Coastal Margin Research Articles

Species diversity of eukalyptorhynch flatworms (Platyhelminthes, Rhabdocoela) from the coastal margin of British Columbia: Polycystididae, Koinocystididae and Gnathorhynchidae

ABSTRACTKalyptorhynchs are abundant members of meiofaunal communities worldwide, but knowledge on their overall species diversity and distribution is poor. Here we report twenty species of eukalyptorhynchs associated with algae and sediments from the coastal margin of British Columbia. Two species, Paulodora artoisi sp. nov. and Limipolycystis castelinae sp. nov., are new to science and described based on their unique stylet morphology. New observations on two morphotypes of Phonorhynchus helgolandicus and two morphotypes of Scanorhynchus forcipatus suggest that the different morphotypes represent different species; accordingly, Phonorhynchus contortus sp. nov., Phonorhynchus velatus sp. nov. and Scanorhynchus herranzae sp. nov. are described here as separate species. Furthermore, we report on the occurrence and morphology of Polycystis hamata, Polycystis naegelii, Austrorhynchus pacificus, Austrorhynchus californicus, Paraustrorhynchus pacificus, Alcha evelinae, Duplacrorhynchus minor, Yaquinaia microrhynchus, Gyratrix hermaphroditus s. l., Scanorhynchus forcipatus, Rhinolasius dillonicus, Itaipusa biglandula, Utelga heinckei, Neognathorhynchus suecicus and Zonorhynchus seminascatus.

Creative cities along water margins / Urban and cultural regeneration of Shkodra, city of water

Water has always influenced human life and has shaped the entire planet. It was the fundamental element for the economic and cultural development of all populations, to the point that the evolution of civilization depends on the way in which man has relied on water. The need of man to have water resources near the inhabited places is a constant necessity in time. The domination of water as a source of energy and wealth for the city is an essential model of urban evolution. The contemporary city no longer tends to territorial expansion, but to the regeneration of marginal areas, especially those rich in resources and potential. From this point of view, the waterfronts are those spaces that transfer to the city the possibility of continuous change and improvement of the entire urban fabric. In the contemporary world the interest in redesigning and exploiting coastal margins has increased more and more, in order to build ever more efficient relations with water and create new images of waterfront.

Retreat of the Western Cordilleran Ice Sheet Margin During the Last Deglaciation

AbstractThe timing of Cordilleran Ice Sheet deglaciation along the central coast of British Columbia, Canada, informs climate forcing and early human migration. Thirty‐two 10Be exposure ages from glacial erratics and local bedrock on the western margin of the former ice sheet represent the earliest exposure ages for the Cordilleran Ice Sheet during the last deglaciation. These data show the western ice margin was retreating by 18.1 ± 0.2 ka, consistent with the global record of ice mass loss. In contrast, parts of the southern margin reached a maximum at ca. 17.6–16.6 ka, and our data demonstrate a diachronous response of the Cordilleran Ice Sheet during deglaciation. We also show that a low altitude site was exposed by at least 17.7 ± 0.3 ka, implying that numerous ice‐free areas existed along the coastal margin by this time, providing a viable route for the first humans entering the Americas.

Eogenetic Karst Control of Carbonate Reservoirs during a Transient Exposure: A Case Study of the Ordovician Yingshan Formation in the Northern Slope of the Tazhong Uplift, Tarim Basin, China

