The ice arches that usually develop at the northern and southern ends of Nares Strait play an important role in modulating the export of Arctic Ocean multi-year sea ice. The Arctic Ocean is evolving ...towards an ice pack that is younger, thinner, and more mobile and the fate of its multi-year ice is becoming of increasing interest. Here, we use sea ice motion retrievals from Sentinel-1 imagery to report on the recent behavior of these ice arches and the associated ice fluxes. We show that the duration of arch formation has decreased over the past 20 years, while the ice area and volume fluxes along Nares Strait have both increased. These results suggest that a transition is underway towards a state where the formation of these arches will become atypical with a concomitant increase in the export of multi-year ice accelerating the transition towards a younger and thinner Arctic ice pack.
On December 22, 2018, the eruption and flank collapse of the Anak Krakatau volcano generated a tsunami in the Sunda Strait causing catastrophic damage to uninhabited coastlines proximal to the ...source. Along the heavily populated shores of Banten and Lampung provinces in Java and Sumatra, tsunami waves caused severe damage, extensive inundation and more than 430 deaths. An international tsunami survey team (ITST) deployed 6 weeks after the event documented the tsunami effects including runup heights, flow depths and inundation distances, as well as sediment deposition patterns and impacts on infrastructure and the natural environment. The team also interviewed numerous eyewitnesses and educated residents about tsunami hazards. This ITST was the first to visit and document the extreme tsunami effects on the small islands in the Sunda Strait closest to Anak Krakatau (Rakata, Panjang, Sertung, Sebesi and Panaitan). Along the steep slopes of Rakata and Sertung islands, located less than 5 km from and facing directly towards the southwest flank of Anak Krakatau, all of the dense coastal vegetation was stripped to bare earth up to elevations of more than 80 m, while on the northeast tip of Sertung Island, facing away from the source, a single tree remained standing after flow depths of > 11 m above ground struck there. The runup distributions on the islands encircling Anak Krakatau highlight the directivity of the tsunami source suggesting that the collapse occurred towards the southwest. This manifested as tsunami runup of < 10 m on Sebesi Island, located 15 km northeast of the source, contrasting with tsunami flow heights > 10 m that stripped away coastal forests to bare rock for up to 400 m inland in the Ujung Kulon National Park, located 50 km to the south-southwest. Inundation and damage were mostly limited to within 400 m of the shoreline, likely the result of the relatively short wavelengths caused by the landslide generated tsunami. A significant variation in tsunami impact was observed along the shorelines of the Sunda Strait, with runup heights rapidly decreasing with distance from the inferred tsunami source. To model the event we applied a hot-start initial condition that roughly reproduced the measured tsunami runup heights along Rakata and Sertung. The waveforms were then propagated through the Sunda Straight using a Boussinesq-type wave model. The results showed a good fit to the observed heights along the Java and Sumatra coastlines, the northern coast of Panaitan Island and Ujung Kulon Nation Park. The model also produced an acceptable fit to the observed amplitudes at tide gauges. Despite the regional volcanic and tsunamigenic history of the region, and 6-months of eruptive activity prior to the event, the tsunami largely caught the local population off guard. This further highlights the need for community-based education and awareness programs as essential to save lives in locales at risk from locally generated tsunamis.
Sand ridges, a common feature of modern open shelves, reflect persistent currents and sediment availability under recent transgressive conditions. They represent the largest bedforms in the oceans ...and, as such, can yield information on long‐term oceanographic processes. However, there is a limited number of tidal sand ridges documented from the rock record, examples of regressive tidal sand ridges are scarce and studies describing ridges in straits are even more rare. This study analyses a Gelasian succession within a structurally controlled, tide‐dominated strait in the Siderno Basin, southern Italy. The strait connected two wider basins, and accumulated sediments reworked by amplified tidal (bi‐directional) currents. A series of tidal sand ridges with superimposed dunes developed close to the south‐eastern end of the strait, where bathymetry was deeper and flow expansion occurred. One of the best‐exposed tidal sand ridges, 65 m thick, crops out along a ca 2 km long cliff. Large‐scale, ESE‐prograding, seaward‐offlapping shingles contain sets of bioclastic–siliciclastic, coarse‐grained, cross‐stratified sandstones, erosionally overlying upper Pliocene shelf marls and fine‐grained sandstones. Cross‐strata show angular, tangential and sigmoidal foresets with compound architectures and a SSE migration, i.e. oblique to the main growth direction. Fossil content indicates open‐marine conditions. The succession changes abruptly across an erosion surface to non‐tidal, highly burrowed mixed siliciclastic–bioclastic fine‐grained sandstones, less than 15 m thick. Documented features reflect stages of nucleation, active accretion and abandonment of an individual sand ridge, during a complete cycle of relative sea‐level change. The ridge formed during a phase of normal regression, with accretion occurring during an initial highstand and the ensuing falling stage. During the lowstand the ridge was split into several minor bodies by enhanced tidal currents. The ensuing transgression draped the moribund ridge with tabular strata, whereas final highstand shelf sedimentation reworked the top of the underlying sand body with weak currents.
