Surface Water Productivity Research Articles

Chlorophyll-a Variability during Upwelling Events in the South-Eastern Baltic Sea and in the Curonian Lagoon from Satellite Observations

Based on the analysis of multispectral satellite data, this work demonstrates the influence of coastal upwelling on the variability of chlorophyll-a (Chl-a) concentration in the south-eastern Baltic (SEB) Sea and in the Curonian Lagoon. The analysis of sea surface temperature (SST) data acquired by the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard Aqua/Terra satellites, together with Chl-a maps from Medium Resolution Imaging Spectrometer (MERIS) onboard Envisat, shows a significant decrease of up to 40–50% in Chl-a concentration in the upwelling zone. This results from the offshore Ekman transport of more productive surface waters, which are replaced by cold and less-productive waters from deeper layers. Due to an active interaction between the Baltic Sea and the Curonian Lagoon which are connected through the Klaipeda Strait, coastal upwelling in the SEB also influences the hydrobiological conditions of the adjacent lagoon. During upwelling inflows, SST drops by approximately 2–8 °C, while Chl-a concentration becomes 2–4 times lower than in pre-upwelling conditions. The joint analysis of remotely sensed Chl-a and SST data reveals that the upwelling-driven reduction in Chl-a concentration leads to the temporary improvement of water quality in terms of Chl-a in the coastal zone and in the hyper-eutrophic Curonian Lagoon. This study demonstrates the benefits of multi-spectral satellite data for upscaling coastal processes and monitoring the environmental status of the Baltic Sea and its largest estuarine lagoon.

Methane paradox in tropical lakes? Sedimentary fluxes rather than pelagic production in oxic conditions sustain methanotrophy and emissions to the atmosphere

Abstract. Despite growing evidence that methane (CH4) formation could also occur in well-oxygenated surface fresh waters, its significance at the ecosystem scale is uncertain. Empirical models based on data gathered at high latitude predict that the contribution of oxic CH4 increases with lake size and should represent the majority of CH4 emissions in large lakes. However, such predictive models could not directly apply to tropical lakes, which differ from their temperate counterparts in some fundamental characteristics, such as year-round elevated water temperature. We conducted stable-isotope tracer experiments, which revealed that oxic CH4 production is closely related to phytoplankton metabolism and is a common feature in five contrasting African lakes. Nevertheless, methanotrophic activity in surface waters and CH4 emissions to the atmosphere were predominantly fuelled by CH4 generated in sediments and physically transported to the surface. Indeed, CH4 bubble dissolution flux and diffusive benthic CH4 flux were several orders of magnitude higher than CH4 production in surface waters. Microbial CH4 consumption dramatically decreased with increasing sunlight intensity, suggesting that the freshwater “CH4 paradox” might be also partly explained by photo-inhibition of CH4 oxidizers in the illuminated zone. Sunlight appeared as an overlooked but important factor determining the CH4 dynamics in surface waters, directly affecting its production by photoautotrophs and consumption by methanotrophs.

Multi-criteria decision making and fairness evaluation of water ecological carrying capacity for inter-regional green development.