The Tazhong area of the Tarim Basin contains abundant oil and gas resources in Ordovician carbonate rocks, especially in the karst pores and caves of the Yingshan Formation. Research has indicated that the Yingshan Formation underwent a 7–11 Ma exposure during the middle Caledonian Period, resulting in large-scale karst pores and caves. However, the continental freshwater karst model cannot adequately explain the origin and distribution of karst pores and caves. In order to develop a more accurate karst model to guide petroleum exploration in the region, we analyzed the karst morphology, cave development statistics, and paleokarst environments. Karst reservoir characteristics were analyzed on the basis of the following analysis: (1) Karst morphological analyses based on core description and formation micro-imager (FMI) log analyses. The results showed that alveolar-like and Swiss cheese-like solution pores, spongy dissolution zones, pit cenotes, and small continuous karst caves developed in the Yingshan Formation. (2) The statistical analysis of pore and cave characteristics indicated that most of the karst pores and caves developed within 50 m below the unconformity where the average height of these features ranged from 0.1 to 3.0 m and their widths ranged up to 100 m. These pores and caves were commonly filled with gravel, clay, and calcite. Horizontal well and seismic attribute analysis indicated that these pores and caves were distributed over a large area. In plain view, the karst pore-cave system is comprised of cross-linked anastomosing networks of horizontal cave passages. And (3) Cathode luminescence and electron microprobe analyses suggested that clay filling within karst caves was freshwater related, while calcite filling was of seawater origin. Cements within solution pores showed three phases of luminescence, suggesting an alternating freshwater and seawater environment. Based on these characteristics, the karsts of the Yingshan Formation in the Tazhong area are interpreted to be similar to the eogenetic karsts in the Yucatan Peninsula of modern Mexico. Accordingly, this study indicates that the pore-caves of the Yingshan Formation can be subdivided into three sections. Further, the development and filling of these pore-cave sections are interpreted to have formed by eogenetic mixed-water karstification during three phases of relatively stable sea level in a coastal margin environment.

Controls on vertical nutrient distributions in the Sansha Yongle Blue Hole, South China Sea

Blue holes are unique geomorphological units characterized by steep redox and biogeochemical gradients. The Yongle Blue Hole (YBH) is located on the largest atoll (Yongle Atoll) of the western Xisha Islands in the South China Sea (SCS). Although its depth was only just determined in July, 2016, the YBH has been known for centuries. The YBH is ca. 300 m in depth and has been recognized as the deepest known marine blue hole in the world. In this work, water column samples were collected from the YBH in March, 2017, and examined for dissolved inorganic nutrients, temperature, salinity, dissolved oxygen (DO), pH, and chlorophyll for the first time in order to better understand the nutrient cycling in this unique marine blue hole. The YBH water column is characterized by well-defined physical and chemical gradients with sharp transitions in salinity, temperature, density, DO and pH occurring at 80 m depth. With the disappearance of DO at 100 m depth, the hydrogeochemistry of the water column in the YBH dramatically changed from oxic to anoxic. Therefore, the YBH water column stratification existed mostly within the depth range of 80–100 m. Most physical and chemical parameters in the YBH remained relatively uniform below the depth of 160 m. Nutrient profiles in the water column varied distinctively in the YBH, with large shifts at the redoxclines. For example, surface waters ( 20 m) had nitrate concentrations that averaged 0.08 μmol/L, but increased to 8.59 μmol/L below 70 m and then decreased rapidly below 100 m. Nitrite were generally low with two peaks in the water column at 40 m (0.49 μmol/L) and 95 m (0.18 μmol/L). Changes in nitrate and nitrite were reflective of nitrification and denitrification within the 100 m depth of the YBH. Concentrations of ammonium was low within the upper 95 m, but increased to ca. 85 μmol/L below 160 m, where nitrate and DO decreased to near zero. The concentrations of phosphate and silicate were also very low within 70 m (0.04 and 1.21 μmol/L in average, respectively), increased rapidly below 70 m, and kept stable below 160 m at 4.9 and 152 μmol/L, respectively. Relatively constant distributions of ammonium, phosphate and silicate below 160 m was likely attributed to the stable conditions of low OM concentration, chlorophyll- a , temperature, salinity and pH. The N/P ratios were high in the surface layer (up to 300) and decreased with depth. The Si/N ratios were low in both surface and bottom layers, and the peak value of 15 appeared at 95 m. The Si/P ratios were high in the surface layer too, but also had peak value at 95 m (up to 70). All nutrient ratios (Si/N, Si/P, and N/P) were also stable below 160 m and were very close to the Redfield ratios. Vertical profiles of nutrients in the YBH were strongly linked to redoxclines and OM concentrations. In general, the YBH is an ideal place for examining the transport and transformation of biogenetic elements across steep redox gradients in the coastal margin.

