Present Sea Level Research Articles

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.

Reindeer prey mobility and seasonal hunting strategies in the late Gravettian mammoth steppe

Reindeer are part of the faunal suite that dominated central Europe during the last glacial cycle. Their importance to Late Gravettian hunters as prey and a source of raw materials (hide, bone, antler) is well attested, however the context of Late Gravettian reindeer predation is lesser understood. This paper presents an investigation of human and reindeer predator-prey interactions at the Late Gravettian kill-butchery site of Lubná VI, Czech Republic. We reconstruct seasonal mobility (87Sr/86Sr, δ18O), diet (δ13C, δ15N) and season of death (dental cementum) of up to nine reindeer prey, to inform on the strategic choices made by Late Gravettian hunters. Results indicate that most hunted reindeer lived year-round in the foothills of the Bohemian-Moravian highlands near where Lubná is located, at altitudes between ~ 200–450 m above present sea level, while a smaller number showed evidence of seasonal migration between this area and the open plains of the Elbe river corridor (Bohemian Cretaceous basin). No evidence for long distance migration of reindeer was detected, indicating that productive local environments were supporting reindeer herds within a single annual territory. Meanwhile, areas higher than ~ 450 m above present sea level were avoided entirely by all analysed individuals, consistent with these areas being topographic barriers to movement due to climate severity. We conclude that hunters visited Lubná as part of a logistically-organised subsistence strategy, deliberately targeting reindeer in late autumn when fat supplies, hides and antler are in prime condition knowing that they would reliably encounter their prey at this location.

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.

Last interglacial and MIS 9e relative sea-level highstands in the Central Mediterranean: a reappraisal from coastal cave deposits in the Cilento area, Southern Italy

A revaluation of the relative sea-level (RSL) indicators in the Baia di Infreschi (Cilento, Southern Italy) supported by new 30 U/Th dating on speleothems indicates that the upper level of Lithophaga burrows identified by Bini et al. (2020) at ∼9 m a.s.l. and correlated to the Last Interglacial (LIG) highstand should be referred to the highstand of the MIS 9e, whereas the local RSL for the highstand of the LIG is now reassessed at 5.3 ± 0.18 m a.s.l. The upper level of the Lithophaga marker can be followed for ∼12 km along the coast, suggesting a substantial absence of important relative tectonic movements. In the Baia di Infreschi an additional marine indicator, a notch sealed by a flowstone dated ∼110 ka, indicates several phases of RSL stationing below the maximum highstand of the LIG. The presence of flowstones as low as 2 m a.s.l. dated to the MIS 7 shows that the highstand of MIS 7 was probably below the present sea level. All these evidences allow us to reassess the stratigraphy of some archaeological caves in the area, indicating that the sedimentary successions preserved there are older than what was previously believed.

Kaiwi shoreline basalts fed by the west rift zone of East Molokaʻi

Bathymetry and acoustic imagery swath mapping, along with observations and samples from four manned submersible and four ROV dives, confirm that a seafloor slope break on the northern approaches to Kaiwi Channel, between the islands of Oʻahu and Molokaʻi, Hawaiʻi is a former shoreline, now submerged ∼800 m below present sea level. Subaerially emplaced, low-relief basaltic lavas above the slope break transition to submarine morphologies below. The entire region has been tilted about 1° to the SSE (150°), and is cut by an 8–15 m-high, north-facing scarp, 100–400 m south of the slope break. The distribution of platy, table-top, and rarer mounded branching corals indicates the former presence of fringing reefs around low-relief paleo-islands. We infer that the regional tilt resulted from loading by younger Hawaiian volcanoes, compounded by flexural uplift and back tilting away from the unloaded footwall of a flank landslide to the north.Basalt samples collected from both above and below the slope break have petrography, chemical composition, and age (1.64–1.80 Ma) indicating correlation with the (late-shield) Lower Member of the East Molokaʻi Volcanics, rather than with the more proximal volcano of West Molokaʻi. The most likely source of the Kaiwi basalts is a submarine ridge (rift zone) that extends northwest away from ʻĪlio Point on West Molokaʻi. Although the submarine ridge was previously assumed to be an extension of West Molokaʻi's northwest rift, we conclude that regional bathymetry and gravity are consistent with this feature being an extension of the west rift of East Molokaʻi. A corallary of this interpretation is that the shoreline slope break (SSB 7 of Taylor, 2019) in this area is distinct from and younger than the southern SSB 7 formed on West Molokaʻi volcano (∼1.65 Ma vs. ∼1.8 Ma).

