Decrease In Sediment Supply Research Articles

Are Beaches Losing Their Capacity to Receive Holidaymakers? The Case of Ofir, Portugal

Coastlines are suffering from the effects of erosive processes, the decrease in sediment supply, the rise in mean sea level, and the construction of coastal infrastructure and drainage works, which are further exacerbated by global climate change. The area of the Parque Natural do Litoral Norte (North Coast Natural Park) reveals worsening erosion rates and the transformations directly affect the natural resources that support tourism activities, particularly beach and nature tourism. As part of the CLICTOUR project, we have selected the coastline from Restinga de Ofir to Bonança Beach as a case study. The ESRI ArcGIS software and the Digital Shoreline Analysis System (DSAS) were used to quantify coastline migration and identify the impacts on beach morphology between 2010 and 2023. Based on this information, we calculated changes in carrying capacity and scenarios for visitor usage availability to ensure the protection of fauna and flora, as well as the safety of beachgoers. The results of the linear regression rate confirm the coastline has retreated during the period analyzed (2010–2023). The outcome of these dynamics is noticeable in the beach area, promoting its reduction in area and leisure quality. Considering climate change, this study shows the importance of developing resilience strategies for coastal territories that serve as traditional summer destinations.

Aeolian sediments in western Mongolia: Distribution and (paleo)climatic implications

The largest dune fields in Mongolia are mainly restricted to the Basin of Great Lakes in western Mongolia. These dune fields extend from 800 m a.s.l. in the basins for 200 to 300 km into the mountains up to about 2100 m a.s.l. Analyses of these dune fields, using an integrative mapping approach, provide evidence for different wind regimes. The dune fields result from a long-term Quaternary sediment cycle. Rivers transported the sand into the basins from where the wind carried the sand eastwards along the dune fields with a concurrent loss of silt-sized particles. Different paleolake levels and sandy plains with mobilized sand at their western ends exist in the lake basins. The largest masses of dune sand are found in the central parts of the dune fields. Towards their eastern ends, lower and more vegetated dunes and sand sheets result from both the decrease in sediment supply and increased vegetation at higher elevations. Three climatic and paleoclimatic implications are derived from the mapping approach. A: Under the modern semi-arid to semi-humid climate, wind systems from north to the north-west prevail, whereas in the southern Mongolian Els also wind from the south-east occurs. B: The highest lake levels occurred during pluvial phases in the basins, caused by increased moisture supply, also due to water supply from glacier- and permafrost retreat. C: The fundamental west-east orientation of the dune fields is a result of westerly winds which were prevalent during arid periods.

Geochemistry of Quaternary sediments in the northwestern South China Sea: Sediment provenance and mid-Pleistocene transition

The Quaternary sediments in the northwestern South China Sea (NW-SCS) provide valuable information about provenance, climate and sea level changes. However, the correlation between the geochemical records in marine sediments and these influencing factors remains less understood in the NW-SCS. Two wells penetrated Quaternary sediments on the shelf and shelf margin of the NW-SCS and provide an excellent dataset. In this study, the major, trace, and rare earth elements in the sediments were analyzed to reveal the Quaternary provenance changes that correlate with the climatic Middle Pleistocene transition (MPT). These results indicate that the core sediments were mainly derived from felsic source rocks and the degree of chemical weathering in the source areas is relatively low (CIA averaged at 58). The Quaternary provenance of the NW-SCS did not undergo significant changes, recording mixed sedimentation from the Red River, Hainan Island, and central Vietnamese sources. The felsic source rocks and negative Eu anomaly indicated the shelf area received sediments primarily from the Red River and Hainan Island. However, a positive Eu anomaly on the shelf margin suggests additional contributions from mafic rocks sourced from central Vietnam. During the MPT (1.3–1.4 to 0.8–0.9 Ma), the dominant periodicity of climate cycles changed from a 40 kyr obliquity cycle to a 100 kyr eccentricity cycle; the cooling climate led to a slight weaking in chemical weathering and a minor decrease in sediment supply from terrestrial sources. After the MPT, the mixed sourced sediments in the shelf and shelf margin areas of the NW-SCS likely suffered from multiple hydrodynamic forces under the influence of the Pleistocene high-frequency and high-amplitude sea level fluctuations. These climate induced changes led to significant fluctuations in element content that provide new insights into Quaternary sources and climatic events in the NW-SCS.

