Eastern Channel Research Articles

Sedimentary and geomorphological evolution of a young tidal flat in the northern part of the Po delta (Italy)

Due to anthropic activities of the last centuries, coastal wetlands worldwide lost wide portions of salt marshes. Since these ecosystems provide fundamental services and benefits to both natural and anthropic components, the natural restoration of these habitats is becoming one of the main objectives of these days, and the opening of new connections between land and sea is becoming a highly used technique to restore portions of intertidal areas. According to recent studies based on analysis of long-term satellite imagery datasets and bathymetric surveys, the Po River Delta (Northern Italy) is currently subjected to a positive sedimentation trend and a constructive process is ongoing at the main river branches. Following an evolution similar to restoration projects, new tidal flats are building up around the tip of the delta, where agricultural fields were inundated by strong floods in the 1950s and the 1960s. This study focuses on a young tidal flat of about 8 ha, located in the Southernmost part of the Barbamarco lagoon. Sediment granulometric distribution and sedimentary pattern were investigated between May 2019 and March 2021 through coring, sediment traps, and orthophotos. The results show that the system is undergoing a progradation and an extended crevasse splay is developing. This covers the central part of the flat and it has developed from the early 2000s, due to human intervention on levees as well as river floods. The levees of the eastern channel stabilized between 2008 and 2012 thanks to vegetation growth, allowing the floods to focus in the NW direction, leading to the development of this recent feature. The presence of the crevasse splay confirms the importance of the river floods on the tidal flat formation. The calculated depositional rates suggest that sedimentation is higher during summer (average 66.89 g/m2 per submersion event) and lower during winter (18.86–20.65 g/m2 per submersion event). These trends are opposite to the seasonal trends observed in the literature, showing that the deposition controlled by the tide is lower compared to the river influence and suggesting that the river is the dominant factor.

Revisiting the connection between variations in the Tsushima Warm Current and winter rainfall along the coast of Japan

AbstractEnhanced autumn transport via the Tsushima Warm Current (TWC) has been reported to increase winter rainfall along Japan’s northern coast. However, observations reveal a significantly weakened correlation after 2006. Although enhanced transport via the Eastern channel of the Tsushima Strait affects rainfall by enhancing latent heat flux along Japan’s northern coast, the role of oceanic flows in varying sea-surface temperatures has weakened since 2006. Stronger northwesterly winds co-occur with enhanced surface heat loss that overwhelms the impact of the TWC. Our findings imply that atmospheric conditions should be considered when using TWC transport as a precursor for winter rainfall.

Late Middle Pleistocene (MIS 10–6) glacial–interglacial records from loess–palaeosol and fluvial sequences from northern France: a cyclostratigraphic approach

This contribution summarizes the most informative loess–palaeosol sequences (LPS) and fluvial terrace records from the late Middle Pleistocene (LMP) of northern France demonstrating the reliability of the cyclostratigraphic approach for the interpretation of pedosedimentary sequences controlled by major glacial–interglacial climatic cycles. In this area, continental mollusc assemblages from interglacial fluvial silts and calcareous tufas are particularly rich and diverse and marker species define the malacological signatures of each interglacial optimum for Marine Isotope Stages (MIS) 11, 9 and 5e. This approach shows that the forest was less developed during MIS 7, suggesting that climatic conditions were either drier and/or cooler than during other Pleistocene interglacials. In the Somme basin, the terrace system shows that two alluvial formations were deposited between early MIS 8 and late MIS 7. In some LPS, the occurrence of two pedosedimentary sub‐cycles (IIa and IIb), separated by a relatively long (~12 ka) and cold period, corresponding to an ‘aborted glacial’ (MIS 7d), underlines the complex pattern of this unusual ‘interglacial’. Overall, during the LMP, each soil complex corresponding to interglacial and early‐glacial periods from MIS 11 to MIS 5 is broadly made up of the same soil facies but exhibits a specific succession pattern or signature. Throughout the area, LPS show a huge change in both the deposition rates and the geographical extent of typical calcareous loess at the beginning of MIS 6. This so‐called ‘Loess Revolution’ probably reflects a change in the palaeogeography of the southern North Sea and eastern Channel source areas at times marked by the coalescence of the British and Scandinavian ice sheets. MIS 6 is also characterized by the oldest evidence of permafrost development in the area. In addition, this work allows the age of the Lower/Middle Palaeolithic boundary to be confirmed, with the oldest occurrence of Levallois technology being around 300 ka.

