Surface Water Salinity Research Articles

Black Sea paleosalinity evolution since the last deglaciation reconstructed from alkenone-inferred Isochrysidales diversity

The Black Sea underwent dramatic changes in salinity from the last glacial maximum to Holocene as it evolved from a large inland lake to become a part of the global ocean due to post-glacial sea level rise. However, the detailed history of the re-connection of the Black Sea to the Mediterranean and the resulting Black Sea salinity variations have been heavily debated. We take advantage of our recent study on alkenones from phylogenetically classified haptophyte groups and their association with variable salinity levels in modern environments to reconstruct detailed salinity changes in the Black Sea over the past 16,000 years. We report the first discovery and documentation of alkenones from Group I Isochrysidales in relation to past salinity changes in the Unit III sediment. Our data indicate that the Black Sea surface salinity gradually increased from near fresh at ∼16 ka (∼1-2 psu) to oligohaline (∼ 5-6 psu) at ∼ 9.4 ka, the time of initial marine inflow, suggesting a negative regional hydrological balance. Although the IMI (initial marine inflow) occurred at 9.4 ka, the relatively low surface water salinity levels persisted to the beginning of sapropel formation at 7.6 ka, suggesting a strongly positive regional hydrological balance. Alkenone profiles also indicate a period of significantly reduced salinity between 3.5 and 1.6 ka, differing from the previous proposed peak salinity at 2.7 ka based on alkenone hydrogen isotope values. We demonstrate that the mismatch originates from the predominance of previously unidentified Group II Isochrysidales over E. huxleyi during this time interval, and when species-specific hydrogen isotopic fractionation of alkenones is taken into consideration, the isotope-inferred salinity between 3.5 and 1.6 ka is consistent with our proposal. Our new assessment of the Black Sea salinity evolution since the last glacial shows broad agreement with other regional records and provides a new basis for evaluating the impact of regional hydrological changes on Neolithic human migrations to Europe.

Dinoflagellate cyst distribution in surface sediments of Ambon Bay (eastern Indonesia): Environmental conditions and harmful blooms

The present study aimed to document dinocyst ecological preferences in Ambon Bay, Eastern Indonesia, and to investigate if the bay sediments serve as a seedbank for toxic bloom events. To this end, dinocyst and geochemical analyses of surface sediment samples were performed, along with physicochemical water column parameters. Twentythree dinocyst species were identified, and high dinocyst concentrations (up to ~12,000 cysts g−1 dry sediment) were found in the inner bay. Environmental factors such as surface water temperature and salinity generally played an important role in dinocyst distribution. The concentration of Polysphaeridium zoharyi cysts showed a strong positive correlation with phosphorus. A statistically significant correlation was also found with the concentration of other autotrophic dinocysts in the sediments, and an inverse correlation was observed with the sediment C/N ratio. Cysts may serve as seedbanks for Pyrodinium bahamense blooms in the area.

Water Mass Variability and Levantine Intermediate Water Formation in the Eastern Mediterranean Between 2015 and 2017

AbstractThe physical characteristics of water masses in the Cilician Basin were analyzed based on recent, comprehensive in‐situ data. Nine seasonal cruises from June 2015 to November 2017 were carried out in an area located in the north‐eastern Levantine Basin between the coasts of Turkey and Cyprus. In this little studied area, the structure of the water column, its seasonal variability, and water formation events are investigated. The extensive data set reveals that in summer Modified Atlantic Water (MAW) is observed at about 50 m depth. Saltier and warmer Levantine Intermediate Water (LIW) lies below the MAW between ∼100 and 250 m. During winter, the water column becomes mixed due to surface cooling and vertical convection, and displays uniform properties from the surface to about 200–300 m depths. The yearly cycle of a vertically uniform water column during winter and the appearance of LIW in the following period suggests that LIW is being formed in this region, which is confirmed through heat and buoyancy flux calculations. It is the first time LIW formation is reported in this area of the north‐eastern Levantine Basin and adds to the areas of LIW formation outside Rhodes Gyre. In the 2.5 years of the study, LIW salinity increased by 0.11 psu in 2017, while surface water salinity increased by 0.5 psu over the same period. The presence of meso‐scale eddies in the study area is observed throughout the year. The eddies are short‐lived, having a time span of a few months, during which they either change location or disappear.

