Mooring at the Mothra Vent Field

Endeavour Map for hydrothermal vents

Today we are in Mothra Vent Field at the edge of axial rift valley. NEPTUNE Canada is installing the southeastern Regional Circulation Mooring (RCM) to measure currents within the axial rift valley. In this mission, we are collaborating with the CCGS John P. Tully (Canadian Coast Guard offshore oceanographic science vessel).

CCGS John P. Tully

The mooring is a long long cable (275 m) which is vertically affixed to a huge concrete anchor (750 kg) at the bottom of the ocean at a depth of 2230 meters.

Concrete anchor at 2230 meters deep

There are four pairs of measurement instruments along the mooring line, one is CTD (remember? Conductivity, Temperature, Depth) and the other is ACM (Acoustic Current Meter).

Pair of CTD (Conductivity Temperature Depth) and ACM (Acoustic Current Meter) after the lemon-shaped float

Here, mini parenthesis for the comparison of Acoustic Current Meter (ACM) and Acoustic Doppler Current Profiler (ADCP): Remember, ADCP is also measuring current, but ADCP monitors current over the water column, whereas ACM measures the current in the water at an exact point where it is located. These instruments are placed in pairs at different depths in the ocean.

Here, it is useful to introduce the abbreviation of "mab" which refers to "meters above the bottom". So, with the usage of mab, once again, on the mooring, there are 4 pairs of current meters and CTDs with a "mab" of 5, 50, 125 and 200 respectively. Considering that we are 2230 meters above from the bottom, the closest CTD and ACM pair is about 2000 meters deep right now!

There are already two moorings up north of the High Rise Vent Field, in the northeast (NE) and northwest (NW). Here, in the south there were not any, so with the help of the Tully, NEPTUNE Canada installed two moorings in the southeast (SE) and southwest (SW) today.

At the top of southeast mooring two ADCPs are located; one looking upward and the other looking downward, both at 250mab.

Upward and downward looking ADCPs at the top of the mooring

Q: How can all these instruments be lined up vertically in the water? Why don't they sink?

Syntactic foam buoy at the top of the mooring

A: Along the mooring there are floats placed in between the pairs of the measurement instruments, and there is a giant buoy at the end of the mooring. Both floats and the buoy are made up of syntactic foam. Syntactic foam is a high-tech composite material. Actually, it is like a foam made up of hollow glass microspheres dispersed in a matrix of epoxy resin (high strength plastic matrix) which provides with very low moisture absorption. Hollow glass microspheres provides low density, and the plastic matrix provides strength. The floats in between the pairs of instruments and the giant buoy at the top of the mooring keep the mooring vertical in the ocean.

The mooring adventure will continue at the High Rise Vent Field tomorrow.

Stay tuned for more on hydrothermal vents!

Key words: hot and cold, larva, metamorphosis, axial valley currents!

Cheers,

Goksenin Sen

Marine Educator