Dynamic evolution of tidal networks under the combined effect of de-reclamation and decrease of sediment supply

De-reclamation is a common strategy used for the restoration of tidal flats. In this study, we investigate the morphodynamic response of tidal channel networks and tidal flats after de-reclamation initiatives using the Delft3D numerical model. We find that tidal channel networks that have undergone reclamation and retreat projects have a lower drainage density (8.95 km−1) than that of channel networks that formed naturally (11.33 km−1), and the drainage efficiency of natural formed channel networks is almost three times greater than restored channel networks. These findings indicate that de-reclamation alone cannot fully erase the imprinting of the previous reclamation. We also find that the ultimate effectiveness of de-reclamation is affected by the geographical layout and unchanneled path length of the inchoate main creek system. In addition, following the implementation of de-reclamation, the immediate opening of previously enclosed areas amplifies the tidal prism, thereby intensifying tidal scouring and resulting in significant erosion, with erosion rate reaching hundreds of millimeters per day. Such losses can be remediated under sufficient sediment supply and prevented through the construction of artificial channels. However, this severe erosion may escalate under an insufficient sediment supply or a heightened tidal prism, potentially leading to permanent loss. These findings constitute an important reference for future engineering practices that support the safety and sustainability of coastal resources.

Landscape evolution during Holocene transgression of a mid‐latitude low‐relief coastal plain: The southern North Sea

AbstractLow‐relief coastal landscapes are at major risk of rising sea levels, as vertical changes in relative sea level have far‐reaching lateral effects. Integration of a dense 2D grid of seismic reflection data with sedimentological and geotechnical data obtained in two offshore wind farm zones allows detailed documentation of postglacial landforms and environmental change over a 1,021 km2 area in the western sector of the southern North Sea. Following the retreat of Last Glacial Maximum ice sheets from the southern North Sea, the resulting postglacial terrestrial landscape provided a surface for peatland formation as climate started to warm and the water table rose in response to relative sea‐level rise. Southward‐draining fluvial networks formed contemporaneously with the peatlands, and remnants of this terrestrial wetland landscape are buried beneath Holocene marine sediments. Distinctive isolated incisional features and discrete widening of fluvial channels that cut through the peats are interpreted as either tidal ponds or relict tidal channels. These features record the evolution of this landscape through the Early Holocene as marine transgression inundated a low‐relief coastal plain. The erosion of the peatlands observed in the cores, the patchy preservation of the organic wetland landscape, and the lack of preserved barrier systems recorded by the seismic reflection data suggest that the rate of relative sea‐level rise outpaced sediment supply during the Late Postglacial and Early Holocene in this area of the southern North Sea. In a regional context, the southward draining river channels contrast to northward fluvial drainage to the North Sea, pointing to a subtle drainage divide in the palaeolandscape and the presence of a low‐relief land bridge separating the North Sea and the English‐Channel/La Manche during the Early Holocene. The documented scenario of rising sea levels combined with decreasing sediment supply in a low‐relief setting is a situation faced by many global deltas and coastlines, which makes the southern North Sea a crucial archive of coastal landscape change.

