Diatom oxygen isotopes have been widely applied in quantitative reconstruction of the paleoclimate and paleoenvironment,but have rarely been reported in China.In the present study,Lake Sihailongwan in Northeast China ...Diatom oxygen isotopes have been widely applied in quantitative reconstruction of the paleoclimate and paleoenvironment,but have rarely been reported in China.In the present study,Lake Sihailongwan in Northeast China was selected for detailed investigation of oxygen isotopic fractionation between diatom frustules and lake water induced by growth temperature.This study involved a 2-year period of field monitoring of the lake water temperature at multiple depths and biweekly collections of traps for both sediment and water at shallow and bottom depths(7 and 49 m below the lake surface,respectively),diatom separation and purification of the trap sediments,and oxygen isotope measurement for diatom silica and lake water samples.The conditioned experiment conducted herein demonstrated that the laboratory device,methods and techniques used in this study were capable of generating reliable data for the typical oxygen isotope composition of diatom frustules.The data obtained revealed a prominent linear relationship between the oxygen isotope composition of the modern diatom and lake temperature during growth.The fractionation coefficient was about-0.185‰/°C-0.238‰/°C in the temperature range of 3.6-24°C,which is consistent with the observations from various aquatic environments and laboratory culture with different diatom taxa.These findings provide strong support for the dominant control of the growth temperature on the oxygen isotope fractionation between the diatom frustules and ambient water.A notable difference in the fractionation coefficient was observed between the surface and bottom diatom oxygen isotopes,suggesting that various depositional processes and taphonomic effects influenced the surface and bottom trap samples.Another factor leading to this difference may be that enrichment by evaporation and dilution by rainfall have a stronger influence on the surface.Overall,the results presented here demonstrate significant progress in evaluation of diatom oxygen isotopes in China and draw attention to the differences between surface and bottom diatom oxygen isotope compositions.展开更多
Volcanic glass compositions and tephra layer age are critical for anchoring their sources and correlating among different sites; however, such work may be imprecise when the tephra has varied compositions. The ash fro...Volcanic glass compositions and tephra layer age are critical for anchoring their sources and correlating among different sites; however, such work may be imprecise when the tephra has varied compositions. The ash from Changbaishan Millennium eruption(940s AD), a widely distributed tephra layer, has been detected in the far-east areas of Russia, the Korean Peninsula, Japan, and in Greenland ice cores. There are some debates on the presence of this tephra from sedimentary archives to the west of Changbaishan volcano, such as lake and peat sediments in the Longgang volcanic field. In this paper, major element compositions for clinopyroxene and Fe-Ti oxides were performed on proximal tephra from Changbaishan and the Millennium eruption ash record in Lake Sihailongwan. Clinopyroxene and Fe-Ti oxides microlites from Sihailongwan show augite-ferroaugite and titanmagnetite compositions, similar to those from dark pumice in Changbaishan proximal tephra, but different from the light grey pumice, which has ferrohedenbergite and ilmenite microlite compositions. This result implies that the tephra recorded in Sihailongwan was mainly from the trachytic eruptive phase of the Millennium eruption, and the rhyolitic eruptive phase made a relatively small contribution to this area. Analyzing clinopyroxene and Fe-Ti oxides microlites is a new method for correlating tephra layers from Changbaishan Millennium eruption.展开更多
基金supported by the National Natural Science Foundation of China(40672114and40872112)the National Basic Research Program of China(2010CB950200)
文摘Diatom oxygen isotopes have been widely applied in quantitative reconstruction of the paleoclimate and paleoenvironment,but have rarely been reported in China.In the present study,Lake Sihailongwan in Northeast China was selected for detailed investigation of oxygen isotopic fractionation between diatom frustules and lake water induced by growth temperature.This study involved a 2-year period of field monitoring of the lake water temperature at multiple depths and biweekly collections of traps for both sediment and water at shallow and bottom depths(7 and 49 m below the lake surface,respectively),diatom separation and purification of the trap sediments,and oxygen isotope measurement for diatom silica and lake water samples.The conditioned experiment conducted herein demonstrated that the laboratory device,methods and techniques used in this study were capable of generating reliable data for the typical oxygen isotope composition of diatom frustules.The data obtained revealed a prominent linear relationship between the oxygen isotope composition of the modern diatom and lake temperature during growth.The fractionation coefficient was about-0.185‰/°C-0.238‰/°C in the temperature range of 3.6-24°C,which is consistent with the observations from various aquatic environments and laboratory culture with different diatom taxa.These findings provide strong support for the dominant control of the growth temperature on the oxygen isotope fractionation between the diatom frustules and ambient water.A notable difference in the fractionation coefficient was observed between the surface and bottom diatom oxygen isotopes,suggesting that various depositional processes and taphonomic effects influenced the surface and bottom trap samples.Another factor leading to this difference may be that enrichment by evaporation and dilution by rainfall have a stronger influence on the surface.Overall,the results presented here demonstrate significant progress in evaluation of diatom oxygen isotopes in China and draw attention to the differences between surface and bottom diatom oxygen isotope compositions.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41472320, 41320104006 and 41272369)
文摘Volcanic glass compositions and tephra layer age are critical for anchoring their sources and correlating among different sites; however, such work may be imprecise when the tephra has varied compositions. The ash from Changbaishan Millennium eruption(940s AD), a widely distributed tephra layer, has been detected in the far-east areas of Russia, the Korean Peninsula, Japan, and in Greenland ice cores. There are some debates on the presence of this tephra from sedimentary archives to the west of Changbaishan volcano, such as lake and peat sediments in the Longgang volcanic field. In this paper, major element compositions for clinopyroxene and Fe-Ti oxides were performed on proximal tephra from Changbaishan and the Millennium eruption ash record in Lake Sihailongwan. Clinopyroxene and Fe-Ti oxides microlites from Sihailongwan show augite-ferroaugite and titanmagnetite compositions, similar to those from dark pumice in Changbaishan proximal tephra, but different from the light grey pumice, which has ferrohedenbergite and ilmenite microlite compositions. This result implies that the tephra recorded in Sihailongwan was mainly from the trachytic eruptive phase of the Millennium eruption, and the rhyolitic eruptive phase made a relatively small contribution to this area. Analyzing clinopyroxene and Fe-Ti oxides microlites is a new method for correlating tephra layers from Changbaishan Millennium eruption.