ABSTRACT
Coastal mud belts, which lie parallel to the coast just seaward of the shoreface, are one of the most important settings where shallow‐marine muddy deposits accumulate. However, sedimentary ...processes and facies distributions of coastal mud belts remain largely uninvestigated. This study uses process‐oriented sedimentology, coupled with provenance analysis and organic geochemistry of sedimentary records at the northern entrance to the Taiwan Strait, to investigate one of the largest such systems in the world, the Changjiang coastal mud belt. Carbon‐14 dates indicate that deposition has been intermittent throughout Marine Isotope Stages 1, 2 and 3, with several cryptic gaps in the muddy succession as a result of exposure or transgressive erosion during periods of lower or rising sea level, respectively. The palaeowater depth of each depositional unit was roughly estimated based on a global sea‐level curve and the elevation and age of the depositional units. Integrated provenance and sedimentology studies suggest that an incised valley most likely cut by the Minjiang, a nearby river draining the Chinese mainland, probably during Marine Isotope Stage 6, was filled with shelf mud during Marine Isotope Stage 3. These results demonstrate that deposition of mud on the Changjiang coastal mud belt was influenced by sea‐level changes that controlled water depth and flow patterns through Taiwan Strait. The Changjiang coastal mud belt migrates landward when sea level rises and moves seaward when sea level drops. In addition, changes in oceanic circulation associated with opening and closing of Taiwan Strait due to sea‐level changes causes significant changes in the source of the mud, with an alternation between sediment contributions from the Changjiang in the north, the nearby Minjiang, and the island of Taiwan to the south‐east. This study also reveals that the Changjiang coastal mud belt deposits are composed of both shallower‐water and deeper‐water facies. The shallower‐water facies predominantly comprises abundant fluid‐mud beds generated by waves and tidal currents. The deeper‐water facies contains shell‐rich mud and bioturbated mud, which were likely deposited by the Chinese coastal current and Taiwan Warm current. The bed types and interpretation of sedimentary processes of the Changjiang coastal mud belt are useful for recognition of ancient deposits of coastal mud belts elsewhere.
Knowledge of the morphological characteristics of coastal foredunes, particularly crest height, is of crucial importance in evaluating coastal vulnerability to marine disasters. However, the factors ...driving variation in foredune height and the corresponding mechanisms remain poorly understood, especially for regional, large‐scale landscapes. In this contribution, an extensive foredune–beach topographic survey and comprehensive data collection, including regional wind regime, wave and tide climate, were conducted along the ~400 km‐long western coast of Taiwan Strait. The results show that the factor with the most significant effect on the spatial variation in foredune height is wave power, followed by aeolian drift potential (shore‐normal component), while beach width and grain size appear to have only marginal impacts for our study sites. Under a relatively high‐energy wave climate, significant volumes of sandy sediments can be delivered to the beach–dune system, and the beach state tends to be more dissipative, thus contributing to a higher/larger foredune. In particular, the in‐phase synchronization of sediment supply (contributed by wave processes) and transport potential (controlled by wind processes) can lead to the greatest potential for foredune growth. Finally, the source (river) to sink (coastal foredune) dispersal of sediments along this ~400 km‐long strait coastal regime is summarized.
Sandy sediments transport from source (rivers) to sink (coastal foredunes) along the western coast of Taiwan Strait. Higher foredunes occur mainly on the more convex and open coasts, roughly along the 1‐m annual average wave height contour, while lower foredunes are present on the more concave and sheltered shorelines with smaller wave height contours.
Despite decades of use as a paleoceanographic proxy, considerable uncertainty still surrounds the temperature dependence of benthic foraminiferal δ18O. Widely applied paleotemperature equations may ...mix non-equilibrium foraminifera with equilibrium synthetic calcite, resulting in temperature sensitivities that are too large. Warm-water foraminiferal calibrations may give temperature sensitivities that are too small for very cold waters. Here we combine new core top measurements from the Florida Straits and the Arctic Ocean with published data to derive new δ18O:temperature relationships for three groups of benthic foraminifera. We derive a quadratic equation for Cibicidoides and Planulina that agrees well with equilibrium synthetic calcite, and that should be applicable over all oceanographic temperatures. We find that Uvigerina is not at equilibrium and is isotopically heavier than Cibicidoides and Planulina by 0.47‰, in contrast to the historically used 0.64‰. Hoeglundina elegans is further enriched and appears to be slightly heavier than equilibrium aragonite. Finally we discuss the implications of the Florida Straits observations for the hypothesis that benthic foraminifera precipitate their shells from a pH-dependent mixture of bicarbonate and carbonate ions.
