Commercial bottom trawling: a driver of deep seascape evolution in the Anthropocene?

EGU General Assembly 2013, 7-12 April, 2013, Vienna, AustriaThe offshore displacement of bottom trawling fleets has raised concerns over the impact of this human activity on deep-sea ecosystems and associated living resources, which are characterized by a lower resilience than shallow water correlatives. However, the effects of bottom trawling on sediment remobilization across continental margins and on the alteration of seafloor morphology still remain largely unaddressed. We present a compilation of results from studies conducted during the last decade in the La Fonera (Palamós) submarine canyon (NW Mediterranean Sea), where a bottom trawling fishing fleet is active on a daily basis at depths from 400 to 800 m. Deployments of mooring lines equipped with punctual and profiling current-meters, turbidimeters and sediment traps have documented that trawling gears passing along the canyon flanks generate daily sediment gravity flows, implying a periodic sediment removal from fishing grounds. These sediment-laden flows are able to reach the main canyon axis and progress to a minimum depth of 1200 m. Also, sediment accumulation rates in the lower canyon have increased since the industrialization of the local trawling fleet (1970s), suggesting a human-induced enhancement of along-canyon transfer of sediments from the fishing grounds to greater depths. Sedimentological and 210Pb analysis of interface sediment cores collected from the canyon flanks confirm that widespread erosion and stirring of surface sediments is notable on trawled areas when compared to control (untrawled) sites at similar depths. This chronic reworking and removal of surface sediments from trawling grounds has ultimately led to modifications of the seafloor morphology over large spatial scales, as revealed by high-resolution multibeam bathymetry and Vessel Monitoring Systems (VMS) data sets. Untrawled canyon flank segments are dominated by a dense network of tributary valleys that progress upslope from the main canyon axis, reaching up to five orders of bifurcation. Such complex morphology is missing in the trawled depth range and slightly below, where the sea floor becomes smoother and only the main branches of the tributary valley networks are preserved. Given the global dimension of commercial bottom trawling, our findings suggest that this human activity may have become a significant driver of sediment dynamics and seascape evolution over substantial parts of the world's upper continental slopesPeer Reviewe

Transient erosion in the Valencia Trough turbidite systems, NW Mediterranean Basin

12 pages, 9 figuresSubmarine canyons can efficiently drain sediments from continental margins just as river systems do in subaerial catchments. Like in river systems, submarine canyons are often arranged as complex drainage networks that evolve from patterns of erosion and deposition. In the present paper we use a morphometric analysis of submarine canyon-channel long-profiles to study the recent sedimentary history of the Valencia Trough turbidite system (VTTS) in the NW Mediterranean Sea. The VTTS is unique in that it drains sediment from margins with contrasting morphologies through a single “trunk” conduit, the Valencia Channel. The Valencia Channel has been active since the late Miocene, evolving in response to Plio-Quaternary episodes of erosion and deposition. The integrated analysis of long-profiles obtained from high-resolution bathymetric data across the entire turbidite system shows evidence for transient canyon incision in the form of knickpoints and hanging tributaries. Multiple factors appear to have triggered these periods of incision. These include a large debris flow at 11,500 yr BP that disrupted the upper reaches of the VTTS and glacio-eustatic lowstands that forced shifting of sediment input to the VTTS. Based on these inferences, long-term time-averaged incision rates for the Valencia Channel have been estimated. The evidence we present strongly suggests that Foix Canyon has played a key role in the drainage dynamics of the VTTS in the past. This study builds conceptually on a recent modeling study that provides a morphodynamic explanation for the long-term evolution of submarine canyon thalweg profiles. The procedure and results from this work are of potential application to other submarine sediment drainage systems, past and present, including those containing mid-ocean type valleys like the Valencia ChannelThis research was supported by the HERMIONE project, EC contract 226354-HERMIONE, funded by the European Commission's Seventh Framework Programme, and the HERMES Project, EC contract GOCE-CT-2005-511234, funded by the European Commission's Sixth Framework Programme under the priority “Sustainable Development, Global Change and Ecosystems”. It has also benefited from inputs by the PROMETEO (CTM2007-66316-C02-01/MAR), EDINSED3D (CTM2007-64880/MAR), and the GRACCIE CONSOLIDER (CSD2007-00067) projects, funded by the Spanish RTD Programme. GRC Geociències Marines is supported by Generalitat de Catalunya “Grups de Recerca Consolidats” grant 2009 SGR 1305Peer reviewe