Provenance, routing and weathering history of heavy minerals from coastal placer deposits of southern Vietnam

Heavy mineral rich sands along the coastal margin of southern Vietnam often contain commercial deposits of ilmenite and zircon but their origin is unknown. A multi-method approach based on petrology, geochemistry and detrital zircon geochronology was used to define the provenance and transport history of these mainly Quaternary sands. A trend of progressive enrichment of ilmenite TiO2 content, from north to south, was observed. This reflects increased levels of weathering attributed to a wider coastal margin and shelf in the south combined with a succession of erosion and reburial events associated with interstadial and interglacial sea-level changes. Weathering took place during lowstands. Detrital zircon UPb age signatures collected from 25 major river outlets along the coast of Vietnam helped to locate potential sand sources. Prominent age groups spanning 90–120 Ma and 220–250 Ma with a minor group at 400–500 Ma are present in all of the detrital zircon UPb age distributions of contemporary beach sands and Quaternary coastal dune placer deposits. Proterozoic grains are also present but constitute <10% of dated grains. The main source terrain for the placer sands is southern Vietnam where there are widespread outcrops of Mesozoic magmatic rocks. Detrital zircon UPb age signatures from river sands that drain this area are identical to zircon age distributions in placer sands. River sands from northern Vietnam, the Mekong and its delta contain abundant Paleozoic and Proterozoic zircons, which are largely absent from the placer sands, and so are ruled out as primary sources.

Electrical Resistivity Imaging and the Saline Water Interface in High-Quality Coastal Aquifers

Population growth and changing climate continue to impact on the availability of natural resources. Urbanization of vulnerable coastal margins can place serious demands on shallow groundwater. Here, groundwater management requires definition of coastal hydrogeology, particularly the seawater interface. Electrical resistivity imaging (ERI) appears to be ideally suited for this purpose. We investigate challenges and drivers for successful electrical resistivity imaging with field and synthetic experiments. Two decades of seawater intrusion monitoring provide a basis for creating a geo-electrical model suitable for demonstrating the significance of acquisition and inversion parameters on resistivity imaging outcomes. A key observation is that resistivity imaging with combinations of electrode arrays that include dipole–dipole quadrupoles can be configured to illuminate consequential elements of coastal hydrogeology. We extend our analysis of ERI to include a diverse set of hydrogeological settings along more than 100 km of the coastal margin passing the city of Perth, Western Australia. Of particular importance are settings with: (1) a classic seawater wedge in an unconfined aquifer, (2) a shallow unconfined aquifer over an impermeable substrate, and (3) a shallow multi-tiered aquifer system over a conductive impermeable substrate. We also demonstrate a systematic increase in the landward extent of the seawater wedge at sites located progressively closer to the highly urbanized center of Perth. Based on field and synthetic ERI experiments from a broad range of hydrogeological settings, we tabulate current challenges and future directions for this technology. Our research contributes to resolving the globally significant challenge of managing seawater intrusion at vulnerable coastal margins.

A new &lt;em&gt;Calliovarica&lt;/em&gt; species (Seguenzioidea: Chilodontidae) from the Eocene of Oregon, USA: Persistence of a relict Mesozoic gastropod group in a unique forearc tectonic setting

A new, enigmatic chilodontid gastropod with distinctive periodic varices is described as Calliovarica oregonensis. It is based on ten specimens from slope deposits of the early late Eocene Nestucca Formation on the coastal Cascadia margin of present day Oregon, U.S.A. It is the last appearance of a Mesozoic group of epifaunal basal gastropods with periodic varices. It is the third species in a Cenozoic genus previously known only from the early Eocene Lodo Formation in California and the late Paleocene to early Eocene Red Bluff Tuff in New Zealand. The type species, C. eocensis, is refigured to clarify the nature of the axial varices as well as a terminal thickening and flaring of the apertural lip immediately following deposition of the final varix. Detailed preservation of microstructure in the nacreous layers of crushed and disintegrating shell fragments demonstrates the value of collecting material typically left behind in the field. Calliovarica oregonensis n. sp. is part of a poorly understood molluscan fauna that lived during an unusual paleoclimatic interval immediately prior to global cooling and extinctions in the late Eocene. It also thrived in an unusual volcano-sedimentary interval at the onset of subduction at the Cascadia margin. The tectonic setting provides a unique snapshot of a depositional environment receiving periodic influxes of ash from the young volcanic arc to the east and periodic basalt intrusions from the underlying asthenosphere into the forerarc over a hotspot or through slab window emplacement. Links between biofacies and lithofacies demonstrate the ability of paleontology and geology to provide reciprocal illumination, especially in dynamic settings with no modern counterparts. The link between local persistence of relict Mesozoic taxa and localized tectonic events merits further integrative investigation.

