Ancient DNA in lake sediment records

The geological record offers our best opportunity for understanding how biological systems function over long timescales and under varying paleoenvironmental conditions. Understanding these ecosystem responses to change is critical for biologists trying to understand how organisms interact and adapt to environmental changes, and for geologists seeking to use these biology-geology relationships in order to reconstruct past climate conditions from sediment records. For example, enumeration of microscopic fossilizing protists, such as diatoms, has become a standard paleoecological approach in the fields of paleoclimatology and paleolimnology. However, the identification constructed MATs from surface sediments seem to be lower than measured MATs. An explanation for this mismatch could be the production of branched GDGTs in situ in lake sediments, which are in fact aquatic soils. Recently, this possibility has indirectly been shown for sediments from a fjord (Peterse et al., 2009) and two tropical lakes (Tierney and Russel, 2009; Figure 2: Ternary diagram showing the relative distribution of the three main types of GDGTs (drawn in Fig. 1) in different sedimentary environments. Lakes plotting in the red boxed area have potential for application of the TEX 86 proxy. See text for further explanation. Adapted from Blaga et al. (2009).