A submarine volcanic eruption leads to a novel microbial habitat

Postprin

Efectes de la pesca d’arrossegament en els sediments dels canyons submarins catalans

Bottom trawling is a nonselective commercial fishing technique whereby heavy nets and gear are pulled along the seafloor, modifying the physical properties of seafloor sediments and altering natural sediment fluxes. Most studies addressing the physical disturbances of trawl gear on the seabed have been undertaken in coastal and shelf environments, where the capacity of trawling to modify the seafloor sediments coexists with high-energy natural processes driving sediment erosion, transport and deposition. Recent studies conducted on the Catalan margin have demonstrated that on continental slopes —where the sediment dynamics is less energetic— the reworking of the deep seafloor by bottom trawling produces periodic resuspension of surface sediments, and ultimately modifies the shape of the submarine landscape over large spatial scales. Trawling-induced sediment displacement and removal from fishing grounds causes the morphology of the deep seafloor to become smoother over time, reducing its original complexity. These results suggest that during the last decades, following the industrialization of fishing fleets, bottom trawling has become an important driver of deep seascape evolution.Fil: Puig, Pere. Consell Superior d’Investigacions Científiques. Institut de Ciències del Mar; EspañaFil: Canals, Miquel. Universidad de Barcelona; EspañaFil: Company, Joan B.. Consell Superior d’Investigacions Científiques. Institut de Ciències del Mar; EspañaFil: Martín de Nascimento, Jacobo. Consell Superior d’Investigacions Científiques. Institut de Ciències del Mar; España. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; ArgentinaFil: Amblas, David. Universidad de Barcelona; EspañaFil: Lastras, Galderic. Universidad de Barcelona; EspañaFil: Palanques, Albert. Consell Superior d’Investigacions Científiques. Institut de Ciències del Mar; EspañaFil: Calafat, Antoni M.. Universidad de Barcelona; Españ

The International Bathymetric Chart of the Arctic Ocean Version 4.0

Funder: The Nippon Foundation of Japan, grant Seabed 2030Funder: Open access funding provided by Stockholm UniversityAbstract: Bathymetry (seafloor depth), is a critical parameter providing the geospatial context for a multitude of marine scientific studies. Since 1997, the International Bathymetric Chart of the Arctic Ocean (IBCAO) has been the authoritative source of bathymetry for the Arctic Ocean. IBCAO has merged its efforts with the Nippon Foundation-GEBCO-Seabed 2030 Project, with the goal of mapping all of the oceans by 2030. Here we present the latest version (IBCAO Ver. 4.0), with more than twice the resolution (200 × 200 m versus 500 × 500 m) and with individual depth soundings constraining three times more area of the Arctic Ocean (∼19.8% versus 6.7%), than the previous IBCAO Ver. 3.0 released in 2012. Modern multibeam bathymetry comprises ∼14.3% in Ver. 4.0 compared to ∼5.4% in Ver. 3.0. Thus, the new IBCAO Ver. 4.0 has substantially more seafloor morphological information that offers new insights into a range of submarine features and processes; for example, the improved portrayal of Greenland fjords better serves predictive modelling of the fate of the Greenland Ice Sheet

Physiographic influences on dense shelf-water cascading down the Antarctic continental slope

