Winter Salinity Research Articles

Dynamics of Noctiluca scintillans blooms: A 20-year study in Jangmok Bay, Korea

This 20-year study (2001–2020) conducted in Jangmok Bay, Korea, assessed the intricate relationships between environmental factors and Noctiluca scintillans blooms. Granger causality tests and PCA analysis were used to assess the impact of sea surface temperature (SST), salinity, dissolved oxygen (DO) concentration, wind patterns, rainfall, and chlorophyll-a (Chl-a) concentration on bloom dynamics. The results revealed significant, albeit delayed, influences of these variables on bloom occurrence, with SST exhibiting a notable 2-month lag and salinity a 1-month lag in their impact. Additionally, the analysis highlighted the significant roles of phosphate, ammonium, and silicate, which influenced N. scintillans blooms with lags of 1 to 3 months. The PCA demonstrates how SST and wind speed during spring and summer, along with wind direction and salinity in winter, significantly impact N. scintillans blooms. We noted not only an increase in large-scale N. scintillans blooms but also a cyclical pattern of occurrence every 3 years. These findings underscore the synergistic effects of environmental factors, highlighting the complex interplay between SST, salinity, DO concentration, and weather conditions to influence bloom patterns. This research enhances our understanding of harmful algal blooms (HABs), emphasizing the importance of a comprehensive approach that considers multiple interconnected environmental variables for predicting and managing N. scintillans blooms.

Seasonal and Inter-annual Variability in the East of the Sea of Marmara Water Masses by Temperature and Salinity Time Series

This study mainly aims to examine the relationship between oceanographic properties and climate change in the conjunction of the Istanbul Strait (IS), specifically in the east of the Sea of Marmara (SoM) via evaluating observational temperature and salinity profiles at six stations with monthly atmospheric pressure and air temperature during the period of 1997-2010. The annual cycle of temperature and salinity of the upper and lower layers in the east of SoM have strong seasonal variation: The upper layer temperature rises during summer while decreases in winter. Conversely, the lower layer temperature is higher in winter compared to spring and summer. Additionally, salinity levels in the upper layer are higher in winter and lower in summer, whereas in the lower layer, the pattern is reversed, with lower salinity in winter and higher salinity in summer. In this context, linear trend analyzes are calculated by using monthly time series of temperature and salinity and compared with the trends of atmospheric conditions and the surrounding seas. The average temperature trend in the east of the SoM is increase of 0.067°C/y in the upper layer and increase of 0.028°C/y in the lower layer during this period. The salinity trend is increase of 0.105 psu/y in the upper layer and increase of 0.012 psu/y in the lower layer. The air temperature trend is increase of 0.086°C/y, and the air pressure trend is decrease of 0.034 mbar/y. These values closely align with those observed in the surrounding seas. The air temperature and upper layer temperatures are consistent with each other in terms of both long-term series and trend values.

Effects of Climate Events on Abundance and Distribution of Major Commercial Fishes in the Beibu Gulf, South China Sea

Improving prediction of ecological responses to climate variability requires understanding how local fish population dynamics are impacted by climate events. The present study was conducted in the Beibu Gulf of the northwestern South China Sea where the fisheries are characterized by high ecological and commercial value. We evaluated the relationship between major commercial fish population dynamics (abundance and distribution) and climate periods, using survey data from 2006–2020. The analysis using random forest and GAM models show that climate events are not the best predictors for the variations of fish abundance, because abundance of most fish stocks decreases significantly with the year, and the increasing fishing pressure over time can better explain the overall downward trend in fishery stocks. However, environmental variables that correlate significantly with interannual variation in ONI may impact fish abundance in short terms. Our research suggests that climate events leading to higher surface seawater salinity in winter favors pelagic fishes by improving habitat availability, and higher near-surface chlorophyll-α concentration during La Niña events provides better food condition for overwintering fish. In addition, there is no clear evidence that climatic events have a significant impact on gravity center of fish distribution, whereas climate change has caused most fishes to move to cooler coastal waters in the north.

