FS SONNE Fahrtbericht / Cruise Report SO214 NEMESYS : 09.03.-05.04.2011, Wellington - Wellington, 06.-22.04.2011 Wellington - Auckland

Abstract

Cruise SO-214 of R/V SONNE headed by IFM-GEOMAR served two legs of project NEMESYS, funded through the German Ministry of Education and Research (BMBF). Major partners of the project are Leibniz Institute of Marine Science (IFM-GEOMAR) and the Federal Institute of Geosciences and Natural Resources (BGR) Germany, as well as the Institute of Geological and Nuclear Sciences (GNS) and the Royal Netherlands Institute for Sea Research (NIOZ). NEMESYS aims to extend understanding and modelling of cold vents along the Hikurangi Margin (HM) off the east coast of the North Island of New Zealand. Since the first findings in the late 80´s several cruises have been dedicated to map and investigate the active seepage of Methane in this area. Results of these cruises headed by New Zealand and international scientists provided the database for the first joint German – New Zealand expedition SO-191 in 2007. During this cruise with R/V SONNE the HM was investigated within three legs comprising all marine geo-scientific disciplines. The major findings in geophysical, geological, geo-chemical, and biological research were published in a special issue by Marine Geology (Vol. 272, 2010). Nevertheless a lot of questions remained or were raised by the upcoming results. Still lateral continuation of feeder channels and a possible relation between internal structure, activity and tectonic regime of a seep site were not understood. The geological, geo-chemical and biological analysis has been related to the overall description and study of the seep sites along the margin. Detailed studies across a seep site and high-resolution sampling to study the internal variation of Methane production and the influences to chemistry and habitat have not been complete with the required intensity. These exemplary listed investigations together with an additional list of questions to seepage led to the follow-up project SO-214 NEMESYS, which was funded through the German Ministry of Education and Research (BMBF). Aim of the project NEMESYS is to confirm derived models of seep structures and to extend the existing database and knowledge by high-resolution sampling in all disciplines. Based on the findings of the SO-191 New Vents project Opouawe Bank and Omakere Ridge were identified as the areas with the highest interest for our additional studies. Opouawe Bank provides a high density of active seep sites with various expressions of feeder channels in seismic images. Omakere did provide the only seep sites that were found without feeder channels underneath. In between the Porangahau Ridge was selected as third target due to the indications of either gas or hydrate formation without active gas expulsion. Cruise SO-214 with R/V SONNE was split into two legs. The seismic part started on 09th March 2011 in the port of Wellington. Two 3D seismic cubes were acquired above active seep sites at Omakere and Opouawe Bank. A third cube at Porangahau Ridge could not be completed due to technical problems with the equipment and rough weather conditions. Intensive Parasound Profiling and extended 2D seismic with high resolution (up to 1.2 m migration grid) were undertaken. Many more feeder channels were identified than previously known from the SO-191 data, although not all of them terminate in a seafloor expression. The second leg left the port of Wellington on 6th April 2011 dedicated to intensive geological, geo-chemical and biological investigations. The major work was completed at Opouawe Bank. Based on images of the seismic data compilation North and South Tower seeps and seep site Takahe were chosen for the intensive sampling program. CTD and gravity cores were taken in dense spacing to investigate the local interaction of seepage and surrounding seafloor and water column. The water column showed limited stratification but seemed to be influenced from stormy weather. Biologic investigations showed limited variations compared with the SO-191 expedition, mainly in the distribution of fauna. The variety of amphipods seems to be a unique feature of the NZ seeps. The second leg suffered from bad weather conditions, which anticipated work during 100 hrs. out of scheduled 330 hrs. All meta data of the cruise are available through the IFM-GEOMAR Data Management Portal (https://portal.ifm-geomar.de/web/guest/home)