Predicting the source areas for Antarctic Bottom Water (AABW) requires knowledge of how cold, dense water masses form and move from the Antarctic shelves to the continental slope. Here we use a review of nearly 50 years of direct hydrographic observations to infer the main broad-scale influences on the distribution of dense shelf-water (DSW) overflows that cascade down the continental slope around Antarctica. The dynamics and distribution of large ice shelves, coastal polynyas and the physiography of the Antarctic continental shelves are each considered. The catalogue we present increases the number of DSW observations to 26, adds 20 additional stations where this process is likely to have occurred, and identifies 41 areas where DSW appears to be absent. Our pan-Antarctic, multi-decadal review enhances the understanding of the formation and export of DSW and highlights the variability and complexity of ice-ocean systems on high-latitude continental margins. The study also provides a context for understanding recent episodes of Antarctic ice-shelf instability, and how the relationship between DSW and AABW may evolve with climatic and oceanographic changes.EU Marie Curi

Antarctic continental shelf break (shapefile)

Antarctic continental shelf break in shapefile format based on IBCSO v. 1.0 (Arndt et al., 2013), manually digitised at a spatial scale of 1:300,000. It is created with the guidance of bathymetric contours at 50 m intervals and slope-gradient maps. In areas permanently covered by ice, the shelf break is linearly interpolated between the two closest ice-free points