Determining water ecological carrying capacity (WECC) is of great significance to ensure inter-regional green development. This study presents a comprehensive evaluation framework for WECC assessment in the Yangtze River Economic Zone (YREZ), China. Effects of water resources, socio-economic, and ecological elements on WECC can be evaluated based on multi-criteria decision analysis. Gini and unbalance coefficients are used for measuring the regional fairness between WECC and socio-economic development. Surface water production pressure (SWPP) and groundwater pollution risk (GPR) are further regarded as indicators for expressing water resources constraint on shale gas extraction in the YREZ. Results disclose that the average WECC level decreases from 0.439 in 2000 to 0.4007 in 2016, which is the opposite of the changing trend in the Beijing-Tianjin-Hebei Region. A high WECC level appears in Zhejiang (0.5126) with a good state, but that of Guizhou (0.3983), Anhui (0.3968), Hunan (0.3914), and Chongqing (0.3651) are at the alert state. The obstacle factors of WECC in the eastern YREZ mostly originate from socio-economic and water resource subsystems, while that in the middle and western YREZ mainly arise from water resources and ecological subsystems. Fairness analysis shows a well-matching characteristic between the overall WECC and socio-economic performances due to a majority of their Gini coefficients lower than 0.4, while a poor matching characteristic exists in terms of provincial differences owing to their varied unbalance coefficients, especially in Guizhou, Jiangsu, and Shanghai. Moreover, Chongqing with most of shale gas reserves is characterized by slight SWPP (1.0202) and GPR (0.0188), but the prospect of shale gas development in Sichuan is not optimistic due to its high SWPP (1.0846) and GPR (0.0647). Recycling of flowback and product waters can significantly lighten regional water resources pressure. This presented framework can be applied into many other Chinese cities (e.g., Beijing-Tianjin-Hebei Region) with slight modifications according to their actual situations for supporting water resource managers and government with decision making.

Paleoceanographic changes in the Southern Ocean off Elephant Island since the last glacial period: Links between surface water productivity, nutrient utilization, bottom water currents, and ice-rafted debris

To understand past changes in ocean–cryosphere interactions in the Southern Ocean off the Antarctic Peninsula, multi-proxy analyses of three sediment cores located off Elephant Island were used to reconstruct changes in paleoproductivity, nutrient utilization, bottom current intensity, and iceberg calving since the last glacial period. The glacial period was characterized by low surface water productivity with high nutrient utilization, indicating surface water stratification. During the deglaciation, surface water productivity increased with decreasing nutrient utilization, implying that the increase is associated with increased nutrient supply from the subsurface water by enhancing Antarctic Circumpolar Current (ACC) influence as fronts migrate southward with warming. Abundant occurrence of grains >1 mm during the deglacial period indicates rapid ice sheet retreat with large-scale melting and calving. During the glacial period, however, coarse silt–fine sand-sized fraction represented ice-rafted debris (IRD). The different IRD grain size characteristics are thought to be related to the IRD source material characteristics. Regardless of IRD input, the running downcore correlation (5 to 9-point) between sortable silt mean grain size and percentage showed that sediments are well sorted by bottom current. However, the cross plot of them showed different temporal relationships. Sediments were sorted by the ACC and southwestward flowing bottom current. Along with southward migration of fronts and the ACC, southwestward flowing bottom current influence diminished, whereas the ACC influence increased particularly from 7 ka. Our results indicate that the sedimentary processes in the Scotia Sea largely depend on the regional interactions between the ocean and the cryosphere.

Variations in coccolithophore productivity off South Africa over the last 500 kyr

Abstract We present a 500-kyr productivity reconstruction of the southwest Indian Ocean (MD96–2077; Natal Valley) and the eastern South Atlantic (Sites 1266; Walvis Ridge) from coccolithophore assemblages and coccolith geochemistry. The study sites are situated in two different hydrographic regimes: one located in the upper boundary of the Agulhas Current (AC) and the other in the open ocean branch of the Benguela Current (BC). We aim to decipher how marine phytoplankton communities responded to variations in water-column characteristics over multiple glacial/interglacial cycles. Gephyrocapsa species (G. caribbeanica, G. ericsonii) dominates the assemblage in the Walvis Ridge whereas Florisphaera profunda is more prominent and co-dominates with Gephyrocapsa species (G. oceanica, G. ericsonii) in the Natal Valley. Higher abundance of F. profunda in MD96–2077 than at Site 1266 suggests that Natal Valley has a deeper nutricline/thermocline and lower productivity than in the Walvis Ridge over the last ~500 kyrs. Asynchrony in the productivity changes is suggested to be related to different driving mechanisms between the eastern and the western sides off South Africa. The equatorward STF migration during glacial periods has potentially reduced the intensity of the AC and promoted surface water productivity in the Natal Valley. By contrast, productivity in the Walvis Ridge shows opposite patterns, showing enhanced productivity during interglacial periods, which we attribute to a localized mixing at the confluence zone between the eastward flowing South Atlantic Current and the Benguela Oceanic Current and/or an increased Agulhas leakage in combination with stronger westerlies, thereby promoting upwelling of nutrients to the surface.

