Postglacial Relative Sea Level Research Articles

Sedimentary and stratigraphic architecture of the Duitschland and Rooihoogte formations (Palaeoproterozoic, South Africa): implications for tempo of the Great Oxidation Event

Abstract Determining the tempo and causality of key palaeoclimate events recorded in sedimentary strata depends on high-resolution numerical ages and well-constrained stratigraphic correlations at regional and global scale. This requirement is not necessarily met in Precambrian strata due to poorer age resolution, limited preservation, and secondary overprints. A good example includes the Palaeoproterozoic Rooihoogte and Duitschland formations in South Africa, which document the disappearance of mass-independent fractionation of sulphur isotopes (MIF-S) and contain glacial diamictites at their base. They are thus key records of Earth’s surface oxygenation during the Great Oxidation Event (GOE). However, previous studies have either correlated these units, resulting in a unidirectional oxidation trend; or have regarded them as successive strata, causing an interpretation of oscillating oxidation. This study uses extensive outcrop and new core material to investigate correlation between these two units, and to establish depositional models. Results show that key stratigraphic markers can be traced around the entire Kaapvaal craton both in outcrop and the subsurface. In particular, the basal Bevets breccia and the top Duitschland breccia are here re-interpreted as two separate units that are present at the base and top of both formations, supporting correlation of the formations. Consequently, the base of both formations records a major craton-wide event of uplift and karstification, leading to carbonate dissolution and chert brecciation. Erosion of older rocks from across the craton also delivered material for the basal glacial diamictite. The majority of mixed siliciclastic-carbonate sediments were deposited on a storm- and/or delta-influenced shelf. Depositional packages in both formations reflect post-glacial relative sea level rise, followed by progradation of a deltaic, storm or shoreline depositional system. There is a relatively short-lived depositional hiatus to overlying shales of the Timeball Hill Formation. Both Rooihoogte and Duitschland formations thus record only a single glacial event at their base, and a unidirectional trend of oxidation.

Postglacial relative sea level histories of northern Vancouver Island, Canada

The northwest coast of North America exhibits highly variable patterns of relative sea-level (RSL) change following the Last Glacial Maximum (LGM) that reflect proximity to the Cordilleran glacial ice loading and local rates of deglaciation. In this paper we present postglacial RSL histories for four coastal zones in a transect across northern Vancouver Island, Canada, derived from multiple proxies (isolation basin cores, geological exposures, archaeological sites, GIS-based landform interpretation), and relate these to the timing of glacial retreat after the LGM. Notably, parts of the west coast of northern Vancouver Island were ice-free by ∼18,200 years ago, earlier than much of the rest of Vancouver Island and the broader region. These four RSL reconstructions demonstrate substantial variation across the north end of Vancouver Island, which we attribute to regional differences in glacial isostatic processes. Additionally, some RSL curves reveal the likely effects of global glacial meltwater pulses. Documenting late Pleistocene and early Holocene coastline change in this region of Vancouver Island is significant for understanding the late Quaternary history of western North America more broadly: the RSL histories help delimit potential refugia and postglacial expansion of plants and animals (including humans ) as the ice retreated.

The Middle to Late Holocene in the Agro Pontino and the Fondi basin (Lazio, Italy): A palaeogeographical overview

The Agro Pontino, a vast plain located south of Rome (southern Lazio, Italy), has served as a valuable resource for central Italian palaeogeographical, vegetational and archaeological studies for decades. This paper reviews the regional development of the Agro Pontino and adjacent Fondi basin from the Würmian (Marine Isotope Stages 2–5d) until the end of the protohistoric, with an emphasis on the period around the Early Bronze Age (EBA) date of the Avellino eruption. Following postglacial relative sea level rise, a dissected Pleistocene landscape drowned and was filled with lagoonal, fluvial, alluvial, lacustrine and marsh deposits. In the Agro Pontino, two lakes emerged divided by an alluvial fan. The unique regionally preserved stack of Middle to Late Holocene sediments, including multiple macroscopically visible tephra layers within a depositional environment, allowed for a detailed regional palaeogeographical, tephrochronological and vegetational reconstruction. This study presents the latest palaeogeographical findings from the Agro Pontino and the Fondi basin for the Middle Holocene and the EBA, for which tephra identification and dating forms the solid basis. It contributes to the reconstruction of the Pontine plain and the Fondi basin during this period and furthers our palaeoenvironmental knowledge of the conditions for human subsistence in this region during the later phase of the EBA, around the time of the Avellino eruption (c. 1900 calBC).

