首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
Two major pulses of sea-level rise are thought to have taken place since the last glacial maximum — meltwater pulses (mwp) 1A (12 cal ka) and 1B (9.5 cal ka). Between mwp 1B and about 6 cal ka, many of the complex coastal ecosystems which ring the world’s oceans began to form. Here we report data for rhenium, carbon isotopes, total organic carbon, and fossil oysters from Chesapeake Bay which span the transition from fresh to brackish water conditions in the bay in the mid-Holocene. These data constrain sea-level change and resulting environmental change in the bay. They indicate that the transition was rapid, and that it was produced by (1) a third pulse of rapid eustatic sea-level rise, or (2) a geometry of the prehistoric Chesapeake Bay basin which predisposed it to a nonlinear response to a steadily rising sea level. Similar nonlinear changes in vulnerable coastal environments are likely to take place in the future due to polar warming, regardless of the timing or rate of sea-level rise.  相似文献   

2.
High-resolution sedimentological and micropaleontological studies of several deep-sea cores retrieved from the levees of the Celtic and Armorican turbidite systems (Bay of Biscay — North Atlantic Ocean) allow the detection of the major oscillations of the British–Irish Ice Sheet (BIIS) and ‘Fleuve Manche’ palaeoriver discharges over the last 30,000 years, which were mainly triggered by climate changes.Between 30 and 20 cal ka, the turbiditic activity on the Celtic–Armorican margin was weak, contrasting with previous stratigraphic models which predicted a substantial increase of sediment supply during low sea-level stands. This low turbidite deposit frequency was most likely the result of a weak activity of the ‘Fleuve Manche’ palaeoriver and/or of a reduced seaward transfer of sediments from the shelf to the margin. However, two episodes of turbiditic activity increase were detected in the Celtic–Armorican margin, during Heinrich events (HE) 3 and 2. This strengthening of the turbiditic activity was triggered by the meltwater releases from European ice sheets and glaciers favouring the seaward transfer of subglacial material, at least via ‘Fleuve Manche’ palaeoriver.At around 20 cal ka, a significant increase of turbidite deposit frequency occurred as a response to the onset of the last deglaciation. The retreat of the European ice sheets and glaciers induced a substantial increase of the ‘Fleuve Manche’ palaeoriver discharges and seaward transfer of continentally-derived material into the Armorican turbidite system. The intensification of the turbiditic activity on the Celtic system was directly sustained by the widespread transport of subglacial sediments from the British–Irish Ice Sheet (BIIS) to the Celtic Sea via the Irish Sea Basin. A sudden reduction of turbiditic activity in the Armorican system, between ca. 19 and 18.3 cal ka, could have been triggered by the first well known abrupt sea-level rise (‘meltwater pulse’, at around 19 cal ka) favouring the trapping of sediment in the ‘Fleuve Manche’ palaeoriver valleys and the decrease of the seaward transfer of continentally-derived material.The maximum of turbiditic activity strengthening in the Celtic–Armorican margin, between ca. 18.3 and 17 cal ka, was induced by the decay of European ice sheets and glaciers producing the most extreme episode of the ‘Fleuve Manche’ palaeoriver runoff and a great seaward transfer of subglacial material into the Bay of Biscay. Between ca. 17.5 and 16 cal ka, the turbiditic activity significantly decreased in both Celtic and Armorican turbidite systems in response to a global re-advance of glaciers and ice sheets in Europe. The last episode of ice sheet retreat, between ca. 16 and 14 cal ka, is well expressed in the Celtic system by a new increase of the turbiditic activity. The major episode of sea-level rise at around 14 cal ka (‘Meltwater Pulse 1A’), precluding the seaward transfer of sediments, induced the end of turbiditic activity in both the Celtic and the Armorican system.Although two main phases of global sea-level rise seem to have had an effect on the Celtic–Armorican margin, this work proposes the BIIS retreat and associated riverine discharges as the main trigger mechanisms of the turbiditic activity in this region during the last 30,000 years.  相似文献   