Chronology by luminescence and radiocarbon on core sediments from the northeastern pearl river plain and implications for delta process

Accurate dating is the basis for deciphering eustatic and climatic changes on deltaic sedimentary processes. In the Pearl River Delta (PRD) plain of south China, scarce robust chronology hinders the detailed interpretation of sedimentary history. In this study, quartz optically stimulated luminescence (OSL) (21 samples), feldspar post-IR IRSL (pIRIR) (4 samples) and radiocarbon (14C) (2 samples) dating were applied to obtain detailed chronological framework of core SXG06 (23-m long to bedrock) from the northeastern PRD. SXG06 consists an upper marine unit (M1) and a lower marine unit (M2), separated by a terrestrial unit (mottled clay, T1). For M1, quartz OSL and 14C samples yielded ages from 5.2 ± 0.3 to 0.32 ± 0.02 ka. The sample on top of T1 produced a quartz OSL age of 35 ± 2 ka. For other 12 samples in T1 and M2, quartz OSL signals reached saturation and generated minimum ages (>51 ka). For these the saturated quartz OSL samples, feldspar pIR50IR250 provides an age range of 123 ± 7–105 ± 7 ka. The compilation of all the above ages and previous sedimentology data reveals that: (1) M2 was formed during marine transgression of Marine Isotope Stage (MIS) 5; (2) A hiatus with an age gap of between ∼35 ka and ∼5 ka was observed, which might be due to the low sea level and resultant weathering scouring; (3) Initial M1 deposits from the northeastern PRD postdated the central and southern PRD by ∼3 ka, indicating delayed delta development in the northeastern PRD during the Holocene. (4) SXG06 experienced slow deposition 0.3 m/ka in ∼5–3 ka because of the coevally decreased sediment supply, followed by accelerated deposition rate of 3 m/ka after ∼3 ka associated with strengthen human activity.

A fluvial‐aeolian system in response to aridification during the Late Mesozoic, Junggar Basin, Central Asia

AbstractAridification of Central Asia in the Late Mesozoic led to drastic environmental changes characterized by widespread aeolian deposits. We systematically investigated fluvial‐aeolian deposits in the Middle Jurassic Toutunhe Formation, Upper Jurassic Kalazha Formation, and Lower Cretaceous Tugulu Group in the Junggar Basin to the north of the Tianshan Orogenic Belt via unmanned aerial vehicle‐based photogrammetry, scanning electron microscope, grain‐size analysis, and detrital zircon geochronology. Paludal and deltaic environments transitioned to a fluvial‐aeolian environment from the late Middle Jurassic to the Late Jurassic. Fan delta and incisive braided river deposits accumulated in the earliest Cretaceous and evolved into a lacustrine environment with aeolian deposits in the lakeshore. Aeolian deposits are characterized by moderate‐ to well‐sorted and subangular to subround sandstones with large‐scale, high‐dip cross‐bedding, inversely graded lamination, dominant saltation grains, crescent‐shaped, and dish‐shaped impact structures. Aeolian deposits contain heavy minerals including more ilmenite, zircon, garnet, and, tourmaline and less magnetite and epidote than the fluvial deposits. The preserved aeolian sediments of the Kalazha Formation extend west–east for more than 100 km, suggesting a wide desert area during the latest Jurassic. The detrital zircon age patterns indicate that the provenance of the aeolian deposits was similar to that of coeval fluvial deposits. The cooccurrence of fluvial and aeolian deposits and the similar provenances but orthogonal flow directions indicate that the aeolian deposits were mainly sourced from the nearby fluvial material within the basin. The evolution of the fluvial‐aeolian system responded to a complete base‐level cycle controlled by the aridification and tectonics. Due to decreased sediment supply caused by aridification, the base level rose, leading to the change from braided rivers to meandering rivers, along with the deposition of aeolian sediments. Due to the tectonic reactivation in the Late Jurassic, the base level fell, causing the occurrence of alluvial fans and the expansion of the aeolian sediments. Previous studies revealed that the Tianshan in the Jurassic exhibited low relief. The fluvial‐aeolian system played an important role in maintaining the limited relief in southern Central Asia.

Does a braided river aggrade or degrade in response to changes in water and sediment fluxes?

