Mesoscale and Nutrient Conditions Associated with the Massive 2008 Cochlodinium polykrikoides Bloom in the Sea of Oman/Arabian Gulf

Cochlodinium polykrikoides formed large blooms in the coastal waters of Oman from October 2008 through mid-January 2009, and satellite images from Aqua-MODIS and region-wide reports suggest that this bloom was found throughout the Arabian Gulf and Sea of Oman for more than 10 months. The unusual occurrence of this species appears to have supplanted the more regularly occurring bloom species, Noctiluca scintillans, in 2008–2009. For the first 2 weeks of the coastal Omani bloom, C. polykrikoides abundance was near monospecific proportions, with cell densities ranging from 4.6?×?10³ to 9?×?10⁶ cells L^?1 and very high levels of chlorophyll a (78.0 μg L^?1) were also recorded. The regional progression of the bloom likely began with stronger than normal upwelling along the Iranian and northern Omani coasts during the southwest monsoon in late summer, followed by discharge of unusually warm coastal plume water along the coast of Oman with the reversal of monsoonal winds in late October. The occurrence and persistence of high densities of C. polykrikoides in Oman coastal water were also significantly influenced by an elevated nutrient load and warmer than normal temperatures. Concentrations of nutrients, especially NH₄ ⁺, urea, PO₄ ^3?, and organic nitrogen and phosphorus, were manyfold higher than observed in the year prior or since. These findings suggest that mesoscale features were important in bloom dynamics more regionally, but locally the bloom was sustained by nutrient enrichment supplemented by its mixotrophic capabilities.     

Oligocene to Present kilometres scale subsidence and exhumation of the Ligurian Alps and the Tertiary Piedmont Basin (NW Italy) revealed by apatite (U–Th)/He thermochronology: correlation with regional tectonics

The Ligurian Alps segment of the Alpine–Apennine orogen in NW Italy is unconformably covered by Upper Eocene to Holocene sediments in the Tertiary Piedmont Basin (TPB) and Po Plain. These sediments dip towards the north demonstrating the erosional nature of the southern border of the succession and implying that the adjacent orogenic belt formed the substratum rather than the margin of the sedimentary basin. Apatite (U–Th)/He and fission track thermochronology shows that the orogen first subsided and was buried at >4 km from 30 to 26 Ma and began its exhumation thereafter. From 26 Ma to present, this upward movement was contemporaneous with subsidence in the northern TPB. The couple exhumation in the S and subsidence in the N migrated northwards through time. Vertical movements in the area are similar to those reconstructed in Corsica. In both cases, the onset of exhumation becomes younger away from the Ligurian‐Provençal basin and has little correlation with the opening of the surrounding oceanic basins.     

Straw Blankets Sewn With Recycled Plastic Threads for Erosion and Urban Sediments Control

Soil erosion, transport and deposition of sediments represent invisible threats that along time can affect negatively the existing infrastructure of roads and dams, and the quality of air and water resources. In the last decades, a great number of researches were devoted to study erosion and sediments transportation processes. However, they addressed mostly areas of agriculture, water impoundments for dams, and land conservation. A lack of studies for erosion processes in urban areas is evident, in special those aiming to diminish the deposition of sediments originated from urban areas into the rivers and air, in special as airborne particulate. Traditionally, the costs associated in controlling erosion and sediments in urban areas are high and in some case, out of the range for most developing countries. Factors responsible for those high prices are the use of heavy equipments for soil grading and transportation, the use of costly building materials, and the need for employing more specialized personnel. In the case of gullies in urban areas, another concern is to ensure proper equipment access to the area for remediation operations. Hereby, it is presented a cost-effective method to recover an extensive gully erosion area of about 11,000 m² located in urban area. Estimated sediments released from this area to the water resources and air were estimated on about 66,000,000 tons. In this study area, bioengineering works were performed in 60 days, with hardly any sediment generated outside the work area resulting from bioengineering operations. A combination of bioengineering techniques were chosen for this study area, which was a mixture of rigid and biological products including biologs, silt fence, biodegradable straw blankets sewn with plastic threads derived from recycled PET bottles, among others. An efficient drainage system was implemented for preventing upland flow, sub-seepage and seepage. Biologs were used aiming to fulfill a double role, the first as barrier to soil sediments flow, and the second as filler for empty spaces, avoiding expensive grading operations. All engineering works were concluded in about 60 days at a cost of US0.89/m < sup > 2 < /sup > . This price is cost-effective if compared with the traditional engineering cost of approximately US 0.89/m². This price is cost-effective if compared with the traditional engineering cost of approximately US 2.92/m² because it includes extensive use of grading and soil transportation. An environmental advantage of the bioengineering method is the immediate reduction of airborne particulates. Furthermore, the overall visual aesthetics improved shortly after the implementation of the works because the bare ground was substituted by native vegetation. After 6 months the vegetation in the gully erosion area was totally established. Monitoring was performed after 12 months and no erosion and sediment transport was visually noticed. The ease implementation of this technique without the need for specialized workers in combination with low prices makes this method a model for developing countries.     

