Holocene Sea-level Change Research Articles

Sedimentary characteristics and evolution process of the Huangqiao sand body in the Yangtze River Delta, China

Sea-level rise and reduced sediment loads have caused erosion in the Yangtze River Delta, which is one of South Asia's largest deltas. Scholars have not reached a consensus regarding the origin and timing of the Yangtze River Delta formation, mainly because of the scarcity of cores at the bottom of the delta. In this study, we recovered three sediment cores from the Huangqiao sand body. We systematically analyzed their parameters, including sedimentary characteristics, down-core changes in grain size, benthic foraminifera and ostracod assemblages, AMS14C dating, and optically stimulated luminescence dating. We also integrated our results obtained with data from previously studied cores of the Yangtze River Delta. Four depositional systems were identified in the Huangqiao sand body: a fluvial system dated 12–10 ka that includes sandy gravel in incised valleys and hard clay in paleo-interfluves; an estuary dated 10–7.5 ka that is characterized by sand-mud couplets in valleys and tidal floodplains in the other regions; a deltaic system dated 7.5–4 ka; and a delta or estuary dated 4–0 ka, which included tidal flat and delta plains. The stratigraphic architecture and origin of the paleo-Yangtze estuary (bottom of the delta) were mainly controlled by Holocene sea-level changes. The timing of transgression at the bottom of the Yangtze River Delta was different due to differences in the post-glacial paleontography during the early Holocene. Compared to the Yangtze River Delta records, the Huangqiao sand body lies between 7.5 and 4 ka. The age of the main body was affected by sea-level fluctuations and developed from 5 to 4 ka with sediment loads carried by the Yangtze River. The Huangqiao sand body is not an estuarine sand body but a sand body formed in a tide-dominated delta. This study provides new evidence for interpreting the origin and evolution of the Yangtze River Delta.

Sea-Level Change along the Emilia-Romagna Coast from Tide Gauge and Satellite Altimetry

Coastal flooding and retreat are markedly enhanced by sea-level rise. Thus, it is crucial to determine the sea-level variation at the local scale to support coastal hazard assessment and related management policies. In this work we focus on sea-level change along the Emilia-Romagna coast, a highly urbanized, 130 km-long belt facing the northern Adriatic Sea, by analyzing data from three tide gauges (with data records in the last 25–10 years) and related closest grid points from CMEMS monthly gridded satellite altimetry. The results reveal that the rate of sea-level rise observed by altimetry is coherent along the coast (2.8 ± 0.5 mm/year) for the period 1993–2019 and that a negative acceleration of −0.3 ± 0.1 mm/year is present, in contrast with the global scale. Rates resulting from tide gauge time series analysis diverge from these values mainly as a consequence of a large and heterogeneous rate of subsidence in the region. Over the common timespan, altimetry and tide gauge data show very high correlation, although their comparison suffers from the short overlapping period between the two data sets. Nevertheless, their combined use allows assessment of the recent (last 25 years) sea-level change along the Emilia-Romagna coast and to discuss the role of different interacting processes in the determination of the local sea level.

Pollen based inference of Holocene sea level changes, depositional environment and climatic history of Cauvery delta, Southern India

Palynological and other sedimentary records in the south-eastern peninsular India where the retreating (North-East) monsoon brings the main rainfall are scarce. This paper tries to address not only this gap in data but also the methodological challenges of interpreting such data in terms of sea level, depositional environment and climatic changes of the area going back nearly 11040 years. In addition to other (chemical) proxies studied previously, pollen data of a chronologically well constrained sediment core (~20 m) from Porayar (11°01.178′N 79°50.446′E), in the coastal marginal part of the Cauvery delta, Southern India, have been analyzed. The three major pollen zones observed since 11,040 years are presented and discussed, as are the methodological challenges of interpreting the vegetation record in such a dynamic and diverse environment (the delta plains of southern India). The zones observed indicate various transitions: from a lower sea level condition to a more stable sea level that created an estuarine environment filled with brackish water that supported pollen assemblages of a marshland but not a true mangrove. Concurrently, pollen assemblages that indicate catchments at multiple spatial scales – local to regional, extending from the North-East monsoon dominated delta to the Western Ghats is also inferred for climate interpretation.

