High Sea Level Research Articles

New model of Si balance in the Late Cretaceous epicontinental European Basin

The Si, which is an important element within the Earth's crust, mostly occurs as a monomeric silicic acid (DSi) in seawater and is utilised by marine organisms to build their skeletons made of opaline silica (BSi). It is also an essential component for many minerals formed in marine environments. The general model of the Si balance, mostly derived from studies of the current oceans, assumes Si input from the weathering of the Earth's crust, its flux in the water column under biological control, and the output via burial in marine sediments. In the Campanian-Maastrichtian (Late Cretaceous), the extremely high sea levels caused the reduction of the continents area and triggered the development of widely spread epicontinental seas. This, combined with extensive volcanic activity, spreading of the ocean floor, and active ocean ridges, elevated the overall Si concentration in the seawater, affected the proportion of Si input from terrestrial weathering and deep-sea fluxes, and influenced the development of the siliceous organisms. The model presented in this study reconstructs the Si balance in the Campanian-Maastrichtian European Basin based on geological records, characterizes the main sources of the DSi input, biological flux, and output via diagenesis. The data presented indicate the significant role of siliceous sponges in the biologically controlled part of the cycle and the DSi-rich inflow from the oceans, which were the principal sources of the (net) inputs of DSi. This data has linked the Si cycle to the bottom zone of the basin, which contrasts with the recent model in which the cycle is concentrated on the subsurface zone of the ocean. The data derived from petrographic studies of chalk and opoka lithofacies broadly show how the Si cycle had affected rock formation and highlighted the role of the mineralogical composition of the seabed mud in the output of DSi from the cycle. The sediment pathway of the DSi burial in the presented Cretaceous model was initiated by the early transformations of biogenic opal-A (BSi) into a more stable form of opal-CT a few centimetres below the seafloor during the early stages of diagenesis, impacting Si recycling. The new model of the Late Cretaceous Si cycle better recognises the role of siliceous sponges and diagenesis in the Si balance in modern environments and provides a paleoecological interpretation of the formation of chalk, opoka, and siliceous nodules during the Late Cretaceous in the European Basin. • In Late Cretaceous the main DSi input was by upwelling currents from deep oceans. • The siliceous sponges play a main role in DSi uptake from water column and its sink. • The Si recycling was limited by its fast burial and diagenetic transformations. • The Si cycle in Late Cretaceous epicontinental seas differs from the modern model.

Understanding of European Cold Extremes, Sudden Stratospheric Warming, and Siberian Snow Accumulation in the Winter of 2017/18

AbstractIt is unclear whether the Eurasian snow plays a role in the tropospheric driving of sudden stratospheric warming (SSW). The major SSW event of February 2018 is analyzed using reanalysis datasets. Characterized by predominant planetary waves of zonal wave 2, the SSW developed into a vortex split via wave–mean flow interaction. In the following two weeks, the downward migration of zonal-mean zonal wind anomalies was accompanied by a significant transition to the negative phase of the North Atlantic Oscillation, leading to extensive cold extremes across Europe. Here, we demonstrate that anomalous Siberian snow accumulation could have played an important role in the 2018 SSW occurrence. In the 2017/18 winter, snow depths over Siberia were much higher than normal. A lead–lag correlation analysis shows that the positive fluctuating snow depth anomalies, leading to intensified “cold domes” over eastern Siberia (i.e., in a region where the climatological upward planetary waves maximize), precede enhanced wave-2 pulses of meridional heat fluxes (100 hPa) by 7–8 days. The snow–SSW linkage over 2003–19 is further investigated, and some common traits among three split events are found. These include a time lag of about one week between the maximum anomalies of snow depth and wave-2 pulses (100 hPa), high sea level pressure favored by anomalous snowpack, and a ridge anchoring over Siberia as precursor of the splits. The role of tropospheric ridges over Alaska and the Urals in the wave-2 enhancement and the role of Arctic sea ice loss in Siberian snow accumulation are also discussed.

