Sea-level Phase Research Articles

Sea level changes and sequence stratigraphy of the Lower-Middle Jurassic Quse and Sewa formations in the Qiangtang Basin, central Tibet: Geochemical and palynological perspectives

ABSTRACT Sequence stratigraphy is a commonly used approach to understand basin-fill history and the occurrence of conventional reservoir and/or probable source rocks. Reconstructing a sequence stratigraphic framework in carbonates, marls, and organic-rich mudstones is challenging due to environmental, petrophysical, and sedimentological variations that can be subtle, whereas seismic data may be lacking or of limited use. For this reason, incorporation between palynological analysis and chemostratigraphic profiles is becoming increasingly common to facilitate sequence stratigraphic reconstruction. This study investigates the Quse (lower Toarcian) and Sewa formations (upper Bajocian-Bathonian) in the Bilong Co section from the Qiangtang Basin of central Tibet. Eighty-three rock samples were analysed for their whole-rock inorganic geochemical composition, of which 25 rock samples were tested for palynological and palynofacies analyses. The palynological composition defined two associations for the study section. The lower part of the Bilong Co section consisted is dominated by a moderate to high abundance of opaque phytoclasts versus low to moderate amorphous organic matter (AOM) content with a high concentration of sphaeromorphs pollen grains, revealing deposition of this interval at times of low relative sea level in fluvio-deltaic settings. The middle to upper parts of the section comprised of significantly high AOM content versus low phytoclasts and high content of sphaeromorphs pollen grains, but with increasing the relative abundance of dinoflagellate cysts, indicating a phase of high sea level. Chemostratigraphic variations relevant to changes in relative sea level delineated the subdivision of the Quse and Sewa formations into two and three third-order transgressive-regressive sequences, respectively. The collision between the Lhasa and Qiangtang blocks during the Early-Middle Jurassic is suggested to control consequent subduction and sea level highstand, especially during deposition of the Sewa Formation. Geochemical proxies that relate to shelf carbonate production are calcium, strontium, whereas proxies that relate to siliciclastics include titanium, zirconium, manganese, aluminium, and silicon, other redox-sensitive proxy like uranium is also implemented. This indicates that chemostratigraphic proxies are a promising tool for the interpretation of sea level cyclicity in terms of systems tracts and bounding surfaces.

Paleoceanographic Conditions of Neo-Tethys Deposits in Northeast Iraq (Shiranish Formation) by Geochemical Proxies

Geochemical proxies provide detailed information on depositional environment and diagenetic processes. The main objectives of the present study are the evaluation of the paleoenvironment and diagenetic conditions of selected three sections of the Shiranish Formation (Late Campanian-Maastrichtian) in Dokan-Sulaymaniyah, Kurdistan Region, northeast of Iraq. The major and some trace elements were analysed by X-Ray Fluoresces. These geochemical results showed a positive correlation of SiO2, Al2O3, Fe2O3, MgO and TiO2 between each other due to the influence of detrital influx from the active oceanic margins and thrust belts of the northeast Arabian Plate. The terrigenous supply of silicates (K-feldspar) and clay minerals (Illite) caused a positive correlation between K2O values and Al2O3. In general, there is a low abundance of SiO2 and Al2O3 contents, referring to the deepening of the Neo-Tythus ocean basin in the formation's lower part. The Mn* factor of the lower and middle part of the formation exhibited anoxic conditions while oxic- suboxic conditions at the upper part. The Mn/Sr ratios were less than one, which means that Shiranish marly limestone was well preserved out of diagenetic processes. The paleoredox proxies {Th/U, V/Cr &V/(V+Ni)} confirmed that the lower part of the Formation was deposited in a relatively anoxic deep-outer shelf environment with a rising in paleoproductivity. In contrast, the upper part was characterised by dyoxic-oxic redox. Due to the inner shelf environment, this redox fluctuation reflects a regression phase of sea level, which is compatible with the closure events of the Neo-Tethys in the Eocene epoch.

