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1.
《Quaternary Science Reviews》2004,23(20-22):2089-2099
IMAGES core MD01-2416 (51°N, 168°E) provides the first centennial-scale multiproxy record of Holocene variation in North Pacific sea-surface temperature (SST), salinity, and biogenic productivity. Our results reveal a gradual decrease in subarctic SST by 3–5 °C from 11.1 to 4.2 ka and a stepwise long-term decrease in sea surface salinity (SSS) by 2–3 p.s.u. Early Holocene SSS were as high as in the modern subtropical Pacific. The steep halocline and stratification that is characteristic of the present-day subarctic North Pacific surface ocean is a fairly recent feature, developed as a product of mid-Holocene environmental change. High SSS matched a salient productivity maximum of biogenic opal during Bølling-to-Early Holocene times, reaching levels similar to those observed during preglacial times in the warm mid-Pliocene prior to 2.73 Ma. Similar productivity spikes marked every preceding glacial termination of the last 800 ka, indicating recurrent short-term events of mid-Pliocene-style intense upwelling of nutrient-rich Pacific Deepwater in the Pleistocene. Such events led to a repeated exposure of CO2-rich deepwater at the ocean surface facilitating a transient CO2 release to the atmosphere, but the timing and duration of these events repudiate a long-term influence of the subarctic North Pacific on global atmospheric CO2 concentration.  相似文献   

2.
王跃  翦知湣  赵平 《第四纪研究》2009,29(2):221-231
利用美国NCAR CAM3大气环流模式,分析了末次盛冰期（LGM）两个不同的热带海表温度重建方案中,北半球冬季热带中、西太平洋对流活动及大气环流对暖池外（赤道东太平洋和热带大西洋）热带SST异常的敏感性。结果表明：  1）SST异常首先引起大气环流的改变。  赤道东太平洋对流层下沉增强,而作为经向补偿,副热带东太平洋上升运动增强,其中南半球尤为明显,同时南半球热带中、西太平洋上升运动增强,加剧了该区纬向逆时针环流,说明冰期热带海气耦合过程受气候背景场（如SST）影响很大;   2）大气环流格局改变引起热带中西太平洋的大气加热、对流活动、表层风场及降雨的巨大变化。  140°E以西的婆罗洲和菲律宾区域,总的大气加热减少是由于对流与辐射加热减少所致,对应于该区风场辐散和降雨减少;   而140°E以东的南半球热带中、西太平洋,大气吸收热量增加,对流与辐射加热均增强,总降雨量也随之增加,反映该区赤道辐合带南移并增强。该项研究为探索热带太平洋在冰期/间冰期旋回中的古海洋学变化提供了新的数据支撑。此外,不同重建SST对赤道辐合带的影响比较大,因此利用重建SST进行数值模拟或者利用耦合模式研究LGM热带海气相互作用时,应该十分重视全球热带SST分布特征。  相似文献   

3.
利用取自东海东北部、冲绳海槽西侧陆坡的重力柱状岩芯DOC082（29°13.93′N,128°08.53′E;水深1128m）,通过对碳酸钙、有机碳和蛋白石等生源组分含量的分析,结合浮游有孔虫、底栖有孔虫、放射虫和硅鞭藻等微体古生物化石丰度的变化以及底栖有孔虫属种组成特征,揭示了全新世东海东北部生物生产力的演变。研究结果显示,近10500cal.aB.P.以来生源组分含量和微体古生物化石丰度的演变趋势十分相似,明显分为3个阶段:约4000cal.aB.P.之前的早、中全新世明显偏低,大约在4000cal.aB.P.左右开始突然大幅度上升,而约3000cal.aB.P.以来的晚全新世以持续的高值为显著特征。生源组分含量、微体古生物化石丰度以及底栖有孔虫内生属种Uvigerina和Bulimina百分含量等指标的变化一致指示,东海东北部近10500cal.aB.P.以来古生产力演变的显著特征是早、中全新世明显偏低,约4000cal.aB.P.左右突然且大幅度上升,大约3000cal.aB.P.之后的晚全新世为生物生产力异常的高值期;同时有研究表明该区域的表层海水年平均温度（SST）也呈现了明显的三段式演变:早全新世10500～8400cal.aB.P.期间为持续的高值期、中全新世SST相对稳定、3100～500cal.aB.P.期间的晚全新世为显著的低SST时期[1]。近3000cal.aB.P.以来古生产力的异常高值和表层海水古温度的大幅度下降说明晚全新世区域海洋环境发生了明显的改变。据东海东北部现代生物生产力和表层海水温度的分布特征和控制机制、结合现代ElNio发生期间中国大陆气候和降水异常以及黑潮暖流变异的分析表明,近3000cal.aB.P.来东海东北部的环境异常可能是对晚全新世ElNio活动显著增强的反应。  相似文献   

