Rapid Relative Sea-level Rise Research Articles

Rising sea levels and the increase of shoreline wave energy at American Samoa

American Samoa is experiencing rapid relative sea level rise due to increases in global sea level and significant post-2009 earthquake land subsidence, endangering homes and critical infrastructure. Wave and water-level observations collected over a fringing reef at Faga‘itua Bay, American Samoa, in 2017 reveal depth-limited shoreline sea-swell wave heights over the range of conditions sampled. Using field data to calibrate a one-dimensional, phase-resolving nonhydrostatic wave model (SWASH), we examine the influence of water level on wave heights over the reef for a range of current and future sea levels. Assuming a fixed reef bathymetry, model results predict rising sea levels will escalate nearshore extreme water levels that are dominated by an increase in nearshore sea-swell wave heights. Model results provide insight into how and at what reef depths rising sea levels reduce reef capacity to dissipate wave energy, compounding shoreline threats. This study aims to bring increased attention to the immediate threats to American Samoa’s way of life, and to demonstrate the utility of SWASH for extrapolating wave transformation to future sea level.

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.

Coastal switching of dominant depositional processes driven by decreasing rates of Holocene sea-level rise along the macrotidal coast of Gochang, SW Korea

ABSTRACTDecreasing rates of eustatic sea-level rise during the Holocene accompanied the deposition of transgressive coastal deposits worldwide. However, unraveling how transgressive deposition varies in response to different rates of relative sea-level (RSL) rise is limited by the scarcity of long (10+ m) well-dated cores spanning the entire middle to late Holocene record along macrotidal coasts. To investigate the sedimentary response of this macrotidal coast to decreasing rates of RSL rise, we acquired four cores up to 32 m in length and Chirp seismic profiles along the west coast of Korea. Core sediments were analyzed in terms of sedimentary texture, structure, and facies. Nineteen optically stimulated luminescence (OSL) and fourteen 14C accelerated mass spectrometry (AMS) ages constrain the timing of deposition of the sandy sediments. This relatively dense distribution of ages is used to determine how deposition rates changed through time. We also use a compilation of previously published RSL indices for the southwestern Korean coast in order to better constrain RSL changes through time. Results show that the evolution of the Gochang coastline switched from a tide-dominated environment to a wave-dominated environment during the latter stage of transgression as the rate of the sea-level rise decreased. Rugged antecedent topography likely led to the development of tidal currents and the formation of a tide-dominated tidal flat during rapid RSL rise from 10 to 6 ka. As the tidal channels filled with fine-grained sediments from 6 to 1 ka, tidal amplification likely waned leading to a greater role of wave energy in shaping the formation of the sandy open-coast tidal flat. Since 1 ka, wave-dominated environments formed sand-rich tidal beaches and flats. Decreasing changes in rates of the RSL rise resulted in changes in depositional environments from a tide-dominated intertidal flat to an open-coast tidal flat and finally a wave-dominated tidal beach. This study highlights the important role that rates of RSL rise play on not only sedimentation rates in a shelf setting but also playing a role in the switch from a tide-dominated to a wave-dominated setting.

Rapid sea-level rise during the first phase of the Littorina transgression in the western Baltic Sea

Glacio-isostatic adjustment (GIA) corrected limiting non-marine and marine sea-level data from the western Baltic Sea indicate a rapid relative sea-level (RSL) rise of 18 m for the first phase of the Littorina transgression using a linear age-elevation model. This accelerated RSL rise occurred in the time period 8.57 to 8.0 ka before present (BP) with an RSL rise rate of 31.5 mm/year. RSL rose from 28 m to 10 m below the mean relative sea level (bmrsl) during the time period of less than 600 years. The first phase of Littorina transgression documents the last big meltwater pulse (MWP), which has been reported also from various other regions in the world as a consequence of the final decay of the Laurentide ice sheet and additional meltwater sources from Antarctica.

