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The record of ice-sheet demise since the last glacial maximum (LGM) provides an opportunity to test the relative importance of instability mechanisms, including relative sea-level (RSL) change, controlling ice-sheet retreat. Here we examine the record of RSL changes accompanying the retreat of the Minch Ice Stream (MnIS) of northwest Scotland during the deglaciation following the LGM as well as use the record to provide additional age constraints on a local late-glacial readvance known as the Wester Ross Readvance. We use new and existing records of RSL change obtained from isolation basins in Wester Ross along the flanks of the former MnIS to test available glacial-isostatic adjustment (GIA) predictions of the deglacial RSL history for the region. Using these GIA model predictions we examine the nature of RSL change across the retreating front of the MnIS through the early deglaciation. Our new radiocarbon ages from these basins confirm the timing of deglaciation within the inner trough of the former MnIS as well as refines the age of the Wester Ross Readvance, both established by earlier cosmogenic-based studies. We find that the Wester Ross Readvance culminated around 15.8 ± 0.1 ka, slightly earlier than recent suggestions. Near Gairloch, Wester Ross, RSL fell from a marine limit ∼20 m above present at ∼16.1–16.5 ka. Three isolation basins record RSL fall over the following ∼0.8 ka allowing a comparison between GIA predictions and RSL observations. Our new analyses suggest that the rate of RSL rise increased at the ice front, in concert with the MnIS encountering a landward sloping bed potentially aiding the rapid retreat of the MnIS from 17.6 to 16.4 ka BP. This observation suggests that GIA during deglaciation does not necessarily induce a stabilizing RSL change to marine-based ice streams as some models have suggested. Along indented ice margins, the RSL field at the front of individual ice streams may be governed by the regional GIA signal driven by the ice sheet as a whole, rather than the local ice front. In addition, the stabilizing impact of post-glacial rebound is dependent on an Earth rheology weak enough to respond quickly to the ice-sheet retreat. In the case of the MnIS, the RSL experienced at the front of the ice stream was likely governed by the earlier ice mass extent, the larger ice masses lying to the east and south of the highly indented ice front, and the relatively strong Earth rheology beneath the British Isles. Thus, the geometry of the ice sheet margins, such as those in Greenland and Antarctica today, and the Earth rheology beneath them need to be taken into account when considering the stabilizing impact of post-glacial rebound on marine ice sheet retreat.

New relative sea-level (RSL) data constrain the timing and magnitude of RSL changes in southern Isle of Skye following the Last Glacial Maximum (LGM). We identify a marine limit at ~23 m OD, indicating RSL ~20 m above present c. 15.1 ka. Isolation basin data, supported by terrestrial and marine limiting dates, record RSL fall to 11.59 m above present by c. 14.2 ka. This RSL fall occurs across the time of global Meltwater Pulse 1A, supporting recent research on the sources of ice melting. Our new data also help to resolve some of the chronological issues within the existing Isle of Skye RSL record and provide details of the sub-Arctic marine environment associated with the transition into Devensian Lateglacial climate at c. 14.5 k cal a BP, and the timing of changes in response to Loch Lomond Stadial climate. Glacio-isostatic adjustment (GIA) model predictions of RSL deviate from the RSL constraints and reflect uncertainties in local and global ice models used within the GIA models. An empirical RSL curve provides a target for future research to address.

We present evidence of land-level change resulting from the 2016 Mw 7.6 Chiloe earthquake from tidal wetlands along the southern coastline of Isla de Chiloe, Chile, to test criteria for the detection of low-level

Determining the rates, mechanisms, and geographic variability of relative sea-level (RSL) change following the Last Glacial Maximum (LGM) provides insight into the sensitivity of ice sheets to climate change, the response of the solid Earth and gravity field to ice-mass redistribution, and constrains statistical and physical models used to project future sea-level rise. To do so in a scientifically robust way requires standardized datasets that enable broad spatial comparisons that minimize bias. As part of a larger goal to develop a unified, spatially-comprehensive post-LGM global RSL database, in this special issue we provide a standardized global synthesis of regional RSL data that resulted from the first ‘Geographic variability of HOLocene relative SEA level (HOLSEA)’ meetings in Mt Hood, Oregon (2016) and St Lucia, South Africa (2017). The HOLSEA meetings brought together sea-level researchers to agree upon a consistent protocol to standardize, interpret, and incorporate realistic uncertainties of RSL data. This special issue provides RSL data from ten geographical regions including new databases from Atlantic Europe and the Russian Arctic and revised/expanded databases from Atlantic Canada, the British Isles, the Netherlands, the western Mediterranean, the Adriatic, Israel, Peninsular Malaysia, Southeast Asia, and the Indian Ocean. In total, the database derived from this special issue includes 5634 (5290 validated) index (n = 3202) and limiting points (n = 2088) that span from ∼20,000 years ago to present. Progress in improving the standardization of sea-level databases has also been accompanied by advancements in statistical and analytical methods used to infer spatial patterns and rates of RSL change from geological data that have a spatially and temporally sparse distribution and geochronological and elevational uncertainties. This special issue marks the inception of a unified, spatially-comprehensive post-LGM global RSL database. Ministry of Education (MOE) National Research Foundation (NRF) Published version NSK and BPH were funded by the Singapore Ministry of Edu- cation Academic Research Fund MOE2018-T2-1-030, the National Research Foundation Singapore, and the Singapore Ministry of Education, under the Research Centres of Excellence initiative. This work is Earth Observatory of Singapore contribution 252. AR ac- knowledges the Institutional Strategy of the University of Bremen, funded by the German Excellence Initiative (ABPZuK-03/2014) and the SEASCHANGE (RO-5245/1-1) from the Deutsche For- schungsgemeinschaft (DFG) as part of the Special Priority Program (SPP)-1889 00Regional Sea Level Change and Society”. TET ac- knowledges support from the Paleo Perspectives on Climate Change program of the US National Science Foundation (OCE- 1502588). We thank Maren Bender for her help in preparing the comparison of data from Southeast Asia. This article is a contribu- tion to PALSEA (Palaeo-Constraints on Sea-Level Rise) and Inter- national Geoscience Program (IGCP) Project 639, “Sea Level Change from Minutes to Millennia”.