Comparison of Extreme Coastal Flooding Events between Tropical and Midlatitude Weather Systems in the Delaware and Chesapeake Bays for 1980–2019

Abstract Coastal flooding is one of the most costly and deadly natural hazards facing the U.S. mid-Atlantic region today. Impacts in this heavily populated and economically significant region are caused by a combination of the location’s exposure and natural forcing from storms and sea level rise. Tropical cyclones (TCs) and midlatitude (ML) weather systems each have caused extreme coastal flooding in the region. Skew surge was computed over each tidal cycle for the past 40 years (1980–2019) at several tide gauges in the Delaware and Chesapeake Bays to compare the meteorological component of surge for each weather type. Although TCs cause higher mean surges, ML weather systems can produce surges just as severe and occur much more frequently, peaking in the cold season (November–March). Of the top 10 largest surge events, TCs account for 30%–45% in the Delaware and upper Chesapeake Bays and 40%–45% in the lower Chesapeake Bay. This percentage drops to 10%–15% for larger numbers of events in all regions. Mean sea level pressure and 500-hPa geopotential height (GPH) fields of the top 10 surge events from ML weather systems show a low pressure center west-southwest of “Delmarva” and a semistationary high pressure center to the northeast prior to maximum surge, producing strong easterly winds. Low pressure centers intensify under upper-level divergence as they travel eastward, and the high pressure centers are near the GPH ridges. During lower-bay events, the low pressure centers develop farther south, intensifying over warmer coastal waters, with a south-shifted GPH pattern relative to upper-bay events. Significance Statement Severe coastal flooding is a year-round threat in the U.S. mid-Atlantic region, and impacts are projected to increase in magnitude and frequency. Research into the meteorological contribution to storm surge, separate from mean sea level and tidal phase, will increase the scientific understanding and monitoring of changing atmospheric conditions. Tropical cyclones and midlatitude weather systems both significantly impact the mid-Atlantic region during different times of year. However, climate change may alter the future behavior of these systems differently. Understanding the synoptic environment and quantifying the surge response and subbay geographic variability of each weather system in this region will aid in public awareness, near-term emergency preparation, and long-term planning for coastal storms.

Late Pleistocene human fossils in Japanese Archipelago

The fossil human remains of the Japanese archipelago represent an abundant documentation, with diverse and complex origins. Essentially, populations appear to come from Southeast Asia, moving northward during phases of low sea level, during ice ages. However, part of the population would also have come from the Korean peninsula, via a almost-connected land bridge then established during the lowering of sea levels. An additional northern influence is also possible. Human bone remains were in limestone rock crevices, shelter, and caves, probably buried there. Their conservation is often delicate but informative enough to consider the Pleistocene people in Japanese Archipelago.

The effects of non-Newtonian rheology in the upper mantle on relative sea level change and geodetic observables induced by glacial isostatic adjustment process

SUMMARY Studies of glacial isostatic adjustment (GIA) provide important constraints on the Earth's mantle viscosity. Most GIA models assume Newtonian viscosity through the mantle, but laboratory experimental studies of rock deformation, observational studies of seismic anisotropy, and modelling studies of mantle dynamics show that in the upper mantle non-Newtonian viscosity may be important. This study explores the non-Newtonian effects on the GIA induced variations in mantle stress and viscosity and on surface observables including vertical displacement, relative sea level (RSL) and gravity change. The recently updated and fully benchmarked software package CitcomSVE is used for GIA simulations. We adopt the ICE-6G ice deglaciation history, VM5a lower mantle and lithospheric viscosities, and a composite rheology that combines Newtonian and non-Newtonian viscosities for the upper mantle. Our results show that: (1) The mantle stress beneath glaciated regions increases significantly during deglaciation, leading to regionally reduced upper mantle viscosity by more than an order of magnitude. Such effects can be rather localized at the periphery of glaciated regions. However, non-Newtonian effects on far-field mantle viscosity are negligibly small. GIA induced stress is also significant in the lithosphere (∼30 MPa) and lower mantle (∼2 MPa). (2) The predicted RSL changes from non-Newtonian models display distinct features in comparison with the Newtonian model, including more rapid sea level falls associated with the rapid deglaciation at ∼14 000 yr ago followed by a more gradual sea level variation for sites near the centres of formerly glaciated regions, and an additional phase of sea level falls for the last ∼8000 yr for sites at the ice margins. Similar time-dependence associated with the deglaciation is also seen for rate of vertical displacement, suggesting a relatively slow present-day rates of vertical displacement and gravity change. These features can be explained by the non-Newtonian effects associated with a loading event which manifest a fast relaxation stage followed by a relative slow relaxation stage. Our results may provide GIA diagnoses for distinguishing non-Newtonian and Newtonian rheology.