Impact of unconventional natural gas development on regional water resources and market supply in China from the perspective of game analysis

This study presents a detailed framework for evaluating water resource constraint and game-based supply strategies of unconventional and conventional natural gases in China. Surface-water production pressure and groundwater-pollution risk level are used to measure the extent of water resource constraint on shale gas development. Cournot and Stackelberg game models are applied to illustrate the oligopoly mechanism between unconventional and conventional natural gas manufacturing. A subsidy multiplier model is then proposed to identify the impact of government subsidy on different game strategies. Results indicate that high amounts of estimated ultimate recovery and recycling wastewater would significantly reduce water resources consumption during shale gas development. An increased subsidy coefficient would increase the amount of unconventional natural gas but decrease the amount of conventional natural gas. However, the majority of subsidy multiplier values would be less than 1, implying an inconspicuous effect of the subsidy. Moreover, the equilibrium production of unconventional natural gas in the Cournot and Stackelberg game models would increase with the increased substitution factor m1 but decrease with the increased substitution factor m2. Conversely, the high amount of equilibrium production of conventional natural gas would increase the substitution factor m2 but reduce the substitution factor m1 within these two models.

Patterns of planktonic foraminiferal extinctions and eclipses during Oceanic Anoxic Event 2 at Eastbourne (SE England) and other mid-low latitude locations

The latest Cenomanian Oceanic Anoxic Event (OAE) 2 represents one of the most extreme perturbations of the global carbon cycle. Planktonic foraminiferal events, variations in the taxonomic composition of assemblages (e.g., appearances, extinctions, temporary crisis of certain taxa) and their correlation with changes in the physico-chemical properties of surface waters are essential to reconstructing the consequences of OAE 2 on this group of calcareous microfossils.We present the results of a high-resolution biostratigraphic and taxonomic study of planktonic foraminifera performed at Eastbourne (SE England), representing the most expanded, complete and well-calibrated OAE 2 record in Europe.In this stratigraphic section, we identify a sequence of step-wise extinctions (i.e., Thalmanninella and Rotalipora species, and “Globigerinelloides” bentonensis) that are followed by an eclipse (temporary disappearance) of planispiral taxa and of hedbergellids with radially elongated chambers. These events are consistently found in approximately coeval stratigraphic intervals across low to mid-latitudes, suggesting that they were controlled by wide-scale environmental perturbations. Moreover, this study suggests that the extinction of rotaliporids might have been influenced by climate changes (i.e., warming for Thalmanninella and cooling during the Plenus Cold Event for Rotalipora) at the onset of OAE 2, whereas the eclipse of planispiral taxa and hedbergellids with radially elongated chambers during the second half of OAE 2 was likely related to enhanced productivity and mixing of surface waters potentially associated to warming after the PCE for planispirals.Finally, we identify two short-range species (Muricohedbergella kyphoma and Praeglobotruncana plenusiensis n. sp.) that co-occur with boreal macrofossils at Eastbourne and might represent the first evidence for a planktonic foraminiferal PCE fauna. The long ranging species Praeglobotrucana gungardensis n. sp. is described as new.

