A 6000-year record of ecological and hydrological changes from Laguna de la Leche, north coastal Cuba

Laguna de la Leche, north coastal Cuba, is a shallow (≤ 3 m), oligohaline (∼ 2.0-4.5‰) coastal lake surrounded by mangroves and cattail stands. A 227-cm core was studied using loss-on-ignition, pollen, calcareous microfossils, and plant macrofossils. From ∼6200 to ∼ 4800 cal yr BP, the area was an oligohaline lake. The period from ∼ 4800 to ∼ 4200 cal yr BP saw higher water levels and a freshened system; these changes are indicated by an increase in the regional pollen rain, as well as by the presence of charophyte oogonia and an increase in freshwater gastropods (Hydrobiidae). By ∼ 4000 cal yr BP, an open mesohaline lagoon had formed; an increase in salt-tolerant foraminifers suggests that water level increase was driven by relative sea level rise. The initiation of Laguna de la Leche correlates with a shift to wetter conditions as indicated in pollen records from the southeastern United States (e.g., Lake Tulane). This synchronicity suggests that sea level rise caused middle Holocene environmental change region-wide. Two other cores sampled from mangrove swamps in the vicinity of Laguna de la Leche indicate that a major expansion of mangroves was underway by ∼ 1700 cal yr BP.     

Late Holocene sea-level changes and isostasy in western Denmark

Cores and exposed cliff sections in salt marshes around Ho Bugt, a tidal embayment in the northernmost part of the Danish Wadden Sea, were subjected to ¹⁴C dating and litho- and biostratigraphical analyses to reconstruct paleoenvironmental changes and to establish a late Holocene relative sea-level history. Four stages in the late Holocene development of Ho Bugt can be identified: (1) groundwater-table rise and growth of basal peat (from at least 2300 BC to AD 0); (2) salt-marsh formation (0 to AD 250); (3) a freshening phase (AD 250 to AD 1600?), culminating in the drying out of the marshes and producing a distinct black horizon followed by an aeolian phase with sand deposition; and (4) renewed salt-marsh deposition (AD 1600? to present). From 16 calibrated AMS radiocarbon ages on fossil plant fragments and 4 calibrated conventional radiocarbon ages on peat, we reconstructed a local relative sea-level history that shows a steady sea-level rise of 4 m since 4000 cal yr BP. Contrary to suggestions made in the literature, the relative sea-level record of Ho Bugt does not contain a late Holocene highstand. Relative sea-level changes at Ho Bugt are controlled by glacio-isostatic subsidence and can be duplicated by a glacial isostatic adjustment model in which no water is added to the world's oceans after ca. 5000 cal yr BP.     

The mid-Holocene sea-level highstand at Bogenfels Pan on the southwest coast of Namibia

The radiocarbon ages of mollusc shells from the Bogenfels Pan on the hyper arid southern coast of Namibia provide constraints on the Holocene evolution of sea level and, in particular, the mid-Holocene highstand. The Bogenfels Pan was flooded to depths of 3 m above mean sea level (amsl) to form a large subtidal lagoon from 7300 to 6500 calibrated radiocarbon years before present (cal yr BP). The mollusc assemblage of the wave sheltered lagoon includes Nassarius plicatellus, Lutraria lutraria, and the bivalves Solen capensis and Gastrana matadoa, both of which no longer live along the wave-dominated southern Namibian coast. The radiocarbon ages of mollusc shell from a gravely beach deposit exposed in a diamond exploration trench indicate that sea level fell to near or 1 m below its present-day position between 6500 and 4900 cal yr BP. The rapid emergence of the pan between 6500 and 4900 cal yr BP exceeds that predicted by glacio-isostatic models and may indicate a 3-m eustatic lowering of sea level. The beach deposits at Bogenfels indicate that sea level rose to 1 m amsl between 4800 and 4600 cal yr BP and then fell briefly between 4600 and 4200 cal yr BP before returning to 1 m amsl. Since 4200 cal yr BP sea level has remained within one meter of the present-day level and the beach at Bogenfels has prograded seaward from the delayed arrival of sand by longshore drift from the Orange River. A 6200 cal yr BP coastal midden and a 600 cal yr BP midden 1.7 km from the coast indicate sporadic human utilization of the area. The results of this study are consistent with previous studies and help to refine the Holocene sea-level record for southern Africa.     

