青藏高原东南巴松措流域和派山谷末次冰盛期冰川与气候重建

末次冰盛期(LGM)时全球大范围降温,青藏高原冰川大规模扩张,重建LGM时期古冰川规模对认识高原冰川水资源演化及古气候条件有重要的科学意义。根据青藏高原东南巴松措流域及派山谷两地的冰川地貌及其10Be暴露年代数据,本文应用冰川纵剖面模型定量重建了两地冰川在LGM时期的范围、冰储量和平衡线高度(ELA)等参数,并通过冰川气候模型恢复了LGM时的气候条件。结果表明：巴松措流域LGM时期的冰川面积约为982.3km²,是现代冰川面积的4.5倍,冰储量约为274.4km³;派山谷无现代冰川分布,LGM时期的冰川面积达5.76km²,冰储量约为0.51km³;LGM时期两冰川的平衡线高度分别为4 460～4 547m和3 569～3 694m,与现代冰川相比分别降低了535m和1 034～1 184m。在降水减少60%的情况下,考虑LGM以来的构造剥蚀对平衡线高度变化的影响,LGM时期巴松措流域和派山谷冰川的夏季平均气温分别比现在低约2.96～4.89℃和5.09～6.99℃。     

龙感湖钻孔揭示的末次盛冰期以来的环境演化

通过龙感湖滩地钻孔24．4m深度以内的沉积物岩性、生物和物理指标分析,在^14C年代测定的基础上,对龙感湖末次盛冰期以来的环境演化进行了恢复,15．0kaBP前和10．0－6．3kaBP,龙感湖区发育河流沉积,以低生物量和高磁化率为特征;约15．0－10．0kaBP期间的晚冰期,龙感湖首次成湖,湖泊中生物量明显提高;现代龙感湖雏形始于约6．3kaBP后,至3．7kaBP后发展为稳定的湖泊环境,此外,花粉结果显示,龙感湖湿地相干被大致形成于3．3kaBP后,然后,龙感湖的成因和演化,及其与长江关系的研究,还必须重视对沉各物物源的追踪。     

末次盛冰期以来冲绳海槽中部沉积物有机碳和磷的地球化学研究

利用元素及同位素地球化学方法研究了冲绳海槽中部沉积物岩芯中有机碳及磷的地球化学特征及影响因素。结果表明,冲绳海槽沉积速率（16.5~32.5 cm/ka）变化小,不是沉积物中有机碳埋藏的重要影响因素。相对于全新世氧化性底水环境,末次盛冰期/冰消期冲绳海槽缺氧底水环境提高了沉积物对有机碳的埋藏效率。冲绳海槽沉积物中各形态磷的相对含量与其他边缘海沉积物中的相似。交换态磷（Ex-P）含量低、变化小。末次盛冰期/冰消期缺氧底水环境下铁氧化物的还原溶解导致铁结合磷（Fe-P）释放以及自生磷矿物（Au-P）的形成。全新世氧化性底水条件有利于铁氧化物的有效再生及对磷的再吸附,但不利于Au-P的保存。总有机碳（TOC）和有机磷（Org-P）之间良好的相关性表明TOC埋藏对Org-P含量的重要控制作用。冲绳海槽沉积物中碎屑磷（De-P）含量低于长江口及东海陆架沉积物中的含量,这与陆源碎屑向外海传输减弱有关。在约9.3 ka BP（岩芯200 cm深度）,TOC、Fe-P、Org-P、De-P以及Fe_HR均出现的极小值可能由物质坡移造成。     

