Validated age, growth, and mortality estimates of the ocean quahog (Arctica islandica) in the western Atlantic     

Kilada  Raouf W.; Campana  Steven E.; Roddick  Dale 《ICES Journal of Marine Science》2007,64(1):31-38

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New age estimates and climatostratigraphic correlations for the Borrobol and Penifiler Tephras: evidence from Abernethy Forest,Scotland     

I. P. Matthews  Hilary H. Birks  A. J. Bourne  S. J. Brooks  J. J. Lowe  A. MacLeod  S. D. F. Pyne‐O'Donnell 《第四纪科学杂志》2011,26(3):247-252

The emerging tephrostratigraphy of NW Europe spanning the last termination (ca. 15–9 ka) provides the potential for synchronizing marine, ice‐core and terrestrial records, but is currently compromised by stratigraphic complications, geochemical ambiguity and imprecise age estimates for some layers. Here we present new tephrostratigraphic, radiocarbon and chironomid‐based palaeotemperature data from Abernethy Forest, Scotland, that refine the ages and stratigraphic positions of the Borrobol and Penifiler tephras. The Borrobol Tephra (14.14–13.95 cal ka BP) was deposited in a relatively warm period equated with Greenland Interstadial sub‐stage GI‐1e. The younger Penifiler Tephra (14.09–13.65 cal ka BP) is closely associated with a cold oscillation equated with GI‐1d. We also present evidence for a previously undescribed tephra layer that has a major‐element chemical signature identical to the Vedde Ash. It is associated with the warming trend at the end of the Younger Dryas, and dates between 11.79 and 11.20 cal ka BP. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Resolving the Holocene alluvial record in southeastern Australia using luminescence and radiocarbon techniques     

Michael D. Cheetham  Annabelle F. Keene  Wayne D. Erskine  Richard T. Bush  Kathryn Fitzsimmons  Geraldine E. Jacobsen  Stewart J. Fallon 《第四纪科学杂志》2010,25(7):1160-1168

A previous assessment of radiocarbon (¹⁴C) dates from alluvial units in southeastern Australia revealed a gap in the geochronological record that coincides with the Holocene climatic optimum. This gap in the alluvial record can be further refined using optically stimulated luminescence (OSL). The chronology of Holocene river terraces on Widden Brook, a sandy alluvial stream in southeastern Australia, was established using ¹⁴C and OSL techniques. Combined use of these independent techniques allows for a more rigorous assessment of the alluvial record. The robust chronology, consisting of 38 ¹⁴C and 11 OSL samples, permitted identification of significant depositional variation within the catchment, resulting from localised geomorphic processes. The three terrace sequences identified yielded distinct chronologies, suggesting alluvial deposition at different times. The sequences exhibited a continuous chronology, which indicated continuous deposition throughout the Holocene. The chronology of terrace sequences within this catchment suggests that terrace formation can be attributed to localised geomorphic processes rather than climatic forcing. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Deep sea circulation of particulate organic carbon in the Japan Sea     

Shigeyoshi Otosaka  Takayuki Tanaka  Orihiko Togawa  Hikaru Amano  Eugeny V. Karasev  Masayuki Minakawa  Shinichiro Noriki 《Journal of Oceanography》2008,64(6):911-923

Seasonal and spatial variations of particulate organic carbon (POC) flux were observed with sediment traps at three sites in the Japan Sea (western and eastern Japan Basin and Yamato Basin). In order to investigate the transport processes of POC, radiocarbon (¹⁴C) measurements were also carried out. Annual mean POC flux at 1 km depth was 30.7 mg m⁻²day⁻¹ in the western Japan Basin, 12.0 mg m⁻²day⁻¹ in the eastern Japan Basin and 23.8 mg m⁻²day⁻¹ in the Yamato Basin. At all stations, notably higher POC flux was observed in spring (March–May), indicating biological production and rapid sinking of POC in this season. Sinking POC in the high flux season showed modern Δ¹⁴C values (>0‰) and aged POC (Δ¹⁴C < −40‰) was observed in winter (December–January). The Δ¹⁴C values in sinking POC were negatively correlated with aluminum concentration, indicating that Δ¹⁴C is strongly related to the lateral supply of lithogenic materials. The Δ¹⁴C values also showed correlations with excess manganese (Mn_xs) concentrations in sinking particles. The Δ¹⁴C-Mn_xs relationship suggested that (1) the majority of the aged POC was advected by bottom currents and incorporated into sinking particles, and (2) some of the aged POC might be supplied from the sea surface at the trap site as part of terrestrial POC. From the difference in the Δ¹⁴C-Mn_xs relationships between the Japan Basin and the Yamato Basin, we consider that basin-scale transport processes of POC occur in the Japan Sea.  相似文献   