Contribution of microphytobenthos to the carbon sink in brackish and freshwater tidal flats of the Yangtze Estuary

Estuarine and coastal wetlands have great potential as carbon sinks; however, the carbon fluxes that occur in unvegetated tidal flats remain largely unknown. The CO2 flux of tidal flats is mainly controlled by CO2 uptake by microphytobenthos (MPB) and CO2 emission by sediment respiration. In this study, a brackish tidal flat (B-TF) and a freshwater tidal flat (F-TF) in the Yangtze Estuary were selected to investigate the effects of salinity on MPB growth (indicated by the content of chlorophyll a and pheopigment) and the CO2 flux of tidal flats (during daytime). The results showed that the sediment salinity at the B-TF was 5-19 times higher than that at the F-TF, depending on the season. Diatoms showed a dominant saltwater community at the B-TF and a freshwater community at the F-TF. Over spring, autumn, and winter, CO2 absorbed by the MPB was on average 113 and 230% of the CO2 emitted through sediment respiration of the B-TF and F-TF, respectively, showing a CO2 sink capacity. High salinity in winter inhibited sediment respiration and improved the physiological status of the MPB, making the B-TF a strong CO2 sink, whereas the F-TF was a strong CO2 sink in summer. The freshwater and dissolved (SiO32-) silicon input to the estuary via the river had significant effects on MPB growth and sediment respiration, which were also influenced by light, temperature, and pH. Our study highlights the importance of estuarine salinity fluctuations in the CO2 sinks of estuarine tidal flats, which should be given additional attention when assessing the role of tidal flats in CO2 mitigation.

Development of a prey-predator species distribution model for a large piscivorous fish: A case study for Japanese Spanish mackerel Scomberomorus niphonius and Japanese anchovy Engraulis japonicus

One of the major challenges of species distribution models (SDMs) is incorporating the influence of prey on the predator. An ensemble modeling approach, the prey-predator species distributabion model (PPSDM), uses environmental variables (sea surface temperature, bathymetry, sea surface salinity, and sea surface current) and a biotic variable (predicted prey distribution: Japanese anchovy) to predict a piscivorous fish (Japanese Spanish mackerel) habitat in the China Seas. PPSDM comprised selected preferable single algorithms from nine algorithms, including tree-based models, machine learning models, regression models, an envelope-style method, and a classification model. Compared with that obtained when using habitat without the Japanese anchovy distribution, the regression models, machine learning models and a classification model have significant improvements. However, tree-based models have only slightly improved. The PPSDM results well reflected the ontogenetic migration of Japanese Spanish mackerel. We found that the wintering ground was distributed in regions with temperatures between 11 and 17 °C and salinities between 33.6 and 34.1. The bottom topography was also closely correlated with Japanese Spanish mackerel, and the suitable habitat was at 50–100 m isobaths as topography determined the position of isotherms (11, 17 °C), salinity isolines (33.6, 34.1), and fronts (temperature, salinity) in winter. The relationships among different climatic indices, temperature, and Japanese Spanish mackerel were analyzed. We found that the East Asian monsoon significantly influenced the Japanese Spanish mackerel habitat by affecting temperature variation. In the future, the suitable habitat of Japanese Spanish mackerel is projected to decrease by 21%, 28%, 36%, and 42% under RCP2.6, RCP4.5, RCP6.0, and RCP8.5, respectively. The Japanese Spanish mackerel in the northern Yellow Sea is projected to experience the ‘cul de sac’ effect, which would drive this species toward local extinction. The Japanese Spanish mackerel in the China Seas will probably shift northeastward through the Tsushima Strait, and the Sea of Japan may form the main habitat at the end of the century.