Evolution of Salinity and Water Table Level of the Phreatic Coastal Aquifer of the Emilia Romagna Region (Italy)

The coastal aquifers of the Mediterranean region are highly susceptible to seawater intrusion due to a combination of challenges such as land subsidence, high aquifer permeability, urbanization, drainage, and an unsustainable use of water during the dry summer months. The present study is focused on a statistical analysis of groundwater data to evaluate the spatial changes of water level and electrical conductivity in the coastal phreatic aquifer of the Emilia-Romagna (Northeast Italy) for the period from 2009 to 2018. Data from 35 wells distributed across the entire regional coastal area are used to establish a temporal trend, as well as correlations between salinity, water table level, and rainfall. Water table and salinity distribution maps for the entire study area are discussed regarding surface geology and water management. Most of the wells are in the beach wedge sand unit, which allows for easy connectivity between groundwater and surface water. Surface water and groundwater salinization are enhanced along the surface water bodies connected to the sea. The lowest water table level occurs in the western and northern parts of the study area, because of the semiconfined behavior of the aquifer. Only in the northernmost, close to the Po River, and in the southernmost parts of the study area does the groundwater remain fresh for the whole period considered due to river aquifer recharge. In the rest of the region, the thickness of freshwater lenses, where present, is less than 4.5 m. The existence of a water table level below sea level and high saline water at the bottom of the aquifer in most of the study area suggest that the aquifer is in unstable hydrodynamic conditions and groundwater quality is not fit for human consumption or for irrigation. This study is the first to provide a regional overview of the state of groundwater level and salinization within the coastal aquifer of the Emilia-Romagna Region; it also suggests that, overall, the salinization trend has slightly decreased from 2009 to 2018.

Impacts of Topsoil and Surface Water Salinity on Agriculture: A Study at Paikgachha, Khulna

Studying the structure, intensity and track of tropical cyclone is very important in effective tropical cyclone warning. In this study, an attempt has been made to simulate the Super Cyclone Amphan to reproduce the structure, intensity and track of the storm that occurred over the Bay of Bengal and made landfall over the coastal zone of Sundarban between Western Bangladesh and Eastern West Bengal of India on 20 May 2020. The Weather Research and Forecasting (WRF) Model was run 120 hours from 0000 UTC of 16 May to 0000 UTC of 21 May 2021 with 9 km horizontal resolution to simulate the selected storm. The model simulated intensity and track of the storm were compared with that of best track data of India Meteorological Department (IMD). The results obtained from the WRF model indicated that the intensity of the selected cyclone in terms of Mean Sea Level Pressure (MSLP) and Maximum Sustained Wind speed (MSW) were 905 hPa and 243 kph whereas the observed MSLP and MSW were close to 920 hPa and 241 kph respectively. It was also indicated that the model predicted the track of the cyclone reasonably well and it was quite close to the best track data throughout its path till landfall with very small deviation and the cyclone made landfall at 7-8 hours before the actual landfall with 167.4 km position error.
 The Dhaka University Journal of Earth and Environmental Sciences, Vol. 8(2), 2019, P 25-32

Salt-Laden Winter Runoff and Freshwater Mussels; Assessing the Effect on Early Life Stages in the Laboratory and Wild Mussel Populations in Receiving Waters

The widespread use of road salt for winter road maintenance has led to an increase in the salinity of surface water in many seasonally cold areas. Freshwater mussels have a heightened sensitivity to salt, which is a concern, because many Canadian mussel species at risk have ranges limited to southern Ontario, Canada’s most road-dense region. This study examined the effect of winter road runoff on freshwater mussels. The impact of two bridges that span mussel habitat in the Thames River watershed (Ontario, Canada), the second most species-rich watershed for mussels in Canada, were studied. During a winter melt event, bridge runoff, as well as creek surface water surrounding the bridges were collected. Chloride concentrations in samples from bridge deck and tile drains varied (99–8250 mg/L). In general, survival of Lampsilis fasciola glochidia exposed to those samples reflected chloride levels (e.g. 84% at 99 mg/L; 0% at 8250 mg/L), although potassium (60 mg/L) may have at least contributed to toxicity in one sample. Serial dilution exposures with the two most toxic runoff samples revealed 48-h glochidia EC50s of 44% (McGregor Creek Tile Drain) and 26% (Baptiste Creek Deck Drain). During the melt event, the chloride concentrations in creek surface waters downstream of the bridges ranged from 69 to 179 mg Cl−/L; effects on glochidia (viability 77–91%) exposed to those waters was minimal. There were no live mussels surrounding one bridge (Baptiste Creek), likely due to poor habitat. At the other targeted bridge (McGregor Creek), fewer mussels were found close (< 100 m up- or downstream) to the bridge than further (> 200 m) away. However, other contributing factors, including agriculture, were present at both study areas.