3.
通过对日本海Ulleung盆地KCES-1孔元素地球化学分析,探讨了过去48 ka以来日本海古生产力和古氧化还原环境的变化规律和影响因素。多种替代指标质量累积速率(总有机碳、CaCO3,磷、过剩钡、镉含量)显示日本海古生产力自48 ka以来发生了显著的变化。在48~18 ka低海平面和有限的水体交换导致表层水古生产力相对较低。在18~11 ka随着海平面的上升,富营养盐水团(亲潮和东海沿岸流水团)的流入导致古生产力逐渐增大,在12.6~11.5 ka古生产力达到最大值。在全新世对马暖流成为影响古生产力变化的重要因素,并且自5 ka以来古生产力保持相对稳定。古氧化还原替代指标(总有机碳、钼、铀、锰、碳与硫含量之比、自生铀、自生钼含量)显示在12~9 ka日本海底层水可能为无氧环境。古生产力高和底层水体有限的交换是诱发底层水缺氧的主要因素,而这又与全球气候变化和海平面变化有关。  相似文献   

4.
The Pagassitikos Gulf in Greece is a semi-enclosed bay with a maximum depth of 102 m. According to the present-day bathymetric configuration and the sea level during the latest Pleistocene, the gulf would have been isolated from the open sea, forming a palaeolake since ~32 cal. ka b.p. Sediment core B-4 was recovered from the deepest sector of the gulf and revealed evidence of a totally different depositional environment in the lowest part of the core: this contained light grey-coloured sediments, contrasting strongly with overlying olive grey muds. Multi-proxy analyses showed the predominance of carbonate minerals (aragonite, dolomite and calcite) and gypsum in the lowest part of the core. Carbonate mineral deposition can be attributed to autochthonous precipitation that took place in a saline palaeolake with high evaporation rates during the last glacial–early deglacial period; the lowest core sample to be AMS 14C dated provided an age of 19.53 cal. ka b.p. The palaeolake was presumably reconnected to the open sea at ~13.2 cal. ka b.p. during the last sea-level rise, marking the commencement of marine sedimentation characterised by the predominance of terrigenous aluminosilicates and fairly constant depositional conditions lasting up to the present day.  相似文献   

5.
According to coastal measurements, global mean sea-level has risen at a rate of 1.8 mm yr−1 between 1950 and 2000, with large spatial variability at regional scales. Within the Bay of Biscay, trends computed from coastal tide gauges records have revealed that sea-level rise is accelerating over this period of time; this is in agreement with rates obtained from satellite imagery in the open ocean since 1993. The objectives of the present study are: (1) to assess the evidence of the relative sea-level rise on coastal morphology and habitats in the Gipuzkoan littoral zone (Basque coast, northern Spain) for the period 1954–2004, and (2) to evaluate the relative contribution of local anthropogenic versus sea-level rise impacts for explaining inter-supratidal habitat changes. A high-resolution airborne laser altimetry data (LIDAR) has been used to derive a Digital Terrain Model (DTM) of 15-cm vertical resolution. Coastal habitats were mapped for two periods, using historic airborne photography (1954) and high-resolution imagery (2004). Analysis of tide gauge records from Santander (northern Spain) has revealed that relative mean sea-level has been rising at a rate of 2.08 ± 0.33 mm yr−1 from 1943 to 2004; this is consistent with sea-level trends from other measurements within the area (St. Jean de Luz and Bilbao), obtained over shorter periods of time, and with previous results obtained in the Bay of Biscay. Based upon this sea-level trend and by means of a LIDAR-based DTM, the results have indicated that the predicted change along the Gipuzkoan coast due to sea-level rise was of 11.1 ha within the 50-yr period. In contrast, comparison of historical and recent orthophotography has detected only 2.95 ha of change, originated possibly from sea-level rise, and 98 ha transformed by anthropogenic impacts. Hence, coastal changes due to sea-level rise might be overwhelmed by excessive human impacts, at the spatial and temporal scales of the analysis. This work highlights that local anthropogenic impact is the major threat to Basque coastal and estuarine habitats, compared with natural erosive processes and global climate change driving forces over recent times.  相似文献   