Turbulent Thermal-Wind-Driven Coastal Upwelling: Current Observations and Dynamics

Abstract A remarkably consistent Lagrangian upwelling circulation at monthly and longer time scales is observed in a 17-yr time series of current profiles in 12 m of water on the southern New England inner shelf. The upwelling circulation is strongest in summer, with a current magnitude of ∼1 cm s−1, which flushes the inner shelf in ∼2.5 days. The average winter upwelling circulation is about one-half of the average summer upwelling circulation, but with larger month-to-month variations driven, in part, by cross-shelf wind stresses. The persistent upwelling circulation is not wind-driven; it is driven by a cross-shelf buoyancy force associated with less-dense water near the coast. The cross-shelf density gradient is primarily due to temperature in summer, when strong surface heating warms shallower nearshore water more than deeper offshore water, and to salinity in winter, caused by fresher water near the coast. In the absence of turbulent stresses, the cross-shelf density gradient would be in a geostrophic, thermal-wind balance with the vertical shear in the along-shelf current. However, turbulent stresses over the inner shelf attributable to strong tidal currents and wind stress cause a partial breakdown of the thermal-wind balance that releases the buoyancy force, which drives the observed upwelling circulation. The presence of a cross-shelf density gradient has a profound impact on exchange across this inner shelf. Many inner shelves are characterized by turbulent stresses and cross-shelf density gradients with lighter water near the coast, suggesting turbulent thermal-wind-driven coastal upwelling may be a broadly important cross-shelf exchange mechanism. Significance Statement A remarkably consistent upwelling circulation at monthly time scales is observed in a 17-yr time series of current profiles in shallow water off southern New England. This is not the traditional wind-driven coastal upwelling; instead, it is forced by cross-shelf buoyancy (density) gradients, released by turbulent stresses in shallow water. The persistent upwelling circulation is strongest in summer, when wind and wave forcing are weak, and flushes the inner portion of the continental shelf in a few days. Consequently, this buoyancy-driven coastal upwelling is important for cooling the inner shelf and provides a reliable mechanism for cross-shelf exchange. Many inner shelves are characterized by cross-shelf density gradients and turbulent stresses, suggesting this may be a broadly important cross-shelf exchange mechanism.

Quantification of the Seasonal Intrusion of Water Masses and Their Impact on Nutrients in the Beibu Gulf Using Dual Water Isotopes

AbstractA new data set of seasonal stable water isotopes (δD and δ18O) and temperature‐salinity profiles was applied to improve our understanding of water mass distributions and their impact on the environment of the Beibu Gulf (BG). Our study revealed that the coastal current (CC), West‐Guangdong coastal current (WGCC), and South China Sea water (SCSW) were the three dominant water masses in the BG, and their influence was exhibited in seasonal variations. The CC was the dominant contributor to the BG water during summer (43%) and fall (45%), while it changed to the intrusion of SCSW with higher salinity in winter (57%). The contribution of WGCC to the BG was relatively stable during the three seasons (24%–31%). In addition, the nutrients in the BG were greatly affected by different water mixing occurring in the gulf. The nutrients mainly originated from the CC in summer (52%–68%) and fall (32%–69%), while the dominant source shifted to the WGCC in winter (36%–69%). Moreover, the contribution of SCSW to the nutrients loading (15%–49%) in the BG was relatively high due to its high contribution (57%) to the BG water during winter. These indicated that the BG has a stable input of external nutrients from different water masses to sustain primary production in the BG. Our study uses dual water isotopes to quantify the seasonal intrusion of water masses and their impact on nutrients, providing a new method to study the impact of the distribution of water masses on nutrients in the gulf.

Migration characteristics of soil salinity in saline-sodic cotton field with different reclamation time in non-irrigation season

Cultivation after converting saline and alkaline wasteland to agricultural land is usually accompanied by accelerated soil salinization. There is general agreement that freezing-thawing process plays a crucial role in soil salinization in mostly cold-arid agricultural areas, which leads to the impoverishment of soil productivity. To investigate the migration characteristics of soil salinity in saline-sodic cotton field with different reclamation time in non-irrigation season, we examined the soil bulk, total porosity, and spatial and temporal migration of soil salinity in winter in an oasis agroecosystem of northern Xinjiang, China. Experimental plots include a saline-alkali wasteland as control and cotton fields under four age categories (cultivation start years were 1998, 2006, 2008, and 2012, respectively). The results showed that converting saline-alkali wasteland to cotton land significantly decreased soil bulk density but increased total soil porosity, especially at 0–40 cm. Conversion significantly decreased soil salinity at 0–200 cm soil depths, with a greater decrease in cotton land after relatively longer time of cultivation. After freezing-thawing process, soil bulk density decreased 4.87% on average, and total porosity increased 5.98%. Soil salt dynamics showed that there were two stages in salt accumulation. Firstly, soil salt storage increased at 0–100 cm depth but decreased at 100–200 cm depth during freezing period; Secondly, rapid increase of salt storage appeared at late thawing period. In addition, salt accumulation positively correlated to initial salt content and bulk density, but negatively correlated to total porosity. At springtime, cotton land with short-term cultivation was desalination comparing with pre-freezing, but salt accumulation occurred after long-term cultivation. These results highlighted that long-term cultivation with mulched drip irrigation decreased soil salinity in the 0–200 cm soil profiles, but freezing-thawing process induced soil salinization which poses a potential risk to agricultural sustainability.