Holocene sea-level changes of the Persian Gulf

High-resolution shallow seismic information supported by sedimentological and geochemical data from sediment cores has been used for reconstruction of Holocene sea-level changes along the northern coast of the Persian Gulf. These investigations in the area of the North Qeshm Island Waterway (NQIW) near the Strait of Hormuz reveal a series of five prominent sea-level fluctuations starting with the second phase of regional postglacial sea-level rise recorded between 15.0 ka and 9.5 ka (ka = thousands of years before present). Based on our study, sea-level had reached −22 m before 9.1 ka. Postglacial sea level high-stand in the study area has been dated to have occurred around 6.0 ka, which was followed by a relative sea-level fall coeval with a regional climate change from humid to arid conditions at about 5.4 ka. After a renewed, but relatively short period of sea level rise associated with climate changes around 4.35 ka, sea-level fell again at about 3.3 ka and remained relatively stable from 3.2 ka until the present. We conclude that major sea-level changes in the Persian Gulf coincided with sea-level fluctuations in the Indian Ocean and observed changes in North Atlantic Ocean and atmospheric circulation and Greenland Ice Sheet melting. Thus, despite of regional tectonic instability, regional sea-level stand in the Persian Gulf has been controlled mainly by eustatic sea-level changes of the global ocean.

Reef response to sea-level and environmental changes in the Central South Pacific over the past 6000 years

Geological records of coastal system evolution during past higher and/or rising sea levels provide an important baseline for developing projections regarding the response of modern coastal systems to future sea-level rise. The mid-late Holocene corresponds to the most recent window into natural variability prior to the Anthropocene and involves slow-rate and low-amplitude sea-level changes that were mostly governed by a limited glacio-eustatic contribution, most likely sourced from Antarctica, and ‘glacial isostatic adjustment’ processes. This paper documents in unprecedented detail the response of coral reefs and coastal systems to changing accommodation space in relation to mid-late Holocene sea-level changes in French Polynesia. The sea-level curve that underpins this study has a global significance and documents a single short-lived sea-level highstand between 4.10 and 3.40 kyr BP. The amplitude of the highstand is less than one metre, within the range of the predicted sea level at the end of the current century. The reported relative sea-level changes are characterized by slow rates ranging from a few tens of millimetres per year to up to 2.5 mm/yr and by significant sea-level stability (stillstands) lasting more than a century and up to 250 years, defining a step-like pattern. Sea-level variability probably driven by climatic oscillations on interannual to millennial time scales is evidenced during the entire time window. The detailed reconstruction of reef development over the last 6000 years brings valuable information regarding coral reef dynamics and coastal processes during periods of higher sea level and wave energy regimes. The persistence of stable and optimal depositional environments over the last 6000 years is demonstrated by the constant overall composition and diversity of reef communities and the almost continuous development of coral microatolls. The facies distribution as well as the lateral extension and shift of facies belts have been governed by variations in accommodation space, which are controlled by relative sea-level changes and antecedent topography. The widespread development of mid-late Holocene reef deposits in coastal areas suggests that they have played a prominent role in global processes related to the formation and shaping of modern islands. • Coral reef responses to slow-rate, low-amplitude, high-frequency sea-level changes. • Continuous reef development over the last 6000 years in optimal conditions. • Mid-late Holocene coral assemblages similar to their modern counterparts. • Facies distribution governed by variations in accommodation space. • Prominent role played by reef deposits in the formation and shaping of modern islands.