6.
全新世胶州湾海侵及大沽河古河口湾的形成和演变   总被引：4，自引：0，他引：4  
晚更新世盛冰期低海面时,胶州湾为陆地,大沽河流于其上,河口在黄海陆架边缘。全新世海侵时,海水沿古河道侵入,约在9．6kaB．P．左右,胶州湾地区被海水淹没,并于湾顶西北侧形成196km^2的大沽河溺谷型河口湾,当时大沽河河口退缩至今谈家庄一沽河镇(李哥庄)一带。随后,河流泥沙在该河口湾快速淤积,形成十余米厚的水下冲积扇和1～2m厚的冲积层,将溺谷湾充填。约在4kaB．P．左右大沽河河口外延至现今营海码头村、三角底一带。  相似文献   

7.
广西钦州湾晚全新世红树林演变及对海平面变化的响应   总被引：2，自引：0，他引：2  
Mangroves, widely distributed along the coasts of tropical China, are influenced by Asia monsoon, relative sea level change and enhanced human activity. To predict the impacts of future climate change on mangrove ecosystems, it can be understood by reconstructing past mangrove dynamics using proxies preserved in coastal sediments. In this study, we quantitatively partitioned buried organic matter(OM) sources, collected from a vulnerable mangrove swamp in the Qinzhou Bay of northwestern South China Sea, using a ternary end-member mixing model of δ~(13)C and C:N values. Mangrove-derived OM(MOM) contribution was used as a tracer for mangrove development since 2.34 cal ka BP. This information, together with paleoclimate records(i.e.,speleothem δ~(18)O values, sea level change, grain size parameters) and human activity, was used to divide mangrove development into three stages during the late Holocene: relative flourish(2.34–1.13 cal ka BP), relative degradation(1.13–0.15 cal ka BP) and further degradation(0.15–0 cal ka BP). Before 1.13 cal ka BP, mangroves flourished with a high MOM contribution((88.9±10.6)%), corresponding to stable and high sea level under a warm and humid climate. After 1.13 cal ka BP, rapid fall in relative sea level coupled with the strengthening of the Asian winter monsoon, resulted in mangrove degradation and MOM reduction((62.4±18.9)%). Compared with air temperature and precipitation, the relative sea level fall was the main controlling factor in mangrove development before entering the Anthropocene(the time of the Industrial Revolution). After ～150 cal a BP, reclamation of mangrove swamps to shrimp ponds is the main factor causing mangrove degradation and MOM reduction.  相似文献   

8.
Annual and interannual variations of sea-level anomaly (SLA) in the Bay of Bengal and the Andaman Sea are investigated using altimeter-derived SLA data from 1993 to 2003. It is found that the SLA annual variation in the study area can be divided into three phases with distinctive patterns. During the southwest monsoon (May-September), positive SLA presents in the equatorial region and extends northward along the eastern boundary of the bay, and the SLA distribution in the interior bay appears to be high in the east and low in the west with two cyclonic cells developing in the north and south of the western bay respectively, between which an anticyclonic cell exists. During the early northeast monsoon (October-December), the whole bay is dominated by a large cyclonic cell with the pattern of high SLA in the east and low in the west still retained, and the SLA distribution outside the bay is changed in response to the reversal of the Indian Monsoon Current (IMC) in November. During the late northeast monsoon (January-April), a large anticyclonic cell of SLA develops in the bay with negative SLA prevailing in the equatorial region and extending northward along the eastern boundary of bay. Therefore, the SLA distribution in the interior bay reverses to be high in the west and low in the east. It is suggested that the SLA annual variation in the bay is primarily driven by the local wind stress curl, involving Sverdrup balance while the abrupt SLA variation during the peak of northeast monsoon may be partly caused by the semiannual fluctuation of wind in the equatorial region. This fast adjustment in the interior bay is induced by the upwelling coastal Kelvin wave excited by the decay of Wyrtki jet during December through January. Besides the annual variation, in the bay, there are obvious SLA fluctuations with the periods of 2 and 3~7 a, which are driven by the interannual variability of large-scale wind field in the equatorial region. The coastal Kelvin wave also provides an important link for the SLA interannual variation between the equatorial region and the interior bay. It is found that the El Nio-Southern Oscillation (ENSO)-induced influence on the SLA interannual variation in the interior bay is stronger than the Indian Ocean dipole (IOD) with the associated pattern of low sea-level presenting along the periphery of the bay and high sea-level in the northeast of Sri Lanka.  相似文献   