Comparison of Carotid Atherosclerosis between Patients at High Altitude and Sea Level: A Chinese Atherosclerosis Risk Evaluation Study

Objectives: To investigate the differences in characteristics of carotid plaques between patients Xining at high altitude and Jinan at sea level using magnetic resonance (MR) imaging. Methods: Subjects were recruited from a cross-sectional, observational, multicenter imaging study of CARE-II study. Forty-nine (mean age 63.3 ± 12.0 years, 33 males) and 51 (mean age 64.5 ± 12.0 years, 34 males) patients were recruited from a site located in a high altitude region and a site located near sea level, respectively. All patients underwent multicontrast MR vessel wall imaging for carotid arteries on 3.0 T MR scanner. The carotid plaques features were compared between 2 patient groups. Results: Compared with patients at sea level, those at high altitude had significantly greater lumen area (58.5 ± 17.8 mm2 versus 50.0 ± 19.6 mm2, P = .008), smaller maximum normalized wall index (48.6% ± 14.2% versus 57.8% ± 16.3%, P = .002), and smaller percentage volume of calcium (0.9% versus 5.6%, P < .001) in the symptomatic carotid artery. After adjustment for clinical risk factors including age, sex, systolic blood pressure, LDL-C, and statin use, these differences in plaque morphology and composition remained statistically significant. After further adjustment for normalized wall index as a measure of plaque burden, percentage volume of calcification was still significantly smaller in patients at high altitude area than that in patients at sea level area (P = .047). Conclusion: Symptomatic subjects from a high altitude area have lower plaque burden and less calcification in the carotid artery compared to those from an area near sea level.

Development of a Dense Cratonic Keel Prior to the Destruction of the North China Craton: Constraints From Sedimentary Records and Numerical Simulation

AbstractIt remains unclear why some cratonic lithospheres like the North China Craton (NCC) have undergone significant thinning and catastrophic destruction. Here we provide evidence for a dense Phanerozoic cratonic keel beneath the NCC that provides a reason for the craton destruction during the late Mesozoic. We observed two long‐lasting (&gt;100 Myr) episodes of surface subsidence that formed the saucer‐shaped basin topography on the NCC from the Paleozoic to early Mesozoic, which was not associated with lithosphere stretching or a high sea level. Based on a detailed geological and geochemical analysis and 2‐D numerical experiments, we show that this subsidence most likely reflects the secular cooling and eclogitization of iron‐rich materials infiltrated into the cratonic mantle since the early Phanerozoic, a process that is the most prominent over the eastern NCC. This result implies that the lithosphere beneath the eastern NCC became gravitationally unstable prior to its Mesozoic destruction as its keel became progressively denser during the Paleozoic. An early Mesozoic partial removal of this dense keel possibly led to widespread surface uplift of the NCC, as indicated by regional basin inversion. We conclude that the long‐term subsidence of a cratonic basin reflects a gradual increase of the lithospheric density and that this type of subsidence should not be considered a characteristic of stable cratons as previously assumed.

Interannual to decadal variability within and across the major Eastern Boundary Upwelling Systems

Climate variability and climate change in Eastern Boundary Upwelling Systems (EBUS) affect global marine ecosystems services. We use passive tracers in a global ocean model hindcast at eddy-permitting resolution to diagnose EBUS low-frequency variability over 1958–2015 period. The results highlight the uniqueness of each EBUS in terms of drivers and climate variability. The wind forcing and the thermocline depth, which are potentially competitive or complementary upwelling drivers under climate change, control EBUS low-frequency variability with different contributions. Moreover, Atlantic and Pacific upwelling systems are independent. In the Pacific, the only coherent variability between California and Humboldt Systems is associated with El Niño Southern Oscillation. The remaining low-frequency variance is partially explained by the North and South Pacific expressions of the Meridional Modes. In the Atlantic, coherent variability between Canary and Benguela Systems is associated with upwelling trends, which are not dynamically linked and represent different processes. In the Canary, a negative upwelling trend is connected to the Atlantic Multi-decadal Oscillation, while in the Benguela, a positive upwelling trend is forced by a global sea level pressure trend, which is consistent with the climate response to anthropogenic forcing. The residual variability is forced by localized offshore high sea level pressure variability.