A study of the construction times of the ancient cities in Ganjia Basin,Gansu Province,China   总被引：1，自引：0，他引：1  

Xia  Huan  Zhang  Dongju  Wang  Qiang  Wu  Duo  Duan  Yanwu  Chen  Fahu 《地理学报(英文版)》2020,30(9):1467-1480

The Ganjia Basin in Xiahe County,Gansu Province,China,is located on the northeastern edge of the Tibetan Plateau.The area lies in the transitional zone between the Plateau ethnic groups dominated by ancestral Tibetans,and the Central Plains dynasties dominated by ancestral Han in history.The Ganjia Basin is therefore well suited to studying the history of the intermixing of the Han and Tibetan peoples.In this study,we collected samples of organic materials from two ancient cities,Bajiaocheng(BJC) and Sirougucheng(SRGC),in the Ganjia Basin,which were used for radiocarbon dating.Our aims were to determine the construction times and function of the cities,based on the radiocarbon ages,Bayesian age modeling,and the analysis of relevant historical records.The results are used to discuss the role of the Ganjia Basin in the conflicts between and the integration of the two ethnic groups during the historical period.We conclude that BJC was established during 663–732 CE(Common Era);its early occupation history can be divided into an initial establishment phase(670–780 CE) and a phase of regeneration(880–1030 CE).SRGC was probably built at the time of the transition between the Song and Yuan dynasties(～1271 CE).Combining the dating results with an analysis of the architectural styles and historical records,we conclude that BJC was originally built by the Tubo Kingdom as a military stronghold,and its major functions were military,economic and religious,and to support the major eastward expansion of the Tubo.SRGC was most likely a temple-focused city intended to promote Tibetan Buddhism which was a major political and religious leadership for the Tibetans at that time,reflecting changes in the status of different religions in the Ganjia Basin.In addition,the intermixing and blending of the Han and Tibetan groups,reflected by the human activities in the Ganjia Basin,was an important demographic and cultural foundation for the formation of the culturally-diverse but spiritually-united modern Chinese people.  相似文献   

放射性碳同位素在土壤碳循环中的应用   总被引：3，自引：0，他引：3  

王琳  欧阳华  周才平  宋明华  田玉强 《地理科学进展》2004,23(4):43-51

文中介绍了放射性碳同位素方法在土壤碳循环中的应用,分析了在土壤有机质、土壤CO2气体研究中的主要方法和模型,并指出土壤有机质的放射性测定可以研究较长时间尺度的碳循环(十几年、几十年至更长时间尺度),而土壤CO2气体的放射性测定可以研究短期(季节变化和年变化)内碳的动态。放射性碳同位素用于土壤中细根周转时间的计算、土地利用变化等方面的研究成果及方法也在文中分别作了介绍和分析。最后提出了国内研究应加强的领域和未来利用放射性碳同位素方法研究土壤碳循环的重点研究方向和发展趋势。  相似文献   

湖泊碳库效应及校正方法   总被引：1，自引：0，他引：1  

王宗礼  何建华  陈亚东 《中国沙漠》2014,34(3):683-688

湖泊作为过去环境变化的信息载体,可以很好地提供高分辨率的连续记录,因此常被用来进行定年研究。湖泊沉积物放射性碳定年由于缺乏陆源植物残体、碳屑等可靠的定年材料,多选用其他材料（如全样有机质、水生残体及各类壳体）,但是这些材料通常受到“碳库效应”（The reservoir effect）的影响,而使得年代结果失真,导致难以建立高精度的年代框架,成为这一领域研究放射性碳年代应用的瓶颈。因此,如何对湖相沉积物¹⁴C年代结果进行有效的碳库效应校正,对高精度年代序列的建立具有重要意义。本文综览了近几十年来针对湖泊碳库效应进行研究所取得的一系列研究成果,详细总结了影响湖泊碳库效应的各种因素,讨论了碳库效应对湖泊沉积物定年结果的影响;分析了目前对湖泊碳库的各类校正方法,包括使用同一测年手段、不同测年材料建立点上碳库大小以及采用不同测年手段对碳库的校正等。本文为湖泊沉积物高精度年代序列的建立提供了一定的参考。  相似文献   