Morpho-stratigraphic features of the northern shelf of the Strait of Gibraltar: Tectonic and sedimentary processes acting at different temporal scales

The northern shelf of the Strait of Gibraltar adjacent to Camarinal Sill, defined here as the Cape Paloma continental shelf, has been investigated by analyzing a set of geophysical data including multibeam bathymetric images, a side-scan sonar mosaic and high-resolution seismic profiles, and the simulation of water-mass circulation patterns along the northern coastal margin. The aim of the study was to establish the significance of factors determining the evolution of this shallow margin at different temporal scales and to assess the implications for bedform generation in strait settings, taking into account the complex tectonic evolution and the energetic hydrodynamic regime of the strait.Deformed basement rocks are part of the Betic-Rif thrust wedge, western Gibraltar Arc, mainly formed by the materials of the Flysch Complex units and covered by Pliocene to Quaternary post-orogenic deposits. A central high (Bajo de los Cabezos High) is delimited by lateral depressions, that nucleated two major depocentres with distinctive filling histories. The eastern depocentre is controlled by WNW-ESE faults cutting the Cretaceous-Miocene basement rocks; these faults generate horsts and grabens that could have contributed to the opening of the Strait of Gibraltar during the Pliocene. The largest and westernmost depocentre is related to the complete infilling of a shelf palaeovalley. The sediment cover is molded by different fields of submarine dunes and comet marks that indicate the influence of hydrodynamic processes on sediment transport at the coastal margin.The observations in the study area regarding bedform development must be placed into a wider context of strait sediment dynamics. The Cape Paloma continental shelf exhibits both erosional and depositional forms, due to its intermediate location between the strait, mostly dominated by erosional processes, and the Barbate Platform (northwest of the study area), mostly characterized by depositional forms. The long-term evolution of the sediment depocentres in the study area appears to be mainly influenced by the morpho-tectonic configuration of the margin, which in turn was established to a large extent by differential uplifting along the coast. In the shelf east of the central high, the basement horst and graben structure trapped sediments in the physiographic lows and fostered the formation of large-scale sediment banks. In the shelf west of the central high, the occurrence of a major infilled palaeovalley is in agreement with a gentle subsidence trend.The physiographic configuration is also thought to play a major role in defining short-term processes, particularly in confining a cyclonic eddy to the east of the Bajo de los Cabezos High during specific conditions of the tidal cycle. This eddy favors the recirculation of sediments in the coastal margin, as evidenced by small bedform fields that apparently show a wider distribution that the larger-scale, confined sediment banks, due to the instauration of the modern sediment dynamics after the complete shelf flooding. The sediment transport pattern established in the study area seems to be eventually captured by a submarine channel that provide an efficient mechanism for sediment export toward deep-water settings, where an extensive contourite depositional system has been documented.

Estado trófico y estructura comunitaria del microfitoplancton en un sector del golfo de Guayaquil, Ecuador

Urban growth in coastal areas has led to eutrophication, which in turn has caused the accumulation of organic in the estuarine system of the gulf of Guayaquil. In this scenario trophic status was determined using the Karydis index in three zones established according to hydrographic affinity one mile from the coastal margin of the province of El Oro. Additionally, multivariate analysis were developed to establish the relationship between micro-phytoplankton and physical and chemical variables. Significant differences in trophic levels and community structure were found in each zone. Zone A (Jambeli channel), had the highest trophic index, nitrate (3.8) and silicate (4.9), and lowest salinity, dissolved oxygen, and transparency; zone B (coastal marine exchange area), the one with the greatest oceanic influence, had medium trophic levels (nitrate: 3.4 and silicate: 4.6); zone C (Puna island), had the highest salinity and lowest trophic indexes (3.2 nitrate and 4.3 silicate). The representative species in zone A were: Nitzschia longissima , Skeletonema costatum , and Pseudonitzschia delicatissima ; zone B: P. delicatissima , Guinardia striata , and Leptocylindrus danicus ; zone C: Paralia sulcata , Thalassionema nitzschioides , and S. costatum . The study area was determined as mesotrophic. However, zone A presented the highest trophic level, probably due to a greater influence from human activities.