Redox conditions and climate control on organic matter accumulation and depletion during the Toarcian in the Qiangtang Basin, eastern Tethys

The Toarcian (Early Jurassic) sediments are regarded as the most significant hydrocarbon source rocks in the Qiangtang Basin, Qinghai–Tibet Plateau. In this study, geochemical and mineralogical data are reported from the Middle to Late Toarcian organic-lean sediments in the Qiangtang Basin, eastern Tethys. Combined with previous studies, the factors that control organic matter (OM) accumulation during the Toarcian are investigated. The Early Toarcian organic-rich sediments were deposited in stratified water column with oxygen-deficient bottom water, which was conducive to OM preservation. A warm and humid paleoclimatic condition favored the growth of organisms, which in turn could enhance the surficial biotic productivity. During the Middle to Late Toarcian, oxic waterbody was widely distributed in the Qiangtang Basin. This condition was unbeneficial to the preservation of OM. During this interval, a cold–arid climate had an adverse effect on organism growth, which in turn would reduce the initial productivity of surface water. The consistently low Ti/Al and Si/Al ratios revealed restricted but rather homogeneous clastic influx conditions during the Toarcian. This may suggest that the dilution of terrigenous material input had a little influence on OM accumulation. In addition, the differential enrichment of OM between shales and marls should attribute to carbonate dilution. These studies emphasize that redox conditions and paleoclimatic conditions were likely responsible for OM accumulation during the Toarcian.

A quantitative analysis of calcareous nannofossils across a late oligocene paleolatitudinal transect of the North Atlantic Ocean

Abstract Samples from six ocean drilling sites were analyzed quantitatively across a paleolatitude transect of the North Atlantic Ocean to determine the paleolatitudinal distribution of calcareous nannofossils in the late Oligocene and the effects of that distribution on biostratigraphic resolution. Quantitative methodology utilized a Detrended Correspondence Analysis (DCA), Nannofossil Temperature Index (NTI), and Shannon Index (H) to examine the paleoenvironmental gradients which exerted the most control over the distribution of species and their abundances. The DCA produced two axes which explain 82% of the data matrix. The DCA1 explaining 57% of the variance significantly correlates with the NTI suggesting that thermal controls were the most important factor in the paleoceanographic distribution of nannofossils. The DCA2 explained 25% of the variance and significantly correlates with the percent abundance of the taxon Reticulofenestra minuta as well as the Shannon Index, suggesting that surface water productivity was an important secondary control. The characteristics of the nannofossil assemblage distributions indicate the existence of a well-developed latitudinal diversity gradient in the late Oligocene of the North Atlantic. Based on the loss of biostratigraphic index taxa in higher paleolatitudes the primary limiter on biostratigraphic resolution for the late Oligocene North Atlantic is sea surface temperature, particularly cold-water regimes.

Discussion on the characteristics and controlling factors of differential enrichment of shale gas in the Wufeng-Longmaxi formations in south China

The annual output of shale gas from the Wufeng-Longmaxi formations in South China reached 15.4 × 109 m3 in 2019, which makes Sichuan basin the second-largest shale gas producing area in the world. Based on the data of more than 1000 shale samples of the Wufeng-Longmaxi formations taken from typical drilling and outcrop profiles in the Weiyuan, Changning, Fuling, and Wuxi areas in South China, the characteristics of differential enrichment of shale gas are analyzed and the main controlling factors are discussed. The study shows that the shale gas from the Wufeng-Longmaxi formations in South China has some differential enrichment characteristics in both vertical and lateral orientations. In vertical orientation, sweet-spot intervals of shale gas developed concentratedly sweet-spot. The key parameters (e.g., thickness, gas content, TOC content) in the sweet-spot intervals vary greatly in regional aspect, among which they are better in the Changning and Fuling areas. The gas contents and TOC contents of the Wufeng-Longmaxi shale in different areas have good positive correlations, indicating that the abundance of organic matters (TOC content) is a key factor that affects the degree of shale gas enrichment (gas content). The high primary productivity of marine surface water during the shale deposition period of the Wufeng-Longmaxi formations is an important prerequisite for the generation of large amounts of organic matters. However, in relatively stable tectonic zones with weak faults development, euxinic bottom water condition is the key factor controlling the formation of sweet-spot intervals of shale gas vertically and the distribution of sweet-spot area laterally, that is the key factor for the differential enrichment of Wufeng-Longmaxi shale gas.