基于浮游有孔虫Mg/Ca温度重建的末次盛冰期以来北欧海次表层温度的变化

对我国第五次北极科考在北欧海所采集的两根岩芯样品进行了冰筏碎屑(Ice-Rafted Debris,IRD)丰度、AMS 14C测年、有孔虫丰度统计、浮游有孔虫Neogloboquadrina pachyderma(sin.)(Nps)稳定氧碳同位素及其Mg/Ca重建的次表层海水古温度等指标分析,建立了20ka以来的年代框架。结果表明,在末次盛冰期(20.0~17.5kaBP),次表层温度整体较低(~3℃),钙质生产力下降,冰筏碎屑输入增加;在冰消期(17.5~11.7kaBP)的Heinrich Stadial 1(HS1)事件中较轻的δ^18O和δ^13C指示大量淡水输入,水体分层加剧,向北输送的北大西洋水聚集在次表层,导致次表层水温逐渐升高。从B?lling-Aller?d(B/A)事件开始,次表层水温度达到4.5℃,表明北大西洋水流入增强。早全新世(11.7~8.2kaBP)早期次表层温度达到6.5℃,钙质生产力升高,冰筏碎屑输入降低;在中全新世(8.2~4.2kaBP)早期(8.2~5.6kaBP),钙质生产力逐渐升高反映通风作用增强,导致营养盐供应增加;6.6~5.6kaBP,明显降低的次表层温度(~4℃)反映夏季太阳辐射量降低以及大西洋水流入减弱;5.6~4.2kaBP期间次表层水变暖导致δ^18O偏轻,而δ^13C轻值反映生产力降低。晚全新世(4.2~0.8kaBP)的新冰期(4.2~3.0kaBP),次表层温度逐渐降低,Nps-δ^13C偏轻反映生产力下降,Nps-δ^18O偏轻以及IRD增加反映冰融水排放。3.0kaBP以来,生产力上升,次表层水体温度不断上升,可能是向北输送的北大西洋水增强。     

基于长时间序列Landsat影像的嘎龙错冰湖变化特征分析及溃决风险评估

冰湖溃决灾害是我国青藏高原地区最严重的自然灾害之一。作为聂拉木县最大的冰川终碛湖,嘎龙错冰湖溃决风险直接威胁着下游居民的生产生活。利用1991—2011年Landsat-5/TM、2012年Landsat-7/ETM+、2013—2017年Landsat-8/OLI近27年的遥感影像、降水量和气温资料对嘎龙错冰湖变化特征进行了研究,对其溃决风险作出评估。结果表明:嘎龙错冰湖明显扩张,面积呈现显著增长趋势,由1991年的2.209 4 km^2增长到2017年的5.465 7 km^2,增幅为147.38%;同时,发现聂拉木气象站年平均气温和年降水量在波动中上升,其中气温上升较为显著,气温和降水量的增加对冰湖扩张有重要影响,特别是气温上升导致的冰川融水增多是造成冰湖面积增加的重要原因。嘎龙错冰湖在遇到冰崩或者冰湖面积持续扩张情况下,湖水会瞬间大规模外泄,形成山洪、泥石流灾害,给下游造成严重的人员伤亡和财产损失。     

Contributions of the Bering Strait throughflow to oceanic meridional heat transport under modern and Last Glacial Maximum climate conditions

Paleo reconstructions and model simulations have suggested the Bering Strait plays a pivotal role in climate change. However, the contribution of the Bering Strait throughflow to oceanic meridional heat transport (OMHT) is about 100 times smaller than the OMHT at low latitudes in the modern climate and it is generally ignored. Based on model simulations under modern and Last Glacial Maximum (LGM,~21 ka;ka=thousand years ago) climate conditions, this study highlights the importance of the Bering Strait throughflow to OMHT. The interbasin OMHT induced by the Bering Strait throughflow is estimated by interbasin-intrabasin decomposition. Similar to barotropic-baroclinic-horizontal decomposition, we assume the nonzero net mass transport induced by interbasin throughflows is uniform across the entire section, and the interbasin term is separated to force zero net mass transport for the intrabasin term. Based on interbasinintrabasin decomposition, the contribution of the Bering Strait throughflow is determined as ~0.02 PW (1 PW=10 15 W) under the modern climate, and zero under the LGM climate because the closed Bering Strait blocked interbasin throughflows. The contribution of the Bering Strait throughflow to OMHT is rather small, consistent with previous studies. However, comparisons of OMHT under modern and LGM climate conditions indicate the mean absolute changes are typically 0.05 and 0.20 PWin the North Atlantic and North Pacific, respectively. Thus, the contribution of the Bering Strait throughflow should not be ignored when comparing OMHT under diff erent climate conditions.     

