Dropstones in the Mar del Plata Canyon Area (SW Atlantic): Evidence for Provenance, Transport, Distribution, and Oceanographic Implications

A variety of gravel- to cobble-sized rocks, recovered from the Mar del Plata (MdP) Canyon area (Western South Atlantic at 38°S) and interpreted as ice-rafted debris, represent the first evidence that large icebergs have floated in the Falkland (Malvinas) Current from the southern polar high latitudes far northward. Detailed petrographic analyses identified the Antarctic Peninsula, sub-Antarctic islands in the Scotia Sea, and Tierra del Fuego as plausible source areas. The drift process could have started as early as at the beginning of the last deglaciation, according to an age obtained from a cold-water coral fragment associated with one of the dropstones. At the end of the Last Glacial Maximum, large icebergs have been supplied to the Antarctic Circumpolar Current, captured by those ocean current branches that circumvent the Falkland (Malvinas) Islands and entered the Argentine Margin. When the iceberg fleets approached the Brazil-Falkland (Malvinas) Confluence Zone with its steep latitudinal temperature gradient, the icebergs got oceanographically trapped and melted off rapidly. The sediment load sinking down to the seafloor formed a dropstone blanket particularly where the MdP Canyon had incised into the continental slope. Here, mass-flow processes, induced by local slope instability, and along-slope sediment resorting, due to the erosional effects of strong and persistent contouritic bottom currents, favored local enrichment in dropstones in the form of a loose, coarse sediment drape inside morphological depressions. The bottom current velocity would be locally strong enough to rework this sediment, leaving coarse rafted debris as a lag deposit.Fil: Bozzano, Graziella. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Cerredo, Maria Elena. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; ArgentinaFil: Remesal, Marcela Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; ArgentinaFil: Steinmann, L.. Universitat Bremen; AlemaniaFil: Hanebuth, Till J.J.. Coastal Carolina University; Estados UnidosFil: Schwenk, T.. Universitat Bremen; AlemaniaFil: Baqués, Michele. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval; Argentina. Ministerio de Defensa. Armada Argentina. Dirección Gral. de Investigación y Desarrollo de la Ara. Dirección de Investigación de la Armada; ArgentinaFil: Hebbeln, Dierk. Universitat Bremen; AlemaniaFil: Spoltore, Daniela Veronica. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; ArgentinaFil: Silvestri, Ornella. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval; Argentina. Universidad de Buenos Aires; ArgentinaFil: Acevedo, Rogelio Daniel. Universidad Nacional de Tierra del Fuego, Antártida e Islas del Atlántico Sur. Instituto de Ciencias Polares, Ambientales y Recursos Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; ArgentinaFil: Spiess, V.. Universitat Bremen; AlemaniaFil: Violante, Roberto Antonio. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval; ArgentinaFil: Kasten, Sabine. Universitat Bremen; Alemania. Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research; Alemani

Acoustic Doppler Current Profiler (ADCP) data of sites GeoB22716-1, GeoB22717-1 and GeoB22732-1 during RV SONNE cruise SO260/1 and rock descriptions

This data set include (1) the detailed petrographic description of the diagnostic rock types used to infer the source areas of the material recovered from the Mar del Plata Canyon area (Western South Atlantic at 38° S) at Sites GeoB13830, GeoB22712, GeoB22717 and L45; and (2) the Acoustic Doppler Current Profiler (ADCP) data obtained from Sites GeoB22716, GeoB22717 and GeoB22732. A variety of gravel- to cobble-sized rocks, recovered from the Mar del Plata Canyon area and interpreted as ice-rafted debris, represents the first evidence that large icebergs have floated in the Falkland (Malvinas) Current from the southern polar high latitudes far northward. Detailed petrographic analyses identified the Antarctic Peninsula, sub-Antarctic islands in the Scotia Sea, and Tierra del Fuego as plausible source areas. In the Mar del Plata Canyon, a combination of local slope instability and strong and persistent contouritic bottom currents, favored local enrichment in dropstones in the form of a loose, coarse sediment drape inside morphological depressions. The bottom current velocity would be locally strong enough to rework this sediment, leaving coarse rafted debris as a lag deposit. Microscopic petrograohic determinations were done on thin sections to identify the mineralogical composition of the rocks. During cruise SONNE SO260-1, the hull mounted Ocean Surveyor Teledyne RDI Acoustic Doppler Current Profiler (ADCP) with a doppler shift of 38 kHz provided real-time current velocity profiles over a range from 38 to 1,200 m water depth. ADCP data from the lowest 10-15 % of the water column have been removed due to possible scattering caused by strong seafloor echo. Doppler shifts were converted into current velocities using real water sound velocities by means of Conductivity-Temperature-Depth (CTD) and Expendable Sound Velocimeter (XSV) profile calibration. Water depth (m), current velocity (cm sec-1) and direction (degrees) measured with ADCP at Site GeoB22732 (La Plata Terrace Moat), at Site GeoB22717 (Ewing Terrace Channel), and at Site GeoB22716 (Ewing Terrace Moat) for water depths greater than 500 m. Current directions: 0º=North; 90º=East; 180º=South and 270º=West

