Relative Sea-level History Research Articles

Cosmogenic surface exposure (10Be) dating of raised beaches in Marguerite bay, Antarctic Peninsula: Implications for relative sea-level history

Understanding the dynamics of ice mass loss in polar regions is crucial for deciphering climate change and Glacio Isostatic Adjustment patterns. This study focuses on Marguerite Bay, located in the south-central Antarctic Peninsula. We dated raised beaches to investigate relative sea-level changes using the cosmogenic surface exposure (10Be) method. Previous studies have provided valuable insights into the region's glacial history, but limitations in dating techniques and age estimates necessitate further investigation. By analysing raised shingle beaches in Gaul Cove of Horseshoe Island and the southern coast of Calmette Bay, this research aims to contribute relative sea-level change history for these areas. In Horseshoe Island's Gaul Cove, raised beaches clustered on prominent steps reveal a 15 m relative sea-level change over the last 3.31 ka. Differently, Calmette Bay exhibits a 36 m relative sea-level fall over the last 7.29 ka. These findings indicate significant and differential glacial-isostatic adjustments in both regions during the middle and late Holocene. Additionally, our data reveal accelerated sea-level fall periods corresponding to Holocene deglaciation and glacial advance events, indicating the shorelines' relative sea-level change sensitivity to climate change.

Holocene to present-day coastal landscapes of Bar al Hikman (Oman): Neolithic waypoints on the shores of the Arabian Sea

Dramatic climatic and environmental changes over the last 12,000 years have significantly impacted Arabian coastal stratigraphy and human populations. The Bar Al Hikman peninsula (BAH), the largest low-lying area (1000 km2) along the Arabian Sea coast of Oman is a monsoon storm-dominated carbonate-evaporite system, where late Neolithic artifacts suggest human presence from at least 5.75–5.05 ka before the present (BP). Despite its archaeological significance at the crossroads of important Neolithic coastal sites in Dhofar, Masirah, and Ja'alan coast, paleoenvironmental interpretation, timing, and expression of relative sea level (RSL) changes in this coastal area remain poorly understood. Fortunately, the extensive size and arid climate of the area have preserved carbonate-dominated Mid-Late Holocene coastal geomorphologies exceptionally well, making this area an excellent geological archive to study past coastal environments, thereby understanding how environmental changes at BAH influenced Neolithic human mobility and settlement patterns. This study reconstructs the paleoenvironment of BAH over the last 12,000 years using a combination of field and remote sensing techniques, including satellite imagery, digital elevation models, bathymetric data, GIA modeling, and Sea Level Index Points to trace RSL history. The Holocene transgression began flooding the extensive continental shelf offshore BAH around 10 ka BP, progressively separating Masirah from the mainland through channel formation between 9.5 and 8.0 ka BP. It then inundated the present-day BAH peninsula around 7.7 ka BP, reaching a highstand of 2.5–3.2 m above present sea level by 6.0 ka BP (Mid-Holocene Highstand; MHHS), before gradually declining to the current level. Human presence documented at BAH (5.75–5.05 ka BP) coincides with the end of the mid-Holocene highstand, and the onset of the regression. This relative sea level history is contemporaneous to the aridification of Arabia, a period of transition from mangrove-dominated intertidal settings to coral reef and carbonate coastal barriers. The disappearance of mangrove-like gastropods around 5.4 cal ka BP and the subsequent appearance of significant coral fragments in the sediment indicates a critical change in terms of environmental settings with less nutrients and a warmer sea surface temperature). Comparing the findings at BAH to well-established nearby Neolithic sites on Masirah Island, the scarcity of prehistoric remains at BAH suggests that during the Mid-Holocene Highstand (MHHS), the small, rocky, paleo-low-lying islands at BAH may have served as waypoints and shelters between Masirah and the mainland.

