Deglacial reservoir age and implications,Foxe Peninsula,Baffin Island

Marine reservoir age is reported for Foxe Basin, Canada, during deglaciation of the Laurentide Ice Sheet. Radiocarbon (¹⁴C) measurements were made on pairs of contemporaneous molluscs and Salix (willow) macrofossils, yielding a mean marine reservoir age of 985 ± 10 ¹⁴C a. Mean regional ΔR is calculated to be 615 ± 20 ¹⁴C a relative to a mean global reservoir age of ca. 400 ¹⁴C a. Previous studies in the Canadian Arctic that have been conducted on modern pre‐bomb molluscs give ΔR values of ca. 100–300 ¹⁴C a. The difference between modern and deglacial reservoir ages indicates that ΔR in Foxe Basin has changed over time, which has implications for the reconstruction of past events based on marine ¹⁴C dates. We recalculate the timing of deglaciation of Hudson Strait with this new reservoir age and relate this to the 8.2 cal. ka event. We recommend that local ΔR be determined for the time period being examined whenever possible, and that in cases where this is impossible a ΔR value of 615 ¹⁴C a be applied when calibrating marine samples from Foxe Basin and vicinity during deglaciation. Copyright © 2010 John Wiley & Sons, Ltd.     

Broughton Island–a reference area for Wisconsin and Holocene chronology and sea level changes on eastern Baffin Island

Broughton Island is 50 km from the eastern margin of the 6,000 km² Penny Ice Cap. During the early Wisconsin (> 54,000 BP) A younger glacial readvance is delimited by lateral moraines and glacio-marine deposits ¹⁴C dated at 24,100±850 BP; sea level was±18 m. During th last Wisconsin the glaciers terminated some distance inland from Broughton Island and sea alevel at 9,850±250BP was +5 m on Broughton Island. The head of Maktak Fiord, which presently contains a majour outlet glacier from the Penny Ice Cap, was deglaciated about 6,000 BP.     

Slope hummock development, Fosheim Peninsula, Ellesmere Island, Nunavut, Canada

Slope hummocks, a type of nonsorted patterned ground, are composed of stratified, organic, silty sand, and develop through the interaction of niveo-eolian deposition, solifluction, slopewash, and vegetation growth. Fields of hummocks show consistent patterns: forms on convex slopes increase in height downslope until the channel is reached, whereas those on convexo-concave slopes increase on the upper convexity but are buried by niveo-eolian deposition downslope of the snowbank remnant. These trends can be reproduced using a simple numerical model based on measured slope and snow depth profiles, sediment concentrations in the snow and solifluction rates. The model indicates that hummocks transit slopes of 20-40 m in about 2-4 ka, a time-frame that is plausible given site emergence, measured rates of solifluction, and published dates for organic horizons within hummocks on northern Ellesmere Island. Sensitivity analyses show that long-term effect of climate warming on hummock heights may differ depending on whether it is accompanied by precipitation increase or decrease. The required combination of two-sided freezing to promote plug-like movement, incomplete vegetation cover and thin snow that enable eolian erosion during winter and spring, and vegetation growth in snow-bed sites to stabilize niveo-eolian deposits may explain why these forms are important regionally but apparently are not present throughout the Arctic.     

Late Quaternary sea‐level change and evolution of Belfast Lough,Northern Ireland: new offshore evidence and implications for sea‐level reconstruction

The interplay of eustatic and isostatic factors causes complex relative sea‐level (RSL) histories, particularly in paraglacial settings. In this context the past record of RSL is important in understanding ice‐sheet history, earth rheology and resulting glacio‐isostatic adjustment. Field data to develop sea‐level reconstructions are often limited to shallow depths and uncertainty exists as to the veracity of modelled sea‐level curves. We use seismic stratigraphy, 39 vibrocores and 26 radiocarbon dates to investigate the deglacial history of Belfast Lough, Northern Ireland, and reconstruct past RSL. A typical sequence of till, glacimarine and Holocene sediments is preserved. Two sea‐level lowstands (both max. ?40 m) are recorded at c. 13.5 and 11.5k cal a bp . Each is followed by a rapid transgression and subsequent periods of RSL stability. The first transgression coincides temporally with a late stage of Meltwater Pulse 1a and the RSL stability occurred between c. 13.0 and c. 12.2k cal a bp (Younger Dryas). The second still/slowstand occurred between c. 10.3 and c. 11.5k cal a bp . Our data provide constraints on the direction and timing of RSL change during deglaciation. Application of the Depth of Closure concept adds an error term to sea‐level reconstructions based on seismic stratigraphic reconstructions.     