The most rapid global sea-level rise event of the last deglaciation, Meltwater Pulse 1A (MWP-1A), occurred ∼14,650 years ago. Considerable uncertainty regarding the sources of meltwater limits understanding of the relationship between MWP-1A and the concurrent fast-changing climate. Here we present a data-driven inversion approach, using a glacio-isostatic adjustment model to invert for the sources of MWP-1A via sea-level constraints from six geographically distributed sites. The results suggest contributions from Antarctica, 1.3 m (0–5.9 m; 95% probability), Scandinavia, 4.6 m (3.2–6.4 m) and North America, 12.0 m (5.6–15.4 m), giving a global mean sea-level rise of 17.9 m (15.7–20.2 m) in 500 years. Only a North American dominant scenario successfully predicts the observed sea-level change across our six sites and an Antarctic dominant scenario is firmly refuted by Scottish isolation basin records. Our sea-level based results therefore reconcile with field-based ice-sheet reconstructions., Meltwater Pulse 1A was the most rapid global sea-level rise event during the last deglaciation, but the source of the freshwater causing this rise is debated. Here, the authors use a data-driven inversion approach to show that the North American and Eurasian Ice Sheets were the dominant contributors.

Tidal marshes rank among Earth’s vulnerable ecosystems, which will retreat if future rates of relative sea-level rise (RSLR) exceed marshes’ ability to accrete vertically. Here, we assess the limits to marsh vulnerability by analyzing >780 Holocene reconstructions of tidal marsh evolution in Great Britain. These reconstructions include both transgressive (tidal marsh retreat) and regressive (tidal marsh expansion) contacts. The probability of a marsh retreat was conditional upon Holocene rates of RSLR, which varied between −7.7 and 15.2 mm/yr. Holocene records indicate that marshes are nine times more likely to retreat than expand when RSLR rates are ≥7.1 mm/yr. Coupling estimated probabilities of marsh retreat with projections of future RSLR suggests a major risk of tidal marsh loss in the twenty-first century. All of Great Britain has a >80% probability of a marsh retreat under Representative Concentration Pathway (RCP) 8.5 by 2100, with areas of southern and eastern England achieving this probability by 2040., Quantifying the vulnerability of tidal marsh ecosystems to relative sea-level rise (RSLR) is essential if the threat is to be mitigated. Here, the authors analyze the response of Great Britain’s tidal marshes to RSLR during the Holocene and predict an almost inevitable loss of this ecosystem by 2100 under rapid RSLR scenarios.

Recent paleoseismological studies question whether segment boundaries identified for 20th and 21st century great, >M8, earthquakes persist through multiple earthquake cycles or whether smaller segments with different boundaries rupture and cause significant hazards. The smaller segments may include some currently slipping rather than locked. In this review, we outline general principles regarding indicators of relative sea-level change in tidal wetlands and the conditions in which paleoseismic indicators must be distinct from those resulting from non-seismic processes. We present new evidence from sites across southcentral Alaska to illustrate different detection limits of paleoseismic indicators and consider alternative interpretations for marsh submergence and emergence. We compare predictions of coseismic uplift and subsidence derived from geophysical models of earthquakes with different rupture modes. The spatial patterns of agreement and misfits between model predictions and quantitative reconstructions of coseismic submergence and emergence suggest that no earthquake within the last 4000 years had a pattern of rupture the same as the Mw 9.2 Alaska earthquake in 1964. From the Alaska examples and research from other subduction zones we suggest that If we want to understand whether a megathrust ruptures in segments of variable length in different earthquakes, we need to be site-specific as to what sort of geological-based criteria eliminate the possibility of a particular rupture mode in different earthquakes. We conclude that coastal paleoseismological studies benefit from a methodological framework that employs rigorous evaluation of five essential criteria and a sixth which may be very robust but only occur at some sites: 1 – lateral extent of peat-mud or mud-peat couplets with sharp contacts; 2 – suddenness of submergence or emergence, and replicated within each site; 3 – amount of vertical motion, quantified with 95% error terms and replicated within each site; 4 – syncroneity of submergence and emergence based on statistical age modelling; 5 – spatial pattern of submergence and emergence; 6 – possible additional evidence, such as evidence of a tsunami or liquefaction concurrent with submergence or emergence. We suggest that it is possible to consider detection limits as low as 0.1–0.2 m coseismic vertical change.

