Present Sea Level Research Articles

Mixed Sand/Gravel Beach Response to the Beast from the East Storms

Dolphin, T.; Burningham, H.; Sifnioti, D.; Manning, W.; Wallbridge, S., and Farcas, A., 2020. Mixed sand/gravel beach response to the Beast from the East storms. In: Malvarez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 463–467. Coconut Creek (Florida), ISSN 0749-0208.Two large, very long-duration, shore-normal (easterly) storms worked on the Minsmere – Sizewell mixed sand and gravel (MSG) beach frontage (Suffolk, UK) in March 2018. These storms were unusual in their sustained high waves (Hs > 2.1 m, 97.5th percentile) for 140 hours from the east (16% occurrence), compared to the regional median duration of 8.5 hours per storm. Patterns in contour advance/retreat were compared with modelled nearshore wave conditions every 100 m along the 3.3 km frontage. Although there was a positive correlation between the upper supra-tidal beach and wave period, patterns in the beach response were inconsistent and zones of common behaviour could not be explained by the wave data. Postulated explanations include spatial variation in the antecedent morphology and particle-size arrangement within the MSG sediment matrix. Despite the high magnitude of work done by these storms, the lack of barrier erosion suggests that barrier stability is likely for the present sea level under these perceived more-erosive, though less common, easterly storms.

NUOVI ELEMENTI FAUNISTICI E STRATIGRAFICI DEL PLEISTOCENE SUPERIORE DEI NEBRODI (SICILIA NORD-ORIENTALE)

A new deposit of gravels containing Pleistocene mammal remains mostly belonging to Hippopotamus sp., but also with remains of some other mammals (Elephas sp., Ursus sp.) has been located at Rocca Scodonì near Torrenova, in the province of Messina (Sicily). The new deposit may be compared with that of the S. Teodoro cave near Acquedolci, which was already known in the literature. The location, the elevation above present sea level, the facies and faunal association are closely similar. Like the deposit of the S. Teodoro cave, the deposit of Rocca Scodonì belongs to a coastal plain now elevated at the altitude of 60—130 m a.s.l., overlying an abrasion terrace which can be referred to the Eutyrrhenian cycle. The facies of deposits show that the morphological terrace which is now elevated at the altitude of 60—130 m a.s.l. and extends along Ionian and Tyrrhenian sides of North—Eastern Sicily, was built up with deposits of different ages and environments, which are connected to the interaction between Pleistocene uplift of the region and three marine transgressions. The size of skeletal elements of Hippopotamus sp. appears to be very near to that of the mainland species H. amphibius. The new deposit shows that other mammal remains can probablv be found in the future along the northern slopes of carbonate massifs present in the area of Rocca Scodonì—S. Teodoro cave.

Geoarchaeological evidence of Ostia\u2019s river harbour operating until the fourth century AD

