D341: Porcupine Abyssal Plain cruise 2009


Cruise blog

Monday 20 July 2009

The weather is still calm and science activities continue 24 hours a day. A couple more pods of common dolphins have been spotted but so far the dolphins have been camera shy with no good shots yet. Yesterday (Sunday 19th July) the sub-surface mooring with Deep-IODA (oxygen consumption devices) attached was successfully deployed for a few weeks. It will be recovered later on during the cruise. The sediment trap mooring (called 'PAP3') has also been successfully deployed for another full year. 3 sediment traps are attached to capture and sample particle flux at 3000m, 3050m and 4700m depth.

Today the ARIES zooplankton nets will be deployed twice and after that the main surface-seafloor mooring (DOMS) will be recovered over the next 24 hours (weather permitting!)

Abyssal Mud Sampling by Nina Rothe

May I introduce “The Megacorer”. As the name suggests it is a very big corer designed to probe the deep-sea floor. When assembled, it stands 2.28 m high and weighs ~ 810 kg, It has been developed to take undisturbed sediment cores of 100 mm diameter by 400 mm long with 200 mm of supernatant water. Up to 12 core tubes can be deployed at any one time to poke about the seafloor. The tubes are driven into the sediment by the weight of the corer head and its attached lead weights. The 12 tubes, each of which is held in a carrier, are arranged in four rows of 3 tubes each, along the sides of a square (Fig 1).

Fig. 1: Loaded megacore
retrieved from 4809 m

Fig. 2: Changes in size classes of benthic fauna at the PAP site (Gooday et al.)

Our goal for D341 is the continuation of the time-series at the PAP site by observing long-term changes in deep-sea communities in the Northeast Atlantic Ocean. The deep-sea floor is linked intimately to ocean surface processes and rapid, large-scale changes can occur in deep-sea ecosystems. For example, it has been suggested that the North Atlantic Oscillation affects the quantity and quality of carbon exported to the deep sea at the PAP site, which is reflected in changes in abundances observed in all components of the benthic community (Fig. 2). Over the duration of the cruise we will obtain samples for macrofauna, meiofauna, and Foraminifera, all of which have displayed similar changes in all size classes since the 1980ies (Fig.2). Whilst using the megacorer to explore macro-and meiofaunal abundances, we will also deploy the Bathysnap camera system to observe changes in inter-annual changes in megafaunal abundance by taking pictures of the seabed over the next year (Fig.3).

Fig. 3: Bathysnap

     Fig. 4: Mud, mud, glorious mud!

A few days ago, the megacorer made its first appearance and was sent down to abyssal depth at nearly 5,000 m to collect deep sediment samples. Once the corer is back on deck, the individual cores are removed from the frame and carried to the cold temperature lab, where they are sectioned into different layers and fixed in formalin (Fig. 4). It’s a muddy business, indeed! Back at the National Oceanography Centre in Southampton, the samples will be studied under the microscope to identify the many critters that roam the sediment of the abyss.

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