A record of late Holocene sea level and human impacts from the southeastern Coast of Sri Lanka

AMS radiocarbon-dated palynological evidence from Embilikala Lagoon in Bundala National Park (one of the Ramsar wetland sites) on the southeast coast of Sri Lanka indicates palaeoenvironmental changes during the last 2,700 years. The persistence of fewer mangroves (eg Rhizophoraceae taxa) suggests that sea level low stands occurred between 2,700 and 1750 cal yr BP. From the later age, the relative sea level rose, and reached the present sea level at 950 cal yr BP as indicated by the mangrove maximum. At 2,250, 700–400 and 200–150 cal yr BP, the sudden increase in marine dinoflagellate cysts (eg Spiniferites mirabilis) and foraminifera (Globigerinoides ruber) suggests increased marine influence. This is consistent with a decrease in mangrove habitats. Between 2,700 and 950 cal yr BP, severely degraded dry monsoon forests and minimal levels mangrove suggest human and marine influences were the critical drivers for changing the major vegetation types along the southeastern coast. Vegetation changes have been drastic over the last millennia.

Coastal Evolution of Satingpra Peninsula, Songkhla Province: Implications for Understanding Songkla Lagoon Formation

Songkhla Lagoon has been studied for decades, but there is no clear evidence of its origin. As a barrier to the lagoon, the Satingpra Peninsula plays a crucial role in understanding its formation. Eleven sediment samples from sand ridges and tidal flats on the Satingpra Peninsular were collected and analysed for granulometry and geochronology. Both coarse-grained and fine-grained quartz-rich fractions were utilised to prepare samples of aliquots. The optically stimulated luminescence (OSL) dating was performed using the single-aliquot regenerative dose method for a determined (deposited) age. In addition, previous research, geological surveys and geochronological data were combined to explain their formation in this region. The OSL ages in the present study indicated that the late Holocene regression occurred between 0.36 and 3.27 ka (ka stands for 1,000 years). Integrated with previous studies, recorded ages dating back to the mid-Holocene sea level rise (ca. 6.5 ka) and the subsequent late-Holocene decline, indicate that both the old lagoon and middle beach ridge exhibit a sand ridge formation that runs parallel to the shoreline, extending from the south to the north. The middle sand, in this study, formed from about 3.02 to 1.5 ka ago resulting in the lagoon being isolated from the sea during that time. The lagoonal tide led the deposition as the present tidal flat from 3.3 to 1.7 ka. About 2.19 ka ago, the inner and middle ridges formed due to wind-driven processes influenced by a dry climate. This was followed by a continued sea level regression, leading to the formation of the outer ridge around 1.5 ka ago when the sea level was 1.4 m below the present sea level. However, it’s essential to consider this sea level data in relation to the tectonic and human-induced land motions in the surrounding area. HIGHLIGHTS OSL ages, based on average dose model at the Northern Satingpra Peninsula were 1.04 - 3.27 ka. The old sand ridges of the Satingpra Peninsula prograde northward after mid Holocene sea level highstand. Paleo sea level based on wind-wave sediments contact was 1.4 m lower than present day at 1.46 ka. GRAPHICAL ABSTRACT

Influence of the last (de)glaciation on a complex cave system: Grønli-Seter cave system, Northern Norway