The new sea-level database for Britain and Ireland contains >2100 data points from 86 regions and records relative sea-level (RSL) changes over the last 20 ka and across elevations ranging from ∼+40 to −55 m. It reveals radically different patterns of RSL as we move from regions near the centre of the Celtic ice sheet at the last glacial maximum to regions near and beyond the ice limits. Validated sea-level index points and limiting data show good agreement with the broad patterns of RSL change predicted by current glacial isostatic adjustment (GIA) models. The index points show no consistent pattern of synchronous coastal advance and retreat across different regions, ∼100–500 km scale, indicating that within-estuary processes, rather than decimetre- and centennial-scale oscillations in sea level, produce major controls on the temporal pattern of horizontal shifts in coastal sedimentary environments. Comparisons between the database and GIA model predictions for multiple regions provide potentially powerful constraints on various characteristics of global GIA models, including the magnitude of MWP1A, the final deglaciation of the Laurentide ice sheet and the continued melting of Antarctica after 7 ka BP.

Understanding relative sea-level changes helps explain critical interactions in Earth environmental systems throughout the Quaternary. Relative sea-level changes record transfers of mass between oceans and continents during expansion and contraction of great ice sheets driven by climate change. They record extreme events, including storm surges and tsunamis, as well as predictable daily tides. They also record vertical movements in the Earth's crust over a wide range of timescales, from co-seismic uplift and subsidence during great, Mw > 8, plate-boundary earthquakes, through century- and millennial-scale movements driven by the process of glacial isostatic adjustment, to timescales beyond the Quaternary, as global ocean volumes change as a result of plate-tectonic movements. Vertical changes in relative sea level result in major horizontal shifts in coastal environments. The combination of all these factors means that no single location on Earth records all of these changes. No location can be considered stable and therefore a record of “absolute” sea-level change. Perhaps the most significant advance in studies of Quaternary sea-level change is the recognition that key questions will only be answered by the integration of multi-proxy based reconstructions of sea level with model predictions.

In this paper we identify four ‘revolutions’ that in our view have shaped the study of sea-level changes in recent decades. (i) The search for ‘eustasy’. One of the most hotly debated issues in the 1960s is still relevant as models of glacial isostatic adjustment (GIA) require input of the amount of meltwater transferred to the world's oceans following the demise of the large Pleistocene ice sheets. (ii) Resolution of sea-level archives. All sea-level archives have limitations in their resolving power but are we willing to define these? From studies of salt-marsh deposits and corals it is highly likely that climate-driven metre-scale sea-level fluctuations have not occurred during the middle and late Holocene. (iii) Rapid sea-level changes. Improved coring technology has resulted in the suggestion of meltwater pulses during the last deglaciation. Low-frequency high-magnitude events have been documented along seismically active shorelines and provide information on seismic hazards and storm impacts. (iv) Merging of empirical sea-level investigations and models. Much sea-level research in the past two decades has embraced the integration of models and field-derived data, providing testable hypotheses and insights into processes. We conclude with some reminders about the ‘inconvenient truths’ that keep the sea-level scientist honest.

Sediment archives of coseismic deformation from regions of maximum coseismic displacement act as key datasets for the development and constraint of models of surface elevation change associated with Holocene great earthquakes. We present new lithologic and biostratigraphic investigations of a previously thought lost core from Portage, at the head of Turnagain Arm, upper Cook Inlet, which is within the zone of maximum coseismic subsidence during the AD 1964 Alaska earthquake. Quantitative analysis of diatoms preserved over six peat–silt couplets before the AD 1964 earthquake show six phases of rapid relative sea-level rise. Radiocarbon dates from each contact show that all six correlate with independently modelled ages of great earthquakes recorded in the Prince William Sound segment of the Aleutian megathrust during the last 4000 years. As with the other sites in the upper Cook Inlet, there is no evidence for an earthquake between the penultimate great earthquake, ∼880 a BP, and AD 1964 in contrast to those separately recorded at Kodiak Island and Katalla. Correlation of the six earthquakes at Portage with those at Girdwood, and no evidence for additional peat–silt couplets, support our previous interpretation that the extra three peat–silt couplets at Girdwood lacking evidence of intertidal sedimentation represent local-scale changes in environment rather than coseismic subsidence and short recurrence intervals of great earthquakes.

The great earthquake, Mw 9.2, of AD 1964 may not be typical of other megathrust earthquakes in the region during the last 4000 years. We present new field data from three sites: Copper River Delta, the lower Katalla River valley and Puffy Slough, to enhance the temporal and spatial resolutions of the paleoseismic records of multiple great earthquakes. Differences in the spatial patterns of coseismic uplift and subsidence suggest different rupture combinations of the Kodiak, Prince William Sound and western Yakutat segments of the plate boundary. The longest and most comprehensive records all come from the Prince William Sound segment. Most sites here reveal net subsidence over multiple earthquake cycles except where probable upper plate faulting contributes locally to net uplift, with measurable differences between sites only a few kilometres apart. We identify the Katalla area as a source of local seismic hazard, similar to other locations in the western part of the Yakutat microplate, including the two Mw8+ ruptures in AD 1899. We use a Bayesian radiocarbon modelling approach to estimate the age and recurrence intervals of multiple great earthquakes for the Prince William Sound segment of the megathrust. The long interval, 883 ± 34 (2σ) years, between the penultimate earthquake and AD 1964 contrasts with the older earthquakes that have intervals ranging from ∼420 to ∼610 years, with a mean of ∼535 years.