Braided rivers undergo continuous morphological evolution in response to variations in water and sediment fluxes associated with a plethora of natural and anthropogenic disturbances, which has to date remained poorly understood. Here, a one-dimensional hydro-sediment-morphodynamic model is proposed for braided rivers. It is built upon an extended synthetic channel geometric model which encodes the essential, three-dimensional morphological information into a one-dimensional synthetic channel. It is first applied to the Rees River (New Zealand) to investigate overall morphological evolution (aggradation/degradation) during a single flood event. It is shown that the channel tends to degrade with increasing peak discharge and decreasing sediment supply, while the effect of baseflow discharge on aggradation/degradation is negligible unless the baseflow discharge exceeds a critical value. Then the proposed model is applied to resolve long-term morphological evolution in the Tuotuo River (China) reach (up to the year 2050), the source region of the Yangtze River, in response to projected water and sediment fluxes. Sustained degradation in the river reach is observed. The present study yields a viable physics-based method to predict overall aggradation or degradation of braided rivers under unsteady water and sediment fluxes over both short and long time scales.

Sequential riparian vegetation alteration in Japanese river landscapes

Bare gravel bed channels have been a common landscape feature of the middle reaches of rivers throughout Japan. They are disappearing these days because of vegetation colonization. Vegetation coverage of the riparian zones in the midstream reaches of rivers distributed throughout Japan was investigated using aerial photo images taken in 1946, 1975, and 2010. It was then compared with hydrological and water quality records, locations of dams and weirs, residential conditions of the surrounding areas, sediment yields, and forest coverage of the upstream mountainous areas. Riparian vegetation coverage has substantially increased in the last 70 years, from nearly 0 to 30-40%. Herbaceous vegetation coverage is higher than tree coverage. The total vegetation coverage did not correlate with water quality parameters. However, vegetation coverage had a significant negative correlation with the upstream basin's sediment yield and a slight negative correlation with the maximum flood peak flow rate. It was positively correlated with the terrestrial area fraction between levees. Riparian vegetation coverage was high within the 2 km downstream of dams or weirs, intercepting sediment flows. These results indicated that the gravelly sediment supplied from the upstream and deposited in the midstream at flood time has been the major contributor to keeping the vegetation coverage low rather than flushing by flood water. Reforestation since World War II has reduced the coarse sediment supply into the midstream river channels. This reforestation, together with gravel mining and intercepting sediment flow by dams and weirs, has caused the recent increase in vegetation coverage of the riparian zones. Human intervention can affect the vegetation conditions in riparian zones by decreasing sediment supply to river channels.

Consequences of limited sediment supply for long-term evolution of offshore tidal sand waves, a 3D model perspective

Field data show that offshore tidal sand waves in areas where sediment supply is limited have different characteristics (shape and dimensions) compared with their counterparts in areas with sufficient sediment supply. So far, only the initial formation of tidal sand waves on a sediment-starved shelf has been studied with a 2DV model that ignores variations along the crests. In this study, a 3D non-linear morphodynamic model is used to investigate the effects of sediment availability on the long-term evolution of offshore tidal sand waves. Overall, the simulated sand waves have characteristics that resemble those of observed sand waves. The mature sand waves that develop in the case of limited sediment supply (i.e., thickness of erodible sediment layer is smaller than the height of sand waves) are more three-dimensional, i.e., having isolated and more irregular crestlines compared with those in the case of sufficient supply. With decreasing sediment supply, sand waves have larger spacings between successive crests, smaller heights and they migrate faster. These differences in the characteristics of the sand waves start to occur once the hard bed underneath the erodible sediment layer is exposed.

Deglacial and Holocene sediment dynamics and provenances off Lancaster Sound: Implications for paleoenvironmental conditions in northern Baffin Bay