Cave studies enable us to unravel valuable information on landscape evolution. In glacial settings, the glacial cycles induced fluctuations in the underground hydraulic regime, sediment availability and base level in adjacent caves. Here, we present our work on the Grønli-Seter cave system in Northern Norway, which comprises >8 km of passage length at an elevation between 250 m and present sea level. By linking cave morphology and deposits to shifting glacier configurations and external base level changes during the last deglaciation and the Early Holocene, we establish how the hydraulic conditions in the cave system shifted in pace with glacier fluctuations. Maze sections and phreatic loops appear in a hydraulic confined setting close to the interface between the calcite marble and the overlying mica schist. Scallops in the cave walls demonstrate slow, ascending water flow, evidence of subglacial speleogenesis under wet-based, topographically constrained glaciers with a gentle surface slope. Moreover, cave morphology and clastic deposits indicate various hydrological phases of descending water flow, stagnant conditions, and excessive flow rates. Our work establishes that the last glaciation and deglaciation had an insignificant effect on the cave system's solutional development. In contrast, the cave sediments reveal diverse hydraulic conditions that may be related to shifting glacier configurations. This research offers valuable insights into glacier ice-contact speleogenesis and landscape development in glacial terrains.

A National‐Scale Coastal Flood Hazard Assessment for the Atoll Nation of Tuvalu

AbstractAtoll nations such as Tuvalu are considered to be amongst those most vulnerable to the effects of climate change. Here we present a national‐scale coastal flood hazard assessment for Tuvalu based on high‐resolution Light Detection and Ranging (LiDAR) topography and bathymetry. We follow a fully probabilistic approach, considering sea level anomalies, tides, and extreme wave conditions from a mixed climate (i.e., from distant extra‐tropical storms and local tropical cyclones). Nearshore processes such as wave setup and runup are also accounted for. Hazard maps were calculated for the present sea level, as well as for sea level rise projections corresponding to different shared socioeconomic pathways (SSP2 4.5 and SSP5 8.5) and time horizons (2060 and 2100). With a mean elevation of 1.55 m above mean sea level (1.37 m above mean high water spring) >25% of land area is inundated once every 5 years and >50% of land area floods once every 100 years nationally. Results indicate that present day 1‐in‐50 years floods (>45% of land area flooded) will occur more than once every 5 years by 2060 (annual exceedance probability >20%), even under the moderate SSP2 4.5 sea level rise projections. Results of this study highlight the pressing need for ambitious and large‐scale adaptation solutions which are commensurate with projected sea level rise and marine hazard impacts. The methodologies presented in this paper can easily be applied to other low‐lying islands in the tropical Pacific, where mixed climates (i.e., regular and TC conditions) and non‐linear nearshore processes dominate extreme water levels and flooding.

Extensive freshened groundwater resources emplaced during the Messinian sea-level drawdown in southern Sicily, Italy

Deep groundwater resources around the world represent an important potential unconventional source of water. Here we document an extensive (17.3 km3) fresh/brackish groundwater body preserved in a deep (between 800 and 2100 m) carbonate platform aquifer (Gela Formation.) in southern Sicily (Italy), by using deep well data and a 3D hydrogeological modelling. We attribute the distribution of this fossil groundwater to topographically-driven meteoric recharge driven by the Messinian sea-level drawdown, which we estimate to have reached 2400 m below present sea level in the eastern Mediterranean Basin. The discovery of such an extensive and deep freshened groundwater has significant implications in terms of resource potential for southern Sicily as well as other Mediterranean coastal regions, which share similar geological setting and water scarcity issues.

Tsunami or storm? A high-level coastal boulder field on the southern tip of Eyre Peninsula, South Australia

A high-level coastal boulder field at Whalers Way, southern Eyre Peninsula, South Australia, occurs at elevations of 20–30 m above present sea-level on a gently seaward-sloping, karst-weathered calcrete-capped structural bench, formed on the Upper Pleistocene Bridgewater Formation and underlying Carnot Gneisses (Archean–Paleoproterozoic Sleaford Complex). More than 1000 ex situ boulders, cobbles and pebbles of gneiss and mafic igneous rocks, as well as fragments of calcrete, occur within the boulder field and cover an area >6000 m2. All the crystalline rock clasts are derived locally from bedrock outcrops along the adjacent coastline, where metasedimentary granulite-facies of the Carnot Gneisses crop out along shore platforms and their backing cliffs, close to present sea-level. The boulder field is younger than Marine Isotope Sub-Stage 5a (MIS 5a; ca 80 ka) based on amino acid racemisation ‘whole-rock’ analyses of calcarenite of the Bridgewater Formation, which forms the calcrete bench on which the boulder field rests. The boulder field wraps around the western extremity of cliff-top dunes dated at 18–17 ka by optically stimulated luminescence, implying that the boulder deposit post-dates the formation of the cliff-top dunes. Given that the clasts in the boulder field show minimal weathering rinds, sea-level during the Last Glacial Maximum was some 125 m lower than present and that between 80 and 7 ka ago, sea-level never attained present levels within the region, emplacement of the boulder field by a high-energy wave event in the Holocene highstand, following the 7000 years BP culmination of post-Glacial sea-level rise, is suggested. Storm waves, rather than a tsunami, most likely explain the emplacement of the boulder field.

