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Here we summarize the motivation and issues surrounding the responses of ice sheets and sea level to past climate warming as part of the PALeo constraints on SEA level rise (PALSEA) working group. Papers in this special issue of Quaternary Science Reviews focus on the timescale of glaciations during the late Pliocene, the magnitude of ice-sheet fluctuations and volume leading up to and during the last glacial maximum, the timing and persistence of ice-sheet impacts on deglacial and future relative sea-level change, and relative sea-level change during peak interglacial climate. A more dynamic cryosphere is noted under both late Pliocene and last glacial cycle climate conditions, while relative sea-level changes during the last deglaciation appear to correspond closely with individual ice-sheet deglaciation. Lastly, relative sea-level change during peak interglacial conditions may have fluctuated by as much as a meter, although the sources of such variability (Greenland, Antarctica or elsewhere) remain elusive.

The most significant climate cooling of the Holocene is centred on 8.2 kyr BP (the ‘8.2 event’). Its cause is widely attributed to an abrupt slowdown of the Atlantic Meridional Overturning Circulation (AMOC) associated with the sudden drainage of Laurentide proglacial Lakes Agassiz and Ojibway, but model simulations have difficulty reproducing the event with a single-pulse scenario of freshwater input. Several lines of evidence point to multiple episodes of freshwater release from the decaying Laurentide Ice Sheet (LIS) between ∼8900 and ∼8200 cal yr BP, yet the precise number, timing and magnitude of these events – critical constraints for AMOC simulations – are far from resolved. Here we present a high-resolution relative sea level (RSL) record for the period 8800 to 7800 cal yr BP developed from estuarine and salt-marsh deposits in SW Scotland. We find that RSL rose abruptly in three steps by 0.35 m, 0.7 m and 0.4 m (mean) at 8760–8640, 8595–8465, 8323–8218 cal yr BP respectively. The timing of these RSL steps correlate closely with short-lived events expressed in North Atlantic proxy climate and oceanographic records, providing evidence of at least three distinct episodes of enhanced meltwater discharge from the decaying LIS prior to the 8.2 event. Our observations can be used to test the fidelity of both climate and ice-sheet models in simulating abrupt change during the early Holocene.

Mangrove sedimentary deposits are sensitive to changes in sea level and can be used to reconstruct mid- to late Holocene sea-level fluctuations in intermediate and far-field locations, distant to the former polar ice sheets. However, they can be difficult to date using 14C because mangrove sediment can contain mixtures of carbon of different ages. The two main potential causes of error are younger mangrove roots penetrating down through the sediment column and bioturbation by burrowing animals which moves carbon up and down the sediment column. Both processes may introduce carbon not representative of the age of deposition of the layer being dated. This study reports new 14C dates on organic concentrates (10–63 µm) from mangrove sediments from Makoba Bay on Zanzibar (Unguja) where previous bulk sediment 14C age–depth profiles contained inversions and were therefore less useful for relative sea-level (RSL) reconstruction. Dates on organic concentrates provide a more coherent sequence of 14C ages compared with those from bulk sediments. These new data provide an improved environmental history and mid- to late Holocene RSL record for this site. Our reconstructions show that RSL rose during the mid-Holocene and reached within −3.5 m of present by c. 7900 cal. yr BP. RSL slowed as it reached present at or shortly after c. 7000 cal. yr BP, with falling and/or stable RSL from c. 4400 cal. yr BP to present. We are not able to determine whether there was a RSL highstand above present on Zanzibar during the mid- to late Holocene. The RSL reconstruction agrees broadly with changes predicted by the ICE-5G geophysical model, which includes 4 m of ice equivalent sea-level rise between 7000 and 4000 cal. yr BP. Our new dating approach has the potential to provide improved chronologies with which to interpret sea level data from this and other mangrove environments.

Unravelling patterns of relative sea-level change during previous interglacials enhances our understanding of ice sheet response to changing climate. Temperate-latitude estuarine environments have the potential to preserve continuous records of relative sea level from previous interglacial (warm) periods. This is important because, currently, we typically only have snapshots of sea-level highstands from low-latitude corals and raised palaeoshoreline indicators while the (continuous) deep-sea oxygen isotope record only provides indirect evidence of sea-level changes. Here, we focus on the Nar Valley in eastern England, in which is preserved evidence of a late middle-Pleistocene marine transgression more than 20 vertical metres in extent. By applying a model of coastal succession and sea-level tendencies, as used in Holocene sea-level studies, we assess the mode (abrupt versus gradual) of sea-level change recorded by the interglacial Nar Valley sequences. Compiled palaeo-stratigraphic evidence comprising foraminifera, pollen and amino acid racemization dating, suggests that the mode of sea-level change in the Nar Valley interglacial sequence was gradual, with potentially two phases of regional transgression and relative sea-level rise occurring at two separate times. The first phase occurred during the latter part of marine oxygen isotope stage (MIS) 11 from ˜8 to 18 m OD; and, the second phase potentially occurred during early MIS 9 from ˜-3 to 3 m OD (with long-term tectonic uplift included in these estimates). We cannot conclusively preclude an alternative MIS 11 age for these lower sediments. The lack of indicators for rapid sea-level oscillations in the Nar Valley adds weight to an argument for steady melt of the ice sheets during both MIS 11 and 9.