Can Winter Road De-Icing Affect Mortality of Organisms in Aquatic Ecosystems? An Experimental Approach

Road maintenance in winter using de-icing agents, which is widely used in Eastern Europe, is the cause of water salinization in neighbouring environments, which might lead to biodiversity loss in aquatic ecosystems. In this study, we investigated NaCl toxicity to test young organisms: Daphnia magna and Poecilla reticulata (standard tests organisms). The salinity of NaCl was measured by electrolytic conductivity (EC). It was statistically demonstrated that the test solutions should be prepared using natural water. For D. magna the NOEC was 7.17 mS/cm and the LC50 9.76 mS/cm. Poecilla reticulata showed resistance to salinity up to a conductivity of 25.2 mS/cm, and no lethal effects were recorded for any individual in the test population. The study showed that winter salinities recorded in inland waters (without emergencies such as sudden influx of pollutants due to industrial accidents) are unlikely to affect fish but may be hazardous to small plankton. However, the high dare of D. magna may result in a reduction of planktivorous fish.

Seasonal dynamics of the carbonate system under complex circulation schemes on a large continental shelf: The northern South China Sea

Based on large-scale surveys conducted during all four seasons from 2009 to 2011, we investigated the carbonate systems on the northern South China Sea (NSCS) shelf featuring much higher variations in both seasonality and spatiality on its inner-shelf (<40 m) as compared to the areas on the mid-outer shelf (>40 m). The most notable forcing on the mid-outer shelf include the intrusion of Kuroshio water leading to high surface salinity and high total alkalinity (TA) in winter, the impact of which is however limited to the northeastern part of the NSCS. The Pearl River Plume (PRP), a prominent feature in summer also has profound impact on the carbonate system on the mid-outer shelf. On the inner-shelf, the carbonate system was much more dynamic, featuring complex modulations by coastal upwelling associated with relatively high dissolved inorganic carbon (DIC) and TA in summer, and the China Coastal Current (CCC) of high DIC in winter, spring and fall. In addition, the influences of coastal plume water from local rivers were identifiable on the inner-shelf in both winter and spring.Such distinction between inner-shelf and mid-outer shelf in the dynamics of DIC, the partial pressure of CO2 (pCO2) and saturation state index of aragonite (Ωarag) is also obvious. On the mid-outer shelf, the salinity normalized DIC (nDIC) fluctuated seasonally between 1974 ± 9 and 2001 ± 9 µmol kg−1. The decline of nDIC from winter to spring and spring to summer mainly results from CO2 outgassing, while the increase in nDIC from summer to fall and from fall to winter is due to entrainment of the carbon-enriched subsurface water. The pCO2 increases from a minimum of 344 ± 9 μatm in winter to a maximum of 387 ± 14 μatm in spring, which is in phase with temperature changes and the fluctuations of nDIC. The Ωarag ranged 3.28–3.68 with the highest value in summer but lowest value in winter, which is consistent with the seasonal cycles of the nDIC. Nearshore on the inner-shelf influenced by the CCC water in winter and the mid-outer shelf influenced by the PRP in summer, the spatial dynamics of sea surface pCO2 and Ωarag are modulated by both temperature and the water mass mixing between CCC, PRP, and shelf waters. Here, the high biological uptake sustained by nutrients in the CCC and PRP drawdown the pCO2 and augmented the Ωarag, while the CO2 sequestration enhanced the sea surface pCO2 but drawdown the Ωarag.