Twenty‐Year Variations in Satellite‐Derived Chlorophyll‐a and Phytoplankton Size in the Bohai Sea and Yellow Sea

AbstractPhytoplankton cell size is a useful ecological indicator for evaluating the response of phytoplankton community structure to environmental changes. Ocean‐color remote observations and algorithms have allowed us to estimate phytoplankton size classes (PSCs) at decadal scale, helping us to understand their trends under ocean warming. Here a large data set of pigments, derived through high performance liquid chromatography, was collected in the Bohai Sea (BS) and Yellow Sea (YS) between 2014 and 2016. The data set was used to reparametrize the sea surface temperature (SST)‐dependent three‐component model of Brewin et al. (2017) to the region. The model was validated using independent in situ data set and subsequently applied to satellite chlorophyll‐a data from Ocean Colour Climate Change Initiative, spanning from 1997 to 2016, to derive percentages of three PSCs to total chlorophyll‐a. Monthly‐averaged PSCs exhibited spatial‐temporal variations in the study area, linked to topography, temperature, solar radiation, currents, and monsoonal winds. In the surface central south Yellow Sea (SYS), influenced by bottom Yellow Sea Cold Water Mass, tight relationships between PSCs and environmental factors were observed, where high SST, high sea level anomaly, low mixed‐layer depth, and low wind speed resulted in higher proportions of nanoplankton and picoplankton from June to October. Significant interannual anomlies in PSCs were found associated with El Niño events in the central SYS, related to anomalies in SST. The refined model characterized 20‐year variations in chlorophyll‐a concentration and PSCs in complicated optical, hydrodynamic, and biogeochemical environments in the BS and YS.

Monthly Variability in Bering Strait Oceanic Volume and Heat Transports, Links to Atmospheric Circulation and Ocean Temperature, and Implications for Sea Ice Conditions

AbstractThe Bering Strait oceanic heat transport influences seasonal sea ice retreat and advance in the Chukchi Sea. Monitored since 1990, it depends on water temperature and factors controlling the volume transport, assumed to be local winds in the strait and an oceanic pressure difference between the Pacific and Arctic oceans (the “pressure head”). Recent work suggests that variability in the pressure head, especially during summer, relates to the strength of the zonal wind in the East Siberian Sea that raises or drops sea surface height in this area via Ekman transport. We confirm that westward winds in the East Siberian Sea relate to a broader central Arctic pattern of high sea level pressure and note that anticyclonic winds over the central Arctic Ocean also favor low September sea ice extent for the Arctic as a whole by promoting ice convergence and positive temperature anomalies. Month‐to‐month persistence in the volume transport and atmospheric circulation patterns is low, but the period 1980–2017 had a significant summertime (June–August) trend toward higher sea level pressure over the central Arctic Ocean, favoring increased transports. Some recent large heat transports are associated with high water temperatures, consistent with persistence of open water in the Chukchi Sea into winter and early ice retreat in spring. The highest heat transport recorded, October 2016, resulted from high water temperatures and ideal wind conditions yielding a record‐high volume transport. November and December 2005, the only months with southward volume (and thus heat) transports, were associated with southward winds in the strait.