The late Quaternary stratigraphy of coastal dunes and associated deposits in southern Africa

Abstract Coastal sand dune sediments with associated intraformational aeolianite, palaeosols and beachrock are found throughout much of the southern African coast, and have important roles as both Quaternary environmental archives and in recording the interplay of sediment supply, coastal processes and sea-level change. This paper examines the stratigraphy and palaeoenvironmental significance of coastal sand dunes and associated sediments, using examples mainly from South Africa but also with reference to the sandy coasts of Namibia and southern Mozambique. Based on morphological, sedimentary and dating evidence reported in the diverse literature, the stratigraphic relationship of coastal sand dune sediments to Marine Isotope Stages (MIS) is summarized, and a chronostratigraphic diagram for the period MIS 6 to 1 along the South African coast is used to identify spatially coherent sedimentary units that correspond to different regional climatic and sea-level phases. This framework provides a stratigraphic context to better examine the relationship between coastal sand dunes and external forcing during the late Quaternary in southern Africa, and to guide future field studies.

Circulation and Upwelling Induced by Coastal Trapped Waves Over a Submarine Canyon in an Idealized Eastern Boundary Margin

AbstractWind‐driven upwelling promotes the onshore transport of dense slope waters onto the continental shelf. New observational evidence suggests that the propagation of coastal trapped waves (CTWs) over a submarine canyon can also cause upwelling within the canyon, independent of the wind forcing. Here, we use idealized numerical experiments to assess the role of CTWs in promoting the onshore transport of deeper waters onto the continental shelf. The experiments are forced with a 7‐days period CTW. Overall, there is accumulated upwelled water in time with increased onshore transport during the low sea level phase of the CTWs. Most of the onshore flow is spread over the upwave side of the canyon during the low sea level phase, but it is advected further downwave during the subsequent high sea level phase. As a result, a dense pool of upwelled water is spread over the shelf extending primarily in the downwave direction.

Palaeoclimatic and sea-level fluctuations from the last deglaciation to late Holocene from western India: Evidence from multiproxy studies

• At least 4 episodes of marginal marine sedimentation environments are reported between last deglaciation to the late Holocene in Western India.. • The first phase of deposition under marine influence is at ~20 ka BP, the second phase between ~11,210 and 9759 cal yr BP and third phase of sea level rise at around ~6118 cal yr BP. The final phase of marine to marginal marine conditions are noted to be of post ~2650 ± 180 cal yr BP until ~1530 ± 350 cal yr BP. • There were coeval dry climatic conditions of the Older Dryas and Younger Dryas periods besides the warm and humid conditions of the Bolling-Allerod period. • During the last deglaciation to late Holocene times, at several times the Gulf of Kachchh extended inland and the rivers debouched into these extended gulfs rather than in the Little Rann as seen at present. A sediment core from a palaeochannel distributary of the Saraswati River basin in western India was investigated through a multi-proxy study using palynology, phytoliths, sedimentology, geochemistry, magnetic mineralogy and chronology. The site is located at the eastern margin of the Little Rann of Kachchh in the northwestern part of the Gujarat Alluvial Plains. The goal was to reconstruct the paleoclimatic and sea level flucutations spanning from the last deglaciation to the late Holocene in the area. The core records suggest at least four episodes of marginal marine environment between the last deglaciation and the late Holocene. The first phase of sediment deposition under marine influence was observed post LGM. The signatures of coeval dry climatic conditions of Older Dryas and Younger Dryas periods besides warm and humid conditions of Bølling-Ållerød period are reflected in the core records. The second phase of rise in sea level occurred between ~11,210 and ~9795 cal yr BP, which falls within the period of high gradient of sea-level rise of western India. The third phase of global sea level rise in the area is at around ~5747 cal yr BP which coincides with a high sea level phase along the west coast of India. The final recurrence of sediments with predominant marine signatures post ~2650 ± 180 cal yr BP until ~1530 ± 350 cal yr BP suggests marine to marginal marine conditions in the area.