Understanding late Holocene to present relative sea-level changes at centennial or sub-centennial scales requires geological records that dovetail with the instrumental era. Salt marsh sediments are one of the most reliable geological tide gauges. In this paper we review the methodological and technical advances that promoted research on ‘high resolution’ late Holocene sea-level change. We work through an example to demonstrate different pathways to quantitative reconstructions of relative sea level based on salt marsh sediments. We demonstrate that any reconstruction is in part a result of the environment from which the record is taken, the modern dataset used to calibrate the fossil changes, statistical assumptions behind calibrating microfossil assemblages and choices made by the researchers. With the error term of typical transfer function models ~ 10–15% of the tidal range, micro-tidal environments should produce the most precise sea-level reconstructions. Sampled elevation range of the modern dataset also has a strong influence on model predictive ability. Model-specific errors may under represent total uncertainty which comes from field practices, sedimentary environment, palaeo-tidal changes and sediment compaction as well as statistical uncertainties. Geological tide gauges require a detailed chronology but we must be certain that apparent relative sea-level fluctuations are not simply a consequence of an age–depth model. We make six suggestions to aid the development and interpretation of geological tide gauge records.

During the last deglaciation, sea levels rose as ice sheets retreated. This climate transition was punctuated by periods of more intense melting; the largest and most rapid of these—Meltwater Pulse 1A—occurred about 14,500 years ago, with rates of sea-level rise reaching approximately 4 m per century1, 2, 3. Such rates of rise suggest ice-sheet instability, but the meltwater sources are poorly constrained, thus limiting our understanding of the causes and impacts of the event4, 5, 6, 7. In particular, geophysical modelling studies constrained by tropical sea-level records1, 8, 9 suggest an Antarctic contribution of more than seven metres, whereas most reconstructions10 from Antarctica indicate no substantial change in ice-sheet volume around the time of Meltwater Pulse 1A. Here we use a glacial isostatic adjustment model to reinterpret tropical sea-level reconstructions from Barbados2, the Sunda Shelf3 and Tahiti1. According to our results, global mean sea-level rise during Meltwater Pulse 1A was between 8.6 and 14.6 m (95% probability). As for the melt partitioning, we find an allowable contribution from Antarctica of either 4.1 to 10.0 m or 0 to 6.9 m (95% probability), using two recent estimates11, 12 of the contribution from the North American ice sheets. We conclude that with current geologic constraints, the method applied here is unable to support or refute the possibility of a significant Antarctic contribution to Meltwater Pulse 1A.

This paper assesses variations in quantitative reconstructions of late Holocene relative sea-level (RSL) change arising from using modern diatom datasets from different spatial scales, applied to case studies from Alaska. We investigate the implications of model choice in transfer functions using local-, sub-regional- and regional-scale modern training sets, and produce recommendations on the creation and selection of modern datasets for reconstructing RSL change over Holocene timescales in tidal marsh environments comparable with those in Alaska. We show that regional modern training sets perform best in terms of providing fossil samples with good modern analogues, and in producing reconstructions that most closely match observations, where these are available. Local training sets are frequently insufficient to provide fossil samples with good modern analogues and may over-estimate the precision of RSL reconstructions. This is particularly apparent when reconstructing RSL change for periods beyond the last century. For reconstructing RSL change we recommend using regional modern training sets enhanced by local samples.

The glacial isostatic adjustment (GIA) of the British Isles is complex due to the interplay between local and non-local signals. A number of recent studies have modelled the GIA response of the British Isles using relative sea-level data. This study extends these previous analyses by using output from a numerical glaciological model as input to a GIA model. This is a necessary step towards more realistic GIA models, and although there have been similar studies for the major late Pleistocene ice sheets, this is the first study to do so for the British Isles. We test three reconstructions, classed as ‘minimal’, ‘median’ and ‘maximal’ in terms of their volume at maximum extent, and find it is possible to obtain good data–model fits. The minimal reconstruction is clearly preferred by the sea-level data. The ice reconstructions tested were not constrained by geomorphological information of past ice extent (lateral and vertical). As a consequence, the reconstructions extend further than much of this information suggests, particularly in terms of ice thickness. It is notable, however, that the reconstructions produce good fits to many sea-level data from central, mountainous regions (e.g. Scottish highlands), which lends support to the suggestion that trimlines, often used as an constraint on the palaeo ice surface location, are in fact features formed at the transition from warm- to cold-based ice and so mark a minimum constraint on the ice surface altitude. Based on data–model misfits, suggestions are made for improving the ice model reconstructions. However, in many locations, the cause of the misfit could be due to non-local, predominantly Fennoscandian ice and so interpretation is not straightforward. As a result, we suggest that future analyses of this type consider models and observations for both Fennoscandia and the British Isles. Copyright © 2012 John Wiley & Sons, Ltd.