A contribution to the PAGES' PALSEA2 Working Group. ABSTRACT: This paper presents new Holocene relative sea level (RSL) data collected from isolation basins close to the town of Paamiut in south west Greenland. The data shows a rapid fall from a marine limit of c. 52masl at c. 10.9cal.ka BP to close to present by c. 9.5cal.ka BP at rates of up to c. 32mm/yr falling below present for the majority of the Holocene before rising to present in the last 2000 years. The elevation of the RSL lowstand is not well constrained but was at least below 3m. This pattern of rapid RSL fall during the early Holocene matches the pattern seen at other southern Greenland locations suggesting rapid largely simultaneous ice retreat from the area surrounding the Qassimiut Lobe at the start of the Holocene occurring c. 2000 years after the initial deglaciation of the extreme southern tip of Greenland. The RSL histories from this and other southern Greenland locations are distinct to those recorded further north along the west coast and are in broad agreement with a pattern of vertical land motion and RSL predicted by the Huy2 model (Simpson etal. 2009) which predicts an 80m drop in the contribution of vertical land motion to RSL at 10cal.ka BP between Sisimiut and Paamiut on the west coast. Despite this broad scale spatial agreement between the RSL data and the Huy2 model it fails to satisfactorily predict the Holocene RSL histories at Paamiut and other southern Greenland locations. Sensitivity tests indicate that the data model misfits are most likely due to an over estimate of the forcing during the Holocene Thermal Maximum (or the response to this forcing) in southern Greenland and error in the North American ice sheets component of the background deglaciation model. Our new data suggests that much of the southern part of the ice sheet acted differently to the area further north. However RSL changes at Paamiut are also largely impacted by regional and larger scale processes including a bulls eye of uplift centred on the west the impact of the Holocene Thermal Maximum and the influence of the collapse of the North American ice sheets. © 2013 Elsevier Ltd.

Precisely-dated records of palaeovegetation and reconstructed palaeoclimate are presented from three lakes in northernmost Finnmark. The lakes lie adjacent to the southern shore of the Barents Sea and are located along a west–east transect. The three records are used to reconstruct spatial patterns in regional vegetation and climatic history since 13,900 cal yr BP. Longer-term shifts in treeline position and in the position of the Pinus–Betula ecotone are recorded. In addition, especially during the regional Holocene thermal maximum, the latter exhibited strong periodic fluctuations. The number and strength of these fluctuations that were recorded at each of the three sites differed systematically, with fewer and weaker fluctuations seen at the easternmost site, in particular. The patterns revealed are used to test the hypothesis that variations in the strength of the North Cape Current have been of primary importance as the proximal driver of climatic variability in the region since deglaciation. The results provide strong support for this hypothesis during the Holocene, the strong periodic fluctuations during the regional Holocene thermal maximum in particular being consistent with the proposed mechanism. During the Lateglacial and earliest Holocene the patterns are less clear, but nonetheless also consistent with the proposed mechanism. Further work on precisely-dated marine sediment cores will be necessary to understand the factors leading to the periodic and longer-term variations in strength of the North Cape Current.

High Arctic raised beaches provide evidence for changes in relative sea-level (RSL), sea-ice extent, storminess, and variations in sediment supply. In many High Arctic areas, driftwood and whale bone are usually the preferred targets for radiocarbon dating, with marine shells a third choice because of their often large age and height uncertainties with respect to former sea level. Here we detail a new approach to sampling marine shells that reduces these problems by targeting juvenile, articulated specimens of Astarte borealis that are washed onto the beach under storm conditions and become incorporated into the beach crest. Radiocarbon dates from articulated valves of A. borealis from eight raised beaches from Billefjorden, Svalbard, provide a chronology for Holocene beach ridge formation and RSL change that compares favourably to the most precise records developed from elsewhere in Svalbard using driftwood or whale bone. We demonstrate the value of this new approach by comparing our record with previously published RSL data from eastern Svalbard to test different models of Late Weichselian ice load in this region. We find support for a major ice dome centred south and east of Kong Karls Land but no evidence for a significant ice dome located over easternmost Spitsbergen or southern Hinlopen Strait as proposed from recent marine geophysical survey. The approach is potentially applicable elsewhere in Svalbard and the High Arctic to address questions of RSL change and beach ridge chronology, and hence wider questions regarding palaeoclimate and ice load history.

Relative sea level (RSL) data provide important long-term (century to millennial-scale) constraints on ice load history in Greenland. In this paper we present the results of a litho-, bio- and chronostratigraphic study designed to reconstruct RSL during the last millennium from salt marsh deposits recovered from a field site near to the town of Sisimiut, west Greenland. The stratigraphy at three marshes typically records an upwards transition from freshwater to salt marsh deposits. We use a quantitative (transfer function) and subjective model to reconstruct palaeomarsh elevation and changes in mean tide level (MTL) from 16 sediment profiles from these marshes. These palaeomarsh elevations are placed in a chronological framework established by 18 radiocarbon dated index points. Both models yield similar results and show MTL rose from −0.60 ± 0.20 m at c. 600 cal a BP to reach −0.10 ± 0.20 m at c. 400 cal a BP. After this time, MTL remained close to present (±0.20 m) until the present day although low sedimentation rates limit the resolution of our reconstructions during this interval. The initial rise in RSL can be explained by the dominance of non-Greenland processes, notably the collapse of the Laurentide forebulge, over local (Greenland) solid Earth uplift caused by postglacial ice unloading. This is despite some reloading of the crust that occurred during the neoglacial expansion of the Greenland Ice Sheet in this part of west Greenland. The slow-down in RSL at 400 cal a BP does not record either a change in the rate of Laurentide forebulge collapse or a change in eustatic sea level. We argue instead that this slow-down records the effects of a sustained reduction in local (Greenland) ice mass that persists over most of the past 400 years. The latter interval is widely acknowledged as a period of generally cooler than present conditions associated with the later stages of the Little Ice Age. During this period, field evidence suggests that in many areas the ice sheet had reached its maximum late Holocene extent. It is not obvious at this stage how to reconcile an expanding ice sheet with a reduction in ice load during this interval although we hypothesise it could reflect one or more of; i) a change in ice sheet dynamics; ii) reduced mass accumulation caused by cold and dry conditions, and; iii) a lagged response to earlier periods of climate warming.

