Major coastal storms, associated with strong winds, high waves and intensified currents, and occasionally with heavy rains and flash floods, are mostly known because of the serious damage they can cause along the shoreline and the threats they pose to navigation. However, there is a profound lack of knowledge on the deep-sea impacts of severe coastal storms. Concurrent measurements of key parameters along the coast and in the deep-sea are extremely rare. Here we present a unique data set showing how one of the most extreme coastal storms of the last decades lashing the Western Mediterranean Sea rapidly impacted the deep-sea ecosystem. The storm peaked the 26th of December 2008 leading to the remobilization of a shallow-water reservoir of marine organic carbon associated with fine particles and resulting in its redistribution across the deep basin. The storm also initiated the movement of large amounts of coarse shelf sediment, which abraded and buried benthic communities. Our findings demonstrate, first, that severe coastal storms are highly efficient in transporting organic carbon from shallow water to deep water, thus contributing to its sequestration and, second, that natural, intermittent atmospheric drivers sensitive to global climate change have the potential to tremendously impact the largest and least known ecosystem on Earth, the deep-sea ecosystem.

The Mediterranean deep sea, being isothermal and longitudinally trophic-graded, is an optimal natural benchmark to test for macro-ecological patterns of species distribution. The relevance of environment−biota interactions on deep-sea megafauna in the Mediterranean Sea, a matter still neglected, is addressed here along longitudinal and bathymetric axes. Benthic and nektobenthic megafauna were collected in the 3 basins of the Mediterranean: the western (Catalan Sea and southern Balearic), central (western Ionian) and eastern (south of Crete) basins, with an otter-trawl Maireta system and an Agassiz dredge between 1200 and 4000 m depth. Simultaneously, environmental data were collected on surface production, near-bottom physical parameters, sediment grain size and carbon content. Megafaunal biomass was higher in the Catalan Sea, decreasing eastward and with depth. Species diversity and evenness were relatively constant in the western and central Mediterranean at all depths, whereas these indices decreased with depth in the eastern Mediterranean. β-diversity analyses indicated a high species turnover between areas. The 3 basins presented significantly different environmental conditions. Sediment particulate organic carbon, surface fluorescence and sediment grain size were the 3 environmental variables that best explained the distribution of megabenthos along the longitudinal Mediterranean axis. These results show that the food supply, from either the surface or from the adjacent deepsea floor, is critical in regulating the biodiversity of deep-sea Mediterranean megafauna and that this diversity is pooled region-wide. The heterogeneity of resources may be essential in maintaining these high levels of local and regional diversity.

Seafloor sediments contain information about many large-scale processes in the ocean such as surface biological productivity, particle export and degradation, hydrothermal activity, and material transport from

Abstract. Surface sediments collected from deep basins (1018-4087 m depth) of the eastern Mediterranean Sea (Ionian Sea, southern Aegean Sea and northwestern Levantine Sea) were analyzed for aliphatic and polycyclic aromatic hydrocarbons as tracers of natural and anthropogenic inputs. Concentrations of total aliphatic hydrocarbons, n-alkanes and the unresolved complex mixture (UCM) of aliphatic hydrocarbons varied significantly, ranging from 1.34 to 49.2 µg g −1 , 145 to 4810 ng g −1 and 0.73 to 36.7 µg g −1 , respectively, while concentrations of total polycyclic aromatic hydrocarbons (PAHs) ranged between 11.6 and 223 ng g −1 . Molecular profiles of determined hydrocarbons reflect a mixed contribution from both natural and anthropogenic sources in deep-sea sediments of the eastern Mediterranean Sea, i.e., terrestrial plant waxes, degraded petroleum products, unburned fossil fuels and combustion of grass, wood and coal. Hydrocarbon mixtures display significant variability amongst sub-regions, reflecting differences in the relative importance of inputs from various sources and phase associations/transport pathways of individual hydrocarbons that impact on their overall distribution and fate. Hydrocarbon concentrations correlated significantly with the organic carbon content of sediments, indicating that the latter exerts an important control on their transport and ultimate accumulation in deep basins. Additionally, water masses' circulation characteristics also seem to influence the regional features and distribution patterns of hydrocarbons. Our findings highlight the role of deep basins/canyons as repositories of both natural and anthropogenic chemical species.

Submarine volcanic eruptions are major catastrophic events that allow investigation of the colonization mechanisms of newly formed seabed. We explored the seafloor after the eruption of the Tagoro submarine volcano off El Hierro Island, Canary Archipelago. Near the summit of the volcanic cone, at about 130 m depth, we found massive mats of long, white filaments that we named Venus's hair. Microscopic and molecular analyses revealed that these filaments are made of bacterial trichomes enveloped within a sheath and colonized by epibiotic bacteria. Metagenomic analyses of the filaments identified a new genus and species of the order Thiotrichales, Thiolava veneris. Venus's hair shows an unprecedented array of metabolic pathways, spanning from the exploitation of organic and inorganic carbon released by volcanic degassing to the uptake of sulfur and nitrogen compounds. This unique metabolic plasticity provides key competitive advantages for the colonization of the new habitat created by the submarine eruption. A specialized and highly diverse food web thrives on the complex three-dimensional habitat formed by these microorganisms, providing evidence that Venus's hair can drive the restart of biological systems after submarine volcanic eruptions.