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The paper by Hannah et al. (this volume) invokes foodweb theory and the ideas of complexity theory to guide the construction of models of intermediate complexity, which sacrifice explicit process detail to increase the number of interacting components of the system and simulate the web of feedback loops. This approach has its merits, if best practice modelling guidelines are followed and the method is used well. However, if this is not the case then the fundamental weakness of the intermediate model approach is that it may end up producing models that are over general and therefore not useful. To make the most of the intermediate complexity approach it is essential to keep the tenets of the middle-out approach in mind. Under the middle-out approach computational models are constructed and tested at the levels where we have the most detailed information, building on our existing knowledge and data and coupling a hierarchy of models rather than being swamped in a morass of detail or missing key feedbacks through over-generality. International audience

Methods based on CO2 and chlorofluorocarbon (CFC) data are used to describe and evaluate the anthropogenic CO2 (Cant) concentrations, Cant specific inventories, and Cant storage rates in the Equatorial Atlantic Ocean. The Cant variability in the water masses is evaluated from the comparison of two hydrographic sections along 7.5°N carried out in 1993 and 2010. During both cruises, high Cant concentrations are detected in the upper layers, with values decreasing progressively towards the deep layers. Overall, the Cant concentrations increase from 1993 to 2010, with a large increment in the upper North Atlantic Deep Water layer of about 0.18 ± 0.03 μmol kg−1 y−1. In 2010, the Cant inventory along the whole section amounts to 58.9 ± 2.2 and 45.1 ± 2.0 mol m−2 using CO2 and CFC based methods, respectively, with most Cant accumulating in the western basin. Considering the time elapsed between the two cruises, Cant storage rates of 1.01 ± 0.18 and 0.75 ± 0.17 mol m−2 y−1 (CO2 and CFC based methods, respectively) are obtained. Below ∼1000 m, these rates follow the pace expected from a progressive increase of Cant at steady state; above ∼1000 m, Cant increases faster, mainly due to the retreat of the Antarctic Intermediate Waters This work was funded by the 7th Framework Programme (EU FP7 CARBOCHANGE, under grand agreement no. 264879) and by the Spanish Ministry of Economy and Competitiveness through Projects GHGMOC (CTM2009-07574-E), MOC2 (CTM2008-06438-C02-01/MAR) and ESCLAT (CTM2009-07405-E/MAR) and by the Deutsche Forschungsgemeinschaft (DFG) (M. Rhein, grant Rh25/36-1). FFP and AFR were supported by the Spanish Government and co-founded by the European Regional Development Fund (CTM2013-41048-P). 15 páginas, 4 tablas, 5 figuras, 3 apéndices.-- Proyecto Carbochange Peer reviewed

Abstract Marine litter represents a widespread type of pollution in the World’s Oceans. This study is based on direct observation of the seafloor by means of Remotely Operated Vehicle (ROV) dives and reports litter abundance, type and distribution in three large submarine canyons of the NW Mediterranean Sea, namely Cap de Creus, La Fonera and Blanes canyons. Our ultimate objective is establishing the links between active hydrodynamic processes and litter distribution, thus going beyond previous, essentially descriptive studies. Litter was monitored using the Liropus 2000 ROV. Litter items were identified in 24 of the 26 dives carried out in the study area, at depths ranging from 140 to 1731 m. Relative abundance of litter objects by type, size and apparent weight, and distribution of litter in relation to depth and canyon environments (i.e. floor and flanks) were analysed. Plastics are the dominant litter component (72%), followed by lost fishing gear, disregarding their composition (17%), and metal objects (8%). Most of the observed litter seems to be land-sourced. It reaches the ocean through wind transport, river discharge and after direct dumping along the coastline. While coastal towns and industrial areas represent a permanent source of litter, tourism and associated activities relevantly increase litter production during summer months ready to be transported to the deep sea by extreme events. After being lost, fishing gear such as nets and long-lines has the potential of being harmful for marine life (e.g. by ghost fishing), at least for some time, but also provides shelter and a substrate on which some species like cold-water corals are capable to settle and grow. La Fonera and Cap de Creus canyons show the highest mean concentrations of litter ever seen on the deep-sea floor, with 15,057 and 8090 items km−2, respectively, and for a single dive litter observed reached 167,540 items km−2. While most of the largest concentrations were found on the canyon floors at water depths exceeding 1000 m, relatively little litter was identified on the canyon walls. The finding of litter ‘hotspots’ (i.e., large accumulations of litter) formed by mixtures of land- and marine-sourced litter items and natural debris such as sea urchin carcasses evidences an efficient transport to the floor of mid and lower canyon reaches at least. High-energy, down canyon near-bottom flows are known to occur in the investigated canyons. These are associated to seasonal dense shelf water cascading and severe coastal storms, which are the most energetic hydrodynamic processes in the study area thus becoming the best candidates as main carriers of debris to the deep. The fact that the investigated canyons have their heads at short distance (

