The early Holocene sea level rise

The causes, anatomy and consequences of the early Holocene sea level rise (EHSLR) are reviewed. The rise, of ca 60m, took place over most of the Earth as the volume of the oceans increased during deglaciation and is dated at 11,650–7000 cal. BP. The EHSLR was largely driven by meltwater release from decaying ice masses and the break up of coastal ice streams. The patterns of ice sheet decay and the evidence for meltwater pulses are reviewed, and it is argued that the EHSLR was a factor in the ca 8470 BP flood from Lake Agassiz-Ojibway. Patterns of relative sea level changes are examined and it is argued that in addition to regional variations, temporal changes are indicated. The impact of the EHSLR on climate is reviewed and it is maintained that the event was a factor in the 8200 BP cooling event, as well as in changes in ocean current patterns and their resultant effects. The EHSLR may also have enhanced volcanic activity, but no clear evidence of a causal link with submarine sliding on continental slopes and shelves can yet be demonstrated. The rise probably influenced rates and patterns of human migrations and cultural changes. It is concluded that the EHSLR was a major event of global significance, knowledge of which is relevant to an understanding of the impacts of global climate change in the future.     

Holocene sea level changes at the nile delta coastal zone of Egypt

Carbon dating data of changes in seal level during the Holocene at the Nile delta coast provide eustatic depth-time curve of the region. The curve reveals that sea level was approximately 41 meters below the present level around 8,500 years ago. Trend analysis indicates that with melting of glaciers there was a rapid rise in sea level of about 3 mm/yr. The constructed data points are found to be comparable with other curves in the Mediterranean and wold-wide regions. The general changes of the data points are fairly correlated with the ancient shoreline indicators of morphological features (shelf terraces and slopes, old dunes, sand accretion ridges) and sediments at continental shelf and its contiguous coastal zone that belong to Holocene transgression.     

Late Holocene relative sea level rise and the Neoglacial history of the Greenland ice sheet

In West Greenland, early and mid Holocene relative sea level (RSL) fall was replaced by late Holocene RSL rise during the Neoglacial, after 4–3 cal. ka BP (thousand calibrated years before present). Here we present the results of an isolation basin RSL study completed near to the coastal town of Sisimiut, in central West Greenland. RSL fell from 14 m above sea level at 5.7 cal. ka BP to reach a lowstand of ?4.0 m at 2.3–1.2 cal. ka BP, before rising by an equivalent amount to present. Differences in the timing and magnitude of the RSL lowstand between this and other sites in West and South Greenland record the varied interplay of local and non‐Greenland RSL processes, notably the reloading of the Earth's crust caused by a Neoglacial expansion of the Greenland Ice Sheet (GIS) and the subsidence associated with the collapse of the Laurentide Ice Sheet forebulge. This means that the timing of the sea level lowstand cannot be used to infer directly when the GIS advanced during the Neoglacial. The rise in Late Holocene RSL is contrary to recently reported bedrock uplift in the Sisimiut area, based on repeat GPS surveys. This indicates that a belt of peripheral subsidence around the current ice sheet margin was more extensive in the late Holocene, and that there has been a switch from subsidence to uplift at some point in the last thousand years or so. Copyright © 2008 John Wiley & Sons, Ltd.     

Catastrophic early Holocene sea level rise,human migration and the Neolithic transition in Europe

The collapse of the Laurentide Ice Sheet and release of freshwater 8740–8160 years ago abruptly raised global sea levels by up to 1.4 m. The effect on human populations is largely unknown. Here we constrain the time of the main sea level rise and investigate its effect on the onset of the Neolithic across Europe. An analysis of radiocarbon ages and palaeoshoreline reconstruction supports the hypothesis that flooding of coastal areas led to the sudden loss of land favoured by early farmers and initiated an abrupt expansion of activity across Europe, driven by migrating Neolithic peoples.     