Sedimentary indications and absolute chronology of Holocene relative sea‐level changes retrieved from coastal lagoon deposits on Samsø, Denmark

Coastal lagoons are a typical feature of the landscape in central Denmark. The lagoons formed when basins within the inherited glacial topography were flooded by the mid‐Holocene sea‐level rise. The transgression initiated coastal geomorphological processes and prompted marine sedimentation in the inundated areas. Despite their common occurrence and wide distribution in the area, coastal lagoons and their deposits have rarely been studied as sedimentary archives. The absolute chronology established for the basal marine deposits in sediment cores retrieved from coastal lagoons on the island of Samsø, southern Kattegat Sea, central Denmark, is evidence of a nearly synchronous onset of marine sedimentation at different elevations. This is interpreted as a new indication of a period of very rapid relative sea‐level (RSL) rise between 7.6 and 7.2 ka BP. Following a period of RSL highstand, a marked facies change in the deposits from an inactive lagoon yields consistent ages of around 4.1 ka BP and may be an indication of a marked RSL fall. This study illustrates the potential of coastal lagoons as sedimentary archives for the reconstruction of RSL in SW Scandinavia and in similar coastal environments elsewhere.     

Mid‐late Holocene sea‐level variability in eastern Australia

A re‐analysis of sea‐level data from eastern Australia based on 115 calibrated C‐14 ages is used to constrain the origin, timing and magnitude of sea‐level change over the last 7000 years. We demonstrate that the Holocene sea‐level highstand of +1.0–1.5 m was reached ～7000 cal yr bp and fell to its present position after 2000 yr bp . These findings are in contrast to most previous studies that relied on smaller datasets and did not include the now common conversion of conventional C‐14 ages to calendar years. During this ～5000 year period of high sea level, growth hiatuses in oyster beds and tubeworms and lower elevations of coral microatolls are interpreted to represent short‐lived oscillations in sea‐level of up to 1 m during two intervals, beginning c. 4800 and 3000 cal yr bp . The rates of sea‐level rise and fall (1–2 mm yr^?1) during these centennial‐scale oscillations are comparable with current rates of sea‐level rise. The origin of the oscillations is enigmatic but most likely the result of oceanographic and climatic changes, including wind strengths, ice ablation, and melt‐water contributions of both Greenland and Antarctic ice sheets.     

Flooding scenarios due to land subsidence and sea‐level rise: a case study for Lipari Island (Italy)

Archaeological and instrumental data indicate that the southern sector of the volcanic island of Lipari has been subsiding for the last 2100 years due to isostatic and tectonic factors, at variable rates of up to ~11 mm a^?1. Based on this data, a detailed marine flooding scenario for 2100 AD is provided for the bay of Marina Lunga in the eastern part of the island from (1) an ultra‐high‐resolution Digital Terrain and Marine Model (DTMM) generated from multibeam bathymetry (MB) and Unmanned Aerial Vehicles (UAV), (2) the rate of land subsidence from Global Positioning System (GPS) data and (3) the regional sea‐level projections of the International Panel on Climate Change (IPCC). When land subsidence is considered, the upper bound of sea‐level rise is estimated at 1.36 m and 1.60 m for RCP4.5 and RCP8.5 climate change scenarios, respectively. Here, we show the expected impact of marine flooding at Lipari for the next 85 years and discuss the hazard implications for the population living along the shore.     

Mid‐ to late Holocene relative sea‐level change in Poole Harbour,southern England

A foraminiferal transfer function for mean tide level (MTL) is used in combination with AMS radiocarbon dated material to construct a record of relative sea‐level (RSL) change from Poole Harbour, southern Britain. These new data, based on multiple cores from duplicate sites, indicate four phases of change during the last 5000 cal. (calendar) yr: (i) rising RSL between ca. 4700 cal. yr BP and ca. 2400 cal. yr BP; (ii) stable to falling RSL from ca. 2400 cal. yr BP until ca. 1200 cal. yr BP; (iii) a brief rise in RSL from ca. 1200 cal. yr BP to ca. 900 cal. yr BP, followed by a period of stability; (iv) a recent increase in the rate of RSL rise from ca. 400–200 cal. yr BP until the present day. In addition, they suggest that the region has experienced long‐term crustal subsidence at a rate of 0.5 mm C¹⁴ yr^?1. Although this can account for the overall rise in MTL observed during the past 2500 yr, it fails to explain the changes in the rate of rise during this period. This implies that the phases of RSL change recorded in the marshes of Poole Harbour reflect tidal range variations or ‘eustatic’ fluctuations in sea‐level. Copyright © 2001 John Wiley & Sons, Ltd.     

