history is of paramount importance for our comprehension of recent and future climate variability
The Lake Cadagno sediments were found to consist of regular, laminated background sediments intercalated with flood layers and slump deposits, the latter of which were sometimes extensive with a thickness of up to 71 cm (Fig. 2)
We argue that the application of the MBT/CBT-paleothermometer to Lake Cadagno sediments provides a robust and quantitative measure for paleo mean annual air temperature (MAAT) and soil pH variations during the Holocene
Summary
The assessment of climate variations in Earth’s history is of paramount importance for our comprehension of recent and future climate variability. H. Niemann et al.: Bacterial GDGTs in Holocene lake sediments and catchment soils reconstruction of pronounced T changes during Earth’s history (e.g. glacial-interglacial cycles) using proxy indicators in marine and terrestrial climate archives (e.g. sediments, ice cores and speleothems), well-constrained T reconstructions for the Holocene, for the continents, are comparably rare (Battarbee and Binney, 2008). Niemann et al.: Bacterial GDGTs in Holocene lake sediments and catchment soils reconstruction of pronounced T changes during Earth’s history (e.g. glacial-interglacial cycles) using proxy indicators in marine and terrestrial climate archives (e.g. sediments, ice cores and speleothems), well-constrained T reconstructions for the Holocene, for the continents, are comparably rare (Battarbee and Binney, 2008) This is partly caused by the fact that the Holocene is considered a rather stable time period with only subtle fluctuations in T (IPCC, 2007), which are difficult to resolve. Pollen and skeletal remains have an undoubted potential for indicating environmental T shifts, but floral and faunal community structure-based T reconstructions can be compromised by ecological and migratory effects (Seppaand Bennett, 2003; Larocque-Tobler, 2010)
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