Glacial rebound and sea-level change in the British Isles

Observations of sea levels around the coastline of the British Isles for the past 10,000–15,000 years exhibit a major regional variation and provide an important data base for testing models of glacial rebound as well as models of the Late Devensian ice sheet. A high-resolution rebound model has been developed which is consistent with both the spatial and temporal patterns of sea-level change and which demonstrates that the observations are the result of (i) the glacio-isostatic crustal rebound in response to the unloading of the ice sheet over Britain and, to a lesser degree, of the ice sheet over Fennoscandia, and (ii) the rise in sea-level from the melting Late Pleistocene ice sheets, including the response of the crust to the water loading (the hydro-isostatic effect). The agreement between model and observations is such that there is no need to invoke vertical crustal movements for Great Britain and Ireland of other than glacio-hydro-isostatic origin. The rebound contributions are important throughout the region and nowhere is it sufficiently small for the sea-level change to approximate the eustatic sea-level rise. The observational data distribution around the periphery as well as from sites near the centre of the former ice sheet is sufficient to permit constraints to be established on both earth model parameters specifying the mantle viscosity and lithospheric thickness and the extent and volume of the ice sheet at the time of the last glaciation. Preliminary solutions are presented which indicate an upper mantle viscosity of (3–5)10²⁰ Pas, a lithospheric thickness of about 100 km or less, and an ice model that was not confluent with the Scandinavian ice sheet during the last glaciation and whose maximum thickness over Scotland is unlikely to have exceeded about 1500 m.     

Glacial deposits in northwest Europe

Book reviewed in this article:
Ehlers, Jürgen (cd.) 1983: Glacial Deposits in North-west Europe .     

Postglacial relative sea‐level observations from Ireland and their role in glacial rebound modelling

The British Isles have been the focus of a number of recent modelling studies owing to the existence of a high‐quality sea‐level dataset for this region and the suitability of these data for constraining shallow earth viscosity structure, local to regional ice sheet histories and the magnitude/timing of global meltwater signals. Until recently, the paucity of both glaciological and relative sea‐level (RSL) data from Ireland has meant that the majority of these glacial isostatic adjustment (GIA) modelling studies of the British Isles region have tended to concentrate on reconstructing ice cover over Britain. However, the recent development of a sea‐level database for Ireland along with emergence of new glaciological data on the spatial extent, thickness and deglacial chronology of the Irish Ice Sheet means it is now possible to revisit this region of the British Isles. Here, we employ these new data to constrain the evolution of the Irish Ice Sheet. We find that in order to reconcile differences between model predictions and RSL evidence, a thick, spatially extensive ice sheet of ～600–700 m over much of north and central Ireland is required at the LGM with very rapid deglaciation after 21 k cal. yr BP. Copyright © 2007 John Wiley & Sons, Ltd.     

Calibrating a glaciological model of the Greenland ice sheet from the Last Glacial Maximum to present-day using field observations of relative sea level and ice extent

We constrain a three-dimensional thermomechanical model of Greenland ice sheet (GrIS) evolution from the Last Glacial Maximum (LGM, 21 ka BP) to the present-day using, primarily, observations of relative sea level (RSL) as well as field data on past ice extent. Our new model (Huy2) fits a majority of the observations and is characterised by a number of key features: (i) the ice sheet had an excess volume (relative to present) of 4.1 m ice-equivalent sea level at the LGM, which increased to reach a maximum value of 4.6 m at 16.5 ka BP; (ii) retreat from the continental shelf was not continuous around the entire margin, as there was a Younger Dryas readvance in some areas. The final episode of marine retreat was rapid and relatively late (c. 12 ka BP), leaving the ice sheet land based by 10 ka BP; (iii) in response to the Holocene Thermal Maximum (HTM) the ice margin retreated behind its present-day position by up to 80 km in the southwest, 20 km in the south and 80 km in a small area of the northeast. As a result of this retreat the modelled ice sheet reaches a minimum extent between 5 and 4 ka BP, which corresponds to a deficit volume (relative to present) of 0.17 m ice-equivalent sea level. Our results suggest that remaining discrepancies between the model and the observations are likely associated with non-Greenland ice load, differences between modelled and observed present-day ice elevation around the margin, lateral variations in Earth structure and/or the pattern of ice margin retreat.     