Ancient Ostia at the mouth of the River Tiber into the Tyrrhenian Sea was largely significant for the economic supply of Rome. Ostia itself experienced an extraordinary period of prosperity in the second century AD. Starting in AD 42, a first new harbour at Portus was built by Emperor Claudius close to Ostia. It reached its full functionality under Emperor Trajan in the early second century AD, only. At Ostia itself, previous archaeological and geoarchaeological studies have brought to light a lagoon-type harbour at the western fringe of the city operating between the fourth and the second century BC in an artificially excavated harbour basin. From the second century BC onwards, a considerably smaller and shallower part of this western harbour basin was still in function as a fluvial harbour. So far, it was unclear whether Ostia’s western harbour was still in use when the harbour at Portus was set into function in the first to second century AD, or if the latter partially replaced Ostia’s harbour infrastructure. According to archaeological evidence, Ostia’s navalia-temple-complex, the main building at the eastern fringe of the western river harbour basin, was built in the second quarter of the first century AD. Was this prestigious harbour building erected although the associated harbour seemed to have been already given up before? We conducted detailed geoarchaeological investigations at the immediate western front of the navalia-temple complex. Results were compared with archaeological data obtained from excavations carried out in 2000/2001. A multi-proxy approach was used to reconstruct the history and evolution of the harbour. It was possible to identify subsurface structures and evaluate the local stratigraphy. Vibracoring brought to light a more than 1 m thick section of an opus reticulatum wall with parts of the original opus latericium on top. Such walls originally separated vaulted shipshed chambers of the navalia-temple complex at Ostia, which in turn formed the substructure of a temple complex located above it. Another core revealed the sedimentary infill of a former chamber of the building. Based on radiocarbon dating, the navalia was in use between the first and the fourth centuries AD with a water depth of maximum ca. 1.2 m at the immediate western front. This is in agreement with the date of construction of the navalia-temple complex in the second quarter of the first century AD. The relative sea level at that time was around 0.64 m below the present sea level. The harbour and the navalia were obviously accessible only for flat-keeled lighters and cargo boats. Larger cargo ships were either unloaded along the riverbank to the north of ancient Ostia (Hadler et al. 2019) or moored offshore, their freight being reloaded to smaller lighters. Chronostratigraphic data further show that the navalia-temple complex was in use until the second half of the fourth century AD. It was not before AD 355–363 or shortly afterwards, that the harbour site was abandoned. Ostia’s western river harbour was neither abandoned nor completely silted up before the harbour at Portus was established as previously assumed by other authors. Actually, the western front of the navalia-temple complex was hit by an extreme wave event, leaving a sand layer approx. 0.5 m thick, at or shortly after AD 355–363 which led to the final abandonment of Ostia’s western river harbour. This event is interpreted as a tsunami that may have hit the wider coastal region.

Postglacial evolution of marine and lacustrine water bodies in Bunger Hills

AbstractUnglaciated coastal areas in East Antarctica provide records of past ice sheet and glacier fluctuations and subsequent environmental conditions. In this paper we review lithological, geochemical, diatom and radiocarbon data from sediment records from inland and epishelf lakes in Bunger Hills, East Antarctica. While some hilltops were unglaciated during the Last Glacial Maximum, till deposits in lake basins indicate infilling by glacier ice prior to the Holocene. Proglacial sedimentation occurred in lakes during the early Holocene. Around 9.6 kabp, deposition of marine sapropel started under relatively warm climate conditions. Inland lakes were affected by high clastic input from meltwater runoff untilc.7.9 kabp, when deposition became highly organic and biogenic proxies indicate a period of cooler conditions. Epishelf lakes experienced a decrease in water exchange with the ocean and increased freshwater input around 7.7 ± 0.2 kabpand after 2.2 kabp. This probably resulted from grounding line advances of the bounding glaciers, which could be either controlled by relative sea level (RSL) lowering and/or climate-driven glacier dynamics. The absence of marine sediments in the postglacial record of Algae Lake indicates that Holocene RSL probably reached a maximum at or below 10 m above present sea level.

The eastern shores of the Baltic Sea in the Early Holocene according to natural and cultural relict data

Exploration of the underwater landscape in Lithuanian waters, in the eastern part of the Baltic Sea, allowed identification of trees stumps in growth position, peat sediments, and traces of people that were living in the now flooded landscape. The exploration has been concentrated on localisation of the former Early Holocene coasts. Based on new data about sediment layers of the Preboreal‒Atlantis I, palynological and dendrohronological analysis, identified vegetation species, and dating of wood and peat samples by radiocarbon methods the Baltic Sea water level dynamics during the stages Yoldia Sea‒Early Litorina Sea could be identified. There are traces of the eroded coasts of the Yoldia Sea at a depth of 39–43 m, which were also observed at depths of 44 and 47 m. During the Ancylus Lake transgression, the RF‐I lagoons and small lakes with the peat layer and the surrounding forests were submerged. The water level could have even risen to 10–9 m below present sea level. The water drop during the Ancylus Lake regression is evidenced by a peat layer dated to 9,150–8,520 cal BP, and similar radiocarbon dating of an oak stump. The changes of the species composition of trees are indicative of the noticeable climate changes during the period 11,410–7,900 cal BP. Litorina transgression is marked by a tree stump found at a depth of 14.5 m dated to 7,900–7,660 cal BP. The preference of the Early Holocene population to the coastal zone is evidenced by poles driven into the seabed (one was dated to 9,510–9,460 cal BP) that were detected at a depth of 11 m and the T‐shaped antler axes dated to the Early Neolithic, washed ashore from the Litorina Sea coastal Stone Age settlements.