Post-glacial RSL changes and the demise of a local remnant Laurentide Ice-Sheet ice cap: A view from Anticosti island beach-ridges (Gulf of St Lawrence, Canada)

Widely spread worldwide, beach-ridge systems are established along prograding coastlines, either fostered by a falling Relative Sea-Level (RSL), by substantial sediment stocks being provided to the coastline, or by the combination of both agents. As such, they can form valuable archives of either large scale RSL and isostatic dynamics and/or of more local coastal processes, e.g. related to variations in riverine sediment supply. In this study, we analyze three raised beach-ridge complexes located on the island of Anticosti (Gulf of St.-Lawrence, Québec, Canada). Using both field and LiDAR DEM data, we produce new RSL histories for the north-eastern and north-western sectors of Anticosti Island region over the ca. 14.400 to 8.300 yrs cal. B.P. period. These new sea-level data allow to considerably refine the postglacial RSL history of the region, hence carrying large implications for the comprehension of the isostatic dynamics of the St-Lawrence region. Considerable misfits between our observations and outputs of the GIA models notably allow to propose refinements on the LIS architecture and melting history as well as on the rheological characteristics of the St-Lawrence valley. Locally, chronologies of progradation of the beach-ridges were mostly forced by RSL changes, yet also apparently recorded the demise of the local Anticosti remnant ice-cap throughout the changes in sediment supply the melting of the latter produced locally. Finally, some results of paleo-oceanographic significance could also be derived from the study of the beach-ridges, pertaining for instance to changes in sea-ice cover.

Postglacial relative sea level change in Norway

We present the first comprehensive postglacial relative sea-level (RSL) database for the Norwegian coast from Oslo to the Kola Peninsula. The database spans the last 20 kyrs and is composed of 413 index points and 610 limiting data points derived from raised beaches, archeological data, glaciomarine terraces, and sedimentary indicators from isolation basins, salt marshes, and peat bogs. The data are quality controlled, assigned standardized indicative meanings, and recalibrated to current standards. We use an ensemble of Bayesian statistical models, trained on sea-level index points and weighted by their fit to both index and sea-level limiting points, to assess the spatiotemporal patterns of Norwegian RSL change. Continuous RSL fall driven by isostatic rebound in response to Eurasian ice sheet collapse dominates the RSL signal at every inland location in Norway. A first transgression (episode of RSL rise), which occurred in southwest Norway during the Younger Dryas (14–11.7 ka), increased RSL by as much as 15 m in some locations. A second transgression, named the Tapes transgression, occurred during the early-mid Holocene between 10 and 5.5 ka. The spatiotemporal model ensemble constrains the timing, amplitude, and spatial distribution of the Younger Dryas and Tapes transgressions. Based on our modeling results, we speculate that the Tapes Transgression was the result of global mean sea level rise temporarily outpacing isostasy-driven RSL fall, while the Younger Dryas Transgression was likely the result of local ice sheet readvance combined with low viscosity asthenosphere and weak lithosphere in the region. We also describe the effects of peripheral bulge migration on Norwegian RSL, which caused increased RSL in the early Holocene and a delayed Tapes transgression. We show that postglacial RSL data in Norway contain complex spatiotemporal patterns of nearfield RSL change that can best be estimated by combining a high-quality data compilation with glacial isostatic adjustment modeling via a robust statistical model.