The variable link between PNA and NAO in observations and in multi-century CGCM simulations

The link between the Pacific/North American pattern (PNA) and the North Atlantic Oscillation (NAO) is investigated in reanalysis data (NCEP, ERA40) and multi-century CGCM runs for present day climate using three versions of the ECHAM model. PNA and NAO patterns and indices are determined via rotated principal component analysis on monthly mean 500?hPa geopotential height fields using the varimax criteria. On average, the multi-century CGCM simulations show a significant anti-correlation between PNA and NAO. Further, multi-decadal periods with significantly enhanced (high anti-correlation, active phase) or weakened (low correlations, inactive phase) coupling are found in all CGCMs. In the simulated active phases, the storm track activity near Newfoundland has a stronger link with the PNA variability than during the inactive phases. On average, the reanalysis datasets show no significant anti-correlation between PNA and NAO indices, but during the sub-period 1973?C1994 a significant anti-correlation is detected, suggesting that the present climate could correspond to an inactive period as detected in the CGCMs. An analysis of possible physical mechanisms suggests that the link between the patterns is established by the baroclinic waves forming the North Atlantic storm track. The geopotential height anomalies associated with negative PNA phases induce an increased advection of warm and moist air from the Gulf of Mexico and cold air from Canada. Both types of advection contribute to increase baroclinicity over eastern North America and also to increase the low level latent heat content of the warm air masses. Thus, growth conditions for eddies at the entrance of the North Atlantic storm track are enhanced. Considering the average temporal development during winter for the CGCM, results show an enhanced Newfoundland storm track maximum in the early winter for negative PNA, followed by a downstream enhancement of the Atlantic storm track in the subsequent months. In active (passive) phases, this seasonal development is enhanced (suppressed). As the storm track over the central and eastern Atlantic is closely related to the NAO variability, this development can be explained by the shift of the NAO index to more positive values.     

Factors contributing to the development of extreme North Atlantic cyclones and their relationship with the NAO

The occurrence of extreme cyclones is analysed in terms of their relationship to the NAO phase and the dominating environmental variables controlling their intensification. These are latent energy (equivalent potential temperature 850 hPa is used as an indicator), upper-air baroclinicity, horizontal divergence and jet stream strength. Cyclones over the North Atlantic are identified and tracked using a numerical algorithm, permitting a detailed analysis of their life cycles. Extreme cyclones are selected as the 10% most severe in terms of intensity. Investigations focus on the main strengthening phase of each cyclone. The environmental factors are related to the NAO, which affects the location and orientation of the cyclone tracks, thus explaining why extreme cyclones occur more (less) frequently during strong positive (negative) NAO phases. The enhanced number of extreme cyclones in positive NAO phases can be explained by the larger area with suitable growth conditions, which is better aligned with the cyclone tracks and is associated with increased cyclone life time and intensity. Moreover, strong intensification of cyclones is frequently linked to the occurrence of extreme values of growth factors in the immediate vicinity of the cyclone centre. Similar results are found for ECHAM5/OM1 for present day conditions, demonstrating that relationships between the environment factors and cyclones are also valid in the GCM. For future climate conditions (following the SRES A1B scenario), the results are similar, but a small increase of the frequency of extreme values is detected near the cyclone cores. On the other hand, total cyclone numbers decrease by 10% over the North Atlantic. An exception is the region near the British Isles, which features increased track density and intensity of extreme cyclones irrespective of the NAO phase. These changes are associated with an intensified jet stream close to Europe. Moreover, an enhanced frequency of explosive developments over the British Isles is found, leading to more frequent windstorms affecting Europe.