Lanternfishes (Myctophidae) are among the most abundant, widespread, and diverse fish groups in the world ocean. They account for a significant part of oceanic fish biomass and play crucial roles in various ecosystem processes, including carbon sequestration and nutrient recycling. However, despite the increasing risks they face (e.g. global warming, plastic pollution, and exploitation of deep-sea resources), many aspects of the lanternfishes ecology still remain poorly known. Here, we investigate the species composition, vertical migration, and trophic ecology of lanternfishes in the Southwestern Tropical Atlantic (SWTA) and the influence of physicochemical factors on their horizontal structuring. We show that lanternfishes are a highly diverse and an abundant fish family of the SWTA, comprising at least 33 species and contributing 40% of all fish collected (in number). We reveal that some of these species may differ in their patterns of prey composition and migratory behaviour, leading to multidimensional niches, underestimated trophic links (e.g. gelatinous organisms), and several mechanisms to avoid competitive exclusion. At least 73% of the lanternfish species reported here seem to migrate to the surface to feed at night. Additionally, they are a central food source for mesopelagic and bathypelagic predators, thereby connecting shallow and deep-sea ecosystems. Finally, we show that the structure of lanternfish assemblages is not strongly affected by environmental conditions analysed here (i.e., throughout the thermohaline structure and current systems), leading to weak horizontal assemblage separation. International audience WOS:000724705600001

International audience

The Strait of Gibraltar is a narrow and shallow channel that controls the Mediterranean Sea thermohaline and biogeochemical balances. Strong tidal currents significantly modulate exchanges across this strait and induce an intense vertical mixing, impacting both the Mediterranean Sea and the Atlantic Ocean on a climatic scale. However, the turbulent processes controlling the tidal mixing location, timing, and magnitude remain unclear. To fill this gap, we investigate tidal mixing at the Strait of Gibraltar in yearly twin tidal and non-tidal simulations from a regional configuration of the three-dimensional numerical model MITgcm, using a high spatial resolution around the Strait of Gibraltar (1/200°, 100 vertical levels). More specifically, we investigate the model turbulence closure scheme, based on a turbulent kinetic energy budget, and illustrate that vertical buoyancy fluxes should be preferred to diapycnal diffusivities as mixing indicators. In agreement with previous literature, we find that tides strongly intensify vertical mixing and motions within the Strait of Gibraltar. We then demonstrate that tidal mixing relies on two main ingredients: a sustained vertical shear of horizontal velocities and a local weakening of stratification. In the Mediterranean layer, the former drives diapycnal mixing near the seafloor and the latter in shallower areas above the prominent sills of the strait. We also evidence the frequent but irregular occurrences of static instabilities in the vicinity of these sills. In the Atlantic layer, both vertical shear and stratification are involved in diapycnal mixing that develops along the trail of the eastward internal bore released at the Camarinal sill. At high frequency, the local weakening of stratification results from convergence and divergence patterns in the vicinity of the Camarinal and Espartel sills, feeding recirculation cells between the Atlantic and Mediterranean layers. In addition, we highlight that diapycnal mixing mainly develops during the westward tidal phase in the Mediterranean layer and the eastward tidal phase in the Atlantic layer. We conclude by proposing a revised conceptual view of tidal mixing at the Strait of Gibraltar, where tidally-induced recirculation cells play an instrumental role in transforming the exchanged water masses. Overall, this study emphasizes the relevance of a realistic representation of both tides and abrupt topography to simulate the exchanges through the Strait of Gibraltar and argues for the use of a specific tidal mixing parameterization otherwise. International audience