Thermal structure of the Panama Basin by analysis of seismic attenuation

Using recordings of earthquakes on Oceanic Bottom Seismographs and onshore stations on the coastal margins of Colombia, Panama, and Ecuador, we estimate attenuation parameters in the upper lithosphere of the Panama Basin. The tomographic images of the derived coda-Q values are correlated with estimates of Curie Point Depth and measured and theoretical heat flow. Our study reveals three tectonic domains where magmatic/hydrothermal activity or lateral variations of the lithologic composition in the upper lithosphere can account for the modeled thermal structure and the anelasticity. We find that the Costa Rica Ridge and the Panama Fracture Zone are significant tectonic features probably related to thermal anomalies detected in the study area. We interpret a large and deep intrinsic attenuation anomaly as related to the heat source at the Costa Rica Ridge and show how interactions with regional fault systems cause contrasting attenuation anomalies.

Terrestrial dissolved organic matter distribution in the North Sea

The flow of terrestrial carbon to rivers and inland waters is a major term in the global carbon cycle. The organic fraction of this flux may be buried, remineralized or ultimately stored in the deep ocean. The latter can only occur if terrestrial organic carbon can pass through the coastal and estuarine filter, a process of unknown efficiency. Here, data are presented on the spatial distribution of terrestrial fluorescent and chromophoric dissolved organic matter (FDOM and CDOM, respectively) throughout the North Sea, which receives organic matter from multiple distinct sources. We use FDOM and CDOM as proxies for terrestrial dissolved organic matter (tDOM) to test the hypothesis that tDOM is quantitatively transferred through the North Sea to the open North Atlantic Ocean. Excitation emission matrix fluorescence and parallel factor analysis (EEM-PARAFAC) revealed a single terrestrial humic-like class of compounds whose distribution was restricted to the coastal margins and, via an inverse salinity relationship, to major riverine inputs. Two distinct sources of fluorescent humic-like material were observed associated with the combined outflows of the Rhine, Weser and Elbe rivers in the south-eastern North Sea and the Baltic Sea outflow to the eastern central North Sea. The flux of tDOM from the North Sea to the Atlantic Ocean appears insignificant, although tDOM export may occur through Norwegian coastal waters unsampled in our study. Our analysis suggests that the bulk of tDOM exported from the Northwest European and Scandinavian landmasses is buried or remineralized internally, with potential losses to the atmosphere. This interpretation implies that the residence time in estuarine and coastal systems exerts an important control over the fate of tDOM and needs to be considered when evaluating the role of terrestrial carbon losses in the global carbon cycle.

High resolution topobathymetry using a Pleiades-1 triplet: Moorea Island in 3D

Worldwide the coastal land-sea interface is increasingly subject to natural and anthropogenic hazards. Monitoring this crucial interface may be addressed with satellite imagery as a cost-efficient mapping solution. Topography and bathymetry, defining the structural complexity of the coast, are commonly studied separately given specific thematic and methodological contexts, yet many science questions and societal challenges require an integrated approach (e.g., coastal inundation). In such cases, triplet multispectral imagery represents an affordable solution based on a single satellite product. Here we examine how Pleiades-1 triplet imagery may be used to retrieve a seamless and accurate topobathymetry digital surface model (DSM, from −20 to 1207 m) over an entire, socio-ecologically complex island: Moorea, French Polynesia. Creation of the topography DSMs was based on stereo and tri-stereo photogrammetry, and the bathymetry DSMs relied on quasi-nadiral multispectral data subject to light/water interaction modelling. Results were compared with over 3.9 million airborne LiDAR topobathymetry measurements to quantify how the spatio-spectral mode, the third imagery, and the level of radiometric correction act on two- and three-dimensional accuracy. Horizontal accuracy of the tri-stereo panchromatic dataset (ERMSE = 4.22 and NRMSE = 7.59 m) was better than the multispectral (ERMSE = 5.06 and NRMSE = 7.51 m) dataset. Topography point cloud density increased by a factor of three in the tri-stereo panchromatic (9.11 points/m2) or multispectral (0.23 points/m2) datasets. Topography vertical accuracy enhanced with tri-stereo + level-1 radiometric correction (RMSE = 7.40 m) for panchromatic and with stereo + level-1/-2 radiometric correction (RMSE = 7.77/7.77 m) as well as tri-stereo without radiometric correction (RMSE = 7.85 m) for multispectral datasets. Bathymetry vertical accuracy improved with level-2 (atmospheric) correction (RMSE = 0.83 m). Topobathymetry DSM derived from this optimized method has a wide spectrum of applications along coastal margins.

