Supplementary information: organic matter analysis in Holocene and Pleistocene
sediments.
Results:
Detailed analysis of the organic biomarker distributions highlighted large differences between
the two sediments. The Pleistocene neutral polar fractions were characterized by highmolecular-weight (HMW) even-carbon-numbered n-alkanols (C22-C28); few sterols, with the
C29 components (24-ethylcholesta-5,22-dienol and 24-ethylcholest-5-ol) being dominant; and
trace quantities of compounds tentatively identified as triterpenoids. Trace C16 and C18 nalkanols were also present but in much lower abundances than the HMW homologues. The
Pleistocene fatty acids have a bimodal distribution with the high-molecular-weight (LMW)
components dominated by the C16 and C18 homologues and other LMW components, e.g. C15
and C17, present at only trace levels. The homologous series continues up to C 30, with the C22
and C24 components being the most abundant of the longer chain compounds; in addition, the
even-over-odd dominance of the HMW fatty acids was relatively minor, with odd-carbonnumber homologues being present at abundances about half of those of the even-carbonnumber homologues. Hopanoic acids were not detected.
Although biomarkers were not quantified, the Holocene sediments contained biomarkers
about an order of magnitude greater in concentration than in Pleistocene sediments. The
distributions also differed. The neutral polar fractions were dominated by C22-C34 n-alkanols,
with the C24-C30 homolgues being dominant. Sterols were also present but represented almost
exclusively by 24-ethylcholest-5-enol; also present were a range of higher plant derived
triterpenoids, including taraxerol and friedelanone. Also present was archaeol, derived from a
range of archaea (Koga et al., 1993). The Holocene sedimentary fatty acid distribution was
also bimodal; however, unlike the Pleistocene sediment, the LMW fatty acids were
subordinate to the HMW components, and the HMW homologues had a stronger even-overodd predominance and were dominated by the C24 to C30 components. Unsaturated LMW C16
and C18 fatty acids were also present. In addition, the Holocene sediment contained abundant
long-chain -OH fatty acids and a range of C31 to C33 hopanoic acids, dominated by
17β,21β(H)-bishomohopanoic acid.
Result interpretation:
The dominance of C29 steroids (Huang and Meinschein, 1976; Volkman, 1986;
Volkman et al., 1998), HMW fatty acids and n-alkanols with an even-over-odd predominance
(Eglinton and Hamilton, 1967; Kolattukyudy 1976), and triterpenoids, indicate that both the
Holocene and Pleistocene sedimentary organic matter is predominantly of terrigenous origin.
However, the Holocene sediments contained higher concentrations of organic matter. It is
also characterised by different biomarker distributions, which suggest it has apparently been
significantly less degraded, as indicated by the presence and greater variety of more
functionalised – and by extension, more labile – biomarkers such as -OH fatty acids. We
suggest that organic matter associated with Pleistocene sediments has been more extensively
oxidised, such that only relatively more recalcitrant biomarker classes have been preserved.
The presence of abundant hopanoids in Holocene sediments is also consistent with higher
concentrations of more labile, e.g. bioavailable, organic matter in the Holocene sediments,
whereas the presence of archaeol, which has been argued to be predominantly derived from
methanogens in terrestrial settings (e.g. Pancost et al., 2011), is consistent with relatively
reduced conditions. Thus, these distributions confirm that both Pleistocene and Holocene
organic matter is predominantly derived from terrigenous sources, but the latter is
characterised by overall higher concentrations of organic matter, more labile substrates and a
larger microbial population.