Vertical land motion caused by continuing glacial isostatic adjustment is one of several important components of sea-level change and is not limited just to previously glaciated regions. A national-scale analysis for the British Isles shows an ellipse of present-day relative uplift (relative sea-level fall), ∼1.2 mm a−1, broadly centred on the deglaciated mountains of Scotland. The pattern of three foci of relative subsidence, ∼1 mm a−1, results from the additional interactions of the deglacial meltwater load on the Atlantic basin and the continental shelf, and the signal due to far-field ice sheets. At a local scale, sediment compaction can more than double the rate of relative land subsidence. Relative land-level change (the negative of relative sea-level change) is not the same as vertical land motion. There is a spatial pattern in the difference between relative land-level change and vertical land motion, with differences at present of approximately −0.1 to −0.3 mm a−1 around the British Isles and +2.5 to −1.5 mm a−1 globally. For the wider scientific and user community, whether or not the differences are considered significant will depend upon the location, time frame and spatial scale of the study that uses such information. Copyright © 2011 John Wiley & Sons, Ltd.

The glacial isostatic adjustment (GIA) of the British Isles is of interest due to the constraints that can be provided on key model parameters such as the global meltwater signal, local ice sheet history and viscoelastic earth structure. A number of recent studies have modelled relative sea-level (RSL) data from this region to constrain model parameters. As indicated in these studies, the sensitivity of these data to both local and global parameters results in a highly non-unique problem. This study aims to address this inherent non-uniqueness by combining a previously published British–Irish ice model that is based on the most recent geomorphological data with a new global ice sheet model that provides an accurate prediction of eustatic sea-level change. In addition, constraints from Global Positioning System (GPS) measurements of present-day vertical land motion are considered alongside the entirety of RSL data from both Great Britain and Ireland. A model solution is found that provides a high-quality fit to both the RSL data and the GPS data. Within the range of earth viscosity values considered, the optimal data model fits were achieved with a relatively thin lithosphere (71 km), upper mantle viscosities in the range 4–6 × 1020 Pa s and lower mantle viscosities ≥ 3 × 1022 Pa s. Copyright © 2011 John Wiley & Sons, Ltd.

Crustal downwarping has occurred throughout southern and south-eastern England and most of Wales for at least the last 4000 years, but the type of movement in some areas of southern and eastern England is more complicated than simple linear subsidence. Highest estimated rates of subsidence (since 4000 BP) are for the Thames Estuary and Norfolk (up to 2 mm/yr). Glacio-isostatic processes have resulted in uplift in northern England and mainland Scotland. The rates of uplift have decreased throughout the Holocene; estimates for the present range from zero in south Lancashire and the Tees Estuary to over 1 mm/yr (though less than 2 mm/yr) in central Scotland. Over 400 sea-level index points, from the databank of 904 cases collected for IGCP Project 200, are grouped into 15 main areas and used to investigate the nature of crustal movements in Great Britain since 8800 BP, but there are significant deficiencies in available data which constrain the analysis.

The contribution of compaction of Holocene strata to sea-level rise, shoreline erosion, and wetland loss is difficult to decipher because of a lack of long-term empirical data. We analyzed more than 360 radiocarbon-dated index points to constrain relative sea levels along the east coast of England during the Holocene and to provide estimates of sediment compaction. The isostatic effect of glacial rebound explains regional-scale differences in relative sea levels. Northeast England, the most northern study area, reveals a middle to late Holocene highstand

Glacial isostatic adjustment and multiple earthquake deformation cycles produce temporal and spatial variability in the records of relative sea-level change across south-central Alaska. Bering Glacier had retreated inland of the present coast by 16 ka BP and north of its present terminus by ∼14 ka BP. Reconnaissance investigations in remote terrain provide new but limited insights of post-glacial relative sea-level change and the palaeoseismology of the region. Relative sea-level was above present ∼9.2 ka BP to at least 5 ka BP before falling to below present. It was above present by the early 20th century, before land uplift in the 1964 M 9.2 earthquake. The pattern of relative sea-level change differs what may be expected in comparison with model predictions for other seismic and non-seismic locations. Buried mud–peat couplets show a great earthquake ∼900 cal BP, including evidence of a tsunami. Correlation with other sites suggest simultaneous rupture of adjacent segments of the Aleutian megathrust and the Yakutat microplate.

Large to great earthquakes and related tsunamis generated on the Aleutian megathrust produce major hazards for both the area of rupture and heavily populated coastlines around much of the Pacific Ocean. Here we use paleoseismic records preserved in coastal sediments to investigate whether segment boundaries control the largest ruptures or whether in some seismic cycles segments combine to produce earthquakes greater than any observed since instrumented records began. Virtually the entire megathrust has ruptured since AD1900, with four different segments generating earthquakes >M8.0. The largest was the M9.2 great Alaska earthquake of March 1964 that ruptured ∼800 km of the eastern segment of the megathrust. The tsunami generated caused fatalities in Alaska and along the coast as far south as California. East of the 1964 zone of deformation, the Yakutat microplate experienced two >M8.0 earthquakes, separated by a week, in September 1899. For the first time, we present evidence that earthquakes ∼900 and ∼1500 years ago simultaneously ruptured adjacent segments of the Aleutian megathrust and the Yakutat microplate, with a combined area ∼15% greater than 1964, giving an earthquake of greater magnitude and increased tsunamigenic potential.