A post-glacial relative sea level curve for the central Douglas Channel area, British Columbia, Canada

We present a post-glacial relative sea level (RSL) curve for the Central Douglas Channel region on the northern Northwest Coast of North America spanning the last 14,500 years, constrained by 68 radiocarbon dated index and limiting points derived from multiple RSL proxies. We evaluate each proxy based on the reliability and specificity of the inference for indicating RSL position, allowing us to weight different methods of data collection. We determine that central Douglas Channel was ice-free following the Last Glacial Maximum by ∼14,500 BP and RSL was at least 90 m higher than today. Isostatic rebound caused RSL to fall to 21 m asl by 11,500 BP, though there may have been a glacial re-advance that would have paused RSL fall around the beginning of the Younger Dryas. RSL fell to 10–15 m asl by 10,000 BP, and continued to drop at a slower rate towards its current position, which it reached by ∼1800 years ago. This is the first well-constrained RSL reconstruction for a nearly 400 km stretch between the northern and central coasts of British Columbia, Canada. This reconstruction provides information about the timing and rate of deglaciation of western North America and exemplifies variability among sea level trends across the region. Long-term RSL reconstructions are integral to explorations of coastal change and archaeological inquiries into early coastal occupations.

Relative sea level changes and glacio-isostatic modelling in the Beagle Channel, Tierra del Fuego, Chile: Glacial and tectonic implications

The Beagle Channel crosses the southernmost tip of South America (Tierra del Fuego), connecting the South Atlantic with the Southeastern Pacific. Raised beaches occur up to 10 m above mean sea level (m a.m.s.l.), especially along the northern (Argentinian) shore, and have been dated using marine shells. The southern (Chilean) shore is well-known for its abundance of shell middens at different levels above the present shore, particularly along the island of Isla Navarino, but the relative sea level history in this glacially impacted landscape has not previously been investigated. In this study we present postglacial relative sea level changes on Isla Navarino, based on sediment cores from six lagoons, bogs or lakes, and stratigraphic investigations of three open sections, of which one is of MIS 5e age. In addition, one core from a lagoon in the south-western Beagle Channel has been analysed and a system of terraces was mapped in the north-western Beagle Channel. The analyses of the core sites have resulted in two tentative relative sea level curves, displaying a rapid sea level rise at 8500−6500 cal yr BP, amounting to ∼10 and 14 m in eastern and western Isla Navarino, respectively, and reaching levels of ∼8 and > 10 m, respectively, followed by a slow relative sea level fall. Our sea level observations have been compared with a range of modelling results of glacial-isostatic adjustments (GIA) for estimating timing of deglaciation and ice sheet thicknesses. Based mainly on the GIA modelling of the altitude of the MIS 5e beach sediments, situated at 13 m, we can conclude that no other uplift than GIA is needed to explain their altitude. Regarding the modelling of postglacial sea levels we can conclude that no model has been found that satisfies all of the observational evidence, but that deglaciation most likely preceded Northern Hemisphere main deglaciation by at least 3 kyr, which agrees with the deglaciation age of Isla Navarino (>16 000 cal yr BP). In addition, our model runs imply that the Patagonian and Tierra del Fuego ice sheet thicknesses were in the order of ∼1500 m.

Millennial variability of rates of sea-level rise in the ancient harbour of Naples (Italy, western Mediterranean Sea)

AbstractWe reconstructed the late Holocene relative sea-level (RSL) evolution of the ancient harbour of Naples, one of the largest coastal conurbations in the Mediterranean. We carried out multiproxy investigations, coupling archaeological evidence with biological indicators. Our data robustly constrain 2000 yr of non-monotonic changes in sea level, chiefly controlled by the complex volcano-tectonic processes that characterize the area. Between ~200 BC and AD ~0, a subsidence rate of more than ~1.5 mm/yr enhanced the postglacial RSL rise, while negligible or moderate land uplift < ~0.5 mm/yr triggered a RSL stabilization during the Roman period (first five centuries AD). This stabilization was followed by a post-Roman enhancement of the sea-level rise when ground motion was negative, attested by a subsidence rate of ~0.5 to ~1 mm/yr. Our analysis seems to indicate very minor impacts of this nonmonotonic RSL evolution on the activities of the ancient harbour of Naples, which peaked from the third century BC to the second century AD. After this period, the progressive silting of the harbour basin made it impossible to safely navigate within the basin, leading to the progressive decline of the harbour.