Submarine Geomorphology of the Southwestern Sardinian Continental Shelf (Mediterranean Sea): Insights into the Last Glacial Maximum Sea-Level Changes and Related Environments

During the lowstand sea-level phase of the Last Glacial Maximum (LGM), a large part of the current Mediterranean continental shelf emerged. Erosional and depositional processes shaped the coastal strips, while inland areas were affected by aeolian and fluvial processes. Evidence of both the lowstand phase and the subsequent phases of eustatic sea level rise can be observed on the continental shelf of Sardinia (Italy), including submerged palaeo-shorelines and landforms, and indicators of relict coastal palaeo-environments. This paper shows the results of a high-resolution survey on the continental shelf off San Pietro Island (southwestern Sardinia). Multisensor and multiscale data—obtained by means of seismic sparker, sub-bottom profiler chirp, multibeam, side scan sonar, diving, and uncrewed aerial vehicles—made it possible to reconstruct the morphological features shaped during the LGM at depths between 125 and 135 m. In particular, tectonic controlled palaeo-cliffs affected by landslides, the mouth of a deep palaeo-valley fossilized by marine sediments and a palaeo-lagoon containing a peri-littoral thanatocenosis (18,983 ± 268 cal BP) were detected. The Younger Dryas palaeo-shorelines were reconstructed, highlighted by a very well preserved beachrock. The coastal paleo-landscape with lagoon-barrier systems and retro-littoral dunes frequented by the Mesolithic populations was reconstructed.

Paleoredox and Environmental Conditions of Southern Neo-Tethys Deposits in South Iraq (Yamama Formation) by Geochemical Indicators

A geochemical and environmental study was carried out for the sediments of the Southern Neo-Tethys Ocean, represented by the Yamama Formation (Berriasian-Valaganian) in southern Iraq. The formation has a particular reservoir importance. The typical WQ-220 and WQ-280 wells were selected from the West Qurna field. Data of Gamma-ray logs were used for 30 depths of the typical well. Ten core samples were analyzed by X-Ray Fluoresces and total organic matter from both wells. The results showed that shaliness was relatively low, with an average of 16.5%, leading to a decrease in the presence of clay minerals and trace elements because the environment of the Yamama Formation is relatively far away from the coast. Qualitative evaluation of clay minerals was carried out by thorium/potassium ratio, which showed the dominance of illite and smectite. This may be due to an increase in the salinity of the ocean at that time or because potassium bonds are strong enough to resist the diagenesis processes. The origin of shale in the Yamama Formation was studied using the relationship TiO2-MgO+Fe2O3; the sources were passive margin group, oceanic island arc and active continental margin. The redox potential of paleoenvironment was determined by the thorium/uranium ratio, which showed that the beginning of depositional environment was slightly oxidized, but with the increase of sedimentation, it turned into a reduced environment, which indicates a transgression phase of sea level. The results of euxinic affinity, based on the relationship between molybdenum and Total Organic Carbon (TOC), reflect dyoxic facies which is deposited in extremely low but non-zero oxygen content, while the upper was approaching anoxic facies zone. The paleoenvironment of the Yamama Formation was of restricted deep marine water (outer shelf - upper part of the benthic zone) which contained a marine transgression phase because of the opening of Southern Neo-Tethys Ocean in the Valanginian age.

Динамика каспийских берегов в концепции “АТласа культурного и природного наследия Дагестана”

Atlas of the cultural and natural heritage of Dagestan is a comprehensive cartographic work, which displays objects of archeology, history, ethnography, socio-economic sphere and nature, cultural, historical and natural heritage. The development of the Atlas is based on previously acquired experience in creating the Geographic and other atlases of Dagestan and involves the use of a number of methodological innovations, one of which is the use of typical contour maps with different physical and geographical outlines of coastal territories in specific historical eras. We are talking primarily about the coastline of the Caspian Sea, which has noticeably changed in the historical timescale. This approach allows to map the main historical milestones of the interaction of resettlement systems and households of the inhabitants of the Mountain Country with a very dynamic natural environment of this region. So, archaeological maps revealing the sites of pre-historic humans within the modern borders of the Republic of Dagestan include the lines of the Caspian coast in the ancient periods of sea transgressions and regressions. The atlas includes maps showing information on the dynamics and evolution of the Caspian coast for different historical eras as a result of sea level fluctuations and the variability of the Dagestan hydrographic network and the dynamics of the Terek delta and the mouth of Sulak. The history of the Caspian Sea level fluctuations was reconstructed starting from the regressive phase of sea level stand during pre-Bakinian time, when sufficiently reliable geological and geomorphological data were available to estimate, the amplitude and age of level changes. The Bakinian transgression, which consisted of two stages: Early Bakinian and Late Bakinian took place in the beginning of the Brunnes Era. Even more data is available for reconstruction of Early and Late Khazarian, and subsequent transgressions and regressions of the Caspian Sea, the boundaries of which are reflected on the map of the Paleolithic Era. The Atlas is divided into two parts, the first is represented by historical and cultural maps, the second – by the maps on natural and economic heritage of the Mountain Country. The introductory section includes basic maps on physical geography, the modern administrative-territorial division of Dagestan and its position in the North Caucasus Federal District. In total and in accordance with the work plan, the Atlas includes 100 major maps and more than 30 inset maps. A total of about 50 scientists and practitioners with different scientific profiles from the Dagestan Federal Research Center of the Russian Academy of Sciences institutes, Makhachkala universities, and Lomonosov Moscow State University took part in this work.