The evolution of sea cliffs over multiple eustatic cycles in high energy, temperate environments

Sea cliffs are steep, erosional features carved out of rocks by marine and subaerial erosive processes. They are defined as a surface at the coast with a slope angle of greater than 20°. The broad morphology of these cliffs is determined by the relative magnitude of the erosive processes and the resistance of the lithology in which they are formed. In this study, an integrated aerial LiDAR and multibeam dataset from +20 to −80 m water depth is used to precisely quantify sea cliff morphology. Over 260 km of cliffed coastline was identified and analyzed along the high-energy temperate coast of Victoria, Australia, with cliffs occurring down to 60 m depth. Cliffs at present sea level were found to range in average slope from 20.8 -53.0° with their base occurring within 6.8 m of mean sea level. Cliffs were also discovered below modern sea level in three locations, each set tending to be lower in height and slope than the contemporary active landforms. Marine erosion acting over the entire face during transgressive events is proposed that as a cause of the more gentle slopes of these landforms as upper parts of the profile are eroded in surf zone as it moves landward during a transgression. As a result, the accuracy of these drowned landforms as sea level proxies (<14.2 m within expected sea level) is less reliable than cliffs formed during the current highstand (<11.3 m within sea level).

Coastal Impacts Driven by Sea-Level Rise in Cartagena de Indias

This work analyzes the coastal impacts of the combined effect of extreme waves and sea level extremes, including surges and projected mean sea level rise in Bocagrande, Cartagena (Colombia). Extreme waves are assessed from a wave reanalysis that are propagated from deep waters to the beach considering the hydrodynamic processes and taking into account the interaction between waves and the coastal elevation within the study area. First, we consider present sea level, storm surges and waves affecting the area. Next, we analyze the effect of sea level rise according to a moderate (RCP4.5) climate change scenario for the 21st century (years 2025, 2050, 2075 and 2100). The most pessimistic scenario (year 2100) yields a percentage of flooded area of 97.2%, thus revealing the major threat that represents sea level rise for coastal areas in the Caribbean Sea.

Reconciling Storegga tsunami sedimentation patterns with modelled wave heights: A discussion from the Shetland Isles field laboratory

AbstractThe Shetland Isles represent an ideal field laboratory for tsunami geoscience research. This is due to the widespread preservation of Holocene tsunami sediments in coastal peat deposits. This study uses published accounts of the Holocene Storegga Slide tsunami to illustrate how two different approaches – mapping of tsunami sediments and numerical modelling – produce radically different run‐up heights. The Storegga Slide is one of the world largest submarine slides and took place ca 8150 cal yr bp on the continental slope west of Norway. The tsunami generated by the landslide deposited locally extensive sheets of marine sand and gravel, as well as redeposited clasts of peat across the contemporary land surface. These sediment accumulations have subsequently been buried by peat growth during the Holocene while exposures of the deposits are locally visible in coastal cliff sections. In several areas, the tsunami sediments can be traced upslope and inland within the peat as tapering sediment wedges up to maximum altitudes of between ca 8·1 m and 11·8 m above present sea level. Since reconstructions of palaeo‐sea level for Shetland for ca 8150 cal yr bp suggest an altitude of 20 m below high tide on the day that the tsunami struck, it has been inferred that the minimum tsunami run‐up was locally between 28·1 m (8·1 + 20 m) and 31·8 m (11·8 + 20 m). However, numerical models of the tsunami for Shetland suggest that the wave height may only have reached a highest altitude in the order of +13 m above sea level on the day the tsunami took place. In this paper a description is given of the sedimentary evidence for tsunami run‐up in the Shetland Isles. This is followed by an evaluation of where the palaeo‐sea level was located when the tsunami occurred. Significant differences are highlighted in tsunami inundation estimates between those based on the observed (geological) data and the theoretically‐modelled calculations. This example from the Shetland Isles may have global significance since it exemplifies how two different approaches to the reconstruction of tsunami inundation at the coast can produce radically different results with modelled wave height at the coast being considerably less than the geological estimates of tsunami run‐up.