Archaeological Exploration at the Site of Tell Jidr (Karkar) in Iraq: Results and Prospects

The article is devoted to archaeological exploration conducted by researchers of the Institute of Oriental Studies, Russian Academy of Sciences in March 2023 at the site of Tell Jidr in Iraq. According to new research, the city of Tell Jidr, named Karkar in the ancient times, was a multi-layered monument that emerged on the eastern channel of the Euphrates – Iturungal – back in the Ubaid III Period, and then existed throughout the Early Dynastic I and Akkadian Periods, the Third Dynasty of Ur, into the Old Babylonian and the Kassite era. At its peak in the Parthian and Sasanian Periods, Tell Jidr, which apparently lost its original name, occupied an area of about 430 ha, stretching 4.4 km from northwest to southeast and 1.9 km from southwest to northeast, and competed with the capital of both empires, Ctesiphon. Remote sensing and ground truthing activities made it possible to clarify the internal structure of the monument, which consisted of northern and southern parts, to identify the system of city blocks and streets, public buildings (temple, palace, citadel), fortification, and to trace the evolution of urban development. Taking into account the finds of ceramic fragments decorated with stamps and fish dishes, as well as mention of Karkar in cuneiform sources of the late Achaemenid and Seleucid times, it is possible to clarify the existing ideas about the stages of the settlement’s development and to confirm the existence of the settlement in the Achaemenid and Hellenistic Periods.

50-year volume transport of the Soya Warm Current estimated from the sea-level difference and its relationship with the Tsushima and Tsugaru Warm Currents

This study provides formulae for monthly estimates of the Soya Warm Current (SYC) transport from the sea-level difference (SLD) across the Soya Strait and along the current, and creates a 50-yr data set of the SYC transport. The formulae are based on the dynamical balance both across the strait and along the current by considering the barotropic and baroclinic components. It is suggested that the barotropic and baroclinic components in transport variability are comparable in summer, whereas the barotropic component is dominant in winter. We compared the 50-year time series of the SYC transport with those of the Tsushima (TSC) and Tsugaru Warm Currents estimated from the SLDs from the viewpoint of the Japan Sea Throughflow (JSTF) system. The variabilities of the SYC and TSC transports are mostly shared for any season, showing relatively high coherence at periods of 2–5 years as well as 1 year. The winter variability of the JSTF transport originates partly from that of the SYC transport caused by the winter monsoon variability in the Sea of Okhotsk. The SYC transport is significantly correlated with the transport through the eastern channel of the TSC, but not that through the western channel. We found difficulty in extracting variability and relationships at periods longer than 5 years among the three transports estimated from the SLDs, probably due to incomplete correction of the ground movements for the sea-level data.

Gateway to the arctic: Defining the eastern channel of the Bering Strait

The Bering Strait is the sole gateway and an oceanographic bottleneck for the seasonally warm and comparatively fresh and nutrient-rich Pacific waters to flow into the Arctic, melting ice, lowering salinity, and feeding bird, mammal, and fish populations. The Diomede Islands split this small strait into two main channels, both with northward flow (in the annual mean). The eastern channel, in U.S. waters, also seasonally carries the warmer, fresher Alaskan Coastal Current. Year-round in situ mooring observations (in place since 1990 with annual servicing) show a significant flow increase in the (northward) throughflow, along with seasonal and annual fluctuations. To help with measuring and modelling water flow estimates, we created the first detailed shore-to-shore bathymetric surface of the Bering Strait’s eastern channel, located its narrowest cross-section (1.8 km2) as occurring 5–10 km south of the moorings, and quantified the cross-section across the moorings (2.0 km2), both slightly larger than previously estimated (1.6 km2). Overlaps between older (∼1950) and newer (∼2010) bathymetry data sets identified clear areas of erosion and deposition, with much of the eastern channel having eroded by > 1 m. Since the depth is uniformly ∼ 50 m across much of the eastern channel, the 1 m of erosion that we quantified would only slightly (2 %) increase the sizes of the cross-sections. Much of the seafloor is hard substrate and probably composed of cobbles, but we hypothesize that friction from strong (∼1 + knot) seafloor currents is the most likely explanation for the erosion that we observed. In softer and siltier areas, the bathymetry showed additional evidence of potential current impacts in the form of small seafloor waves (∼0.5 to ∼ 1.0 m tall) and a shore-parallel bar offshore of Cape Prince of Wales Spit. There are large (∼2 m tall) seafloor waves seaward of Cape Prince of Wales Shoal. A previously undescribed (∼1 to 2 km wide, ∼4 m deep) seafloor channel of unknown origin occurred along a linear north/south axis for the full 75 km extent of the bathymetric surface. The southern end of this seafloor channel was near the end of three larger seafloor channels extending westerly out of nearby Norton Sound, suggesting a common origin. These Norton Sound channels may be paleodrainages, as their eastern ends point toward Seward Peninsula inlets with large drainages where paleoglaciers were reported to have existed, but the morphology of these channels is also consistent with tidal channels.