Sedimentary response of a structural estuary to Holocene coseismic subsidence

AbstractStratigraphic evidence for coseismic subsidence has been documented in active-margin estuaries throughout the world. Most of these studies have been conducted in subduction zone or strike-slip settings; however, the stratigraphic response to coseismic subsidence in other tectonic settings would benefit from further study. Here we show evidence of late Holocene coseismic subsidence in a structural estuary in southern California. Below the modern marsh surface, an organic-rich mud containing marsh gastropods, foraminifera, and geochemical signatures indicative of terrestrial influence (mud facies) is sharply overlain by a blue-gray sand containing intertidal and subtidal bivalves and geochemical signatures of marine influence (gray sand facies). We use well-established criteria to interpret this contact as representing an abrupt 1.3 ± 1.1 m rise in relative sea level (RSL) generated by coseismic subsidence with some contribution from sediment compaction and/or erosion. The contact dates to 1.0 ± 0.3 ka and is the only event indicative of rapid RSL rise in the 7 k.y. sedimentary record studied. Consistent with observations made in previous coseismic subsidence studies, an acceleration in tidal-flat sedimentation followed this abrupt increase in accommodation; however, the recovery of the estuary to its pre-subsidence elevations was spatially variable and required 500–900 years, which is longer than the recovery time estimated for estuaries with larger tidal ranges and wetter climates.

As Inland Becomes Coastal: Shifting Equity and Flood Risk in the Amite River Basin (USA)

Abstract Coastal Louisiana is experiencing the most rapid relative sea-level rise in the US due to a combination of a subsiding delta and rising coastal waters. Consequently, the influences of extreme coastal weather are reaching farther inland and impacting urban areas where traditional environmental policy, organised at the parish (county) level, is unable to address this changing flood risks. This situation is most prominent in the metro Baton Rouge region with the largest city situated upstream from two small, but rapidly growing, parishes. Following a massive flood in 2016, the upstream parishes have undertaken policy adjustments to facilitate the expulsion of water toward downstream neighbors and foster redevelopment in the floodplain. The lower parish has expressed concerns about the anticipated increases in discharge to be sent its way. Although the state is concerned with rising sea levels, it has not merged coastal and inland flood policy considerations. Downstream residents have little voice in upstream policy making and the absence of basin-wide management strategy perpetuates emergent risks and environmental injustices. As climate change drives coastal conditions inland, the misalignment between locally based governance and regional environmental realities will become more pronounced and exacerbate social injustices.

Comparing public perceptions of sea level rise with scientific projections across five states of the U.S. Gulf Coast region

Sea level rise (SLR) in the twenty-first century poses fundamental risks to coastal residents. The US Gulf of Mexico Coast (Gulf Coast) is among the regions experiencing the most rapid relative SLR. Beyond its increasing exposure to SLR and related coastal flooding, the Gulf Coast is home to a large population and displays high social vulnerability. How the coastal population in this vulnerable region perceives the impending risks posed by SLR warrants further examination. Do coastal residents’ perceptions of SLR conform to the scientific projections? We adopt an integrative approach based on a 2019 survey merged with contextual data including percentage of population living within the Special Flood Hazard Area (SFHA) and social vulnerability at the county level, both of which are extracted from the Centers for Disease Control and Prevention. We find that public risk perceptions of sea level change are influenced by political predisposition, with Republicans being less likely than Democrats to expect SLR in the future. Moreover, SLR remains a temporally distant issue among coastal residents. We then directly compare public expectations and scientific estimations of SLR in five states of the US Gulf Coast region and find that coastal residents in states that have experienced faster SLR in the past are more optimistic about future SLR by underestimating its magnitude compared to those experiencing slower SLR. Moreover, we find that people likely conflate the severity with likelihood of SLR risk. The contextual force represented by percentage of population living within the SFHA designated by the Federal Emergency Management Agency (FEMA) can significantly influence individuals’ estimations of future SLR, with higher percentages leading to higher estimates. We suspect that the SFHA has become a powerful risk communication tool that influences coastal residents’ judgments about future risk.