Test of AMS 14C dating of pollen concentrates using tephrochronology     

Rewi M. Newnham  Marcus J. Vandergoes  Mark H. Garnett  David J. Lowe  Christine Prior  Peter C. Almond 《第四纪科学杂志》2007,22(1):37-51

Previous attempts to radiocarbon date sediments >10 kyr from the high rainfall region of Westland, New Zealand, a critical location for investigation of interhemispheric patterns of climate change, have been problematic. This study, building on recent work by Vandergoes and Prior ( 2003 ), shows that AMS ¹⁴C dating of pollen concentrates has potential to provide more reliable ages than other sediment constituents, including plant macrofossils. The method was applied to sediments from three sites containing the 22.6k ¹⁴C yr Kawakawa Tephra, which provided an independent test of the ¹⁴C ages. Although some minor laboratory contamination was detected in tests on background standards, the modelled relationship between sample mass and measured ¹⁴C content permitted an appropriate correction to be determined. Improved pollen concentrations derived by density separation between 1.4 and 1.2 specific gravity and sieving in the range 10–50 μm provided either older ages than other fractions of the same sample or, where in situ contamination was not evident, equivalent ages. Differences in degree of in situ contamination between depositional environments indicated that, in Westland, lake sites may be less susceptible to contamination by younger carbon than peat sites, where this process may be facilitated by root penetration into underlying sediments. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Evidence of climatic change from oxygen and carbon isotope variations in sediments of a small arctic lake,Canada     

F. A. Michel  P. Fritz  R. J. Drimmie 《第四纪科学杂志》1989,4(3):201-209

Radiocarbon dating of the organic-rich sediments of Lake Illisarvik in the outer Mackenzie Delta indicates that formation of the lake occurred approximately 9500yr BP, with maximum expansion around 6000 yr BP. Sedimentation rates have remained relatively constant at an average of 0.3mm/yr. ¹³C results on biogenic and inorganic carbonates and organics indicate a change from dominantly terrestrial organics (?27 to ?28%₀) to submerged aquatic vegetation or plankton (?18 to ?23%₀) upon formation of the lake (9500yr BP), and a dramatic return to dominantly terrestrial organics at 5800yr BP (δ¹³C = ?27 to ?30%₀). This latter shift is accompanied by a drastic reduction in the macroflora and fauna populations. ¹⁸O results suggest that a warmer climate than today existed prior to the shift at 5800yr BP.  相似文献   

环渤海海岸带¹⁴C数据集（Ⅰ）   总被引：16，自引：5，他引：11       下载免费PDF全文

王宏  李凤林  范昌福  M.Frechen  M.van Strydonck  裴艳东  王云生 《第四纪研究》2004,24(6):601-613

环渤海泥质海岸带近30年来获得的600余个放射性碳测年数据,确定了该地区晚更新世晚期以来的基本年代地层序列。但是,对¹⁴C数据的系统校正,迄未得到应有的重视,致使在应用¹⁴C数据解释地层和地质现象的年代时,存在着一定程度的混乱。文章对作者自己所采集和由国内外有关实验室测定的126个¹⁴C数据进行了系统校正,主要步骤包括分馏效应、地区性海洋贮存库效应及大气¹⁴C含量变化校正等。建议以-2.68‰PDB作为环渤海晚更新世晚期以来半咸水和开放浅海区(潮间带与潮下带上部)贝壳的地区性^δ13C平均值。另外,讨论了在地区性海洋贮存库效应值获得之前的1990年代,以MARINE93与INTCAL93程序的平均校正年龄近似地视作该地区贝壳的校正值,以抵消这一类地区小型水体与大气迅速进行¹⁴CO₂交换而对年龄值的影响。CALIB4.4校正结果表明,前述近似校正是可行的,其结果仍可沿用。文章经统一校正的年龄,最大限度地接近其太阳历纪年的"真实"年龄,从而有助于更加准确地重建该地区的晚更新世晚期以来的地质年代史,并可与考古纪年及其他测年方法获得的绝对年龄直接对比。  相似文献