Lacustrine organic geochemistry--an overview of indicators of organic matter sources and diagenesis in lake sediments

The factors affecting the amounts and types of organic matter in lacustrine sediments are summarized in this review, and synthesis, of published studies. Biota living in the lake and in its watershed are the sources of the organic compounds initially contributed to the lake system. Microbial reworking of these materials during sinking and early sedimentation markedly diminishes the total amount of organic matter while replacing many of the primary compounds with secondary ones. Much of the organic matter content of sediments is the product of this microbial reprocessing. Various organic matter components of lake sediments nonetheless retain source information and thereby contribute to the paleolimnological record. Carbon/nitrogen ratios of total organic matter reflect original proportions of algal and land-derived material. Carbon isotopic compositions indicate the history of lake productivity and carbon recycling. Biomarker compounds provide important information about contributions from different biota. Sterol compositions and chainlength distributions of n-alkanes, n-alkanoic acids, and n-alkanols help distinguish different algal and watershed sources and also record diagenetic alterations.Stabilization of functional-group-containing biomarkers by conversion into saturated or aromatic hydrocarbons or by incorporation into bound forms improves their preservation and hence record of source information. Lignin components provide important evidence of watershed plant cover, and pigments reflect algal assemblages. The interplay of the factors influencing the organic matter content of lake sediments is illustrated by overviews of sedimentary records of four lake systems--Lake Biwa (Japan), Lake Greifen (Switzerland), Lake Washington (Pacific Northwest), and the Great Lakes (American Midwest).Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30617/1/0000257.pd

Source identification of Malaysian atmospheric polycyclic aromatic hydrocarbons nearby forest fires using molecular and isotopic compositions

We report measurements of molecular and carbon isotopic compositions of Malaysian atmospheric polycyclic aromatic hydrocarbons (PAHs) in smoke haze from the 1997 Indonesian forest fire. Comparison of the carbon isotopic compositions (δ13C) of individual PAHs from the smoke haze, with those from other PAHs sources (soot collected from gasoline and diesel vehicle muffler, woodburning smoke), enables us to discriminate among the diverse sources of atmospheric PAHs. Soot PAHs extracted from gasoline and diesel vehicles show heavy isotopic signatures with a large inter-species δ13C variation from −12.9‰ to −26.6‰, compared to soot PAHs extracted from woodburning smoke which are isotopically light, and have a small inter-species δ13C variation from −26.8‰ to −31.6‰. Values from −17.7‰ to −27.9‰ were obtained for the corresponding PAHs extracted from the smoke haze, indicating that they are derived mainly from automotive exhaust. Molecular and isotopic compositions of PAHs extracted from smoke haze were similar to those extracted from non-haze aerosol. Quantitative estimation shows that woodburning contribution to Malaysian atmospheric PAHs ranges from 25% to 35% with no relation to haze intensity, while automotive contribution ranges from 65% to 75%. These results suggest that the major contributor of PAHs in Malaysian air is automotive exhaust whether smoke haze is observed or not

Calcium carbonate and organic carbon concentrations of ODP Holes 111-677A and 111-678B

The results of a preliminary organic analysis conducted on sediment samples from Sites 677 and 678, ODP Leg 111, indicate that the lipids are derived mainly from marine organisms, with bacterially-derived lipids. Terrestrial higher plant wax residues exist only in trace amounts. Diagenesis of organic matter by thermal stress is not extensive at either site

(Table 1) Oxygen isotope composition and comparison between ages and sea surface temperature from sediment core KH-79-3_L-3

The Japan Sea experienced bottom water anoxia at the last glacial maximum (LGM) since it is surrounded by four shallow straits, the sill depths of which are close to, or shallower than, the drop in sea level (~120 m) that occurred then. A distinctive negative d18O excursion of planktonic foraminifera also took place during the LGM. This excursion has been interpreted from foraminiferal data as recording a drop in the paleosalinity of surface waters on the assumption of a constant low sea surface temperatures between 34 and 11 ka. We present here a profile of alkenone-based sea surface temperatures (alkenone-SSTs) over the past 36 kyr. Our results suggest that SSTs during the LGM were much higher than those previously assumed. After considering the factors that might affect estimation of alkenone-SSTs and comparisons of core-top alkenone-SSTs values with values for modern seawater we conclude that the higher alkenone-SSTs during the LGM are reliable and reasonable. These warm SSTs were probably caused by radiative equilibrium associated with the development of stable water stratification in the Japan Sea during the LGM

(Table 1) Organic carbon, nitrogen and sulphur concentrations and δ¹³C of TOC from ODP Hole 167-1017E sediments

A high-resolution analysis of Hole 1017E revealed that total organic carbon (TOC) concentrations (24.8 ± 2.9 mg/g) and d13C of TOC (-21.3 ± 0.2 per mil) in Holocene sections are higher than those in glacial sediments (14.2 ± 4.8 mg/g and -22.1 per mil ± 0.1 per mil, respectively). The 306- to 280-cm section has high total sulfur concentrations, which may correspond to anoxia Event 1 (1 of the warm interstadials of GISP2) in the Santa Barbara Basin