Palaeoenvironmental and sea level changes during the Holocene in eastern Saudi Arabia and their implications for Neolithic populations

This paper presents the key findings of a multidisciplinary study investigating the nature and timing of coastal landscape evolution in eastern Saudi Arabia during the Holocene. To date, most sea level reconstructions for the Arabo-Persian Gulf are based on uncalibrated 14C ages without correction for marine reservoir effects, or lack precision with regard to the effects of neotectonic changes, indicators of sea level used, errors in elevation of sedimentary units used, and the relationship with actual tides. As a consequence, the nature and timing of relative sea level (RSL) changes during the Late Pleistocene and Holocene remain poorly understood. To help address this, we use sea level index points (SLIPs) based on calibrated 14C ages to present a RSL curve for the central-southern Gulf of Saudi Arabia from coastal sabkha deposits near the archaeological site of Dosariyah. The sediments record rapid transgression during the early Holocene with a mid-Holocene high-stand immediately prior to 6880–6560 cal. BP when the upper limit for the palaeo Mean Highest High tide water (MHHW) was 2.8–3.10 m above present day mean sea level. Transgression continued until shortly after 5575–5310 cal. BP with an upper limit to the palaeo-MHHW of 3.75 m above present sea levels. Thereafter a fall in RSL was recorded, with the regression leading to the progradation of the coastal system and the development of coastal sabkhas. Nonetheless later transgressions are recorded in the region between 4848–4536 and 4335–3949 cal BP. Radiometric dating results from archaeological excavations at Dosariyah, one of the most important Neolithic coastal sites in the Gulf, suggest that occupation of the site during the Neolithic coincides with the mid-Holocene marine transgression (ca. 7200–6500 cal. BP). Whilst the close proximity of the site to the sea may have facilitated maritime exchange activities, occupation of the site was short-lived and the phase of abandonment occurred during a period of rapid RSL rise, which would have transformed the area around Dosariyah into an island or certainly cut it off tidally from the mainland.

Field‐Based Estimate of the Sediment Deficit in Coastal Louisiana

AbstractCoastal and deltaic sediment balances are crucial for a region's sustainability. However, such balances remain difficult to quantify accurately, particularly for large regions. We calculate organic and mineral sediment mass and volume balances using field measurements from 273 Coastwide Reference Monitoring System sites across the Louisiana Coast between 2006 and 2015. The rapid relative sea level rise rate (average 13.4 mm/year) is offset by the small dry bulk densities observed (average 0.3 g/cm3) to produce a 16.2 ± 41.1% mass deficit and 24.1 ± 14.0% volume deficit, significantly smaller than recent predictions for 2000–2100 (73–79% mass deficit). Geostatisical estimates show that this deficit is primarily located in areas not directly nourished by major rivers, yet these regions still accumulate ~24 MT/year of mineral sediment. A fluvial sediment discharge of 113.8 MT/year suggests a coast‐wide trapping efficiency of 31.5 ± 15.8% of the riverine sediment, excluding subaqueous deposition. Organic accumulation accounts for 25% of all mass accumulation during our study period, and total organic mass accumulation per unit area is relatively constant in both directly and indirectly nourished regions. Sediment characteristics in the modern coastal wetlands differ from the Holocene deposit, suggesting secular changes within the system that will likely continue to influence coastal dynamics over the coming decades. Our results suggest that the gap between accommodation and accumulation (mass or volume) during this decade was not as large as the previously predicted century average.