Global glacial ice volume and Last Glacial Maximum duration from an extended Barbados sea level record

Fundamental characteristics of the climate system during the most recent precessional cycle of the Earth's orbit around the Sun consist of the final expansion of land ice to its maximum extent, the subsequent episode of deglaciation, and the variations of global sea level that accompanied these events. In order to address the important issue of the variation of continental ice volume and related changes in global sea level through the late glacial period, we employ an extended set of observations of the pre-glacial and postglacial history of sea-level rise at the island of Barbados, together with a refined model of continental deglaciation and an accurate methodology for the prediction of postglacial sea-level change. Although our results provide unambiguous evidence that the post LGM rise of eustatic sea-level was very close to the widely supported estimate of 120 m, the data also provide evidence that LGM must have occurred 26,000 years ago, approximately 5000 yr earlier than the usually assumed age.     

Testing the consistency of Holocene and Last Glacial Maximum spatial correlations in temperature proxy records

Holocene temperature proxy records are commonly used in quantitative synthesis and model-data comparisons. However, comparing correlations between time series from records collected in proximity to one another with the expected correlations based on climate model simulations indicates either regional or noisy climate signals in Holocene temperature proxy records. In this study, we evaluate the consistency of spatial correlations present in Holocene proxy records with those found in data from the Last Glacial Maximum (LGM). Specifically, we predict correlations expected in LGM proxy records if the only difference to Holocene correlations would be due to more time uncertainty and more climate variability in the LGM. We compare this simple prediction to the actual correlation structure in the LGM proxy records. We found that time series data of ice-core stable isotope records and planktonic foraminifera Mg/Ca ratios were consistent between the Holocene and LGM periods, while time series of Uk'37 proxy records were not as we found no correlation between nearby LGM records. Our results support the finding of highly regional or noisy marine proxy records in the compilation analysed here and suggest the need for further studies on the role of climate proxies and the processes of climate signal recording and preservation.     

Marine evidence for climatic instability during the last interglacial in shelf records from northwest Europe

Data from the Greenland ice sheet and continental records from Europe have indicated climatic fluctuations during the last interglacial (Eemian: Oxygen Isotope Substage 5e). Similar fluctuations have not, however, been documented previously from marine environments. Here, we show the existence of two cold events during substage 5e in two marine, benthic foraminiferal, shelf records from northwest Europe and suggest that these cooling events are a result of fluctuations in the strength of the North Atlantic surface-water circulation.     

Alpine Evidence for Atmospheric Circulation Patterns in Europe during the Last Glacial Maximum

The configuration of Alpine accumulation areas during the last glacial maximum (LGM) has been reconstructed using glacial–geological mapping. The results indicate that the LGM ice surface consisted of at least three major ice domes, all located south of the principal weather divide of the Alps. This implies that the buildup of the main Alpine ice cover during oxygen isotope stage (OIS) 2 was related to precipitation by dominant southerly atmospheric circulation, in contrast to today's prevalent westerly airflow. Such a reorganization of the atmospheric circulation is consistent with a southward displacement of the Oceanic Polar Front in the North Atlantic and of the associated storm track to the south of the Alps. These results, combined with additional paleoclimate records from western and southern Europe, allow an interpretation of the asynchronous evolution of the different European ice caps during the last glaciation. δ¹⁸O stages (OIS) 4 and 3 were characterized by location of the Polar Front north of 46°N (Gulf of Biscay). This affected prevailing westerly circulation and, thus, ice buildup in western Scandinavia, the Pyrénées, Vosges, and northern Alps. At the LGM, however, the Polar Front lay at 44°N, causing dominating southerly circulation and reduced precipitation in central and northern Europe.     

