Marine Geophysics and Hydroacoustics

MSM87 IODP NW-Africa

Summary - MSM87 November 17th to November 25th, 2019 Las Palmas (Canary Islands, Spain) - Mindelo (Cape Verde)

A seismic pre-site survey for an International Ocean Discovery Program (IODP) was conducted on Maria S. Merian research cruise MSM87 in order to find a potential drill-site on the Cape Verde Plateau offshore NW Africa.
The IODP pre-proposal ‘Neogene Climate of NW Africa’ suggests investigating: i) NW Af-rican climate in a warmer world, and ii) High productivity ecosystem response to climates different from today.Sediment cores should be retrieved at five locationsoff NW-Africa. more A central site is proposed on the Cape Verde Plateau close to ODP Site 659but no modern high-resolution seismic data are available for this area. The main goal of Cruise MSM87is to carry out a seismic pre-site sur-vey for an IODP site on the Cape Verde Plat-eau. The survey aims in identifying a site where the Plio-Pleistocene is thinner and the Miocene is thicker than at Site 659. This would allow to APC-XCB deeper into the Mi-ocene, which is crucial for retrieving high-quality cores for paleoclimate investigations.

MSM87 Gruppe

Group Photo on deck of Maria S. Merian.

Hydroacoustic data collection started at 02:40h on November 17 after leaving the Spanish EEZ. A short survey at the headwall area of the Sahara Slide was carried out in the afternoon of the same day. The data were collected to complement the site survey data for two proposed IODP-sites in this area. We also collected some additional data of a landslide scar located slightly south of the Sahara Slide. The transit was continued on November 18. It was interrupted for  a  short  test  of  the  seismic  equipment  in  the  afternoon. 

TDeploymenthe  test  revealed  problems  with  one streamer section and a trigger box. Both problems could be quickly solved following the test. We reached  the  northern  boundary  of  the  Cape  Verde  Plateau  on  November  19  at  08:00h  local  time. Deployment of the seismic equipment was very smooth. The initial profiles crossed the Cape Verde Plateau from North to South. This set of profiles included crossings of a proposed IODP site at the northern  part  of  the  plateau  and  the  old  ODP  Site  659.  The  data  show  relatively  homogeneous sediment patterns with a slight thickness decrease of the Plio/Pleistocene sediments to the north. We crossed  DSDP-Site  368  around  noon  on  November  20.  November  21  was  used  for  a  acquiring  a long line at the western edge of the Cape Verde Plateau, where the GEBCO bathymetry shows a few embayments of the 3200 m contour, which may indicate erosional processes. The line showed only small  variations  of  the  Plio/Pleistocene  sediment  thickness.  MSM87 seismic

Preliminary results of a seismic line across the Cape Verde Plateau acquired in November 2019.

A  cross  line  for  a  potential  site identified on the first seismic line north of the plateau was collected in the evening the same day. This was followed by a long line on the eastern site of the plateau in the night November 21/22. The survey  was  interrupted  for  short  period  in  the  morning  of  November  22  due  to  a  leakage  of  the airgun.  This  problem  was  fixed  very  quickly.  The  data  analysis  revealed  relatively  homogenous sediment patterns for most parts of the surveys but significant variations with a potential thinning ofthe Plio/Pleistocene sediments were identified south of ODP-Site 659. A detailed survey of this area was carried out from noon November 22  and continued until the evening of November 23. These data  show  some  significant  thinning  of  the  near  surface  sedimentary  successions  and  we  are optimistic  to  locate  promising  drill  sites  along  these  seismic  lines.  On  our  way  to  the  west,  we collected another line across the ODP site 659 and a potential new site on the eastern edge of the Cape  Verde  Plateau.  The  seismic  gear  was  retrieved on  November  24  at  08:00h.  Hydroacoustic imaging was continued until 18:00h the same day during the transit to Mindelo. We arrived in the port of Mindelo on November 25 at 08:30h. RV  MARIA  S.  MERIAN-Cruise  MSM87  was  a  great  success.  Hydroacoustic  data  were  collected along the entire cruise. Continuous seismic data acquisition at the Cape Verde Plateau over 5 days resulted in 1000 km of  high-quality high-resolution seismic data. The data will allow to  collected promising sites for drilling in the frame of the International Ocean Discovery Program. In addition, the data can be used to investigate the sedimentary architecture of the Cape Verde Plateau.

Contact persons:  Prof. Dr. Sebastian Krastel, Henriette Wilckens

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