Stepwise accelerations in the rate of sea-level rise in the area north of Tokyo Bay during the Early Holocene

Tokyo Bay is situated near the triple junction of the North America, Pacific, and Philippine Sea plates, where relative sea-level changes since the Last Glacial Maximum (LGM) have been strongly affected by subduction tectonics. In this study, 55 sea-level index points were extracted from the post-LGM incised valley fills beneath the lowlands north of Tokyo Bay and used to construct a detailed relative sea-level curve for the Early Holocene. Sea-level jumps were detected at 10.1–10.0, 9.2–9.1, and 8.9–8.7 ka, each of 2–7 m and each followed by an acceleration in the rate of sea-level rise. These paired phenomena are attributed to coseismic subsidence and an interseismic decrease in the rate of uplift, respectively. The Early Holocene sea-level changes in Tokyo Bay are characterized by remarkably short sea-level jumps of <100 years and accelerations in the rates of sea-level rise with relatively long durations of 200–800 years. After separating these tectonic effects from relative sea-level changes, sea-level jumps that have been hypothesized to be eustatic events, such as Meltwater Pulses 1C and 1D and the pre-8.2-ka event, were not identified based on a sea-level detection limit of 3 m, but a decrease in the rate of sea-level rise at 8.2 ka, which can be regarded as a global phenomenon, was verified in Tokyo Bay.

Holocene sea-level change on the central coast of Bohai Bay, China

Abstract. To constrain models on global sea-level change regional proxy data on coastal change are indispensable. Here, we reconstruct the Holocene sea-level history of the northernmost China Sea shelf. This region is of great interest owing to its apparent far-field position during the late Quaternary, its broad shelf and its enormous sediment load supplied by the Yellow River. This study generated 25 sea-level index points for the central Bohai coastal plain through the study of 15 sediment cores and their sedimentary facies, foraminiferal assemblages and radiocarbon dating the basal peat. The observational data were compared with sea-level predictions obtained from global glacio-isostatic adjustment (GIA) models and with published sea-level data from Sunda shelf, Tahiti and Barbados. Our observational data indicate a phase of rapid sea-level rise from c. −17 to −4 m between c. 10 and 5 ka with a peak rise of 6.4 mm a−1 during 8.7 to 7.5 ka and slower rise of 1.9 mm a−1 during 7.5 to 5.3 ka followed by a phase of slow rise from 5 to 2 ka (∼0.4 mm a−1 from −3.58 m at 5.3 ka cal BP to −2.15 m at 2.3 ka cal BP). The comparison with the sea-level predictions for the study area and the published sea-level data is insightful: in the early Holocene, Bohai Bay's sea-level rise is dominated by a combination of the eustatic and the water load components causing the levering of the broad shelf. In the mid to late Holocene the rise is dominated by a combination of tectonic subsidence and fluvial sediment load, which masks the mid-Holocene highstand recorded elsewhere in the region.

Stratigraphic evolution of the Nakdong River valley in response to late Quaternary sea-level changes

Sequence analysis using borehole samples and high-resolution seismic data in the Nakdong River valley yielded a good example of a river-valley sequence influenced by the complex interplay between the bottom morphology of the steep paleo-valley, varying sediment supply, and Holocene sea-level change associated with coastal currents. The late Quaternary stratigraphic sequence in the Nakdong River Estuary, approximately 60–70 m thick, forms a high-frequency sequence consisting of a set of lowstand, transgressive, and highstand systems tracts that corresponds to a fifth-order (20 ka) sea-level cycle. Four main depositional systems, including ten sedimentary facies, constitute these systems tracts: fluvial, estuarine, coastal/shoreface, and deltaic. The lowstand systems tract (LST), consisting of gravelly sand, forms a fluvial depositional system (Unit I) which fills the thalweg of river valley mainly developed before 12 ka. The transgressive systems tract (TST), showing a succession of retrograding or backstepping depositional arrangements, can be divided into two depositional systems (Unit II and III). The riverine sediments were trapped within the paleo-estuary, forming an estuarine depositional system (Unit II) developed between 12 and 7 ka. As the transgression continued, the coarse sediments were deposited and redistributed by coastal processes, resulting in coastal/shoreface depositional system (Unit III). It is characterized by an isolated sand body and thin sand veneer. The HST is composed of deltaic depositional system including delta plain, delta front, and prodelta (Unit IV). During the delta progradation, most coarse-grained sands derived from the river were deposited in the lower delta plain and delta front, forming sand bars and shoals less than 15 m deep. The remaining fine-grained sediments were transported further offshore in a suspension mode and deposited in the inner shelf off the present river mouth, forming a subaqueous prodelta. Radiocarbon and optically stimulated luminescence (OSL) dating suggest that the Holocene deltaic system was initiated by aggradational and progradational stacking patterns at approximately 8 ka during the last stage of decelerated sea-level rise, and was then followed by a prograding clinoform after the highest sea level at approximately 7 ka.