Pattern of abrupt climatic fluctuation in the East Asian Monsoon during the Last Glacial: Evidence from Chinese loess records

Records of two loess sections located in mid-eastern and western margins of the East Asian Monsoon area captured 20 Dansgaard-Oescher events and six Heinrich events. All these suggested that the climate in the East Asian Monsoon area fluctuated rapidly on millennial to century timescales during the whole Last Glacial. We found that these loess-based events of rapid climate fluctuations were generally synchronous with those of GRIP records, but that there were differences between the Shagou loess section in the west and the Wangguan loess section in the east: the former was more sensitive to climate change than the latter. Compared with earlier studies on loess records covering the Last Glacial from neighboring areas, we discovered that the magnitude of Dansgaard-Oeschger cycles decreased gradually from west to east and we suggest that it resulted from the combined effect of the Westerlies and the East Asian Monsoon.     

Late Holocene sea levels in Ireland

The course of Irish sea levels during the late-Holocene is not well-known, yet it is an understanding of this period that will prove crucial in the definition and management of future sea-level changes. The coastline of Ireland embraces wide environmental and glacio-isostatic contrasts, which serve and, to some extent, control sea-level events at both local and regional scales, making definitive resolution of relative sea-level changes difficult. In the southwest, the picture is of inexorable relative sea-level rise. Studies in Co. Kerry show a gradual submergence of terrestrial facies, by estuarine and, in places, marine materials. Pollen and diatom studies, together with ¹⁴C dates, suggest a decreasing rate of relative sea-level rise in the last 2500 years, often associated with geomorphological changes. Sites on the south coast of Ireland confirm the evidence from the southwest. In Cork Harbour, recent relative sea-level rise since 2100 BP was responsible for marginal land submergence, while elsewhere rising water levels appear to have caused rapid barrier migrations and coast erosion. Palaeoenvironmental evidence from this region suggests a distinctive pattern of sea-level change, associated with sedimentary and/or crustal dynamics, which is not encountered elsewhere in northwest Europe. The overall rate of relative sea-level change on the south and southwest coasts falls between 0.6 and 1.1 mm/year over the last 5000 years. In the north, there is a clear east to west variation in relative sea-level trends, following an isostatically-controlled peak (+3 to ?1 m OD) between 6500 BP (east) and 3500 BP (west). Falling sea levels from 3500 to 1500 BP have been followed by a general slow rise, although there are still local anomalies to this pattern, most noticeably at Malin Head, where sea level is currently falling at 2.4mm/year. Relative sea-level signatures in Ireland differ markedly between the north and south coasts. Furthermore geomorphological and ecological contexts of this rise vary from east to west, providing a complex all-Ireland framework for future investigations.     

Glacial lake levels and Eastern Great Lakes Palaeo‐Indians

This article investigates changing lake levels in the late Pleistocene eastern Great Lakes in order to gain insights into the Early Palaeo‐Indian occupations. Significant new information bearing on lake level history is provided, notably the first well‐documented deposits of a high water level above modern in the ca. 11,000–10,300 B.P. period in the southern Lake Huron basin. The lake level information, along with paleoenvironmental and site data, reinforces site age estimates to the 11th millennium B.P.; suggests significant numbers of sites have been inundated by rising water levels; provides specific information on the setting of archaeological sites such as placing the Parkhill site adjacent to a large lake estuary; indicates reasons for the attractiveness of shorelines to Palaeo‐Indians including persistence of more open areas conducive to higher game productivity; and points to ideal areas for future archaeological site survey, particularly in the Lake Erie drainage. © 2000 John Wiley & Sons, Inc.     

Late Quaternary landscape evolution in a region of stable postglacial relative sea levels,British Columbia central coast,Canada