127I and 129I species in the English Channel and its adjacent areas: Uncovering impact on the isotopes marine pathways

Radioactive iodine-129 has been released from the La Hague nuclear fuel reprocessing facility (NRF) into the English Channel, but the distribution and transformation of the isotope species, and environmental consequences have not been fully characterized in the Channel. Here we present data on iodine isotopes (129I and 127I) species in surface water of the English Channel and the southern Celtic Sea. Compared to 127I species, the concentrations of 129I− and 129IO3− show more variations, but iodate is the major species for both 129I and 127I. Our data provide new information regarding iodide-iodate inter-conversion showing that water dilution and mixing are the main factors affecting the 127I and 129I species distribution in the Channel. Some reduction of iodate occurs within the English Channel and mainly in the west part because of biotic processes. The 129I species transformation is overall insignificant, especially in the eastern Channel, where a constant value of 129IO3−/129I is observed, which might characterize the La Hague wastewater signal. In the Celtic Sea, oxidation of iodide can be traced by 127I and 129I species. On a larger scale, 129I generally experienced an oxidation process in the Atlantic Ocean, while in the coast of shallow shelf seas, new produced 129I− can be identified, especially in the German Bight and the Baltic Sea. The data of 129I species in the English Channel can provide estimate of redox rates in a much broader marine areas if the transit time of 129I from La Hague is well-defined. Furthermore, estimate of inventories for 129I and its species in the Channel, and fluxes of 129I species from the English Channel to the North Sea add important information to the geochemical cycle of 129I.

Evolution of submarine channel morphology in intra-slope mini-basins: 3D-seismic interpretation from offshore Niger delta

The morphological characteristics of a submarine channel system, within buried intra-slope mini-basins in the offshore Niger Delta have been investigated on 3D seismic data. The studied submarine channel named Amaku Channel Levee System (ACLS) initiated after avulsion of a feeder channel called Amaku Major System (AMS). The ACLS runs across three folds (A, B, and C), related to mobile shale deformation, being underlain by mass transport complexes (MTCs), lobes, and levees. From three defined channel reaches (upper, middle, and lower reaches), we have used seismic facies description, channel architecture characterization and quantitative analyses to decipher the spatial and temporal evolution of the channel levee system. Our results reveal that the western channel margin was controlled by structural barriers associated with mobile shale deformation, while the eastern channel margin was influenced by depositional barriers linked to levees and mass transport complexes (MTCs). We argue that the depositional barriers are in some cases more efficient than the structural barriers in controlling channel pathways, since pre-channel sediments confine the channel elements and divert them against positive reliefs. Seismic observations show that channels migrate from folds to structural lows causing flow stripping processes. Downstream variations of morphological parameters (such as sinuosity, width, and levee width), indicate that pre-existing deposits prevented these basin-ward migrations, driving straightening and narrowing of the channel system. This study reveals that submarine channels can undergo dramatic morphological and stratigraphic changes in structurally complex areas because of the configuration of sidewall reliefs, which is controlled, in turn, by the interplay between structural deformation and pre-channel deposition.