Depth-Differentiation and Seasonality of Planktonic Microbial Assemblages in the Monterey Bay Upwelling System.

Coastal upwelling regions are hotspots of biological productivity, supporting diverse communities of microbial life and metabolisms. Monterey Bay (MB), a coastal ocean embayment in central California, experiences seasonal upwelling of cold, nutrient-rich waters that sustain episodes of high phytoplankton production in surface waters. While productivity in surface waters is intimately linked to metabolisms of diverse communities of Archaea and Bacteria, a comprehensive understanding of the microbial community in MB is missing thus far, particularly in relation to the distinct hydrographic seasons characteristic of the MB system. Here we present the results of a 2-year microbial time-series survey in MB, investigating community composition and structure across spatiotemporal gradients. In deciphering these patterns, we used unique sequence variants (SVs) of the 16S rRNA gene (V4–V5 region), complemented with metagenomes and metatranscriptomes representing multiple depth profiles. We found clear depth-differentiation and recurring seasonal abundance patterns within planktonic communities, particularly when analyzed at finer taxonomic levels. Compositional changes were more pronounced in the upper 0–40 m of the water column, whereas deeper depths were characterized by temporally stable populations. In accordance with the dynamic nutrient profiles, the system appears to change from a Bacteroidetes- and Rhodobacterales-dominated upwelling period to an oceanic season dominated by oligotrophic groups such as SAR11 and picocyanobacteria. The cascade of environmental changes brought about by upwelling and relaxation events thus impacts microbial community structure in the bay, with important implications for the temporal variability of nutrient and energy fluxes within the MB ecosystem. Our observations emphasize the need for continued monitoring of planktonic microbial communities in order to predict and manage the behavior of this sensitive marine sanctuary ecosystem, over projected intensification of upwelling in the region.

Late pleistocene paleoceanographic changes in the Ross Sea – Glacial-interglacial variations in paleoproductivity, nutrient utilization, and deep-water formation

The outer Ross Sea continental shelf has experienced large variations in ice sheet extent over the Pleistocene that are theorized to be largely driven by changes in the westward-flowing Antarctic Slope Current (ASC) at the continental shelf break. This current regulates southward incursions of warm modified Circumpolar Water, and it is thought to have triggered past marine ice sheet retreat. Additionally, expansions of grounded ice sheets on the continental shelf have fundamentally altered the Ross Sea water mass formation processes, influencing surface water salinity, sea ice cover, nutrient utilization, deep-water ventilation, and primary productivity. Here, we report the geochemical, physical properties, grain size, bulk δ15N, and diatom records during the late Pleistocene from two sediment cores from the Iselin Bank on the outermost continental shelf in the Ross Sea. These core sites were not overridden by grounded ice sheets during the late Pleistocene glacial-interglacial cycles, allowing for a continuous archive of glacimarine environments that were influenced by the ASC. Interglacial periods are typically characterized by high surface water productivity and nutrient utilization, with Chaetoceros resting spores indicating nutrient limitation under open ocean conditions, and glacial periods are typically characterized by low surface water productivity and nutrient utilization, with sea ice diatoms and planktonic foraminifers indicating light limitation under extensive sea ice/ice margin proximal conditions. A grain size analysis indicates coarse-skewed distributions and winnowing in the Iselin Bank region during cold periods. The winnowing may be related to enhanced ASC flow instead of density driven shelf water outflow.

Community composition and photosynthetic physiology of phytoplankton in the western subarctic Pacific near the Kuril Islands with special reference to iron availability.