Salty Port: Environmental Conflicts Resulting from the Açu Port, Rio de Janeiro state, Brazil

Abstract The aim of this article is to analyze the dynamics that marked the coexistence between different actors in the environmental conflict caused by the salinization of surface and underground waters during the implantation of the Açu Port, in the municipality of São João da Barra, which is located in the Northern Fluminense region. The work seeks to demonstrate the links between this particular conflict and the profile of the major projects established to expand Brazil’s insertion in the world economy as an exporter of primary and semi-benefited products. From a methodological point of view, the work used a qualitative methodology based on a bibliographic and documentary survey related to the environmental impacts and conflicts caused by the Açu Port. The research results demonstrate the importance of having a transparent, participatory decision-making process guided by the sustainability of state actions in the planning and implementation of Large Investment Projects.

A comparative study to assess surface water's anthropic and natural vulnerability using the DKPR and RUSLE approaches. Case of the watershed of the Joumouaa dam (Coastal basin of Ghiss, North East Morocco)

The salinization of surface water in a coastal context leads to a qualitative degradation of this resource by various sources of anthropogenic and natural pollution. In this context, we present the results of a comparative study using "DKPR" and "RUSLE" models to evaluate the degree of surface water vulnerability against pollution, especially in the sub-watershed of the Joumouaa dam, a hydraulic infrastructure providing drinking water for the Targuist city. The "DKPR" model adopted as a qualitative approach involves four parameters: Accessibility of the aquatic environment (D), Water functioning of the soil and subsoil (K), Physiography watershed (P), Rainfall erosivity (R). The final result is a resource vulnerability map obtained by combining index maps of these four parameters using remote sensing and GIS. The "RUSLE" model applied as a quantitative approach integrates five factors in a multiplying function, namely: rainfall erosivity (R), soil erodibility (K), slope length and steepness (LS), cover-management (C), and soil conservation practices (P) in a remote sensing and GIS environment. The analysis of the final vulnerability maps of the approaches mentioned above will be helpful support for water resource managers and decision-makers better identify areas of high risk and their protection.

Spatial and temporal variability of temperature, salinity and chlorophyll-a in the Magdalena River mouth, Caribbean Sea

Variations in the physico-chemical characteristics of estuaries, such as surface water salinity and temperature, lead to the establishment of gradients that are closely related with the distribution of nutrients and suspended sediment. This affects light penetration, which in turn influences Chlorophyll-a (Chl-a) concentration and primary productivity. We used MODIS imagery to identify spatio-temporal patterns of sea surface salinity, temperature, and Chl-a concentrations from 2003 to 2017, to explore relationships between these variables and oceanographic factors, such as streamflows, winds and currents in the mouth of Colombia's Magdalena River, which discharges to the Caribbean Sea. Sea surface salinity (SSS) in the study zone varied in time and space from estuarine to marine. Mean SSS was 10.8 ± 3.4 at Bocas de Ceniza, and 28.4 ± 0.4 in the Caribbean Sea, with the horizontal salinity gradient providing evidence for the existence of a salinity plume. Mean monthly sea surface temperatures (SST) averaged across all years were 27.6 ± 1.5 °C at Bocas de Ceniza, and 27.6 ± 1.3 °C in the Caribbean Sea. A significant, increasing trend in temperature was observed throughout the years of the study period. Average Chl-a values were 3.3 ± 1.4 mg m−3 at Bocas de Ceniza, and 1.5 ± 1.2 mg m−3 in the Caribbean Sea and the calculated average Trophic State Index (TSI) for Bocas de Ceniza indicated that the estuary trophic state varied between oligo-mesotrophic (30 < TSI≤40) and mesotrophic (40 < TSI≤50). The highest concentrations of Chl-a were found in intermediate salinities in the estuarine zone. Outside the saline plume, there is a considerable decrease in Chl-a concentrations (<0.5 mg m−3). Winds played the most important role in influencing spatio-temporal distribution of chemical and physical variables in the study zone. Our results emphasize the importance of physical processes on biological dynamics in the Magdalena River mouth.