Long-term variation in volume transport of the Tsushima warm current estimated from ADCP current measurement and sea level differences in the Korea/Tsushima Strait

ADCP current data and sea level data from tide gauges and satellite altimetry were used in order to analyze long-term variation of the Tsushima Warm Current (TWC) volume transport passing through the Korea/Tsushima Strait. The annual mean transport of the TWC estimated from ADCP current measurement for about 17 years (1997–2013) is 2.64 ± 0.41 Sv (Sv = 106 m3s−1) in the Korea/Tsushima Strait, 1.53 ± 0.36 Sv (about 58% of the total transport) in the western channel, and 1.11 ± 0.14 Sv (about 42%) in the eastern channel. The TWC shows the minimum transport (1.74 Sv) in January and the maximum transport (3.10 Sv) in October, with seasonal variation of up to 1.36 Sv (51.5% of the annual mean transport). The seasonal variation of the total TWC transport in the Korea/Tsushima Strait is mainly similar to that in the western channel. The annual mean transport of the TWC and its seasonal variation in the Korea/Tsushima Strait, the western and eastern channels are all similar in three datasets (ADCP, tide gauge, satellite altimetry). The annual mean volume transport of the TWC estimated from long-term tide gauge data was 2.57 ± 0.37 Sv (total volume transport) for 44 years (1975–2018) in the Korea/Tsushima Strait, 1.51 ± 0.32 Sv in the western channel and 1.06 ± 0.14 Sv in the eastern channel. Long-term variation of the TWC transport shows a decreasing trend for 1975 to 1988, and an increasing trend from 1989 to 2018. For the latter period (1989 to 2018), monthly transport tends to increase in all months throughout the years, showing a greater increase, especially in spring and summer months. The increase of the transport in the eastern channel was about 2.8 times larger than that in the western channel. It is suggested that the increasing trend of the TWC transport since 1989 is related to the Pacific Decadal Oscillation (PDO), which has been changed to negative direction since mid-1980s. During the period when the negative PDO index is strong, the negative wind stress curl weakens in the mid-latitudes of the North Pacific, and the Kuroshio in the East China Sea also weakens. As a result, the flow is strengthened toward the Korea/Tsushima Strait, increasing the TWC transport.

Addressing the Governance of Harmful Algal Bloom Impacts: A Case Study of the Scallop Fishery in the Eastern French Coasts of the English Channel

Harmful Algal Blooms (HAB) are phenomena that result from alterations to ecosystems. Due to their potential toxicity, the level of danger depends on the species concerned, their frequency and intensity. They can cause impacts on biodiversity and on the anthropic activities that take place in maritime and coastal areas. Primary industries such as shellfish fisheries are mainly affected. To deal with this issue, the French administration has built a governance system based on two pillars. The first relies on a water quality monitoring system that assesses the risks of HAB contamination of coastal waters. The second is a regulatory system of production and commercial bans of seafood products from the impacted areas. This public action has two objectives. The first is human health-related and aims to protect consumers of seafood. The second is economic-based and aims to minimize the economic impacts associated with the commercial bans suffered by the businesses concerned. These two objectives may appear to be antagonistic. Using the case study of the French scallop fishery in the eastern Channel and based on an analysis of the commercial bans associated with HAB and associated potential economic impacts, this paper analyses the governance scheme dealing with HAB events in France. The authors highlight that this governance is not only a matter of applying administrative closures when toxicity thresholds are exceeded, but is a dynamic decision-making process involving experts and the Administration that attempts to balance acceptable health risks and economic impacts.

Seasonal variability of ocean circulation near the Dotson Ice Shelf, Antarctica

Recent rapid thinning of West Antarctic ice shelves are believed to be caused by intrusions of warm deep water that induce basal melting and seaward meltwater export. This study uses data from three bottom-mounted mooring arrays to show seasonal variability and local forcing for the currents moving into and out of the Dotson ice shelf cavity. A southward flow of warm, salty water had maximum current velocities along the eastern channel slope, while northward outflows of freshened ice shelf meltwater spread at intermediate depth above the western slope. The inflow correlated with the local ocean surface stress curl. At the western slope, meltwater outflows followed the warm influx along the eastern slope with a ~2–3 month delay. Ocean circulation near Dotson Ice Shelf, affected by sea ice distribution and wind, appears to significantly control the inflow of warm water and subsequent ice shelf melting on seasonal time-scales.

Research on the continuation of mining works in the license perimeter of the Peşteana Nord quarry

Exploitation works at the North Pesteana Quarry is located in areas with mineral energy resources, and contributes to ensuring the country’s energy security, based on an efficient system of supply of primary resources, production, transport, distribution and supply, to ensure food of all consumers in terms of accessibility, availability and affordability of prices, taking into account the evolution of the quality of the environment. The exploitation surface is isolated from the protected area Jiu Corridor ROSCI0045 through the neighborhoods from the eastern limit-the regularization channel of the river Jiu and the villages Balteni, Peșteana Jiu, Cocoreni, Olari and the neighborhoods from the western limit - the villages Valea cu Apa, Pesteana de Jos, Hotaroasa, Urdari. Lignite mining works do not affect the integrity of the protected natural area; by carrying out the works, the artificial barriers between the natural and the anthropic terrain are not created. The paper presents the results of the research undertaken in 2019 through the technical expertise in File no. 14666/3/2017*, Archive of the Bucharest Tribunal [1]. Measures are proposed to prevent, reduce and, where possible, offset significant adverse effects on the environment, including: measures for the protection of water quality, air quality, protection against noise and vibration, in the field of soil and subsoil quality, biodiversity and measures for the rehabilitation of the land for its subsequent use, etc.