Sedimentary morphodynamics of passive siliciclastic continental margins

181 pages.-- Memòria de tesi doctoral presentada per David Amblàs i Novellas per optar al grau de Doctor en Ciències de la Terra de la Facultat de Geologia de la Universitat de Barcelona (UB), realitzada sota la direcció del Dr. Miquel Canals i Artigas i del Dr. Roger Urgelés i Esclasans de l'Institut de Ciències del Mar (ICM-CSIC)“El present és la clau del passat”. James Hutton (1788), amb aquesta prou coneguda asserció uniformista, posà els fonaments pel desenvolupament de la investigació geològica moderna des de la perspectiva actualista. L’estratigrafia es val d’aquest principi per interpretar l’origen de les formacions geològiques a partir de l’observació de processos i geometries actuals i subactuals. Alhora, la geomorfologia estudia els processos afaiçonadors del relleu per conèixer l’origen i l’evolució del paisatge actual. Conceptualment, aquesta Tesi se situa a cavall entre l’estratigrafia i la geomorfologia amb l’objectiu general de reconèixer el per què i el com de la variabilitat morfosedimentària dels marges continentals passius silicoclàstics a llarg termini. Per atènyer aquest objectiu adoptem la hipòtesi de partida següent: la variabilitat morfològica dels marges continentals silicoclàstics passius pot ésser classificada per categories de forma objectiva i sistemàtica. Les diferències morfològiques observades responen principalment a l’acció d’uns pocs processos sedimentaris claus. Els mètodes i conceptes emprats en aquesta Tesi són propis de la hidrodinàmica i la sedimentologia. L’observació detallada de la morfologia i l’estratigrafia dels marges continentals, junt amb l’estudi dels processos hidrodinàmics que les han generades i l’anàlisi de la variabilitat espaciotemporal de les condicions ambientals en què s’han format, permet establir lleis de transport geomòrfic, altrament dites lleis de la morfodinàmica. En els successius capítols d’aquesta Tesi abordem aquests aspectes mitjançant l’anàlisi de dades geofísiques de reconeixement del fons i del subsòl marins, amb un especial èmfasi en les xarxes de drenatge del talús continental i la conca profunda. Els resultats d’aquesta anàlisi se sintetitzen en el plantejament d’un model morfodinàmic predictiu sobre la forma del perfil longitudinal dels canyons submarins. Aquest model dóna peu a discutir sobre transitorietat i equilibri en les formes de drenatge observades a les dades geofísiques considerades. Així doncs, en aquest treball advoquem per la complementarietat i interdependència de les anàlisis observacionals i la modelització basada en la formulació teòrica de processos. Els principals resultats obtinguts en aquest treball demostren la possibilitat d’extreure informació sobre l’evolució de les conques sedimentàries a partir de l’estudi de les seves morfologies, tan modernes com relictes i fòssils, i indiquen la necessitat d’entendre els canyons submarins com a sistemes capaços d’evolucionar a partir de mecanismes netament deposicionals, a més dels mecanismes erosius ja prou coneguts. Aquests resultats es poden traduir en una millora de les prediccions estratigràfiques al talús continental, en un millor coneixement de la distribució de reservoris sedimentaris d’hidrocarburs o aigua en aquests ambients, i a replantejar els models establerts sobre el desenvolupament dels canyons submarins a escala globalAquesta Tesi ha estat realitzada al Departament d’Estratigrafia, Paleontologia i Geociències Marines de la Universitat de Barcelona, dins el Grup de Recerca en Geociències Marines amb reconeixement de la Generalitat de Catalunya com a Grup de Recerca Consolidat (refs. 2001SGR-00076 i 2009 SGR 1305). Durant el període d’elaboració de la Tesi el doctorand ha gaudit d’una beca predoctoral de Formación de Profesorado Universitario (FPU) del Ministerio de Educación y Ciencia (ref. AP2002-1012), d’una Beca de Col∙laboració en Projectes de Recerca de la UB (projecte TRANSFER, ref. 037058) i de contractes com a ajudant d’investigació en els projectes HERMES (ref. GOCE-CT-2005-511234-1), HERMIONE (EC Contract 226354) i GRACCIE-CONSOLIDER (ref. CSD2007-00067). L’estada que el doctorand realitzà a la Universitat de Duke (Carolina del Nord, Estats Units d’Amèrica) fou finançada pel Ministerio de Educación y Ciencia dins el programa Estancias Breves associat a la beca FPU (ref. AP2002-1012). Altres beques que el doctorand ha rebut per realitzar estades breus i assistir a congressos han estat concedides per la European Science Foundation (refs. 69103 i 04052007), per l’American Geophysical Union (ref. ER88585) i per la Facultat de Geologia de la Universitat de Barcelona a través del programa d’Ajuts a la Recerca de la Comissió de Recerca de la Facultat. A més dels projectes esmentats anteriorment, la recerca que es presenta en aquesta Tesi ha estat finançada pels projectes COSTA (ref. EVK3-1999-00028), EUROSTRATAFORM (ref. EVK3-CT-2002-00079), EURODELTA (ref. EVK3-CT-2002-1020001), EURODOM (ref. HPRN-CT-2002-00212), PRODELTA (ref. REN2002-02323), WEST-MED (ref. REN2002-11216-E MAR), TopoMed (ref. CGL2008-03474-E/BTE), SPACOMA (ref. REN2002-11217-E MAR), EUROMARGINS (ref. ERAS-CT-2003-980409) d’ESF-EUROCORES, U.S. National Science Foundation (ref. OCE-04-05515), PROMETEO-2 (ref. CTM2007-66316-C02-01/MAR), EDINSED3D (ref. CTM2007-64880/MAR) i DOS MARES (ref. CTM2010-21810-C03-01/MAR)Peer Reviewe

Review of dense shelf water observations around Antarctica (presence or absence)

Shapefile with a review of georeferenced water column observations of dense shelf water flows around Antarctica, including observation number (N), location, type of observation (T; A: active, P: passive, N: Nil), date of observation, method of acquisition and reference. Different publications that refer to the same station site are grouped under the same observation number while stations separated by less than 1º of arc are coded with the same number but different letter. B&C (following Baines and Condie, 1998). ADCP is Acoustic Doppler Current Profiler; LADCP is Lowered ADCP; CTD is Conductivity Temperature Depth; XCTD is expandable CTD; XBT is Expandable Bathy Thermograph; SACM is Smart Acoustic Current Meter (suspended through the ice); CTD-ES is CTD installed on elephant seals. Moorings include current meters, and temperature and salinity sensors. For details about the instrumentation see the original references