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11.
Inception of the Northern European ice sheet due to contrasting ocean and insolation forcing 总被引：1，自引：0，他引：1
Bjørg Risebrobakken Trond Dokken Eystein Jansen Yongqi Gao Helge Drange 《Quaternary Research》2007,67(1):128-135
About 115,000 yr ago the last interglacial reached its terminus and nucleation of new ice-sheet growth was initiated. Evidence from the northernmost Nordic Seas indicate that the inception of the last glacial was related to an intensification of the Atlantic Meridional Overturning Circulation (AMOC) in its northern limb. The enhanced AMOC, combined with minimum Northern hemisphere insolation, introduced a strong sea-land thermal gradient that, together with a strong wintertime latitudinal insolation gradient, increased the storminess and moisture transport to the high Northern European latitudes at a time when the Northern hemisphere summer insolation approached its minimum. 相似文献
12.
By assimilating information required for the estimation of the Atlantic meridional overturning circulation (AMOC) by the Rapid-MOCHA array, we investigate how transports should be constrained. For the period 2004–2011, we find that even the large adjustments in Florida Strait transport (FST) imposed by assimilating FST data do not impact the AMOC strength at 26.5° N while the AMOC away from this section changes due to the baroclinic response. Moreover, the high correlation between the FST and AMOC previously reported cannot be confirmed for this longer period. When assimilating FST and AMOC transports in conjunction, simulated transports can both be brought easily into consistency with the Rapid estimates while the representation of the hydrographic data at the mooring locations improves mainly at the eastern boundary. The dynamical constraint through the equations of motion conditions that the errors of the components are correlated and the total AMOC error is a much smaller than the sum of its components. Although Ekman and mid-ocean transports improve when AMOC is assimilated, the excellent AMOC representation relies on error compensation through adjustments of mainly the Ekman component. Assimilating the mooring data together with FST does not improve the representation of the AMOC. Density information is difficult to extract via assimilating temperature and salinity because of the strong density compensation in the subtropical gyre. Alternatively assimilating density from the mooring data directly was of limited success. 相似文献
13.
利用中国科学院大气物理研究所大气科学和地球流体力学数值模拟国家重点实验室（LASG/IAP）发展的耦合的气候系统模式FGOALS-s2工业革命前控制试验结果研究了大西洋经向翻转流（Atlantic Meridional Overturning Circulation,AMOC）的年代际变率及其物理机制。传统AMOC是利用深度坐标下的质量流函数来表征,本文通过对密度坐标下49.5°N的AMOC指数与其余纬度的AMOC指数作相关分析,发现AMOC的变化有从深水形成区向南传播的过程,且密度坐标下的AMOC变率在北大西洋高纬度明显大于低纬度。分析进一步表明,模式模拟的AMOC具有年代际振荡,周期约为70年。这个低频振荡主要是由与AMOC变化相关的温度和盐度的变化与海表风场之间的相互作用引起,具体机制如下:格陵兰-冰岛-挪威海有异常强的海表风场,导致蒸发增强,继而使海表盐度增加,深水形成增多,从而使AMOC增强。AMOC加强后,会使得向北的热量和盐度输送增加,减弱此处的经向温度梯度,风场随之减弱,从而完成位相的反转。 相似文献
14.
利用2个关于大西洋经向翻转流(Atlantic Meridional Overturning Circulation,AMOC)的指数:AMOC指数(15oN~65oN、深度为500 m以下的AMOC的最大值)和AMOC扩展指数(15oN~65oN、深度为2000~2500m的AMOC的最大值),研究了耦合模式FGOALS-g2(Grid-point Version 2 of Flexible Global Ocean-AtmosphereLand System Model)中的AMOC在CMIP5(Coupled Model Intercomparison Project Phase 5)的3个典型浓度路径(Representation Concentration Pathways,RCP)(RCP2.6、RCP4.5和RCP8.5分别对应于2100年时490、650和1370 ppm的CO2浓度水平)下的响应问题,发现:在RCP2.6和RCP4.5浓度路径下,2006~2040年时间段内AMOC指数和AMOC扩展指数都呈现快速下降的趋势,2041~2100年时间段内AMOC指数逐渐恢复,AMOC扩展指数基本维持不变;在RCP8.5浓度路径下,2006~2100年时间段内AMOC指数和AMOC扩展指数都表现出快速下降的趋势。通过分析FGOALS-g2中北大西洋深水的成因发现:3个典型浓度路径下AMOC的长期变化趋势主要受到GIN(Greenland–Iceland–Norwegian)海域的深水形成率的调控,而AMOC的年代际尺度的变化则主要受到Labrador海域深水形成率的控制。同时揭示了:由于北大西洋2000 m深度附近的层结稳定性在RCP2.6和RCP4.5下(相比于1980~2005年)提高了30%~40%,使得由AMOC指数恢复产生的深水无法继续下沉,从而导致AMOC扩展指数没有出现恢复的现象。 相似文献
15.