Effect of environmental factors and density-dependence on somatic growth of Eastern Georges Bank haddock (Melanogrammus aeglefinus)

Haddock (Melanogrammus aeglefinus) is an important commercial fish species in the Northwest Atlantic, with the Eastern Georges Bank population a transboundary resources utilized by both Canada and the United States. With the dramatic increase recruitment of this population in the last decade, in particular concentrations of fish on the eastern portion of the Bank, there has been a precipitous decrease in somatic growth, raising concerns for managers and stakeholders. In this study, the effect of environmental factors and density-dependence on somatic growth of eastern Georges Bank haddock was studied using a 2-step Generalized Additive Model (GAM) regression approach. The biotic and abiotic factors examined in the regression analysis included haddock density, sampling location, local sea surface and bottom temperature, salinity and short time series of phytoplankton bloom statistics. The relative importance of each covariate in the best selected model was investigated using the nested GAMs. We found that density-dependence explained most of the variation in haddock growth, where the impact of temperature varied by season. Though of less model importance, annual winter salinity and phytoplankton bloom magnitude (lagged by one year) also contributed the growth model fits. These relationships have the immediate application of contextualizing the observed change in haddock growth, but may also inform various aspects of the stock assessment process.

A high-resolution coupled ice–ocean model of winter circulation on the Bering Sea Shelf. Part II: Polynyas and the shelf salinity distribution

The sea ice component of a regional high-resolution ocean model is improved, with particular attention to accurate representation of the salinity budget for the coupled system. The impact of this improvement is shown first using a one-dimensional test and then the realistic model simulation of the Eastern Bering Sea for the relatively high sea ice extent winter of 2009–10. Improvements to the model ice–ocean salt flux parameterization are demonstrated by comparison of model shelf salinity fields with observations from moorings and CTDs. As polynya regions can strongly influence winter salinity distributions on the Bering Sea shelf, model ice concentrations are compared to satellite estimates for several regions. Areas with a tendency to exhibit higher than average winter open water area include St. Lawrence Island and the southern coast of the Chukotka Peninsula. A new methodology is proposed analyzing the evolution of the salinity distribution with the aid of salt flux tracers that track occurrence of brine and meltwater separately. These demonstrate how cold winters on the Bering Sea shelf are characterized by a freshening and stratifying of the mid- to outer-shelf and an increase of salinity on the inner shelf. Use of an ice-age tracer in the model reveals an anticyclonic circulation of sea ice in mid-winter, as the Bering slope current and Anadyr current recirculate ice that has been transported south–southwestward by the predominant winds. The characteristics of coastal polynya regions are quantitatively compared and a model transect extending from the St. Lawrence polynya to the shelf break is analyzed to help illustrate the temporal and spatial variability of stratification and circulation occurring as the sea ice advances and retreats over the winter season.

Spartina alterniflora invasion alters soil microbial metabolism in coastal wetland of China

The invasion of Spartina alterniflora Loisel, a perennial herb that was introduced into China in 1979, has become an important environmental problem in coastal zones of Jiangsu Province. Although microorganisms play an important role in the structure of ecosystems, the effect of S. alterniflora on soil microbial metabolic diversity remains unexplored. In this work, the variations produced by S. alterniflora in the seasonal dynamics of soil microbial metabolism were examined and compared with the soil microbial metabolism of bare flat. The obtained results indicated that S. alterniflora increases soil total carbon content during the whole year, and decreases soil salinity in spring, summer and winter. The presence of S. alterniflora enhanced the metabolic activity of soil microbes in summer. In autumn, Shannon (H’) and Pielou (J) indices were significantly decreased in S. alterniflora-invaded soil. S. alterniflora altered microbial carbohydrate, amino acid, carboxylic acid, and phenolic acid metabolism in a season-dependent manner, and enhanced microbial amine metabolism during the four seasons. Redundancy analysis demonstrated that soil pH and salinity are driving the metabolic functional diversity in coastal wetlands. Taken together, these results confirmed that the invasion of S. alterniflora is modifying soil physicochemical properties and, subsequently, altering soil microbial metabolic diversity.

