1994: Transpolar Drift IOEB Deployed

IOEB Deployment in 1994
Early in the morning of Thursday, March 31, 1994, five scientists departed McGuire Air Force Base in Wrightstown, NJ onboard a C-141 aircraft bound for Thule, Greenland. From JAMSTEC were Takatoshi Takizawa and Kiyoshi Hatakeyama; from CRREL was Bill Bosworth; and from WHOI were John Kemp, and Rick Krishfield. After a six hour flight, we were met at the Thule airport by the SPAWAR coordinator of operations, Imants Virsnieks, and subsequently housed for the night in AREA 94 barracks. The following morning we departed on C-130 aircraft for Nord, the Danish outpost in northeastern Greenland. Staffed year round by only five Danish military volunteers, this outpost very generously hosts the additional traffic caused by the AREA activity, including our IOEB deployment. When we arrived in Nord on April 1, we expected to be flying North two days later, however, because of weather delays, we were not able to leave to begin setting our camp until April 9. Previously, our two pallets of gear had already arrived in Nord. During our time there, we moved the buoy apex inside a workshop and installed the lithium battery packs, and powered the ARGOS platform transmit terminals (PTTs), meteorological sensor module, and ice sensor loggers. Consequently, the apex could be transported intact to the ice camp. On Friday, April 8, the site for the "WHOI Remote" ice camp was selected based on criteria for landing the aircraft and positioning the IOEB. The aircraft need a relatively smooth surface for takeoffs and landings, consistent with ice formed by refrozen leads. Furthermore, alternate runways should be available nearby, in case cracks form across the primary runway. On the other hand, the ideal deployment site for the IOEB would be on a large multi-year floe that is between 4 and 6 m thick. Due to the fact that most of the ice around 86 N was ruble, our choices were limited, and we decided to deploy the buoy on the selected 2 m thich icefloe. The following morning, Jeff Lord (our camp leader from PAI) and John Kemp departed on the first two flights out of Nord filled with camp gear (i.e. tents, heaters, sleds, etc.). In the afternoon, two flights departed with science gear, and Bill Bosworth). By the end of the first evening, both tents which comprised the WHOI Remote camp were already assembled, and occupied by half of our personnel. On the following day (April 10), the remaining gear and personnel arrived in three flights. Work immediately began on installing the deployment gantry and winch stand, which requires a large amount of melted ice for freezing in mounts to the icefloe. Not until the following afternoon was this apparatus deemed sufficiently secured to the ice. During Monday, April 11, many of the underwater instruments were initialized, having warmed sufficiently by being in the work tent overnight. The work tent (which also housed two of our ice party) was positioned next to the deployment gantry so that the underwater instruments could be kept warm until just before deployment. A cargo door on the end of the tent allow for the removal of the largest devices. The other tent at WHOI Remote was the communications tent which housed our VHF radio, four of our ice party, and our cooking gear. The distance between tents was about 30 to 40 m. Each tent was supplied with either a shotgun or rifle for protection against large white visitors. Fortunately, during this operation, the weapons were used for target practice only; having no encounters with polar bears. In the late afternoon when the gantry was properly frozen, work began on melting the deployment hole through the ice. Using a CRREL hot water drill ring, a 39" hole was cut through the ice and the removed in pieces using a chainsaw. Melting the hole took only about 2 hours through the 2.8 m thick ice. When the plug was removed, there was 30 cm of freeboard of the ice over the seawater. The stage was set for the buoy deployment beginning the next morning. The IOEB mooring system is deployed anchor first through the ice hole. At the very bottom is the 500 lb. lead weight, followed by an S4 current meter, a biogeochemical/sediment trap package, three C/T reorders, and a 75kHz ADCP. While each instrument is connected to the mooring cables, it is exposed the the frigid Arctic air for 15 to 30 minutes. The air temperature at WHOI Remote was between 0 and -25 F while we occupied the site. Since the underwater instruments could not be exposed to these extreme temperatures for extended periods, we used a Herman Nelson heater to blow hot air into a plastic wrap around the instruments as soon as they were removed from the work tent. We were very successful in keeping the instruments temperate using this method, as we could visually see that none of the water in the sediment trap bottles or water transfer system tubing ever froze. As another check to test the operation of each unit as it was deployed, we connected to the RS485 network with a laptop computer and converter and manually interogated each unit in the water. All units up and down the network responded properly several times during the deployment. When the apex was installed at 14:28, I can say with certainty that all instruments were communicating over the network. However, after 3 or 4 hours in the water, the ADCP/DPM combination began sending zeros. Without any spare electronic parts to repair the ADCP or DPM, we decided not to remove the underwater mooring system. Consequently, until recovery we will not be able to determine which unit has failed, or whether any data is being acquired and stored internally by the ADCP. Having made this decision, the deployment gantry and winch were disassembled for transportation back. In fact, on this day, both the hot water drill apparatus and gantry were backhauled on two separate flights. With the apex and mooring system installed, the meteorological mast containing the wind monitor and air temperature sensor was mounted. Ice stress sensors were installed in the ice surrounding the buoy (at 0.5, 1, and 2 m depths), as were an ice thermistor string and upward-pointed echo sounder. The top of the thermistor mount was situated 73 cm above sea level. The distance from the echo sounder face to the top surface of the icefloe was 4.75 m. Now the IOEB installation was complete. In three flights the following day, all the remaing gear and personnel were evacuated from the camp and returned to Nord. On April 15, we returned to McGuire AFB, completing our journey. Unfortunately, besides the ADCP/DPM, the echo sounder and the tensiometer appear to not be sending good data. Otherwise all other meteorological and ice sensors are transmitting valid information, as are the C/T recorders, current meter and transmissometer module. Both the sediment trap and water transfer system indicate that they have collected, or are in the process of collecting their respective first samples. In summary, the operation to deploy the 1994 was slightly delayed due to weather, but proceeded smoothly and succesfully, once begun. The successful transmission of the wealth of real-time data from the wide variety of air, ice, and ocean sensors will allow valuable intercomparisons to be made between the variables and processes affecting the Arctic environment in the Transpolar Driftstream.