A new high-resolution Late Glacial-Holocene climatic record from eastern Nanling Mountains in South China

A 350-cm-long sediment core sequence from Dahu Swamp situated in the eastern Nanling Mountains was selected for high-resolution paleoclimatic reconstruction since the Late Glacial period. The multi-proxy records of this paper reveal several evidently dry and cold events that may coincide with the Oldest Dryas, the Older Dryas, the Younger Dryas in the late deglacial period. Two relatively wetter and warmer phases occurred in ca. 15,000–14,400 cal yr B.P. and 13,500–12,800 cal yr B.P. respectively may correspond to the Bølling and Allerød warming events. The Younger Dryas event (ca. 12,800–11,500 cal yr B.P.) revealed by multi-proxies was characterized by relatively colder and drier climate. A warmer and wetter climate, occurred in ca. 10,000–6000 cal yr B.P., was consistent with the Holocene Optimum, which coincided with the maximum Northern Hemisphere insolation. The “8.2kyr cool event” and even the “8.8kyr cool event” were indicated as well from our sediment core. A dry mid-Holocene period (ca. 6000–3000 cal yr B.P.) indicated by multi-proxies does not follow the traditional concept of the wet mid-Holocene conditions observed in other regions in China.     

MET-IRSL used to track pre-depositional sediment transport history

This paper explores a series of single grain MET-IRSL (multiple elevated temperature infra-red stimulated luminescence) determinations undertaken in order to assess the potential of this approach, developed over the last decade and previously applied to a range of applications, in determining how eroded material moves through environments. Three different approaches are explored here, namely: i) an assessment of the potential to use the technique for improving the robustness of IRSL or P-IR-IRSL age estimates by identifying only well-bleached grains, ii) a means to characterise patterns of grain transport within a catchment using a newly established parameter, the “burial-bleach ratio”, and iii) a novel proxy that responds to changes in light availability through time, here referred to as palaeophotochronometry. For the second approach that we explore, a direct comparison of the MET-IRSL results from several sites with particle size analysis (PSA) data for the same sediment is included. This comparison highlights striking similarities between dispersal of single grain (SG) MET-IRSL burial-bleach ratio data and PSA distributions for some samples, suggesting that we may be able to place a timescale on the acquisition of this fundamental sedimentary characteristic. Common to these three SG MET-IRSL approaches is the importance of characterising and interpreting the previous bleaching records for individual grains.     

Micromorphology of ice keel scour in pebbly sandy mud and fine‐grained sands: Scarborough Bluffs,Ontario, Canada

The keels of icebergs and ice‐pressure ridges plough through unconsolidated sea/lake sediments gouging out long grooves known as ice keel scour marks. Although the surface and (more recently) subsurface morphology of scours are well‐documented, little is known of the effect of grain size on the detectability, style and intensity of sub‐scour deformation. This investigation macroscopically and microscopically (two‐dimensional thin sections) examines suspected ice keel scour in: (i) glaciolacustrine pebbly sandy mud and (ii) fine‐grained sands at Scarborough Bluffs, Ontario, Canada. In this investigation, there is an almost identical suite of deformation structures (individual structures and overprinted structural patterns) to those identified in iceberg‐scoured clays from former Glacial Lake Agassiz (Manitoba, Canada); this confirms that deformation in the pebbly sandy mud and fine‐grained sands at Scarborough Bluffs is likely to be indicative of ice keel scour. Discrete differences in the detectability, style and intensity of deformation between the Scarborough Bluffs and Glacial Lake Agassiz sediments are probably a function of grain size in response to ice keel scour. This research provides additional information on the types of structures that are associated with sediment deformation by processes of ice keel scour in a variety of grain sizes. This information is particularly valuable to inform palaeoenvironmental reconstruction and offshore engineering in areas where ice keel scour occurs in a variety of grain sizes. It also demonstrates the potential value of micromorphology where, for example, the study of cores is necessary.