Seeking the true time: Exploring otolith chemistry as an age-determination tool.

Fish otoliths' chronometric properties make them useful for age and growth rate estimation in fisheries management. For the Eastern Baltic Sea cod stock (Gadus morhua), unclear seasonal growth zones in otoliths have resulted in unreliable age and growth information. Here, a new age estimation method based on seasonal patterns in trace elemental otolith incorporation was tested for the first time and compared with the traditional method of visually counting growth zones, using otoliths from the Baltic and North seas. Various trace elemental ratios, linked to fish metabolic activity (higher in summer) or external environment (migration to colder, deeper habitats with higher salinity in winter), were tested for age estimation based on assessing their seasonal variations in concentration. Mg:Ca and P:Ca, both proxies for growth and metabolic activity, showed greatest seasonality and therefore have the best potential to be used as chemical clocks. Otolith image readability was significantly lower in the Baltic than in the North Sea. The chemical (novel) method had an overall greater precision and percentage agreement among readers (11.2%, 74.0%) than the visual (traditional) method (23.1%, 51.0%). Visual readers generally selected more highly contrasting zones as annuli whereas the chemical readers identified brighter regions within the first two annuli and darker zones thereafter. Visual estimates produced significantly higher, more variable ages than did the chemical ones. Based on the analyses in our study, we suggest that otolith microchemistry is a promising alternative ageing method for fish populations difficult to age, such as the Eastern Baltic cod.

Variability and decadal trends in the Isfjorden (Svalbard) ocean climate and circulation – An indicator for climate change in the European Arctic

Isfjorden, a broad Arctic fjord in western Spitsbergen, has shown significant changes in hydrography and inflow of Atlantic Water (AW) the last decades that only recently have been observed in the Arctic Ocean north of Svalbard. Variability and trends in this fjord’s climate and circulation are therefore analysed from observational and reanalysis data during 1987 to 2017. Isfjorden experienced a shift in summer ocean structure in 2006, from AW generally in the bottom layer to AW (with increasing thickness) higher up in the water column. This shift, and a concomitant shift to less fast ice in Isfjorden are linked to positive trends in the mean sea surface temperature (SST) and volume weighted mean temperature (VT) in winter (SSTw/VTw: 0.7 ± 0.1/0.9 ± 0.3 °C 10 yr−1) and summer (SSTS/VTS: 0.7 ± 0.1/0.6 ± 0.1 °C 10 yr−1). Hence, the local mean air temperature shows similar trends in winter (1.9 ± 0.4 °C 10 yr−1) and summer (0.7 ± 0.1 °C 10 yr−1). Positive trends in volume weighted mean salinity in winter (0.21 ± 0.06 10 yr−1) and summer (0.07 ± 0.05 10 yr−1) suggest increased AW advection as a main reason for Isfjorden’s climate change. Local mean air temperature correlates significantly with sea ice cover, SST, and VT, revealing the fjord’s impact on the local terrestrial climate.In line with the shift in summer ocean structure, Isfjorden has changed from an Arctic type fjord dominated by Winter Deep and Winter Intermediate thermal and haline convection, to a fjord dominated by deep thermal convection of Atlantic type water (Winter Open). AW indexes for the mouth and Isfjorden proper show that AW influence has been common in winter over the last decade. Alternating occurrence of Arctic and Atlantic type water at the mouth mirrors the geostrophic control imposed by the Spitsbergen Polar Current (carrying Arctic Water) relative to the strength of the Spitsbergen Trough Current (carrying AW). During high AW impact events, Atlantic type water propagates into the fjord according to the cyclonic circulation along isobaths corresponding to the winter convection. Tides play a minor role in the variance in the currents, but are important in the side fjords where exchange with the warmer Isfjorden proper occurs in winter. This study demonstrates that Isfjorden and its ocean climate can be used as an indicator for climate change in the Arctic Ocean. The used methods may constitute a set of helpful tools for future studies also outside the Svalbard Archipelago.