Rauk - A Forgotten Witness of Holocene Sea-level Change and Development of Baltic Rocky Coasts: A Pilot Geomorphological Study in Lergrav Raukar Field

Strzelecki, M.C.; Duszyński, F.; Tyszkowski, S.; Zbucki, Ł., and Kasprzak, M., 2020. Rauk - Forgotten witness of Holocene sea-level change and development of Baltic rocky coastal zone: A pilot geomorphological study in Lergrav raukar field. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 659–663. Coconut Creek (Florida), ISSN 0749-0208.The Holocene history of Baltic Sea evolution is definitely one of the most interesting and intriguing stories of environmental change in Europe. To date, the key information on changes in sea-level and shifts in the environment associated with climate fluctuations were found in coastal lakes, marshes and wide stripe of barrier-lagoon systems of southern Baltic. Only limited research was conducted along rocky coasts, so characteristic features for Baltic islands from Bornholm, through Oland, Gotland, Fårö, Hiiumaa, Saarema to thousands of isles of Åland Archipelago. Among the most thrilling natural wonders found along Baltic coasts are rauks or raukars, unique limestone stacks—often with humanlike features—that tower above rocky shore platforms in northern Gotland and on Fårö, Gotland's sister island. Raukar coasts are one of the greatest touristic attractions in Sweden and the mythical coastal landscape of northern Gotland and Fårö had inspired many artists, including Ingmar Bergman. Surprisingly, what attracts tourists and artists, have been neglected by geomorphologists and those fascinating landforms still wait for detailed explanation of their origin and preservation. This paper provides insight into pilot geomorphological study of raukar coast in Lergrav, NE Gotland. Schmidt hammer rock tests were applied to characterize the degree of weathering of rock surface of well-preserved notches. The results of notch rock surface resistance and elevation above present sea-level are discussed with recent relative sea-level curves developed in the region.

Recent Sea Level Change in the Black Sea from Satellite Altimetry and Tide Gauge Observations

Global mean sea level has been rising at an increasing rate, especially since the early 19th century in response to ocean thermal expansion and ice sheet melting. The possible consequences of sea level rise pose a significant threat to coastal cities, inhabitants, infrastructure, wetlands, ecosystems, and beaches. Sea level changes are not geographically uniform. This study focuses on present-day sea level changes in the Black Sea using satellite altimetry and tide gauge data. The multi-mission gridded satellite altimetry data from January 1993 to May 2017 indicated a mean rate of sea level rise of 2.5 ± 0.5 mm/year over the entire Black Sea. However, when considering the dominant cycles of the Black Sea level time series, an apparent (significant) variation was seen until 2014, and the rise in the mean sea level has been estimated at about 3.2 ± 0.6 mm/year. Coastal sea level, which was assessed using the available data from 12 tide gauge stations, has generally risen (except for the Bourgas Station). For instance, from the western coast to the southern coast of the Black Sea, in Constantza, Sevastopol, Tuapse, Batumi, Trabzon, Amasra, Sile, and Igneada, the relative rise was 3.02, 1.56, 2.92, 3.52, 2.33, 3.43, 5.03, and 6.94 mm/year, respectively, for varying periods over 1922–2014. The highest and lowest rises in the mean level of the Black Sea were in Poti (7.01 mm/year) and in Varna (1.53 mm/year), respectively. Measurements from six Global Navigation Satellite System (GNSS) stations, which are very close to the tide gauges, also suggest that there were significant vertical land movements at some tide gauge locations. This study confirmed that according to the obtained average annual phase value of sea level observations, seasonal sea level variations in the Black Sea reach their maximum annual amplitude in May–June.