The hemispheric origins of meltwater pulse 1B

SUMMARY Antarctica has been proposed as a significant source of the meltwater that entered the oceans during meltwater pulse 1B (MWP1B) approximately 11 500 yr ago. Support for this scenario has been provided by evidence that the deep fjords of coastal Antarctica, which were heavily glaciated at the maximum of glaciation, were deglaciated at this time. Further support for this scenario was provided by the observation that the inter-hemispheric sea-level teleconnection associated with significant Southern Hemisphere deglaciation at this time provided an explanation of the highly non-monotonic relative sea-level histories recorded at sites on the coast of Scotland, a region which had also been heavily glaciated at the last glacial maximum. Furthermore, it has been argued that a significant contribution to MWP1B must have also been delivered to the oceans by the abrupt Northern Hemisphere warming that occurred at the end of the Younger Dryas (YD) cold reversal, which also occurred approximately 11 500 yr ago. Our focus in this paper is to distinguish between these two possible primary sources of MWP1B. The investigation of how local alterations to ice thicknesses are able to explain evidence which has previously been used to argue for an Antarctic dominant MWP1B will lead us to the conclusion that the Laurentide may be primary source of MWP1B.

Forward numerical modelling of pleistocene marine strata, North-West of Morocco

Numerical stratigraphic forward modelling is useful to understand and reconstruct the relative sea-level and sediment supply history responsible for particular strata. This analysis uses BARSIM, a simple 2D forward stratigraphic process-response model that simulates wave and storm processes, applied with an inverse modelling optimisation method to better understand the history of Pleistocene strata in the Achakkar basin of the Tangier region, Morocco. Observations of grain size and bed thickness in four outcrop vertical sections are matched with BARSIM model output to estimate the lowest-error best-fit relative sea level and sediment supply histories that may have controlled deposition of the observed strata assuming deposition over a 10 ky period, consistent with available dating from outcrop sections. The best-fit relative sea level history drops from 4.88 to −2.82 m with two lower-amplitude highstands in between, most likely representing interglacial eustatic and tectonic event. The best-fit sediment supply is variable through time and different for each vertical section, with greatest variation from 11.7 to 2.11 m2y-1 over the 10 ky interval in the north-east vertical section. The spatial and temporal variation of sediment supply in the four vertical sections represents typically dynamic depositional conditions in shallow marine nearshore areas. On the other hand, it can indicate high stratigraphic incompleteness caused by periods of non-deposition or erosion with temporal variations in sediment supply. The optimum way for the simple model to reproduce short intervals of high sedimentation rate separated by longer periods of hiatus and deposition followed by erosion results in a discontinuous stratigraphic record.

New insights into the glacial and relative sea-level history of the western Fraser Lowland based on sediment cores from geotechnical drilling for the Evergreen Tunnel, British Columbia, Canada

Abstract Geotechnical drilling for a tunnel between Port Moody and Burnaby, BC, Canada, uncovered a buried fjord. Its sedimentary fill has a thickness of at least 130 m and extends more than 37 m below present mean sea level. Recovered sediments record cyclical growth and decay of successive Cordilleran ice sheets. The oldest sediments comprise 58 m of almost stoneless silt conformably overlying ice-proximal sediments and till, which in turn overlie bedrock. These sediments may predate Marine Isotope Stage (MIS) 4. Glacial sediments assigned to MIS 4 overlie this basal succession and, in turn, are overlain by MIS 3 interstadial sediments and sediments from two MIS 2 glacial advances. Indicators of relative sea-level elevations that bracket glacial deposits of MIS 4 and 2 indicate the cyclic existence of moat-like isostatic depressions in the front of expanding ice sheets. Compared with present sea level, these depressions were at least 160 m during the onsets of MIS 4 and MIS 2. Assuming a maximum eustatic drawdown of 120 m during MIS 2, isostatic depression may have exceeded 200 m during retreat of glacial ice from the Evergreen tunnel area. This is consistent with region-specific low mantle viscosity and rapid Cordilleran Ice Sheet buildup and wasting.