The offshore and coastal geomorphology of southwest Greenland records evidence for the advance and decay of the Greenland Ice Sheet during the Last Glacial Maximum. Regional ice flow patterns in the vicinity of Sisimiut show an enlarged ice sheet that extended southwestwards on to the shelf, with an ice stream centred over Holsteinsborg dyb. High level periglacial terrain composed of blockfield and tors is dated to between 101 and 142 ka using 26Al and 10Be cosmogenic exposure ages. These limit the maximum surface elevation of the Last Glacial Maximum ice sheet in this part of southwest Greenland to ca 750–810 m asl, and demonstrate that terrain above this level has been ice free since MIS 6. Last Glacial Maximum ice thickness on the coast of ca 700 m implies that the ice sheet reached the mid to outer continental shelf edge to form the Outer Hellefisk moraines. Exposure dates record ice surface thinning from 21.0 to 9.8 ka, with downwasting rates varying from 0.06 to 0.12 m yr−1. This reflects strong surface ablation associated with increased air temperatures running up to the Bolling Interstadial (GIS1e) at ca 14 ka, and later marine calving under high sea levels. The relatively late retreat of the Itilleq ice stream inland of the present coastline is similar to the pattern observed at Jakobshavn Isbrae, located 250 km north in Disko Bugt, which also retreated from the continental shelf after ca 10 ka. We hypothesise that the ice streams of West Greenland persisted on the inner shelf until the early Holocene because of their considerable ice thickness and greater ice discharge compared with the adjacent ice sheet.

Temperate latitude salt marshes are a proven environment from which high precision (±0.10–0.20 m) relative sea level (RSL) records can be developed over recent decades and centuries. Such records provide an important link between millennial histories of RSL change and instrumental records. The high latitude salt marshes in Greenland have not previously been explored as potential archives of recent RSL change. Here we develop four diatom-based transfer functions using contemporary diatom data collected from three salt marshes located 40 km south of the coastal town of Sisimiut, West Greenland. Our preferred model has a good fit between observed and predicted elevations ( r 2 = 0.94) and a root mean square error prediction of ±0.19 m. We apply the four models to a short sediment profile collected from one of the marshes that formed between c. 600 cal. year BP and the present. Three of the four models predict the same trend in which RSL rose from −0.55 ±0.19 m mean tide level (MTL) to −0.05 ± 0.19 m MTL between c. 600 and 400 cal. year BP at a rate of c. 2.7 mm year −1 . After 400 cal. year BP RSL slowed and remained stable until the present day. The results of this study demonstrate that Greenland salt marshes are potentially valuable archives of data for developing quantitative estimates of RSL change during the last few centuries, thereby bridging the gap between existing millennial-scale approaches and more recent direct observations of ice sheet behaviour and associated vertical land motions.

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.

The Kuannersuit Glacier surged 11 km between 1995 and 1998. The surge resulted in the formation of an ice cored thrust moraine complex constructed by subglacial and proglacial glaciotectonic processes. Four main thrust zones are evident in the glacier snout area with phases of compressional folding and thrusting followed by hydrofracture in response to the build-up of compressional stresses and the aquicludal nature of submarginal permafrost and naled. Various types of stratified debris-rich ice facies occur within the marginal zone: The first (Facies I) comprises laterally continuous strata of ice with sorted sediment accumulations, and is reworked and thrust naled ice. The second is laterally discontinuous stratified debris-rich ice with distinct tectonic structures, and is derived through subglacial extensional deformation and localised regelation (Facies II), whilst the third type is characterised by reworked and brecciated ice associated with the reworking and entrainment of meteoric ice (Facies III). Hydrofracture dykes and sills (Facies IV) cross-cut the marginal ice cored thrust moraines, with their sub-vertically frozen internal contact boundaries and sedimentary structures, suggesting supercooling operated as high-pressure evacuation of water occurred during thrusting, but this is not related to the formation of basal stratified debris-rich ice. Linear distributions of sorted fines transverse to ice flow, and small stratified sediment ridges that vertically cross-cut the ice surface up-ice of the thrust zone relate to sediment migration along crevasse traces and fluvial infilling of crevasses. From a palaeoglaciological viewpoint, marginal glacier tectonics, ice sediment content and sediment delivery mechanisms combine to control the development of this polythermal surge valley landsystem. The bulldozing of proglacial sediments and the folding and thrusting of naled leads to the initial development of the outer zone of the moraine complex. This becomes buried in bulldozed outwash sediment and well-sorted fines through surface ablation of naled. Up-ice of this, the heavily thrust margin becomes buried in sediment melted out from basal debris-rich ice and subglacial diamicts routed along thrusts. These mechanisms combine to deliver sediment to supraglacial localities, and promote the initial preservation of structurally controlled moraines through insulation, and the later development of kettled dead ice terrain.

