A study of paleoclimatic changes in the marine environment using stable isotope and lipid biomarkers

Abstract

Organic matter sources and sea surface temperatures recorded by lipid bi-omarkers in the sediment of the western Arctic Ocean for the last 100 years Lipid biomarkers from sediment cores from the Western Arctic Ocean were identified and quantified in order to determine the origin and transport of organic matter in the Chukchi shelf and Canada Basin. The average concentration of the hy-drocarbon marker (n-C15, n-C17, n-C19, n-C27, n-C29 and n-C31) from of the cores (01MUC 03 and 01MUC 27) was approximately 201.17 μg/g (dry sediment) and 174. 89 μg/g (dry sediment) respectively. The hydrocarbon and fatty acid molecular markers indicated a higher contribution from marine organisms in the shelf than in the basin with minor contributions by terrestrial organic matter. The calculated diol index value ranges from 30.2 to 78.8 and 8.0 to 26.8 on the shelf and the basin re-spectively with the basin recording a lower diol index. In order to reconstruct the change in sea surface temperature (SST) from the shelf and the basin, we investigat-ed the alkenone temperature (UK'37 temperature) and long chain alkyl diol tempera-ture indices in the core sediments. Variations seen in the alkenone and long chain al-kyl diol concentrations is to be as a result of the production by haptophyte algae and eustimatophyte algae, respectively. The significant difference between the diol com-positions of the Chukchi shelf and the Canada Basin, probably reflects the differ-ences in the water masses. An offset of approximately ~1 °C (although within the calibration error of both proxies) was seen between the inferred alkenone and the long chain alkyl diol temperatures in the Canada Basin. This difference might be aattributed to the production of both organisms (haptophyte algae and eustigmatophyte algae) at different seasons or depths, thereby showing different trends in the SSTs. These results suggest that the combination of the alkenone tem-perature (UKʹ37 temperature) and the long chain alkyl diol temperature (LDI tempera-ture) can be useful instruments for analyzing changes in ocean surface temperature in the western Arctic.

A paleoenvironmental reconstruction of the last 15,000 cal yr BP via Yellow Sea sediments using biomarkers and the isotopic composition of organic matter This study is the first reconstruction of the paleoenvironment and paleovegetation during the Holocene (interglacial) and glacial periods of the Yellow Sea. We report the carbon isotopic and biomarker (n-alkane and alkenone) composi-tions of organic matter from Yellow Sea sediments since the glacial period. Our find-ings show that the variability of the East Asian Monsoon (EAM) affected the sedi-mentary profile of total organic carbon (TOC), the stable isotopes of bulk organic carbon (δ13Corg), the atomic ratio of carbon and nitrogen (C/N ratio), and biomarker content. The sedimentary δ13Corg profile along the core exhibited more negative δ13Corg values under cold/dry climatic conditions (Younger and Oldest Dryas). The carbon preference index (CPI), the pristane to phytane ratio (Pr/Ph) and the pristane to n-C17 ratio (Pr/n-C17) were used to determine the early stages of diagenesis along the sediment core. Two climatic conditions were distinguished (warm/humid and cold/dry) based on an n-alkane proxy, and the observed changes in δ13C of individual n-alkane (δ13CALK) between the Holocene and glacial periods were attributed to changes in plant distribution/type. Clear differences were not found in the calculated alkenone sea surface temperature (SST) between those of the Holocene and glacial periods. This anomaly during the glacial period might be attributed to the seasonal water mass distribution in the Yellow Sea or a seasonal shift in the timing of maxi-mum alkenone production as well as the Bølling/Allerød interstadial.

Paleohydrological and paleoenvironmental changes reconstructed by organic carbon and biomarker analyses of sediments from the northern East China Sea during the last 15,000 years The paleohydrological and paleoenvironmental variations were reconstructed by sedimentary records from the northern East China Sea during the last 15,000 years (from Last Glacial Period to Holocene). The n-alkane distributions show changing origins (plant types) of organic matter input to marine sediments. Two climatic con-ditions were distinguished (warm/humid and cold/dry) on the comparing of organic carbon isotope ratio (δ13Corg) with reported planktonic foraminiferal oxygen isotope ratio (δ18O) of Globigerinoides ruber from East China Sea. A shift in n-alkane spe-cific δ13C values reveal the hydrological changes in the Northern East China Sea as-sociated with the carbon source for aquatic macrophytes. Alkenone SSTs (UKʹ37) rec-ord of the 07YSPC12 has a range of 20.3 °C to 26.5 °C (average 22.9 °C) Lower temperature SSTs were recorded during the Younger Dryas having an average of 21.7 °C . Variation in alkenone SSTs is interpreted to emulate the environmental condition of growth of alkenone synthesized organisms.