Preliminary Studies of the Radiocarbon Reservoir Effects in Lake Qinghai (china) Sediments and Their Relationship to Improved Geochronology of Lake Qinghai.
A key part of any paleoclimatic reconstruction based on lake sediments is establishment of a firm geochronology for the cores. In order to determine the geochronological problems which might confront the Lake Qinghai project, we have undertaken a pilot study, to investigate the 14C reservoir effects in some cores already collected. Past studies have anticipated some of the potential concerns with radiocarbon dating of the lake sediments. Preliminary sediment trap studies were carried out in 1989 by the Institute for Saltwater Lake Studies (Xining) at a site near the Fishery village on the south shore of the lake, by Kelts et al., (1989). Subsequent studies (Henderson, 2004; Shen et al., 2005) indicated there are substantial apparent reservoir effects - with discordances between carbonate and organic material from the same horizons. A modern water sample collected by Jull (2003) also indicated there could be an input of old carbon. It appears there may be "old" carbon inputs to either the dissolved organic carbon (DOC) or dissolved inorganic carbon (DIC). Particulate matter has not been studied, and this also needs to be quantified. Jull (2003) also established that the surface water sample DIC was approximately 111 pMC in October 2003, which implies a residence time of DIC of about 10 years. Recently, Yu et al. (2007) proposed a two-box model to explain the reservoir ages observed previously of ~1100 14C yr BP (derived from Henderson, 2004) and Shen Ji et al (2003) arrived a similar average value of 1039 14C yr BP. We have therefore undertaken a fresh study, using recently-collected short cores, to compare the radiocarbon reservoir effects in organic and inorganic fractions. Our results indicate that there is a variable component to the reservoir effect, suggesting that inputs to the lake are an important contribution to these effects. Better understanding of these effects is vital to an accurate geochronology of Lake Qinghai sediments.
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- 1100 GEOCHRONOLOGY;
- 1115 Radioisotope geochronology;
- 1135 Correlative geochronology