Postglacial relative sea level change and glacier activity in the early and late Holocene: Wahlenbergfjorden, Nordaustlandet, Svalbard

Sediment cores from Kløverbladvatna, a threshold lake in Wahlenbergfjorden, Nordaustlandet, Svalbard were used to reconstruct Holocene glacier fluctuations. Meltwater from Etonbreen spills over a threshold to the lake, only when the glacier is significantly larger than at present. Lithological logging, loss-on-ignition, ITRAX scanning and radiocarbon dating of the cores show that Kløverbladvatna became isolated from Wahlenbergfjorden c. 5.4 cal. kyr BP due to glacioisostatic rebound. During the Late Holocene, laminated clayey gyttja from lacustrine organic production and surface runoff from the catchment accumulated in the lake. The lacustrine sedimentary record suggests that meltwater only spilled over the threshold at the peak of the surge of Etonbreen in AD 1938. Hence, we suggest that this was the largest extent of Etonbreen in the (mid-late) Holocene. In Palanderbukta, a tributary fjord to Wahlenbergfjorden, raised beaches were surveyed and organic material collected to determine the age of the beaches and reconstruct postglacial relative sea level change. The age of the postglacial raised beaches ranges from 10.7 cal. kyr BP at 50 m a.s.l. to 3.13 cal. kyr BP at 2 m a.s.l. The reconstructed postglacial relative sea level curve adds valuable spatial and chronological data to the relative sea level record of Nordaustlandet.

Postglacial relative sea-level histories along the eastern Canadian coastline

We have assembled a database of Relative Sea Level (RSL) data points from the eastern coast of Canada from Hudson Bay to the border with the USA. In compiling this database we have critically reviewed 1092 radiocarbon dated samples from raised beaches, isolation basins, intertidal and marine deposits, and archaeological indicators to produce 405 sea-level index points and 687 sea-level limiting points. Our comprehensive, systematic, and quality-controlled RSL database allowed for the reconstruction of the postglacial evolution of 34 regions of eastern Canada providing new basin-scale insights into the processes driving RSL changes in the last ∼16 ka. The combination of a database of sea-level index points with an innovative empirical-Bayesian spatio-temporal statistical model provided new insights into rates and magnitude of the spatially-variable glacial isostatic adjustment (GIA), which dominated the postglacial RSL evolution in this sector of North America. A continuous postglacial RSL fall is observed at latitudes ≥ ∼50° N with higher rates (up to 35 mm a−1) recorded in southeastern Hudson Bay. At lower latitudes, the evolution is non-monotonic with RSL that dropped to a spatially variable early-Holocene lowstand, followed by a mid-Holocene highstand and, eventually, a gradual drop to present RSL. This pattern is particularly evident in the St Lawrence corridor. Along the majority of the Newfoundland, New Brunswick and western Nova Scotia coasts, a late-Pleistocene/early-Holocene RSL lowstand was followed by a continuous rise through the Holocene. At the margin of the former ice-sheet (i.e. eastern Nova Scotia), our data identify a continuous RSL rise through the Holocene. These records are characterized by decreasing rates of RSL rise through time, commencing with a rapid rise during the early Holocene (up to ∼17 mm a−1), a slowdown in the mid-Holocene (average rates ≤ ∼9 mm a−1), and a further reduction in the late Holocene (average rates < 2 mm a−1). Finally, our database allowed the identification of regions, including the Labrador coast and part of the St Lawrence corridor, where further investigations are required to better constrain the RSL evolution and improve our ability to assess the variability of RSL histories.

Quantifying variable rates of postglacial relative sea level fall from a cluster of 24 isolation basins in southern Norway

Sediment sequences obtained from 24 isolation basins located on the Skagerrak coastline are used to develop new sea level index points for southern Norway. The basins are located near a common shoreline isobase and extend from marine limit at c. 83 m asl. to present sea level. The abundance of bedrock isolation basins within the small study area enables a high-resolution reconstruction of postglacial relative sea-level change. For most of the basin records, 3–5 samples of terrestrial plant macrofossils were radiocarbon dated across the biostratigraphically-defined isolation boundary. Eight of the isolation events were further constrained by Bayesian modelling of the radiocarbon age results. The overall reconstructed sea-level history is as expected for a formerly glaciated coastline; consisting of a rapid regression from marine limit followed by a slower pace of relative sea level fall from early-mid Holocene to present. The new dataset of sea level index points, however, further delineates century-scale oscillations in rates of sea level regression, which record past changes in sea surface height and vertical land motion (glacial isostatic adjustments, GIA). Results provide new constraints for future numerical models aimed at reducing uncertainty in century-scale relative sea-level projections for Fennoscandia.