Examining the plankton acoustic response with a vessel mounted ADCP across oceanic fronts located in the Drake Passage

On December 2001 and January 2006, during the LMG01-9 and LMG06-1 cruises to Antarctic Peninsula, at-sea oceanographic and acoustic measurements were conducted onboard the R/V L. M. Gould icebreaker along two transects located between (55.15 °S, 65 ºW) and (64.65 °S, 65 ºW) and between (55.15 ºS, 64.91 ºW) and (62.7 ºS, 62.21 ºW), respectively. The scientific crew consisted of researchers from two US institutes, and a scientific observer from the Argentinean Naval Service of Research & Development under the frame of the US National Science Foundation Antarctic Program. The present work accomplishes an alternative application for a vesselmounted Acoustic Doppler Current Profiler (ADCP) with an operating frequency of 153.6 kHz. Volume Acoustic Backscattering Strengths, S V, were computed from the recorded ADCP's voltages. The obtained values fell in a range of -92 dB to -62 dB, for the layer of the water column comprised between 26 m - 300 m on 2001 and in the range of -93 dB to -58 dB for the water column between 22 m - 300 m on 2006. Depth-averaged, S V, for the upper water column (about the first 150 m) on experiment transects were computed as well as S V values averaged in depth and latitude. Data processing revealed interesting features about the upper ocean acoustic behaviour. On December 2001, a significant non-uniform scattering response in the ensonified water column with quite high values of S V, associated with the diel vertical migration, was obtained. Additionally, a remarkable increment in the scattering response was observed at the estimated location of the Antarctic Divergence (AD). This feature was also observed on January 2006 in addition to remarkable high values of S V, in coastal waters of the Antarctic Peninsula. Plotting and exhaustive analyses of S V (z) profiles enabled the visualisation of three distinct types of qualitative patterns, namely, curves with: (I) two observable maxima, (II) only one maximum, (III) a depth-interval of variable width with a minimum acoustic response. Along the experiment transects the obtained results suggest an eventual correlation between the three distinct obtained behaviours of the backscattered acoustic intensity and the oceanic fronts location, leading us to consider the feasibility of using the S V (z) profiles, as an eventual indicator of oceanic fronts and eddies' presence.<br>En diciembre de 2001 y enero de 2006 durante los respectivos cruceros LMG01-9 y LMG06-1 a la Península Antártica fueron efectuadas mediciones oceanográficas y acústicas en el mar a bordo del rompehielos R/V L. M. Gould a lo largo de dos trayectos ubicados respectivamente entre (55.15 °S, 65 ºW) y (64.65 °S, 65 ºW) y entre (55.15 ºS, 64.91 ºW) y (62.7 ºS, 62.21 ºW). La tripulación científica consistió en investigadores pertenecientes a dos institutos estadounidenses y una observadora científica del Servicio Naval Argentino de Investigación & Desarrollo, en el marco del Programa Antártico de la Fundación Nacional de Ciencias de los Estados Unidos de Norteamérica. En el presente trabajo se lleva a cabo una aplicación alternativa del Perfilador de Corrientes por Efecto Doppler (ADCP) montado en el buque, con una frecuencia de operación de 153.6 kHz. Fueron calculadas las Fuerzas de Retrodispersión Acústica de Volumen S V, a partir de los voltajes registrados por el ADCP. Los valores resultaron comprendidos en el rango -92 dB y -62 dB, para la columna de agua de mar comprendida entre 26 m y 300 m, en el 2001 y y en el rango -93 dB a -58 dB para la columna de agua entre 22 m y 300 m, en el 2006. Se calcularon promedios en profundidad de S V para la columna superior de agua (aproximadamente los primeros 150 m) sobre los trayectos experimentales, así como valores promedios en profundidad y latitud de S V. El procesamiento de datos reveló características interesantes acerca del comportamiento acústico del estrato superior oceánico. En diciembre de 2001, se obtuvo una respuesta significativa con valores relativamente altos y no uniformes de retro-dispersión acústica S V en la columna de agua sonorizada, asociada a la migración vertical diurna. Asimismo, se observó un llamativo incremento de la respuesta de dispersión en la posición estimada para la Divergencia Antártica. (AD). Este mismo comportamiento fue observado en enero de 2006; asimismo se hallaron valores considerablemente altos de S V en aguas costeras de la Península Antártica. La graficación y el análisis exhaustivo de los perfiles S V (z) permitió a la visualización de tres tipos de diagramas cualitativos diferentes, a saber, curvas con: (I) dos máximos observables; (II) un único máximo; (III) un intervalo de profundidades de espesor variable con una respuesta acústica mínima. A lo largo de los trayectos experimentales, los resultados obtenidos sugieren una aparente correlación entre los tres comportamientos particulares de la intensidad acústica retro-dispersada y la localización de los frentes oceánicos, lo que lleva a considerar la factibilidad de usar los perfiles S V (z) como un eventual indicador de la presencia de frentes y eddies oceánicos