Analysis of the changing patterns of seasonal flooding along the U.S. East Coast

Sea level rise (SLR) is causing acceleration in the frequency and duration of minor tidal flooding (often called “sunny-day” or “nuisance” flooding) along the U.S. East Coast. Those floods have a seasonal pattern that often follows the monthly mean sea level anomaly which peaks in September–October for stations between New York and south Florida. However, there are large differences between coasts: for example, over 75% of the minor floods occur during the fall in Florida, but during the spring and winter in Boston. Various data and forcing, such as tide gauge records, surface temperatures, winds, long-term tidal cycles, and the Gulf Stream flow, were analyzed to examine potential drivers and mechanisms that can contribute to the seasonal pattern of floods. The seasonal water temperature cycle, with maximum temperatures in August, could not by itself explain the seasonal sea level pattern, but two mechanisms that significantly correlate with the seasonal sea level and flooding patterns are the annual and semi-annual tidal cycles (correlation of ~ 0.97) and changes in the Gulf Stream (GS) flow (correlation of − 0.6; the GS shows a maximum decline in September–October during the period of peak flooding). The combination of the seasonal pattern of tropical storms and high coastal sea level can explain the high frequency of fall flooding along the Southeastern U.S. coasts, while winter storms have more influence on the northeastern coasts. In recent decades however, the seasonal pattern seemed to have shifted so that increased flooding is seen on the northeastern coasts during spring and summer, while in the Mid-Atlantic and southeastern coasts, a dramatic increase in flooding is seen almost exclusively during the fall. A long-term change in the mean zonal wind pattern along the coast can contribute to the recent shift in the seasonal flooding pattern. The study can help regional adaptation and resilience planning for flood-prone coastal cities and communities.

Potential fate of wetland soil carbon in a deltaic coastal wetland subjected to high relative sea level rise

The fate of soil carbon in eroding coastal wetlands is of great concern, given the potential for a feedback loop from coastal wetland soil that would dramatically increase atmospheric CO2 concentrations. The biogeochemical transformations and overall fate of this soil carbon upon coastal erosion were investigated through geophysical and spectroscopic analysis of soil and associated dissolved organic matter. Bay water and core sections were collected across transects encompassing both intact and eroded, submerged, sections of a coastal marsh in Barataria Bay, Louisiana. We noted: i) a vertical increase in carbon content, humification of organic matter, and decrease in biotic degradation with depth at all sites; ii) an erosion and ultimate collapse of the top ~ 0–20 cm of the intact marsh’s edge into the bay water due to the undercutting caused by tidal/wave forces; iii) the loss of the stored carbon from the submerged site’s top 10 cm layer; and iv) leaching, dilution, abiotic, and biotic degradation of the marsh carbon due to the exposure to the bay water. This erosion and degradation of wetland soil carbon stores demonstrates the potential impact of rising sea levels on the future fate of coastal wetland carbon and atmospheric CO2 levels.

Between an ocean and a high place: coastal drainage isolation generates endemic cryptic species in the Cape kurper Sandelia capensis (Anabantiformes: Anabantidae), Cape Region, South Africa.

This study investigated the range-wide phylogenetics and biogeography of the Cape kurper Sandelia capensis, a primary freshwater fish endemic to and widespread within the Cape Floristic Region (CFR) of South Africa. Maximum likelihood, Bayesian phylogenetic and haplotype network analyses, based on two mitochondrial and two nuclear genes, revealed the existence of three reciprocally monophyletic, deeply divergent and allopatric clades that probably represent cryptic species. The West Coast Clade is largely confined to the Langvlei, Verlorenvlei, Berg and Diep Rivers, the Klein River Clade is endemic to the Klein River and the South Coast Clade is found everywhere else in the range of S. capensis sensu lato. It was hypothesised that divergences within S. capensis sensu lato probably occurred because of isolation of coastal drainages by persistent drainage divides or vicariance of current tributaries by the drowning of their confluences by high sea levels. The current distribution of lineages could be due to historical range expansion and gene flow via river capture or some other mode of transdivide dispersal or dispersal during periods of low sea level via palaeoriver confluences of currently isolated coastal rivers. Comparison of BEAST2 estimated divergence times with the timing of climatic, geological and geomorphological events supported long-term coastal drainage isolation, punctuated by rare transdivide dispersal events and limited palaeoriver dispersal, as the best explanation of current phylogeographic and divergence patterns in S. capensis. Hydrological barriers that block upstream passage in palaeotributaries could hypothetically explain why S. capensis failed to disperse through certain palaeoriver confluences. There were several sites where biogeographic patterns have likely been confounded by human translocation of S. capensis. Alien fish predators and water extraction may threaten the three cryptic species more severely than previously realised, due to their smaller population sizes and inhabitation of only a portion of the range previously ascribed to S. capensis sensu lato. The preponderance of cryptic diversity and endemism in the CFR suggests that additional undescribed cryptic species of obligate freshwater fishes may be found in short coastal river systems around the world, especially in regions with a history of geological stability and a narrow continental shelf.