Since the last deglaciation, Baffin Bay between Greenland and Canada developed from an isolated marginal sea to a major Arctic-Atlantic throughflow closely linked to the North Atlantic circulation. While the initial steps of gateway openings through Lancaster Sound and Nares Strait to northern Baffin Bay are reasonably well documented, far less is known about related regional deglacial-to-Holocene changes in sediment sources and depositional processes due to a lack of continuous and well-dated paleoenvironmental records from northern Baffin Bay. Sedimentological, mineralogical, and radiogenic isotope data of the well-dated sediment core GeoB22336-4 from the mouth of Lancaster Sound provide new insights on the impacts of ice-sheet retreat and opening of the gateways to the Arctic Ocean on the depositional setting. Basal subglacial till deposits point to a grounded ice stream at the mouth of Lancaster Sound before ∼14.5 ka BP. Subsequent glaciomarine sedimentation is characterized by the input of ice-rafted detritus (IRD), bioturbation traces, and foraminifera shells. Decreasing sediment supply and input of IRD through time reflects a period of ice-sheet recession to predominantly land-terminating positions during the Early Holocene. Changes in radiogenic isotope signatures reveal the openings of Lancaster Sound between ∼10.4 and 9.9 ka BP and of Nares Strait between 8.5 and 8.2 ka BP, in alignment with earlier studies. The rapid mid-Holocene (up to ∼5.8 ka BP) deposition of fine-grained sediments is most likely caused by enhanced sea ice-rafted sediment input released under a strong West Greenland Current influence. Finally, a slight increase in IRD input during the last ∼2 ka BP is linked to the neoglacial re-advance of regional glaciers.

Dominant role of deglaciation in Late Pleistocene–Early Holocene sediment aggradation in the Upper Chenab valley, NW Himalaya

AbstractSediment transfer from the interiors of the Himalaya is complex because the archives are influenced by both glacial and monsoonal cycles. To deconvolve the coupling of glacial and monsoonal effects on sediment transfer processes, we investigate the Late Pleistocene–Holocene sediment archive in the Upper Chenab valley. Optically stimulated luminescence (OSL) ages from the archive indicate major aggradation during ca. 20–10 ka. Isotopic fingerprinting using Sr-Nd isotopes in silt fractions together with clast counts in boulder-pebble fractions indicate a decreasing Higher Himalayan sediment flux in the archive with time. Decreasing clast size, increasing clast roundness, increasing matrix to clast ratio, and dominance of the Higher Himalayan sourcing unequivocally suggest strong glacial influence during the initial stages of the archive formation. This evidence also agrees with the existing retreat ages of glaciers in the Upper Chenab valley. Results of our study also show that the upper parts of the archive contain significant fluvial sediment contribution from the Lesser Himalaya, which suggests an active role of the stronger Indian Summer Monsoon (ISM) in the region during the Early Holocene. The apparent decrease in sediment supply from the Higher Himalayan sources could have been due to longer source-to-sink transport in the Early Holocene and/or increased hillslope flux from Lesser Himalayan sources.

Mapping the most heavily reclaimed shorelines of the Yangtze River delta urban agglomerations

Objectively understanding the characteristics and evolution of coastal geomorphology, and predicting the growth potential of intertidal flats are the prerequisites for the effective conservation and development of shoreline resources. However, the vulnerability of shorelines in the long term and large space scale needs to be assessed since human intervention in recent decades has intensified the double oppression of river delta system transformation and land reclamation. The Yangtze River Delta Urban Agglomerations (YRDUA) is a highly developed global economy, therefore, the YRDUA with the most intense reclamation, and their dynamic shoreline changes before and after the sharply decreasing sediment supply were detected based on 4,596 remote sensing images and corresponding hydrodynamic data. We found that the sediment replenishment from the radial sand ridges on the middle Jiangsu Coast made the shoreline expansion rate reach 4–5 times that of other Jiangsu coasts. Specifically, a close correlation between the shoreline accretion rate and the amount of sediment supply was found on the eastern Chongming Wetland. Generally, there were still sufficient sediments on the Yangtze River Estuary and Hangzhou Bay interface to support the shoreline expansion despite the upstream sediment reduction. The longshore sediment transport from the delta-front erosion and the land reclamation including vegetation ecological responses were the main factors promoting the shoreline advance. Human interventions, dominated mainly by reclamation, formed positive feedback with local hydrodynamic processes and promoted continuous shoreline accretion. This study focused on the external and internal drivers and their interactions of long-term shoreline evolution with very intensive human activities, which can provide the decision-making reference for the regional coastal zone management and conservation.

