Thursday 26 May 2011

Porcupine Bank Groundtruthing CE11_017

The Marine Institute Research Vessel the R.V. Celtic Explorer completed mobilisation for the INFOMAR ground-truthing survey, CE11017, on the10th May 2011. INFOMAR is a joint research program between GSI and MI. Associated research partners for this cruise are the following Irish universities; DCU, NUIG, NUIM and UCD.

On the 11h of May the vessel departed from Cork at midday heading to the Atlantic Ocean. The first stop was Dunmanus Bay in the SW of Ireland where we arrived at 5 a.m. the following day. Several shallow cores were taken targeting a small cluster of pockmarks in shallow gas sediments in about 40m water depth. After completion, the survey work continued in fairly good weather conditions running a long shallow seismic line towards the outer bay to get a better understanding of the shallow stratigraphy.

After completion of the seismic line, the vessel transited to the second research location on the Porcupine Seabight to study the Nephrops habitat. Shortly after arrival, two underwater video transects were run using the MI video sled. This was followed by sediment sampling in the vicinity of these transects using a grab sampler (Day Grab). It was decided, based on the weather forecast for the upcoming 24 hours, to begin transiting to the M6 weather buoy position to deploy the buoy. Halfway to the buoy position, vibrocores at two stations were taken and short cores were retrieved in a complex gravelly seabed terrain with low ridges. The M6 buoy was deployed on the morning of the 14th of May and the one in the water was brought on-board successfully.

The survey resumed towards the Porcupine Bank, our next research area, which up to now was a relatively unknown seabed. Several vibrocores, grab samples and three rock dredge transects were taken during the rest of the 15th May. Two video lines were run in that area displaying a variety of seabed types from boulder fields to fine sand with macro benthic fauna present. On the 16th May, the survey continued entirely on the top of the Porcupine Bank using grab samples and finally rock dredge transects to obtain sediments and rock samples form the hardest areas. Several video lines run overnight, were used to correlate some of the rock dredge transects. On the 17h May, after a few grabs on gravelly ground, the weather improved and it was decided to spend most of the day vibrocoring. 7 stations were occupied in a transect around the Porcupine “Saddle” in water depths from 220m to 330m targeting a variety of ridges. Most of the targets were successfully cored and they provided a mixture of gravels and clay.

On the 18th May the weather worsened and it was decided to spend the morning taking water samples in deep waters (2200 m) using the rosette. After completion, an attempt to recover the cetacean hydrophones was carried out but it was not possible to recover them due to the high swells. Swell of up to 7m and gales, forced the expedition to leave the area and head back towards the SW coast of Ireland again.

On the 19th May, on reaching the SW, the weather was significantly better and allowed for coring. Several vibrocores in relatively deep waters (c. 400 m) were obtained in an area shaped with low mounds. A transect of grab samples from the 500m contour to the 100m contour followed with finality to observe changes in the benthic fauna and living foraminifera. Finally, five more vibrocore stations were taken in the inner shelf in an area of possible glacial ridges.

On the 20th May we spent most of the time in Dunmanus Bay running video lines and taking several vibrocres, 6 in total, for additional shallow stratigraphy research. Later in the evening the final transit to Cork commenced which would finish the survey.

The vessel proceeded for demobilisation in Cork and the ship docked around midnight on the 20th May completing a successful expedition despite the adverse weather conditions.

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