Climate-forced sea-level lowstands in the Indian Ocean during the last two millennia

Sea-level reconstructions over the past two millennia provide a pre-industrial context to assess whether the magnitude and rate of modern sea-level change is unprecedented. Sea-level records from the Indian Ocean over the past 2,000 years are sparse, while records from the Atlantic and Pacific Oceans show variations less than 0.25 m and no significant negative excursions. Here, we present evidence of two low sea-level phases in the Maldives, Indian Ocean, based on fossil coral microatolls. Microatoll growth is constrained by low water levels and, consequently, they are robust recorders of past sea level. U–Th dating of the Maldivian corals identified lowstands at ad 234–605 and ad 1481–1807 when sea level fell to maximum depths of −0.88 m and −0.89 m respectively. These lowstands are synchronous with reductions in radiative forcing and sea surface temperature associated with the Late Antiquity Little Ice Age and the Little Ice Age. Our results provide high-fidelity observations of lower sea levels during these cool periods and show rates of change of up to 4.24 mm yr−1. Our data also confirm the acceleration of relative sea-level rise over the past two centuries and suggest that the current magnitude and rate of sea-level rise is not unprecedented. Two intervals of distinctly lower Indian Ocean sea level during the last two millennia occurred during times of relatively low incoming solar radiation, according to an analysis of U–Th dated coral microatolls in the Maldives.

To be allochthonous or autochthonous? The late Paleocene–late Eocene slope sedimentary succession of the Latium–Abruzzi carbonate platform (Central Apennines, Italy)

Margins, slopes, and toe-of-slopes represent regions of sediment transfer and bypass from shallow-water settings to the basin. They are zones of sediment flux triggered by different types of physical process including sediment-gravity flows, storm-driven currents, unidirectional currents, and oscillatory flows. As a consequence, they are zones where sediment can be remobilized and strongly reworked from inner environments to offshore settings and deposited as a mixture of autochthonous/allochthonous sediments. In the Monte La Serra and Monte Torretta (Central Apennines) lower-to-upper Eocene reworked sedimentary succession, two main facies associations are differentiated on textural characteristics and tested for robustness by hierarchical cluster analysis: a grain-supported (packstone-to-grainstone) facies FA1 and a mud-supported (mudstone-to-wackestone) facies FA2. The outcrops allow investigation of the transition zone between the margin of the Latium–Abruzzi platform and the adjoining basin and especially the identification of the carbonate factories that supplied the sediment to the slope zone of the Latium–Abruzzi platform. During the Paleogene, this platform was a shaved isolated platform under the action of waves, with sediment deposition during the transgressive and highstand phases of sea level, and erosion of this material during a subsequent lowstand phase. During these phases, storm-driven currents acted on the carbonate platform, remobilizing, resuspending, and reworking sediments. The remobilized material was transferred from the inner platform on to the slope, generating a mixture of detrital shallow- and deep-water biotic assemblages and depositing autochthonous/allochthonous units mainly constituted by alveolinids, large rotaliids, hooked gypsinids, nummulitids, and orthophragmines (discocyclinids and orbitoclypeids) assemblages. This mixture of shallow- and deep-water biotic assemblages demonstrates that a systematic study of the provenance of carbonate-producing biota, even if they are not preserved in their original context, can be useful in palaeoenvironmental reconstruction of the original carbonate factory system.