In this study, a hybrid approach that combines the Fuzzy Analytical Hierarchy Process (FAHP) and Proportional Risk Assessment Technique (PRAT) methods was developed for use within the scope of risk ...analysis. Using a hybrid approach for risk assessment enables researchers to overcome the disadvantages and limitations of a single method. The approach proposed in this study provides an opportunity to eliminate misconceptions that may arise from subjective judgments based only on expert opinions and inconsistencies that may occur from insufficient data. With the proposed approach, realistic analysis results were obtained by combining expert opinions and statistical data. The Turkish Straits System was chosen as a case study application area. One of the most important results of the study is that ships passing through the Turkish Straits face different risks in each Vessel Traffic Services (VTS) sector. The results proved that the proposed method could effectively be used as a consistent and accurate risk assessment tool. The study can contribute to safe strait passages by defining sector-specific risks that ships passing through the strait may encounter.
•The feasibility of a hybrid Fuzzy-AHP and PRAT approach is introduced in the study.•The hybrid approach combines expert opinions with statistical data.•The approach eliminates inconsistencies arising from insufficient statistical data.•This study provides the estimation of potential risks in the Turkish Straits in a sector-specific manner.
The cyclic growth and decay of continental ice sheets can be reconstructed from the history of global sea level. Sea level is relatively well constrained for the Last Glacial Maximum (LGM, 26,500 to ...19,000 y ago, 26.5 to 19 ka) and the ensuing deglaciation. However, sea-level estimates for the period of ice-sheet growth before the LGM vary by > 60 m, an uncertainty comparable to the sea-level equivalent of the contemporary Antarctic Ice Sheet. Here, we constrain sea level prior to the LGM by reconstructing the flooding history of the shallow Bering Strait since 46 ka. Using a geochemical proxy of Pacific nutrient input to the Arctic Ocean, we find that the Bering Strait was flooded from the beginning of our records at 46 ka until Formula: see text ka. To match this flooding history, our sea-level model requires an ice history in which over 50% of the LGM's global peak ice volume grew after 46 ka. This finding implies that global ice volume and climate were not linearly coupled during the last ice age, with implications for the controls on each. Moreover, our results shorten the time window between the opening of the Bering Land Bridge and the arrival of humans in the Americas.
Concentrations and spatial distributions of organophosphate esters (OPEs) in marine sediment samples in the western Taiwan Strait were investigated and analyzed for the first time. The total OPE ...concentration (∑OPE) in sediments was in the range of 5263–34,232 pg/g (dry weight), with an average value of 12,796 pg/g. Generally, there was a higher abundance of non-halogenated OPEs than halogenated OPEs and aryl OPEs, with tributyl phosphate, tris (2-ethylhexyl) phosphate, and tri-(1-chloro-2-propyl) phosphate being the main components. The ∑OPE concentrations in the western coastal and northern sampling sites were relatively high. The results indicated that OPEs in the study region originated mainly from terrestrial river inputs and local emission sources, as well as exogenous influxes by ocean currents.
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•Organophosphate esters were found in coastal sediment in the Taiwan Strait•Organophosphate esters originated mainly from terrestrial river discharges•More than 13.0 tones organophosphate esters were deposited in the Taiwan Strait
John Askin, a Scots-Irish migrant to North America, built his fur trade between the years 1758 and 1781 in the Great Lakes region of North America. His experience serves as a vista from which to view ...important aspects of the British Empire in North America. The close interrelationship between trade and empire enabled Askin's economic triumphs but also made him vulnerable to the consequences of imperial conflicts and mismanagement. The ephemeral, contested nature of British authority during the 1760s and 1770s created openings for men like Askin to develop a trade of smuggling liquor or to challenge the Hudson's Bay Company's monopoly over the fur trade, and allowed them to boast in front of British officers of having the "Key of Canada" in their pockets. How British officials responded to and even sanctioned such activities demonstrates the vital importance of trade and empire working in concert. Askin's life's work speaks to the collusive nature of the British Empire-its vital need for the North American merchants, officials, and Indigenous communities to establish effective accommodating relationships, transgress boundaries (real or imagined), and reject certain regulations in order to achieve the empire's goals.
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