Morphology of fore-reef slopes and terraces, Takapoto Atoll (Tuamotu Archipelago, French Polynesia, central Pacific): The tectonic, sea-level and coral-growth control

A dataset of 41 bathymetric profiles detected by satelline imagery and echo-sounding to a maximum depth of 38 m along the fore-reef slopes of Takapoto Atoll (Tuamotu Plateau, French Polynesia, central Pacific) were qualitatively and quantitatively analyzed in order to identify the main geomorphological features. In addition, scuba-diving investigations from a selected site resulted in defining coral composition and cover rate. Six distinct fore-reef sectors were morphologically differentiated on the basis of seaward extension and slope gradient. Only the north end, and a restricted area of the mid-south-east side extend seawards over an average distance of 150 m, with a relatively low gradient (23°–38°). Most of the outer-slope areas are narrow (<100 m on average) and steep (average slope equals to 45° to up to 70°). Geomorphic features include spur-and-groove systems, sub-horizontal to gently dipping terraces (23–45 m wide) ending seawards in vertical steps (<10 m high) and drop-offs (>10 m high), outer-reef crest-like reliefs (0.5 m–1.5 m high), pinnacles (2 m–17 m high), coral heads (<2 m high), trenchs and concave scars. The recognized seven terrace levels occur at the respective depths of about −5 m, −10 m, −15 m, −20 m, −24 m, −30.5 m and −38 m. Based on comparison with subsurface chronostratigraphy of drilled reef sequences from some other Pacific atolls, the terraces are interpreted as remnants of reef tracts formed during Pleistocene interglacial, high sea-stands, respectively during MIS substage 5e (about −125 ka), MIS substages 7a (about −195 ka), 7c (about −210 ka), 7e (about −240 ka) and 9e (−330 ka). After depth correction of ground lowering during periods of emergence and subsidence effects, terrace elevations were expected to indicate eustatic sea-level positions at each identified high sea-stand, at approximately 7 m (MIS 5e) and 2.2 m (MIS 7a) above present sea level and 9.5 m (MIS 7c), 11 m (MIS 7e) and 8.6 m (MIS 9e) below present sea level. During the post-glacial sea-level rise, from about 9.5 ky, the studied portions of fore-reef slopes were re-flooded. It was assumed that coralgal deposits in the form of thin veneers, coral heads, outer-reef crest-like reliefs and pinnacles have simply overlapped pre-existing structures. Locally, the fore-reef zones are carved by trenchs, i.e. incipient detachment faults, and scars, i.e. imprints of former landslides. Similarly, some drop-offs may be regarded as fault walls. The prevailing direction of faulting–collapsing surfaces is consistent with the SW–NE orientation of the main axis of the atoll and submarine ridges rising up from the north-western floor of the Tuamotu Plateau. Analysis of the composition and distribution of coral communities to −30 m depth revealed high, downslope-increasing coral coverage (24% to 67% on average) and the sharp replacement of robust-encrusting Pocillopora by sub-massive to plate-like Porites from depths greater than −10 m. Significant inter-regional differences were detected with atolls in west Pacific, probably due to local ecological constraints.

New Estimation of the Post Little Ice Age Relative Sea Level Rise

The study area is located in NW Sardinia Island (Italy), Mediterranean Sea. Sardinia is considered stable since the late Pliocene with a negligible subsidence of about 0.01 mm/y. It is therefore normally used to reconstruct the Pleistocene and Holocene sea level curves. Our research focusses on the sea-facing city of Alghero that from 1353 to 1720 was under the Spanish government. During this time, the city was renovated and new buildings edified. Dimension stones were quarried all around Alghero both in the nearby inland and along the coast. Coastal quarries were considered the most suitable for both rock quality and the easiest way to transport the quarried material by boat. The quarried rocks are late Pleistocene dune and beach sandstones deposited from the 132 ka (Marine Isotopic Stage—MIS5) to about 65 ka (MIS4). Sandstones crop out from few cm to 3 m above the present sea level and underwent several consolidation processes related to loading and marine weathering. This latter favoured dissolution and circulation of calcium carbonate which cemented the rocks. It is reported that the Spanish were looking for these “marine” sandstones for their high geotechnical characteristics. Different rules were adopted through time for the size of the dimension stones and this has allowed us to establish a quarry exploitation chronology. For example, “40 × 60 × 20” cm was the size of the dimension stones used for the Alghero Cathedral dated at 1505–1593. Nowadays most of the coastal Spanish quarry floors are 30 centimetres below mean sea level (tidal range is 30 cm). Accordingly, we infer that relative sea level from 1830 AD (and of the Little Ice Age) rose in about 200 years to the present level at the rate of about 1.4 mm/y. Considering that relative sea level rise during the Medieval warm period was of 0.6 mm/y over a period of about 400 years, we may deduce that human influence was strong enough to lead to a relative sea-level rise faster and in shorter time.