4.
南大洋CaCO3沉积在记录生物泵调节大气CO2的同时,也记录了南大洋表层锋面系统和深部环流格局的重要转变.通过南塔斯曼海ODP 1170站位2 Ma以来CaCO3％和MAR-CaCO3的研究发现,CaCO3％以冰期低和间冰期高的“大西洋”型溶解作用旋回为主,并以MIS 34/35期(约1.15 Ma BP)和MIS 14/15期(约0.55 Ma BP)为界线,表现出3种沉积模式.而MAR-CaCO3以MIS 57/58,21/22,13/14和11/12为界表现出“两高三低”5个阶段.CaCO3％与轨道参数ETP和底栖有孔虫δ18O的交叉频谱和小波分析显示,其主导周期明显具有从40 ka向100 ka转变的中更新世气候转型(MPT)特征,转型起始与终止时间为1.15～0.55 MaBP.CaCO3沉积模式的转变与南大洋太平洋区西风带和环南极表层锋面系统的迁移密切相关,在时间上与MPT同步.MPT时期,西风带和环南极表层锋面系统的快速南北迁移,导致CaCO3沉积受到硅质和陆源物质稀释作用的影响.而MAR-CaCO3的阶段性变化主要与南大洋深层环流的变化格局和水团化学性质的变化有关.在1.5～0.85 MaBP期间,南大洋太平洋区深层水通风增强,利于CaCO3的保存和埋藏,MAR-CaCO3增加;在0.85 ～0.55 Ma BP期间,CO32-处于不饱和状态的CDW增强,导致南大洋深部CaCO3溶解作用增强,溶跃面上升,MAR-CaCO3降低.  相似文献   

5.
Dust transported by Southern Hemisphere mid-latitude westerly winds from Australia and deposited in the Tasman Sea shows no evidence for stronger winds during the last glacial maximum (LGM), compared to the Holocene. Features of the particle-size distributions of the dust do, however, indicate enhanced dry deposition of dust in the LGM changing to rainfall scavenging during deglaciation and the early Holocene as climate ameliorated. From these results it appears that activation of desert dunefields over 40% of Australia during the LGM was the result of a reduction in stabilizing vegetation and more frequent episodes of sand movement rather than of increased wind strength. The LGM climate of inland Australia must have been considerably more stressful for plants as a result of lower precipitation and/or carbon dioxide stress to achieve the implied levels of surface destabilization. Enhanced atmospheric dust loads in the Southern Hemisphere and deposition over Antarctica were most likely the result of greatly expanded source areas in the mid-latitude southern continents and a weaker hydrological cycle rather than greater entrainment or more efficient transport by stronger winds. During the LGM wind strength appears to have varied regionally, and predominantly in high latitudes, rather than uniformly for all zonal winds.  相似文献   

