Bulk organic geochemistry of sediments from Puyehue Lake and its watershed (Chile, 40°S): Implications for paleoenvironmental reconstructions

Abstract

(376 words)Since the last deglaciation, the mid-latitudes of the southern Hemisphere have undergone considerable environmental changes. In order to better understand the response of continental ecosystems to paleoclimate changes in southern South America, we investigated the sedimentary record of Puyehue Lake, located in the western piedmont of the Andes in south-central Chile (40°S). We analyzed the elemental (C, N) and stable isotopic ( was then used to estimate the fraction of terrestrial carbon (ƒ T ) preserved in the lake sediments. Our approach was validated using surface sediment samples, which show a strong relation between ƒ T and distance to the main rivers and to the shore. We further applied this equation to an 11.22 m long sediment core to reconstruct paleoenvironmental changes in Puyehue Lake and its watershed during the last 17.9 kyr. Our data provide evidence for a first warming pulse at 17.3 cal kyr BP, which triggered a rapid increase in lake diatom productivity, lagging the start of a similar increase in sea surface temperature (SST) off Chile by 1500 years. This delay is best explained by the presence of a large glacier in the lake watershed, which delayed the response time of the terrestrial proxies and limited the concomitant expansion of the vegetation in the lake watershed (low ƒ T ). A second warming pulse at 12.8 cal kyr BP is inferred from an increase in lake productivity and a major expansion of the vegetation in the lake watershed, demonstrating that the Puyehue glacier had considerably retreated from the watershed. This second warming pulse is synchronous with a 2°C increase in SST off the coast of Chile, and its timing corresponds to the beginning of the Younger Dryas Chronozone. These results contribute to the mounting evidence that the climate in the mid-latitudes of the southern Hemisphere was warming during the Younger Dryas Chronozone, in agreement with the bipolar see-saw hypothesis.

Geochemistry of surface sediments from the fjords of Northern Chilean Patagonia (44–47°S): Spatial variability and implications for paleoclimate reconstructions

“…1) by Hebbeln et al (2000) (N/C = 0.130, δ 13 C = -19.86) and the terrestrial end-member as the average of five sediment samples (fraction <125 μm) collected in rivers that discharge into the fjords (N/C = 0.0624, δ 13 C = -27.72). The N/C value obtained on the river samples is very similar to the average of the seven soil samples (N/C = 0.0680) but it is preferred because it is known that N/C ratios are affected by transport in rivers and by weathering in soil profiles (Bertrand et al, 2010). Although bulk sedimentary δ 13 C data can also be used to calculate F terr (e.g., Sepúlveda et al, 2011), we prefer using the N/C data because δ 13 C values of marine organic matter are affected by several processes such as changes in productivity (e.g., Bickert, 2006).…”

Spatial distribution and sources of organic carbon in the surface sediment of Bosten Lake, China

“…For example, aqueous organic matter has low C : N ratios (4-10) (Meyers, 2003) whereas vascular land plants have much higher C : N ratios (> 20) (Rumolo et al, 2011;Lamb et al, 2004;Sifeddine et al, 2011). On the other hand, due to the difference in isotopic fractionation during photosynthesis, δ 13 C org value is more negative (ranging from −33 to −22 ‰) in terrestrial C 3 plants (Pancost and Boot, 2004;Wang et al, 2013) and lake plankton (Bertrand et al, 2010;Vuorio et al, 2006) than in C 4 plants (ranging from −16 to −9 ‰) (Pancost and Boot, 2004;Wang et al, 2013).…”

Elemental (C/N ratios) and isotopic (δ15Norg, δ13Corg) compositions of sedimentary organic matter from a high-altitude mountain lake (Meidsee, 2661 m a.s.l., Switzerland): Implications for Lateglacial and Holocene Alpine landscape evolution

“…Indeed, land-derived OM has C/N ratio higher than 14-20, while phytoplankton and aquatic macrophytes exhibit C/N ratios between 4 and 10 ( Meyers and Teranes, 2001). The carbon and nitrogen stable-isotope composition of autochtonous sedimentary OM can also be used to reconstruct changes in aquatic productivity rates and sources of nutrients (Bertrand et al, 2009). This is due to the fact that during periods of enhanced aquatic productivity, lacustrine algae preferentially consumes the dissolved light carbon isotope ( 12 C) during photosynthesis.…”