Coastal Wetlands: Ecosystems Affected by Urbanization?

Coastal wetlands are ecosystems that provide multiple benefits to human settlements; nonetheless, they are seriously threatened due to both a lack of planning instruments and human activities associated mainly with urban growth. An understanding of their functioning and status is crucial for their protection and conservation. Two wetlands with different degrees of urbanization, Rocuant-Andalién (highly urbanized) and Tubul-Raqui (with little urbanization), were analyzed using temperature, salinity, dissolved oxygen, pH, turbidity, granulometry, fecal coliform, and macroinvertebrate assemblage variables in summer and winter. In both wetlands marked seasonality in salinity, temperature and sediment texture classification, regulated by oceanic influence and changes in the freshwater budget, was observed. In the Rocuant-Andalién wetland, the increases in pH, dissolved oxygen, gravel percentage, and coliform concentration were statistically significant. Urbanization generated negative impacts on macroinvertebrate assemblage structure that inhabit the wetlands; greater richness and abundance (8.5 times greater) were recorded in the Tubul-Raqui wetland than in the more urbanized wetland. The multivariate statistical analysis reflects the alteration of these complex systems.

δ18O-inferred salinity fromLittorina littorea(L.) gastropods in a Danish shell midden at the Mesolithic–Neolithic transition

Norsminde Fjord has received extensive geoarchaeological investigation, hosting one of the classic Stone Age shell midden sites in Denmark, and one of the best examples of the widespread oyster decline at the Mesolithic–Neolithic transition. Here, intra-shell δ18O (and δ13C) analyses from the common periwinkle Littorina littorea (L.) are used to infer inter-annual environmental changes at the Mesolithic–Neolithic transition (four from each period). This study utilises a modern δ18O L. littorea-salinity training set previously developed for the Limfjord, Denmark to quantify winter salinity. δ18O values range between +1.6% and +4.0% in the late Mesolithic and ‒6.3% to +2.0% in the early Neolithic. Using maximum δ18O values, winter salinity at the known temperature of growth cessation in L. littorea (i.e. +3.7 ± 1°C) for the first annual cycle of each shell ranges between 25.5 and 26.8 psu (standard deviation (SD): 0.56) for the late Mesolithic, with an average salinity of 26.1 psu. Early-Neolithic shells range between 19.4 and 28.2 psu (SD: 4.59) with an average salinity of 23.7 psu. No statistically significant change in salinity occurs between the late Mesolithic and early Neolithic. This result supports recent diatom/mollusc-based inferences that salinity was not the sole cause of the oyster decline, although some evidence is presented here for more variable seasonal salinity conditions in the early Neolithic, which (along sedimentary change and temperature deterioration) might have increased stress on oyster populations in some years. It is recommended here that for robust palaeoenvironmental inferences, where possible, multiple specimens should be used from the same time period in conjunction with multiproxy data.

Distribution and (palaeo)ecological affinities of the main Spiniferites taxa in the mid-high latitudes of the Northern Hemisphere