6.
在冲绳海槽北部B-3GC孔高分辨率地层年代框架的基础上,利用多种分子生物标志物和生源组分指标,重建了该地区全新世以来表层海水温度和生产力的变化历史.研究发现,U37K-表层海水温度和生产力的变化指示了全新世黑潮及对马暖流分支的变迁.10.6～7.3 ka BP期间,冲绳海槽北部主要受东海陆架冷水团影响,陆源物质输入量增加,初级生产力比较高,表层海水温度较低.7.3～4.6 ka BP期间,黑潮暖流对该区的影响迅速增强,表层海水快速增温,陆源物质输入减少,但是各种生产力指标显示出上升趋势,与该区上升流的出现和迅速发育有关.4.6～2.7 ka BP期间,即全新世普林虫低值事件(PME)期间,表层海水温度明显降低了0.8～1.4℃,陆源物质输入增加,初级生产力和各种生源组分的含量也达到较高水平,说明此时黑潮强度减弱,或者黑潮主流轴向太平洋方向发生偏移,该区再次受到陆架冲淡水的影响.2.7 ka BP以来,虽然黑潮暖流再次影响到该海区,但初级生产力和生源物质输出量继续大幅增高,可能与该地区上升流的持续发育有关.  相似文献   

7.
Here we provide three new Holocene (11–0 cal ka BP) alkenone-derived sea surface temperature (SST) records from the southernmost Chilean fjord region (50–53°S). SST estimates may be biased towards summer temperature in this region, as revealed by a large set of surface sediments. The Holocene records show consistently warmer than present-day SSTs except for the past ~ 0.6 cal ka BP. However, they do not exhibit an early Holocene temperature optimum as registered further north off Chile and in Antarctica. This may have resulted from a combination of factors including decreased inflow of warmer open marine waters due to lower sea-level stands, enhanced advection of colder and fresher inner fjord waters, and stronger westerly winds. During the mid-Holocene, pronounced short-term variations of up to 2.5°C and a cooling centered at ~ 5 cal ka BP, which coincides with the first Neoglacial glacier advance in the Southern Andes, are recorded. The latest Holocene is characterized by two pronounced cold events centered at ~ 0.6 and 0.25 cal ka BP, i.e., during the Little Ice Age. These cold events have lower amplitudes in the offshore records, suggesting an amplification of the SST signal in the inner fjords.  相似文献   

8.
To investigate land–sea interactions during deglaciation, we compared proxies for continental (pollen percentages and accumulation rates) and marine conditions (dinoflagellate cyst percentages and alkenone-derived sea surface temperatures). The proxies were from published data from an AMS-radiocarbon-dated sedimentary record of core GeoB 1023-5 encompassing the past 21,000 years. The site is located at ca. 2000 m water depth just north of the Walvis Ridge and in the vicinity of the Cunene River mouth. We infer that the parallelism between increasing sea surface temperatures and a southward shift of the savanna occurred only during the earliest part of the deglaciation. After the Antarctic Cold Reversal, southeast Atlantic sea surface temperatures no longer influenced the vegetation development in the Kalahari. Stronger trade winds during the Antarctic Cold Reversal and the Younger Dryas period probably caused increased upwelling off the coast of Angola. A southward shift of the Atlantic anti-cyclone could have resulted in both stronger trade winds and reduced impact of the Westerlies on the climate of southwestern Africa.  相似文献   

9.
This article examines Holocene environmental change in Zhuye Lake in the marginal area of the Asian monsoon, NW China. Holocene environment records were obtained for the QTH01 and QTH02 sections in Zhuye Lake. The fluctuations in grain size, pollen, total organic carbon content and C/N ratios record notable environmental variation. The early Holocene (11.0 to 7.4 cal. kyr BP) was relatively arid, while vegetation coverage was sparse and primary productivity low. The optimal environment prevailed during the mid-Holocene (7.4 to 4.7 cal. kyr BP). Vegetation coverage was the densest and primary productivity the highest during the mid-Holocene. During the late Holocene (4.7 to 0 cal. kyr BP), the environment became arid, as shown by low lake level and sparse vegetation coverage. After 1.6 cal. kyr BP another strong aridification occurred. In this area, the environment was likely to have been influenced by both the Westerlies and the East Asian monsoon during the Holocene. During the early Holocene, the relatively arid environment lay in the background of the increasing East Asian monsoon and dry westerly wind. During the mid-Holocene, central Asia was controlled by the humid Westerlies, while a strong East Asian monsoon prevailed in Central China. The mid-Holocene optimum in this area benefited from an expanded East Asian monsoon and the humid Westerlies. Weakening of the East Asian monsoon caused aridification of the environment during the late Holocene. Intensification of this aridification after 1.6 cal. kyr BP might be correlated with appearance of the arid environments in the Westerly domain after ∼1.5 cal. kyr BP. These arid conditions might be affected by the decreased moisture content of the Westerlies.  相似文献   