Outer- to inner-shelf response to stepped sea-level rise: Insights from incised valleys and submerged shorelines

Shorelines respond to rising sea-level through processes such as erosion, landward migration and in-situ drowning (i.e. overstepping). Submerged and preserved shorelines on the continental shelf play a key role in examining coastal response to rising sea levels as they provide important information on how modern shorelines may evolve in time and space within the context of changing climate and post-glacial sea-level rise. This study identifies and assesses the response of a continental shelf to stepped rises in sea level with particular focus on the stepwise evolution of incised valleys and shorelines from the shelf-edge to the inner shelf. Multibeam bathymetry from the mid-outer allows for the analysis of seafloor morphology, including the Protea Banks Reef (a palaeo-shoreline complex), and the adjacent incised, sediment starved continental shelf. Six seismic units and intervening surfaces are identified using interpretations from sub-bottom profiles, these include the incised acoustic basement, variable incised valley fill successions, aeolianite ridges and post-transgressive shoreface and associated sediments that withstood wave ravinement processes. The incised valleys of the outer-shelf are manifested as distinctive seafloor depressions, filled at their bases by fluvial deposits overlain, in the unfilled valley, by deposits derived from cascading subaqueous dunes which comprise the upper-most post-transgressive sediments. A core intersecting the dune material yields a maximum age of deposition of 1191–1263 cal yr BP (68% range), synchronous with a period of higher than present sea-levels in the region suggesting reworking and redistribution of coastal sediment as shelf sediment post-transgression. During the stepped rises in sea level, the shoreface has disconnected from the contemporary shoreline and is preserved by means of topographic barriers formed by antecedent topography as relict shoreface deposits. We provide a new perspective of shoreline response to stepped rises in sea level by integrating the seismic architecture of incised valley fills and shorelines across the continental shelf thus allowing for the assessment of variation in rates of relative sea-level rise since the last glacial maximum.

Assessing the Multiple Impacts of Extreme Hurricanes in Southern New England, USA

The southern New England coast of the United States is particularly vulnerable to land-falling hurricanes because of its east-west orientation. The impact of two major hurricanes on the city of Providence (Rhode Island, USA) during the middle decades of the 20th century spurred the construction of the Fox Point Hurricane Barrier (FPHB) to protect the city from storm surge flooding. Although the Rhode Island/Narragansett Bay area has not experienced a major hurricane for several decades, increased coastal development along with potentially increased hurricane activity associated with climate change motivates an assessment of the impacts of a major hurricane on the region. The ocean/estuary response to an extreme hurricane is simulated using a high-resolution implementation of the ADvanced CIRCulation (ADCIRC) model coupled to the Precipitation-Runoff Modeling System (PRMS). The storm surge response in ADCIRC is first verified with a simulation of a historical hurricane that made landfall in southern New England. The storm surge and the hydrological models are then forced with winds and rainfall from a hypothetical hurricane dubbed “Rhody”, which has many of the characteristics of historical storms that have impacted the region. Rhody makes landfall just west of Narragansett Bay, and after passing north of the Bay, executes a loop to the east and the south before making a second landfall. Results are presented for three versions of Rhody, varying in the maximum wind speed at landfall. The storm surge resulting from the strongest Rhody version (weak Saffir–Simpson category five) during the first landfall exceeds 7 m in height in Providence at the north end of the Bay. This exceeds the height of the FPHB, resulting in flooding in Providence. A simulation including river inflow computed from the runoff model indicates that if the Barrier remains closed and its pumps fail (for example, because of a power outage or equipment failure), severe flooding occurs north of the FPHB due to impoundment of the river inflow. These results show that northern Narragansett Bay could be particularly vulnerable to both storm surge and rainfall-driven flooding, especially if the FPHB suffers a power outage. They also demonstrate that, for wind-driven storm surge alone under present sea level conditions, the FPHB will protect Providence for hurricanes less intense than category five.