A relative sea-level history for Arviat,Nunavut, and implications for Laurentide Ice Sheet thickness west of Hudson Bay

Thirty-six new and previously published radiocarbon dates constrain the relative sea-level history of Arviat on the west coast of Hudson Bay. As a result of glacial isostatic adjustment (GIA) following deglaciation, sea level fell rapidly from a high-stand of nearly 170 m elevation just after 8000 cal yr BP to 60 m elevation by the mid Holocene (~ 5200 cal yr BP). The rate of sea-level fall decreased in the mid and late Holocene, with sea level falling 30 m since 3000 cal yr BP. Several late Holocene sea-level measurements are interpreted to originate from the upper end of the tidal range and place tight constraints on sea level. A preliminary measurement of present-day vertical land motion obtained by repeat Global Positioning System (GPS) occupations indicates ongoing crustal uplift at Arviat of 9.3 ± 1.5 mm/yr, in close agreement with the crustal uplift rate inferred from the inferred sea-level curve. Predictions of numerical GIA models indicate that the new sea-level curve is best fit by a Laurentide Ice Sheet reconstruction with a last glacial maximum peak thickness of ~ 3.4 km. This is a 30–35% thickness reduction of the ICE-5G ice-sheet history west of Hudson Bay.     

A dinoflagellate cyst record of Holocene climate and hydrological changes along the southeastern Swedish Baltic coast

A high-resolution, well-dated dinoflagellate cyst record from a lagoon of the southeastern Swedish Baltic Sea reveals climate and hydrological changes during the Holocene. Marine dinoflagellate cysts occurred initially at about 8600 cal yr BP, indicating the onset of the Littorina transgression in the southeastern Swedish lowland associated with global sea level rise, and thus the opening of the Danish straits. Both the species diversity and the total accumulation rates of dinoflagellate cysts continued to increase by 7000 cal yr BP and then decreased progressively. This pattern reveals the first-order change in local sea level as a function of ice-volume-equivalent sea level rise versus isostatic land uplift. Superimposed upon this local sea level trend, well-defined fluctuations of the total accumulation rates of dinoflagellate cysts occurred on quasi-1000- and 500-yr frequency bands particularly between 7500 and 4000 cal yr BP, when the connection between the Baltic basin and the North Atlantic was broader. A close correlation of the total accumulation rates of dinoflagellate cysts with GISP2 ice core sea-salt ions suggests that fluctuations of Baltic surface conditions during the middle Holocene might have been regulated by quasi-periodic variations of the prevailing southwesterly winds, most likely through a system similar to the dipole oscillation of the modern North Atlantic atmosphere.     

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。     

A 24,700-yr paleolimnological history from the Peruvian Andes

A new paleolimnological dataset from Lake Pacucha (13 °S, 3095 m elevation) in the Peruvian Andes provides evidence of changes in lake level over the past 24,700 yr. A late-glacial highstand in lake level gave way to an early-Holocene lowstand. This transition appears to have paralleled precessional changes that would have reduced insolation during the wet-season. The occurrence of benthic/salt-tolerant diatoms and CaCO₃ deposition suggest that the lake had lost much of its volume by c. 10,000 cal yr BP. Pronounced Holocene oscillations in lake level included a second phase of low lake level and heightened volatility lasting from c. 8300 to 5000 cal yr BP. While a polymictic lake formed at c. 5000 cal yr BP. These relatively wet conditions were interrupted by a series of drier events, the most pronounced of which occurred at c. 750 cal yr BP. Paleolimnological changes in the Holocene were more rapid than those of either the last glacial maximum or the deglacial period.     