Abstract We analyzed the copepod assemblages over two decades (1984–2006) in a coastal ongoing time-series at Station MC in the inner Gulf of Naples (Tyrrhenian Sea, Western Mediterranean), which is part of the International network of Long-Term Ecological Research (LTER). The seasonal and interannual time courses of species abundance and composition were related to depth integrated temperature, salinity, and chlorophyll a , which provide essential information on the local environmental dynamics. Our aims were to characterize the main modes of copepod variability and to highlight possible changes occurred in the period in relation to the local environmental dynamics. Despite the great variability at seasonal and interannual scales, our site did not show evidence of discontinuities or trends in water column properties as compared to other Mediterranean sites for the same period, which we interpret as resulting from the position of Station MC that is exposed to the influence of a complex climate forcing. Abrupt changes did not appear for most of the key representative species (e.g., Acartia clausi , Centropages typicus , Paracalanus parvus , Temora stylifera , and juveniles of Clausocalanus spp./ P. parvus ) beyond the high interannual variability in the abundance patterns. A few indications suggest that our station might have acquired less coastal characters (e.g., decreasing chlorophyll a concentrations), but the signals from the copepod assemblages appeared only in rare species. A significant increase was observed in the occurrence of some typical offshore calanoids (e.g., Neocalanus gracilis , Scolecithricella spp.), while a few species typical of confined areas disappeared (e.g., Acartia margalefi , Paracartia latisetosa ). STATICO analysis showed a significant resilience in the seasonal cycle of the copepod assemblages at Station MC, even when there was high variability in the environmental parameters. While the changes recorded in the least abundant species may be indicative of long-term variations, we interpret the overall persistence of the basic community as resulting from the flexibility of coastal species to adapt to variation in environmental conditions.

A simulation based on a hydro-sedimentary model was conducted for the period between summer 2010 and spring 2012 in the Gulf of Lion (northwestern Mediterranean Sea) to understand the spatial and temporal variability of sediment transport, erosion and deposition on the continental shelf and slope. Datasets of both simulated and observed current, temperature and suspended matter from the shelf and the Cap de Creus Canyon which is the main export route towards the continental slope, were first compared to assess the reliability of the simulation. The simulation shows the massive sediment accumulation near the Rhone River mouth (∼56 % of the inputs), the accretion along the mid-shelf mud belt, and the impact of dense shelf water cascading on sediment resuspension and erosion inside the Cap de Creus Canyon. The two studied autumn–winter periods were strongly contrasted in terms of meteorological conditions and subsequent impacts on the sediment dynamics. During the first period (2010–2011) dominated by marine storms, the shelf sediment underwent strong changes, the Rhone River sediment load accumulated in a relatively small area, stock of littoral sands moved to the inner shelf (20–40 m) while inner shelf fine particles fed the mid-shelf mud belt and the upper Cap de Creus Canyon. During the second period (2011–2012) with very little marine wind and a particularly cold winter, sediment on the shelf underwent little change except for a southwestward growth of the Rhone River prodeltaic deposit. Sediment from the southwestern end of the shelf as well as from the upper Cap de Creus Canyon was flushed toward deeper reaches by dense shelf water cascading. Cascading also had a more moderate impact in the various canyons incising the continental shelf. Our work supports the view of an unbalanced sedimentary system, with a deficit mainly over the inner shelf, whose main driver is probably the strong and fast reduction of particulate matter inputs from the Rhone River (by a factor of 4 in less than one century) This study (including the PhD and Postdoc of G. Mikolajczak) was mainly funded by the AMORAD-project (grant ANR-11-RSNR-0002 of the French program Investissement d’Avenir run by the Agence Nationale de la Recherche). We also benefited from the support of the CHIFRE and DeltaRhone projects of the national EC2CO program. The simulations were performed using HPC resources from CALMIP (Grant P09115) and CINES OCCIGEN (Grant A0040110088). This research was also supported by grant PID2020-114322RB-I00 (FAR-DWO) funded by MCIN/AEI/ 10.13039/501100011033 With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S) 20 pages, 15 figures, 3 tables.-- Data availability: Data will be made available on request Peer reviewed