Consistent CO2 release by pyrite oxidation on continental shelves prior to glacial terminations

Previous evidence suggests enhanced pyrite oxidation on exposed continental shelves during glacial phases of low sea level. While pyrite oxidation directly consumes atmospheric oxygen, acid generated by this reaction should increase the release of CO2 through carbonate dissolution. This scenario represents a climate control loop that could temper or even prevent glacials because increasing CO2 triggers warming and rising sea level. However, the amplitudes of sea-level changes increased over the Quaternary, and CO2 concentrations co-varied with sea level throughout most of the past 800,000 years. Only during peak glacial conditions did CO2 levels reach an apparent lower threshold independent of falling sea level. Here we suggest that during the last nine glacial–interglacial cycles, pyrite-oxidation-driven release of CO2 and consumption of O2 occurred during 10 kyr to 40 kyr periods preceding glacial terminations. We demonstrate that repeated sea-level lowstands force pyrite oxidation to ever-greater depths in exposed shelf sediments and cause CO2 release that could explain the glacial CO2 threshold. When the duration of interglacials with high sea level is insufficient to restock the shelf pyrite inventory, this CO2-releasing process represents a discharging ‘acid capacitor’. Minimum atmospheric CO2 levels during glacial intervals were set, in part, by repeated CO2 release from pyrite oxidation on exposed continental shelves, according to a geochemical model of the past 3 Myr.

Factors controlling frequency of turbidites in the Bengal fan during the last 248 kyr cal BP: Clues from a presently inactive channel

The seafloor of the Bay of Bengal is covered by thick sediment deposits that constitute the largest turbiditic system in the world. This system is fed primarily by the Ganges and Brahmaputra rivers, which drain the high Himalayan ranges. Sediment transfers from the delta to the deep-sea fan take place as turbidity currents in channel-levee systems. Previous studies have shown that, during high sea-level stand periods, the sediments were being mainly stored in the Ganges-Brahmaputra delta, and turbiditic transfer was occurring through active channels. Most of these channels are now inactive and sealed by hemipelagic deposits. However, the evolution of the inactive channels during the last sea-level variations has never been described in detail. Sedimentation in the currently active channel, the Active Valley, was particularly important during the last sea-level rise, which suggests a very good connection between the fluvial systems and the deep turbidite system at this time. During the MONOPOL cruise (2012), we retrieved a giant piston core (MD12-3412) near the currently inactive E4 channel. Previous studies have hypothesized that this channel is connected to the Swatch of No Ground canyon on the upper fan. The upper part of the core covers the last ~250 kyr. It reveals that, contrary to what is known about the Active Valley, the turbidite activity in E4 took place mainly during low sea-level phases (glacial stages), and stopped around 11.8 kyr cal BP. This different mode of activity suggests that (i) E4 was not abandoned but served as a secondary channel, and (ii) that the supply of turbidite material at the site of core MD12-3412 was not related to past changes in summer monsoon strength. Periods of activation of the E4 channel observed on core MD12-3412 were previously identified on the shelf area, by Hubscher and Spiess (2005), as thick Forced Regression System Tracts (FRST) after a displacement of deltaic edifices. High turbidites record on the deep basin are mainly synchronous with sea-level fall and rise conditions, but mostly during low sea-level periods. This could be explained by a residual connection between the coastal system and the E4 channel during sea level low stands.

TRACING ORIGIN AND COLLAPSE OF HOLOCENE BENTHIC BASELINE COMMUNITIES IN THE NORTHERN ADRIATIC SEA

The shallow northern Adriatic Sea has a long history of anthropogenic impacts that reaches back many centuries. While the effects of eutrophication, overfishing, pollution, and trawling over recent decades have been extensively studied, the major ecological turnovers during the Holocene as a whole remain poorly explored. In this study, we reconstruct ecological baselines defining benthic ecosystem composition prior to major anthropogenic changes at four stations characterized by low sedimentation and millennial-scale time averaging of molluscan assemblages. We discriminate between natural and anthropogenic drivers based on (1) stratigraphic changes in the composition of molluscan communities observed in sediment cores and (2) changes in concentrations of heavy metals, pollutants, and organic enrichment. The four 1.5-m long sediment cores reach back to the Pleistocene–Holocene boundary, allowing for a stratigraphic distinction of the major sea-level phases of the Holocene. During the transgressive phase and maximum flooding, sea-level and establishment of the modern circulation pattern determined the development of benthic communities in shallow-water, vegetated habitats with epifaunal biostromes and, in deeper waters, with bryozoan meadows. After sea-level stabilization, the composition of these baseline communities remained relatively uniform and started to change markedly only with the intensification of human impacts in the late highstand, leading to a dominance of infauna and a decline of epifauna at all sites. This profound ecological change reduced species richness, increased the abundance of infaunal suspension feeders, and led to a decline of grazers and deposit feeders. We suggest that modern soft-bottom benthic communities in the northern Adriatic Sea today do not show the high geographic heterogeneity in composition characteristic of benthos prior to anthropogenic influences.

