JC010: Mud volcanoes and submarine canyons


 JC10



Cruise diary


Day 9: Sunday 10 June 2007
Position: 39º 34.5558N, 10º 18.1341 - Nazare Canyon
Weather: Moderate short swell, light to moderate seas, partly cloudy, with scattered rain showers


Helen writes:

"Due to the dive plan I didn’t need to get up at 3.30am this morning! Hoorah! I got up in time for breakfast and then spent this morning working on an organogram of the ship and resources required to capture a sea star. Andy the Boswain showed us some ropework that he had done. It was truly spectacular, made from a range of knotting, splicing and weaving techniques that are traditionally used a sea (apparently this type of ropework is in high demand from publicans who attach it to the bell at the bar to ring for last orders!).

After a stint in the gym, it was time for lunch – a Sunday roast! And then a nap before I spent some time tracking down people to help me to answer all your questions (check the Q&A page to see).

I was back on the ROV van at pm – the team had a busy but fruitless day looking for a lander that was abandoned two years ago!  After 5 hours of hunting, the search was called off, having used SONAR and the ROV’s cameras to search a wide area of the canyon floor.

The second part of the watch was spent collecting xenophyophores (large single-celled organisms) for study and identification in the lab. The mini box corer was used for the first time to do this today.

Dinner was blackened Cajun swordfish, served with spring vegetables and potato croquettes. It was the first time I had tried swordfish, and I enjoyed it very much.

Having come off watch, we’ve settled down to watch a video this evening before bed. So, goodnight from here, you’ll hear more tomorrow!"

 

Virginia writes:

"Last night R.R.S. James Cook moved from the 3400 m site (leaving Teresa’s experiments for about two days) and returned to the 4300 m site where Ursula's experiments are located. Last night were collected a set of new megacores at the 4300 m site, and the ROV brought up another lot of new push cores.

The megacorer prior to launch

On the night shift: Sybille, Silvia, Kostas and Teresa
eagerly await the return of the corer

And here it is, filled with the top few cm of
sediment from the seafloor

Silvia and Teresa analysed the bacterial enzymatic acivity from the sediments of the area where Teresa’s experiments were carried out. They work in a cold laboratory with an atmospheric temperature controled and kept at about 4 ºC. Andy also works in this laboratory. The selected cores to be analysed for Andy, Silvia and Teresa are placed in the cold laboratory as soon as they arrive on deck. Like Silvia and Teresa, Andy also needs to conserve the organic matter in the cores, so he usualy slices the cores and sieves the sediments using very cold water and a sieve of 125 microns mesh size, here in this lab before using the microscope to look at the samples. This morning, Andy sliced the first centimentres of two megacores and one of the push cores for micofaunal analysis. Andy needs to extract living benthic foraminifera and other microorganisms from the sediment and conserve them for molecular analysis.

Silvia taking notes on her cores

Andy preparing a core for slicing

Virginia working in the cold lab

We also studied the sediment's provenance (where it comes from) at the 4300 m site. To do this, we looked at all the benthic foraminifera (microscopic marine organisms with calcium carbonate shells). Differrent species of foram live in different water depths, so by looking at the species found in the mud at the bottom of the canyon we can deduce something about where that mud came from. We identified and counted about 423 specimens, belonging to 53 species. About 58% of the specimens were transported into the canyon from shallow waters, perhaps from the Portuguese inner (0-30 m water depth) and middle (30-80 m water depth) continental shelf. The most abundant group of shallow water species are usually at their highest abundance in inner shelf waters - examples of these species are Planorbulina mediteranensis or Ammonia beccarii. You can see high-magnification photos of these both species below, taken using a scanning microscope (not on the ship!).

Planorbulina mediterranensis

Ammonia beccarii

The sieved sediment we studied is rich in terrigenous (land-sourced) material such as the mineral mica, which is very abundant here. The sediment also contains a high abundance of plant fragments transported into the canyon from the nearby continent. This results, combined with those from the foram study, tell us that the sediments washing through the Nazare Canyon are being transported from shallower waters. On the nearby land, there are no big rivers and as the head of the Nazare Canyon lies close to the shoreline we can deduce that the currents that run parallel to the coastline are transporting sediment (including foraminifera shells) into the Nazare Canyon. This canyon is similar a submarine river, transporting sediments from the shallow ocean to very deep ocean environments like the 4300 m site.

Doug Masson told us that the sedimentation rate (the rate at which sediment accumulates on the seafloor) is very high in some parts of Nazare Canyon, reaching 1 cm per year. So a large proportion of sediment deposited in the canyon is supplied from shallow waters located near the continent. It is important to know this so that we can trace the pathway of any pollutants that may be released in shallow waters, or monitor the knock-on effects of any changes to the shallow environment.



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