Crustal heat production and estimate of terrestrial heat flow in central East Antarctica, with implications for thermal input to the East Antarctic ice sheet

Abstract. Terrestrial heat flow is a critical first-order factor governing the thermal condition and, therefore, mechanical stability of Antarctic ice sheets, yet heat flow across Antarctica is poorly known. Previous estimates of terrestrial heat flow in East Antarctica come from inversion of seismic and magnetic geophysical data, by modeling temperature profiles in ice boreholes, and by calculation from heat production values reported for exposed bedrock. Although accurate estimates of surface heat flow are important as an input parameter for ice-sheet growth and stability models, there are no direct measurements of terrestrial heat flow in East Antarctica coupled to either subglacial sediment or bedrock. As has been done with bedrock exposed along coastal margins and in rare inland outcrops, valuable estimates of heat flow in central East Antarctica can be extrapolated from heat production determined by the geochemical composition of glacial rock clasts eroded from the continental interior. In this study, U, Th, and K concentrations in a suite of Proterozoic (1.2–2.0 Ga) granitoids sourced within the Byrd and Nimrod glacial drainages of central East Antarctica indicate average upper crustal heat production (Ho) of about 2.6 ± 1.9 µW m−3. Assuming typical mantle and lower crustal heat flux for stable continental shields, and a length scale for the distribution of heat production in the upper crust, the heat production values determined for individual samples yield estimates of surface heat flow (qo) ranging from 33 to 84 mW m−2 and an average of 48.0 ± 13.6 mW m−2. Estimates of heat production obtained for this suite of glacially sourced granitoids therefore indicate that the interior of the East Antarctic ice sheet is underlain in part by Proterozoic continental lithosphere with an average surface heat flow, providing constraints on both geodynamic history and ice-sheet stability. The ages and geothermal characteristics of the granites indicate that crust in central East Antarctica resembles that in the Proterozoic Arunta and Tennant Creek inliers of Australia but is dissimilar to other areas like the Central Australian Heat Flow Province that are characterized by anomalously high heat flow. Age variation within the sample suite indicates that central East Antarctic lithosphere is heterogeneous, yet the average heat production and heat flow of four age subgroups cluster around the group mean, indicating minor variation in the thermal contribution to the overlying ice sheet from upper crustal heat production. Despite these minor differences, ice-sheet models may favor a geologically realistic input of crustal heat flow represented by the distribution of ages and geothermal characteristics found in these glacial clasts.

Sea-level change and demography during the last glacial termination and early Holocene across the Australian continent

Future changes in sea-level are projected to have significant environmental and social impacts, but we have limited understanding of comparable rates of change in the past. Using comprehensive palaeoenvironmental and archaeological datasets, we report the first quantitative model of the timing, spatial extent and pace of sea-level change in the Sahul region between 35-8 ka, and explore its effects on hunter-gatherer populations. Results show that the continental landmass (excluding New Guinea) increased to 9.80 million km2 during the Last Glacial Maximum (LGM), before a reduction of 2.12 million km2 (or ∼21.6%) to the early Holocene (8 ka). Almost 90% of this inundation occurs during and immediately following Meltwater Pulse (MWP) 1a between 14.6 and 8 ka. The location of coastlines changed on average by 139 km between the LGM and early Holocene, with some areas >300 km, and at a rate of up to 23.7 m per year (∼0.6 km land lost every 25-year generation). Spatially, inundation was highly variable, with greatest impacts across the northern half of Australia, while large parts of the east, south and west coastal margins were relatively unaffected. Hunter-gatherer populations remained low throughout (<30,000), but following MWP1a, increasing archaeological use of the landscape, comparable to a four-fold increase in populations, and indicative of large-scale migration away from inundated regions (notably the Bass Strait) are evident. Increasing population density resulting from MWP1a (from 1/655 km2 to 1/71 km2) may be implicated in the development of large and complex societies later in the Holocene. Our data support the hypothesis that late Pleistocene coastal populations were low, with use of coastal resources embedded in broad-ranging foraging strategies, and which would have been severely disrupted in some regions and at some time periods by sea-level change outpacing tolerances of mangals and other near-shore ecological communities.