Postglacial relative sea-level history of the Prince Rupert area, British Columbia, Canada

This paper presents a history of relative sea level (RSL) change for the last 15,000 years in the Prince Rupert region on the northern coast of British Columbia, Canada. One hundred twenty-three radiocarbon ages of organic material from isolation basin cores, sediment sequence exposures, and archaeological sites having a recognized relation to past sea levels constrain postglacial RSL. The large number of new measurements relating to past sea-level provides a well constrained RSL curve that differs in significant ways from previously published results. After deglaciation following the Last Glacial Maximum, the region experienced an isostatically-induced rapid RSL drop from as much 50 m asl to as low as −6.3 m asl in as little as a few centuries between 14,500 BP and 13,500 BP. After a lowstand below current sea level for about 2000 years during the terminal Pleistocene, RSL rose again to a highstand at least 6 m asl after the end of the Younger Dryas. RSL slowly dropped through the Holocene to close to its current position by 2000-1500 BP, with some potential fluctuations between 3500 and 1500 BP. This study highlights variation in RSL histories across relatively short distances, which must be accounted for by local RSL reconstructions such as this one. This RSL curve aided in the identification of an 8000–9000 year old archaeological site on a 10–12 m asl terrace, which is currently the earliest dated archaeological site in the area, and it provides guidance for searching for even older archaeological remains. We highlight the utility and potential of this refined RSL history for developing surveys for other archaeological sites associated with paleoshorelines.

Postglacial relative sea level change at Fildes Peninsula, King George Island (West Antarctic)

Analysis and integration of data obtained in our field and laboratory investigations of 2008–2012 together with results of previous paleogeographic studies were conducted to reveal parameters and factors of the post-glacial changes in the relative sea-level on the Fildes Peninsula and the King George Island. Results of dating of organic material taken from cross-sections of Quaternary deposits, data on morphology of marine landforms as well as on bottom sediments in lakes were used to construct a curve of changes in the relative sea-level. Our research has shown that the rapid rise of relative sea level in the area (since the beginning of the Holocene) decelerated about 8000 years BP, achieving its maximum about 7000 years BP. This was followed by the fall of relative sea-level (the land elevation) by 18–20  m in total, and it was characterized by relatively high rate of fall during periods of 6000– 5000 years BP, 4000–2500 years BP, and during the last 1500 years; the rate decreased in 5000–4000 years BP and 2500– 1600 years BP. The changes in relative sea level in this region were determined by the following factors: the eustatic component of the global changes in sea-level and, possibly, oscillations in the global sea level of another nature; local parameters of the Last glacial maximum; a course of the Peninsula deglaciation; regional physical characteristics of the Earth's crust and the mantle substances; local tectonic processes, including the isostatic rebound. Since the beginning of the Holocene up to about 7000 years BP, the main contribution to changes of the relative sea-level in this area was made by the global eustatic factor. The subsequent fall of the relative sea-level (elevation of the Peninsula surface) proceeded under condition of reduced role of the eustatic factor and predominance of other factors.

Holocene relative sea-level changes and glacial isostatic adjustment of the U.S. Atlantic coast

The fi rst quality-controlled Holocene sea-level database for the U.S. Atlantic coast has been constructed from 686 sea-level indicators. The database documents a decreasing rate of relative sea-level (RSL) rise through time with no evidence of sea level being above present in the middle to late Holocene. The highest rates of RSL rise are found in the mid-Atlantic region. We employ the database to constrain an ensemble of glacial isostatic adjustment models using two ice (ICE-5G, ICE-6G [global ice sheet reconstructions]) and two mantle viscosity (models VM5a,VM5b [VM—radial variation of viscosity in the sublithospheric mantle]) variations to assess whether the spherically symmetric viscoelastic models are able to survive intercomparison with a more refi ned database of postglacial RSL history. We identify signifi cant misfi ts between observations and predictions using ICE-5G with the VM5a viscosity profi le. ICE-6G provides some improvement for the northern Atlantic region, but misfi ts remain elsewhere. Decreasing the upper mantle and transition zone viscosity by a factor of 2 to 0.25 ◊ 10 21 Pa s (VM5b) removes signifi cant discrepancies between observations and predictions along the mid-Atlantic coastline, although misfi ts remain in the southern Atlantic region. These may be an indication of the importance of laterally heterogeneous viscosity in the upper mantle.