The southeast sector of the Greenland Ice Sheet is currently experiencing rapid changes in mass balance and ice sheet dynamics at low elevations. However, to what extent these changes are typical of the behaviour of this sector of the ice sheet is uncertain, as our understanding of the longer-term controls on ice sheet dynamics in this region is limited. Two models exist for Last Glacial Maximum (LGM) ice sheet configuration in east Greenland. The first “minimum” model envisages a restricted ice sheet, with exposed nunataks in coastal areas and limited ice extent onto the continental shelf fed by ice flowing through bedrock troughs. A second, “maximum” model entails a thicker ice sheet with limited coastal nunataks, and ice filling the coastal valleys and extending across the entire continental shelf. Radiocarbon dates on foraminifera collected from seabed cores on the southeast Greenland continental shelf suggest that the ice sheet reached a maximum extent at ca 22 kcal. yr, before retreating, perhaps as early as ca 17 kcal. yr BP, and reaching the present coast at ca 10 kcal. yr BP. This paper presents the results of a study designed to test these different ice sheet models based on geomorphological mapping and cosmogenic isotope analyses in the Torqulertivit Imiat valley, an area to the east of the coastal town of Ammassalik. 26Al and 10Be measurements on abraded bedrock surfaces in terrain above local trimlines yield surface exposure ages of ca 11.8–9.9 ka. This demonstrates warm-based glacial erosion of high level surfaces (ca 740 m asl), followed by trimline formation during deglaciation and intense postglacial weathering. Our work constrains minimum ice thickness during the LGM to at least 740 m and supports a “maximum” ice sheet model in this sector of the GIS. Ice sheet retreat from the continental shelf to the southern edge of Sermilik Fjord is dated to ca 11.1–9.7 ka and helps to constrain the timing of the early Holocene retreat of the Helheim Glacier ice stream. Within the Torqulertivit Imiat valley, age determinations from glacially abraded terrain above the local marine limit on the coast (11.1–9.7 ka) and those from 10 km up-valley (12.8–9.9 ka), suggest rapid surface ablation during these intervals, coincident with rapid atmospheric warming observed in the Greenland ice core records.

This study investigates the marginal subglacial bedrock bedforms of Jakobshavns Isbrae, West Greenland, in order to examine the processes governing bedform evolution in ice stream and ice sheet areas, and to reconstruct the interplay between ice stream and ice sheet dynamics. Differences in bedform morphology (roche moutonnee or whaleback) are used to explore contrasts in basal conditions between fast and slow ice flow. Bedform density is higher in ice stream areas and whalebacks are common. We interpret that this is related to higher ice velocities and thicker ice which suppress bed separation. However, modification of whalebacks by plucking occurs during deglaciation due to ice thinning, flow deceleration, crevassing and fluctuations in basal water pressure. The bedform evidence points to widespread basal sliding during past advances of Jakobshavns Isbrae. This was encouraged by increased basal temperatures and melting at depth, as well as the steep marginal gradients of Jakobshavns Isfjord which allowed rapid downslope evacuation of meltwater leading to strong ice/bedrock coupling and scouring. In contrast to soft-bedded ice stream bedforms, the occurrence of fixed basal perturbations and higher bed roughness in rigid bed settings prevents the basal ice subsole from maintaining a stable form which, coupled with secondary plucking, counteracts the development of bedforms with high elongation ratios. Cross-cutting striae and double-plucked, rectilinear bedforms suggest that Jakobshavns Isbrae became partially unconfined during growth phases, causing localised diffluent flow and changes in ice sheet dynamics around Disko Bugt. It is likely that Disko Bugt harboured a convergent ice flow system during repeated glacial cycles, resulting in the formation of a large coalesced ice stream which reached the continental shelf edge.

Benthic foraminifera from two cores collected from Disko Bugt, a large marine embayment in West Greenland, are used to investigate hydrographic changes during the mid to late Holocene. The records document fluctuations in the West Greenland Current (WGC) linked to large-scale changes in North Atlantic circulation and, for one core, impacts of local climate changes. In particular, changes in the cold East Greenland Current (EGC) and the warm, more saline Irminger Current (IC) influence the WGC and propagate into Disko Bugt. The cores record subsurface warming associated with the `Holocene Thermal Maximum' (HTM) from c. 6 to 5 ka cal. BP. Gradual cooling of WGC from 5 ka cal. BP was interrupted by an abrupt warm interval from 3.9 to 3.5 ka cal. BP, before cooling became more prominent from 3.5 to 2 ka cal. BP. This cold period corresponds to the well-documented Northern Hemisphere cooling of the neoglacial and we interpret it as reflecting enhanced flux from the EGC and reduced IC flux to the WGC in Disko Bugt. Colder subsurface conditions from 3.5 ka cal. BP correspond to major hydrographic and climate changes elsewhere in West Greenland, reflecting the final transition from HTM to the neoglacial in this region. Relatively warm conditions identified from c. 2.0 to 1.4 ka cal. BP are followed by gradual cooling to 0.7 ka cal. BP, interrupted by a brief warm episode around 1 ka cal. BP. The late-Holocene fluctuations in WGC recorded in Disko Bugt can be linked to North Atlantic oceanographic changes identified on the East Greenland and North Icelandic shelf.