Holocene relative sea‐level changes in Harris,Outer Hebrides,Scotland, UK

Evidence for relative sea‐level changes during the middle and late Holocene is examined from two locations on the Atlantic coast of Harris, Outer Hebrides, Scotland, using morphological mapping and survey, stratigraphical, grain size and diatom analysis, and radiocarbon dating. The earliest event identified is a marine flood, which occurred after 7982–8348 cal. a (7370 ± 80 ¹⁴C a) BP, when the sea crossed a threshold lying at ?0.08 m Ordnance Datum Newlyn (OD) (?2.17 m mean high water springs (MHWS)) before withdrawing. This could have been due to a storm or to the Holocene Storegga Slide tsunami. By 6407–6122 cal. a (5500 ± 60 ¹⁴C a) BP, relative sea levels had begun to fall from a sandflat surface with an indicated MHWS level of between 0.08 and ?1.96 m (?2.01 to ?4.05 m). This fall reached between ?0.30 and ?2.35 m (?2.39 to ?4.44 m) after 5841–5050 cal. a (4760 ± 130 ¹⁴C a) BP, but was succeeded by a relative sea‐level rise which reached between 0.54 and ?1.57 m (?1.55 to ?3.66 m) by 5450–4861 cal. a (4500 ± 100 ¹⁴C a) BP. This rise continued, possibly with an interruption, until a second sandflat surface was reached between 2.34 and ?0.26 m (0.25 to ?2.35 m) between 2952–3375 cal. a (3000 ± 80 ¹⁴C a) and 1948–2325 cal. a (2130 ± 70 ¹⁴C a) BP, before present levels were reached. The regressive episode from the earliest sandflat is correlated with the abandonment of the Main Postglacial Shoreline. It is maintained that the fluctuations in relative sea level recorded can be correlated with similar events elsewhere on the periphery of the glacio‐isostatic centre and may therefore reflect secular changes in nearshore sea surface levels. Despite published evidence from trim lines of differential ice sheet loading across the area, no evidence of variations in uplift between the locations concerned could be found. Copyright © 2009 John Wiley & Sons, Ltd.     

Late Devensian and Holocene relative sea‐level change in North Wales,UK

Deglacial sea‐level index points defining relative sea‐level (RSL) change are critical for testing glacial isostatic adjustment (GIA) model output. Only a few observations are available from North Wales and until recently these provided a poor fit to GIA model output for the British‐Irish Ice Sheet. We present results of an integrated offshore geophysical (seismic reflection), coring (drilling rig), sedimentological, micropalaeontological (foraminifera), biostratigraphical (palynology) and geochronological (AMS ¹⁴C) investigation into a sequence of multiple peat/organic sediment horizons interbedded within a thick estuarine–marine sequence of minerogenic clay‐silts to silty sands from the NE Menai Strait, North Wales. Ten new sea‐level index points and nine new limiting dates from the Devensian Late‐glacial and early Holocene are integrated with twelve pre‐existing Holocene sea‐level index points and one limiting point from North Wales to generate a regional RSL record. This record is similar to the most recent GIA predictions for North Wales RSL change, supporting either greater ice load and later deglaciation than in the GIA predictions generated before 2004, or a modified eustatic function. There is no evidence for a mid‐Holocene highstand. Tidally corrected RSL data indicate initial breaching of the Menai Strait between 8.8 and 8.4 ka BP to form a tidal causeway, with final submergence between 5.8 and 4.6 ka BP. Final breaching converted the NE Menai Strait from a flood‐dominated estuary into a high energy ebb tidal delta with extensive tidal scouring of pre‐existing Late‐glacial and Holocene sequences. The study confirms the value of utilising offshore drilling/coring technology to recover sea‐level records which relate to intervals when rates of both eustatic and isostatic change were at their greatest, and therefore of most value for constraining GIA models. Copyright © 2011 John Wiley & Sons, Ltd.     