High‐resolution distribution pattern of surface water nitrous oxide along a cruise track from the Okhotsk Sea to the western Arctic Ocean

AbstractNitrous oxide in the surface water was measured using an automatic underway system, along with measurements of surface water pCO2, dissolved oxygen, salinity, temperature, and sea ice coverage, along a cruise track through the Bering Sea and Chukchi Sea to the Canadian Basin during the 7th Chinese National Arctic Research Expedition. The results show that, overall, the regions along the cruise track are net sources of N2O to the atmosphere. Several N2O oversaturation maxima were observed along the cruise track, with an absolute maximum of approximately 60%. According to the hydrographic setting and the distribution patterns of pCO2, dissolved oxygen, and sea ice coverage in the study area, it was concluded that the N2O oversaturation maxima may result from hydrographic processes, such as mixing of different water masses, upwelling or convection, and possible production beneath the sea ice. Additionally, the lowest value of approximately 90% may result from dilution related to the melting of sea ice. An evaluation of the air–sea flux along the cruise track shows that the continental shelf and upwelling region are N2O sources, whereas the study area in the open Arctic Ocean does not show obvious source or sink characteristics.

First report of Anopheles (Cellia) multicolor during a study of tolerance to salinity of Anopheles arabiensis larvae in Nouakchott, Mauritania

BackgroundAnopheles multicolor is known to be present in the arid areas of Africa north of the Sahara Desert, especially in oases. To date, its presence in Mauritania has not been reported. Here, we present the first record of its presence in Nouakchott, the capital of Mauritania. The larvae of An. multicolor, together with those of An. arabiensis, the major malaria vector in the city, were found thriving in highly saline surface water collections.MethodsEntomological surveys were carried out during 2016–2017 in Nouakchott. Mosquito larval habitats were investigated through larval surveys while indoor resting culicid fauna were collected using hand-held aspirator. Physicochemical parameters of the larval habitats were measured on-site, at the time mosquitoes were collected. Larvae and pupae were reared to adults in the insectaries. Morphological and polymerase chain reaction (PCR)-based methods were used to identify newly emerged adults. Batches of fourth-instar larvae were used to assess salinity tolerance by exposing them to increasing concentrations of NaCl, and mortality was monitored throughout development.ResultsMorphological and molecular results confirmed that the specimens were An. multicolor and An. arabiensis. Sequences of 24 An. multicolor adult mosquitoes showed 100% nucleotide identity with the published sequences of An. multicolor from Iran. The physicochemical analysis of the water from the two larval habitats revealed highly saline conditions, with NaCl content ranging between 16.8 and 28.9 g/l (i.e. between c.50–80% seawater). Anopheles multicolor and An. arabiensis fourth-instar larvae survival rates at 17.5 g/l NaCl were 86.5% and 75%, respectively. Anopheles arabiensis larvae showed variable levels of salt tolerance according to the larval habitat. Adult An. multicolor specimens were collected resting indoor at low frequency (0.7%) compared to the other culicid mosquitoes.ConclusionsTo the best of our knowledge, this paper is the first report of An. multicolor in Mauritania, extending the known distributional range of the species to the south, as well as to the west. Highly salt-tolerant populations of An. arabiensis and An. multicolor were observed. Because salt-water collections are widespread in Nouakchott, the relevance of these findings for the dynamics and epidemiology of malaria transmission needs to be assessed.

Exploration and utilisation of groundwater resources in extreme arid regions of the Tibetan Plateau: A case study on Ali area, China