The sediments of a small lake on Nordkinnhalvoya, Finnmark, Norway, were investigated in order to test the hypothesis that this region was sensitive to centennial–millennial climatic fluctuations during the Holocene related to changes in ocean circulation. Sedimentation at the site began during the Younger Dryas, although the site chronology, developed using a series of 14C age measurements, reveals an early Holocene hiatus in accumulation. Pollen analysis confirmed that the regional vegetation responded to Holocene climatic variability at centennial–millennial time scales and provided data used to make quantitative palaeoclimate reconstructions. The latter indicate that marked changes in seasonality characterised Holocene climatic fluctuations. Intervals with warmer summers, higher temperature sums and higher precipitation, but cooler winters and generally reduced moisture availability, alternated with intervals with cooler summers, lower temperature sums, lower precipitation, warmer winters and greater moisture availability. The former conditions were more prevalent between ca 8950 and 3950 cal BP, whereas the latter were predominant before ca 8950 and since ca 3950 cal BP. Sediment geochemistry indicates minerogenic material deposited in the lake was probably derived from two or more distinct sources or transport pathways that differed in their responses to palaeoclimatic conditions. A series of cryptotephras were located, although the small size of the shards rendered them unsuitable for electron microprobe analyses. Time-series analysis of pollen analytical and sediment geochemical data indicates that each exhibits statistically significant periodic behaviour (at periods of ca 190, 410, 1050, 1650 and 1810 yr). The periods detected suggest this behaviour may reflect regional expression of climate system responses to solar variability and/or of effects upon tides and ocean circulation of periodic lunar orbital variation. Comparison with records of fluctuations in ocean thermohaline circulation strength indicate some concordance with respect to timing of warmer and cooler intervals, but also some differences. The 8.2 ka event, that is evident in marine records from the Barents Sea, is clearly expressed by both the palaeovegetation and geochemical records. Distinctive temporal behaviour of the palaeovegetation and of different geochemical components indicates complexity in the underlying causes and mechanisms of regional climatic variability; ocean circulation variability alone cannot account for the complex climatic variability observed.

We present a new, diatom-based sea-level reconstruction for Iceland spanning the last similar to 500 years, and investigate the possible mechanisms driving the sea-level changes. A sea-level reconstruction from near the Icelandic low pressure system is important as it can improve understanding of ocean atmosphere forcing on North Atlantic sea-level variability over multi-decadal to centennial timescales. Our reconstruction is from Vioarholmi salt marsh in Snafellsnes in western Iceland, a site from where we previously obtained a 2000-yr record based upon less precise sea-level indicators (salt-marsh foraminifera). The 20th century part of our record is corroborated by tide-gauge data from Reykjavik. Overall, the new reconstruction shows ca 0.6 m rise of relative sea level during the last four centuries, of which ca 0.2 m occurred during the 20th century. Low-amplitude and high-frequency sea-level variability is superimposed on the pre-industrial long-term rising trend of 0.65 m per 1000 years. Most of the relative sea-level rise occurred in three distinct periods: AD 1620-1650, AD 1780-1850 and AD 1950-2000, with maximum rates of similar to 3 +/- 2 mm/yr during the latter two of these periods. Maximum rates were achieved at the end of large shifts (from negative to positive) of the winter North Atlantic Oscillation (NAO) Index as reconstructed from proxy data. Instrumental data demonstrate that a strong and sustained positive NAO (a deep Icelandic Low) generates setup on the west coast of Iceland resulting in rising sea levels. There is no strong evidence that the periods of rapid sea-level rise were caused by ocean mass changes, glacial isostatic adjustment or regional steric change. We suggest that wind forcing plays an important role in causing regional-scale coastal sea-level variability in the North Atlantic, not only on (multi-)annual timescales, but also on multi-decadal to centennial timescales.

Holocene data from the Caribbean and the Atlantic coast of South America have been critically assessed and a subset of the best quality data are presented. These data cover a large north–south geographic extent and display a distinct spatial variation. We make the first comparisons of this data set to predictions based on a realistic model of glaciation-induced sea-level change with the main aims of understanding the cause of the observed spatial trend and estimating a eustatic signal for the Holocene. The spatial variation is dominated by the influence of the ice and ocean mass redistribution on sea-level change, with the ice-induced effect dominating the observed north–south trend. A best-fitting model is applied to estimate a Holocene eustatic signal from the observations. We find that the model-corrected data are consistent with a relatively rapid rise of 7–8 mm/yr in the early Holocene with a marked reduction in this rate around 7 cal. kyr BP. From this time until present, the model-corrected data suggest that the volume of mass transfer between ice sheets and oceans was no more than ∼ ± 1 m (eustatic sea-level equivalent).

New relative sea-level (RSL) data from Disko Bugt, a large marine embayment in West Greenland, are used to examine the deglacial history of the Jakobshavns Isbrae ice stream. RSL data show rapid deglaciation after 10.3rka cal. yr BP. Once deglaciation began, a bedrock high in the west of the bay exerted no discernible influence on the deglacial chronology. Following initial rapid retreat, ice stream recession slowed as it approached the eastern shores of the bay. Seabed elevations increase here and the ice stream terminus lingered for several thousand years before retreating into the narrow bedrock-confined Jakobshavns Isfjord. The seabed topography of Disko Bugt includes several deep channels which probably record the former course of the ice stream. Using a simple water depth/calving velocity relationship it is estimated that the maximum calving velocity on deglaciation was c. 4.8rkm am1. This is less than the present rate (6-7rkmram1), although ice discharge was two to four times that observed today. Initiation of rapid ice stream retreat was probably caused by ice stream thinning and increased surface melting. A critical point in time was the retreat of the ice stream from shallow continental shelf waters (c. 400rm) into the deep bedrock trough (>800rm) which marks the entrance to Disko Bugt.