9.
王龙  王张华  李翠玉 《海洋学报》2022,44(9):109-123
重建高质量的全新世相对海平面变化曲线,可为海岸带人类社会科学预测及应对未来海平面上升风险提供重要的地质历史依据和长时间尺度的数据参考。目前已发表了多条福建海岸带全新世相对海平面变化曲线,然而已有曲线反映的相对海平面变化历史存在较大差异,甚至是矛盾结果。同时,相对海平面长期变化机制及影响因素也不明确。本研究收集、整理了福建沿海已发表的全新世相对海平面数据,对已有数据的年代、高程、指示意义等属性信息进行重新检查和校正,根据国际方法体系,建立了该区域一个标准化的全新世“相对海平面数据库”,共包括海平面数据183个。在此基础上,采用“变量误差–综合高斯（EIV-IGP）”统计学模型,提出了一条新的福建沿海全新世相对海平面变化曲线。并应用“冰川–水均衡调整”（GIA）理论,开展了相对海平面变化GIA模拟。最后,综合相对海平面变化地质记录及GIA模拟结果,得出以下结论:（1）福建沿海距今11.28～7.08 cal ka,相对海平面由（–23.55±6.94）m快速连续上升至（–1.51±1.80）m;距今7.08～4.08 cal ka,相对海平面由（–1.51±1.80）m缓慢上升至约（1.09±1.38）m;距今3.48 cal ka前后,相对海平面高于现代海平面约（1.35±1.23）m;此后,波动下降并逐渐接近现代位置;（2）“冰川–水均衡调整”作用是福建全新世相对海平面变化的主要长期作用机制;距今11.28～7.00 cal ka,相对海平面变化主要受冰盖融水控制;距今7.00 cal ka以来,“水均衡调整”作用逐渐占据主导;（3）福建沿海中–晚全新世（距今6.75～0.16 cal ka）期间,存在高于现今海面位置的“高海平面”现象;不同于传统构造运动主导观点,研究认为GIA引起的“陆地掀斜”和“海洋虹吸”作用,可能是该区域“高海平面”现象产生的主要原因;（4）福建沿海全新世相对海平面变化,存在一定程度的空间差异。不同岸段之间的沉积物压实、差异性构造运动和潮差变化等非GIA因素,可能是这一现象产生的重要原因。  相似文献   

