1 TECHNICAL NOTE

2 Revisiting the Challenger Deep

3 using the ROV Kaiko

4 AUTHORS 23 of normal human experience—it is descent. The launcher, about 5.2 m in 55 5 James P. Barry 24 the same distance as the altitude of a length, 2.6 m wide, and 3.2 m high, 56 6 Monterey Bay Aquarium 25 commercial transcontinental or trans- acts as a heavy weight (5.8 tons in air) 57 7 Research Institute 26 oceanic flight. Although sitting in the to help the Kaiko system to sink rapidly 58 27 ROV control room (Figure 2) aboard to depth. It has limited capabilities for 59 8 Jun Hashimoto operation near the seabed, but can be 60 9 Nagasaki University FIGURE 2 used without the vehicle as a towed sys- 61 tem equipped with side-scan sonar, 62 ROV control room on the R/V Kairei during 11 fter the remotely operated vehi- a sub-bottom profiling system, and a 63 descent of the Kaiko in the Challenger Deep. 12 cle Kaiko (Figure 1) was launched sensor package (CTD). For use with 64 Two primary pilots operate the Kaiko thrusters 13 A Kaiko vehicle 65 from the deck of its support ship, the and manipulators while other support personnel the ,thetwoaremated 14 research vessel Kairei, it descended for and researchers watch. through a 250 m long tether that un- 66 15 more than 3 h through nearly 11 km reels from a spool mounted in the 67 16 from the surface of the calm seas launcher,allowingthevehicle a relatively 68 17 ∼320 km SW of Guam to the seabed short but unconstrained ambit. The 69 18 at the bottom of the Challenger Deep vehicle is the heart of the Kaiko system, 70 19 in the Marianas Trench. Even watch- and once released from the launcher,it 71 20 ing the Kaiko system in operation, it canuseitsfourhorizontalandthree 72 21 is difficult to imagine just how deep vertical thrusters (∼5 kW each) to ma- 73 22 11kmisuntilyouputitinthecontext neuver freely near the launcher, explor- 74 ing and sampling the seabed. It is 75 FIGURE 1 smaller (3.0 m long × 2.0 m wide, and 76 36 the Kairei in 1998 could not have 2.1 m long) and lighter (3.9 tons in air) 77 Kaiko ROV during recovery from the Challenger 37 equaled the intensity of a descent in- than the launcher and is equipped with 78 Deep. The launcher (top half) and vehicle (lower 38 side the cramped sphere of the Trieste several CCD and wide angle color video 79 half) are both visible. 39 38 years earlier, watching as the dis- cameras, a digital still camera, several 80 40 play of Kaiko’s depth sensor in the high-intensity lights, and several sen- 81 41 ROV control room counted past sors (forward looking sonar, altimeter, 82 42 5,000, 7,000, and 10,000 m was depth, compass, GPS). Two highly 83 43 captivating, to say the least. When dexterous manipulator arms (six axes 84 44 the seabed finally appeared through and seven axes of motion) enable op- 85 45 the darkness as the ROV reached erators to deploy and recover samples 86 46 10,924 m, we knew we had witnessed or gear from the front-mounted sam- 87 47 somethingveryspecial. ple basket. 88 48 JAMSTEC, the Japan Agency for Deployment, positioning, and re- 89 49 Marine-Earth Science and Technology, covery of a massive system like the 90 50 developed the ROV Kaiko in 1995 to Kaiko are complicated operations. At 91 51 enable scientific research in the deepest 106 m length and 4500 tons displace- 92 52 trenches of the oceans. The Kaiko is a ment, the R/V Kairei is a very capable 93 53 two-body system with a smaller mobile support ship, with berthing for 22 re- 94 54 vehicle latched to the launcher during searchers, and is outfitted with a large 95

Winter 2009 Volume 43, Number 5 1 96 multipurpose A-frame and winch sys- 109 tensioning system, across the aft deck FIGURE 5 97 tem. The Kaiko is protected in a hanger 110 to the A-frame pulley, and over the Collection of sediment core samples at 98 Kairei 111 when aboard the (Figure 3). Be- side. Very accurate navigation of the 10,924 m in the Challenger Deep. 112 Kaiko is accomplished using a set of FIGURE 3 113 three acoustic transponders arranged Aft hanger for ROV Kaiko maintenance, looking 114 as a long-baseline system that can toward the stern A-frame. The primary tether is 115 be pinged from the launcher and vehi- visible above the coarse net. 116 cle.OncetheKaiko system is within 117 100 m of the seabed, the vehicle is un- 118 latched from the launcher and the sec- 119 ondary cable (∼3 cm diameter) is paid 120 out to allow the vehicle to wander the 121 nearby seabed. Transiting long dis- 157 122 tances (several hundred m or more) of inhabiting hadal depths must have 158 123 while the Kaiko is deployed is difficult proteins, enzymes, and membranes 159 124 but possible by towing the launcher tuned to extreme pressures. Food is an- 160 125 using the Kairei. Recovery of the Kaiko other problem. Deep-sea ecosystems fi depend on the rain of organic debris de- 161 99 fore each dive, it is rolled to the aft deck 126 rst requires re-reeling the primary launcher rived from surface production, which in 162 100 deployment station on rails. Upon de- 127 cable on the and re-mating vehicle the oligotrophic waters over the Chal- 163 101 ployment, the A-frame lifts the nearly 128 the , then rewinding the primary Kaiko lenger Deep is typically quite low. In 164 102 10-ton mated Kaiko system over the 129 cable until the can be reattached addition, consumption and recycling 165 103 stern. The primary tether, ∼4.5 cm 130 to the A-frame and lifted aboard the Kairei Kaiko of organic material as it sinks toward 166 104 diameter with optical and copper con- 131 .The made numerous hadal depths burn much of its nutri- 167 105 ductors, is then paid out at ∼1m/s 132 dives in various trench systems until vehicle tional value through each kilometer 168 106 from a single massive (>7 m in diam- 133 2003, when the was lost near of depth, resulting in well less than 169 107 eter) steel spool (Figure 4) holding 134 the surface when the secondary tether 1% of surface levels expected to reach 170 108 12,000 m of cable, through a cable- 135 was severed during a storm. Unfortu- ∼ 171 136 nately, a power failure on the vehicle 11 km. Consequently, little food is available for any life tolerant of the 172 FIGURE 4 137 had prevented re-mating it with the 173 138 launcher prior to ascent. The Kaiko high pressures in the Challenger Primary tether spool for ROV Kaiko. 174 139 was returned to service in 2004 as the Deep. Future visits to the Challenger 175 140 Kaiko 7000 II (rated to 7,000 m) after Deep using new deep-diving vehicles 176 141 adapting a 7,000 m rated ROV as a will allow researchers to test hypotheses 177 142 vehicle compatible with the original related to the role of extreme pressure, 178 143 launcher. food limitation, or perhaps other fac- fi 179 144 The ROV Kaiko completed a series tors in de ning the boundaries of life 180 145 of dives at the Challenger Deep in 1998 in this extreme environment. 146 and succeeding years during which 147 researchers saw very sparse life on the 148 seabed (Figure 5). Two major factors— 149 great ocean pressure and potentially 150 severe food limitation—make the 151 Challenger Deep one of the most ex- 152 treme environments on Earth. The 153 weight of seawater reaching nearly 154 1,100 atmospheres affects protein sta- 155 bility and membrane permeability in 156 all organisms, such that any capable

2 Marine Technology Society Journal