Geoarcheomorphosites under Strong Urbanization Pressure at the Tineh Plain, NE of the Nile Delta, Egypt

Most geologic and geomorphologic features emerged on a deltaic plain resulted from the interplay of marine, land and river, of which are some have the potential to be a geoheritage site, this is called a geomorphosite. Over time, human impact due to settlements on the geomorphosite, reshaped and transformed the site to geoarcheomorphosite. The Great Pelusium, or Tell El-Farama, which is located along the Tineh Plain at the NE extreme of the Nile Delta between the third and fifth c. AD, is classified as a geoarcheomorphosite. The location includes several geomorphosites, such as the accreted coastal ridges, which record Late Holocene sea level changes. It also includes traces of the flash flood on the Pelusiac branch during the eighth c. AD, with the fluvial flood plain, natural levee, and crevasse splays, on which the Great Pelusium, Tell El-Luli, Tell El-Fadah, and Tell El-Makhzan were constructed. Recently, the area subjected to a hub development project, which may represent anthropogenic hazards that threaten the Great Pelusium. This study aims to quantify the potential anthropogenic hazards. The change detection shows that in 1984 the area of the geoarcheomorphosites was 424.8 km2, representing approximately 67.1% of the Tineh Plain, in addition to the sand dune area of 75 km2, representing 11.8%. In 2018, the area saw agricultural activities, fish farms, and an urban expansion that covered approximately 244.2 km2, representing 38% of the Tineh Plain. The construction of a new hub in the Suez Canal corridor and the addition of a new community of one million people in an area of 164 km2, representing 30.3% of the plain, will add more pressure on the geodiversity. A conservation plan is recommended in the form of sustainable development to save an important area of geoheritage in Egypt and convert the area into a tourism destination.

Consolidating sea level acceleration estimates from satellite altimetry

More than 27 years of high precision satellite altimetry enables analysis of recent changes in global mean sea level (GMSL). Several previous studies present estimates of the trend and acceleration in GMSL; however, all are exclusively performed with data from the TOPEX/Poseidon, Jason-1, Jason-2 and Jason-3 missions (TPJ data). In this study we extend the altimetry record in both time and space by including independent data from the ERS-1, ERS-2, Envisat and CryoSat-2 missions (ESA data). This increases the time-series to span more than 27 years (1991.7–2019.0) and the spatial coverage is extended from ± 66° to ± 82° latitude. Another advantage of the ESA data is that it is independent of the issues associated with the TOPEX altimeter which introduce a significant uncertainty to the first part of the record. GMSL based on ESA data on the 1991–2019 period within ± 82° latitude exhibit an acceleration of 0.095 ± 0.009 mm/yr2. The corresponding value for the TPJ data is 0.080 ± 0.008 mm/yr2 for the 1993–2019 period and within ± 66° latitude. The ERS-1 satellite was launched shortly after the large Pinatubo eruption in 1991. The satellite observes a decrease of 6 mm in GMSL during the first 1.7 years until the launch of TOPEX/Poseidon. The distribution of sea level acceleration across the global ocean is highly similar between the ESA and TPJ dataset. In the Pacific Ocean regional sea level acceleration patterns seem related to the El-Niño Southern Oscillation (ENSO) whereas around Greenland a clear negative acceleration is seen.