10.
Holocene deposits exhibit distinct, predictable and chronologically constrained facies patterns that are quite useful as appropriate modern analogs for interpreting the ancient record. In this study, we examined the sedimentary response of the Po Plain coastal system to short-term (millennial-scale) relative fluctuations of sea level through high-resolution sequence-stratigraphic analysis of the Holocene succession.Meters-thick parasequences form the building blocks of stratigraphic architecture. Above the Younger Dryas paleosol, a prominent stratigraphic marker that demarcates the transgressive surface, Early Holocene parasequences (#s 1–3) record alternating periods of rapid flooding and gradual shoaling, and are stacked in a retrogradational pattern that mostly reflects stepped, post-glacial eustatic rise. Conversely, Middle to Late Holocene parasequences (#s 4–8) record a complex, pattern of coastal progradation and delta upbuilding that took place following sea-level stabilization at highstand, starting at about 7 cal ky BP. The prominent transgressive surface at the base of parasequence 1 correlates with the period of rapid, global sea-level rise at the onset of the Holocene (MWP-1B), whereas flooding surfaces associated with parasequences 2 and 3 apparently reflect minor Early Holocene eustatic jumps reported in the literature. Changes in shoreline trajectory, parasequence architecture and lithofacies distribution during the following eustatic highstand had, instead, an overwhelming autogenic component, mostly driven by river avulsions, delta lobe switching, local subsidence and sediment compaction. We document a ∼1000-year delayed response of the coastal depositional system to marine incursion, farther inland from the maximum landward position of the shoreline. A dramatic reduction in sediment flux due to fluvial avulsion resulted in marine inundation in back-barrier position, whereas coastal progradation was simultaneously taking place basinwards.We demonstrate that the landward equivalents of marine flooding surfaces (parasequence boundaries) may be defined by brackish and freshwater fossil assemblages, and traced for tens of kilometers into the non-marine realm. This makes millennial-scale parasequences, whether auto- or allogenic in origin, much more powerful than systems tracts for mapping detailed extents and volumes of sediment bodies.The Holocene parasequences of the Po coastal plain, with strong age control and a detailed understanding of sea-level variation, may provide insight into the driving mechanisms and predictability of successions characterized by similar depositional styles, but with poor age constraint, resulting in more robust interpretations of the ancient record.  相似文献   

11.
Within the Russian–German research project on “Siberian River Run-off (SIRRO)” dealing with freshwater discharge and its influence on biological, geochemical, and geological processes in the Kara Sea, sedimentological and organic-geochemical investigations were carried out on two well-dated sediment cores from the Yenisei Estuary area. The main goal of this study was to quantify terrigenous organic carbon accumulation based on biomarker and bulk accumulation rate data, and its relationship to Yenisei river discharge and climate change through Holocene times. The biomarker data in both cores clearly indicate the predominance of terrigenous organic matter, reaching 70–100 and 50–80% of total organic carbon within and directly north of the estuary, respectively. During the last ca. 9 cal ka b.p. represented in the studied sediment section, siliciclastic sediment and (terrigenous) organic carbon input was strongly influenced by postglacial sea-level rise and climate-related changes in river discharge. The mid-Holocene Climatic Optimum is documented by maximum river discharge between 8.2 and 7.3 cal ka b.p. During the last 2,000 years, river discharge probably decreased, and accumulation of both terrigenous and marine organic carbon increased due to enhanced coagulation of fine-grained material.  相似文献   

12.
全新世东海内陆架泥质区有孔虫特征及其古环境意义   总被引：5，自引：0，他引：5  
东海内陆架泥质区是东海全新世高海平面以来的沉积中心,保存了冰后期海平面上升以来完整的全新世沉积记录,是研究东海古海洋环境变化的良好载体,也是研究全新世古气候、古环境变迁的绝佳材料。选取了位于东海内陆架泥质区中部的MZ02孔长岩心作为研究对象,通过对沉积物中有孔虫进行属种鉴定分析,并结合岩心沉积物的岩性特征和AMS14 C测年数据,主要依据底栖有孔虫组合,恢复了研究区全新世以来的沉积环境演化。研究表明,全新世以来东海内陆架泥质区的沉积环境呈现阶段性演化特征,经历了以下4个阶段的演化:阶段I(10.8～10.5cal.kaBP)为滨岸沉积环境;阶段II(10.5～8.3cal.kaBP)随海面快速上升沉积环境由内陆架滨岸向中—内陆架过渡;阶段III(8.3～5.2cal.kaBP)为台湾暖流十分靠近的中—内陆架沉积环境;阶段IV(5.2～0cal.kaBP)为沿岸流较强的内陆架沉积环境。暖水种丰度在8.4cal.kaBP出现高值,推测为台湾暖流形成之时。约4.0cal.kaBP以来表生种丰度呈现高值和底栖有孔虫18 O变轻,推测与沿岸流增强密切相关。  相似文献   