Long-term morphodynamic evolution in the Modaomen Estuary of the Pearl River Delta, South China

Anthropogenic activities and natural disturbances will cause large-scale changes in the morphology of estuarine systems. Studies of estuarine morphology tended to focus on a single driving factor, however, the intertwined effects (e.g., land reclamation, sand excavation, tides, waves, runoff) are rarely mentioned in the literature. This work characterizes and conceptualizes the morphodynamics of the Modaomen Estuary (ME), the largest estuary in the Pearl River Delta (PRD), China, based on Landsat satellite imagery, high-resolution bathymetry survey data, and in situ hydrographic measurements. The morphodynamic evolution of the ME since the 1970s–2010s is analyzed with respect to planform configuration and bathymetry. Quantification of estuarine hydrodynamic and sediment parameters for the most recent years indicates that the ME has transformed from a traditional fluvial- and tide-dominated estuary into a fluvial- and wave-dominated estuary. Ocean currents intrude along the eastern channel and draw down along the western channel, in which estuarine flow deflection is induced by the combined effect of upstream runoff, coastal waves, and littoral currents. Furthermore, a life-cycle model of the morphological migration of the ME is presented by synthesizing hydrodynamics and sediment dynamics. This conceptual model of three geomorphological states clearly shows that the main channel experiences a life cycle covering several decades, from the origin of the main channel to its bifurcation into two distributaries, and finally a recovery and westward deflection of the main channel. The cognition of the appearance and disappearance with one sandbar and two channels will be helpful in numerical modeling of estuary evolution, and it also has important implications for the regulation of estuarine regions, hazard prevention and channel navigability.

Pathways, Volume Transport, and Seasonal Variability of the Lower Deep Limb of the Pacific Meridional Overturning Circulation at the Yap-Mariana Junction

The lower deep branch of the Pacific Meridional Overturning Circulation (L-PMOC) is responsible for the deep-water transport from Antarctic to the North Pacific and is a key ingredient in the regulation of global climate through its influence on the storage and residence time of heat and carbon. At the Pacific Yap-Mariana Junction (YMJ), a major gateway for deep-water flowing into the Western Pacific Ocean, we deployed five moorings from 2018 to 2019 in the Eastern, Southern, and Northern Channels in order to explore the pathways and variability of L-PMOC. We have identified three main patterns for L-PMOC pathways. In Pattern 1, the L-PMOC intrudes into the YMJ from the East Mariana Basin (EMB) through the Eastern Channel and then flows northward into the West Mariana Basin (WMB) through the Northern Channel and southward into the West Caroline Basin (WCB) through the Southern Channel. In Pattern 2, the L-PMOC intrudes into the YMJ from both the WCB and the EMB and then flows into the WMB. In Pattern 3, the L-PMOC comes from the WCB and then flows into the EMB and WMB. The volume transports of L-PMOC through the Eastern, Southern, and Northern Channels all exhibit seasonality. During November–April (May–October), the flow pathway conforms to Pattern 1 (Patterns 2 and 3), and the mean and standard deviation of L-PMOC transports are −4.44 ± 1.26 (−0.30 ± 1.47), −0.96 ± 1.13 (1.75 ± 1.49), and 1.49 ± 1.31 (1.07 ± 1.10) Sv in the Eastern, Southern, and Northern Channels, respectively. Further analysis of numerical ocean modeling results demonstrates that L-PMOC transport at the YMJ is forced by a deep pressure gradient between two adjacent basins, which is mainly determined by the sea surface height (SSH) and water masses in the upper 2,000-m layer. The seasonal variability of L-PMOC transport is attributed to local Ekman pumping and westward-propagating Rossby waves. The L-PMOC transport greater than 3,500 m is closely linked to the wind forcing and the upper ocean processes.