Holocene sea‐level reconstruction in the Young Sound region,Northeast Greenland

A relative sea‐level curve over the Holocene is constructed for the Young Sound region in northeastern Greenland. The reconstruction is derived by dating the heights of raised beach ridges in coastal plains using optically stimulated luminiscence (OSL), and by dating palaeoterrestrial surface levels now buried beneath the intertidal frame using the ¹⁴C technique. The relative sea‐level curve reveals a rapid fall of at least 10 mm a^?1 from ca. 9500 to 7500 a ago, which slowed to 2 mm a^?1 until it reached the present sea level ca. 3000 a ago. This part of the curve is based on the raised beach ridge data. Thereafter, relative sea level continued to fall, to reach a minimum level at about 0.5 m below the present sea level ca. 2300 a ago. Since then, relative sea level has experienced a slow rise of about 0.2 mm a^?1. This part of the curve uses the data from the palaeoterrestrial surfaces. The study supplements other estimates of Holocene relative sea‐level changes and supports the observations of a decreasing trend in the timing of the cross point and in minimum relative sea level from South to North Greenland. Copyright © 2011 John Wiley & Sons, Ltd.     

A new Holocene relative sea‐level curve for Terra Nova Bay,Victoria Land,Antarctica

More than 100 radiocarbon dates of penguin guano and remains, shells and seal skin afford ages for raised beaches adjacent to Terra Nova Bay, Antarctica. These dates permit construction of a new relative sea‐level curve that bears on the timing of deglaciation. Recession of the Ross Sea ice‐sheet grounding line from Terra Nova Bay occurred no earlier than 7200 ¹⁴C yr (8000 cal. yr) BP. Retreat along the Victoria Land coast may have been rapid, possibly contributing to eustatic sea‐level rise centred at ca. 7600 cal. yr BP. The presence of a significant amount of ice remaining in the Ross Sea Embayment in Holocene time lessens the chance that Antarctica contributed significantly to meltwater pulse 1A several thousand years earlier. Copyright © 2004 John Wiley & Sons, Ltd.     

Late quaternary sea‐level changes,crustal movements and coastal evolution in Northumberland,UK

Northumberland lies in the transition between Holocene emergence and submergence and is thus a critical zone for testing models of isostatic rebound. We have collected data from this area to reconstruct relative sea‐level changes and lateral coastline movements for the last 14000 y. These are deposits from tidal marsh, back‐barrier wetland and terrestrial environments producing 47 sea‐level index points from 12 sites. There is no unequivocal evidence for Late Devensian sea levels above present and the reliable sea‐level index points are restricted between −6 m and +2.5 m relative to present and 9.0–2.5 kyr cal. BP. Analysis of these quantifies differential responses to glacio‐ and hydroisostatic rebound, with the northern sites recording a mid‐Holocene sea‐level maximum ca. 2.5 m above present, whereas the southern sites show a maximum ca. 0.5 m above present. These observations show a reasonable fit with the predictions from quantitative models of glacio and hydroisostatic rebound, but there is currently no unique solution of Earth and ice model parameters that will explain all the sea‐level observations. Copyright © 2000 John Wiley & Sons, Ltd.     

Geochemical arguments for identifying second‐order sea‐level changes in hemipelagic carbonate ramp deposits

Second‐order transgressive–regressive (T–R) cycles, previously recognized using sedimentological criteria in Lower Jurassic hemipelagic deposits from northern Spain, are distinguishable based upon bulk‐rock organic geochemistry [total organic carbon (TOC) and hydrogen index (HI)] and the stable carbon isotope compositions from belemnite rostra. There is a coincidence between regressions and decreasing δ¹³C_bel, TOC and HI values, and between transgressions and increasing δ¹³C_bel, TOC and HI values. The δ¹⁸O and Mg/Ca records from the belemnite rostra are not always in phase with the T–R cycles. The δ¹⁸O_bel record reveals, however, a prominent excursion towards higher values within the spinatum Zone that correlates, according to our results, with a regression and with negative shifts in Mg/Ca, δ¹³C_bel and TOC. On the other hand, an excursion in the δ¹⁸O_bel towards lower values in the serpentinus Zone also correlates with a peak transgression and with positive shifts in Mg/Ca, δ¹³C_bel and TOC. These two excursions have been identified in other European regions as geochemical perturbations of the same characteristics. This suggests a link between second‐order relative sea‐level changes and variations in seawater geochemistry that may reflect local and regional palaeoceanographic perturbations in sea‐water temperature, salinity and water circulation during the Early Jurassic. Terra Nova, 18, 233–240, 2006     

Postglacial relative sea‐level rise in the Limfjord region,northern Jutland,Denmark

A new core drilled at Nørrekær Enge, Løgstør, Denmark, shows terrestrial lake and bog sediments lying beneath 10 m of marine sediments. Pollen analysis, ¹⁴C dating and sedimentary observations show that these sediments relate to an ancient lake basin that was flooded when the rising sea levels reached 8.0 m b.s.l. This new study has allowed a review of previous data relating to shoreline displacement from the Limfjord region of northern Jutland, Denmark. Here we present a new shoreline displacement curve spanning the period between c. 11 700 and 7700 cal. a BP and built upon the Nørrekær Enge data and data from seven other boreholes and excavations from the Limfjord region. A previous shoreline displacement curve for this region suggested a very rapid relative sea‐level rise of 3 to 5 m 100 a^?1 whereas this new curve suggests a much slower rise of around 1 m 100 a^?1, similar to global rates.     