Mid Holocene Sea-Level Changes in and around Dhaka City, Bangladesh

Bengal basin, the largest fluvio-deltaic sedimentary system on Earth, is located in Bangladesh and three eastern states of India. Sediment accumulates in the basin from the Ganges, Brahmaputra, and Meghna (GBM) river systems and is dispersed into the Bay of Bengal, forming the largest submarine fan in the world. The present-day geomorphology is dominated by the extensive Holocene GBM floodplain and delta. The initiation of the modern GBM delta at the onset of the Pleistocene glacial maximum and its evolution to the present configuration are intricately related to Holocene fluvio-dynamic processes, eustatic sea-level changes, and tectonic movements. Quaternary System in Bengal basin has varieties of depositional environment. Sediment characteristics of different geomorphic units are different. Late Quaternary monsoon climatic episodes played the vital role in creating the present morphology of the Madhupur surfaces. During the Holocene, the central part of the basin experienced cyclic transgression and regression phase in several times. This was the evidence by mangrove pollens. The presence of mangrove pollen specially Phoenix paludosa, Avicennia sp, Phoenix sylvestris, Prosopis grandis, Sonneratiopollis sp found in Chatbari, Dubadia and Mirertek area of Dhaka city along with radiocarbon dating indicated that marine influence occurred during Mid Holocene time. Two phases of transgression and regression have been recorded during mid Holocene time. First transgression was noticed around 6500 cal BP and then a subsequent regression of the bay had been observed around 5500-3500 cal BP. This was again followed by another transgression episode around 3500-1500 cal BP. and then a regression during between 1500 cal BP onwards.

Population Genetic Structure of A Marine Pelagic Egg Producer and Popular Marine Aquarium Species, the Mandarinfish Synchiropus splendidus.

The mandarinfish Synchiropus splendidus is extensively collected in Southeast Asia (mainly in the Philippines) and highly favoured for the marine aquarium trade. Males are more popular than females for their large first dorsal fins and the fishery is not managed. To examine possible population replenishment dynamics arising as a result of selective fishing, the effects of sex-selective fishing on sex ratios and population connectivity were considered. This study determined the sex ratios and analyzed the population genetic structure from mandarinfish collected at six locations: one from Palau, where the species is not exploited, and five from Bohol in the Philippines, where the species has long been heavily fished. The findings reported very low male to female ratios (0.12 to 0.30) from four of the five locations in Bohol, with relatively more males to females in the specimens collected from Palau (2.3). The analyses from allozymes (43 alleles from 10 loci) and microsatellites (118 alleles from 5 loci) revealed that genetic connectivity was high among the five locations in the Philippines as well as with the specimens collected from the more-distant Palau. The genetic homogeneity observed across the geographical range considered is inconsistent with the hypothesized limited dispersal ability of the species and could be explained by recent species range expansion associated with sea level rise in the region. The results suggest that the present genetic structure, at least in the geographic region considered, may not be determined by current patterns of gene flow, but may, instead, be driven by recent sea-level changes associated with periods of glaciation. Caution is suggested to ensure that heavily localized fishing does not produce excessively biased adult sex ratios.

New insights into the Holocene development history of a Pacific, low-lying coral reef island: Takapoto Atoll, French Polynesia

Low-lying atoll islands are known to be made up of unconsolidated, coral-rich detritus, together with high amounts of foraminifera, derived from both outer-reef and lagoonal environments. While regarded as highly vulnerable to ongoing global changes, these islands are poorly constrained in term of development history. Herein is presented a detailed chronostratigraphic study of Tuamotu atoll islands (French Polynesia, south central Pacific) based on analyses of sedimentary sequences through seven excavations along two transects across both windward and leeward rim areas around Takapoto Atoll. The island accretionary chronology is supported by radiometric dating of 62 coral and molluscan clasts. The sequences range between 3.80 m and 1.20 m in thickness, from the oceanic shoreline lagoonwards. Four lithofacies were identified from sediment composition and texture: a coral (pocilloporid)-rich, gravel-supported, preferentially located in the outermost rim areas; a coral-rich, gravelly sand-supported, locally interbedded with gravel-supported units; a foraminifera (amphisteginid)-rich, sand-dominated, mainly located at the central and innermost rim settings; and an organic-rich, sand facies atop of some sequences. A model of atoll islet formation is drawn up in relation to mid to late Holocene sea-level changes. The foundations of islets (motus), namely conglomerate platforms, started to form with deposition of patchy, rubble spreads over the upper reef-rim surfaces from ca 4,500 yr BP as sea level was about 0.80 m above its present mean level. On these platforms, islets started to accrete not before ca 2,300 yr BP, from isolated depocentres located midway between outer-reef and lagoon margins. At that time, sea level at about +0.60 m above present mean sea level was starting to slowly decrease to its present position. The major growth phases occurred in a context of continued sea-level fall. Islets continued to accrete through concentric ridges mainly until the last 300 years. Accretion was dominantly driven by low-frequency, high-energy wave-surge events. From dating of coral clasts, a number of one to two events by century were identified as having apparently contributed to island formation at Takapoto. Regionally predicted increase in the rates of sea-level rise may have negative impacts on such islands since these have evolved under conditions of falling sea level.