Surface water temperature impacts on coastal wetland denitrification: Implications for river reconnection

Louisiana, located in the southeast United States, is home to 40% of the continental US's coastal wetlands yet accounts for 80% of the nation's coastal wetland loss. This loss is generally attributed to decreased sediment supply, hydrologic alteration from levees, channelization, subsidence, sea-level rise, and wave and tidal induced marsh edge erosion. The Mid-Barataria Sediment Diversion is a US $1.3 billion coastal restoration project that will divert up to 2100 m3 s−1 of sediment-laden Mississippi River water directly into Barataria Basin. The influx of colder, nutrient-rich, springtime river water could negatively impact water quality of the receiving basin. We quantified the effects of colder, surface water temperature on the nitrate (NO3−) reduction rate in vegetated marsh and open water bay sediments. Colder water limited NO3− removal processes averaging 17.1 mg N m−2 d−1 in the range of 5–14 °C, before increasing almost 3-fold in the 20 °C treatments at 50.6 mg N m−2 d−1. Low N removal rates, especially near the project inflow where temperatures will be coldest will favor transport of NO3− further into Barataria Basin where eutrophic conditions could become expressed. These results will inform coastal managers around the world of the potential ecosystem response to coastal restoration aimed at river reconnection where colder waters enter warmer, shallow basins.

Fluvial and coastal landform changes in the Aceh River delta (northern Sumatra) during the century leading to the 2004 Indian Ocean tsunami

AbstractRiver deltas are strongly affected by demographic growth and by the intensification of land use. The migration of deltaic coastlines is often rapid, threatening urban settlements, coastal farming, and coastal biotopes. Some deltas benefit from centuries of monitoring, such that the evolution of their coastline is well documented. For most deltas, however, such long records do not exist. The study of their geomorphological evolution can benefit from overlapping maps drafted over time, combined with aerial photographs and satellite images, to track the evolution of fluvial and coastal landforms. Both fluvial and coastal landforms are sensitive to variations in water and sediment supply, such that covariations in the evolution of these landforms, or the lack thereof, provide clues on the contribution of water and sediment supply to delta evolution. We document the evolution of river channels and coastlines in the delta of the Aceh River in northwest Sumatra, by overlying maps, ortho‐rectified aerial photographs, and satellite images covering the past 130 years. We assess the accuracy of the overlays, and then use multivariate statistics to analyze the co‐evolution of fluvial and coastal landforms. We propose that a progressive decrease in sediment supply spurred river channel lengthening and narrowing, landward migration of the shoreline, and narrowing of beach ridges. The 2004 Indian Ocean tsunami generated an instantaneous retreat of the coastline that amounts to ∼53% of the coastal retreat from 1884 to 2019 ce. Post‐tsunami evolution is marked by an irreversible acceleration of previous trends. Beach ridges located up‐drift of rivers and tidal channel mouths are more sensitive to long‐term landward retreat and tsunamigenic erosion.

Sediment budget and riverbed deformation in the uppermost part of the lower Yangtze River, China

The Yangtze River (YR), similar to most large rivers in the world, has experienced significant changes in its depositional environment due to anthropogenic disturbances and climatic influences in recent decades. However, knowledge of how the river channel and bed deformation respond to these changes in the uppermost part of the lower YR, a 200-km-long branched channel, is limited. In the current study, historical bathymetric data collected from 1992 to 2013 and high-resolution multibeam echo sounder (MBES) data obtained from 2015 to 2016 were analyzed to address the changes in the depositional environment. The results indicate that the whole riverbed in the Hukou to Datong reach (HDR) has been scouring over the past two decades and this trend is expected to continue in the future due to decreasing sediment supply from the upper watershed. The amount of net erosion from the HDR during 1992–2013 approximately accounted for 7.2% of total sediment load in the Yangtze River (5.02 billion metric tons at Datong). The evolution of the riverbed is trending towards stabilization even though the patterns of erosion and/or deposition in the HDR have dramatically changed in the last two decades. The part of the channel from the upper 100 km to Datong was found to be a sensitive reach that first showed erosion from 1992 to 2003 and showed deposition during 2003–2008, and then mild erosion during 2008–2013 in response to environmental changes. Thus, the findings indicate that riverine channel deformation in response to anthropogenic disturbance and climate influence is dynamic in different reaches, and this finding has both scientific and practical significance in terms of understanding channel stability and its response to external stressors.