10.
海洋上部水体垂向结构变化对于理解热带海区在全球气候变化中的作用有着重要意义。通过分析印度尼西亚穿越流(ITF)出口处东印度洋帝汶海区SO18480-3孔中的浮游有孔虫表层种Globigerinoides ruber和温跃层种Pulleniatina obliquiloculata壳体氧碳同位素,并借助12个AMS14C测年数据重建了末次盛冰期(LGM)以来该区温跃层深度和营养盐水平的演化序列。壳体氧同位素(δ18O)记录表明温跃层古海洋学特征的变化幅度要大于表层海水,其差值(Δδ18O(P-G))有效地反映了温跃层深度的变化,即冰消期和晚全新世温跃层较浅,LGM和早中全新世温跃层较深;并揭示出与全新世相比,LGM期间ITF总流量未显著减小,ITF对该区上部水体结构的影响受到了东西太平洋之间不对称性的调节。碳同位素(δ13C)记录则表明该区的古海洋学变化在不同程度上受到了南大洋的影响,并受本区上部水体垂向结构的控制,其差值(Δδ13(G-P))在一定程度上反映了该区上部水体营养盐水平的变化。  相似文献   

11.
Arabian Sea sediments record changes in the upwelling system off Arabia, which is driven by the monsoon circulation system over the NW Indian Ocean. In accordance with climate models, and differing from other large upwelling areas of the tropical ocean, a 500,000-yr record of productivity at ODP Site 723 shows consistently stronger upwelling during interglaciations than during glaciations. Sea-surface temperatures (SSTs) reconstructed from the alkenone unsaturation index (UK′37) are high (up to 27°C) during interglaciations and low (22-24°C) during glaciations, indicating a glacial-interglacial temperature change of >3°C in spite of the dampening effect of enhanced or weakened upwelling. The increased productivity is attributed to stronger monsoon winds during interglacial times relative to glacial times, whereas the difference in SSTs must be unrelated to upwelling and to the summer monsoon intensity. The winter (NE) monsoon was more effective in cooling the Arabian Sea during glaciations then it is now.  相似文献   

12.
The coastal upwelling system offshore Namibia is ideally suited to address a focal question of the Integrated Marine Biogeochemistry and Ecosystem Research Programme: what are the mechanisms that drive long-term changes in ecosystems? Considerable interannual variability in climatic forcing is indicated by long time series of meteorological and remote sensing observation; these accompany considerable interannual to interdecadal changes in the upwelling intensity over the last 100 years, as well as a centennial trend. On longer time scales, the only archives available are sediment records spanning the late Holocene. To decipher the sediment record, we mapped surface-sediment patterns of proxies for physical (sea surface temperature/SST from alkenone unsaturation indexes) and nutrient (δ15N on bulk sedimentary N) variables. Their present-day surface-sediment patterns outline the coastal upwelling cells and filaments and associated high productivity area. Analysed in an array of dated sediment cores, the spatial patterns of SST suggest long-term (>100 years) variability in the location and intensity of individual upwelling cells. The patterns of δ15N outline an area of intense denitrification near the coast, and advection of water with low-oxygen concentrations in the undercurrent from the North. δ15N exhibits considerable downcore variability, in particular over the last 50 years. The variability appears to be governed by differences in extent of denitrification and thus of the shelf oxygen balance, which appears to have deteriorated in the last 50 years. Together, the data suggest that SST and denitrification conditions have remained in the narrow bounds outlined by today’s patterns in surface sediments, but that spatially small variability in upwelling intensity and make-up of upwelling feed waters induced considerable changes in the lower trophic levels of the coastal upwelling ecosystem over the last 6,000 years. Attempts to correlate proxy records from sediments with observational time series and regional climate reconstructions were not successful, possibly because annual to interannual environmental signals are erased in the process of sediment formation.  相似文献   

