Expedition to the Mariana forearc

Mar. 23 - May 4, 2003

Day 16, April 7th

(click on any image for the larger version)

Day 16 Water, Water, Everywhere

The DSL-120 sonar survey of Pacman Seamount was completed without complications and the equipment was back onboard by 1600. This expedition is the first time the DLS-120 has been used to map mountain tops and everyone has learned a lot, not only about the mountains but also how to swing the equipment in frequent tight turns in deep water. In the past the DSL-120 has been used to map areas like midoceanic ridges. Mapping ridges can be done making long transects, mapping miles between turns. Mapping the seamounts was a challenge. Each transect would take about 1.5 hours but the turns often took up to 5 hours. It was a challenge but the results have been well worth the effort.

An evening piston core at Pacman was successful as well. I like piston cores better than gravity cores. Piston cores are more complex and more time consuming but I get to help. Even if all I do is hold a line and clean up, it’s fun to be in on the action. The night was cloudy with a thin crescent moon peeking through the clouds. The lights of the ship lured squid that swam in and out of view as the core was brought to the surface. It doesn’t matter how many squid or fish I see, every new arrival brings a new excitement.

overloading the washer Tom F. overloading the washer

The sign on the ship announcement board today read, “FOLLOW DIRECTIONS: Start washers 3 minutes apart to avoid floods. This is the second flood of trip 154!”

The laundry room, on the lowest level of the ship, has 3 washers and 4 dryers. Everyone has a scheduled wash day—crew Monday through Thursday and scientists on the weekend. The only rule is that if you want to use more than one washer, start them 3 minutes apart. Two or three washers on the same cycle overload the drain pipes and cause flooding. Seems like a simple rule but so far we’ve flooded the washroom twice.

The laundry room is the largest user of fresh water on the ship. Richard, the Chief Engineer, explained that the ship actually gets fresh water from salt water by a process called reverse osmosis or RO. Ships that make their own water use RO or evaporators, or both. An evaporator uses heat. The ship’s engines generate a lot of heat which can be used to heat the water for evaporation. The RO system is less expensive to purchase and install but it is more costly to maintain.
Reverse Osmosis Reverse osmosis system in the engine room
Stuffing the dryerTom F. stuffing the dryer

The intake of sea water is on the starboard (right) side of the ship because all waste water is discharged on the port (left) side. Care is taken to intake only the cleanest water. Any oil in the water clogs the membranes of the RO system and they can’t be cleaned of oil. A membrane cost about $3000 and each RO unit has 5 membranes.

As the water comes onboard it is strained. It’s not uncommon to find jellies and krill in the filters. Jellyfish can quickly clog the strainers. The sea water is then sent through filters of progressively smaller mesh from 25 down to 5 microns. Next it goes through a sand filter and then a high pressure pump sends it thought the RO membranes at 750 psi (pounds per square inch).

rinse water Rinse water

The water is treated with bromine to kill microbes. It is again filtered and then sampled. The water is really pure at this point and has a pH of about 9. A pH this high will cause the pipes to corrode. To neutralize the pH, minerals are added to obtain a pH of about 7.4.

The water is tested for pH and bromine content, 4 times a day. This is one of the most important operations on the ship. Contaminated water would end the expedition and send us back to shore.

Science Summary - Days 15 and 16, April 6th and 7th

Science Objectives, Day 15 & 16:

The fifteenth and sixteenth days of the cruise, Apr. 6 and 7, after finishing deployment of transponders at the site of Cerulean Springs on Pacman Seamount’s southeast arm. We will do a piston core on the seamount immediately to the south (the grad students nicknamed it Ms. Pacman). We will then do a DSL120 survey of the southeast arm of Pacman Seamount. This will take the remainder of the day and part of tomorrow. After the survey we will do a piston core at Cerulean Springs then move to Conical Seamount to set transponders and navigate them in as the Jason2 group switches the control van from DSL120 operations to Jason2/Medea operations.

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