13.
San Sebastian Bay is a large, semicircular coastal embayment situated on the Atlantic coast of Tierra del Fuego, Argentina. It is a high-energy, subantarctic environment with a tidal range of 10.4 m, influenced by large waves of Atlantic and local origin and swept by constant, strong westerly winds. A 17 km long gravel spit protects the Northern part of the Bay giving rise to a gradient in sedimentary processes. From south to north, are seven distinct sedimentary environments. Coastal sedimentation started at least 5200 years before present (BP) and a rapid progradation related to a relative sea-level drop has infilled about 6 kilometres of the Bay with a sedimentary sequence 10–11 m thick. 14-C dating of unabraded shells in the Chenier ridges of the relict part of the complex allows for a precise reconstruction of the stages of the progradation, that has slowed from 2.35 m/year at 5000 years BP to 0.6 m/year at present. The possible causes of the sea-level drop are discussed.  相似文献   

14.
A multi-proxy study including sedimentological, mineralogical, biogeochemical and micropaleontological methods was conducted on sediment core PS69/849-2 retrieved from Burton Basin, MacRobertson Shelf, East Antarctica. The goal of this study was to depict the deglacial and Holocene environmental history of the MacRobertson Land–Prydz Bay region. A special focus was put on the timing of ice-sheet retreat and the variability of bottom-water formation due to sea ice formation through the Holocene. Results from site PS69/849-2 provide the first paleo-environmental record of Holocene variations in bottom-water production probably associated to the Cape Darnley polynya, which is the second largest polynya in the Antarctic. Methods included end-member modeling of laser-derived high-resolution grain size data to reconstruct the depositional regimes and bottom-water activity. The provenance of current-derived and ice-transported material was reconstructed using clay-mineral and heavy-mineral analysis. Conclusions on biogenic production were drawn by determination of biogenic opal and total organic carbon. It was found that the ice shelf front started to retreat from the site around 12.8 ka BP. This coincides with results from other records in Prydz Bay and suggests warming during the early Holocene optimum next to global sea level rise as the main trigger. Ice-rafted debris was then supplied to the site until 5.5 cal. ka BP, when Holocene global sea level rise stabilized and glacial isostatic rebound on MacRobertson Land commenced. Throughout the Holocene, three episodes of enhanced bottom-water activity probably due to elevated brine rejection in Cape Darnley polynya occured between 11.5 and 9 cal. ka BP, 5.6 and 4.5 cal. ka BP and since 1.5 cal. ka BP. These periods are related to shifts from warmer to cooler conditions at the end of Holocene warm periods, in particular the early Holocene optimum, the mid-Holocene warm period and at the beginning of the neoglacial. In contrast, between 7.7 and 6.7 cal. ka BP, brine rejection shut down, maybe owed to warm conditions and pronounced open-water intervals.  相似文献   

15.
The response of mangrove ecosystems to the Asian monsoon in the future global warming can be understood by reconstructing the development of mangrove forests during the Holocene climatic optimum(HCO), using proxies preserved in coastal sediments. The total organic matter in sediments of a segmented core, with calibrated age ranges between 5.6 and 7.7 cal. ka BP and corresponding to the HCO, from the Qinzhou Bay in Guangxi, China, is quantitatively partitioned into three end-members according to their sources: mangrove-derived, terrigenous,and marine phytoplanktonic, using a three-end-member model depicted by organic carbon isotope(δ13Corg) and the molar ratio of total organic carbon to total nitrogen(C/N). The percentage of mangrove-derived organic matter(MOM) contribution is used as a proxy for mangrove development. Three visible drops in MOM contribution occurred at ca. 7.3, ca. 6.9, and ca. 6.2 cal. ka BP, respectively, are recognized against a relatively stable and higher MOM contribution level, indicating that three distinct mangrove forest degradations occurred in the Qinzhou Bay during the HCO. The three mangrove forest degradations approximately correspond to the time of the strengthened/weakened Asian winter/summer monsoon. This indicates that even during a period favorable for the mangrove development, such as the HCO, climatic extremes, such as cold and dry events driven by the strengthened/weakened Asian winter/summer monsoon, can trigger the degradation of mangrove forests.  相似文献   