After retreat of the Cordilleran Ice Sheet (CIS) and subsequent glacio‐isostatic adjustment of the central coast of British Columbia (BC), Canada, a complex coastline emerged as relative sea level rapidly reached equilibrium and maintained stability over the end of the Late Pleistocene and Holocene. This study provides a late Quaternary reconstruction of the landscape evolution of a geographically distinct location on the central BC coast, northwest Calvert Island, which experienced a re‐advance of the CIS near the end of the Late Pleistocene and minimal subsequent relative sea‐level change. Geomorphological observations from LiDAR imagery, sedimentological and palaeoecological evidence from exposures, cores and shovel pits, and a robust luminescence and ¹⁴C‐based chronology spanning the last 15 000 years are used to reconstruct the landscape of northwest Calvert Island following CIS retreat. A single‐aliquot regenerative dose protocol that was developed specifically for luminescence dating of the sediments on Calvert Island was utilized in this study. Localized proglacial sedimentation was linked to the glacial re‐advance experienced at the end of the Late Pleistocene. Extensive coastal reconfiguration (e.g. rapid shoreline progradation of >1 m a⁻¹) occurred in the absence of extensive RSL change, which was the main driver of coastal change elsewhere along the BC coast. Changes in climate, small magnitude changes in RSL, and fire all probably played a role in isolated aeolian landform development and stabilization in the study area. An important contribution of this study is the documentation of the multi‐disciplinary approach for reconstructing palaeogeography, using multiple geochronological methods, micro‐ and macro‐sedimentology, the palaeoecology inferred from both macro and microfossils (e.g. diatoms and foraminifers), stratigraphy, field mapping and remote sensing. In addition, these findings inform our understanding of the drivers of coastal sedimentary processes, particularly in the temperate coastal rainforest region of BC, and the role that fire may play in those processes. Coastal palaeogeography studies in the region will become increasingly important as discoveries of Late Pleistocene human habitation along the coastal migration route continue to be documented.     

Postglacial uplift and relative sea level changes in Finnmark,northern Norway

The outer coast of Finnmark in northern Norway is where the former Fennoscandian and Barents Sea ice sheets coalesced. This key area for isostatic modelling and deglaciation history of the ice sheets has abundant raised shorelines, but only a few existing radiocarbon dates constrain their chronology. Here we present three Holocene sea level curves based on radiocarbon dated deposits from isolation basins at the outermost coast of Finnmark; located at the islands Sørøya and Rolvsøya and at the Nordkinn peninsula. We analysed animal and plant remains in the basin deposits to identify the transitions between marine and lacustrine sediments. Terrestrial plant fragments from these transitions were then radiocarbon dated. Radiocarbon dated mollusk shells and marine macroalgae from the lowermost deposits in several basins suggest that the first land at the outer coast became ice free around 14,600 cal yr BP. We find that the gradients of the shorelines are much lower than elsewhere along the Norwegian coast because of substantial uplift of the Barents Sea. Also, the anomalously high elevation of the marine limit in the region can be attributed to uplift of the adjacent seafloor. After the Younger Dryas the coast emerged 1.6–1.0 cm per year until about 9500–9000 cal yr BP. Between 9000 and 7000 cal yr BP relative sea level rose 2–4 m and several of the studied lakes became submerged. At the outermost locality Rolvsøya, relative sea level was stable at the transgression highstand for more than 3000 years, between ca 8000 and 5000 cal yr BP. Deposits in five of the studied lakes were disturbed by the Storegga tsunami ca 8200–8100 cal yr BP.     

Solar and proxy-sensitivity imprints on paleohydrological records for the last millennium in west-central Europe

This paper presents a lake-level record established for the last millennium at Lake Saint-Point in the French Jura Mountains. A comparison of this lake-level record with a solar irradiance record supports the hypothesis of a solar forcing of variations in the hydrological cycle linked to climatic oscillations over the last millennium in west-central Europe, with higher lake levels during the solar minimums of Oort (around AD 1060), Wolf (around AD 1320), Spörer (around AD 1450), Maunder (around AD 1690), and Dalton (around AD 1820). Further comparisons of the Saint-Point record with the fluctuations of the Great Aletsch Glacier (Swiss Alps) and a record of Rhône River floods from Lake Bourget (French Alps) give evidence of possible imprints of proxy sensitivity on reconstructed paleohydrological records. In particular, the Great Aletsch record shows an increasing glacier mass from AD 1350 to 1850, suggesting a cumulative effect of the Little Ice Age cooling and/or a possible reflection of a millennial-scale general cooling until the mid-19th century in the Northern Hemisphere. In contrast, the Saint-Point and Bourget records show a general trend toward a decrease in lake levels and in flood magnitude anti-correlated with generally increasing solar irradiance.     