The last 750 ka in loess–palaeosol sequences from northern France: environmental background and dating of the western European Palaeolithic

ABSTRACTThis study presents an overview of Middle Pleistocene loess–palaeosol sequences (LPS) in northern France and discusses the palaeoclimatic significance of the pedosedimentary record in the context of western European LPS and of global climatic cycles for the last 750 ka. In this area, the oldest loess deposits (early Middle Pleistocene) are preserved in sedimentary traps (leeward scarps of fluvial terraces and dissolution sinkholes). They result from local deflation processes reworking Pleistocene sandy fluvial deposits or relicts of Tertiary sands. A large extension of typical calcareous loess over the landscape, the Loess Revolution, is then observed during MIS 6, with heavy mineral assemblages testifying to long‐distance transport from the polar desert area of the dried eastern Channel. A correlation scheme is proposed between the global records of northern France in continental environments and both global palaeoclimatic records and other main western European LPS. After 30 years of research, northern France LPS stand as a fundamental archive of the impact of interglacial–glacial climatic cycles as well as millennial events. Finally, these works provide a robust chronoclimatic framework for the study of the western European Late Acheulean and Middle Palaeolithic and for the relative dating of the various fluvial terraces that they fossilise.

Remote Sensing of Spatial-Temporal Distribution of Suspended Sediment Concentrationin East Dongting Lake, China

Three Landsat 8 OLI scenes acquired from 2016 to 2017 were used to estimate the suspended sediment concentration (SSC) in East Dongting Lake, China. The results show that SSC in East Dongting Lake is generally low, only the SSC of sediment transport channel connecting South Dongting Lake is significantly high, and that in the west of the lake is relatively small. From 2016 to 2017, the average SSC in the eastern channel was33-120 mg/L, the average SSC in the north branch of the west area was15-43 mg/L, and the average SSC in the south branchof the west area was17-46 mg/L. Under the influence of the dilute water of the Yangtze River in flood season, the overall SSC in the lake area is lower than that in non-flood season, and the average SSCis within 40 mg/L. The variation law of SSC in lake area revealed by remote sensing is consistent with the measured data, which verifies the feasibility of this method and provides a new perspective for dynamic tracking and mastering the distribution law and variation trend of suspended sediment in East Dongting Lake.

Managing the Agri-Food System of Watersheds to Combat Coastal Eutrophication: A Land-to-Sea Modelling Approach to the French Coastal English Channel

The continental coastal waters of the Eastern Channel, from Normandy to Hauts-de-France, are subject to the major influence of unbalanced nutrient inputs from inflowing rivers. Several episodes of harmful algal blooms (HABs) compromising fishing and shellfish farming activities have been observed at the coast. For a better understanding of how the land-to-sea aquatic continuum functions, the GRAFS-RIVERSTRAHLER river biogeochemical model was implemented to cover the watersheds of 11 rivers flowing into this area (including the Seine) and chained with the ecological marine ECO-MARS3D model, applied to the French Northern coastal zone. Human activities strongly impact on the functioning of coastal ecosystems. Specifically, for these fertile soils of Northern France, intensive agricultural nitrogen (N) deliveries in excess over silica (Si) and phosphorus (P), essentially of diffuse origin, are potentially responsible for coastal eutrophication. Phosphorous is today equally supplied by diffuse and point sources, after a drastic reduction of inputs from wastewater treatment plants since the 2000s, and is better balanced regarding Si, as shown by the indicators of coastal eutrophication potential (P-ICEP versus N-ICEP). However, despite this drastic P reduction, HABs still appear repeatedly. Exploration of several scenarios of agro-food chain reorganization shows that (i) further progress in urban wastewater treatment to fully comply with current European regulations will not result in a significant reduction of nutrient fluxes to the sea, hence including HABs, and (ii) radical structural changes in agriculture, based on generalization of long and diversified organic crop rotations, reconnection of crop and livestock farming and changes in the human diet have the capacity to significantly reduce nutrient flows, coastal eutrophication and HABs.

