title: Biogeochemical, Isotopic and Bacterial Distributions Trace Oceanic Abyssal Circulation.
abstract: We explore the possibility of tracing routes of dense waters toward and within the ocean abyss by the use of an extended set of observed physical and biochemical parameters. To this purpose, we employ mercury, isotopic oxygen, biopolymeric carbon and its constituents, together with indicators of microbial activity and bacterial diversity found in bottom waters of the Eastern Mediterranean. In this basin, which has been considered as a miniature global ocean, two competing sources of bottom water (one in the Adriatic and one in the Aegean seas) contribute to the ventilation of the local abyss. However, due to a recent substantial reduction of the differences in the physical characteristics of these two water masses it has become increasingly complex a water classification using the traditional approach with temperature, salinity and dissolved oxygen alone. Here, we show that an extended set of observed physical and biochemical parameters allows recognizing the existence of two different abyssal routes from the Adriatic source and one abyssal route from the Aegean source despite temperature and salinity of such two competing sources of abyssal water being virtually indistinguishable. Moreover, as the near-bottom development of exogenous bacterial communities transported by convectively-generated water masses in the abyss can provide a persistent trace of episodic events, intermittent flows like those generating abyssal waters in the Eastern Mediterranean basin may become detectable beyond the availability of concomitant measurements.
authors.affiliation: Dipartimento di Scienze Ambientali, Informatica e Statistica, Università Ca' Foscari di Venezia, Campus Scientifico, Via Torino 155, 30172 Mestre, VE, Italy.
authors.forename: Angelo
authors.initials: A
authors.lastname: Rubino
authors.affiliation: Istituto Nazionale di Oceanografia e di Geofisica Sperimentale, OGS, B.go Grotta Gigante 42/c, Sgonico, Trieste, Italy.
authors.forename: Manuel
authors.initials: M
authors.lastname: Bensi
authors.affiliation: CEN, Institut für Meereskunde, University of Hamburg, Bundesstraße 53, 20146, Hamburg, Germany.
authors.forename: Dagmar
authors.initials: D
authors.lastname: Hainbucher
authors.affiliation: Dipartimento di Scienze Ambientali, Informatica e Statistica, Università Ca' Foscari di Venezia, Campus Scientifico, Via Torino 155, 30172 Mestre, VE, Italy.
authors.forename: Davide
authors.initials: D
authors.lastname: Zanchettin
authors.affiliation: Dipartimento di Scienze per gli Alimenti, la Nutrizione e l'Ambiente, Università degli Studi di Milano, Milan, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: Mapelli
authors.affiliation: Department of Environmental Sciences, "Jožef Stefan" Institut, Jamova 39, 1000, Ljubljana, Slovenia.
authors.forename: Nives
authors.initials: N
authors.lastname: Ogrinc
authors.affiliation: Dipartimento di Scienze Molecolari e Nanosistemi, Università Ca' Foscari di Venezia, Campus Scientifico, Via Torino 155, 30172, Mestre, VE, Italy.
authors.forename: Davide
authors.initials: D
authors.lastname: Marchetto
authors.affiliation: Dipartimento di Scienze per gli Alimenti, la Nutrizione e l'Ambiente, Università degli Studi di Milano, Milan, Italy.
authors.forename: Sara
authors.initials: S
authors.lastname: Borin
authors.affiliation: Istituto Nazionale di Oceanografia e di Geofisica Sperimentale, OGS, B.go Grotta Gigante 42/c, Sgonico, Trieste, Italy.
authors.forename: Vanessa
authors.initials: V
authors.lastname: Cardin
authors.affiliation: Department of Environmental Sciences, "Jožef Stefan" Institut, Jamova 39, 1000, Ljubljana, Slovenia.
authors.forename: Vesna
authors.initials: V
authors.lastname: Fajon
authors.affiliation: Department of Environmental Sciences, "Jožef Stefan" Institut, Jamova 39, 1000, Ljubljana, Slovenia.
authors.forename: Milena
authors.initials: M
authors.lastname: Horvat
authors.affiliation: Dipartimento di Fisica, Università di Torino, Torino, Italy.|Osservatorio Astrofisico di Torino, INAF, Pino Torinese, Italy.
authors.forename: Carla
authors.initials: C
authors.lastname: Taricco
authors.affiliation: Dipartimento di Scienze Molecolari e Nanosistemi, Università Ca' Foscari di Venezia, Campus Scientifico, Via Torino 155, 30172, Mestre, VE, Italy.
authors.forename: Franco
authors.initials: F
authors.lastname: Baldi
mesh_terms: D001419:Bacteria / Q000378:metabolism*; D044822:Biodiversity; D005843:Geography; D019083:Mediterranean Region; D009792:Oceans and Seas; D010103:Oxygen Isotopes; D014867:Water; D014872:Water Movements
chemical_list: D010103:Oxygen Isotopes; D014867:Water