Multibeam bathymetry processed data (Kongsberg EM122 working area dataset) of RV SONNE during cruise SO260/1, Argentine Continental Margin

The data comprise processed bathymetry and backscatter grids from the Ewing Terrace on the Argentine Continental Margin that were acquired during RV SONNE cruise SO260/1 in 2018. Bathymetric and backscatter data acquired using the 12 kHz Kongsberg EM122 echosounder were processed using the Open Source software MB-System. This includes navigation editing, interactive sound velocity corrections, erroneous beam flagging and grid generation. Backscatter grids of the recorded amplitude variations were created after normalizations using an angle varying gain (AVG) correction considering the seafloor morphology

Evolution of complex giant seafloor depressions at the northern Argentine continental margin (SW Atlantic Ocean) under the influence of a dynamic bottom current regime

Seafloor depressions (SD) are features commonly observed on the ocean floor. They often occur as circular, small-sized (up to 10 s of m) incisions caused by fluid expulsion. Larger depressions (100s m to km) are considerably less abundant, and their origin and development have been scarcely studied. This study investigated two giant morphological depressions (>5 km) using recently acquired multibeam bathymetry and backscatter, sediment echosounder, and high-resolution seismic data. An arc-shaped (SD-N) and a sub-circular depression (SD-S) are located on the Ewing Terrace at the Argentine Continental Margin north and south of the Mar del Plata Canyon, respectively. The study area is influenced by the Brazil-Malvinas Confluence, where major counterflowing ocean currents affect sedimentation, and northward flowing currents form a large contourite depositional system. Using an existing seismo-stratigraphy, the onset of SD-N was dated to the middle Miocene (∼15–17 Ma), whereas SD-S started developing at the Miocene/Pliocene boundary (∼6 Ma). Acoustic anomalies indicate the presence of gas and diffuse upward fluid migration, and therefore seafloor seepage is proposed as the initial mechanism for SD-S, whereas we consider a structural control for SD-N to be most likely. Initial depressions were reworked and maintained by strong and variable bottom currents, resulting in prograding clinoform reflection patterns (SD-N) or leading to the build-up of extensive cut-and-fill structures (SD-S). Altogether, this study highlights the evolution of two unique and complex seafloor depressions throughout the geologic past under intense and variable bottom current activity in a highly dynamic oceanographic setting.Fil: Warnke, Fynn. Universitat Bremen; AlemaniaFil: Schwenk, Tilmann. Universitat Bremen; AlemaniaFil: Miramontes, Elda. Universitat Bremen; AlemaniaFil: Spiess, Volkhard. Universitat Bremen; AlemaniaFil: Wenau, Stefan. Universitat Bremen; AlemaniaFil: Bozzano, Graziella. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval. Departamento Oceanografía; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Baqués, Michele. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval. Departamento Oceanografía; ArgentinaFil: Kasten, Sabine. Universitat Bremen; Alemani

Sediment echosounder processed data (Atlas Parasound P70 echosounder working area dataset) of RV SONNE during cruise SO260/1, Argentine Continental Margin

The data comprise PARASOUND profiles from the Ewing Terrace on the Argentine Continental Margin that were acquired during RV SONNE cruise SO260/1 in 2018. PARASOUND data was acquired using the hull-mounted parametric sub-bottom profiler PARASOUND P70 using a SLF frequency of 4 kHz and a non-rectangular pulse shape of ~0.25 ms length in quasi-equidistant mode. The trace envelope was computed for interpretation and visualization purposes

Multichannel reflection seismic processed data (working area dataset) of RV SONNE during cruise SO260/1, Argentine Continental Margin

The data comprise high-resolution multi-channel reflection seismic profiles from the Ewing Terrace on the Argentine Continental Margin that were acquired during RV SONNE cruise SO260/1 in 2018. Multichannel seismic data were acquired with a SERCEL Mini GI-Gun and GI-GUN with 0.2 l and 0.4 l volumes for generator and injector, respectively. For receiving the signal, a 96-channel analogue TELEDYNE streamer was deployed featuring varying channel spacing of 1 m to 4 m distance. Shot intervals varied between 4 to 6 seconds depending on the water depth, yielding shot spacing of ~10-15 m at a ship's speed of 5 to 5.5 kn. The sampling rate was set to 0.25 ms and the recording length varied between 3 and 4 seconds. The data were band-pass filtered, stacked and migrated with an emphasis on high resolution imaging and noise reduction. Velocity fields were picked interactively for NMO-correction and post-stack time migration. CMP bin distance was set to 2 m. Processing was conducted using the VISTA 2014 seismic data processing software