IOEB Recovery in 1994
On November 9, 1994, at approximately 06:00 Z, the 1994 Transpolar Drift IOEB was successfully recovered in the East Greenland Sea at location 73 53.8' N, 8 3.5' W. Unfortunately most of the mooring system was not recovered, due to a break in the mooring cable prior to the arrival of the recovery team.
On the morning of November 6, four scientists departed Bergen, Norway on the Norwegian ship H.U. Sverdrup II for the purpose of recovering the IOEB deployed earlier in 1994 from an ice camp at 86 N latitude. The scientific party consisted of JAMSTEC scientists Dr. Takatoshi Takizawa and Kiyoshi Hatakeyama, and WHOI scientists John Kemp and Richard Krishfield. It would take three days of steaming to reach the buoy which was located near 74 N latitude. During this time, ARGOS locations were faxed to the ship twice a day to update the location of the drifting buoy.

The Sverdrup II reached the location of the IOEB in the dark early morning hour of 05:10 Z on November 9 and proceeded to locate the buoy in the relatively calm, ice-free ocean in only 40 minutes time using an ARGOS direction finder. The apex was tilting greatly and the surface top plate was encased in ice. Working in a light snow, crew members were lowered in a small boat to chip ice and attach a recovery line to the apex, whereupon the surface package was hoisted onto the ship using the stern A-frame. Because only the surface Seacat package remained attached to the lower mooring system, that unit was able to be pulled on deck by hand, and the recovery operation was complete.