Low-accommodation foreland basin response to long-term transgression: A record of change from continental-fluvial and marginal-marine to open-marine sequences over 60,000 km2 in the western Canada foreland basin

Low-accommodation foreland basins have been of recent interest because their stratigraphic architectures provide insight into the interaction of tectonic subsidence and eustasy. Aptian-aged strata in Alberta, Canada (McMurray Formation and Wabiskaw Member) were deposited under the influence of a continental-scale river that longitudinally transported and debouched sediment into the southward-transgressing Boreal Sea in the distal, low-accommodation Western Canada Foreland Basin (WCFB). In this study, we present a high-resolution stratigraphic framework for the McMurray-Wabiskaw interval, which was deposited during a long-term transgression. Using wireline logs from >20,000 wells and more than 500 cores, regional mapping focused on resolving stratigraphic relationships and the distribution of depositional environments across approximately 60,000 km2 in the Athabasca Oil Sands Region of northeastern Alberta. The studied stratigraphic interval is part of a third-order sequence: the McMurray Formation developed during a period of relative sea-level fall, lowstand, and early transgression, while the overlying Wabiskaw Member was deposited during late transgression. Within the McMurray Formation, superimposed fourth-order sea-level fluctuations in this low accommodation setting created a complex amalgam of deltaic strata vertically and laterally juxtaposed with valley-fill deposits. Relative sea-level rises resulted in rapid transgressions in which the shorelines migrated >400 km landward. Thin (5–15 m thick), widespread deltaic parasequence sets were deposited during subsequent sea-level highstands. During relative sea-level falls, fluvial meandering channel belts developed in downcutting valleys, with associated shorelines dramatically prograding basinward. In the Wabiskaw Member, continued sea-level rise coupled with potentially decreasing sediment supply resulted in the development of tide-influenced/dominated channels and bars in estuaries. The final phase of the third-order transgression was marked by a regional transgressive ravinement event and several southwestward backstepping wave-dominated shorefaces/strandplains. This low-accommodation foreland basin succession demonstrates a transition from deposition in continental fluvial and marginal-marine settings subject to high-frequency eustatic changes, to open-marine conditions over a long-term transgression.

Eocene-Oligocene paleoenvironmental changes in the South Orkney Microcontinent (Antarctica) linked to the opening of Powell Basin