Relative sea-level changes during the Holocene in Bangladesh

This paper presents a reconstruction of the Holocene paleo-environment in the central part of Bangladesh in relation to relative sea-level changes 200 km north of the present coastline. Lithofacies characteristics, mangal peat, diatoms and paleophysiographical evidence were considered to reconstruct the past position and C-14 ages were used to determine the time of formation of the relative sea level during the Holocene. With standard reference datum, the required m.s.l. at the surface of five sections was calculated. The relative sea-level (RSL) curve suggests that Bangladesh experienced two mid-Holocene RSL transgressions punctuated by regressions. The curve shows an RSL highstand at approximately 7500 cal BP, although the height of this highstand could not be determined because the transgressive phase was observed in a bioturbated sand flat facies. The curve shows a regression of approximately 6500 cal BP, and the RSL was considerably lower, perhaps 1–2 m, than the present m.s.l. The abundant marine diatoms and mangrove pollens indicate the highest RSL transgression in Bangladesh at approximately 6000 cal BP, being at least 4.5 to 5 m higher than the modern m.s.l. After this phase, the relative sea level started to fall, and consequently, a freshwater peat developed at approximately 5980–5700 cal BP. The abundant mangrove pollens in the salt-marsh succession shows the regression at approximately 5500 cal BP, when it was 1–2 m higher than the modern sea level. The curve indicates that at approximately 5000 cal BP and onwards, the RSL started to fall towards its present position, and the present shoreline of Bangladesh was established at approximately 1500 cal BP and has not noticeably migrated inland since.     

Late Holocene great earthquakes and relative sea‐level change at Kenai,southern Alaska

Kenai, located on the west coast of the Kenai Peninsula, Alaska, subsided during the great earthquake of AD 1964. Regional land subsidence is recorded within the estuarine stratigraphy as peat overlain by tidal silt and clay. Reconstructions using quantitative diatom transfer functions estimate co‐seismic subsidence (relative sea‐level rise) between 0.28±0.28 m and 0.70±0.28 m followed by rapid post‐seismic recovery. Stratigraphy records an earlier co‐seismic event as a second peat‐silt couplet, dated to ～1500–1400 cal. yr BP with 1.14±0.28 m subsidence. Two decimetre‐scale relative sea‐level rises are more likely the result of glacio‐isostatic responses to late Holocene and Little Ice Age glacier expansions rather than to co‐seismic subsidence during great earthquakes. Comparison with other sites around Cook Inlet, at Girdwood and Ocean View, helps in constructing regional patterns of land‐level change associated with three great earthquakes, AD 1964, ～950–850 cal. yr BP and ～1500–1400 cal. yr BP. Each earthquake has a different spatial pattern of co‐seismic subsidence which indicates that assessment of seismic hazard in southern Alaska requires an understanding of multiple great earthquakes, not only the most recent. All three earthquakes show a pre‐seismic phase of gradual land subsidence that marked the end of relative land uplift caused by inter‐seismic strain accumulation. Copyright © 2005 John Wiley & Sons, Ltd.     

Postglacial vegetation history of Mitkof Island, Alexander Archipelago, southeastern Alaska

An AMS radiocarbon-dated pollen record from a peat deposit on Mitkof Island, southeastern Alaska provides a vegetation history spanning ∼12,900 cal yr BP to the present. Late Wisconsin glaciers covered the entire island; deglaciation occurred > 15,400 cal yr BP. The earliest known vegetation to develop on the island (∼12,900 cal yr BP) was pine woodland (Pinus contorta) with alder (Alnus), sedges (Cyperaceae) and ferns (Polypodiaceae type). By ∼12,240 cal yr BP, Sitka spruce (Picea sitchensis) began to colonize the island while pine woodland declined. By ∼11,200 cal yr BP, mountain hemlock (Tsuga mertensiana) began to spread across the island. Sitka spruce-mountain hemlock forests dominated the lowland landscapes of the island until ∼10,180 cal yr BP, when western hemlock (Tsuga heterophylla) began to colonize, and soon became the dominant tree species. Rising percentages of pine, sedge, and sphagnum after ∼7100 cal yr BP may reflect an expansion of peat bog habitats as regional climate began to shift to cooler, wetter conditions. A decline in alders at that time suggests that coastal forests had spread into the island's uplands, replacing large areas of alder thickets. Cedars (Chamaecyparis nootkatensis, Thuja plicata) appeared on Mitkof Island during the late Holocene.     