中国近海潮汐变化对外海海平面上升的响应

针对外海海平面上升对中国沿海潮波系统和潮汐水位可能带来的影响,通过西北太平洋潮波数学模型对边界海平面上升后潮波变化进行了数值模拟。研究发现边界海平面上升后,在无潮点附近东侧迟角增加,西侧迟角减小;无潮点北侧振幅增加,南侧振幅减小;辽东湾、渤海湾顶、辽东半岛东海域、海州湾至鲁南沿海、苏北沿海、台湾海峡至浙东沿海和南海平均潮差增加,海平面上升0.90 m后潮差最大增幅达0.40 m;长江口、杭州湾至对马海峡、朝鲜西海岸和莱州湾海域潮差减小。随着海平面上升量值的增加,渤海、台湾海峡潮差变化速率相对稳定,黄海、东海和南海站位变化速率有所变动;平均高水位的变化趋势与潮差一致;潮差增加的区域,高水位抬升幅度超过边界海平面上升幅度。海平面上升引起的高水位超幅变化,增加了沿海地区对风暴潮和其他灾害防护的风险。     

末次间冰期ENSO对全球海平面上升响应的模拟研究

末次间冰期的全球年平均地表气温比现今高0~2 ℃, 这一增温幅度与未来预估的增温幅度相当。因此, 末次间冰期气候往往被认为是未来气候的一个类比。本研究利用挪威地球系统模式(NorESM1-F)开展末次间冰期模拟, 并进一步讨论全球平均海平面上升5 m和10 m时末次间冰期的ENSO海温变率。模拟结果表明: 模拟的末次间冰期热带太平洋年平均海表面温度较工业革命前普遍偏低, 这与地质记录重建基本一致。与工业革命前相比, 模拟的末次间冰期El Niño事件强度偏弱, 极端El Niño事件偏少; 而La Niña事件强度偏强, 极端La Niña事件偏多; 随着全球平均海平面的上升, 海表温度异常出现变化, 表现为小于0.5 ℃的海温异常出现的频率减少, 而大于0.5 ℃的海温异常出现频率增加, 表明全球平均海平面的上升会使海温的异常更加明显, 但全球平均海平面的上升对模拟的末次间冰期ENSO事件的频次及平均强度影响并不显著。

     

How a river submerges into the sea: a geological record of changing a fluvial to a marine paleoenvironment during early Holocene sea level rise

Coastal seas, and in particular estuarine systems, were significantly affected by Quaternary sea level changes. Furthermore, the dynamics of shelf and coastal evolution have had a strong impact on coastal landscapes inhabited by humans. The postglacial evolution of the vast North Sea shelf with its huge drainage systems, e.g. the Elbe Paleovalley and its tributary system, is an excellent research target to understand how coastal shelf environments change in response to sea level rise. In this study, we investigate infill sediments of the Paleo‐Ems valley – a drowned extension of the modern Ems River and part of the Elbe Paleovalley drainage system. Radiocarbon‐dated transgression sequences provide several new observations regarding the mode and rate of the river system submerging due to the Holocene transgression. Thus, the Paleo‐Ems valley submerged within a short time span of~200 years since the river was not able to adjust its gradient to the rapid rising sea level. The fate of the Paleo‐Ems is exemplary for the rapid change of a former fluvial landscape into a coastal landscape and finally into a submarine seascape. © 2019 The Authors. Journal of Quaternary Science Published by John Wiley & Sons Ltd.     

On the character of Black Sea level rise during the Holocene

The character of changes in the mollusk fauna in the Late Pleistocene and Holocene sediments within the Bulgarian, Northwestern, Crimean, and Kerch segments of the Black Sea shelf has been examined. A bed containing fossil remains of brackish-water and marine mollusks was recognized in these sediments; the bed accumulated, based on results of radiocarbon datings, 500–1000 years ago. The obtained data do not support the existing notion of a catastrophic fill-up of the Black Sea Basin by marine Mediterranean water [19].     