Subaqueous effusive and explosive phases of late Deccan volcanism: evidence from Mumbai Islands, India

About 30 m of massive basaltic lava sheets and pillows belonging to the Deccan Traps are exposed at Borivali in the Sanjay Gandhi National Park, Mumbai (India). These lavas are conformably overlain by ~ 100 m of volcaniclastic deposits exposed in the Kanheri Caves. The pillows are plagioclase-clinopyroxene-phyric, very poorly vesicular, tholeiite basalts and commonly develop one to few central large cavities. Pillow rinds are holohyaline with swallow-tailed lanceolate or slender needle-shaped plagioclase and fan-spherulitic or dendritic textures in clinopyroxene that indicate rapid cooling under water. The volcaniclastic succession lying on top of the pillow lavas is chiefly composed of non-vesicular to scoriaceous/pumiceous, basaltic and andesitic clasts. The numerous sediment dykes within the volcaniclastic succession and the conformably underlying pillow lavas imply that the entire sequence was emplaced in a submarine environment. The fluidal texture and quenched margins in some of the volcanic clasts strongly suggest that at least part of the volcanic clasts were produced by underwater explosive eruptions. This study describes subaqueous erupted pillow lavas in context of continental flood basalts and provides a significant analogy to recent submarine-erupted intraplate oceanic basalts. The occurrence of pillow lavas and volcaniclastic deposits well above the present-day high tide line (160 m) indicates either high eustatic sea level during the Danaian age (61.8–62.9 Ma), or post-rifting regional uplift in the western Deccan Traps.

Large mammals of the Palaeo-Agulhas Plain showed resilience to extreme climate change but vulnerability to modern human impacts

Recent evidence indicates that the now submerged continental shelf, the Palaeo-Agulhas Plain (PAP), formed a novel ecosystem during periods of low sea level. This landscape provided nutrient-rich forage and habitats to a variety of large mammals. This is in contrast to the modern faunal assemblage found in the present-day Cape Floristic Region, which is dominated by landscapes with nutrient-poor soils and unpalatable plants. We used archaeological and paleontological records for the region to reconstruct past large mammal communities. We build on this approach by using modern knowledge of ecosystems and ecosystem processes to help us understand how systems functioned in the past. We reconstruct species communities for the PAP of the last 300 ka and investigate potential gaps in the record using Hutchinson's weight ratio theory. We then compare the results to modern occurrences of mammals on the Cape South and West Coasts and the Serengeti (a comparable migratory system) using general linear models. Both sea-level and sampling effort influenced species richness in both the South and West coast regions during the last seven marine isotope stages. In the South coast we observed a decrease in species richness during intermediate sea levels which indicates patterns of use by early humans and habitat availability. Large mammals showed an extraordinary resilience to extreme habitat loss and survived as refugee species during high sea levels and low habitat availability. However the combination of habitat loss and modern human weapons were the cause of severe extinction rates during the last 400 years.

Oceanic environment changes caused the Late Ordovician extinction: evidence from geochemical and Nd isotopic composition in the Yangtze area, South China

AbstractThe Ordovician–Silurian (O–S) transition was a critical interval in geological history. Multiple geochemical methods are used to explore the changes in oceanic environment. The Nd isotopic compositions in the Yangtze Sea are controlled by two sources: the continental erosion and the Panthalassa Ocean. HighεNd(t) values during the Katian, late Hirnantian and Rhuddanian intervals are associated with the high sea level, which resulted in less terrestrial input based on the low Ti/Al and Zr/Al ratios. In contrast, lowεNd(t) values during the early Hirnantian interval are related to the sea-level fall; in this case, the exposure of submarine highs and the growth of Yangtze Oldlands could lead to more continental materials being transported into the Yangtze Sea based on high Ti/Al and Zr/Al ratios. In addition, the negativeεNd(t) excursion can also be attributed to the weak circulation between the Yangtze Sea and Panthalassa Ocean when sea level was low. Furthermore, the sea-level eustacy plays a significant role in the changes in redox water conditions. The redox indices, mainly UEF, Ce/Ce* and Corg/PT, across the O–S transition show a predominance of anoxic ocean over the Yangtze Sea during the Katian, late Hirnantian and Rhuddanian intervals, and an oxygenated episode was briefly introduced during the early Hirnantian period because of the fall in sea level. The Late Ordovician biotic crisis was marked by two-phase extinction events, and the change in sea level and redox chemistry may be the important kill mechanisms.