David Gallego-Torres Oscar E. Romero Francisca Martínez-Ruiz Jung-Hyun Kim Barbara Donner Miguel Ortega-Huertas 《Quaternary Research》2014
Previous paleoceanographic studies along the NW African margin focused on the dynamics of surface and intermediate waters, whereas little attention has been devoted to deep-water masses. Currently, these deep waters consist mainly of North Atlantic Deep Waters as part of the Atlantic Meridional Overturning Circulation (AMOC). However, this configuration was altered during periods of AMOC collapse. We present a high-resolution reconstruction of bottom-water ventilation and current evolution off Mauritania from the last glacial maximum into the early Holocene. Applying redox proxies (Mo, U and Mn) measured on sediments from off Mauritania, we describe changes in deep-water oxygenation and we infer the evolution of deep-water conditions during millennial-scale climate/oceanographic events in the area. The second half of Heinrich Event 1 and the Younger Dryas were recognized as periods of reduced ventilation, coinciding with events of AMOC reduction. We propose that these weakening circulation events induced deficient deep-water oxygenation in the Mauritanian upwelling region, which together with increased productivity promoted reducing conditions and enhanced organic-matter preservation. This is the first time the effect of AMOC collapse in the area is described at high resolution, broadening the knowledge on basin-wide oceanographic changes associated with rapid climate variability during the last deglaciation. 相似文献
16.
南京葫芦洞石笋微量元素记录的末次冰消期气候变化 总被引：2，自引：0，他引：2
采用Avaatech型岩芯X射线荧光光谱扫描仪技术,对发育有连续3900年纹层(18.3～14.4ka B.P.时段)的南京葫芦洞YT石笋进行了Sr,Ba和Pb微量元素分析.选择Sr/Ca,Ba/Ca和Pb/Ca作为代用指标,研究了末次冰消期洞穴地点岩溶水文条件和气候变化特征.Ba/Ca和Pb/Ca值从大约17.5ka B.P.开始呈现出减小的趋势变化,而Sr/Ca呈现出在大约16.1ka B.P.发生转折的“V”型演化趋势.Sr/Ca反映了岩溶水在上覆围岩中的滞留时间(与夏季降水相关),而Ba/Ca和Pb/Ca指示了土壤及其基岩的本底值和淋滤作用强度.Sr/Ca比值与纹层厚度、δ13C记录在数百年-千年尺度上呈现一致的变化,共同指示了南京葫芦洞地点有效湿度的变化过程,与δ18O的对应性表明葫芦洞石笋δ18O可以指示当地季风降雨量的变化过程.此外,石笋Ba/Ca和Pb/Ca与格陵兰粉尘和Ca2+记录在长期趋势上呈现一致变化,表明该类元素比值主要反映与冬季风强度密切相关的粉尘活动强度变化.研究结果表明,东亚冬、夏季风对神秘期内发生的冰漂碎屑事件(H1a,16.1ka B.P.和H1b,17.5ka B.P.)具有不同的响应方式.Ba/Ca和Pb/Ca序列的功率谱分别呈现出66a、35a、23a、14a和61a、46a、22a、19a、17a、15a周期,说明北大西洋涛动和太阳活动影响着冬季风强度的高频变化. 相似文献
17.
Mechanisms of Atlantic Meridional Overturning Circulation (AMOC) Variability in a Coupled Ocean–Atmosphere GCM简 总被引：1，自引：0，他引：1
The mechanisms involved in the variability of Atlantic Meridional Overturning Circulation （AMOC） are studied using a 2000-yr control simulation of the coupled Fast Ocean-Atmosphere Model （FOAM）.This study identifies a coupled mode between SST and surface heat flux in the North Atlantic at the decadal timescale,as well as a forcing mode of surface heat flux at the interannual timescale.The coupled mode is regulated by AMOC through meridional heat transport.The increase in surface heating in the North Atlantic weakens the AMOC approximately 10 yr later,and the weakened AMOC in turn decreases SST and sea surface salinity.The decreased SST results in an increase in surface heating in the North Atlantic,thus forming a positive feedback loop.Meanwhile,the weakened AMOC weakens northward heat transport and therefore lowers subsurface temperature approximately 19 yr later,which prevents the AMOC from weakening.In the forcing mode,the surface heat flux leads AMOC by approximately 4 yr. 相似文献