Preface: Celebration of the Career of Robert Nathan Ginsburg

Preface: Celebration of the Career of Robert Nathan Ginsburg

A global delta dataset and the environmental variables that predict delta formation on marine coastlines

Abstract. River deltas are sites of sediment accumulation along the coastline that form critical biological habitats, host megacities, and contain significant quantities of hydrocarbons. Despite their importance, we do not know which factors most significantly promote sediment accumulation and dominate delta formation. To investigate this issue, we present a global dataset of 5399 coastal rivers and data on eight environmental variables. Of these rivers, 40 % (n=2174) have geomorphic deltas defined either by a protrusion from the regional shoreline, a distributary channel network, or both. Globally, coastlines average one delta for every ∼300 km of shoreline, but there are hotspots of delta formation, for example in Southeast Asia where there is one delta per 100 km of shoreline. Our analysis shows that the likelihood of a river to form a delta increases with increasing water discharge, sediment discharge, and drainage basin area. On the other hand, delta likelihood decreases with increasing wave height and tidal range. Delta likelihood has a non-monotonic relationship with receiving-basin slope: it decreases with steeper slopes, but for slopes &gt;0.006 delta likelihood increases. This reflects different controls on delta formation on active versus passive margins. Sediment concentration and recent sea level change do not affect delta likelihood. A logistic regression shows that water discharge, sediment discharge, wave height, and tidal range are most important for delta formation. The logistic regression correctly predicts delta formation 74 % of the time. Our global analysis illustrates that delta formation and morphology represent a balance between constructive and destructive forces, and this framework may help predict tipping points at which deltas rapidly shift morphologies.

Holocene coastal environmental change and ENSO-driven hydroclimatic variability in East Asia

Understanding the past natural behavior of coastal hydroclimates at multi-centennial time scales is essential for planning coastal strategies in preparation for anticipated climate change. We investigated the elemental and isotopic features of 10-m-long coastal sedimentary cores from Goheung Bay located on the southern coast of Korea to extract such natural variability. Based on the relationships among total organic carbon (TOC), total sulfur (TS) content, and their isotopic values (δ13CTOC and δ34STS), we reconstructed the long-term coastal evolution in the area and compared this with the reported Holocene sea level change. Time series data of the titanium (Ti)/aluminum (Al) ratio, as a proxy for riverine terrigenous input, revealed a strong link to terrestrial plant contribution, as indicated by δ13CTOC variability, suggesting past hydroclimatic change in the study area. The short-term variability of Ti/Al ratios correlated well with flooding events reconstructed for the Nakdong River in Korea. Moreover, periods in which the Ti/Al ratio was higher corresponded to those of stronger El Niño Southern Oscillation (ENSO) activity, suggesting ENSO-driven hydroclimatic changes in southern Korea. Especially, the periods of higher Ti/Al ratios during the late Holocene corresponded to a higher frequency of typhoon-driven overwash events along the southwestern coast of Japan. These similarities suggest that past freshwater input events along the southern coast of Korea were influenced considerably by typhoon-driven heavy rains during stronger ENSO activity. Spectral analysis of the Ti/Al ratios revealed significant periodicities of 1550, 780, 140, 120 and 105 years, suggesting centennial to millennial-timescale variability in hydroclimatic change and typhoon activity over East Asia.