Late Quaternary sedimentological history of a submerged gravel barrier beach complex, southern Namibia

Through comprehensive seismic, stratigraphic, and sedimentological analysis, this paper describes the stratigraphic architecture of the late Quaternary sediments and depositional dynamics in a region ~ 3.5 km offshore of the current south-west Namibian coastline. The landscape evolution model of this area is based on 2D seismic reflection profiles calibrated to approximately 500 boreholes, which yielded sedimentary and seismic facies data of exceptionally high resolution. The data permitted the characterization of four sedimentary facies units and the reconstruction of the submerged landscape dominated by a barrier complex. We compare this barrier complex with the sediment bodies preserved along the adjacent coastline, and account for their geological evolution in response to late Quaternary relative sea-level fluctuations along the West Coast. The most noteworthy depositional units in the study area are the normal regressive coarse gravel beaches trending shore parallel, with the primary gravel barrier and its preserved coeval back-barrier deposits that exceed 7 km in length along the coast. Based on the radiocarbon dates from the rarely preserved early flooding facies (14.0 and 13.3 ka BP), the primary barrier complex formed during a stage of slowing rising relative sea-level subsequent to Meltwater Pulse 1A. Moreover, the barrier beach complex formed on a low-gradient palaeo-bathymetry slope that is punctuated by a break on its landward side (i.e., a regional knick point), which promoted the local accommodation of sediments. The preservation of the barrier beach complex and back-barrier deposits is attributed to rapid relative sea-level rise, linked to the early Holocene Meltwater Pulse 1B between ~ 11.5 and 11.2 ka BP, and an increase in back-barrier accommodation facilitated by the antecedent topography.

Current and future mudflat losses in the southern Huanghe Delta due to coastal hard structures and shoreline retreat

Coastal wetlands, especially broad mudflats, are facing an unprecedented crisis due to combined influence of intensified coastal development activities, drastic river sediment reduction and rapid relative sea level rise. However, it is still a huge challenge to accurately assess the evolution of mudflats for the lack of reliable shoreline indicators on satellite images, especially the indicators for shoreline at low tide. This study, based on instantaneous shoreline positions derived from 430 Landsat satellite images during 1983–2019, uses sea level correction and statistical analysis methods to study the evolution of Laizhou Mudflat, and the intertidal mudflat loss in Laizhou Mudflat was accurately assessed and the effects of multiple factors, especially the effects of various coastal hard structures, on the evolution of Laizhou Mudflat were quantitatively estimated for the first time. The results show that the intertidal mudflat loss caused by the construction of cofferdams was 98 km2, 93% of the total intertidal mudflat loss. Although the previous intertidal mudflat loss caused by shore-parallel structures was less, the shore-parallel structures will cause great mudflat loss in the future, and the broad Laizhou Mudflat will disappear in 110 years owing to the barrier effect of the widespread shore-parallel structures if the current rapid shoreline retreat is not improved. The construction of shore-normal structures can slow the shoreline retreat of adjacent mudflat but accelerate downstream shoreline retreat. As far as coastal protection is concerned, the construction of shore-normal structures in Laizhou Mudflat is inadvisable. Diverting 13 M ton/year of Huanghe sediment can totally offset the mudflat loss on the upstream of Dongying Pier, however, the mudflat located on the downstream of Dongying Pier is hard to restore owing to the block effect of the shore-normal structures to the alongshore transported sediment. Another option is demolishing the shore-parallel structures to recover the landward movement of shoreline, avoiding the mudflat loss at the expense of land loss.

Topographic and hydrodynamic controls on barrier retreat and preservation: An example from Dogger Bank, North Sea

Barrier retreat can occur due to in-place drowning, overstepping or rollover, depending on the interplay of controls such as sea-level rise, sediment supply, coastal hydrodynamic regime and topography. Offshore sedimentary archives of barriers active during rapid Holocene sea-level rise provide important records of marine transgression, which are vital analogues to support appropriate mitigation strategies for future coastal realignment under projected relative sea-level rise scenarios. This study analyses the sedimentary archive at Dogger Bank, which is a formerly-glaciated area in the North Sea. Dogger Bank experienced marine transgression due to Early Holocene rapid relative sea-level rise. An integrated dataset of vibrocores and high-resolution seismic reflection data permits a stratigraphic framework to be established, which reveals the buried coastal geomorphology of the southern Dogger Bank for the first time. A transgressive stratigraphy was identified, comprising a topographically complicated basal glacial and terrestrial succession, overlain by two phases of barrier and tidal mudflat deposition, prior to shallow marine sedimentation. Barrier phase A was a recurved barrier drowned in place, and discontinuously overstepped to barrier phase B, which experienced continuous overstepping. By linking barrier elevations to relative sea-level curves, the timing of each barrier phase was established. Both barrier phases retreated during periods of rapid sea-level rise with abundant sediment supply. Coastal hydrodynamics (increasing wave energy) and antecedent topography with spatially variable accommodation are suggested to be the main reason for differing retreat mechanisms, rather than the rate of sea-level rise. Antecedent coastal geomorphology plays a critical role in erosional and depositional patterns during transgression, and therefore on the timing, rate and location of marine inundation, which needs to be included in models that aim to forecast hazards in coastal areas.