Relative Sea Level Variations at Alexandria (Nile Delta, Egypt) over the Last Millennia: Archaeological Implications for the Ancient Harbour

During the 19th century, remains of an ancient harbour were found underwater at a depth of 5 to 6 meters in the eastern port of Alexandria. A research program was undertaken to determine when the harbour of Alexandria submerged underwater. Data were collected through underwater surveys by scuba diving and by campaigns of corings on land. Geomorphological (i.e. notches and pebble beaches), archaeological (harbour structures), and biological (i.e. marine macrofauna, bioconstructions, and biodepositions) sea level indicators were correlated to understand changes in relative sea level during the last 6 millennia. For each proxy, the altitudinal (vertical) and chronological ranges of imprecision were discussed. The results indicate that the rate of the relative sea level rise is ~80 mm per century between the middle of the 6th millennium and the 5th‒6th c. AD. An abrupt relative sea level rise (3.5 m + 1.5 m) occurred during the mid 8th c. to the end of 9th c. A D. I n t he 8 th c. A D, a s imilar p henomenon was observed for Heracleion (25 km east of Alexandria). Thus, a wide movement of sinking affected in a synchronous manner the western coastal margin of the Nile delta. Since this 8th- 9th c. AD event, the subsidence has increased around 2 m. The role of abrupt sinking events and subsidence remain determining in the deltaic context to anticipate future coastal adaptations and the risk of submersion.

Vertical distribution of major, minor and trace elements in sediments from mud volcanoes of the Gulf of Cadiz: evidence of Cd, As and Ba fronts in upper layers

Mud volcanoes are feature of the coastal margins where anaerobic oxidation of methane triggers geochemical signals. Elemental composition, percentage of fine particles and loss on ignition were determined in sediment layers of eleven gravity cores retrieved from four mud volcanoes (Sagres, Bonjardim, Soloviev and Porto) and three undefined structures located on the deep Portuguese margin of the Gulf of Cadiz. Calcium was positively correlated to Sr and inversely to Al as well as to most of the trace elements. Vertical profiles of Ba, Cd and As concentrations, and their ratios to Al, in Porto and Soloviev showed pronounced enhancements in the top 50-cm depth. Sub-surface enhancements were less pronounced in other mud volcanoes and were absent in sediments from the structures. These profiles were interpreted as diagenetic enrichments related to the anaerobic oxidation of methane originated from upward methane-rich fluxes. The observed barium fronts were most likely caused by the presence of barite which precipitated at the sulphate-methane transition zone. Cd and As enrichments have probably resulted from successive dissolution/precipitation of sulphides in response to vertical shifts of redox boundaries.