A Bird's Eye View: Hesperornithiforms as Environmental Indicators in the Late Cretaceous Western Interior Seaway

Seabirds are considered indicators of ecological hotspots in modern ecosystems because their biogeographic distribution is correlated with physical, chemical, and biological oceanographic factors. Pursuit diving seabirds – those that actively pursue prey underwater – are generally more limited in distribution and more closely tied to oceanographic factors, as diving ability is often gained at the expense of flight capabilities. Today, wing propelled pursuit diving seabirds are restricted to colder waters; foot propelled divers have a broader latitudinal distribution, but do not forage far from shore in marine environments. In comparison, Late Cretaceous Northern Hemisphere seas were host to foot propelled pursuit diving seabirds called hesperornithiforms. Their Western Interior Seaway fossil record, in particular, reflects the broad latitudinal distribution of modern foot propelled divers, but with occurrences of offshore foraging more typical of modern wing propelled divers. The presence of hesperornithiforms in such a wide variety of environments (Boreal, Tethyan, coastal, nearshore, and offshore) suggests different ecological and oceanographic conditions affected biogeographic patterns of Late Cretaceous divers. The purpose of this study is to explore Late Cretaceous hesperornithiform paleobiogeography in light of what is known about how biotic and environmental factors affect modern pursuit diving seabirds to better understand WIS paleoecology.The Late Cretaceous was characterized by greenhouse climate, high sea levels, and epicontinental seas that provided marine paleoenvironments with no modern analogs. Two notable ecological differences between the Late Cretaceous and today are the presence of marine reptiles (and absence of marine mammals) as apex predators and the lack of acanthomorph fish diversity. Spatio-temporal overlap among hesperornithiforms, marine reptiles, and large predatory fishes implies different competition and predator-prey relationships among marine carnivores than today. Differences in swimming capabilities between marine reptiles and marine mammals may partially account for the presence of hesperornithiforms in warm, offshore waters. Additionally, environmental factors relating to the unique paleoceanography of the WIS would have also influenced hesperornithiform populations. Ample shoreline, abundant shallow water habitats, and high primary production made epicontinental seas hotspots for pursuit diving seabirds, despite warmer temperatures. Together, ecosystem structure and the unique oceanographic factors characterizing epicontinental seas both contribute to differences in seabird biogeography between the Late Cretaceous and today.

Investigation of variations, causes and component distributions of PM2.5 mass in China using a coupled regional climate-chemistry model

China experiences severe particulate matter (PM) pollution. Although a monitoring network for PM2.5 (diameter < 2.5 μm) has been set up in more than 100 major Chinese cities, insufficient spatial coverage of observations limits the study of the temporal and spatial characteristics, influencing factors, and component of PM2.5. In this study, we conducted a one year air quality simulation using a regional climate–chemistry model and evaluated the simulation's performance based on in situ observations concerning meteorological elements and PM2.5 concentrations. The simulated results showed that, higher PM2.5 concentrations appeared in northern China and the Sichuan Basin, and the maximal value occurred in winter. Furthermore, Vertical PM2.5 concentrations presented a gradual decreasing trend from the surface, whereas in southern coastal cities the profiles were unsteady with a secondary peak in the lower layer. Meteorological conditions were conducive to both pollutant diffusion and removal in summer, whereas stagnant conditions appeared in winter, characterized by high sea level pressure (SLP), the lowest planetary boundary layer height (PBLH), and 2-m temperature (T2). In provincial capital cities, PM2.5 was positively correlated with residential emissions but negatively correlated with precipitation, 10-m wind speed, T2, PBLH, and industrial emissions. Finally, we utilized the simulation results to investigate the component variations of PM2.5. Results indicated that primary PM2.5 components had significantly higher concentrations in northern China where residential heating is the major source of PM2.5 emissions, whereas they had lower concentrations in southern China. Secondary components played a crucial role in PM2.5 mass in eastern China. This study provided a clear perspective of seasonal variations, horizontal and vertical distributions of PM2.5 and its components and influence factors, which could be used in subsequent studies to investigate the formation mechanism and emission sources of PM2.5.