A late Quaternary chironomid-inferred temperature record from the Sierra Nevada, California, with connections to northeast Pacific sea surface temperatures

Chironomid remains from a mid-elevation lake in the Sierra Nevada, California, were used to estimate quantitative summer surface water temperatures during the past ∼15,000 yr. Reconstructed temperatures increased by ∼3°C between lake initiation and the onset of the Holocene at ∼10,600 cal yr BP (calibrated years before present). Temperatures peaked at 6500 cal yr BP, displayed high variability from 6500 to 3500 cal yr BP, and stabilized after 3500 cal yr BP. This record generally tracks reconstructed Santa Barbara Basin sea surface temperatures (SSTs) through much of the Holocene, highlighting the correspondence between SST variability and California land temperatures during this interval.     

MIS3中期以来北黄海中部陆架古环境演化

通过对北黄海中部陆架DLC70-2孔的岩性、粒度、微体古生物以及AMS14C年代学的分析,探讨了研究区MIS3中期以来的古环境演化。研究表明,北黄海中部陆架MIS3中期以来的沉积环境演化与海平面变化存在良好的对应关系,具有明显的阶段性特征:岩芯22.89~18.50 m段(43 639~42 558 cal yr B.P.)对应MIS3中期海平面上升过程中形成的河口湾相,与上覆地层之间存在明显的沉积间断;随着海平面的逐渐上升,海水自14 602 cal yr B.P. 开始侵入研究区,形成了18.50 m以上的沉积地层,自下而上可划分为末次冰盛期以来海平面上升过程中的河口充填相(18.50~10.02 m,14 602~12 602 cal yr B.P.)-新仙女木事件中晚期海平面停滞期间的河流泛滥平原相(10.02~5.10 m,12 602~10 357 cal yr B.P.)-全新世早中期海平面上升过程中的滨海、浅海相(5.10~0 m,10 357~4 913 cal yr B.P.)。岩芯10.02~5.10 m段(12 602~10 357 cal yr B.P.)记录的源自河流泛滥平原沉积的硬质黏土层与新仙女木事件的全球效应密切相关,可作为新仙女木事件在北黄海陆架响应的一个重要证据。     

Holocene relative sea-level changes in the Qaqortoq area, southern Greenland

We present results from an investigation of relative sea-level changes in the Qaqortoq area in south Greenland from c. 11 000 cal. yr BP to the present. Isolation and transgression sequences from six lakes and two tidal basins have been identified using stratigraphical analyses, magnetic susceptibility, XRF and macrofossil analyses. Macrofossils and bulk sediments have been dated by AMS radiocarbon dating. Maximum and minimum altitudes for relative sea level are provided from two deglaciation and marine lagoon sequences. Initially, relative sea level fell rapidly and reached present-day level at ∼9000 cal. yr BP and continued falling until at least 8800 cal. yr BP. Between 8000 and 6000 cal. yr BP, sea level reached its lowest level of around 6-8 m below highest astronomical tide (h.a.t.). At around 3750 cal. yr BP, sea level has reached above 2.7 m below h.a.t. and continued to rise slowly, reaching the present-day level between ∼2000 cal. yr BP and the present. As in the Nanortalik area further south, initial isostatic rebound caused rapid isolation of low elevation basins in the Qaqortoq area. Distinct isolation contacts in the sediments are observed. The late Holocene transgression is less well defined and occurred over a longer time interval. The late Holocene sea-level rise implies reloading by advancing glaciers superimposed on the isostatic signal from the North American Ice Sheet. One consequence of this transgression is that settlements of Palaeo-Eskimo cultures from ∼4000 cal. yr BP may have been transgressed by the sea.     