Research campaigns over the last decade have yielded a growing stream of data that highlight the dynamic nature of Arctic cryosphere and climate change over a range of time scales. As a consequence, rather than seeing the Arctic as a near static environment in which large scale changes occur slowly, we now view the Arctic as a system that is typified by frequent, large and abrupt changes. The traditional focus on end members in the system – glacial versus interglacial periods – has been replaced by a new interest in understanding the patterns and causes of such dynamic change. Instead of interpreting changes almost exclusively as near linear responses to external forcing (e.g. orbitally-forced climate change), research is now concentrated on the importance of strong feedback mechanisms that in our palaeo-archives often border on chaotic behaviour. The last decade of research has revealed the importance of on-off switching of ice streams, strong feedbacks between sea level and ice sheets, spatial and temporal changes in ice shelves and perennial sea ice, as well as alterations in ice sheet dynamics caused by shifting centres of mass in multi-dome ice sheets. Recent advances in dating techniques and modelling have improved our understanding of leads and lags that exist in different Arctic systems, on their interactions and the driving mechanisms of change. Future Arctic research challenges include further emphases on rapid transitions and untangling the feedback mechanisms as well as the time scales they operate on.

The mid- and late-Holocene vegetation of Walland Marsh (situated on the south coast of England) is reconstructed through multi-proxy (pollen, plant macrofossil and diatom analyses and radiocarbon dating) investigations of an extensive peat layer at five locations. These data, combined with previous work from southern England and regions bordering the southern North Sea, are used to assess the processes controlling the development of, and successional trends in, coastal mire vegetation. On Walland Marsh fen carr vegetation, with Alnus glutinosa , was sustained at sites influenced by the flow of base-rich groundwater from the uplands and more widely promoted by rising relative sea level (RSL). Acidophilous vegetation, including ombrotrophic bog (with Sphagnum imbricatum ssp. austinii present), developed at sites isolated from base-rich water. Spatial isolation was enhanced by the accumulation of peat, while vertical isolation was induced by a decline in the rate of RSL rise and, at ca. 2600 cal. yr BP, by climate change. Similar patterns of mire development can be identified in the other areas reviewed. Vegetation development in coastal lowlands reflects a unique interplay between regional and local processes. These processes can only be disentangled by multi-site investigations.

A common problem facing sea-level researchers lies in determining the cause of rapid changes observed in coastal stratigraphic sequences. Such changes are commonly ascribed to the interaction of processes that operate over differing temporal and spatial scales, i.e. rapid local and regional sea-level trends and storm magnitude/frequency. At least some of the difficulty in distinguishing between these processes lies in the often limited stratigraphic database upon which palaeoenvironmental reconstruction is based. Here, we present the results of detailed morphostratigraphic and micropalaeontological investigations from a series of sites located at the interface between the protective gravel barrier complex of Dungeness and the barrier estuary sediments of Romney Marsh, England. A period of rapid coastal regression is identified between c. 4500 and 3000 cal. yrs BP, during which time the sea level continued to rise but was outpaced by sediment accretion and peat accumulation. A subsequent acceleration in the rate of rise led to a reversal of this excess of sediment supply over sea-level rise, and to rapid inundation of the entire barrier estuary between c. 2800 and 1900 cal. yrs BP. At the local level, coastal development reflects an interdependence between storms and long-term relative sea-level (RSL) rise; processes which lie at opposite ends of the magnitude/frequency spectrum. However, when viewed from a holistic perspective encompassing the Holocene development of Romney Marsh as a whole, storms are of secondary importance in controlling coastal evolution. Rather, our study suggests that at this macro-scale coastal evolution responds primarily to the combined effects of RSL rise and sediment supply

Much geological evidence points to repeated plate-boundary earthquakes on the Cas-cadia subduction zone, Pacific Northwest USA. Current land motions, calculated. using shortterm (-1 100 krn’. High precision microfossil and RSL data from Johns River (Washington) and Netarts Bay (Oregon) register repeated episodes of late-Holocene coseismic submergence. This is contrary to the coseismic uplift expected, based on differences in uplift rates calculated using late-Quaternary marine terrace data from the region. Moreover, the magnitudes of coseismic submergence inferred from these RSL data are typically half the modelled predictions based on current deformation rates. Lastly, we identify evidence from Netarts Bay for pre-seismic RSL rise of up to 0.4 mm yr’ in the decades immediately preceding each episode of marsh burial. Together, our findings shine new light on models of rapid relative sea-level rise in the Pacific Northwest, and highlight the need to strengthen further the dialogue between long-term geological and short-term geodetic studies in this region.