A Mississippian black shale record of redox oscillation in the Craven Basin, UK

Early diagenetic redox oscillation processes have been rarely recognised in the ancient rock record but potentially exert an important control on mineral authigenesis, hydrocarbon prospectivity and supply of metals and/or reduced S as part of associated mineral systems. The upper unit of the Mississippian Bowland Shale Formation is a candidate record of diagenetic redox oscillation processes because it was deposited under a relatively high sediment accumulation rate linked to a large delta system, and under dominantly anoxic and intermittently sulphidic bottom-water conditions. In order to characterise the syngenetic and early diagenetic processes, sedimentological and geochemical data were integrated through the Upper Bowland Shale at three sites in the Craven Basin (Lancashire, UK). Organic matter (OM) comprises a mixture of Type II, II-S, II/III and III OM. ‘Redox zones’ are defined by patterns of Fe-speciation and redox-sensitive trace element enrichment and split into two groups. ‘Sulphidic’ zones (EUX, AN-III, AN-I and AN-IT) represent sediments deposited under conditions of at least intermittently active sulphate-reduction in bottom-waters. ‘Non-sulphidic’ zones (OX-RX, OX-F and OX) represent sediments deposited under non-sulphidic (oxic to ferruginous anoxic) bottom-waters. Operation of a shelf-to-basin ‘reactive Fe’ (FeHR) shuttle, moderated by sea level fluctuation and delta proximity, controlled the position and stability of redoxclines between zones of Fe and sulphate reduction, and methanogenesis. Early diagenetic redoxclines were capable of migration through the shallow sediment column relatively quickly, in response to sea level fluctuation. Preservation of syngenetic and early diagenetic geochemical signals shows redoxclines between Fe and sulphate reduction, and the upper boundary of sulphate-methane transition zone, were positioned within decimetres (i.e., 10 s cm) of seabed. Falling sea level and increasing FeHR supply is recognised as a switch from zones EUX (high sea level), AN-III and ultimately AN-I and AN-IT (low sea level). Zone AN-I defines the operation of ‘redox oscillation’, between zones of Fe and sulphate reduction in shallow porewaters, associated with enhanced degradation of OM and complete dissolution of primary carbonate. Preservation of OM and carbonate, in this system, was a function of changing bottom and pore water redox processes. Redox oscillation operated in a siliciclastic, prodeltaic environment associated with a relatively high sediment accumulation rate and high loadings of labile organic matter and metal oxides. These findings are important for understanding Late Palaeozoic black shales in the context of hydrocarbon and mineral systems.

Late Holocene mangrove development and response to sea level change in the northwestern South China Sea

Mangroves, widely distributed along the coasts of tropical China, are influenced by Asia monsoon, relative sea level change and enhanced human activity. To predict the impacts of future climate change on mangrove ecosystems, it can be understood by reconstructing past mangrove dynamics using proxies preserved in coastal sediments. In this study, we quantitatively partitioned buried organic matter (OM) sources, collected from a vulnerable mangrove swamp in the Qinzhou Bay of northwestern South China Sea, using a ternary end-member mixing model of δ13C and C:N values. Mangrove-derived OM (MOM) contribution was used as a tracer for mangrove development since 2.34 cal ka BP. This information, together with paleoclimate records (i.e., speleothem δ18O values, sea level change, grain size parameters) and human activity, was used to divide mangrove development into three stages during the late Holocene: relative flourish (2.34–1.13 cal ka BP), relative degradation (1.13–0.15 cal ka BP) and further degradation (0.15–0 cal ka BP). Before 1.13 cal ka BP, mangroves flourished with a high MOM contribution ((88.9±10.6)%), corresponding to stable and high sea level under a warm and humid climate. After 1.13 cal ka BP, rapid fall in relative sea level coupled with the strengthening of the Asian winter monsoon, resulted in mangrove degradation and MOM reduction ((62.4±18.9)%). Compared with air temperature and precipitation, the relative sea level fall was the main controlling factor in mangrove development before entering the Anthropocene (the time of the Industrial Revolution). After ∼150 cal a BP, reclamation of mangrove swamps to shrimp ponds is the main factor causing mangrove degradation and MOM reduction.