The western subarctic Pacific (WSP) is known as one of the most productive regions among the world's oceans in spring. However, its oceanic waters are also known as a High Nutrient, Low Chlorophyll (HNLC) region during summer due to low iron (Fe) availability in seawater. Indeed, recent studies have demonstrated that the distribution of Fe in the WSP is complex and heterogeneous. This study thus investigated the effects of Fe availability on the community composition and photophysiology of surface phytoplankton from coastal to offshore waters in the WSP in the summer of 2014. Although relatively high concentrations (>2 mg m-3) of chlorophyll (chl) a were found in the Sea of Okhotsk and some coastal waters, low chl a concentrations (<1 mg m-3) were commonly observed in offshore waters. Based on dissolved Fe and macronutrient concentrations, we deduced that low Fe availability limited phytoplankton growth in offshore waters, whereas low silicate and/or nitrate levels limited growth in the shelf areas. Scanning electron microscopy also revealed that the centric diatom Chaetoceros exclusively dominated the diatom assemblages in the shelf and coexisted with pennate diatoms in offshore waters, respectively. Primary productivity in surface waters was negatively correlated with the bottom of the euphotic layer or the light saturation index of the photosynthesis-irradiance curve, which indicates that the phytoplankton assemblages were well acclimated to in situ light conditions regardless of the water masses.

Evaluating Bank-Filtration Occurrence in the Province of Quebec (Canada) with a GIS Approach

Due to the abundance of surface water in the province of Quebec, Canada, it is suspected that many groundwater wells are pumping a mixture of groundwater and surface water via induced bank filtration (IBF). The regulatory framework in Quebec provides comprehensive guidelines for the development and monitoring of surface water and groundwater drinking water production systems. However, the regulations do not specifically address hybrid groundwater-surface water production systems such as IBF sites. More knowledge on the use of IBF in the province is needed to adjust the regulations with respect to the particularities of these systems. In order to provide a first evaluation of municipal wells potentially using IBF and the corresponding population served by these wells, a Geographic Information Science framework (GISc) was used to implement an IBF spatial database and calculate the distance from each well to the nearest surface water body. GISc is based on open source GIS programs and openly available data, to facilitate the reproducibility of the work. From this provincial scale approach, we show that nearly one million people are supplied by groundwater from municipal wells located &lt;500 m from a surface water body, and half a million have a significant probability to be supplied by IBF wells. A more focused look at the watershed scale distribution of wells allows us to improve our interpretations by considering the aquifer type and other regional factors. This approach reveals strong spatial variability in the distribution of wells in proximity to surface water. Of the three selected regions, one has a high potential for IBF (Laurentides), one requires additional information do draw precise conclusions (Nicolet), and the third region (Vaudreuil-Soulanges) is unlikely to have widespread use of IBF. With this study, we demonstrate that extensive use of IBF is likely and that there is a need for improved understanding and management of these sites in order to properly protect the drinking water supply.

The effect of sediment grain properties and porewater flow on microbial abundance and respiration in permeable sediments

Sandy sediments cover 50–60% of the continental shelves and are highly efficient bioreactors in which organic carbon is remineralized and inorganic nitrogen is reduced to N2. As such they seem to play an important role, buffering the open ocean from anthropogenic nitrogen inputs and likely remineralizing the vast amounts of organic matter formed in the highly productive surface waters. To date however, little is known about the interrelation between porewater transport, grain properties and microbial colonization and the consequences for remineralization rates in sandy sediments. To constrain the effect of theses factors on remineralization in silicate sands, we incubated North Sea sediments in flow-through reactors after separating into five different grain size fractions. Bulk sediment and sediment grain properties were measured along with microbial colonization and cell abundances, oxygen consumption and denitrification rates. Volumetric oxygen consumption ranged from 14 to 77 µmol O2 l−1 h−1 while nitrogen-loss via denitrification was between 3.7 and 8.4 µmol N l−1 h−1. Oxygen consumption and denitrification rates were linearly correlated to the microbial cell abundances, which ranged from 2.9 to 5.4·108 cells cm−3. We found, that cell abundance and consumption rates in sandy sediments are influenced (i) by the surface area available for microbial colonization and (ii) by the exposure of these surfaces to the solute-supplying porewater flow. While protective structures such as cracks and depressions promote microbial colonization, the oxygen demand is only met by good ventilation of these structures, which is supported by a high sphericity of the grains. Based on our results, spherical sand grains with small depressions, i.e. golf ball like structures, provide the optimal supporting mineral structure for microorganisms on continental shelves.