A model for oblique accretion on the South China Sea margin; Red River (Song Hong) sediment transport into Qiongdongnan Basin since Upper Miocene

Located on the northwestern margin of the South China Sea, the origin of asymmetrical shelf-slope clinoforms accumulated on the continental margin of the Qiongdongnan Basin since the late Miocene is ambiguous and it likely is the first case of oblique sediment transport and dispersal among the most studied mud-rich shelves of the world during Neogene to Recent sea-level changes. We calculate the paleo-sediment flux required to build the shelf-slope clinoforms based on 2-D seismic data, and the results are 3 to 17 time larger than the estimated paleo-sediment discharge from the proximal catchment area of Hainan Island. This large mismatch suggests that sediments on the shelf-edge of Qiongdongnan Basin were not only from Hainan Island but more likely from a larger drainage system. The strong (tens km) southward migration of the western portion of the Qiongdongnan shelf-edge break compared to the weak (1–2 km) shelf-edge progradation in the eastern portion, suggests that the Qiongdongnan shelf prism is highly asymmetric and is caused by a large sediment supply centered to the west, with most likely the Red River (Song Hong) as the sediment supply driver. The fine-grained lithology of the studied shelf margin sediments off Hainan Island, especially since the end Miocene, suggests that they were derived mainly from the Red River and were transported southeastward from the Gulf of Tonkin by shelf currents. We propose a model for asymmetric shelf-slope accretion of mud-rich shelves in which a significant part of the sediment-prism volume was obliquely dispersed across the subsiding shelf as fluid mud during highstand sea-levels. The model presented here describes oblique construction of shelf-slope clinoforms in a mud-rich system in response to variations in sediment dispersal and depocenter during multiple sea-level cycles. This model of long-term (~107 years), lateral asymmetric accretion contrasts with oblique sediment transport in other source-to-sink sedimentary systems around the world.

Tidal strait to embayment: Seismic stratigraphy and evolution of a rock-bounded embayment in the context of Holocene sea level change

Elongate, rock-framed Santa Catarina Island partly encloses a low-energy marine embayment that communicates with the ocean via narrow, rock-bounded inlets with ebb and flood-tide deltas. The bay shoreline consists of low-energy sandy beaches, strandplains, mangroves and bayhead deltas while the exposed Atlantic shoreline comprises a series of headland-embayment littoral cells in a linked, north-directed longshore drift system.New and previously published seismic stratigraphic investigations enable assessment of the palaeogeographic/geomorphic evolution of the area since the early Holocene. At a sea level of ca. −50 m a sandy mainland-attached shoreline complex (dune and beach) developed on a coastal plain setting some 6–7 km offshore of the present shoreline. North of the island, a barrier island and tombolo were formed in a coastal re-entrant adjacent to the northern entrance to Florianopolis Bay. The open coast beach/dune system was overstepped by rapid sea-level rise during MWP-1B whereas the barrier island and tombolo continued to accrete until MWP-1C when they too were overstepped.The back-island embayment contains up to 40 m of sediment overlying an irregular bedrock surface. It was initially flooded during MWP-1C and the early muddy sedimentation suggests a distal, sheltered marine embayment. The subsequent development of many large bioherms on bedrock and mud suggests a change to more fully marine conditions as sea-level continued to rise. In the North Bay, these were subsequently enveloped by tidal dunes migrating north from the mid-bay. The vertical stacking of 3-D and 2-D sandy bedforms suggests that a tidal strait had developed with strong tidal currents radiating from a constriction in the vicinity of modern Florianopolis City. The strong tidal currents may be linked to the Holocene sea-level high that is well documented for this region.A fall in sea level from this highstand, coupled with accumulation of tidal strait sediments, reduced the tidal prism and strength of tidal currents in the bay. At the same time, regressive beachridge plains developed in open coast and bay environments. This coincided with development of the contemporary tidal inlet complexes at the north and south outlets of the bay. As a consequence, the upper surface of the tidal strait sand deposits experienced tidal ravinement and the bay switched to a sheltered back-barrier environment dominated by deposition of mud and silt which blanket the contemporary bay floor. The tidal inlets sequestered sand from the littoral drift system in ebb and flood-tide deltas, which created breaks in the longshore drift system, causing littoral sediment to accumulate at the north of the island in a series of spits, and promoting strandplain development south of the island.