Sediment routing from shelf to basin floor in the Quaternary Golo System of Eastern Corsica, France, western Mediterranean Sea

Abstract How and when sediment moves from shallow marine to deep-water environments is an important and poorly understood control on basin-scale sediment dispersal patterns, the evolution of continental margins, and hydrocarbon exploration in deep-water basins. The Golo River (Eastern Corsica, France), its delta, canyons, and fans provide a unique opportunity to study sediment routing from source to sink in a relatively compact depositional system. We studied this system using an array of high-frequency seismic data, multi-beam bathymetry, and five cores for lithology and age control. Movement of sediment to deep water was controlled by interactions between the Golo River, the Golo Delta, and shelf-penetrating submarine canyons. Sediment moved to deep water when lobes of the Golo Delta prograded to the heads of these canyons, or when the Golo River itself flowed directly into one of them. Sand accumulated in canyons, deep-water channels, and submarine fans during glacial periods of low sea level, while mud was deposited throughout the slope, in the relatively short reach of leveed-confined channels, and in the mud-rich fringes around the sandy fans. During interglacial periods of high sea level, the basin was blanketed by mud-rich deposits up to 10 m thick interbedded with distinctive carbonate-rich sediments. Deposition rates in the basin ranged from 0.07 m/ka to 0.59 m/ka over the last 450 ka. Mud deposition rates remained relatively constant at ∼0.16 m/ka during all time periods, while sand deposition only happened during glacial periods of low sea level with an average rate of 0.24 m/ka. In addition to sea-level controls on sediment delivery, avulsions of the Golo River and its deltaic lobes preferentially routed sediment down either the North or South Golo canyons. Thus, while the larger, sequence-scale architecture of the basin is controlled by allogenic sea level forcing, millennial-scale autogenic processes operating on the shelf and in deep water shaped the distribution of sand and mud, and the internal geometry of the deltas and submarine fans that they fed. While some aspects of the Golo system are characteristic of steep, tectonically active margins, others such as the nature of connections between rivers and shelf-penetrating submarine canyons are observed in most margins with active submarine fans regardless of their tectonic setting.

The ecosystem service of property protection and exposure to environmental stressors in the Gulf of Mexico

Environmental stressors such as sea-level rise, erosion, and increased storm frequency and intensity are exposing coastal properties to greater amounts of damage. Coastal habitats like beaches, dunes, seagrasses, and wetlands can help reduce exposure and property damage. Using InVEST's Coastal Vulnerability Model, an exposure index value was calculated for every 250 m2 segment along the coastline in Escambia and Santa Rosa counties in Florida, USA. Nineteen sea level-by-habitat management scenarios were evaluated for a suite of shoreline segments across multiple exposures that can be used to inform local decision making as part of larger strategies for coastal management. Overall, a rise in sea level and degradation of coastal habitats could decrease the number of lower exposed shoreline segments and increase the number of higher exposed shoreline segments. These results were used to identify changes in the amount of potential residential property damage among different scenarios. Under high sea levels, additional protection to coastal habitats could reduce the amount of residential property damage resulting from one tropical cyclone event by $50.4 million (2018 US dollars (USD)) (by the year 2050) and by $71.8 million (2018 USD) (by the year 2100) in Escambia and Santa Rosa counties. This research demonstrates the effects that habitat type/abundance and sea-level rise could have on vulnerable coastlines. The results of the modeled scenarios can be incorporated into several recent community resiliency planning initiatives in the region to develop more robust management plans and preparations for a changing environment.

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.