Sedimentary records of Marine Isotopic Stage 3 (MIS 3) in southern Brazil

In this paper, a reinterpretation of the older 14C ages of the Pleistocene substrate of the Holocene barrier-lagoon system of three coastal localities in southern Brazil is presented (Hermenegildo, Cassino, and Curumim). Sedimentological, geochronological, palynological, and diatom analyses of a sedimentary deposit formed in an estuarine/shallow marine environment are examined. This sedimentary deposit is presently found between 22 and 25 m depth below sea level in the Pinheira coastal plain. Results from all studied sites indicate that the deposit was formed under a former sea level of Marine Isotopic Stage 3 (MIS 3) that may have oscillated in the study region between 5 and 23 m depth below present sea level, from 36.2 to 47.7 ka. These results are reinforced by studies of nearby sites, including southeast Brazil. The Pleistocene substrate of the Holocene lagoonal-barrier system, at depths lower than 5 m below sea level, seems to correspond to sedimentary deposits of the Pleistocene barrier formed during MIS 5, while at depths greater than 5 m below sea level, they might correspond to sedimentary deposits that were formed during the relative high sea levels of MIS 3.

Quantifying spatial variability in shell midden formation in the Farasan Islands, Saudi Arabia.

During the past decade, over 3000 shell middens or shell matrix deposits have been discovered on the Farasan Islands in the southern Red Sea, dating to the period c. 7,360 to 4,700 years ago. Many of the sites are distributed along a palaeoshoreline which is now 2–3 m above present sea level. Others form clusters with some sites on the shoreline and others located inland over distances of c. 30 m to 1 km. We refer to these inland sites as ‘post-shore’ sites. Following Meehan, who observed a similar spatial separation in shell deposition in her ethnographic study of Anbarra shellgathering in the Northern Territory of Australia, we hypothesise that the shoreline sites are specialised sites for the processing or immediate consumption of shell food, and the post-shore sites are habitation sites used for a variety of activities. We test this proposition through a systematic analysis of 55 radiocarbon dates and measurement of shell quantities from the excavation of 15 shell matrix sites in a variety of locations including shoreline and post-shore sites. Our results demonstrate large differences in rates of shell accumulation between these two types of sites and selective removal of shoreline sites by changes in sea level. We also discuss the wider implications for understanding the differential preservation and visibility of shell-matrix deposits in coastal settings in other parts of the world extending back into the later Pleistocene in association with periods of lowersea level. Our results highlight the importance of taphonomic factors of post-depositional degradation and destruction, rates of shell accumulation, the influence on site location of factors other than shell food supply, and the relative distance of deposits from their nearest palaeoshorelines as key variables in the interpretation of shell quantities. Failure to take these variables into account when investigating shells and shell-matrix deposits in late Pleistocene and early Holocene contexts is likely to compromise interpretations of the role and significance of shell food in human evolutionary and socio-cultural development.

Evolution of Damodar Fan Delta in the Western Bengal Basin, West Bengal

ABSTRACT Fan delta is formed when an alluvial fan prograde directly into the standing body of water from the adjacent highland. An ancient fan delta was developed 6-10m above from the present sea level at the lower course of Damodar river in the western part of Bengal basin. The present study attempted to represent the evolutionary history of Damodar fan delta in the context of many associative features favor to fan delta formation such as adjacent highland, basin margin faults, accommodation space and standing water body. These elements have been taken into consideration to identify the location, time and processes for the fan delta formation. Data related to tectonic and depositional history, sea level fluctuation and palaeodrainage network have been collected from various sources. These reveal that the western part of Bengal basin is characterized by numbers of north-south trending normal faults, shifting river courses and repeated marine transgression and regression phases. After collecting a huge amount of sediment from Chhotanagpur plateau, Damodar river deposited its sediment in the eastern side of these north-south trending faults in the subaerial and subaqueous environment throughout the geological period. In this region Chhotanagpur plateau, fault-dominated stable shelf and transgressed Bay of Bengal play the role of adjacent highland, accommodation space and standing water body respectively to develop Damodar fan delta. Sedimentation process started in late Cretaceous and still it is continuing in a subaerial environment. These fan forming processes led Damodar river to shift its course and make this region flood prone.