This paper presents estimates of rates of mean sea level (MSL) change around the UK based on a larger tide gauge data set and more accurate analysis methods than have been employed so far. The spatial variation of the trend in MSL is found to be similar to that inferred from geological information and from advanced geodetic techniques, which is a similar conclusion to that arrived at in previous, less precise and complete studies. The tide gauge MSL trends for 1901 onwards are estimated to be 1.4 +/- 0.2 mm/year larger than those inferred from geology or geodetic methods, suggesting a regional sea level rise of climate change origin several 1/10s mm/year lower than global estimates for the 20th century. However, UK MSL change cannot be described in terms of a simple linear increase alone but includes variations on interannual and decadal timescales. The possible sources of variation in a ‘UK sea level index’ are explored. Air pressure is clearly one such possible source but its direct local forcing through the ‘inverse barometer’ accounts for only one third of the observed variability. A number of larger scale atmospheric and ocean processes must also play important roles, but modelling them satisfactorily and separating the individual contributions presents a major challenge. As regards future regional UK sea level changes, one concludes that there is no basis for major modification to existing projections for the 2080s included in the 2002 UK Climate Impacts Programme studies.

PUBLISHED, 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?700m over much of north and central Ireland is required at the LGM with very rapid deglaciation after 21 k cal. yr BP., This research was funded by an Enterprise Ireland Basic Research Grant (Edwards?Project No. SC/2003/0215/Y: Holocene Sea-Level Change and Glacio-Isostatic Adjustment in Ireland). We are grateful to James Scourse for his comments on this paper. This publication is a contribution to IGCP Project 495 `Quaternary Land? Ocean interactions: driving mechanisms and coastal responses?.

New records of paleoenvironmental change from two lakes near Cordova, south central Alaska, combined with analysis of previously reported sediment sequences from the adjacent Copper River Delta, provide quantitative constraints on a range of Earth system processes through their expression in relative sea-level change. Basal sediment ages from Upper Whitshed Lake indicate ice-free conditions by at least 14,140–15,040 cal yr BP. While Upper and Lower Whitshed Lakes provide only upper limits to relative sea-level change, interbedded layers of freshwater peat and intertidal silt extending more than 11 m below present sea level in Copper River Delta indicate net submergence over the last 6000 years and multiple earthquake deformation cycles. In contrast, Lower Whitshed Lake, situated just above present high tide level, records only one episode of marine sedimentation, commencing AD 1120–1500, that we interpret as the result of isostatic subsidence due to Little Ice Age mass accumulation of the Chugach Mountain glaciers. Lower Whitshed Lake also records isostatic uplift at the end of the Little Ice Age before the end of marine sedimentation caused by ∼1.5 m coseismic uplift in the great Alaska earthquake of AD 1964. We successfully explain the records of relative sea-level change from both Copper River Delta and the Whitshed Lakes by integrating the effects of eustatic sea-level rise, glacial isostasy, earthquake deformation cycles, sediment loading, sediment compaction and Late Holocene changes in glacier mass into a single model. This approach provides initial quantitative constraints on the individual contributions of these processes. Taking reasonable estimates of eustasy, post-Last Glacial Maximum and Neoglacial glacial isostatic adjustment and a simple earthquake deformation cycle, we demonstrate that sediment loading and sediment compaction are both contributors to relative sea-level rise at Copper River Delta, together producing subsidence averaging approximately 1.2 mm yr−1 over the mid to Late Holocene. Further isolation basin studies have the potential to greatly improve our understanding of the individual contributions of these processes in this highly dynamic region.

In this paper we adopt a quantitative biostratigraphic approach to establish a 1000-year-long coastal record of megathrust earthquake and tsunami occurrence in south central Chile. Our investigations focus on a site in the centre of the rupture segment of the largest instrumentally recorded earthquake, the AD 1960 magnitude 9.5 Chile earthquake. At Chucalén coseismic subsidence in 1960 is recorded in the lithostratigraphy and biostratigraphy of coastal marshes, with peat overlain by minerogenic sediment and changes in the assemblages of diatoms (unicellular algae) indicating an abrupt increase in relative sea level. In addition to the 1960 earthquake, the stratigraphy at Chucalén records three earlier earthquakes, the historically documented earthquake of 1575 and two prehistoric earthquakes, radiocarbon dated to AD 1270–1450 and 1070–1220. Laterally extensive sand sheets containing marine or brackish diatom assemblages suggest tsunami deposition associated with at least two of the three pre-1960 earthquakes. The record presented here suggests a longer earthquake recurrence interval, averaging 270 years, than the historical recurrence interval, which averages 128 years. The lack of geologic evidence at Chucalén of two historically documented earthquakes, in 1737 and 1837, supports the previously suggested hypothesis of variability in historical earthquake characteristics. Our estimates of coseismic land-level change for the four earthquakes range from meter-scale subsidence to no subsidence or slight uplift, suggesting earthquakes completing each ∼270 year cycle may not share a common, characteristic slip distribution. The presence of buried soils at elevations below their modern equivalents implies net relative sea-level rise over the course of the Chucalén paleoseismic record, in contrast to relative sea-level fall over preceding millennia inferred from sites on the mainland. Sea-level rise may contribute to the preservation of evidence for multiple earthquakes during the last millennium, while net relative sea-level fall over the last 2000–5000 years may explain the lack of evidence for older earthquakes.

