ALBERT

Description: We use seismic oceanography to document and analyze oceanic thermohaline fine structure across the Tyrrhenian Sea. Multichannel seismic (MCS) reflection data were acquired during the MEDiterranean OCcidental survey in April–May 2010. We deployed along‐track expendable bathythermograph probes simultaneous with MCS acquisition. At nearby locations we gathered conductivity‐temperature‐depth data. An autonomous glider survey added in situ measurements of oceanic properties. The seismic reflectivity clearly delineates thermohaline fine structure in the upper 2,000 m of the water column, indicating the interfaces between Atlantic Water/Winter Intermediate Water, Levantine Intermediate Water, and Tyrrhenian Deep Water. We observe the Northern Tyrrhenian Anticyclone, a near‐surface mesoscale eddy, plus laterally and vertically extensive thermohaline staircases. Using MCS, we are able to fully image the anticyclone to a depth of 800 m and to confirm the horizontal continuity of the thermohaline staircases of more than 200 km. The staircases show the clearest step‐like gradients in the center of the basin while they become more diffuse toward the periphery and bottom, where impedance gradients become too small to be detected by MCS. We quantify the internal wave field and find it to be weak in the region of the eddy and in the center of the staircases, while it is stronger near the coastlines. Our results indicate this is because of the influence of the boundary currents, which disrupt the formation of staircases by preventing diffusive convection. In the interior of the basin, the staircases are clearer and the internal wave field weaker, suggesting that other mixing processes such as double diffusion prevail.

Description: Between 08.08.2003 and 02.09.2003, bathymetric data was acquired offshore Guatemala and Costa Rica during the R/V SONNE cruise SO173/2. The expedition comprised geophysical and biological research objectives. One aim was the acquisition of geophysical data for a better understanding of recent and long-term evolution of the Middle America Landbridge and mass flux into the subduction system. Moreover, the cruise was also dedicated to studying the sensory systems of mesopelagic fish, cephalopods, crustaceans and teleosts by using trawl gear and morphometric studies. Bathymetric mapping with the multibeam echosounder (MBES) SIMRAD EM120 was utilized to obtain a full coverage bathymetric map along the El Salvador and Guatemalan continental slope and to complete previous maps by filling gaps along the continental slope and oceanic plate of Nicaragua. Further geophysical instruments, such as the sub-bottom profiler PARASOUND, magnetometer, a dredge and seismic instrumentation, and biological equipment including trawling gear and lab instrumentation, complemented the research equipment. CI Citation: Paul Wintersteller (seafloor-imaging@marum.de) as responsible party for bathymetry raw data ingest and approval. Description of the data source: During the SO173/2 cruise, the hull-mounted multibeam echosounder (MBES) SIMRAD EM120 was utilized to perform bathymetric mapping. It allows to conduct surveys in water depths of up to 11,000 m. Two transducer arrays transmit successive frequency coded acoustic signals (11.25 to 12.6 kHz). Data acquisition is based on successive emission-reception cycles of the signal. While the emission beam has a dimension of 150° across and 2° along track, the reception is obtained from 191 overlapping beams with widths of 2° across and 20° along track. The beam footprint has a dimension of 2° by 2°. The beam spacing can be set to equidistant or equiangular. For further information on the system, consult: https://www.km.kongsberg.com/ Depth is estimated from each beam by using the two-way travel time and the beam angle known from each beam, and taking into account the ray bending due to refraction in the water column by sound speed variations. Combining phase and amplitude is used to provide measurement accuracy practically independent of the beam pointing angle. During the SO173 cruise, the EM120 was used continuously. At the beginning of the cruise, a sound velocity profile was measured to a depth of 2000 m. Responsible person during this cruise / PI: Wilhelm Weinrebe (wweinrebe@ifm-geomar.de) Chief Scientist: Wilhelm Weinrebe (wweinrebe@ifm-geomar.de) CR: http://oceanrep.geomar.de/13407/1/Geomar-Report-116.pdf CSR: https://www2.bsh.de/aktdat/dod/fahrtergebnis/2003/20040060.htm This dataset was published as part of: Geersen, Jacob (2019): Collated bathymetric data from convergent margins that experienced tsunami earthquakes. PANGAEA, https://doi.org/10.1594/PANGAEA.899049

Description: During the cruise M69/2 of the German RV Meteor a West-East trending seismic refraction and wide-angle profile was obtained, sampling the structure of the Western Algerian-Balearic Basin and the Eastern Alboran Sea. In total, 25 ocean-bottom-seismometers and ocean-bottom hydrophones sampled seismic shots along the 250 km long profile. Seismic data are in standard segy-format. Data are reduced with a reduction velocity of 6 km/s and the origin of the time series is at -2 sec.

Description: In September of 2018, the Spanish research vessel Sarmiento de Gamboa shot the seismic profile FRAME-p03 across the continent-to-ocean transition zone in the Iberia Abyssal Plain of the Western Iberia passive continental margion to the west of Portugal. Seismic shots were recorded on 30 ocean-bottom-seismometers (OBS) and ocean-bottom-hydrophones (OBH). Spanish instruments were OBS from the Spanish Pool operated by the Marine Technology Unit (UTM) of Consejo Superior de Investigaciones Científicas (CSIC) and German istruments were OBH from the GEOMAR Helmholtz Centre for Ocean Research Kiel. Seismic data in SEGY format of the all seismic stations of both partners are archived at the PANGAEA Datacenter. Please note that the data have a time offset of 1 sec and a reduction velocity of 8 km/s. The seismic FRAME (Formation of Geological Domains in the Western Iberian Margin and Tectonic Reactivation of their Limit) cruise was funded by the Spanish Ministry of Science.

Description: Seismic data was acquired to study the transition from rifted continental crust to oceanic crust at the Deep Galicia Margin from June to August 2013. 3D Multichannel reflection and coincident wide-angle seismic data were acquired simultaneously as part of a seismic experiment over an area of 80 km long and 25 km wide in the Deep Galicia margin. The multichannel reflection seismic volume was acquired by the R/V Marcus G. Langseth, which provided a source for the ocean bottom seismic data. A total of 86 ocean bottom hydrophones/seismometer deployments were carried out by F/S Poseidon. Two airgun arrays with total gun volumes of 3,300 cu.in. were deployed as seismic sources. Shots were fired alternately using two source arrays every 37.5 m (shot interval of ~ 16 s with ship speed of 4.5 knots). Data were converted into SEGY format. Further details are available at https://doi.org/10.1038/NGEO2671.