Relative sea‐level changes since 15 000 cal. yr BP in the Nanortalik area,southern Greenland

We present new results for relative sea‐level change for southern Greenland for the interval from 9000 cal. yr BP to the present. Together with earlier work from the same region this yields a nearly complete record from the time of deglaciation to the present. Isolation and/or transgression sequences in one lake and five tidal basins have been identified using lithostratigraphic analyses, sedimentary characteristics, magnetic susceptibility, saturated induced remanent magnetisation (SIRM), organic and carbonate content, and macrofossil analyses. AMS radiocarbon dating of macrofossils and bulk sediment samples provides the timescale. Relative sea level fell rapidly and reached present‐day level at ～9300 cal. yr BP and continued falling until at least 9000 cal. yr BP. Between 8000 and 6000 cal. yr BP sea level reached its lowest level of around ～10 m below highest astronomical tide. At around 5000 cal. yr BP, sea level had reached above 7.8 m below highest astronomical tide and slowly continued to rise, not reaching present‐day sea level until today. The isostatic rebound caused rapid isolation of the basins that are seen as distinct isolation contacts in the sediments. In contrast, the late Holocene transgressions are less well defined and occurred over longer time intervals. The late Holocene sea‐level rise may be a consequence of isostatic reloading by advancing glaciers and/or an effect of the delayed response to isostatic rebound of the Laurentide ice sheet. One consequence of this transgression is that settlements of Palaeo‐Eskimo cultures may be missing in southern Greenland. Copyright © 2006 John Wiley & Sons, Ltd.     

A 5000 year record of intertidal peat stratigraphy and sea level change from northwest Alaska

Coastal environments of northwest Alaska preserve a detailed record of sea level change during the past 5000 ¹⁴C yr. Rapid burial of intertidal marshes by storm overwash processes, a short open water period, and the arctic maritime climate contribute to the preservation of marine and eolian facies. Eustatic and storm-controlled changes in sea level can be identified from interbedded sequences of marsh peat and coastal flood deposits on barrier islands and estuaries along northwest Seward Peninsula. Mean eustatic sea level has risen about 1.5 m during the last 5000 years, at an average of ca. 0.028 cm yr⁻¹, based on the depth and age relationship of a suite of 23 peat horizons sampled from a 140 km-long reach of coast. Nearshore erosion and sedimentation are controlled by secular variations in wave climate. Peaks in tidal amplitude and storminess correlate with transgressive sedimentary regimes and occurred during the periods 3300–1700, 1200–900, and since about 400 ¹⁴C yr BP. Short-term fluctuations in relative sea level are superimposed on the long-term regional eustatic trend, and record the coastal response to variable rates of sea-level change during the late Holocene.     

Mid-to-late Holocene sea level influence on coastal wetland development in Trinidad

Understanding how Holocene sea levels influenced coastal wetland development in the Caribbean will aid wetland management in the context of predicted sea level rise. Nine radiocarbon dates from the Maracas and Nariva Swamps on wave-dominated coasts from Trinidad, show sea level was –9 m approximately 7000 yr BP, and rose gradually to –2 m by 2000 yr BP. Since then there may have been isostatic readjustment. Wetlands developed with a transgression of dry upland habitats by rising seas and the facultative halophyte Rhizophora colonized the new brackish water environment. A freshwater plant community gradually replaced the Rhizophora as the marine influence decreased. At Maracas, higher sea levels caused wetland retreat as beach and lagoon habitats migrated inland. Sand ridges in Nariva Swamp indicate that, as in Maracas Swamp, sea level rise created beaches and lagoons, but that these landforms prograded as additional nearshore sediments were deposited. Basins were also filled with sediment delivered by streams that drain the watershed, and by mangrove peat accumulation.     