Preservation of a drowned gravel barrier complex: A landscape evolution study from the north-eastern English Channel

Landscape response to post-glacial relative sea level during the Quaternary is documented using an integrated dataset of multibeam bathymetry and 2D seismic reflection profiles from the Hastings Bank area in the north-eastern English Channel. Mapping of nine seismic stratigraphic units calibrated to lithological information from multiple vibrocores has enabled the interpretation of fluvial, shoreface, barrier, washover fan, back-barrier and tidal environments of deposition. The interpreted landscape evolution is as follows: (i) fluvial incision of bedrock during sea-level lowstand; (ii) progradation of a shoreline and then development of a barrier complex as sea-level rose; (iii) recycling and breaching of the barrier; (iv) rapid drowning of the barrier complex; (v) landward migration of the shoreline through continued sea-level rise; and (vi) complete abandonment and submarine preservation of the barrier complex during sea-level highstand. The previously undocumented, yet exceptionally well preserved, drowned barrier complex at Hastings Bank records phases of barrier initiation, breakdown and retreat, and documents coastal response to high rates of relative sea-level rise. Initial development of the barrier complex required a sufficient supply of sediment, maintained by offshore sources, to keep pace with rising sea level, which permitted progradation of a shoreline and development of a barrier complex. Inherited topography in the north-eastern English Channel is an important factor in the development of the barrier complex. Phases of barrier breakdown occur when sediment supply is outpaced by a rapid increase in accommodation controlled by existing basement morphology and rising sea levels. Subsequently, the barrier responds through internal reorganisation by breaching and reworking of existing sediment bodies. Barrier retreat is characterised by a phase of ‘sediment surplus’ overstepping under rapid rates of sea-level rise where increased water depths limit wave reworking, followed by a phase of discontinuous retreat where the shoreline steps back through ‘sediment deficit’ overstepping. Hastings Bank presents a rare opportunity to examine the conditions and processes that control barrier response to sea-level rise and, to assess the preservation potential of barrier deposits as a function of the style of retreat.

Holocene relative sea-level changes and glacial isostatic adjustment of the U.S. Atlantic coast

The first quality-controlled Holocene sea-level database for the U.S. Atlantic coast has been constructed from 686 sea-level indicators. The database documents a decreasing rate of relative sea-level (RSL) rise through time with no evidence of sea level being above present in the middle to late Holocene. The highest rates of RSL rise are found in the mid-Atlantic region. We employ the database to constrain an ensemble of glacial isostatic adjustment models using two ice (ICE-5G, ICE-6G [global ice sheet reconstructions]) and two mantle viscosity (models VM5a,VM5b [VM—radial variation of viscosity in the sublithospheric mantle]) variations to assess whether the spherically symmetric viscoelastic models are able to survive intercomparison with a more refined database of postglacial RSL history. We identify significant misfits between observations and predictions using ICE-5G with the VM5a viscosity profile. ICE-6G provides some improvement for the northern Atlantic region, but misfits remain elsewhere. Decreasing the upper mantle and transition zone viscosity by a factor of 2 to 0.25 × 10 21 Pa s (VM5b) removes significant discrepancies between observations and predictions along the mid-Atlantic coastline, although misfits remain in the southern Atlantic region. These may be an indication of the importance of laterally heterogeneous viscosity in the upper mantle.

