After the sampling at station #2 had been completed in the early hours of 17 April, the Ron Brown started for station #3 around 0700. Station #3 was some 600 nm and approximately two days steam to the southeast. It was a time to catch up on processing the samples, review the performance of the sampling gear, and to repair and enhance the 10- m2 MOCNESS, which had suffered some damage to the nets and towing wire on the last tow.
The weather during the first day of the transit was warm (air and water temperatures about 23 C) and the winds were around 20 kts. In late afternoon, the winds had dropped to around 13 kts and the skies remained nearly cloud free.
In an examination of the second deep 10-m2 MOCNESS tow, the contamination issue loomed large. For reasons that are not clear, the opening/closing of the nets on this tow did not show any significant angle change, as is usual when one net is closed and the next one opened. A plot of the angle versus time data for both tow #1 and #2 clearly showed the angle change spike associated with the closure of net 1 and the opening of net 2, the closure of net 2 (which also resulted in the closure of net 3 and the opening of net 4 [because of the broken tab]) and the closure of net 4. No such spikes were associated with the commands to step the toggle on tow 2. In discussions with Martin Angel, Francesc Pages, Tracey Sutton, and Dhugal Lindsey, all taxonomic experts on a variety of zooplankton and fish groups, only net 1 on tow #2 seemed to be a true bathypelagic catch, albeit with lots of nearer surface species also present in the sample. The other nets had poor catches and few deep-sea animals. In working up the catch from net 2, Martin made the assessment that most of it was from contamination.
In looking carefully at the gap between the bars when the system was cocked and the cables were tight, there was a gap about 2 to 3 cm wide by 300 cm long. Although seemingly small, when the area was computed and then multiplied by the length of a tow, a considerable volume of water could have passed through the gap and into the net, even when closed. For tow #2, the ship traveled nearly 33 nm (~61,000 m) and gap volume could have been around 4800 m3. This is huge and could very easily explain the contamination problem. Discussion about how to reduce or eliminate the gap contamination problem took place during the day and a plan was devised to construct some net bar flaps that would hang from each net bar and cover the gap between it and the bar below. After dinner on the 17th, concerted work ensued to perfect the design and then construct the flaps out of a plasticized cloth material that the Bosun provided. Eight panels were needed that were147 cm long and 42 cm wide, with two panels per net bar, one on either side of the middle support for the net retaining rods. The first panel was installed and then some additional discussion took place between those concerned with the contamination about the design and possible problems. All thought the flaps would work while the bars were at the top of the frame, but they were skeptical that the flaps would stay outboard of the bars after they were released. In fact they thought they would be folded inside the net and not close the gap. So an idea to put stays made out of the stiff tie-wraps was put forth to keep the flap fairly stiff and even if they folded in, the material would likely still block the opening enough to reduce the contamination. The rest of the evening was spent making up the flaps with tie-wrap stays, which were installed on the morning of the 18th.
During the evening, the wind picked up and on the morning of the 18th velocities between 19 and 26 kts were recorded. A front went through the area around 0800 and there was a wind shift from 240 degrees to about 210. A rain squall line passed through, although there was no rain on the ship. The wind shift put the wind and seas coming in on the starboard beam, causing the ship motion to increase significantly. This made it difficult for investigators to work on the samples using the microscopes. So the lab was a bit empty during the morning.
There was some excitement around 1030 on the 18th when the bridge sighted a small (~15 feet) overturned boat drifting out here in the middle of nowhere (at 26 53.37N; 64 21.73W). The ship slowed and maneuvered to bring the hull close enough for inspection. As it passed along the starboard side, some large fish were sighted swimming around it. Shortly after this we again picked up speed and headed for Station #3.
In the afternoon, the wind picked up substantially and sustained speeds were between 25 and 31 kts from the southwest. With the sea abeam, the water was coming up onto the starboard deck and flooding out into the aft deck area, making working conditions there more difficult.
The issue of the kink in the 0.68" trawl wire was resolved just after lunch as a result of consultations with Jeff Hill (ET), Jonathan Shannahoff (MT), and Bruce Cowden, the Bosun. All indicated that the cable should be re-terminated. Shortly after, the termination was unbolted from the trawl and carried into the staging bay. There the wire was cut and the process of removing the stainless steel fitting from the wire and then re-installing it on the new end of the cable was started. Erich Horgan did most of the work, which was completed around 2200.
During steams between stations, a seminar series of talks had been planned and the first of the series started at 1300 on the 18th. The first two lectures were by Martin Angel and Leo Bercial. Martin talked about Ostracods and the web site he has constructed to provide students and experts easy access to the literature, keys, illustrations, data about the distribution abundance and size of the 200+ Ostracods in the world’s oceans. Leo talked about the copepod genus, Clausocalanus, that he has been working on. He is developing a genetic method to easily distinguish between species of this genus, a number of which are exceedingly hard to distinguish morphologically.
The second of the safety drills occurred around 1500 and consisted of a ship collision drill and an abandon ship drill. For the latter, people mustered in their alternate sites inside the ship in order to have dry space to put on their survival suits.
Following the drill, the lecture series continued with Nancy Copley describing the Silhouette technique for measuring the abundance, biomass, and size distribution of zooplankton in a sample by taxa.
After dinner there was an intense period of activity to finish setting up the 10-m MOCNESS. A last addition to the frame was a pair of canvas deflector flaps that Larry Madin and Erich Horgan had made a couple of days ago. Holes were drilled in the side I-beam to attach the flaps to the frame. A check of net 1 revealed more extensive damage to the net than had been suspected and this net was replaced by the spare. The nets were then loaded and arranged for launching with all the cod-ends on and at the bottom of the frame. With all the nets inside the frame, the side deflector flaps were bolted onto the frame with 3/8 cap screws. Finally, we put grommets in the corners of the deflector flaps and then tied a bungee cord to the each grommet and put a clip on the other end. This was attached to the frame so that the flap would tow streaming around the outside of the frame, thus covering the open portion of the closed nets.
While this was going on, Erich Horgan was finishing the new termination. About 2200 on the 18th, the cable was attached to the underwater unit on the trawl and tested with the MOCNESS software. The software ran with no problem.
The evening came to an end with the winds having died down some to between 15 and 20 kts from the southwest. Sea and air temperature remained the same at 23 C. Work was set to begin at 0630 on the 19th upon arrival at station #3.
A couple of brief reports from investigators on board highlight the work going on to identify the species in the net tows:
Martin Angel on planktonic Ostracoda:
Forty-eight species of planktonic ostracods have been picked out of the samples from stations 1 and 2. One of these species is totally new and another has been collected from deep water in the north-east Atlantic, but is yet to be described. The others are all known species, but four have previously been reported less than five times. Thirty-three have already been picked out for sequencing. Seventy-five species have been reported previously from the waters around Bermuda and so my target of sequencing at least 50 species looks to be achievable.
Francesc Pages on planktonic cnidarians: Our main goal is to increase the knowledge of the species composition and vertical distribution of siphonophores and medusae below 1000 metres depth. Many species have been identified since the start of the cruise, mostly mesopelagic medusae. However, one of the nicest and more interesting specimens is an epipelagic narcomedusan of the genus Pegantha, whose 2 otoporpae (lines of cnidocysts) per marginal lappet bifurcate ending in 4 statocysts (sensorial organs), a splitting never reported in the rest of narcomedusae. This may be a new species.
Figure 1. An unidentified Pegantha, which was collected by the 1-m MOCNESS on tow# 3, net 8 (upper 25 m).