Identifying a good site for groundwater exploitation in arid areas with scarce hydrogeological data is a challenging task. In this study, west of the Tibet Autonomous Region located at the peak of the world ridge that belongs to the extreme water-scarce poverty zone is used as the study area. This study is the first to determine the formation and controlling factors affecting the groundwater resources in Ali area via comprehensive geophysical and geochemical prospecting. The meteorological and hydrological characteristics of the study area are analysed, and the source and characteristics of water vapour in the study area are determined. Although the Indian peninsula and the Arabian Sea water vapour transmission paths exist, only small amounts of water vapour enter the area because of the distance limit and alpine barrier, which is the main reason for the drought in the study area. An overall conclusion of the hydrogeological condition and groundwater resources in Ali area is drawn on the basis of geophysical surveying, hydrogeological drilling, and water chemical analysis. The distribution of water resources in the Quaternary Aquifer, which is controlled by water vapour transport, aquifer-forming deposits, river distribution, and temperature, is not well-proportioned. The aquifer potentiality reduces from the southern to the northern direction in sequence. Thus, the great mass of midlands and the northern region belong to drought zones. Groundwater salinity, which is affected by drought, is higher than surface water salinity and obviously increases in constituent concentrations. The findings promote the understanding and utilisation of water resources in the study area.

Integrated Pliocene-Pleistocene magnetostratigraphy and tephrostratigraphy of deep-sea sediments at IODP Site U1424 (Yamato Basin, Japan Sea)

Sediments from the semi-enclosed Japan Sea are sensitive to paleoclimatic perturbations and they offer great opportunities for many regional and global paleoceanographic and paleoclimatic studies. These studies often require a robust chronology. However, due to rare preservation of calcareous microfossils and drastic changes in surface water salinity during glacial lowstands, the construction of a traditional oxygen isotope stratigraphy for Japan Sea sediments is often difficult. Here, we use sediments recovered at Integrated Ocean Drilling Program (IODP) Expedition 346 Site U1424 to build an integrated Pliocene-Pleistocene reference magnetostratigraphy and tephrostratigraphy for sedimentary sequences from the region. Rock magnetic experiments indicate that magnetic remanence of Site U1424 sediments are carried primarily by (titano)magnetite with small contributions from high coercivity minerals (e.g., hematite) and possibly iron sulphides (pyrrhotite and/or greigite). Dark-colored sediments appear to contain less (titano)magnetite probably due to reductive diagenesis under euxinic conditions. Natural remanent magnetization (NRM) of u-channel samples covering a continuous ~ 167.6 m sediment sequence at Site U1424 was repeatedly measured at 1 cm intervals before and after stepwise demagnetization. Despite lower NRM intensity in dark-colored sediments, NRM directional data from both dark- and light-colored sediments are considered suitable for the construction of magnetostratigraphy. Site U1424 sediments clearly recorded the majority of the polarity chrons and subchrons within the last ~ 4.89 Myr, with the Cobb Mountain subchron, the end of Kaena subchron, and the onset of Nunivak subchron less well preserved. Sixteen tephra layers from the site were sampled for chemical composition analyses and the results were correlated to reference tephrostratigraphy of the region. Ages of the identified tephras are consistent with and can be well integrated with the magnetostratigraphy. The resulting age model suggests that sedimentation rates at Site U1424 range between ~ 1.7 and 7.6 cm/kyr with an average of ~ 3.3 cm/kyr. The acquired magnetostratigraphy and tephrostratigraphy at Site U1424 provide a reference chronology that can be correlated with and transferred to other sediment sequences in the region to study paleoceanographic and paleoclimatic changes of the region as well as their links to other regional and global changes.Graphical abstract

Mid to late-Holocene sea-surface temperature variability off north-eastern Newfoundland and its linkage to the North Atlantic Oscillation

In recent decades the surface water temperature and salinity in the Labrador Sea have been influenced by atmospheric circulation patterns, such as the North Atlantic Oscillation (NAO), as well as a trend to increasingly warm atmospheric temperatures in recent years. These changes are concerning, given the important role that temperature and salinity have on deep convection in the Labrador Sea. Yet, due to the shortness of available records, the long-term patterns of climate variability in the region are not clear. Here, a diatom-based reconstruction of summer sea-surface temperature (SST) developed from Trinity Bay, Newfoundland, provides insight into variations of SST since 7.2 cal ka BP in the southwestern Labrador Sea. The results show that the Holocene Thermal Maximum (HTM) lasted until c. 5.2 cal ka BP, which was followed by a gradual cooling trend overprinted by centennial temperature fluctuations of 1–2°C. Long-term cooling was likely the result of declining Northern Hemisphere orbital summer insolation, potentially amplified by long-term changes in surface and bottom water salinity, which led to a gradual reduction in the stratification of the water column. Centennial fluctuations in temperature vary in-phase with reconstructed variations in the NAO, supporting a consistent relationship between atmospheric circulation and SST over centennial-millennial timescales. Other factors influencing the SST variability may have been solar forcing during the mid-Holocene and variations in the strength of the subpolar gyre during the late-Holocene. The most prolonged cool period at 5.2–4.1 cal ka BP coincides with sharply reduced salinity in the Labrador Sea and a weakening of deep ventilation in the northeast Atlantic, highlighting a period with altered ocean surface conditions and circulation across the northern North Atlantic.