13.
The aragonite compensation depth (ACD) fluctuated considerably during the last glacial until the Holocene with a dominant pteropod preservation spike during the deglacial period, which is prominently seen in three well‐dated cores covering the Andaman Sea, northeastern Indian Ocean. The precise time period of the preservation spike of pteropods is not known but this knowledge is crucial for stratigraphical correlation and also for understanding the driving mechanism. Isotopic and foraminiferal proxies were used to decipher the possible mechanism for pteropods preservation in the Andaman Sea. The poor preservation/absence of pteropods during the Holocene in the Andaman Sea may have implications for ocean acidification, driven by enhanced atmospheric CO2 concentration. Strengthening of the summer monsoon and the resultant high biological productivity may also have played a role in the poor preservation of pteropods. The deglacial pteropod spike is characterized by high abundance/preservation of the pteropods between ～19 and 15 cal. ka BP, associated with very low atmospheric CO2 concentration. Isotope data suggest the prevalence of a glacial environment with reduced sea surface temperature, upwelling and enhanced salinity during the pteropod preservation spike. Total planktic foraminifera and Globigerina bulloides abundances are low during this period, implying a weakened summer monsoon and reduced foraminiferal productivity. Based on the preservation record of pteropods, it is inferred that the ACD was probably deepest (>2900 m) at 16.5 cal. ka BP. The synchronous regional occurrence of the pteropod preservation spike in the Andaman Sea and in the northwestern Indian Ocean could potentially be employed as a stratigraphic marker.  相似文献   

14.
The North West Shelf is an ocean‐facing carbonate ramp that lies in a warm‐water setting adjacent to an arid hinterland of moderate to low relief. The sea floor is strongly affected by cyclonic storms, long‐period swells and large internal tides, resulting in preferentially accumulating coarse‐grained sediments. Circulation is dominated by the south‐flowing, low‐salinity Leeuwin Current, upwelling associated with the Indian Ocean Gyre, seaward‐flowing saline bottom waters generated by seasonal evaporation, and flashy fluvial discharge. Sediments are palimpsest, a variable mixture of relict, stranded and Holocene grains. Relict intraclasts, both skeletal and lithic, interpreted as having formed during sea‐level highstands of Marine Isotope Stages (MIS) 3 and 4, are now localized to the mid‐ramp. The most conspicuous stranded particles are ooids and peloids, which 14C dating shows formed at 15·4–12·7 Ka, in somewhat saline waters during initial stages of post‐Last Glacial Maximum (LGM) sea‐level rise. It appears that initiation of Leeuwin Current flow with its relatively less saline, but oceanic waters arrested ooid formation such that subsequent benthic Holocene sediment is principally biofragmental, with sedimentation localized to the inner ramp and a ridge of planktic foraminifera offshore. Inner‐ramp deposits are a mixture of heterozoan and photozoan elements. Depositional facies reflect episodic environmental perturbation by riverine‐derived sediments and nutrients, resulting in a mixed habitat of oligotrophic (coral reefs and large benthic foraminifera) and mesotrophic (macroalgae and bryozoans) indicators. Holocene mid‐ramp sediment is heterozoan in character, but sparse, most probably because of the periodic seaward flow of saline bottom waters generated by coastal evaporation. Holocene outer‐ramp sediment is mainly pelagic, veneering shallow‐water sediments of Marine Isotope Stage 2, including LGM deposits. Phosphate accumulations at ≈ 200 m water depth suggest periodic upwelling or Fe‐redox pumping, whereas enhanced near‐surface productivity, probably associated with the interaction between the Leeuwin Current and Indian Ocean surface water, results in a linear ridge of pelagic sediment at ≈ 140 m water depth. This ramp depositional system in an arid climate has important applications for the geological record: inner‐ramp sediments can contain important heterozoan elements, mid‐ramp sediments with bedforms created by internal tides can form in water depths exceeding 50 m, saline outflow can arrest or dramatically slow mid‐ramp sedimentation mimicking maximum flooding intervals, and outer‐ramp planktic productivity can generate locally important fine‐grained carbonate sediment bodies. Changing oceanography during sea‐level rise can profoundly affect sediment composition, sedimentation rate and packaging.  相似文献   