New observations on the relative sea level and deglacial history of Greenland from Innaarsuit, Disko Bugt

Relative sea level (RSL) data derived from isolation basins at Innaarsuit, a site on the south shores of the large marine embayment of Disko Bugt, West Greenland, record rapid RSL fall from the marine limit (ca. 108 m) at 10,300-9900 cal yr B.P. to reach the present sea level at 3500 cal yr B.P. Since 2000 cal yr B.P., RSL rose ca. 3 m to the present. When compared with data from elsewhere in Disko Bugt, our results suggest that the embayment was deglaciated later and more quickly than previously thought, at or slightly before 10,300 cal yr B.P. The northern part of Disko Bugt experienced less rebound (ca. 10 m at 6000 cal yr B.P.) compared with areas to the south. Submergence during the late Holocene supports a model of crustal down-warping as a result of renewed ice-sheet growth during the neoglacial. There is little evidence for west to east differences in crustal rebound across the southern shores of Disko Bugt.     

Preboreal climate oscillations in Europe: Wiggle-match dating and synthesis of Dutch high-resolution multi-proxy records

In order to compare environmental and inferred climatic change during the Preboreal in The Netherlands, five terrestrial records were analysed. Detailed multi-proxy analyses including microfossils (e.g., pollen, spores, algae, and fungal spores), macroremains (e.g., seeds, fruits, wood, mosses, etc.), and loss on ignition measurements were carried out with high temporal resolution. To link the five Preboreal records, accurate chronologies were produced by AMS ¹⁴C wiggle-match dating. The Dutch records show that following the Lateglacial/Holocene climate warming, birch woodlands expanded between 11,530 and 11,500 cal BP during the Friesland Phase of the Preboreal. After the Friesland Phase, two distinct climatic shifts could be inferred: (1) around 11,430–11,350 cal BP the expansion of birch forests was interrupted by a dry continental phase with open grassland vegetation, the Rammelbeek Phase. This phase was coeval with the coldest part of the Preboreal oscillation (PBO) as observed in the δ¹⁸O record of the Greenland ice-core records and has been attributed to a large meltwater flux that resulted in a temporary decrease of the thermohaline circulation in the North Atlantic. (2) At the start of the Late Preboreal, between 11,270 and 11,210 cal BP, a sudden shift to a more humid climate occurred and birch forests expanded again. A simultaneous increase in the cosmogenic nuclides ¹⁴C and ¹⁰Be suggests that these changes in climate and vegetation were forced by a sudden decline in solar activity. Expansion of pine occurred during the later part of the Late Preboreal. At the onset of the Boreal, between 10,770 and 10,700 cal BP, dense woodlands with hazel, oak, elm and pine started to develop in The Netherlands.     

晚冰期月亮湖炭屑记录反映的古气候演化

位于大兴安岭中段的月亮湖地处季风/非季风影响过渡地带,其沉积岩心下部886～546 cm的炭屑记录揭示了末次冰期晚期到全新世早期(20.9～10.8 cal.ka B.P.)的古气候演化历史,反映了东亚季风对研究区气候的影响。研究区炭屑浓度的变化主要由可供燃烧的生物量决定,生长在气候温暖时期的森林草原能够提供更多可供燃烧的生物量。在同一植被类型的条件下,气候寒冷湿润时炭屑浓度低,气候温暖干旱时炭屑浓度高。20.9～18.0 cal.ka B.P.炭屑浓度较低, 气候寒冷偏干,18.0～15.3 cal.ka B.P.炭屑浓度最低,气候寒冷湿润,15.3～14.4 cal.ka B.P.炭屑浓度增高,气候开始向温暖的方向发展,14.4～11.8 cal.ka B.P.炭屑浓度快速变化,气候也经历了一系列的快速变化,11.8～10.8 cal.ka B.P.炭屑浓度总体较高,气候温暖湿润。<50 μm的炭屑浓度指示了区域火演化的历史, >50 μm的炭屑则反映了当地野火发生的状况。