A Warm, Stratified, and Restricted Labrador Sea Across the Middle Eocene and Its Climatic Optimum.

Several studies indicate that North Atlantic Deep Water (NADW) formation might have initiated during the globally warm Eocene (56–34 Ma). However, constraints on Eocene surface ocean conditions in source regions presently conducive to deep water formation are sparse. Here we test whether ocean conditions of the middle Eocene Labrador Sea might have allowed for deep water formation by applying (organic) geochemical and palynological techniques, on sediments from Ocean Drilling Program (ODP) Site 647. We reconstruct a long‐term sea surface temperature (SST) drop from ~30°C to ~27°C between 41.5 to 38.5 Ma, based on TEX86. Superimposed on this trend, we record ~2°C warming in SST associated with the Middle Eocene Climatic Optimum (MECO; ~40 Ma), which is the northernmost MECO record as yet, and another, likely regional, warming phase at ~41.1 Ma, associated with low‐latitude planktic foraminifera and dinoflagellate cyst incursions. Dinoflagellate cyst assemblages together with planktonic foraminiferal stable oxygen isotope ratios overall indicate low surface water salinities and strong stratification. Benthic foraminifer stable carbon and oxygen isotope ratios differ from global deep ocean values by 1–2‰ and 2–4‰, respectively, indicating geographic basin isolation. Our multiproxy reconstructions depict a consistent picture of relatively warm and fresh but also highly variable surface ocean conditions in the middle Eocene Labrador Sea. These conditions were unlikely conducive to deep water formation. This implies either NADW did not yet form during the middle Eocene or it formed in a different source region and subsequently bypassed the southern Labrador Sea.

Climate impacts on the landings of Indian oil sardine over the south‐eastern Arabian Sea

AbstractThe landings of Indian oil sardine (Sardinella longiceps, Clupeidae) along the south‐eastern Arabian Sea are about 43.8% of total Indian oil sardine production. The annual landings of this species exhibit large‐scale variability with prolonged years of surplus or deficit landings without identified reason. Evaluating Indian oil sardine landings along the Kerala coast during 1961–2017 in relation to environmental variations, we have elucidated a putative link between variability in landings versus environmental parameters and climate indices. The variables examined in this study, such as salinity and temperature along with physical indices such as upwelling and mixed layer depth (MLD) of the ocean help to propose a mechanism to temporal variability in the landings of Indian oil sardine. Colder temperature and timely intense upwelling lead to nutrient enrichment in the surface water, which promotes the growth of phytoplankton (chl‐a) and thereby food availability to Indian oil sardine are found during years with surplus catch. Less saline surface waters and shoaling of MLD at these times could lead to the aggregation of fish at particular depths and thereby a good catches. The reverse mechanism, such as more surface saline water, warm temperature, downwelling or weak upwelling, and less nutrient enrichment, leads to deficit landings. Further, it was noticed that the Pacific decadal oscillation and Atlantic multidecadal oscillation have a more pronounced impact on Indian oil sardine landings over the coast of south‐eastern Arabian Sea than previously reported ENSO associated impacts. All these point towards climate change implications for the Indian oil sardine fishery.

Features of the dynamics of the surface water layer temperature and salinity in the Bosporus Strait and on its Black Sea Shelf

Features of the dynamics of the surface water layer temperature and salinity in the Bosporus Strait and on its Black Sea Shelf

River plume and sediment transport seasonality in a non-tidal semi-enclosed brackish water estuary of the Baltic Sea