16.
Here we present interannual rare earth element (REE) records spanning the last two decades of the 20th century in two living Porites corals, collected from Longwan Bay, close to the estuarine zones off Wanquan River of Hainan Island and Hong Kong off the Pearl River Delta of Guangdong Province in the northern South China Sea. The results show that both coral REE contents (0.5-40 ng g?1 in Longwan Bay and 2-250 ng g?1 in Hong Kong for La-Lu) are characterized with a declining trend, which are significantly negative correlated with regional sea-level rise (9.4 mm a?1) from 1981 to 1996 in Longwan Bay, 13.7 mm a?1 from 1991 to 2001 in Hong Kong). The REE features are proposed to be resulted from seawater intrusion into the estuaries in response to contemporary sea-level rise. However, the tendency for the coral Er/Nd time series at Hong Kong site is absent and there is no significant relation between Er/Nd and total REEs as found for the coral at Longwan Bay site. The observations are likely attributed to changes of the water discharge and sediment load of Pearl River, which have been significantly affected by intense human activities, such as the construction of dams/reservoirs and riverbed sediment mining, in past decades. The riverine sediment load/discharge ratio of the Pearl River decreased sharply with a rate of 0.02 kg m?3 a?1, which could make significant contribution to the declining trend of coral REE. We propose that coastal corals in Longwan Bay and similar unexplored sites with little influences of river discharge and anthropogenic disruption are ideal candidates to investigate the influence of sea-level change on seawater/coral REE.  相似文献   

17.
Previous models of the evolution of Hurst Castle Spit over-emphasised longshore growth at the expense of other processes, particularly rise in sea-level. Initially, a Pleistocene valley system was submerged creating a tidal strait, the West Solent, between Christchurch Bay and the East Solent. This almost certainly caused a major hydrodynamic change, transforming much of Christchurch Bay and the West Solent from a low to a high tidal energy environment. Hurst Castle Spit and the Shingles Bank then began to form due to a combination of an easterly littoral drift, offshore gravel movement due to the high tidal energy, a rising sea-level, the transgression of Hurst Beach due to overwashing and the formation of recurves due to waves in the West Solent. The growth of the Shingles Bank due to offshore sediment movement from Hurst Castle Spit was of particular importance because of its influence on the wave energy along Hurst Beach. Significant local supplies of shingle in the vicinity of Hurst Castle Spit, reworked from Quatenary deposits, were also of importance. Thus, it is not a classic multi-recurved spit and the transgressive segment, Hurst Beach, has much in common with barrier coastlines.The same processes are continuing to shape Hurst Castle Spit at present, with the additional effects of human interference in the coastal sediment system. The construction of sea defences at Milford-on-Sea in the period 1936 to 1968 has modified the sediment budget and Hurst Castle Spit is experiencing a phase of rapid evolution: maximum recession rates have increased from 1.5m a−1 (1867–1968) to 3.5m a−1 (1968–1982). It is difficult to quantify the exact role of sea-level rise in the present evolution of Hurst Castle Spit.The future evolution of Hurst Castle Spit will depend largely on man. If there is no further interference, which is highly unlikely, the beach volume will continue to decline, resulting in a further increase in the rate of recession. Ultimately, a true tidal breach will probably form, marking a new phase in the evolution of Hurst Castle Spit and its environs. However, shingle renourishment, or another coastal engineering solution will probably be undertaken. The future rate of sea-level rise will have important long-term influences on all these options.  相似文献   