New stratigraphic data collected from six sites in the Humber estuary establish a record of Holocene relative sea-level (RSL) change, and enable testing of four possible causes of rapid coastal change: sea-level rise, changes in sedimentation, storm-surge history, and human impact. Mean high water of spring tides (MHWST) in the Humber rose from c. 9 m OD at 7500 cal. yrs BP to 0 m OD by 4000 cal. yrs BP, at an average long-term rate of c. 3.9 mm yr-1. After this, the rate of rise gradually decreased to c. 1 mm yr’. Discrete episodes of rapid RSL rise are not identified although their absence may reflect limited data availability. However, we do observe two episodes of rapid coastal change in the Humber estuary. The first occurs between c. 3200 and 1900 cal. yrs BP, as marine conditions expand to their Holocene maximum and then contract. This pattern of coastal development differs from that in the East Anglian Fenlands, suggesting local processes control sedimentation at one or both of these sites. The second period of rapid change relates to a well-documented episode of increased storm surge activity in the Humber estuary and elsewhere in the UK and the North Sea region between c. 700 and 500 cal. yrs BP. Coastal development during this period varies considerably with erosion, accretion and flooding in different parts of the estuary system. Finally, we examine evidence for accelerated sediment delivery to the Humber estuary due to woodland clearance and prehistoric agriculture from 5700 cal. yrs BP onwards. Maximum sediment input is likely at c. 3200 to 1900 cal. yrs BP; a period which tentatively correlates with an episode of estuary infilling and shoreline advance.

This is the second investigation where we apply the methods and scientific framework common to sea-level investigations in northwest Europe to test a model of coseismic land subsidence followed by land uplift during interseismic strain accumulation, used to explain alternating peat–mud couplets of late Holocene age found in many of the estuaries of the Pacific Northwest of the USA and Canada. Recent studies in this region interpret such couplets as the product of repeated large (magnitude 8 or 9) earthquakes on the Cascadia subduction zone. Stratigraphic investigations of the intertidal sediments at Netarts Bay, Oregon, using lithological, pollen and diatom analyses reveal different types of submergence associated with peat–mud couplets during the last 3500 yr. Three peat-mud couplets record gradual sedimentation changes within an infilling body of water. Four other couplets record rapid submergence, burial of tidal marshes and their replacement by low marsh environments. In three of the events rapid submergence is small, 0–0.5 m. The most recent marsh submergence event, around AD 1700, was 0.4±0.3 m. Most of the buried peats contain microfossil evidence for a gradual increase in marine influence before the rapid change from organic to minerogenic sedimentation. Similar gradual changes are common in comparable palaeoenvironments on non-seismic coasts and are strong evidence against a simple interseismic strain accumulation-coseismic subsidence model. One hypothesis is that the gradual increase in marine influence before each submergence represents pre-seismic relative sea-level rise caused by a reduction in the rate of land uplift. The microfossil analyses provide evidence of three stages within an earthquake deformation cycle: coseismic subsidence; interseismic land uplift; and pre-seismic reduction in the rate of land uplift. At present the microfossil data do not differentiate between rapid post-seismic land uplift and rapid sedimentation.

Many of the estuaries of the Pacific Northwest of the U.S.A. and Canada contain stratigraphic sequences typified by alternating peat-mud couplets. Recent studies in this region interpret such couplets as the product of repeated large (magnitude S or 9) earthquakes on the Cascadia subduction zone. The resultant pattern of land-level movements is described by a model, the ‘earthquake deformation cycle’, of coseismic land subsidence followed by land uplift during interseismic strain accumulation. However, peat-mud couplets similar to those recorded in the Pacific Northwest are found on other less tectonically active temperate-latitude coasts, such as northwest Europe and the Atlantic coast of the U.S.A., where they have been interpreted as the product of non-seismic coastal processes. In this paper we apply the methods and scientific framework common to sea-level investigations in northwest Europe to a sequence of peat-mud couplets recorded in the lower Johns River, an estuary in southern Washington, to provide a test of the ‘earthquake deformation cycle’. Stratigraphic investigations of the intertidal sediments along the lower Johns River, using lithological, pollen, diatom and foraminiferal data, show evidence for eight coastal submergence events during the last 5000 years. To evaluate the ‘earthquake deformation cycle’ we assess the lateral extent of peat-mud couplets, the synchroneity of submergence, the presence of tsunami deposits accompanying submergence, and the suddenness and amount of submergence. Each submergence is shown to be accompanied by changes in coastal sedimentation broadly commensurate with those predicted by the ‘earthquake deformation cycle’, demonstrating the continued intermittent seismic activity of the Cascadia subduction zone throughout the mid and late-Holocene. Quantitative analyses of contemporary and fossil biostratigraphic data, using TWINSPAN and Detrended Correspondence Analysis, enable us to estimate the magnitude of submergence accompanying each peat-mud couplet. One event was accompanied by submergence of about 1.5 m or more, four events by intermediate submergence of about 1±0.5 m, and a further three events by submergence of

Isolation basins are natural topographic depressions that at various times in their history may be connected to or isolated from the sea by changes in relative sea-level (RSL). They provide a valuable source of data for tracking large scale (tens of meters) changes in RSL over millennia, as well as quiet-water depositional environments where abrupt changes caused by tsunami, iceberg roll or storms may be recorded. In this paper we review isolation basins as sources of RSL data with a particular focus on their use in Greenland to constrain the Holocene history of the ice sheet. A new RSL curve from Disko Fjord, West Greenland is presented, which shows that local ice free conditions were established at c. 11 k cal yr BP, after which RSL fell rapidly from a marine limit at c. 80 m to reach close to present sea level by c. 4 k cal yr BP. We compare this record with other isolation basin RSL data from six other sites in Disko Bugt and note a strong northwest/southeast differential rebound across the area during the early and mid-Holocene that reflects variations in ice load history. We compare the Disko Bugt data with other previously published isolation basin RSL records from Sisimiut (central West Greenland), Nanortalik (south Greenland) and Ammassalik (southeast Greenland). RSL fell below present during the early-Holocene at Nanortalik (c. 10 k cal yr BP) and during the mid to late Holocene elsewhere before rising to present. These differences reflect variations in the timing and amount of Greenland ice load change since the last glacial maximum, as well as non-Greenland processes, notably the collapse of the Laurentide forebulge and also changes in ice equivalent sea-level. Isolation basin data have relatively small age and height uncertainties compared with other RSL indicators, enabling them to resolve between different earth and ice sheet models, especially during periods of large ice load and RSL change.