Holocene depocenter shift in the middle-lower Changjiang River basins and coastal area in response to sea level change

Authors collected 38 sedimentary boreholes and numerous seismic profiles from previous publications to delineate the Holocene sedimentation rate of six major depositional sinks in the middle-lower Changjiang River basins and its river coast. The results demonstrate that the highest sedimentation rate of ca. 15 m/ka occurred in the mono-depositional sink of the former Changjiang River mouth during 10 000–8000 aBP, when post-glacial transgression happened and the Changjiang water level remained at lower stand. With the rising of the Changjiang water level in response to sea level rise, Jianghan Basin of the middle Changjiang River becomes the other important depositional sink with highest sedimentation rate of 10 m/ka since 7000 aBP. As Jianghan Basin was mostly filled up at ca. 4000 aBP, Dongting Basin and the lower Changjiang valley trapped sediments in great amounts like in the river mouth. A considerable amount of Changjiang sediments has been delivered, both eastward and southward, to the inner continental shelf of the East China Sea, especially after 2000 aBP. This indicates reduced sediment storage capacity of the middle-lower Changjiang valley and the river mouth. In total, ca. 1307.4 billion tons of sediment have deposited in the middle-lower Changjiang floodplain since 7000 aBP. In the meantime, ca. 947 billion tons of sediment have been deposited in the river coast to form the Changjiang subaqueous delta and the Zhejiang-Fujian along-shelf mud wedge. Our result also reveals two time stages with lower sedimentation rates(< 4 m/ka) in all basins during 8000–7000 aBP and in the estuarine area during 4000–2000 aBP, probably owing to stengthened chemical weathering of decline of monsoon precipitation. __________ Translated from Journal of Palaeogeography, 2007, 9(4):419–429 [译自: 古地理学报]     

黄海中部泥质区底栖有孔虫群落对早全新世海平面快速上升的响应

末次冰消期以来全球海平面经历了很大变动,本文通过陆架泥质区资料,对黄海中部泥质区5个沉积物柱样进行了AMS ¹⁴C年代测试,结合沉积物粒度组成与底栖有孔虫资料探讨黄海中部泥质区底栖有孔虫对早全新世海平面快速上升的响应。结果表明,约13.0 ka以来底栖有孔虫群落对海平面变化的响应呈现明显的3个阶段：早期阶段(约13.0~10.0 ka期间),底栖有孔虫以近岸浅水组合为主,与这一时期海平面相对较低对应,泥质区整体呈滨岸环境,水动力环境较强,有机质等食物供给相对丰富,底栖有孔虫丰度相对较高;中期阶段(约10.0~7.0 ka期间),底栖有孔虫群落几乎消失,可能是由于海平面快速上升,动荡的海洋环境不利于有机质沉降,造成底栖有孔虫食物供给不稳定,不利于底栖有孔虫生存所致;晚期阶段(约7.0 ka以来),底栖有孔虫群落逐渐繁盛,以黄海中部冷水团特征组合为主,反映了区域海平面相对稳定、泥质沉积的形成以及黄海冷水团核心区域的出现等海洋环境变化为底栖有孔虫带来了稳定的有机质供给,故而底栖有孔虫丰度迅速增加到与现在相当的水平。黄海中部泥质区多柱样底栖有孔虫群落变化对早全新世海平面上升有较一致的响应,为该区全新世早期海平面快速上升以及黄海现代环流体系的形成提供了更直接的证据。

     

莱州湾南岸全新世相对海平面变化重建

在对莱州湾南岸8个钻孔沉积物沉积结构及有孔虫特征分析基础上,识别相关海面标志层位,辅以加速器质谱AMS14C测年,重建了全新世相对海面变化历史,并讨论了海面变化的沉积响应及控制因素。约9200cal BP以前,海面快速上升,研究区海侵时海面于-21.5m左右;9200~8400cal BP海面上升速率减缓至约2mm/a;8400~8000cal BP海面由-14m快速上升至-5.5m,速率约为33mm/a;8000~7600cal BP,海面持续数百年停滞或微弱下降;7600~7000cal BP海面由-5.5m快速上升至0m以上,速率至少约为13mm/a;7000~6000cal BP海面缓慢上升至+2~+3m位置,速率约为3mm/a;约6000cal BP以后海面缓慢下降至现今水平。约9200cal BP以前、8400~8000cal BP、7600~7000cal BP时期的3次海面快速上升,是MWP-1C融水脉冲、诱发8.2ka冷事件的融水脉冲,以及MWP-2融水脉冲的中纬度地区响应。中全新世全球冰融趋于停滞后,由于研究区沉积盆地沉降速度较慢,在冰川均衡调整效应下,使+2~+3m的相对高海面得以呈现。     