Real-time detection of airborne fluorescent bioparticles in Antarctica

Abstract. We demonstrate, for the first time, continuous real-time observations of airborne bio-fluorescent aerosols recorded at the British Antarctic Survey's Halley VI Research Station, located on the Brunt Ice Shelf close to the Weddell Sea coast (lat 75°34′59′′ S, long 26°10′0′′ W) during Antarctic summer, 2015. As part of the NERC MAC (Microphysics of Antarctic Clouds) aircraft aerosol cloud interaction project, observations with a real-time ultraviolet-light-induced fluorescence (UV-LIF) spectrometer were conducted to quantify airborne biological containing particle concentrations along with dust particles as a function of wind speed and direction over a 3-week period. Significant, intermittent enhancements of both non- and bio-fluorescent particles were observed to varying degrees in very specific wind directions and during strong wind events. Analysis of the particle UV-induced emission spectra, particle sizes and shapes recorded during these events suggest the majority of particles were likely a subset of dust with weak fluorescence emission responses. A minor fraction, however, were likely primary biological particles that were very strongly fluorescent, with a subset identified as likely being pollen based on comparison with laboratory data obtained using the same instrument. A strong correlation of bio-fluorescent particles with wind speed was observed in some, but not all, periods. Interestingly, the fraction of fluorescent particles to total particle concentration also increased significantly with wind speed during these events. The enhancement in concentrations of these particles could be interpreted as due to resuspension from the local ice surface but more likely due to emissions from distal sources within Antarctica as well as intercontinental transport. Likely distal sources identified by back trajectory analyses and dispersion modelling were the coastal ice margin zones in Halley Bay consisting of bird colonies with likely associated high bacterial activity together with contributions from exposed ice margin bacterial colonies but also long-range transport from the southern coasts of Argentina and Chile. Dispersion modelling also demonstrated emissions from shipping lanes, and therefore marine anthropogenic sources cannot be ruled out. Average total concentrations of total fluorescent aerosols were found to be 1.9 ± 2.6 L−1 over a 3-week period crossing over from November into December, but peak concentrations during intermittent enhancement events could be up to several tens per litre. While this short pilot study is not intended to be generally representative of Antarctic aerosol, it demonstrates the usefulness of the UV-LIF measurement technique for quantification of airborne bioaerosol concentrations and to understand their dispersion. The potential importance for microbial colonisation of Antarctica is highlighted.

Multidecadal fCO2 Increase Along the United States Southeast Coastal Margin

AbstractCoastal margins could be hotspots for acidification due to terrestrial‐influenced CO2 sources. Currently there are no long‐term (&gt;20 years) records from biologically important coastal environments that could demonstrate sea surface CO2 fugacity (fCO2) and pH trends. Here, multidecadal fCO2 trends are calculated from underway and moored time series observations along the United States southeast coastal margin, also referred to as the South Atlantic Bight (SAB). fCO2 trends across the SAB, derived from ∼26 years of cruises and ∼9.5 years from a moored time series, range from 3.0 to 4.5 µatm yr−1, and are greater than the open ocean increases. The pH decline related to the fCO2 increases could be as much as −0.004 yr−1; a rate greater than that expected from atmospheric‐influenced pH alone. We provide evidence that fCO2 increases and pH decreases on an ocean margin can be faster than those predicted for the open ocean from atmospheric influence alone. We conclude that a substantial fCO2 increase across the marginal SAB is due to both increasing temperature on the middle and outer shelves, but to lateral land‐ocean interactions in the coastal zone and on inner shelf.

Sea-level rise and archaeological site destruction: An example from the southeastern United States using DINAA (Digital Index of North American Archaeology).

The impact of changing climate on terrestrial and underwater archaeological sites, historic buildings, and cultural landscapes can be examined through quantitatively-based analyses encompassing large data samples and broad geographic and temporal scales. The Digital Index of North American Archaeology (DINAA) is a multi-institutional collaboration that allows researchers online access to linked heritage data from multiple sources and data sets. The effects of sea-level rise and concomitant human population relocation is examined using a sample from nine states encompassing much of the Gulf and Atlantic coasts of the southeastern United States. A 1 m rise in sea-level will result in the loss of over >13,000 recorded historic and prehistoric archaeological sites, as well as over 1000 locations currently eligible for inclusion on the National Register of Historic Places (NRHP), encompassing archaeological sites, standing structures, and other cultural properties. These numbers increase substantially with each additional 1 m rise in sea level, with >32,000 archaeological sites and >2400 NRHP properties lost should a 5 m rise occur. Many more unrecorded archaeological and historic sites will also be lost as large areas of the landscape are flooded. The displacement of millions of people due to rising seas will cause additional impacts where these populations resettle. Sea level rise will thus result in the loss of much of the record of human habitation of the coastal margin in the Southeast within the next one to two centuries, and the numbers indicate the magnitude of the impact on the archaeological record globally. Construction of large linked data sets is essential to developing procedures for sampling, triage, and mitigation of these impacts.