Holocene relative sea-level reconstructions reveal spatial and temporal patterns, indicating the importance of regional- to local-scale processes for understanding coastal evolution. We reconstruct the Holocene sea-level history and coastal evolution of the north-western Fenland using detailed analyses of lithostratigraphy, microfossil (foraminifera and pollen) assemblages and a suite of 18 radiocarbon dates. We illustrate the balance between sea-level change, sedimentary palaeoenvironment and coastline movements. An initial transgression occurred c. 7700 cal. BP as sea level rose around 8 mm/yr, reaching its maximum inland extent c. 4150 cal. BP. As the rate of sea-level rise reduced to less than 2 mm/yr, a series of local regressive and transgressive phases followed. A regional transgressive event inundated much of the area after c. 2600 cal. BP. Salt marsh peat and intertidal mud dominate inland sequences whereas further seawards, intertidal and subtidal nearshore sand occur, comparable with modern sediments of the adjacent Wash embayment. The north-western Fenland sequence shows similarities with sequences in southern Fenland and The Wash, indicating some regional sea-level control.

The glacial isostatic adjustment of the UK region has been considered in a number of recent studies. We have revisited this problem in order to: (i) highlight some key issues with regard to limitations in the ice modelling approach adopted in these studies and (ii) consider the constraints provided from observations of crustal motion available via continuous global positioning system monitoring. With regard to the first aim, we have found that: (i) previous studies have significantly overestimated ice thicknesses in regions where trim line field constraints were adopted and (ii) the duration of the glaciation phase of the UK ice sheet is a critical aspect of the model and that discrepancies in this model component have led to inconsistent inferences of Earth model parameters. With regard to the second aim, we have found that predictions of horizontal velocities (relative to a chosen site) based on a UK ice model calibrated to fit the regional sea-level database capture the geometry of the signal well but only account for 10% of the magnitude (for a range of Earth models).

Alternating beds of peat and mud in sediment sequences on the south-central Alaskan coast record coseismic and inter-seismic relative land and sea-level movements caused by repeated great earthquakes on the Alaska–Aleutian subduction zone. During the AD 1964 Mw=9.2 earthquake, tidal marshes and wetlands around upper Cook Inlet experienced up to 2 m of subsidence, burying peat-forming communities with intertidal mud. Here we use quantitative analyses of fossil diatoms within peat–mud couplets to reconstruct land/sea-level changes for the 1964 and five earlier great earthquakes during the past 3300 years. In contrast to geodetic observations that are limited to the present post-seismic phase, we quantify varying spatial patterns of uplift and subsidence through complete earthquake cycles. Relative land uplift characterises most of the inter-seismic phase of each cycle at our sites, whereas each great earthquake was preceded by a short period of pre-seismic relative land subsidence.

Observations of relative sea-level change and local deglaciation in western Scotland provide critical constraints for modelling glacio-isostatic rebound in northern Britain over the last 18 000 years. The longest records come from Skye, Arisaig and Knapdale with a shorter, Holocene, record from Kintail. Biostratigraphic (diatom, pollen, dinoflagellate, foraminifera and thecamoebian), lithological and radiocarbon analyses provide age and elevation parameters for each sea-level index point. All four sites reveal relative sea-level change that is highly non-monotonic in time as the local vertical component of glacio-isostatic rebound and eustasy (or global meltwater influx) dominate at different periods. Copyright © 2006 John Wiley & Sons, Ltd.

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Multiple peat–silt couplets in tidal marsh sediment sequences at Anchorage suggest up to five possible great earthquakes during the last 2500 years. Litho-stratigraphic, diatom and radiocarbon data of the youngest two couplets record the last two great earthquakes, AD 1964 and ∼950–850 cal yr BP. Similar multiple peat–silt couplets around Cook Inlet suggest recurring great earthquakes associated with marsh subsidence over large areas, comparable in extent to that recorded in AD 1964. Potential difficulties in interpreting evidence include lack of modern analogues for applying quantitative diatom transfer functions to parts of the fossil record and the observation that under certain sedimentary conditions co-seismic subsidence, in the case of AD 1964 of known magnitude, is recorded by a transitional peat–silt boundary. This differs in diatom stratigraphy from a phase of pre-seismic relative sea-level rise recorded for other great earthquakes. A field experiment to simulate co-seismic subsidence identifies limited mixing at the top of submerged marsh sediment and indicates how mixing must be shown to differ from evidence for pre-seismic relative sea-level rise. Analysis of diatom assemblages from ice, frozen intertidal sediment and melt-out sediment demonstrates the importance of winter processes in transporting diatoms and their interpretation in fossil sequences. Winter processes may also be important in transporting organic material that leads to significant differences, ∼120–2800 yr, between radiocarbon ages from plant macrofossils and bulk peat samples. This necessitates a new approach for establishing between-site correlations, recurrence intervals and spatial extent of great Holocene earthquakes in southern Alaska.