Nutritional strategies in an elite wheelchair marathoner at 3900\u2009m altitude: a case report

BackgroundAltitude training is a common practice among middle-distance and marathon runners. During acclimatization, sympathetic drive may increase resting metabolic rate (RMR), therefore implementation of targeted nutritional interventions based on training demands and environmental conditions becomes paramount. This single case study represents the first nutritional intervention performed under hypobaric hypoxic conditions (3900 m) in Paralympic sport. These results may elucidate the unique nutritional requirements of upper body endurance athletes training at altitude.Case presentationThis case study examined the effects of a nutritional intervention on the body mass of a 36-year-old professional wheelchair athlete (silver medalist at the Paralympic Games and 106 victories in assorted road events) during a five-week altitude training camp, divided into pre-altitude at sea level (BN), acclimatization to altitude (Puno, 3860 m) (BH), specific training (W1,2,3,4) and return to sea level (Post) phases. Energy intake (kcal) and body mass (kg) were recorded daily. Results demonstrated significant decrease in body mass between BN and BH (52.6 ± 0.4 vs 50.7 ± 0.5 kg, P < 0.001) which returned to pre-altitude values, upon returning to sea level at Post (52.1 ± 0.5 kg). A greater daily intake was observed during BH (2899 ± 670 kcal) and W1,2,3 (3037 ± 490; 3116 ± 170; 3101 ± 385 kcal) compared to BN (2397 ± 242 kcal, P < 0.01) and Post (2411 ± 137 kcal, P < 0.01). No differences were reported between W4 (2786 ± 375 kcal), BN and Post. The amount of carbohydrates ingested (g · kg− 1) was greater in W1,2,3, (9.6 ± 2.1; 9.9 ± 1.2; 9.6 ± 1.2) than in BN (7.1 ± 1.2) and Post (6.3 ± 0.8, P < 0.001). Effect sizes (Cohen’s d) for all variables relative to BN (all time points) exceed a large effect (d > 0.80).ConclusionsThese results suggest an elite wheelchair marathoner training at 3860 m required increased nutrient requirements as well as the systematic control needed to re-adapt a nutritional program. Moreover, our findings highlight training and nutritional prescription optimization of elite wheelchair athletes, under challenging environmental conditions.

Climatic and anthropogenic impacts on the Ría de Vigo (NW Iberia) over the last two centuries: A high-resolution dinoflagellate cyst sedimentary record

A high-resolution dinoflagellate cyst record spanning the period of ~1830–2012 CE from Ría de Vigo (Atlantic margin of NW Iberia) is presented. Changes in concentrations and percentages of dinoflagellate cysts and freshwater algal spores reflect climatic and anthropogenic influences on the ria, i.e. coastal inlet formed by the partial submergence of a river valley. Statistical analyses (PCA and clustering) were used to identify the main patterns of change in the cyst assemblages. The cyst record was compared with reconstructed and measured instrumental environmental data (NAO, temperatures, mean sea level, etc.) to support (palaeo)reconstructions. Four main phases were identified: the first phase (~1830–1855 CE) of lower relative sea level (RSL), temperatures and precipitations represents the last stages of the LIA (Little Ice Age); the second phase (~1855–1910 CE) is interpreted as a transition between the colder LIA and the wetter and warmer conditions that prevailed through the 20th century; the third phase (~1910–1975 CE) is characterized by strong river inputs and water stratification in the ria; and the fourth phase (~1975–2012 CE) reflects impacts of anthropogenic warming and pollution. The anthropogenic signal consists of increases in heterotrophic cyst proportions and cysts diversity, as well as of a marked decline of potentially toxic Lingulodinium machaerophorum. Increasing organic matter content, nutrients and industrial wastes have likely caused detrimental impacts on the autotrophic dinoflagellates, by increasing turbidity and toxicity. The B5-cyst record and its comparison with previously published data suggest that increased concentrations of L. machaerophorum in the 20th century were mainly related to river flow variations, that in turn were primarily driven by NAO changes, rather than cultural eutrophication. We also report high abundances of Peridinium ponticum in our record, determining that this species is not exclusive to the Black and Marmara Seas and has much wider natural distribution.