Kelp DNA records late Holocene paleoseismic uplift of coastline, southeastern New Zealand

Holocene paleoseismic activity on the Akatore Fault zone, southeastern New Zealand, has caused uplift of a 23 km section of coastline by several metres. Prominent relict shoreline terraces are preserved at 6 m and 3 m above the present sea level, and the latter terrace was formed 1000-1400 yrs BP. The main fault strand farther inland has 6 m of late Holocene vertical offset, but the relationships between coastal offsets and fault offsets are not understood. There is no preserved geological evidence on the coastline to distinguish between incremental uplift (e.g., numerous centimetre-scale events) and major, metre-scale, uplift events: a distinction that is important for evaluating regional paleoseismicity. We have used genetic characterisation of populations of live kelp, Durvillaea antarctica growing along the shoreline to investigate whether or not there has been a catastrophic uplift event, greater than the two metre tidal range, that was sufficient to extirpate intertidal kelp populations. Our results show that all kelp along the southeastern New Zealand coastline belongs to the same distinctive clade of D. antarctica, and inhabits the same ecological niches on exposed rocks and reefs. However, the kelp population on the uplifted coastline is genetically uniform, and clearly distinct from those of flanking shorelines. This regional genetic anomaly is consistent with a major extirpation event, followed by recolonisation from source populations some 30-120 km to the northeast of the uplifted coast. The uplift event caused vertical crustal movement with similar amounts of uplift on the fault plane and the coastline 3 km away. This approach, using genetics of intertidal biota, has potential applications for evaluation of paleoseismicity of other tectonically active shorelines around the world.

Impact of latest-glacial to Holocene sea-level oscillations on central Aegean shelf ecosystems: A benthic foraminiferal palaeoenvironmental assessment of South Evoikos Gulf, Greece

Abstract A high-resolution palaeoenvironmental investigation was conducted on the benthic foraminiferal record of two continuous sediment cores (DEH 5, DEH 1) in order to reconstruct the latest-Pleistocene to Holocene history of the South Evoikos Gulf (central Aegean Sea). This shallow (max. depth ~75 m), semi-enclosed continental shelf setting has been heavily affected by the latest-glacial to modern-interglacial relative sea-level and climate oscillations that strongly affected the benthic foraminiferal community. The identified meiofaunal biofacies associated with the chronological framework allowed the recognition of four main time phases in the palaeoenvironmental and palaeobathymetric evolution of the gulf: (i) During the latest glacial-interglacial transition (>15.17 ka BP), highly-stressed confined shallow lagoonal conditions correspond to the Last Glacial Maximum (LGM) sea-level lowstand. During that time, a natural barrier located at the mouth of the gulf effectively prevented communication with the open Aegean Sea and amplified the contribution of the local aquifers. (ii) The early post-LGM sea-level rise was initially marked by a weak marine connection, dominated by a pronounced seaward river progradation of local aquifers. However, immediately after (~14.7 ka BP), an enhanced rate of sea-level rise, synchronous with the Meltwater Pulse 1A (MWP-1A), is observed. At the end of the Pleistocene, the sedimentation rates decreased dramatically, as a result of the Younger Dryas (YD) cooling event. (iii) The Holocene sea-level rise was characterized by an extremely abrupt marine transgression (~11.29 ka BP), during which the sea-level in the Aegean Sea reached 55 m below present sea level (b.p.s.l) and forcedly overcame the barrier that previously separated the gulf from the open sea. At ~8.67–7.77 ka BP, an upper circalittoral eutrophic environment emerged, which coincided with the coeval deposition of the sapropel S1 in the Eastern Mediterranean Sea. Immediately after, re-ventilation conditions were reinstated. (iv) The Holocene sea-level high-stand is characterized by upper circalittoral high-energy and vegetated conditions on the sea floor. Regional index terms Eastern Mediterranean; Central Aegean Sea; Greece; South Evoikos Gulf.