Origin of a Preferential Avulsion Node on Lowland River Deltas

AbstractRiver deltas are built by cycles of lobe growth and abrupt channel shifts, or avulsions, that occur within the backwater zone of coastal rivers. Previous numerical models differ on the origin of backwater‐scaled avulsion nodes and their consistency with experimental data. To unify previous work, we developed a numerical model of delta growth that includes backwater hydrodynamics, river mouth progradation, relative sea level rise, variable flow regimes, and cycles of lobe growth, abandonment, and reoccupation. For parameter space applicable to lowland deltas, we found that flow variability is the primary mechanism to cause persistent avulsion nodes by focusing aggradation within the backwater zone. Backwater‐scaled avulsion nodes also occur under less likely scenarios of initially uniform bed slopes or during rapid relative sea level rise and marine transgression. Our findings suggest that flow variability is a fundamental control on long‐term delta morphodynamics.

Holocene relative sea-level records from coral microatolls in Western Borneo, South China Sea

The spatial variability of Holocene relative sea level (RSL) in the South China Sea is unknown, with data restricted to Thailand, the Malay Peninsula, and a few other isolated sites. In this study, we present new continuous RSL records for Borneo using surveyed and U–Th dated coral microatolls from four sites in western Sarawak. The record spans 450 years of RSL from 7450 to 7000 yr BP. Our data suggest that RSL was higher than present and rapid RSL rise had ceased by 7450 yr BP. We compare these RSL reconstructions with a regional model of glacial-isostatic adjustment (GIA). The RSL reconstructions from three sites off the coast of Sarawak show a spatial gradient opposite to that predicted by the GIA model. This disagreement can best be explained by tectonic deformation since 7000 yr BP, which was previously unrecognized. We propose vertical land motion of 0.7–1.45 m due to slip on the Serabang fault, which runs between our four sites. This slip may have occurred in response to the loading of the Sunda Shelf by rising sea level.

Deglacial sea level history of the East Siberian Sea and Chukchi Sea margins

Abstract. Deglacial (12.8–10.7 ka) sea level history on the East Siberian continental shelf and upper continental slope was reconstructed using new geophysical records and sediment cores taken during Leg 2 of the 2014 SWERUS-C3 expedition. The focus of this study is two cores from Herald Canyon, piston core SWERUS-L2-4-PC1 (4-PC1) and multicore SWERUS-L2-4-MC1 (4-MC1), and a gravity core from an East Siberian Sea transect, SWERUS-L2-20-GC1 (20-GC1). Cores 4-PC1 and 20-GC were taken at 120 and 115 m of modern water depth, respectively, only a few meters above the global last glacial maximum (LGM; ∼ 24 kiloannum or ka) minimum sea level of ∼ 125–130 meters below sea level (m b.s.l.). Using calibrated radiocarbon ages mainly on molluscs for chronology and the ecology of benthic foraminifera and ostracode species to estimate paleodepths, the data reveal a dominance of river-proximal species during the early part of the Younger Dryas event (YD, Greenland Stadial GS-1) followed by a rise in river-intermediate species in the late Younger Dryas or the early Holocene (Preboreal) period. A rapid relative sea level rise beginning at roughly 11.4 to 10.8 ka ( ∼ 400 cm of core depth) is indicated by a sharp faunal change and unconformity or condensed zone of sedimentation. Regional sea level at this time was about 108 m b.s.l. at the 4-PC1 site and 102 m b.s.l. at 20-GC1. Regional sea level near the end of the YD was up to 42–47 m lower than predicted by geophysical models corrected for glacio-isostatic adjustment. This discrepancy could be explained by delayed isostatic adjustment caused by a greater volume and/or geographical extent of glacial-age land ice and/or ice shelves in the western Arctic Ocean and adjacent Siberian land areas.