Persistence of Holocene ice cap in northeast Svalbard aided by glacio-isostatic rebound

The deglaciation of the Svalbard-Barents Sea Ice Sheet was driven by relative sea-level rise, the incursion of North Atlantic waters around Spitsbergen, and increasing summer insolation. However, ice retreat was interrupted by asynchronous re-advances that occurred into high relative seas, during a period associated with warm regional waters and elevated summer temperatures. Better understanding of this complex style of deglaciation and the dynamic response to a warming climate can serve as an important analogue for modern warming and today's ice sheets. We present evidence from northern Svalbard of glacier re-advances during the Late Glacial-Early Holocene in hand with relative sea-level history and the occurrence of thermophilous molluscs. We argue that glacio-isostatic adjustment during the transition into the Holocene influenced ice marginal dynamics and as a result, the southern region of the Åsgardfonna ice cap persisted through the Holocene Thermal Maximum.

Refining Holocene sea‐level variations for the Lofoten and Vesterålen archipelagos, northern Norway: implications for prehistoric human–environment interactions

ABSTRACTThe Lofoten and Vesterålen archipelagos are located off the outer coast of northern Norway far from the center of the former Fennoscandian Ice Sheet and near the continental shelf edge. Existing relative sea‐level (RSL) data indicate a pronounced mid‐Holocene transgression and interesting connections with the region's prehistoric human settlement history. Here we present seven new sea‐level index points from isolation basins and five terrestrial limiting points from a coastal sedimentary sequence to refine the region's RSL history. Ingression and isolation contacts in isolation basin sediment cores are identified using sedimentary geochemical data, scanning X‐ray fluorescence profiles and phytoplankton analysis. The ages of these contacts are determined using radiocarbon‐based age models. Our index points range from 11.2 to 1.5k cal a bp and are combined with previously published data to predict the spatiotemporal evolution of sea level in this region using an ensemble of spatiotemporal empirical hierarchical models (STEHME). The new RSL curve constrains the timing of the mid‐Holocene transgression, which occurred from c. 9 to 6k cal a bp when sea level increased from −4 to 7 m above present day. From c. 6 to 5k cal a bp, RSL rapidly fell to c. 4 m above present values, and more gradually declined at an average rate of c. 0.8 m ka−1 over the last 5k cal a bp. Isobase maps derived using the STEHME show a decrease in the regional shoreline gradients since the transgression maximum from 0.25 to 0.07 m km−1. Our data also better define how RSL variations influenced the location and preservation of coastal settlement locations and harbors from the early Stone Age through historic intervals, improving understanding of regional human–environment interactions.

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.

Imprint of relative sea level histories on Last Interglacial coral preservation

SUMMARY Fossil corals are commonly used to reconstruct Last Interglacial (∼125 ka, LIG) sea level. Sea level reconstructions assume the water depth at which the coral lived, called the ‘relative water depth’. However, relative water depth varies in time and space due to coral reef growth in response to relative sea level (RSL) changes. RSL changes can also erode coral reefs, exposing older reef surfaces with different relative water depths. We use a simplified numerical model of coral evolution to investigate how sea level history systematically influences the preservation of corals in the Bahamas and western Australia, regions which house >100 LIG coral fossils. We construct global ice histories spanning the uncertainty of LIG global mean sea level (GMSL) and predict RSL with a glacial isostatic adjustment model. We then simulate coral evolution since 132 ka. We show that preserved elevations and relative water depths of modelled LIG corals are sensitive to the magnitude, timing and number of GMSL highstand(s). In our simulations, the influence of coral growth and erosion (i.e. the ‘growth effect’) can have an impact on RSL reconstructions that is comparable to glacial isostatic adjustment. Thus, without explicitly accounting for the growth effect, additional uncertainty is introduced into sea level reconstructions. Our results suggest the growth effect is most pronounced in western Australia due to Holocene erosion, but also plays a role in the Bahamas, where LIG RSL rose rapidly due to the collapsing peripheral bulge associated with Laurentide Ice Sheet retreat. Despite the coral model's simplicity, our study highlights the utility of process-based RSL reconstructions.