Holocene Relative Sea-Level Changes Along the Southern Coast of Bodrum Peninsula, SW Anatolia

Bodrum Peninsula, which developed under the influence of the extensional tectonic regime in the west of the Anatolian plate, is one of the areas where indicators reflecting relative sea-level changes are seen above the present sea level. These indicators appear in different types throughout the peninsula. This study examined shorelines from sea level to +2.6 m at 6 locations on the southern coast of the Bodrum Peninsula. Suitable indicators for dating were found at two different locations in the study area, and two relative sea-level indicators using mollusk shells were dated by radiocarbon method. One of the indicators is a +1.3 m high beach deposit at Gerenkuyu and was dated to 2678.5±79.5 yr BP. The other indicator is a +1.2 m high beach deposit at Gerindere, which is thought to be compatible with the tidal notch and dated to 2241±88 yr BP. Based on the age data and the reliability of tidal notches as a shoreline indicator, the uplift rate of this indicator in Gerindere for the last 2241±88 years has been calculated to be 0.53 mm/yr.

Earliest Neolithic occupation and maritime adaptation on the West Pacific coast

Maritime adaptation plays a significant role in the dispersal of modern humans and the transition of subsistence strategies. The real timing of the worldwide intensification of maritime adaptation has been debated mainly because of the presumed inundation of archaeological sites (prior to 7000 cal yr BP) by early Holocene sea-level rise. In this study, we present a coastal shell midden submerged ∼8 m below the present sea level at the Jingtoushan site, containing robust evidence of the earliest Neolithic occupation and maritime adaptation on the West Pacific. Bayesian modelling of 15 14C dates, cultural deposits, and microfossils (pollen, phytolith, and diatom) indicated that the Jingtoushan site was an anthropogenic deposit originally accumulated on the coastline during the stable sea-level period (8000–7600 cal yr BP) and subsequently submerged by sea-level jumps. In addition to being largely dependent on marine food resources, humans also utilised the stable sea-level window of meltwater pulses and began rice cultivation. This study not only pushed back the timing of maritime adaptation to 8000 cal yr BP but also provides promise for future investigations of coastal underwater settlements, shedding new light on the understanding of the West Pacific coastal environment and cultural succession.

LATE GLACIAL PALAEOENVIRONMENT AND DEVELOPMENT OF PROGLACIAL LAKES ON THE NORTHERN COAST OF THE SAMBIAN (KALININGRAD) PENINSULA<a href="#FN1"><sup>1</sup></a>

Comprehensive investigations of the northern coast of the Sambian (Kaliningrad) Peninsula, that included geomorphological survey, lithostratigraphic description of the section logs, diatom, botanical and LOI analyses, radiocarbon dating, and GNSS survey relating lithological boundaries and sampling levels to the sea level and determining terrace elevations, were performed. New data on the regional palaeogeographic settings of the Late Glacial period and the stages of development of the large proglacial basin, the Baltic Ice Lake (BIL) were obtained. It has been established that after the degradation of the last glaciation, erosional (subaquatic) processes prevailed in the coastal area, while in the interval of 14–13 cal kyr BP subaerial conditions established at the study site, and tree-moss phytocenoses formed during the Allerød warming. At the end of the warming period there was a shallow, isolated lake, with decreasing depth. During the Younger Dryas oscillation, ca. 12 000 cal kyr BP, the area was flooded by waters of a vast freshwater, ultra-oligotrophic basin with high content of suspended fine mineral particles. The conditions of a shallow bay of the BIL sheltered from the main basin by a moraine ridge at least 4–5 m high, are suggested for this period. The lake drainage took place around 11 660 cal kyr BP. Since then, no accumulation or alternating accumulation and erosion conditions prevailed in the study site until the late Holocene. The obtained results allow us to speak about two stages of flooding of the northern coast of the Sambia Peninsula during the Late Glacial, possibly caused by the BIL transgressions. The occurrence of BIL deposits in the northern part of the Sambia Peninsula above sea level suggests that the Late Glacial basin level in the study area may have exceeded the present sea level.