Wadi flood impact assessment of the 2002 cyclonic storm in Dhofar, Oman under present and future sea level conditions

Oman witnessed exposure to various cyclones during the last decade including Gonu (2007), Phet (2010), Keila (2015; Dhofar), and Mekunu (2018; Dhofar). The purpose of this study is to assess flood damage due to flash wadi (dry river bed) flooding in Dhofar under present and future sea level conditions. This study uses a 3Di hydrodynamic model and a damage model to quantify the flood extent and flood damage due to the 2002 cyclonic storm (ARB01) and to identify vulnerable infrastructure in two watersheds: Zayk and Ghadow. The impact of the storm is assessed under present day and predicted 1.41 m sea level rise (SLR) conditions. The results show that with present sea level conditions the residential damage was estimated at US$ 10.79M and US$ 32.98M for Zayk and Ghadow respectively. Under a 1.41 m SLR scenario, the residential damage is projected to increase to US$ 13.65M (26.5%) and US$ 40.28M (22.1%) for Zayk and Ghadow respectively under a similar cyclonic storm event. These results provide knowledge to make informed policy decisions that contribute to the development of resilient infrastructure. It also provides a flood damage assessment of a potential future to prepare Oman for challenges under sea level rise.

Reconstruction of Sea Level Change in Indonesia: Preliminary Evidence From Maratua-Kakaban Complex

This research was conducted in Maratua-Kakaban Islands, East Kalimantan, Indonesia. This location was chosen because of its stable tectonic activity and its geographical setting as the front most island in Indonesia. This location is also known as its tourism destination and beautiful scenery. A small island like in Indonesia is prone to climate change, especially sea level changes. This research is needed to formulate adaptation and mitigation of sea level change in Indonesia. This research also important to understanding the global sea change. This research also important from national sovereignty and coastal resources management point of view. This research aims to: (1) identify water level changes evidence by marine terraces analysis, cave morphology and speleothem; (2) define the highest and lowest water level in Maratua Island, and (3) reconstruct the sea water level fluctuation during Holocene. Sea level fluctuation data were interpreted using marine terrace data, marine notch, and cave morphology. The data were collected by field survey using profiling method to find surface topography and measuring sea floor profile using echo sounder. Based on the field measurement, there are major and minor marine terraces found in the ocean floor in 82 and 180 m depth (major), 155 and 205 m depth (minor). Marine terrace also found in +6 m above present sea level. Below, marine notch was found covered with sediment.

Geological records of South China Sea tsunamis on Penghu Islands, Taiwan

The coasts around the South China Sea are highly populated and threatened by the ubiquitous tsunamigenic structures of the Manila trench-arc system. However, owing to limited historical records and rare geological findings of tsunamis, our comprehension of and preparation for regional tsunami risks are far from sufficient. Located in the NE South China Sea, the Penghu Islands in Taiwan’s western offshore area are selected for a geological tsunami survey because of their advantages of lengthy coastlines and abundant upper Holocene deposits.Three gravel layers of marine incursion events were identified and correlated between three far-separated coastal sections based on the constraints of radiocarbon dating. Intercalated with talus, soil, and dune sand, the gravel layers are poorly sorted, matrix-supported, up to boulder in size, and dominated by marine bioclastics and rounded basalts, which are identical to modern beach gravels. The deposits are located 3–4 m above present sea level, which is significantly higher than the local high tide levels and maximal typhoon surges of 2–3 m high. Furthermore, the deposits are distributed extensively on south-facing shores, indicating relatively large and abnormal inundation events from the South China Sea.Based on the radiocarbon dating results of the event deposits, three tsunamis likely occurred in the periods from the 4th to 6th, 11th to 12th, and 15th to 16th centuries. A recurrence interval of 400–500 years is accordingly associated with these event deposits. These findings demonstrate great tsunami risks exist in the South China Sea basin and call for more attestations and future studies. The major contribution of this study is also supported by the AD 1076 Guangzhou tsunami, which is comparable in age to the middle event deposit.