Organic carbon stocks of Great British saltmarshes

Coastal wetlands, such as saltmarshes, are globally widespread and highly effective at capturing and storing ‘blue carbon’ and have the potential to regulate climate over varying timescales. Yet only Australia and the United States of America have national inventories of organic carbon held within saltmarsh habitats, hindering the development of policies and management strategies to protect and preserve these organic carbon stores. Here we couple a new observational dataset with 4,797 samples from 26 saltmarshes across Great Britain to spatially model organic carbon stored in the soil and the above and belowground biomass of Great British saltmarshes. Using average values derived from the 26 marshes, we deliver first-order estimates of organic carbon stocks across Great Britain’s 448 saltmarshes (451.66 km2). The saltmarshes of Great Britain contain 5.20 ± 0.65 Mt of organic carbon, 93% of which is in the soil. On average, the saltmarshes store 11.55 ± 1.56 kg C m-2 with values ranging between 2.24 kg C m-2 and 40.51 kg C m-2 depending on interlinked factors such as geomorphology, organic carbon source, sediment type (mud vs sand), sediment supply, and relative sea level history. These findings affirm that saltmarshes represent the largest intertidal blue carbon store in Great Britain, yet remain an unaccounted for component of the United Kingdom’s natural carbon stores.

Middle and Late Holocene relative sea level changes and coastal development at Rugård, Denmark

Denmark has been subject to complex interactions of isostatic uplift and eustatic sea level changes since the last deglaciation. Prominent coastal beach ridges as well as lagoonal and lake deposits from this period have been investigated at a number of sites in the region to constrain the relative sea level (RSL) changes. However, despite the common occurrence of former coastal lagoons and lakes in proximity to raised beach ridges, they have rarely been studied in combination. In this study, we use a multiproxy approach including geospatial data, lake sediment coring, ground penetrating radar and optically stimulated luminescence dating to investigate the Holocene coastal evolution and RSL history at Rugård in Mols Bjerge National Park, on the east coast of the Jutland Peninsula. Our results show that the coastal area at Rugård was transgressed between c. 7.6 and 7.0 cal. ka BP and that RSL was ~4.5 m higher than present between c. 6.6 and 5.9 ka ago, when the highest section of the beach ridge plain was deposited. The elevation and timing of this relative highstand are in good agreement with previous estimates of the Littorina transgression and contribute to our combined knowledge about RSL history and coastal evolution in the southern Kattegat. Subsequently, isostatic adjustment has caused uplift and erosion of the beach ridge plain, but renewed progradation and deposition of a lower beach plain have taken place since c. 1740 CE. Our results demonstrate the value of using a multiproxy approach to study RSL changes and coastal evolution.

New datings and elevations of a fossil reef in Lembetabe, southwest Madagascar: eustatic and tectonic implications

The study of geological sea-level proxies formed during previous interglacials is a common approach to assess how global sea level will evolve under warmer climate conditions. Over the last decades, technical advancements in both survey and geochronology have allowed improving our knowledge of past sea-level highstands. This is of prime importance to refine our understanding of processes contributing to sea-level changes, and ultimately to improve both local and global sea-level projections. Last Interglacial sea-level proxies in the Western Indian Ocean (and more specifically the island nation of Madagascar), have been less investigated than in other intertropical oceans over the last decades. As a result, paleo sea-level data in this region are less abundant and less precise than elsewhere. Here, we report the results of two field campaigns aimed at studying the site of Lembetabe, southwest Madagascar, where a fossil reef was first described by the researcher René Battistini more than 50 years ago. We estimate paleo relative sea level history in space and time from 15 new U-series ages from a fossil reef platform mapped with differential GNSS and drone photogrammetry. Our data suggest that, between 129 ka and 115 ka, paleo relative sea level at this location was about 3.4 ± 1.4 m above modern. Once corrected for glacial isostatic adjustment, we find that paleo global mean sea level did not exceed 3 m above modern. Only slight crustal subsidence would reconcile the peak Last Interglacial sea level measured at Lembetabe with the 5–10 m range reported in the literature.