15.
In this study, we present grain-size distributions of the terrigenous fraction of two deep-sea sediment cores from the SE Atlantic (offshore Namibia) and from the SE Pacific (offshore northern Chile), which we ‘unmix’ into subpopulations and which are interpreted as coarse eolian dust, fine eolian dust, and fluvial mud. The downcore ratios of the proportions of eolian dust and fluvial mud subsequently represent paleocontinental aridity records of southwestern Africa and northern Chile for the last 120,000 yr. The two records show a relatively wet Last Glacial Maximum (LGM) compared to a relatively dry Holocene, but different orbital variability on longer time scales. Generally, the northern Chilean aridity record shows higher-frequency changes, which are closely related to precessional variation in solar insolation, compared to the southwestern African aridity record, which shows a remarkable resemblance to the global ice-volume record. We relate the changes in continental aridity in southwestern Africa and northern Chile to changes in the latitudinal position of the moisture-bearing Southern Westerlies, potentially driven by the sea-ice extent around Antarctica and overprinted by tropical forcing in the equatorial Pacific Ocean.  相似文献   

16.
The effect of seasonally reversing monsoons in the northern Indian Ocean is to impart significant changes in surface salinity (SS). Here, we report SS changes during the last 32 kyr in the Lakshadweep Sea (southeastern Arabian Sea) estimated from paired measurements of d18O and sea surface temperature (SST) using Globigerinoides sacculifer, an upper mixed layer dwelling foraminifera. The heaviest d18OG.sacculifer (–0.07±0.08‰) is recorded between 23 and 15 ka, which could be defined as the last glacial maximum (LGM). The d18OG.sacculifer shift between the LGM and Holocene is 2.07‰. The SST shows an overall warming of 2°C from the LGM to Holocene (28°C to 30°C). However, coldest SSTs are observed prior to LGM, i.e., ~27 ka. The SS was higher (~38 psu) throughout most of the recorded last glacial period (32.5–15 ka). This high salinity together with generally lower SSTs suggests a period of sustained weaker summer or stronger winter monsoons. The deglacial warming is associated with rapid reorganization of monsoons and is reflected in decreased salinity to a modern level of ~ 36.5 psu, within a period of ~5 kyr. This indicates intensification of summer monsoons during cold to warm climate transition.  相似文献   

17.
A multivariable approach utilising bulk sediment, planktonic Foraminifera and siliceous phytoplankton has been used to reconstruct rapid variations in palaeoproductivity in the Peru–Chile Current System off northern Chile for the past 19 000 cal. yr. During the early deglaciation (19 000–16 000 cal. yr BP), our data point to strongest upwelling intensity and highest productivity of the past 19 000 cal. yr. The late deglaciation (16 000–13 000 cal. yr BP) is characterised by a major change in the oceanographic setting, warmer water masses and weaker upwelling at the study site. Lowest productivity and weakest upwelling intensity are observed from the early to the middle Holocene (13 000–4000 cal. yr BP), and the beginning of the late Holocene (<4000 cal. yr BP) is marked by increasing productivity, mainly driven by silicate‐producing organisms. Changes in the productivity and upwelling intensity in our record may have resulted from a large‐scale compression and/or displacement of the South Pacific subtropical gyre during more productive periods, in line with a northward extension of the Antarctic Circumpolar Current and increased advection of Antarctic water masses with the Peru–Chile Current. The corresponding increase in hemispheric thermal gradient and wind stress induced stronger upwelling. During the periods of lower productivity, this scenario probably reversed. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