The scarcity of paleo-records from the Antarctic Peninsular region of the Southern Ocean hinders our understanding of the timing of the opening of Drake Passage, specifically in the region of the South Orkney Microcontinent (SOM) and Powell Basin, between the Scotia and Antarctic plates. At Ocean Drilling Program (ODP) Hole 696B, SOM sediments recovered from the upper Eocene-lower Oligocene (~37.6–32.2 Ma) enable us to gain insight into paleoceanographic and paleoclimatic changes during gateway opening across the major Cenozoic climate shift —the Eocene-Oligocene transition— when the Antarctic ice sheet first reached sea-level. We propose the following sequence of events, based on a multi-proxy analysis of sediment facies, mineralogy, and organic matter geochemistry (TOC, TN, C/N ratio, δ 13 C, δ 15 N, and n -alkanes). During the late Eocene (~37.6–35.5 Ma) the SOM was attached to the Antarctic Peninsula, and terrigenous sediments of likely local origin were deposited in shallow waters under conditions of reduced‑oxygen/low-salinity, and temperate climate. In the latest Eocene (~35.5–34.1 Ma), terrigenous input was reduced due to the separation of the SOM from the Antarctic Peninsula by proto-Powell Basin opening. Decreased sediment supply during continuous deepening of the SOM led to deposition of a condensed section with significant glauconitization, recurrent winnowing by bottom currents, and suboxic conditions near the sediment-water interface. At the time of the Eocene-Oligocene transition (EOT; ~34.1–33.6 Ma) two upward-coarsening sediment sections were deposited within an overall upward-fining section, which we interpret as records of regressive phases due to ice sheet expansion. During the early Oligocene (~33.6–33.2 Ma) the SOM deepened further because of continued opening of Powell Basin, and organic-rich sediments were deposited as a result of enhanced biological production, partially driven by enhanced upwelling. Major cooling caused a change from forests indicating relatively humid temperate conditions in the late Eocene, to forests indicative of dry and cool conditions in the Oligocene, as shown by biomarker records, which also indicate weakening contributions of terrestrial organic matter to the marine sedimentary record. We thus conclude that a shallow gateway, the proto-Powell Basin, formed at ~35.5 Ma, as seen in the decreased delivery of proximal, coarse terrigenous sediments to the SOM margin; this was followed by a long-term deepening trend, interrupted by EOT regression due to continent-wide ice sheet build-up. Opening of the proto-Powell Basin could have provided a shallow-water pathway for water flowing from the Drake Passage-Scotia Sea towards the northern Weddell Sea, enhancing upwelling at the southern SOM shelf margin. Hence, increased marine productivity across the EOT might have resulted from the combined effects of the opening of Powell Basin and climate cooling. • Eocene-Oligocene sediments at Site 696 evidences a sustained relative sea-level rise in the SOM. • Our results point to the formation of the proto-Powell Basin at ~35.5 Ma. • Opening of Powell Basin provided a shallow-water pathway for water flowing towards the Weddell Sea. • We describe enhancing upwelling at the southern margin of the SOM shelf. • A shift from relatively humid temperate to dry and cool forests occurs between the Eocene and Oligocene.

Recent decline in streamflow and sediment discharge in the Godavari basin, India (1965–2015)

Godavari River representing the largest catchment in Peninsular India records a significant decline in streamflow and sediment discharge since 1965 with a sharp fall after ~1990. The present study documented changes in water and sediment discharge based on analysis of a large time-series database of daily streamflow from 57 gauging stations and sediment discharge from 25 stations during the period from 1965 to 2015 in the Godavari basin. Linear regression, Mann-Kendall non-parametric test, Sen’s slope, and Pettitt tests were conducted to examine the trends and abrupt changes in the time series. Many stations recorded a decline in sediment discharge (up to 90%) after 1990. At the terminal gauging station (Polavaram), the average annual sediment discharge for the period between 1970 and 1990 was 142 × 106 t, while it decreased to 59 × 106 t from 1991 to 2013. The outcomes of this study revealed a critical drop in sediment discharge after 1990 because of very high sediment entrapment by extensive dam constructions. This resulted in a substantial decrease in sediment supply contrasting to the increasing sea level, further implicating significant coastal erosion in the near future.

Holocene development and coastal dynamics at the Keta Sand Spit, Volta River delta, Ghana

Field process measurements and OSL/AMS-dating methods were employed in combination to examine the Holocene evolution of the Keta Sand Spit, east of the Volta River delta in Ghana, as well as the hydrodynamic processes driving present spit dynamics. Large-scale changes in shoreline configuration, with far-field implications for sediment supply to downdrift coasts along the Bight of Benin, have been rooted in river mouth switches, which are dated at approximately 5–7000 yr BP and 2500 yr BP. The most recent barrier stage is the present Keta Sand Spit, which originated about 2500 yr BP. The spit migrates slowly in an easterly direction due to gradients in longshore sediment transport induced by morphodynamic interactions between wave-induced currents and shoreline orientation. These autochthonous longshore transport gradients are the major reason for the large coastal erosion rates in the lee of the Sand Spit, rather than a decreased sediment supply caused by damming of the Volta River.