Early Holocene estuary development of the Hesselø Bay area, southern Kattegat, Denmark and its implication for Ancylus Lake drainage

High-resolution shallow seismic data, sediment core information, radiocarbon dating and sequence stratigraphy have been used to interpret the late glacial to early Holocene geological evolution of Hesselo Bay in the southern Kattegat, Denmark. A reconstruction of the early Holocene coastal environment and a description of coastal processes associated with a river outlet into the bay are presented. Weichselian glacial deposits form the lowermost interpreted unit, covered by late glacial (LG) and postglacial (PG, Holocene) sediments. A funnel-shaped estuary existed at the mouth of channels in the period 10.3–9.2 cal. ka BP; the channels drained water from south to north. The early PG is characterised by estuarine and coastal deposits. The early Holocene bars that developed in the estuary are preserved as morphological features on the present-day seabed, possibly as a result of rapid relative sea-level rise. The estuary existed simultaneously with the occurrence and drainage of the Ancylus Lake. The drainage of this lake occurred through the Dana River (palaeo-Great Belt channel) into the southern Kattegat and then into the study area. The level of the Ancylus Lake in the Baltic Sea region dropped significantly at about 10.2 cal. ka BP at the same time as the estuary developed in the Kattegat region. One outcome of the present study is an enhanced understanding of the Ancylus Lake drainage path. No evidence of major erosion is seen, which indicates non-catastrophic continuous water flow from the south without major drainage events of the Ancylus Lake to the southern Kattegat. During the Littorina transgression, coastal estuarine conditions characterized the Hesselo Bay area where elongated ridges formed a bar system. As the Littorina transgression continued, back-stepping of the bar system and coastline occurred. When the transgression breached the Great Belt threshold, flooding caused major erosion throughout the study area.

Deformed cross-stratified deposits in the Early Pleistocene tidally-dominated Catanzaro strait-fill succession, Calabrian Arc (Southern Italy): Triggering mechanisms and environmental significance

The Early-Pleistocene Catanzaro strait-fill succession consists of large-scale tidal sets, accumulated in a tectonically confined basin during a phase of rapid relative sea-level rise. It crops out mainly in the present-day Catanzaro Trough where numerous field sections supported the characterization of the vertical and lateral facies variations and the documentation of a variety of soft-sediment deformation structures, exposed throughout their vertical and lateral extents. The soft-sediment deformation structures (SSDS) are the result of liquefaction and fluidization processes that deformed cross-laminations and other primary structures into folds, fluid-escape structures, and structureless expanses. Three different groups of SSDS have been documented in the cross-stratified deposits of the Catanzaro strait. The detailed description of these soft-sediment deformation structures in a depositional context established by facies analysis enables interpretation in terms of possible trigger mechanisms. Consistent relationships between the occurrence of distinctive SSDS and specific tidally dominated facies have been established, indicating a probable autogenic origin for the soft-sediment deformations. Liquefaction and fluidization features are interpreted as the result of increases in water pore-pressure, induced by overloading. In particular, two types of overloading agents are hypothesized, which affect the lee and stoss sides of the migrating dunes in distinct events, and inducing the deformation of foreset laminae or sets of cross-strata, respectively.

