Tuesday morning, we got out on the water shortly after 10am, and Anibal Santiago Mercado ("Nibo") maneuvered the boat so that it was anchored into the current with the stern hanging back exactly level with the pylon. Throughout Tuesday's and Thursday's work it was extremely easy to step from boat to pylon and back again, even despite some moderate wind and waves. We started with a quick pylon climb to shut off the station's power so that the underwater instruments and cables could be removed without worrying about whether the cable plugs needed to be kept out of the water.
As mentioned previously here, two of the station's four underwater instruments had already failed and been removed, so there remained only two more instruments to remove today: the shallow light sensor and the deep CTD. As soon as we saw the deep CTD (see right), it was obvious why the station was without power -- the CTD's plug was snapped off and hanging at a 45-degree angle, with its internal wiring clearly visible. It's impossible to say for sure whether this happened back in April when the station last lost power, or whether something else failed in April and this CTD connector broke more recently, but it seems reasonable to assume that this broken plug was the cause of the April power failure. Note too that this CTD did not come back online at the point in time that the station recovered from its February 27th - March 31st downtime, so its communication wiring may have been impacted as early as late February.
The morning's dive took about half an hour and by noon we were done.
Next, I climbed the pylon to disconnect and lower the "brain" (control unit), the three aerial masts with their four instruments (Vaisala integrated weather transmitter or "WXT," anemometer, electronic compass and surface light sensor), and the two battery packs. As mentioned in yesterday's blog entry, these batteries had been continuously deployed since January of 2006 and in this trip we would be replacing them with new batteries of the same model. The photo at left shows me lowering one of the two battery packs down to the boat.One unpleasant surprise was that the Vaisala WXT's custom-made bird deterrent had not survived its maltreatment by the boobies that like to sit on every available surface of this station. More so than at any other CREWS station, this station's surface instruments are returned to us with a very thick layer of bird guano covering everything. Since we don't ship new WXT bird deterrents for each swapout (although henceforth, we will do so), and since only one of the deterrent's original six spikes remained (and even this spike was bent flat), this means that the new WXT will have to be deployed with no bird deterrent and its wind/rain measurements may therefore degrade more quickly than usual.
Another problem is that the station's grounding cables, used to electrically connect all the aluminum masts with the electrical ground of the electronics, the lightning diffuser brush, and the grounding plate mounted near the ocean floor, are now falling apart. The spare grounding cables brought along on this trip were built with a different station design in mind and were too short to be useful for this station, but I repaired/replaced them as far as was possible.
Last on today's agenda was replacing the underwater cables. This station is unique among CREWS stations in that its internal conduits (which run from just below the solar panels down to the ocean) have their openings beneath the ocean's surface. This experimental design was not repeated elsewhere because those internal conduits quickly fill with barnacles and other sharp growth and this greatly impedes any effort to add, remove or replace the underwater cables on this station.
A survey of the underwater cables during our dive revealed that there were two cables emerging from the south conduit (which were used for the two deep instruments) and four cables in the north conduit. This was one more cable than I recalled, but the fourth cable was originally installed for the SAMI pCO2 sensor which has not been present for many years, and the SAMI cable is a simpler (less tough) design compared to the "fishbite" cables used for all other instruments. Since the SAMI cable was no longer being used and its polyurethane coating was cracking open where it had been exposed to the sunlight, we simply removed and discarded it during this visit.
The five new cables had been prepared by taping their ends (for when they would briefly be submerged during installation) and attaching a distinct number of cable ties (one through five) to each end so that the cable ends could be matched up and the correct cable could be wired to the correct instrument. During this operation we ran cables #1, #4 and #5 up the northern conduit for the shallow instrument and cables #2 and #3 up the southern conduit for the deep instruments.
We started with the southern conduit. We taped the end of a "fishtape" spool of hard plastic wire to the clipped ends of the deep instrument cables, and pulled them down the conduits from below. Throughout this part of the work, I (Mike) stayed atop the pylon and Pamela frequently entered the water on snorkel to pull or push the cables past some obstruction or other. Nibo stayed in the boat and taped the end of the new cables to the fishtape. We were pleased and gratified when the two old cables pulled free of the station with almost zero resistance but met with difficulty when trying to pull the two new cables back up the conduit to replace them. This was mostly due to debris and growth inside the underwater conduit. After three tries, we eventually managed to feed a single cable up the conduit and then tie the second cable end to the middle of the first cable and feed both cables that way.
Turning to the northern conduit, there was one additional complication -- this conduit also held a green grounding wire (see photo at right, taken during Thursday's work) that ran from the mast/electronics/brush grounding system to the grounding plate at the base of the pylon. Even if we'd wanted to try feeding all three new cables up to the top of the pylon (which we did not, given the frustration we'd had with trying to feed two cables at once up the other side), we did not want to pull out all four cables from the conduit at once for fear that they might be wrapped around the grounding wire and might cause it to pull loose or break.So we decided to feed the new cables one by one. We started by pulling out the SAMI cable, since it was distinguishable from the other three at both the top and the bottom, and fed a new cable to replace it. Then it occurred to us that we could pull free a second cable at random without using it to feed a new cable, thereby freeing up some space in the conduit. After that we replaced the last two cables one by one. This took much longer than expected and we didn't leave the station that afternoon until almost 5:30pm. But we were well-poised for the rest of the week's work.
[All photos taken by Pamela Fletcher.]