18.
王强 《地质力学学报》2019,25(5):877-888
文章回顾了1965年李四光先生追寻末次冰期对环境影响的讲话,以及40余年来在天津-河北沿海钻孔地层中、末次盛冰期下切河谷的发现过程。在源到汇过程中,起码自晚更新世以来,研究区已经是古黄河沉积区,多处发现的末次盛冰期下切河谷底板多位于30~32 m深度,低于全新统底板一般在20 m的深度;与长江口地区钻孔末次盛冰期下切河谷深62 m相比,研究区下切河谷规模不如前者,也没有一个统一的大河口。末次盛冰期下切河谷最远地点,是距现代海岸约80 km的河北省孟村回族自治县县城北侧,即西汉黄河亚三角洲叶瓣顶部。众多钻孔见早全新世快速沉积,只能是黄河支流有这样充足的泥沙供给,在局部顶托了早全新世海侵作用发生。   相似文献   

19.
Planktonic foraminifera and pollen data from core GNS84-C106 (Gulf of Salerno, Tyrrhenian Sea) were analysed through the Modern Analogue Technique, Constrained Cluster Analysis and relative variation biplots. A long period of mild climate, centred around 25 ka BP, is evident in both marine and continental reconstructions. The cooling phase from 17 to 14.7 ka BP, correlated to the H1 Heinrich event, is indicated by a sea surface temperature (SST) decrease, which roughly coincides with the cold-arid phase identified by annual and January temperatures. A rapid increase in atmospheric temperatures and precipitation, culminating at 13.8 ka BP, marks the BA cronozone. The corresponding increase in summer and winter SSTs, of 11 and 6.5 °C, respectively, occurred over 600 years. The beginning of the YD, centred around 12.5 ka BP, is marked by a decrease in summer and winter SSTs of, respectively, 4.5 and 3.5 °C in one century. The atmospheric evidence of the YD is primarily reflected in low January temperatures, reaching −6 °C, the lowest values ever experienced in the analysed time interval. The Late Glacial–Holocene transition is clearly recorded in both the continental and marine realms. From 11.5 to 9 ka BP, atmospheric temperatures record a period of substantial stability followed by a drop at 8.9 ka BP, which chronologically fall within the first RCC event (9–8 ka BP) of Mayewski et al. [2004. Holocene climate variability. Quaternary Research 62, 243–255], in correspondence with a phase of relatively high seasonality, indicated by foraminifera.  相似文献   

20.
We conducted paired measurements of the Mg/Ca ratio and δ18O of planktonic foraminifera, Globigerina bulloides, from a sediment core (MD01‐2420) off central Japan in the northwest Pacific, to reconstruct current movements since the Last Glacial Maximum (LGM). These methods make it possible to determine the magnitude and timing of the sea surface temperature (SST) changes and to reconstruct the variations of the past seawater δ18O (δ18Ow) off central Japan. The amplitude of Mg/Ca‐based SST changes between the Holocene and the LGM was about 10°C. The strong resemblance of the SSTs estimated from both methods, Mg/Ca‐based and δ18O‐based, suggests that the SST changes were caused primarily by latitudinal displacement of the Kuroshio–Oyashio currents and no distinct change in the carbonate dissolution of the core. The southward migration of the water mass was 5–6° in latitude at the LGM. The values for regional δ18Ow changes, which were obtained by subtracting the ice volume contribution from the calculated δ18Ow, describe the millennial‐scale water mass migration over the last 30 kyr. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

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