Lake Maggiore: geomorphological genesis, lake-level evolution, and present and future ecosystems importance

Lake Maggiore, the second deeper and larger south alpine lake, was selected as a model system to detect the potential damages on water resources, biodiversity and ecosystem health caused by different water levels during the lake-level regulation period (March to November). With a drainage basin exceeding an altitude difference of 4400 m, Lake Maggiore fills a deep valley floor whose bedrock reaches up to 700 m below the present sea level. The cryptodepression occupied by the lake was probably formed during the end of the Miocene and the Pliocene and was shaped successively during the Pleistocene glaciations. Lake Maggiore originated following the Last Glaciation, when it reached its maximum lake-level and extension just after its deglaciation. The mean secular lake-level progressively decreased throughout the Holocene, causing a gradual shrinkage of the lake because of the constant depositional input that created the fluvio-deltaic plains at the mouth of the main tributaries of the lake. The regime of the tributaries is of mixed type, with a spring maximum mainly due to snowmelt and an autumn maximum exclusively of pluvial origin. Water levels naturally tend to reflect the amount of rain or snow precipitation and are expressed through a double cycle: winter and summer characterised by low waters, and spring and autumn by high waters. In 1943, the need to use the waters of the great lakes to have water available in the less favourable periods, led to the construction of a dam at the Lake Maggiore outlet. This structure allows to store water during heavy rainfall or snowmelt periods. The accumulated water is then supplied during the irrigation periods to agriculture (spring and summer) and to industrial users (mainly in autumn and winter). The geomorphological genesis and the ecosystems description was focused on riparian, fluvio-deltaic, and ephemeral systems. For these ecosystems, their evolution considering the hydrological regime of the tributaries, the anthropogenic activities in the watershed and the effects of lake-level management since 1943, was also described. Considering the summer increase, between April and July, to +1.25 m (with possible peaks to +1.50 m) experimentally tested between 2015 and 2020, and the approval of the proposal to continue the test for the next five-year period (2022-2026), we finally emphasise the potential further reduction of reeds and natural habitats and the subsequent loss of biodiversity related to the plan of raise the lake-level to +1.50 m all year round.

40Ar/39Ar Age Constraints on MIS 5.5 and MIS 5.3 Paleo‐Sea Levels: Implications for Global Sea Levels and Ice‐Volume Estimates

AbstractWe integrate 10 new with five published 40Ar/39Ar age determinations, both on primary volcanic deposits and on detrital sanidine, which provide precise geochronologic control on the Marine Isotope Stage (MIS) 5.5 and MIS 5.3 sea‐level indicators that occur at three coastal caves in a tectonically stable region of the central Tyrrhenian Sea of Italy. The age of a Strombus‐bearing bioclastic conglomerate, associated with a tidal notch occurring at 9.5 m a.s.l. at Cape Circeo, is constrained to between 121.5 ± 5.8 and 116.2 ± 1.2 ka. Moreover, backbeach deposits intercalated in the sedimentary filling of Guattari and Capre coastal caves are directly correlated with a tidal notch at ∼2.5 m associated with another bioclastic conglomerate at Cape Circeo and dated to 110.4 ± 1.4–104.9 ± 0.9 ka. The latter deposit is also correlated with the adjacent marine terrace, occurring at 3–5 m on the coast between Capes Circeo and Anzio, for which a maximum age of 100.7 ± 6.6 ka was previously reported. These data provide evidence for a maximum sea level around 9.5 m above the present sea level and a duration of MIS 5.5 highstand until 116 ka, in agreement with estimates from other regions in the world. In contrast, they suggest a maximum sea level during MIS 5.3 highstand that is similar to the present level, and only ∼7 m lower than the MIS 5.5 highstand, challenging the reconstructions of the MIS 5 ice‐sheet volumes and derived global sea levels that are based on benthic oxygen isotope records.