It is apparent that this IOEB suffered excessive ice forces during its drift along the east coast of Greenland. However, the apex package appears in relatively excellent condition, with only minor surface scratches on the foam flotation collar. The top plate and bellmouth flange were undamaged, and the interior electronics tube was completely sealed, intact, and operational. Of course, the ice sensors had been previously pulled from the package, and the mast containing meteorological instruments broken off. At the bottom of the apex, a slightly cocked bellmouth flange correspond to stress wrinkles on the bottom of the foam. Whereas the potted chain cable appeared intact at first glance, it was later noted upon removal that the urethane was cracked in a complete circle around the top termination inside the bellmouth about 6" from the end.

The surface Seacat package had been damaged. The fluorometer was completely missing from its mount, and the Seacat pump was dangling from its electonics cable. Furthermore, the floation balls that mounted on the stainless steel frame were completely missing, and the frame itself was distorted. The lower termination was still attached to the frame, but just below the strain relief boot the 3/8" wire rope had broken. Surprisingly, the SeaCat was still operational, and the full data set was retrieved from the instrument.

Based upon the physical evidence from the retrieved buoy and the following synopsis of events as determined from data transmitted from the IOEB, we theorize the following scenario caused the destruction of the suspended mooring system.

Before August 29, 1994, the IOEB drifted southward intact on the icefloe it was mounted on, as indicated by stable tilt measurements inside the apex of the buoy. During all this time, data was reliably transmitted from the surface electronic instruments, and all but one underwater instrument. The IOEB had already passed through the Fram Strait, and now was located above the Hovgaard Fracture Zone at approximately 78.5 N, 0.4 E.

Late in the day on August 28 the barometer of the IOEB began to drop and wind speeds increased, indicating the onset of an Arctic storm. As the wind speed increased up to 8 m/s, the drift of the buoy to the southwest also increased up to 75 cm/s. After a slight lull in the storm on the morning of August 29, the winds and ice drift again increased; by afternoon, the wind speed was up to 12 m/s and the buoy was drifting at a rate of nearly 50 cm/s. At 13:00 Z, a major change in the status of the IOEB occurred, concurrent with a slowing and change of direction of the buoy drift. The apex tilt sensor indicated a list of 15 degrees which later increased up to 40 degrees. The air temperature and barometric pressure sensors henceforth began registering unreal fluctuations, while the wind monitor no longer transmitted wind speed information; each of these problems presumably due to the influence of seawater. Furthermore, erroneous data from all the ice sensors after this time indicate that their wires were pulled from the surface package at this same time. Concurrently, the last reliable transmissions from the underwater mooring system of the IOEB were received by the ARGOS satellite. These indicators suggest that it was at this time that the icefloe containing the IOEB broke apart; probably as a result of being rammed into stronger floes. Because of the damage to the meteorological sensors, we suspect that surface package may have temporarily been submerged below the surface of the seawater. In addition, we believe that it was also at this time that the ice penetrator cable was damaged. However, since the tilt readings rebounded after this time, we feel that the mooring system was still secured intact to the surface float. Even the meteorological sensor mast appears to have been intact up until September 7, when the air temperature readings change abruptly.

The next major change in the status of the IOEB occurred on October 4 at 18:00 Z at 76.9 N, 3.5 W. Concurrent with an increase and change of direction of the drift of the IOEB, the tilt sensor began indicating consistently higher list values of the apex. It appears that this is when the mooring system parted from the surface package.

We see three possible causes for the mooring cable to break: 1) a strain break, probably caused by rafting of icefloes around the IOEB, 2) a shear break, possibly caused by an overturning icefloe capturing the IOEB mooring, 3) a fatigue break due to vertical motion of the mooring system. The physical evidence suggests that a combination of a strain break and fatigue may be the cause. It is very likely that on September 29, that due to the storm conditions, the IOEB was caught between rafting icefloes which severely damaged the mooring system. The bottom of the apex bellmouth and the ADCP frame are likely points where edges of icefloes could catch. This would suggest that that the icefloes rafted over each other by a distance of nearly 10 m. However, since the tilt sensors suggest that the mooring system was still intact up until October 4, it is likely that vertical motion between the buoyant apex and sea-anchor sediment trap created the working fatigue required to finally part the damaged wire rope of the mooring system.