Our study aims to determine the development of sediment-rich freshwater plumes in a non-tidal brackish water-dominated (salinity < 6) estuary in the Halikonlahti Bay, Northern Baltic Sea. We studied three seasons with different wind conditions and discharges: two open water periods, one with low (~0.2 m³/s) and one with high (31–40 m³/s) river discharges, and one ice-covered period with high (28–40 m³/s) river discharge. To conduct our analyses, we measured suspended sediment concentration (SSC), turbidity, salinity and temperature of bottom and surface waters together with current measurements along the estuary. Water samples were collected with LIMNOS water sampler and current measurements were done with acoustic Doppler current profiler. The results indicate that river plume develops under high river discharge, while during low river discharge the plume is very limited in extent. In open water conditions, SSC increased approximately ten-fold in the estuary head, with increased discharge from 0.2 m³/s to 31 m³/s. Buoyant plumes developed in both open channel and ice-cover conditions during high river discharge periods even in a weakly stratified environment, where the salinity difference was less than five over the entire water column. Unlike salinity, small temperature differences between river and seawater did not contribute the development of buoyant sediment plume. Weak stratification together with reduced wind-induced mixing was found to limit the sediment mixing between fresh surface and saline (~5) bottom layers in both ice-covered and open water conditions. For example, even 2–5 times higher SSCs were found at surface waters compared to bottom waters over a shallow (~4 m) water column. Wind and river discharge induced estuarine currents were found. Inverse estuary circulation developed under the conditions of low river discharge and inshore directed wind. High river discharge together with salinity stratification formed a positive estuarine circulation pattern, with surface outflow and bottom inflow.

Global patterns for the spatial distribution of floating microfibers: Arctic Ocean as a potential accumulation zone

Despite their representativeness, most studies to date have underestimated the amount of microfibers (MFs) in the marine environment. Therefore, further research is still necessary to identify key processes governing MF distribution. Here, the interaction among surface water temperature, salinity, currents and winds explained the patterns of MF accumulation. The estimated density of floating MFs is ∼5900 ± 6800 items m−3 in the global ocean; and three patterns of accumulation were predicted by the proposed model: (i) intermediate densities in ocean gyres, Seas of Japan and of Okhotsk, Mediterranean and around the Antarctic Ocean; (ii) high densities in the Arctic Ocean; and (iii) point zones of highest densities inside the Arctic Seas. Coastal areas and upwelling systems have low accumulation potential. At the same time, zones of divergences between westerlies and trade winds, located above the tropical oceanic gyres, are predicted to accumulate MFs. In addition, it is likely that the warm branch of the thermohaline circulation has an important role in the transport of MFs towards the Arctic Ocean, emphasizing that surface water masses are important predictors. This study highlights that the Arctic Ocean is a dead end for floating MFs.

Major and trace element characterization of Oceanic Anoxic Event 1d (OAE 1d): Insight from the Umbria-Marche Basin, central Italy

The Pialli Level in the Umbria-Marche Basin (central Italy) correlates with the lowermost part of the positive carbon isotopic excursion characterizing the late Albian–early Cenomanian Oceanic Anoxic Event 1d (OAE 1d). High-resolution litho-, bio- and chemostratigraphic data from the Monte Petrano and Le Brecce sections allow for a bed-by-bed comparison of the two successions, and discriminate local from basin-scale signals. We present new X-ray fluorescence, ICP-MS and TOC data for both the limestones and the Pialli Level shales integrated with available carbonate carbon isotopes and nannofossil temperature and nutrient indices. Data indicate a homogenous background sedimentation dominated by pelagic carbonates, biogenic silica with little contribution by clays. The limited variation in lithogenic elements points to an essentially homogeneous detrital source area with limited fluvial terrigenous input. Higher Mn concentrations coupled with low enrichments in redox-sensitive elements, such as U, Fe, S, Re, Mo, Ag, suggest that the Pialli Level shales represent temporary suboxia without reaching anoxia. Furthermore, P, authigenic Ba, Cd and Ni enrichments, together with nannofossil nutrient index indicate generally low primary productivity conditions along the entire succession, with only minor increases for some of the black-to-dark grey shales of the Pialli Level. The nannofossil temperature index highlights a warm climate during the OAE 1d, with the warmest conditions experienced during the deposition of the Pialli Level shales. During the late Albian, the warm and humid climate was interrupted by brief episodes of relatively warmer and less saline surface waters ensuring slower rates of bottom water renewal and producing temporary suboxic conditions. Such paleoceanographic dynamics would be the continuation of episodic warmer and humid pulses characterizing the late Albian interval in the Umbria-Marche Basin. As such, the Pialli Level can be considered the result of a last episode closing a cycle before the establishment of a steadier climate during the early Cenomanian.