Holocene Sea Level Recorded by Beach Rocks at Ionian Coasts of Apulia (Italy)

Beach rocks are located along many coasts of the Mediterranean basin. The early diagenesis environment and the mean sea level along the shoreline make these landforms useful in the reconstruction of relative sea-level changes and, in particular, as SLIPs (sea-level index points). The beach rocks surveyed along the Ionian coast of Apulia were found to be well preserved at three specific depth ranges: 6–9 m, 3–4 m, and from the foreshore to about 1.20 m. Morpho-bathymetric and dive surveys were performed to assess both the geometries and the extension of the submerged beach rocks. Samples were collected at these different depths in the localities of Lido Torretta, Campomarino di Maruggio, San Pietro in Bevagna, and Porto Cesareo. Bivalve shells were identified and isolated from the beach rock samples collected at a depth of 7 m; AMS dating provided a calibrated age of about 7.8 ka BP. Their morphology and petrological features, along with the time constraints, enabled us to (i) reconstruct the local sea-level curve during the Holocene, (ii) corroborate acquired knowledge of the relative sea-level history, and (iii) identify possible local vertical land movement (VLM).

Holocene relative sea-level histories of far-field islands in the mid-Pacific

Holocene relative sea-level (RSL) data from far-field islands in the mid-Pacific have been used to validate the ice-melting histories of glacial isostatic adjustment (GIA) models. However, a lack of quality control in the reconstruction of RSL hinders the understanding of regional variability that can constrain ice-equivalent sea-level changes. Here, we present a standardised database of Holocene RSL data from five regions in the mid-Pacific (Cook Islands, Tuamotu Islands, Christmas (Kiritimati) Island, Gilbert Islands and Fiji). We categorised the data as high or low quality based on the susceptibility of samples to age and/or elevation errors. Of the 614 data points that were reviewed, 25% were rejected and 100 sea-level index points (SLIPs) were reinterpreted as limiting data. The new database consists of 141 SLIPs and 262 marine and 56 terrestrial limiting data points reconstructed from a variety of sea-level indicators (e.g., coral microatolls, mangrove peat, beachrock, and beach ridges), of which 71% provide high-quality constraints on RSL. The early to mid Holocene RSL evolution in the Cook Islands, Gilbert Islands and Fiji are poorly constrained due to a lack of high-quality SLIPs and limiting data during this period. The Tuamotu Islands provided the only record of early to mid Holocene evolution of RSL, indicating rapid RSL rise from between −22.9 m and −15.2 m at ∼9.0 ka to between −0.2 m and 0.5 m by ∼6.5 ka, at rates as high as 9.8 ± 5.1 mm/a, with a slowdown in the rate of RSL rise sometime between ∼8.2 ka and ∼6 ka. The Christmas (Kiritimati) Island record indicates stable RSL within ∼1.5 m of present-day levels over the past ∼6.6 ka. In the late Holocene, the Cook Islands record suggests a gradual fall in RSL over the past ∼2.9 ka at rates below 0.1 ± 4.3 mm/a. SLIPs at Fiji also indicate a slight fall in RSL at rates of less than 0.5 ± ∼4.4 mm/a at ∼4 ka, following which RSL fell from above 0.9 m at ∼3 ka to between −0.3 m and 0.6 m by ∼2.5– ∼2.1 ka. We highlight the importance of standardisation and quality control to critically evaluate the processes controlling RSL and validate GIA models. Indeed, the new standardised database has implications for the timing of the mid- Holocene highstand, which has been used to support the ICE-4G and ICE-7G_NA models. Due to the poor constraints of data in the mid-Pacific islands, particularly in the early Holocene, there remains no unique solution for a global ice-melting history.