Paleo-environmental variation and its control on organic matter enrichment of black shales from shallow shelf to slope regions on the Upper Yangtze Platform during Cambrian Stage 3

To understand the evolution of oceanic redox conditions and organic matter (OM) accumulation in the shelf and slope regions of the Upper Yangtze Platform during Cambrian Stage 3, high-resolution geochemical data were obtained from two wells respectively representing shelf and slope environments. Based on redox proxies, widespread anoxic/euxinic waters with intermittent sulfidic water columns were formed from shallow shelf to deep water slope and basinal regions during Stage 2 and early Stage 3; then, widespread anoxic waters were reduced and oxic waters expanded during the middle Stage 3, after which fluctuating suboxic and oxic (occasionally anoxic) environments became predominant during late Stage 3. The presence of hyalophane and positive Eu anomalies suggest strong Ba-rich hydrothermal activities in the shelf and deep basin regions during early and middle Stage 3. The Ba-rich hydrothermal fluids and upwelling events enhanced the primary productivity in surface waters and subsequently promoted organic matter enrichment. During Stage 2 and early Stage 3, the high primary productivity driven by coastal upwelling and hydrothermal activity were the main factors controlling OM enrichment; during middle Stage 3, the local anoxic water condition became responsible for OM enrichment when oxic waters began to gradually expand; during late Stage 3, both primary productivity and redox conditions became the main control factors for OM enrichment. According to the analysis of primary productivity, redox conditions, hydrothermal activity and upwelling events, an evolution model is proposed to account for the paleo-environmental variation and the OM enrichment from shallow shelf to slope regions during Cambrian Stage 3.

DEVELOPMENT AND APPLICATION OF A SEASONAL FURROW IRRIGATION MODEL (SFIM)

AbstractIf furrow irrigation is properly designed and implemented, this method would be one of the best surface irrigation systems. To achieve high irrigation efficiency and uniformity in surface irrigation, the use of simulation models is inevitable. The purpose of this study was to develop a seasonal furrow irrigation model to simulate the whole irrigation season (every irrigation event). The model called ‘SFIM’ was developed using the FORTRAN programming language. SFIM consists of four sub‐models to simulate surface flow, subsurface flow, crop yield, water productivity and irrigation evaluation indices. Three data sets of furrow irrigation for maize crop production in the Alborz Province of Iran (College of Agriculture and Natural Resources and Seed and Plant Improvement Institute farms) were used for evaluation of the proposed model. Average relative error of the model ranged from 11.5 to 17.2%, 7.5 to 11.3% and 6.8 to 9.0% in estimating infiltrated water volume, crop yield and water productivity, respectively. The model could also well simulate temporal soil moisture variations and water stress in the root zone. As a consequence, the SFIM model could successfully simulate all irrigation events during the maize‐growing season. © 2020 John Wiley &amp; Sons, Ltd.

Ontogenetic changes in the buoyancy and salinity tolerance of eggs and larvae of polar cod (Boreogadus saida) and other gadids