Multi-proxy record of postglacial environmental change, south-central Melville Island, Northwest Territories, Canada

A sediment core from Lake BC01 (75°10.945′N, 111°55.181′W, 225 m asl) on south-central Melville Island, NWT, Canada, provides the first continuous postglacial environmental record for the region. Fossil pollen results indicate that the postglacial landscape was dominated by Poaceae and Salix, typical of a High Arctic plant community, whereas the Arctic herb Oxyria underwent a gradual increase during the late Holocene. Pollen-based climate reconstructions suggests the presence of a cold and dry period ~12,000 cal yr BP, possibly representing the Younger Dryas, followed by warmer and wetter conditions from 11,000 to 5000 cal yr BP, likely reflective of the Holocene Thermal Maximum. The climate then underwent a gradual cooling and drying from 5000 cal yr BP to the present, suggesting a late Holocene neoglacial cooling. Diatom preservation was poor prior to 5000 cal yr BP, when conditions were warmest, suggesting that diatom dissolution may in part be climatically controlled. Diatom concentrations were highest ~4500 cal yr BP but then decreased substantially by 3500 cal yr BP and remained low before recovering slightly in the 20th century. An abrupt warming occurred during the past 70 yr at the site, although the magnitude of this warming did not exceed that of the early Holocene.     

渤海湾西岸BT113孔35ka以来的沉积环境演化与海陆作用

根据渤海湾西岸有孔虫和介形虫与年代学(AMS14C和OSL测年)研究,将该段岩心自下而上划分为6个沉积单元(U1—U6),它们依次形成于晚更新世的河流及全新世的潮滩、浅海、前三角洲、三角洲前缘和三角洲平原沉积环境,结束于约35 ka的U1单元的陆相环境,证实晚更新世低海面时渤海湾西岸未受海水影响。U1和U2单元之间,存在历时约27 ka的沉积间断(35～8.5 ka cal BP),研究区因此缺失早全新世沉积。U2单元的潮滩环境指示全新世海侵于8.5 ka cal BP到达渤海湾西岸,当时相对海平面为-16.7 m。U3单元为浅海环境,约6 ka cal BP时相对海平面上升到-6.8～-1.8 m。8.5～6 ka cal BP期间的海面上升速率是0.4～0.6 cm/a,可能与MWP1C事件有关。U4—U5单元,转为三角洲环境,沉积速率增大,反映自3.7 ka cal BP河流输入影响加强,约1.3 ka cal BP时成陆,形成U6单元。晚更新世35 ka以来的陆海环境演化,总体上是对气候变化控制下的海面变化的响应。     

Reconstruction of late Quaternary sea-level change in southwestern British Columbia from sediments in isolation basins

Bracketing ages on marine—freshwater transitions in isolation basins extending from sea level to 100 m elevation on Lasqueti Island, and data from shallow marine cores and outcrops on eastern Vancouver Island, constrain late Pleistocene and Holocene sea-level change in the central Strait of Georgia. Relative sea level fell from 150 m elevation to about —15 m from 14000 cal. yr BP to 11 500 cal. yr BP. Basins at higher elevations exhibit abrupt changes in diatom assemblages at the marine-freshwater transition. At lower elevations an intervening brackish phase suggests slower rates of uplift. Relative sea level rose to about +1 m about 9000 cal. yr BP to 8500 cal. yr BP, and then slowly fell to the modern datum. The mean rate of glacio-isostatic rebound in the first millennium after deglaciation was about 0.11 in a ^-1, similar to the peak rate at the centres of the former Laurentide and Fennoscandian ice complexes. The latter feature smooth, exponential-style declines in sea level up to the present day, whereas in the study area the uplift rate dropped to less than one-tenth of its initial value in only about 2500 years. Slower, more deeply seated isostatic recovery generated residual uplift rates of <0.01 m a^-1 in the early Holocene after the late-Pleistocene wasting of the Cordilleran ice sheet.