18.
丁瑞  朱良生 《海洋工程》2018,36(4):147-154
以海口湾为例,通过建立天文潮与风暴潮耦合数值模型,以典型强台风海鸥为基础,对未来台风增强、海平面上升和填海工程对海口湾风暴潮的影响分别进行了诊断分析,并计算了三者的共同作用在未来100年对风暴增水最大值的变化幅度。结果表明:1)台风强度增强大幅度增加海口湾沿岸风暴增水最大值,台风强度增强10%时,海口湾沿岸控制点风暴增水最大值增加12%~18%;2)海口湾地区在海平面上升的影响下风暴增水最大值反而减小,仅有部分岸段风暴增水值最大增加,不同海域风暴增水变化对海平面上升的响应不同;3)不合理的人工岛建设方案会显著增加对岸风暴最大增水值;4)在台风增强、海平面上升和不合理的海湾填海共同影响下,未来100年风暴增水最大值将增加12%~28%。显然这样的风暴增水变化会引起严重的灾害和后果,本研究可为海口湾防灾减灾工作提供依据。  相似文献   

19.
Salt marshes accrete both organic and inorganic sediments. Here we present analytical and numerical models of salt marsh sedimentation that, in addition to capturing inorganic processes, explicitly account for above- and belowground organic processes including root growth and decay of organic carbon. The analytical model is used to examine the bias introduced by organic processes into proxy records of sedimentation, namely 137Cs and 210Pb. We find that accretion rates estimated using 210Pb will be less than accretion rates estimated using the 137Cs peak in steadily accreting marshes if (1) carbon decay is significant and (2) data for 210Pb extend below the 137Cs peak. The numerical model expands upon the analytical model by including belowground processes such as compaction and root growth, and by explicitly tracking the evolution of aboveground biomass and its effect on sedimentation rates. Using the numerical model we explore how marsh stratigraphy responds to sediment supply and the rate of sea-level rise. It is calibrated and tested using an extensive data set of both marsh stratigraphy and measurements of vegetation dynamics in a Spartina alterniflora marsh in South Carolina, USA. We find that carbon accumulation in marshes is nonlinearly related to both the supply of inorganic sediment and the rate of sea-level rise; carbon accumulation increases with sea-level rise until sea-level rise reaches a critical rate that drowns the marsh vegetation and halts carbon accumulation. The model predicts that changes in carbon storage resulting from changing sediment supply or sea-level rise are strongly dependent on the background sediment supply: if inorganic sediment supply is reduced in an already sediment poor marsh the storage of organic carbon will increase to a far greater extent than in a sediment-rich marsh, provided that the rate of sea-level rise does not exceed a threshold. These results imply that altering sediment supply to estuaries (e.g., by damming upstream rivers or altering littoral sediment transport) could lead to significant changes in the carbon budgets of coastal salt marshes.  相似文献   

20.
A suite of organic geochemical, micropaleontological and palynological proxies was applied to sediments from Southwest Florida, to study the Holocene environmental changes associated with sea-level rise. Sediments were recovered from Hillsborough Bay, part of Tampa Bay, and studied using biomarkers, pollen, organic-walled dinoflagellate cysts and diatoms. Analyses show that the site flooded around 7.5 ka as a consequence of Holocene transgression, progressively turning a fresh/brackish marl-marsh into a shallow, restricted marine environment. Immediately after the marine transgression started, limited water circulation and high amounts of runoff caused stratification of the water column. A shift in dinocysts and diatom assemblages to more marine species, increasing concentrations of marine biomarkers and a shift in the Diol Index indicate increasing salinity between 7.5 ka and the present, which is likely a consequence of progressing sea-level rise. Reconstructed sea surface temperatures for the past 4 kyrs are between 25 and 26 ° C, and indicate stable temperatures during the Late Holocene. A sharp increase in sedimentation rate in the top ∼50 cm of the core is attributed to human impact. The results are in agreement with parallel studies from the area, but this study further refines the environmental reconstructions having the advantage of simultaneously investigating changes in the terrestrial and marine environment.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号