Multiple peat-silt couplets preserved in tidal marsh sediment sequences suggest that numerous great plate boundary earthquakes caused the coast around Cook Inlet, Alaska, to subside over the past 3500 years. Field and laboratory analyses of the two youngest couplets record the well-documented earthquake of AD 1964 and the penultimate one, approximately 850 cal yr BP. Diatom assemblages from a range of modern day estuarine environments from tidal flat through salt marsh to acidic bog produce quantitative diatom transfer function models for elevation reconstructions based on fossil samples. Only nine out of 124 fossil assemblages analysed, including previously published data for the AD 1964 earthquake, have a poor modern analogue. Calibration of fossil samples indicate co-seismic subsidence of 1.50±0.32 m for AD 1964, similar to measurements taken after the earthquake, and 1.45±0.34 m for the ∼850 cal yr BP earthquake. Elevation standard errors for individual fossil samples range from ∼0.08 m in peat layers to ∼0.35 m in silt units. Lack of a chronology within fossil silt units prevents identification of changes in the rate of recovery and land uplift between the post-seismic and inter-seismic periods. However, preservation of multiple peat-silt couplets indicates no net emergence over multiple earthquake cycles. Glacio-isostatic movements from Little Ice Age glacier advance and retreat explains a ∼0.15 m relative sea-level oscillation recorded within the peat layer subsequently submerged as a result of the AD 1964 earthquake. Before both this and the ∼850 cal yr BP earthquake, diatom assemblages suggest pre-seismic relative sea-level rise of ∼0.12±0.13 m, representing possible precursors to great earthquakes.

Isolation basins, raised tidal marshes, coastal wetlands and dune systems around Arisaig in northwest Scotland produce a ∼16 000-year record of relative sea-level (RSL) change from the time of local deglaciation following the Last Glacial Maximum (LGM) to the present. New sea-level index points from Mointeach Mhor North define the culmination of the mid-Holocene RSL highstand to ∼7600–7400 cal yr BP and 6.74±0.2 m above present. Numerous sea-level index points indicate that the RSL highstand persisted more than 1000 years before the onset of any significant RSL fall. This points to a gradual cessation of melting of the Laurentide and Antarctic ice sheets, rather than an abrupt termination. Isolation basin evidence, from a marine limit ∼34 to 38 m above present down to sites close to current sea level, constrain the acceleration of eustatic sea-level rise during meltwater pulse 1a to ∼30 mm yr−1 or ∼11 km3 yr−1 meltwater discharge. Comparison of RSL observations with glacial isostatic adjustment (GIA) model predictions show differences in the pattern of residuals dependent upon the GIA model used. Changes to the far-field ice model components can partly explain the patterns of residuals.

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.

We present palaeoenvironmental results from two cores, Winterton Holmes (GY2) and Somerton Holmes (GY3), south of Horsey, East Norfolk. The upper transgressive contact of the peat of cores GY2 and GY3 is dated to 2355–2742 cal. years bp and 2761–2949 cal. years bp, respectively. The litho- and biostratigraphical data show that both these peat contacts represent sea-level index points formed around mean high water spring tides during a positive tendency of sea-level movement, as saltmarsh indicators near the top of, and immediately above the peat show its deposition within intertidal environments. These sea-level index points when combined with other sea-level observations and predictions from East Norfolk, confirm an upward trend of Holocene relative sea-level change typical of an area at, or beyond, the margins of the last British ice sheet; rapid in the early Holocene then at a much reduced rate in the mid- and late Holocene. Late Holocene rates of relative uplift or subsidence are calculated for East Norfolk by subtracting a model of relative sea level from each index point and then calculating the best-fit linear trend. The late Holocene rate of relative sea-level rise (or land subsidence) is 0.67 ± 0.06 mm −1 which is c . 1 mm a −1 less than the twentieth-century mean sea-level trend estimated from Lowestoft tidal station, thus agreeing with the consensus of opinion that global sea levels have risen between 10 and 20 cm over the past century.

Microfossil diatom and pollen data from a number of cores at coastal marshes at Girdwood Flats and Kenai Flats in Cook Inlet, Alaska, suggest that there was a phase of gradual land subsidence prior to the main shock of the ad 1964 earthquake. This phase followed a long period of gradual land uplift since the last large earthquake, which occurred about 730–900 years ago. Caesium (137Cs) records indicate that subsidence started approximately 15 years before the 1964 earthquake. This pre-seismic subsidence is evident in the coastal marsh sediment sequences in changes in diatom and pollen assemblages that indicate changes in tidal-marsh environments or a change from raised-bog to marsh conditions. The microfossil evidence indicates|0.15 m pre-seismic land subsidence at both Girdwood Flats and Kenai Flats and co-seismic subsidence of|1.8 m and|0.2 m respectively.

Analysis of more than 1200 radiocarbon dated samples that constrain relative sea-levels in Great Britain over the past 16 000 yr provides estimates of current land-level changes (negative of relative sea-level change). Maximum relative land uplift occurs in central and western Scotland, ca. 1.6 mm yr-1, and maximum subsidence is in southwest England, ca. 1.2 mm yr-1. Sediment consolidation, arising from autocompaction as the sediment accumulates and from land drainage, increases the subsidence in areas with thick sequences of Holocene sediments, with an average effect equivalent to at least an extra ca. 0.2 mm yr-1 land subsidence, but more in parts of southeast England, 0.5-1.1 mm yr-1. Modelled changes in tidal range during the mid- to late Holocene in eastern England suggest that the calculated rate of land subsidence is overestimated unless such changes are quantified. The effect is most significant for large coastal lowlands, the Fenland and Humber (ca. 0.5 and 0.6 mm yr-1), that were tidal embayments during the mid- to late Holocene.