Fields of glacioisostatically uplifted beach ridges on the eastern Varanger Peninsula coast in northern Norway record the occurrence of major storms since deglaciation. More than 70 radiocarbon dates of palaeoshoreline indicators establish the Late Weichselian and Holocene history of beach-ridge building and relative sea-level change. Optimal ridge-building in the region requires sustained, strong easterlies driving high waves across the Barents Sea. Such winds occur when low pressure systems are forced across the North Sea and the Baltic landmass to the region of the Gulf of Bothnia and the Kola Peninsula. This situation probably frequently occurs during transition periods from milder to cooler climate in the region. The beach-ridge morphology reveals a fall of local sea level following the stormy episodes. Over the short term, this is related to the end of storm-induced set-up and the termination of mild-phase-related warm coastal currents. Over the long term, local sea-level falls with the onset of sustained calm winter-type conditions and continued glacioisostatic uplift. Pre- and early-Holocene changes in climate regime occurred with a frequency of several decades to several centuries. The mid- to late-Holocene records show increased climatic stability, transitions occurring with less frequency, and mild phases frequently lasting many hundreds of years.

Terrestrial and marine geological archives in the Arctic contain information on environmental change through Quaternary interglacial–glacial cycles. The Arctic Palaeoclimate and its Extremes (APEX) scientific network aims to better understand the magnitude and frequency of past Arctic climate variability, with focus on the “extreme” versus the “normal” conditions of the climate system. One important motivation for studying the amplitude of past natural environmental changes in the Arctic is to better understand the role of this region in a global perspective and provide base-line conditions against which to explore potential future changes in Arctic climate under scenarios of global warming. In this review we identify several areas that are distinct to the present programme and highlight some recent advances presented in this special issue concerning Arctic palaeo-records and natural variability, including spatial and temporal variability of the Greenland Ice Sheet, Arctic Ocean sediment stratigraphy, past ice shelves and marginal marine ice sheets, and the Cenozoic history of Arctic Ocean sea ice in general and Holocene oscillations in sea ice concentrations in particular. The combined sea ice data suggest that the seasonal Arctic sea ice cover was strongly reduced during most of the early Holocene and there appear to have been periods of ice free summers in the central Arctic Ocean. This has important consequences for our understanding of the recent trend of declining sea ice, and calls for further research on causal links between Arctic climate and sea ice.

In a study of the Holocene sediments in the Hacklinge-Deal area of the East Kent Fens, Southeastern England, hand-coring data has shown that the pre-Holocene surface in this area is incised by one or more valley features, now infilled with unconsolidated Holocene sediments. A shear-wave seismic refraction survey was carried out along profiles where hand-coring had failed to penetrate to bedrock in an attempt to define the detailed form of the pre-Holocene surface. The seismic refraction work was successful because of the large velocity contrast for seismic shear-waves between the Holocene sediments and the Cretaceous chalk bedrock. The seismic data showed that the maximum depth to chalk in the area was almost 20 m, and the results obtained from one profile were subsequently confirmed by hand-coring to a depth of 9 m. Hand-coring, seismic, and Ordnance Survey spot height data have been combined to produce a first estimation of the three-dimensional form of the pre-Holocene surface in the study area.

The margin of the Greenland Ice Sheet retreated rapidly during the first few thousand years of the Holocene. During this period of relative warmth, known as the Holocene thermal maximum, ice core records identify a significant short-lived cooling event at approximately 8.4–8.0 ka cal. yr BP (the ‘GH-8.2 event’) associated with a 5–7 °C fall in mean annual air temperature over the centre of the ice sheet. In this paper we constrain the history of the ice sheet margin in Disko Bugt (west Greenland) and that of a major ice stream, Jakobshavns Isbrae, during the early Holocene, which incorporates the interval of the GH-8.2 event. Our work is based on a new relative sea-level curve and minimum age estimates for the timing of deglaciation from two field sites, combined with a review of previously published research from the study area. We identify important differences in the chronology of ice margin recession during the early Holocene, most noticeably, the margin of Jakobshavns Isbrae retreated well inland of the adjacent ice sheet at this time. We conclude that the early Holocene ‘Fjord Stade’ moraines in Disko Bugt do not record a uniform ice sheet margin response to the GH-8.2 event. Rather, these moraines are diachronous and formed between c. 10–8 ka cal. yr BP, their age varying as a function of the interplay between topography and ice sheet/ice stream dynamics. We hypothesise that one cause for the lack of an identifiable response to the GH-8.2 event is because topographic controls dominated ice sheet behaviour at this time. In lowland areas, any increase in ice sheet mass balance was probably associated with an increase in calving rather than any major advance of a grounded ice sheet margin.