Pb-210 Dating of Ice Scour in the Kara Sea

Ice scours are formed when the keels of floating icebergs or sea ice hummocks penetrate unlithified seabed sediments. Until now, ice scours have been divided into “relict” and “modern” according to the water depth that corresponds with the possible maximum vertical dimensions of the keels of modern floating icebergs. However, this approach does not consider climatic changes at the present sea level, which affect the maximum depth of ice keels. We present an application of 210Pb dating of the largest ice scour in the Baydaratskaya Bay area (Kara Sea), located at depths of about 28–32 m. Two sediment cores were studied; these were taken on 2 November 2021 from the R/V Akademik Nikolay Strakhov directly in the ice scour and on the “background” seabed surface, not processed via ice scouring. According to the results of 210Pb dating, the studied ice scour was formed no later than the end of the Little Ice Age. Based on the extrapolation of possible sedimentation rates prior to 1917 (0.22–0.38 cm/year), the age of the ice scour is estimated to be 1810 ± 30 AD. The mean rate of ice scour filling with 70 cm thick sediments from the moment of its formation is around 0.33 cm/year.

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.

Relationship of Satellite Altimetry Data, and Bathymetry Observations on the West Coast of Africa

The sea surface is variable in time and space; therefore, many researchers are currently interested in searching for dependencies and connections with the elements influencing this diversity, e.g., with the seabed topography. An important problem is combining or comparing models obtained based on different data sets with different accuracies and spatial resolutions. These studies are designed to discover the relationship that may exist between observations of the shape of the seabed and changes in sea level. The aim of this study is to investigate the relationship by checking the correlation between the observations from the point recording of satellite altimetry measurements and the bathymetric data. The object of research is the capital city of Gabon—Libreville, located on the west coast of Africa and three point in Las Palmas. The results present sea level, salinity, and potential temperature variations in selected points. The highest trends of sea level changes occur, at one point, in the open ocean (P6) and at coastal points (Libreville, P3, Pointe Noire). The study indicates that, from 1993 to 2020, the temperature trend at the assessed points is on average 0.018 ± 0.012 °C·year−1, while the average salinity trend is 0.008 ± 0.005 1e−3 year−1. The correlation coefficients for the sea water temperature trend and the sea water salinity trend—determined at 0.20 and 0.08—present a weak linear relationship. Correlation takes slightly higher values for elevation, which is determined at 0.38. Research shows that there is a relationship between satellite and bathymetric observations on the east coast of Africa; however, the strength of the correlation depends on the location.

Implications of anomalous relative sea-level rise for the peopling of Remote Oceania

Beginning ~3,500 to 3,300 y B.P., humans voyaged into Remote Oceania. Radiocarbon-dated archaeological evidence coupled with cultural, linguistic, and genetic traits indicates two primary migration routes: a Southern Hemisphere and a Northern Hemisphere route. These routes are separated by low-lying, equatorial atolls that were settled during secondary migrations ~1,000 y later after their exposure by relative sea-level fall from a mid-Holocene highstand. High volcanic islands in the Federated States of Micronesia (Pohnpei and Kosrae) also lie between the migration routes and settlement is thought to have occurred during the secondary migrations despite having been above sea level during the initial settlement of Remote Oceania. We reconstruct relative sea level on Pohnpei and Kosrae using radiocarbon-dated mangrove sediment and show that, rather than falling, there was a ~4.3-m rise over the past ~5,700 y. This rise, likely driven by subsidence, implies that evidence for early settlement could lie undiscovered below present sea level. The potential for earlier settlement invites reinterpretation of migration pathways into Remote Oceania and monument building. The UNESCO World Heritage sites of Nan Madol (Pohnpei) and Leluh (Kosrae) were constructed when relative sea level was ~0.94 m (~770 to 750 y B.P.) and ~0.77 m (~640 to 560 y B.P.) lower than present, respectively. Therefore, it is unlikely that they were originally constructed as islets separated by canals filled with ocean water, which is their prevailing interpretation. Due to subsidence, we propose that these islands and monuments are more vulnerable to future relative sea-level rise than previously identified.