Systematics and phylogeography of the Mediterranean Helichrysum pendulum complex (Compositae) inferred from nuclear and chloroplast DNA and morphometric analyses

AbstractMultiple factors related to complex geomorphological and climatic history, in addition to biological factors such as hybridization, hinder the definition of some Mediterranean plant groups. The existence of controversial taxonomic treatments, the possible hybridization events involved, and its unknown evolutionary history, make the Helichrysum pendulum complex of H. sect. Stoechadina an ideal model to understand general processes of Mediterranean plant systematics and evolution. The mosaic range of the complex, which is distributed over several islands and continental areas in the western‐central Mediterranean Basin, provides an opportunity to investigate how past connections and disconnections between landmasses may have determined the current geographic distribution of genetic variation in this area. The cpDNA region rpl32‐trnL intergenic spacer and the nrDNA region ETS were sequenced for 1–8 individuals from each of the 44 populations sampled, covering all taxa and the whole geographic range of the complex. These individuals were analysed together with a broad sampling of the remaining members of sect. Stoechadina. In addition, detailed multivariate analyses of morphological characters were performed for the whole section and for the H. pendulum complex. Considering together distinctive genetic and morphological traits, our species concept is presented and discussed in a context of integrative taxonomy, and five species are recognized within the complex: H. errerae, H. melitense, H. pendulum, H. saxatile and H. valentinum. The first three species are recognizable by qualitative and quantitative morphological traits, and are genetically distinguishable from the rest as shown by the molecular markers analysed. The two last species are reported here to have a putative ancient hybrid origin and are also genetically distinguishable from the rest but morphologically recognisable only by quantitative characters. Phylogenetic relationships shown by nuclear and chloroplast markers, and an intermediate morphology between the two putative parental taxa, point to H. pendulum and H. italicum as the putative parental taxa for H. saxatile, and H. pendulum and H. stoechas as putative parental taxa for H. valentinum. In a discriminant analysis of the five species, 97.8% of all individuals were classified correctly. The high level of haplotype and ribotype diversity observed in North Africa indicates that this region is either the area of origin of the complex or a secondary contact zone. Our results suggest that the complex colonized several islands and migrated through the Gibraltar and Sicilian Straits during phases of low sea level, favoured by local dispersal events that promoted its gradual range expansion. The occurrence of the complex in the Balearic Islands, which have remained isolated even during low sea level phases, could be explained by stochastic long‐distance dispersal events.

Fossil bog soils (‘dwog horizons’) and their relation to Holocene coastal changes in the Jade Weser region, southern North Sea, Germany

After the deceleration of the postglacial marine transgression, the German North Sea coast was subject to deposition of a complex pattern of subtidal to terrestrial facies. This study aims at reconstructing these facies changes in the ‘Land Wursten’ region (Lower Saxony) by focussing on so-called dwog horizons (incipient soil horizons of the pre-engineered salt marshes). We explore their implications for relative sea-level reconstructions and their indication for early settlement activities. Archive drilling data (1960, provided by the ‘Landesamt fur Bergbau, Energie und Geologie’) were analysed to create five high-resolution stratigraphic cross sections. Three new drilling records were subjected to sedimentological and microfaunal investigations and interpreted to verify and calibrate the archive data. Two dwog horizons were found and 14C-AMS dated. We found basal salt marsh deposits inundated by a high-energy event and covered by tidal flat sediments. The thick tidal flat unit is again overlain by salt marsh deposits indicating the transition from a shallow marine to a terrestrial environment where dwogs were developed and covered by episodic marine incursions. The ages of the dwogs (1128–969 cal BC; cal AD 1426–1467) do not correlate with known layers of adjacent settlement sites and are critically discussed. However, we show that they correlate with phases of stagnant regional relative sea level (RSL) and can be used as RSL indicators. The combined archive and modern data provide valuable information for the RSL reconstruction and palaeoenvironmental changes. However, further research is recommended to accomplish more detailed information about coastal response during the Holocene sea-level changes and implications for settlement dynamics.