Holocene relative sea-level changes in northwest Ireland: An empirical test for glacial isostatic adjustment models

The late-Quaternary relative sea-level (RSL) history of Ireland is complex, positioned at the margins of the former British-Irish Ice Sheet, and subject to the influence of ice unloading and forebulge collapse. Geophysical models of post-glacial isostatic adjustment (GIA) provide estimates of the pattern of RSL change since deglaciation which may be tested and validated with empirical data from proxy records. For the region of northwest Ireland, there is a paucity of high-quality RSL data and, therefore, equivocal evidence to support the GIA models that predict a mid to Late-Holocene RSL highstand of between +0.5 and +2 m above present. This study aims to investigate this model-data discrepancy by reconstructing RSL change from a near continuous salt-marsh sequence at Bracky Bridge, Donegal, spanning the last ca. 2500 years. We develop a transfer function model to reconstruct the vertical position of sea level using a regional diatom training set to quantify the indicative meaning and predict the palaeomarsh elevation of the core samples. A chronology is provided by a combination of 14C and 210Pb data, with sample specific ages derived from an age-depth model using a Bayesian framework. Our reconstruction shows ca. 2 m of relative sea-level rise in the past 2500 years. This is not compatible with some previously published sea-level index points from the region, which we re-interpret as freshwater/terrestrial limiting data. These results do not provide any evidence to support a Mid-Holocene RSL highstand above present sea level. Whilst none of the available GIA models replicate the timing and magnitude of the Late-Holocene RSL rise in our reconstruction, those which incorporate a thick and extensive British-Irish Sea Ice Sheet provide the best fit.

A re-evaluation of Holocene relative sea-level change along the Fujian coast, southeastern China

The southeastern China coast is a region of special interest in the study of past and present relative sea-level change, given its distal location from giant ice sheets (far-field regions). During the past decades, a large number of biological, geological, and archaeological sea-level indicators have been retrieved from the Fujian coastal region which allows for recalibration and recalculation of sea-level index points (SLIPs). This study constructs a database of Holocene relative sea-level (RSL) observations for the Fujian coast, southeastern China. The database contains 59 quality-controlled SLIPs which show that RSL for the Fujian coast did not exceed present (0 m) during the Holocene, except potentially during 7.5–5.5 cal. kyr BP and 1.8–0.7 cal. kyr BP. Rates of RSL change were highest during the early Holocene and have decreased over time, due to the diminishing response of the Earth's mantle to glacial isostatic adjustment (GIA) and reduction of meltwater input. A series of sea-level oscillations were recorded in our SLIPs-based reconstructions which might correspond to global climate warming or cooling events. We assessed the spatial variability of RSL histories and compared these with the ICE-6G_C and ANU-ICE GIA model predictions. Substantial misfits between GIA predictions and regional RSL reconstructions were recognized: (1) the deceleration of the early-Holocene sea-level rise ended about one millennia earlier in the ICE-6G_C model than in the SLIPs-based reconstructions; (2) GIA model predictions show a mid-Holocene sea-level highstand of 1–3 m which is absent from our SLIPs-based reconstructions; and (3) all GIA model predicted a gradual RSL fall to 0 m since the middle Holocene, while our reconstruction displays significant RSL oscillations. It is presently unknown whether these misfits are caused by uncertainties in regional tectonic movement estimation or parameters used in the GIA models. Future applications of spatiotemporal statistical techniques are required to better quantify the gradient of the isostatic contribution and to provide improved context for the assessment of the ongoing acceleration of sea-level rise.

Robbins Island: The index site for regional Last Interglacial sea level, wave climate and the subtropical ridge around Bass Strait, Australia

A unique index-record of Last Interglacial (Marine Isotope Stage 5e MIS5e) relative sea level (RSL) and wave climate history in South-east Australia is presented from Robbins Island, in western Bass Strait. This is applied to interpret the wider MIS5e coastal evidence around Bass Strait. At Robbins Island, the combination of low wave and wind energy, a tide-modified regime and a sand supply resulted in the shoreline progradation throughout MIS5e. This preserved a time-series of paleo-sea level across a 7 km wide strandplain (Remarkable Banks). After a highstand, MIS5e RSL attained a stillstand of +5.75 ± 0.5 m above modern mean sea level during 126 to ∼119 ka BP. The MIS5e RSL interpretation is underpinned by modern analogues and hydrodynamic modelling of waves, tides and currents. A high resolution LiDAR Digital Elevation Model (DEM) supported by morpho-sedimentary studies, ground-penetration radar (GPR) surveys and a geochronology based upon Optically Stimulated Luminescence (OSL) methods were used to define the proxy RSL record. The observed RSL history was compared to modelled RSL history that accounted for the theoretical fall in RSL (regression) throughout MIS5e, due to the Glacio-Isostatic Adjustment (GIA) forcing.