Timing of juvenile fish settlement at offshore oil platforms coincides with water mass advection into the Santa Barbara Channel, California

Recent pathways taken by pelagic juvenile fishes to offshore oil platforms were reconstructed from remotely sensed and in situ measurements of currents and hydrography. Juvenile fishes comprised 52.8% (16,952 of 23 species) of all individuals (32,080 juveniles and adults of 35 species) observed during scuba surveys conducted about twice per week at two platforms in the eastern Santa Barbara Channel from May to August 2004. Blacksmith, Chromis punctipinnis (Cooper, 1863), and rockfishes (genus Sebastes, at least 18 taxa) comprised 95.1% of the recruits. Almost all rockfishes recruited to the deepest part of the platforms surveyed (26 and 31 m), while most blacksmith recruited in shallower waters. The onset of the recruitment season for juvenile rockfishes (genus Sebastes, Scorpaenidae) coincided with the advection of a low salinity water mass into the channel from the Southern California Bight. Before arrival of this water mass, water at the platforms resembled upwelled, high salinity water around the Point Conception region at the western channel entrance. Settlement pulses of rockfishes and blacksmith were observed during advective events when salinity decreased in the upper 40 m and currents turned northwestward or intensified in that direction. Two abundant rockfish species [bocaccio, Sebastes paucispinis Ayres, 1854, and treefish, Sebastes serriceps (Jordan and Gilbert, 1880)] showed synchronous patterns of juvenile settlement between platforms separated by 7 km. Our findings indicate that currents from the bight, rather than from central California, supplied recruits to settlement habitat in the eastern channel and that the spatial scale of connectivity for some fish populations in this region is greater than the channel itself.

Upper Ocean Distribution of Glacial Meltwater in the Amundsen Sea, Antarctica

AbstractPine Island Ice Shelf, in the Amundsen Sea, is losing mass due to increased heat transport by warm ocean water penetrating beneath the ice shelf and causing basal melt. Tracing this warm deep water and the resulting glacial meltwater can identify changes in melt rate and the regions most affected by the increased input of this freshwater. Here, optimum multiparameter analysis is used to deduce glacial meltwater fractions from independent water mass characteristics (standard hydrographic observations, noble gases, and oxygen isotopes), collected during a ship‐based campaign in the eastern Amundsen Sea in February–March 2014. Noble gases (neon, argon, krypton, and xenon) and oxygen isotopes are used to trace the glacial melt and meteoric water found in seawater, and we demonstrate how their signatures can be used to rectify the hydrographic trace of glacial meltwater, which provides a much higher‐resolution picture. The presence of glacial meltwater is shown to mask the Winter Water properties, resulting in differences between the water mass analyses of up to 4‐g/kg glacial meltwater content. This discrepancy can be accounted for by redefining the “pure” Winter Water endpoint in the hydrographic glacial meltwater calculation. The corrected glacial meltwater content values show a persistent signature between 150 and 400 m of the water column across all of the sample locations (up to 535 km from Pine Island Ice Shelf), with increased concentration toward the west along the coastline. It also shows, for the first time, the signature of glacial meltwater flowing off‐shelf in the eastern channel.

Benthic macro-faunal abundance and diversity and sediment distribution in Akhziv submarine canyon and the adjacent slope (eastern Levant Basin, Mediterranean Sea)

The Israeli coastline is generally characterized by a broad and shallow continental shelf. Akhziv submarine canyon (ASC), in its northern reach, creates a locally unique marine ecosystem. The present study is the first to investigate the benthic macro-fauna of ASC, in order to assess its importance as a potential productivity ‘hotspot’ within its ultra-oligotrophic surroundings. Seven research cruises were conducted during 2010-2013, along ASC’s two channels and at iso-bathic control sites on the adjacent slope (AS), encompassing 8 sampling stations, at depths of 40-450 m. Bottom samples were collected by a Van Veen Grab, gravity corer and a GOMEX box corer. The infauna (≥500 µm) were counted and identified to the lowest possible taxonomic level. Sediments were analysed for grain size & composition and total organic carbon concentration. Mean benthic macro-faunal abundance (individuals/500ml ± SD) was higher inside the canyon (13.0±19.4) compared to the AS (2.9±3.3) (p=0.004), as was estimated true taxon richness (Chao1): 42.2 versus 10, respectively. Sediments’ mode grain size was found to be significantly higher in ASC’s eastern channel compared to AS (p=0.028), along with sand enrichment of up to 36%. The higher macrofaunal abundance and taxon richness may relate to a more heterogeneous sea bed provided by the higher diversity in grain size existing inside ASC. A relatively rich benthic realm, such as that observed in the ASC, may serve as a refuge for certain species and by hosting a relatively diverse assemblage, stands a better chance of adapting to changing conditions such as climate change.