Factors determining subsidence in urbanized floodplains: evidence from MT‐InSAR in Seville (southern Spain)

Major rivers have traditionally been linked with important human settlements throughout history. The growth of cities over recent river deposits makes necessary the use of multidisciplinary approaches to characterize the evolution of drainage networks in urbanized areas. Since under‐consolidated fluvial sediments are especially sensitive to compaction, their spatial distribution, thickness, and mechanical behavior must be studied. Here, we report on subsidence in the city of Seville (Southern Spain) between 2003 and 2010, through the analysis of the results obtained with the Multi‐Temporal InSAR (MT‐InSAR) technique. In addition, the temporal evolution of the subsidence is correlated with the rainfall, the river water column and the piezometric level. Finally, we characterize the geotechnical parameters of the fluvial sediments and calculate the theoretical settlement in the most representative sectors. Deformation maps clearly indicate that the spatial extent of subsidence is controlled by the distribution of under‐consolidated fine‐grained fluvial sediments at heights comprised in the range of river level variation. This is clearly evident at the western margin of the river and the surroundings of its tributaries, and differs from rainfall results as consequence of the anthropic regulation of the river. On the other hand, this influence is not detected at the eastern margin due to the shallow presence of coarse‐grain consolidated sediments of different terrace levels. The derived results prove valuable for implementing urban planning strategies, and the InSAR technique can therefore be considered as a complementary tool to help unravel the subsidence tendency of cities located over under‐consolidated fluvial deposits. Copyright © 2017 John Wiley & Sons, Ltd.     

Deep-water stands of Cystoseira zosteroides C. Agardh (Fucales,Ochrophyta) in the Northwestern Mediterranean: Insights into assemblage structure and population dynamics

Populations dominated by Cystoseira zosteroides, an endemic and threatened Mediterranean seaweed, colonize deep-water rocky habitats down to more than 50 m depth. Assemblages dominated by this species display high algal and invertebrate species richness. Algal biomass averages 1134 g dw m⁻². Erect and turf algae account for only 25% of total algal dry weight, while encrusting corallines are responsible for the remaining 75%. Sponges, bryozoans and ascidians constitute the dominant sessile macrofauna. Cystoseira zosteroides is the dominant erect algae, with a mean biomass of 60.6 g dw m⁻², and densities ranging from 4 to 7 plants m⁻². The alien turf alga Womersleyella setacea has a biomass of 104.2 g dw m⁻² and covers most of the understory substrate. The size-frequency distribution of C. zosteroides populations shows differences over time. Mean annual growth of the main axis is around 0.5 cm and mean annual mortality rate is lower than 2%. Recruitment was almost nil during the studied period of time (10 years). Processes structuring these deep-water Cystoseira stands must be driven by episodic disturbances, after-disturbance recruitment pulses, and long periods of steady growth that last at least 10 years. However, it is also possible that recruitment is irreversibly inhibited by the alien alga W. setacea in which case these old-growth stands are faced with extinction. The highly diversified assemblages and the low growth and low mortality rates of C. zosteroides indicate high vulnerability to natural and anthropogenic disturbances, and call for effective measures to ensure their conservation.     

Use of different intertidal habitats by faunal communities in a temperate coastal lagoon

The faunal communities of four intertidal habitats namely sand, mud, seagrass (Zostera noltii) and seagrass patches (mixSM) of a temperate coastal lagoon, Ria Formosa (southern Portugal), were sampled. A total of 47 species were taken in 428 bottomless drop sampler samples, with the highest number of species and the more commonly occurring species belonging to the Mollusca phylum. The dominance of these gastropod species underlines the importance of the grazing food chain in these habitats. Bittium reticulatum was the most abundant species, being especially abundant in the seagrass habitat. The most frequent and highest biomass species in the community was Carcinus maenas, a predator that makes use of the available resources and that is adapted to the highly variable intertidal environment. Pomatoschistus microps was the most abundant fish species, with highest densities in the mud habitat, which demonstrates an ability to occupy a low depth area. The seagrass habitat had the highest diversity, abundance and biomass, followed by the mixSM habitat and was different from all the others. Assemblages were highly influenced by the presence of vegetation, providing forage and refuge from predation. A well defined summer group was identified in all habitats. These results highlight the importance of seagrass beds and the idea that their decrease implies the decrease of lagoon production through the impoverishment of the trophic structure of the lagoon.