Relative sea level response to mixed carbonate-siliciclastic sediment loading along the Great Barrier Reef margin

The continental shelf along northeastern Australia is the world's largest mixed carbonate-siliciclastic passive margin and the location of the Great Barrier Reef (GBR). Following sea-level transgression during the last deglaciation, extensive sediment was deposited along the GBR due to neritic carbonate deposition (including shelf edge reefs, Holocene reefs and Halimeda bioherms) and fluvial discharge of terrigenous siliciclastic sediments. Such sediment loading can alter local relative sea level (RSL) by several metres through the sediment isostatic adjustment (SIA) process, a signal that is poorly constrained at the GBR. In this study, we used a glacial isostatic adjustment (GIA) model to develop an ensemble-based sediment loading history for the GBR since Marine Isotope Stage 2 (MIS 2). A Bayesian style framework is adopted to calibrate the sediment history ensemble and GIA model parameters using a sea-level database. According to our results, 1853.7 Gt (1613.1-2078.7 Gt, 95% confidence interval) of sediment have been deposited across the GBR since MIS 2 (28 ka BP), causing spatially variable relative sea-level change with the highest magnitude (0.9-1.1 m) found in the outer shelf of the southern central GBR (18.4-21.6∘ S). Because the SIA-induced RSL rise is unrelated to ice mass loss, failing to correct for this signal will lead to systematic overestimation of grounded ice volume by up to ∼4.3 × 105 km3 during the Last Glacial Maximum. Additionally, we found that spatial variation in sediment loading and coastal environment may explain the different RSL history documented by published fossil coral reef records from Noggin Pass and Hydrographer's Passage. These results highlight the importance of considering SIA for any postglacial sea-level studies adjacent to large sediment systems. Lastly, by quantifying both the GIA and SIA signals, we provide a spatially and temporally complete RSL reconstruction that is well-suited to be used as a boundary condition to study the evolution of the GBR shelf and slope sedimentary system.

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.

Sea level response to late Pliocene-Quaternary erosion and deposition in Scandinavia

Erosion and deposition can perturb regional sea level significantly by altering the Earth's surface and by redistributing mass. However, no studies have investigated the importance of these geomorphic processes for glacial settings on glacial-interglacial time scales, despite large erosion rates and the inherent importance of sea-level changes for ice-sheet dynamics and stability. Here we quantify how glacial erosion and depositional processes have affected relative sea level in western Scandinavia where glacial activity has reoccured periodically throughout the late Pliocene-Quaternary. By comparing offshore sediment volumes with onshore topographic relief, we quantify erosion and deposition for the last two glacial cycles as well as the entire late Pliocene-Quaternary. Specifically, we develop a history of erosion and deposition for the last two glacial cycles by scaling the erosion rate with the normalised global ice volume through time. We use the ice model ICE6G_C as a global ice history and calculate sea-level changes through time as a result of ice, water, and sediment loading using a global gravitationally self-consistent sea-level model. Our results show that geomorphic mass redistribution, excluding direct changes in ocean depth owing to erosion and deposition, has caused a sea-level fall of ≈50–100 m along the southern coast of Norway during the last two glacial cycles reaching ≈120 m in the offshore Skagerak region. During the late Pliocene-Quaternary, the total sea-level fall reach as much as ≈ 310 m in Skagerak. These results showcase the importance of erosion and deposition for the relative sea-level history of Scandinavia with implications for studies of ice-sheet history and regional glacial rebound in this region and elsewhere.