未来上海地区海平面上升对土压缩模量的影响分析

未来上海地区海平面上升将引起地下水位抬升,将会对土压缩模量E产生影响。E是土的最重要的物理力学参数指标之一,尤其在地基沉降计算中具有重要意义。本文主要针对土压缩模量Es的预测分析工作,进行了地基变形的探讨研究,供交流参考。     

Coastal response to the Holocene transgression in the Bahamas: episodic sedimentation versus continuous sea-level rise

Sedimentological and petrographic study of Holocene deposits in the Eastern Bahamas shows that sedimentation occurred episodically during this period of continually rising sea-level.

The Holocene stratigraphic record exposed on the islands of San Salvador, Lee Stocking and Cat consists of two distinctive units separated by a paleosol: (1) 5000 year-old oolitic eolianites deposited when sea-level was lower than today, and (2) 3000 to 500 year-old bioclastic paleo-beaches and dunes that are congruent with the present stand of sea-level.

A five-stage model that reconciles intermittent sedimentation pattern with continuous sea-level rise is presented. Pre-Holocene topography and changes in the rate of the transgression seem to regulate local⁴ hydrodynamic conditions, which in turn control onset and offset of sedimentary processes.

This Holocene example of episodic sedimentation during an uninterrupted transgression should be considered when studying ancient discontinuities that are systematically interpreted in terms of relative sea-level fall.     

Impact of sea level rise on aquifer system of Agatti Atoll

The freshwater aquifer of Agatti Island varies from a depth of 6 m to 27 m from mean sea level. A 50-cm sea level rise may cause 26.69 percent freshwater contamination due to salt water intrusion.     

Mangrove forest sedimentation and its reference to sea level rise,Cananeia, Brazil

The stability of a mangrove ecosystem in Cananeia, Brazil, is assessed based on investigations of the site-specific temporal rise in relative sea level during the past 50 years, 100-year sediment accumulation rates (SAR) and sources of organic matter (OM). Addressing this, three sediment cores were collected in a transect, intertidal mud flat, mangrove margin and well into the forest. The net SAR, as estimated by the age–depth relationships of ²¹⁰Pb and ¹³⁷Cs, is between 2.5 and 3.9 mm year⁻¹. These rates are comparable to the estimates based on the Pb and Zn contaminant markers corresponding to mining initiation in the region in 1918. Further, the SARs are lower than the rate of regional relative sea level rise (4 mm year⁻¹) as indicated by the past 50-year tide gauge record, but the rate is higher than the eustatic sea level rise (1.7 ± 0.3 mm year⁻¹). The stratigraphies of TOC/TN, δ¹³C_(OC), OP and δ¹⁵N indicate site-specific mangal vegetal litter, which is the predominant source of OM at all core sites, during the past century and reflects a stable mangal system over that time span.     

On the significance of incorporating shoreline changes for evaluating coastal hydrodynamics under sea level rise scenarios

Natural Hazards - The influence of including the dynamic effects of future shoreline changes associated with sea level rise into hydrodynamic modeling is evaluated for the coast of the Northern...     

长江三角洲全新世海平面重建研究综述

通过综述国内外全新世海平面重建研究进展,总结了全新世海平面重建的各种指标和海平面重建存在的科学问题,认为冰川—水均衡作用、区域差异性构造沉降、沉积物压实和侵蚀再沉积作用是各地区全新世海平面差异性存在的主要原因;对长江三角洲各海平面重建指标进行了有效性分析,得出基底泥炭、硅藻、有孔虫转换函数,海相地层、古人类遗址、TOC/TN和δ13C、TOC/TS和自生铁硫化物是重建海平面的有效指标,并对每个指标的优缺点及重建时需要考虑的问题进行了阐述。