Post-glacial relative sea level, isostasy, and glacial history in Icy Strait, Southeast Alaska, USA

We use the radiocarbon ages of marine shells and terrestrial vegetation to reconstruct relative sea level (RSL) history in northern Southeast Alaska. RSL fell below its present level around 13,900 cal yr BP, suggesting regional deglaciation was complete by then. RSL stayed at least several meters below modern levels until the mid-Holocene, when it began a fluctuating rise that probably tracked isostatic depression and rebound caused by varying ice loads in nearby Glacier Bay. This fluctuating RSL rise likely reflects the episodic but progressive advance of ice in Glacier Bay that started around 6000 cal yr BP. After that time, RSL low stands probably signaled minor episodes of glacier retreat/thinning that triggered isostatic rebound and land uplift. Progressive, down-fjord advance of the Glacier Bay glacier during the late Holocene is consistent with the main driver of this glacial system being the dynamics of its terminus rather than climate change directly. Only after the glacier reached an exposed position protruding into Icy Strait ca. AD 1750, did its terminus succumb – a century before the climate changes that marked the end of the Little Ice Age – to the catastrophic retreat that triggered the rapid isostatic rebound and RSL fall occurring today in Icy Strait.

Prehistoric cultures, reconstructed coasts: Maritime Archaic Indian site distribution in Newfoundland

We argue that variable and complex post-glacial relative sea level (RSL) in Newfoundland is linked to (1) the uneven distribution around the coastline of late Maritime Archaic Indian (MAI) sites (5500–3200 bp) and (2) the apparent absence of early MAI sites (8000–5500 bp), despite their presence in nearby southern Labrador. Three post-glacial RSL histories are described for different regions of Newfoundland: continuous emergence (type A), initial emergence followed by submergence (type B) and continuous submergence (type C). In areas characterized by type B or C curves, where the lowstand is greater than 20m water depth, late MAI sites older than 3000 bp are today submerged. In all areas other than those characterized by a type A curve, early MAI sites would be under water. The Northern Peninsula is the only region of Newfoundland described by a type A curve. If early MAI did occupy Newfoundland, we predict where on the Northern Peninsula those sites would be found.

Mantle viscosity beneath the Hudson Bay: An inversion based on the Metropolis algorithm

We revisit the problem of inferring mantle viscosity from postglacial relative sea level (RSL) data across the Hudson Bay. We invert a recently revised data set using the Metropolis algorithm together with an annealing schedule: this method, which is well established in geophysics, is applied here for the first time to the glacial isostatic adjustment problem. The Metropolis algorithm performs a search, which is not limited to downhill moves in the model space and thus is less influenced by local minima of the misfit than traditional inverse approaches. Furthermore, its CPU requirements are far superior to Monte Carlo methods. The major drawbacks include slow convergence and the need for careful tuning of crucial variables such as the temperature schedule and the increment in the model space. When all the Hudson Bay RSL data are considered, and the viscosity of the upper mantle above the 670 km discontinuity is inverted, the best fitting solution is characterized by a viscosity close to 2 × 1020 Pa s. However, when the shallow upper mantle and transition zone viscosity are separately inverted, other less traditional solutions with a more complex viscosity structure are found to be equally possible. A stable feature is the lower mantle viscosity, which is generally found to be close to the value of 1021 Pa s in all of the stochastic inversions we have performed. The solutions agree with previous findings concerning both postglacial rebound observables and global geodynamics signatures.

Holocene emergence and shoreline delevelling, southern Eureka Sound, High Arctic Canada

This paper is a reconstruction of postglacial relative sea level change and shoreline delevelling in southern Eureka Sound, High Arctic Canada. Postglacial emergence of up to 150 m is recorded in this area by raised marine deltas, beaches and washing limits that date from the early Holocene. Marine limit is metachronous and formed successively with glacier retreat. Marked contrasts in the form of relative sea level curves and rate of initial emergence are recorded from the study area. In Blind Fiord, relative sea level fell continuously following deglaciation. Initial emergence was characterised by rates of ≥ 5 m/century. This contrasts with curves from Starfish and Irene bays, where the rate of initial emergence was ≤ 1 m/century. Isobases drawn on the 8.5 ka shoreline for greater Eureka Sound demonstrate that a cell of highest emergence (≥ 130 m asl) extends along the length of the channel, and closes in the vicinity of the entrance to Norwegian Bay. This pattern confirms a distinct loading centre over Eureka Sound during the Last Glacial Maximum, and is compatible with independent glacial geological evidence indicating that the thickest ice was centred over the channel during the Late Wisconsinan.