Climate change in Arctic and sub-Arctic seas is leading to rapid changes in the dispersal potential of marine organisms. In Alaskan waters, loss of sea ice and salinity changes associated with warming may have a strong effect on the distribution and survival of eggs and larvae of key fish species at the Pacific–Arctic interface, such as polar cod (Boreogadus saida) in the Chukchi Sea and walleye pollock (Gadus chalcogrammus) in the northern Bering Sea. We conducted laboratory experiments to investigate how changes in ontogeny and salinity influenced the buoyancy and survival of eggs and larvae of these and two other gadids (Pacific cod, Gadus macrocephalus and saffron cod, Eleginus gracilis). Polar cod egg density varied among family groups, but eggs were more buoyant than those of walleye pollock overall. Eggs of both species followed a typical pattern of increasing density early in development. After hatching, polar cod and walleye pollock larvae were similar in density, and were notably more buoyant than the larvae of species with demersal eggs (Pacific cod and saffron cod). Larvae of the two Arctic species (polar cod and saffron cod) were less sensitive to salinity challenges than the sub-Arctic gadids, but polar cod became more sensitive at 6 weeks post-hatch. These results highlight possible adaptations of polar cod to ensure that their eggs are positioned under or near ice after spawning so that larvae hatch in productive surface waters during ice break-up. A comparison of modeled seawater densities to egg densities during the post-spawning period suggests that walleye pollock eggs would only be in contact with seasonal sea ice on the northern edge of their distribution at latitudes above ~ 63 °N. The synergic effects of environmental variables on vertical distribution of eggs and their survival potential will be important biogeographic mechanisms to consider with climatic warming and continued loss of sea ice.

Coastal acidification induced by biogeochemical processes driven by sea-ice melt in the western Arctic ocean

To better understand the extent of acidification in the Arctic Ocean, we present pH measurements collected along a shelf-slope-basin transect from the Chukchi Sea shelf to the Chukchi Abyssal Plain (CAP) in the western Arctic Ocean during the summer 2010 Chinese Arctic National Research Expedition (CHINARE) cruise. We observed low pH values in the Chukchi Sea shelf bottom waters (~30 m-bottom) and CAP upper haloline layer (UHL) (100–200 m). In the shelf bottom waters, the pH values were 7.66–8.13, about 0.07–0.68 pH units lower than the surface values of 8.20–8.24. In the CAP subsurface waters, the pH values were 7.85–7.98, about 0.08–0.31 pH units lower than the surface values of 8.20–8.24. Biogeochemical model simulations suggest that remineralized CO2 driven by sea-ice loss is primarily responsible for the low pH values in the bottom waters of the Chukchi Sea (shelf) and the UHL waters of the CAP (basin). Recent sea-ice melt enhanced organic matter production in surface waters and subsequent supported the increased microbial respiration of organic matter in bottom waters. Moreover, low pH bottom waters were flushed into the UHL during winter to sustain the low pH characteristics in the subsurface basin layers. In addition, our simplified model suggests that the thermodynamic effect of pH is small. However, increasing temperature significantly increased aragonite saturation (Ωarag) which slowed down the speed of acidification.

Oceanic versus continental influences over the last 7 kyrs from a mid-shelf record in the northern Bay of Biscay (NE Atlantic)

We discuss paleoenvironments of north-western France over the last 7 kyrs in terms of: i) long-term changes (relative sea-level rise and boreal summer insolation), ii) rapid climate changes (millennial-scale Bond events and multi-decadal regimes of the North Atlantic Oscillation: NAO) and iii) growing human impacts in watersheds. Our study focuses on the CBT-CS11 core, retrieved in the northern Bay of Biscay, with new high-resolution (70 years) palynological data (dinoflagellate cysts and pollen), combined with sedimentological and oxygen stable isotopic records. This multiproxy approach enabled us to gain a better understanding of the influence of varying Middle to Late Holocene climate regimes on marine, coastal and terrestrial ecosystems as well as on human coastal societies. We especially show that the slowdown of the relative sea-level rise, starting at around 5.9 ka BP, led to the stabilization of tidal flats in estuarine environments. Subsequently, increasing river flows to the ocean resulted in a progressive seasonal stratification of the shelf under increasing winter precipitations and establishment of the modern winter thermohaline front at 3.3 ka BP. In addition, within the 4–2 ka BP interval, palynological and sedimentological evidence suggests increasing river discharges in north-western France, in a context of a weakened Atlantic subpolar gyre and recurrent negative “NAO-like” conditions. Finally, we identified a major transition at around 1.2 ka BP (Early Middle-Ages) that appears to be linked to a period of maximal anthropogenic landscape opening and soil erosion, implying stronger primary productivity in coastal surface waters of the studied region.