April 27, 2006

Flying the MOCNESS Lonster

The last zooplankton net came up this morning and we are now steaming for Puerto Rico. We spent the rest of the day disassembling and packing supplies. This will be a lot of work. I am not sure how many days it will take to get to Puerto Rico, but we are scheduled to arrive sometime Sunday morning. No more Lock Ness Monsters to be found at sea or should I say no more MOCNESS Lonsters. This spoonerism is an enduring term that Dr. Peter Wiebe, the Chief Scientist, aboard the cruise, calls his net system. For a side note, the word spoonerism is named after Rev. William Archibald Spooner, Warden of New College, Oxford. Rev. Spooner was well-noted for transposing first consonants in words while speaking, such as referring to a bride about to be married, when he said, "It is kisstomary to cuss the bride". Peter is the designer of the MOCNESS net systems, from the operating software to the mechanical release mechanism. Peter is not an engineer by training. He did however enjoy dismantling and reassembling his car when he was younger. Dr. Wiebe is a population ecologist who studies zooplankton. He has published papers on such topics as organic matter transportation in the deep-sea, zooplankton association with hydrothermal vents, and the biology of Gulf Stream Rings. Many of the scientists on this cruise have been in deep-sea submersibles, including Peter. He tells a story about traveling three miles down to collect plankton from a hydrothermal vent. The pilot of the submersible was jamming out to rock music, while giant anemones clung to the canyon wall. Peter described the surreal experience of cruising over deep-sea smokers and witnessing the bizarre environment of the deep. This job may be scarce in the future students, as many submersibles are being replaced with ROVs. Perhaps the ARMADA Project should send a teacher to the bottom of the sea, before robots only will venture to those depths. Peter, among others, has enjoyed very little sleep during this cruise. Peter is either running out to get the nets ready to deploy or sitting by the monitor, communicating with the deck, the bridge, and the MOCNESS miles below. While the net is in the water a person must be at the computer and ready to communicate with the bridge and the winch. Therefore it is a 24-hour job while we are on station. Periodically I would stand computer watch, typically when nothing was suppose to be happening to the nets, such as on its slow dive down. A special cable with a wire is used to tow the nets. This wire feeds into a computer in the lab. The software program monitors depth, net angle, salinity, temperature, battery charge, and tow velocity. There is also an electronic switch to drop nets. Since the MOCNESS has multiple nets, the nets can be opened and closed at varying depths.

Our last station was of particular interest to Peter and others. The water column that we sampled has an unusual depth profile. The depth profile graphically shows a staircase pattern for both salinity and temperature. That means instead of a constant continual drop in temperature and in turn salinity with depth, there are regions were the salinity and temperature are constant. This is indicative of intense mixing of water with varying salinities. These staircase patterns are called salt fingers. The variable water in this region is coming from several sources. The low salinity water is from equatorial regions where rainfall exceeds evaporation rates. There may even be some influence of Amazon River water on these salt fingers. The warmer and highly saline water originates over the doldrums in the eastern Atlantic, where evaporation rates are high. There is also a low salinity influence from the Antarctic Intermediate Water on the staircase's profile. This water is part of the thermohaline circulation. The staircase is an unusual aspect of the ocean's water column. We specifically sampled these fingers to investigate if zooplankton communities in the column show varying association within the mixing zones. Peter took care to sample in both the mixing regions and the stable regions of the staircase. There did not seem to be an obvious difference, when comparing the general appearance of the samples in the processing lab, but many of the animals are microscopic. Further examination will be needed to determine if patterns can be measured. A detailed study of the salt fingers in this region of the ocean can be found at the following source.

Schmitt, R.W., Ledwell, J.R., Montgomery, K.L., Polzin, K.L., and Toole, J.M. 2005. Enhanced Diapycnal Mixing by Salt Fingers in the Thermocline of the Tropical Atlantic. Science Vol 308, pp.685-688

Daily question: What does 'ROV' stand for?


Picture 1: Peter Wiebe, from WHOI, flying the MOCNESS.

Picture 2: MOCNESS computer readout.

Picture 3: Erich Horgan, from WHOI, launching the MOC-1m2 net system.

Picture 4: Russ Hopcroft, University of Alaska, assisting in net launch.

Picture 5: Aft deck, Ron H. Brown, and MOC-10m2 net system.

Picture 6: Launching the MOC quarter-meter net system off starboard.

Picture 7: Peter Wiebe and Martin Angel lowering cod-end buckets.

Picture 8: MOC-10 beginning to collect zooplankton.