Late Quaternary glacial and climatic history of northern Cumberland Peninsula,Baffin Island,N.W.T., Canada

Radiocarbon dates on molluses in marine facies associated with glacial deposits in northern Cumberland Peninsula indicate both main fiord (Laurentide) ice and local glaciers remained at their late Wisconsin maxima until ca. 8000 BP. Essentially continuous deglaciation followed; local corrie glaciers melted out by 7100 BP and by 5500 BP fiord glaciers had receded behind the present margin of the Penny Ice Cap. The Hypsithermal warm interval probably lasted from ca. 8000 to 5000 BP. Lichenometry and radiocarbon dates on peat and buried organic horizons delimit a detailed Neoglacial chronology. Of 46 outlet and corrie glaciers investigated, the oldest Neoglacial moraines are dated lichenometrically at 3200 ± 600 BP. Subsequent advances terminated immediately prior to ca. 1650, 780, 350, and 65 yr BP, the most recent of which marked the most extensive ice coverage during the Neoglacial. The highest occurrence of lateral moraines from late Wisconsin advances of local and Laurentide ice suggest that at the late Wisconsin glacial maximum, depression of snowline varied from 450 m below present at the coast to 350 m below present level in the vicinity of the Penny Ice Cap. Moraines, surrounded by glacial ice and lying above the present steady-state ELA, suggest that during the Hypsithermal snowline was up to ca. 200 m above its present elevation. A radiometrically controlled reconstruction of relative summer paleotemperatures for the postglacial derived independently of lichenometry agrees well with the lichenometric age dating of moraines. The data suggest that between ca. 1650 and 900 BP climatic conditions were unfavorable for glacier growth, whereas the period ca. 800-65 yr BP was one of general glacial activity. During the last decade permanent snow cover has been increasing in the area. Previously reported data on climatic trends in the Canadian Arctic based on palynological analyses are similar to the chronology reported here.     

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

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

Wisconsinan Late-glacial environmental change on the southeast Baffin shelf,southeast Baffin Island and northern Labrador

The importance of the Baffin-Labrador region is explained in terms of the channelling through this area of the mass flux of meltwater from the Laurentide Ice Sheet and the probable effects of this on the thermohaline circulation of the North Atlantic. The chronology of glaciation and deglaciation in the region is summarised. Reference is made to recent marine records from the Baffin Shelf. Isotopic changes recorded in foraminiferal assemblages obtained from marine sediments in the Baffin Shelf-Labrador Sea area indicate the timing and possible magnitude of meltwater fluxes during the period 14.0-11.0 ka BP.     

Lateglacial and Holocene relative sea‐level changes and first evidence for the Storegga tsunami in Sutherland,Scotland

We reconstruct one of the longest relative sea‐level (RSL) records in north‐west Europe from the north coast of mainland Scotland, using data collected from three sites in Loch Eriboll (Sutherland) that we combine with other studies from the region. Following deglaciation, RSL fell from a Lateglacial highstand of +6?8 m OD (Ordnance Datum = ca. mean sea level) at ca. 15 k cal a BP to below present, then rose to an early Holocene highstand and remained at ca. +1 m OD between ca. 7 and 3 k cal a BP, before falling to present. We find no evidence for significant differential Holocene glacio‐isostatic adjustment between sites on the north‐west (Lochinver, Loch Laxford), north (Loch Eriboll) and north‐east (Wick) coast of mainland Scotland. This suggests that the region was rapidly deglaciated and there was little difference in ice loads across the region. From one site at the head of Loch Eriboll we report the most westerly sedimentary evidence for the early Holocene Storegga tsunami on the Scottish mainland. The presence of the Storegga tsunami in Loch Eriboll is predicted by a tsunami wave model, which suggests that the tsunami impacted the entire north coast of Scotland and probably also the Atlantic coastline of north‐west Scotland.