Facies development and paleoecology of rudists and corals: an example of Campanian transgressive sediments from northern Croatia, northeastern Slovenia, and northwestern Bosnia

At six localities in northern Croatia (Donje Oresje, Gornje Oresje), Slovenia (Stranice, Slovenj Gradec), and Bosnia (Bespelj and Kober), successions of shallow-water Campanian deposits transgressively covered a tectonically uplifted and eroded paleorelief. They constitute different lateral parts of a transgressive subtidal environment, where rudists and corals are typical macrofossils. At the investigated localities, two types of succession were distinguished: (a) clastic and (b) carbonate. Most localities are within the extended chronostratigraphic range of Calveziconus cf. lecalvezae (80.5–79.03 Ma), which comprises the upper part of the Vaccinites alpinus interval zone (for Stranice and Slovenj Gradec localities) and beginning of the Pironaea polystyla interval zone (for Bespelj and Kober localities). In clastic successions, corals are the most abundant macrofossils, whereas rudists predominate within carbonate sections. The depositional setting of the investigated localities results from rapid relative sea-level rise with a tectonic overprint, which covered different types of paleorelief. In cases when the paleorelief is gentle, a transgressive succession starts with clastic coral-rich sediments or carbonates with radiolitids. In areas of steeper paleorelief carbonate sediments were deposited with a mixed radiolitid-hippuritid community, and the rudists, as the major macrofossils, indicate higher sedimentation rates in comparison with the clastic situations.

Tectonic subsidence provides insight into possible coral reef futures under rapid sea-level rise

Sea-level rise will change environmental conditions on coral reef flats, which comprise extensive habitats in shallow tropical seas and support a wealth of ecosystem services. Rapid relative sea-level rise of 0.6 m over a relatively pristine coral reef in Solomon Islands, caused by a subduction earthquake in April 2007, generated a unique opportunity to examine in situ coral reef response to relative sea-level rise of the magnitude (but not the rate) anticipated by 2100. Extent of live coral was measured from satellite imagery in 2003, 2006, 2009 and 2012. Ecological data were obtained from microatolls and ecological surveys in May 2013. The reef was sampled at 12 locations where dense live hard coral remained absent, remained present or changed from absent to present following subsidence. Ecological data (substratum depth, live coral canopy depth, coral canopy height, substratum suitability, recruitment, diversity and Acropora presence) were measured at each location to identify factors associated with coral response to relative sea-level rise. Vertical and horizontal proliferation of coral occurred following subsidence. Lateral expansion of live coral, accomplished primarily by branching Acropora spp., resulted in lower diversity in regions which changed composition from pavement to dense live coral following subsidence. Of the ecological factors measured, biotic factors were more influential than abiotic factors; species identity was the most important factor in determining which regions of the reef responded to rapid sea-level rise. On relatively pristine reef flats under present climatic conditions, rapid relative sea-level rise generated an opportunity for hard coral to proliferate. However, the species assemblage of the existing reef was important in determining response to sea-level change, by providing previously bare substrate with a source of new coral colonies. Degraded reefs with altered species composition and slower coral growth rates may be less able to respond to climate change-induced sea-level changes.

Holocene Relative Sea-Level Change on the Isle of Skye, Inner Hebrides, Scotland

ABSTRACTHolocene relative sea-level (RSL) changes are described for the Isle of Skye, based upon evidence from isolation basins and back barrier environments. RSL rose across low-lying coastal areas in the early Holocene, inundating isolation basins in the Sleat peninsula, and then fell back in the early-middle Holocene before a fluctuating rise occurred later in the middle and late Holocene. A short-lived marine inundation at one site may have been caused by an episode of rapid RSL rise after the discharge of Lakes Agassiz–Ojibway in North America and/or the Holocene Storegga Slide tsunami, generated by submarine landsliding off South-West Norway. The empirical evidence for RSL change on Skye is compared with a recent shoreline-based glacio-isostatic adjustment model, which includes Skye, showing altitudes for the Holocene Storegga Slide tsunami, Main Postglacial, Blairdrummond and Wigtown shorelines in the area. The empirical evidence is shown to be in accord with the altitudes predicted by the model.