Prof Ingo Grevemeyer, a marine geophysicist in the Research Division “Dynamics of the Ocean Floor” at GEOMAR, run the expedition together with Co-PI Prof Timothy Henstock (University of Southampton & National Oceanography Centre). The goal of the survey was to study the architecture of fast spreading oceanic crust, its variability in the Guatemala Basin, and hydration when being forced into the subduction zone of Central America. Onboard 60 ocean-bottom-seismometers (OBS) from GEOMAR and the British OBS pool were available, receiving after deployment shots from a large airgun source to study crustal and upper mantle structure from wide-angle seismic refraction technology. In addition, multi-channel seismic (MCS) data from a 6-km long multichannel hydrophone streamer provided by UK partners revealed images of the internal structure of the oceanic crust. In the trench area, University of Bremen and University of Southampton studied heat flow pattern and fluid migration, respectively.
The survey offshore of Central America was split into two legs. Both legs issued and terminated in the harbour of Caldera in Costa Rica. The first 38-days long leg was led by Ingo Grevemeyer, collecting seismic, gravimetric and magnetic data. In total, 96 successful OBS deployments recorded 800 line-kilometres of 2-D wide-angle seismic data. The MCS streamer provided over 1000 km of 2-D seismic data. During the second 10-days long leg run by Dr Ingo Klaucke (GEOMAR), 64 successful heat flow sites were measured and 16 gravity cores for pore water analysis taken. Unfortunately, efforts to collect high-resolution near seabed bathymetry using an Autonomous Underwater Vehicle (AUV) failed due to technical issues. Last, during the entire survey roughly 5000 line-kilometres of swath-mapping bathymetry and gravity field measurements were obtained. All acquired data provide a unique insight into the structure and architecture of the oceanic crust. The data were also acquired to issue a campaign of deep-drilling into the oceanic crust to penetrate and sample an entire crustal section of the oceanic crust and the underlying mantle.
The scientific party greatly appreciates the collection of fantastic geophysical data and acknowledges the professional and friendly support aboard RRS JAMES COOK, including the celebration of Christmas and New Year during the first leg. The expedition JC228 is a great example of the benefits provided by the OFEG's barter program.