abstractIn marine sediments of late Cenozoic age, Spiniferites is a very common genus of dinoflagellate cysts (dinocysts). Despite some taxonomical ambiguities due to large range of morphological variations within given species and convergent morphologies between different species, the establishment of an operational taxonomy permitted to develop a standardized modern database of dinocysts for the mid-high latitudes of the Northern Hemisphere. In the database that includes 1490 surface sediment samples, Spiniferites mirabilis-hyperacanthus, Spiniferites ramosus and Spiniferites elongatus were counted in addition to Spiniferites belerius, Spiniferites bentorii, Spiniferites bulloideus, Spiniferites delicatus, Spiniferites lazus and Spiniferites membranaceus. Among these taxa, Spiniferites mirabilis-hyperacanthus, Spiniferites ramosus, and Spiniferites elongatus are easy to identify and are particularly common. Spiniferites bentorii and Spiniferites delicatus also are morphologically distinct and occur in relatively high percentages in many samples. Spiniferites lazus and Spiniferites membranaceus also bear distinctive features, but occur only in a few samples. The identification of other taxa (Spiniferites belerius, Spiniferites bulloideus, notably) may be equivocal and their reported distribution has to be used with caution. The spatial distribution of Spiniferites species, with emphasis on the five most common taxa, is documented here with reference to hydrography (salinity and temperature in winter and summer, sea ice cover), primary productivity and geographical setting (bathymetry, distance to the coastline). The results demonstrate distinct ecological affinities for Spiniferites elongatus, which has an Arctic-subarctic distribution and appears abundant in low productivity environments characterized by winter sea ice and large temperature contrast between winter and summer. Spiniferites mirabilis-hyperacanthus, which occurs in warm temperate water sites, is more abundant in high salinity environments. It shares its environmental domain with Spiniferites bentorii, which appears to have a narrower distribution towards the warm and high salinity end of the Spiniferites mirabilis-hyperacanthus distribution. In contrast, Spiniferites delicatus, which occurs in warm-temperate to tropical environments, shows preference for relatively low salinity and low seasonal contrasts of temperature. Spiniferites ramosus exhibits a particularly wide distribution that overlaps both cold and warm Spiniferites taxa. Its cosmopolitan occurrence and its long-ranging biostratigraphical distribution suggest a high plasticity of the species and/or co-occurrence of several cryptic species. Hence, whereas Spiniferites elongatus and Spiniferites mirabilis-hyperacanthus are useful palaeoecological indicators despite their large morphological variability, Spiniferites ramosus is a taxon with an unconstrained ecological significance.

Submerged aquatic vegetation mapping in coastal Louisiana through development of a spatial likelihood occurrence (SLOO) model

Determining the spatial distribution of coastal foundation species is essential to accurately determine restoration goals, predict the ecological effects of climate change, and develop habitat management strategies. Mapping the distribution of submerged aquatic vegetation (SAV) species assemblages, which provide important habitat resource and ecological services in Louisiana, has been difficult due to the dynamic nature of SAV occurrence and the limited water clarity across much of the coast. Species distribution models (SDMs) link ecological conditions species occurrence across landscapes, and can predict the distribution of species across un-sampled or hard to sample areas and support the development of habitat maps. To predict SAV distribution in coastal Louisiana, a SDM was developed and projected across the landscape to create a spatial likelihood of occurrence (SLOO) model describing the probability of SAV presence in aquatic habitats. SAV presence and absence data were examined from over 500 field observations in relation to physical and hydrologic variables, including exposure, turbidity, water level, and salinity. A binary logistic regression model (p < 0.0001) identified three significant predictors of SAV presence: mean winter salinity, exposure, and turbidity. As each of these variables increased, the probability of SAV presence in the summer growing season decreased. The spatial application of this SDM helps to predict the likelihood of occurrence across the coastal landscape, creating a valuable tool to describe un-sampled SAV habitat and estimate future changes in habitat availability.

Observed winter salinity fields in the surface layer of the Arctic Ocean and statistical approaches to predicting large-scale anomalies and patterns

AbstractSignificant salinity anomalies have been observed in the Arctic Ocean surface layer during the last decade. Our study is based on an extensive gridded dataset of winter salinity in the upper 50 m layer of the Arctic Ocean for the periods 1950–1993 and 2007–2012, obtained from ~20 000 profiles. We investigate the interannual variability of the salinity fields, identify predominant patterns of anomalous behavior and leading modes of variability, and develop a statistical model for the prediction of surface-layer salinity. The statistical model is based on linear regression equations linking the principal components of surface-layer salinity obtained through empirical orthogonal function decomposition with environmental factors, such as atmospheric circulation, river runoff, ice processes and water exchange with neighboring oceans. Using this model, we obtain prognostic fields of the surface-layer salinity for the winter period 2013–2014. The prognostic fields generated by the model show tendencies of surface-layer salinification, which were also observed in previous years. Although the used data are proprietary and have gaps, they provide the most spatiotemporally detailed observational resource for studying multidecadal variations in basin-wide Arctic salinity. Thus, there is community value in the identification, dissemination and modeling of the principal modes of variability in this salinity record.