Dr. Harris B. Stewart, Chief Oceanographer of the Coast and Geodetic Survey, and chief scientist aboard the USC&GS Ship PIONEER during the International Indian Ocean Expedition, explains scientific apparatus to visiting newsmen at Colombo, Ceylon.

Self contained underwater breathing apparatus was used by Dr. Harris B. Stewart, Jr., Ens. Paul Larsen, and QMS Dick Rogers to investigate two locations during the Pioneer's Indian Ocean Expedition--Seahorse Shoal in the South China Sea at 10o46'N, 117o44.6'E and Invisible Bank in the Andaman Sea at 11o11.3'N, 93o31.0'E. A recompression chamber was carried abroad the Pioneer as part of the equipment for the diving program. A summary of events approaching Seahorse Shoal, as adapted from the daily log of Dr. Stewart follows:

"My pocket alarm went off a bit before 0600 (March 17, 1964). I was up in the chart room with the Precision Depth recorder by about 0615. At 10 minutes past midnight (1610 GMT), we had crossed the crest of a seamount having a depth of 170 fathoms and rising from general depths of about 2,000 fms. The location was at approximately 12o45'N, 119o02'E--52 nautical miles due west of the NW tip of Busuanga Island in the Calamian group--but this feature was not shown on our chart. The PDR record showed a double peak along the trackline across it; and the towed-magnetometer record showed a marked magnetic anomaly coinciding with it.

"We were due at Seahorse Shoal about 0830, according to our dead-reckoning track as computed the night before. By 0930 (0130 GMT), we thought we had strayed west of the shoal and turned left to 090o and reduced speed to one-third. Immediately the bottom was observed to shoal from 670 fms. Lookouts were posted to observe discolored water or any change in the texture of the sea surface that might indicate the Shoal. The Captain was in the crow's nest doing likewise. By 0945, the bottom had shoaled to 500 fms. Three minutes later it was 240 fms and we decided to pull in the magnetometer fish. In two more minutes the depth was 30 fms.
Lcdr. Barbee raced to the bridge to signal "all stop" just as we heard someone shout "bottom in sight." I went to the starboard wing of the bridge and looked straight down. Alternating dark and light patches appeared to be sliding past the ship. By then the depth reading was 8 fms, less than 50 feet of water below keel depth. The bottom had risen like the front of the empire State Building as we coasted along in dark shallow water, 66 nm from the nearest land--Piedras Point on Palawan Island, the westernmost tip of the Philippine Archipelago, bearing 120o.

"Since we were over the Shoal, we decided to dredge there first. The rock dredge was put over the side at 1000 local time. This dredge had been made aboard ship and had a somewhat lighter frame than the dredges generally used. The bottom depth was now 6 to 7 fms (36 to 40 ft), so we put out 60 ft of dredge line. We had a good pull almost immediately, and then a really good one that lifted the tension dial on the big winch console off the peg for the first time. Lcdr. Barbee ordered more cable to release the tension and we put out a maximum of 325 ft. We then sneaked up on the dredge as we hauled in the cable. Nearly all hands were lining the rail as the dredge broke the surface at 1025. It looked empty and badly broken up. The pull had opened the seams of the frame and the inner wire mesh was badly torn, but a few pieces of coral were inside. Dredge No. 1 had been successful.

"As we started the dredge haul, Captain Brown asked if we would like to dive here. I answered `yes' but said I would like to reserve judgment as to whether we should or not until I had some indication about the currents over the Shoal. By 1015 I could see there was little current, although the set the night before had been to the south and southeast at about 2 knots. Preparations were made for the diving operation as the first dredge haul was completed.

"I was equipped with the following items for the dive: Geology hammer, collecting bag, wrist compass, leg knife, watch, writing slate, inflatable life preserver, tanks, fins, and mask. The other two divers had similar equipment. Larsen and I stayed under and Rogers popped up to the surface to get his camera--a French Calypso with flash--from the tending boat. Then we all met at about 20 ft., checked our watches, and headed for the bottom so wonderfully visible in the warm clear water some 30 ft. below us. Once on the bottom, we could see the full 311 ft. of the Pioneer, and horizontally, the visibility was a good 200 ft. We saw no rock other than coral and algae, but there was lots of that. This was not the luxuriant reef type of Swan Island in the Caribbean, but more open, with more coral rubble and isolated patches of intense and varied growth (fig. 111). The topography was gently rolling with occasional NW-SE trending broad gentle swales. Flat and slightly meandering valleys between the swales might not have been noticed if it had not been for the deposits of white sands and gravels in these valleys (fig. 112). These deposits were made up of coral detritus, some Halimeda segments, and lots of the big coral reef foraminifera (marginulina?).

"After looking in vain for some sign of sedimentary or igneous rock, I resigned myself to being a biological specimen collector (fig. 113). The specimens were beautiful indeed. There were occasional crinoids. The two I collected for the sack were about 8 inches high and had perhaps 50 feathery arms each (fig. 114). One was a brilliant yellow, the other was black and white. One holothurian (Sticopus?) measured two ft. long and a good 5 inches in diameter. It was a brilliant red, but lost both its shape and color once it was aboard ship and placed in formalin. Several really fine corals were collected, some of which should end up in the museum back in Washington. By the time our dive was over, Roger had shot some 24 of his 36 shots with the camera.

"After the planned 30 minutes, we started up with the three of us pulling on the bag which weighed about 100 pounds by then. My pockets were filled with sediment samples and we just could not get up. We unhooked our lifebelts, fastened them to the top of the bag, and inflated them. This provided just enough buoyancy and we broke the surface just 34 minutes after we began the dive. The boat towed us to the ship where we used the diving ladder to bridge the gap between the bottom of the starboard Jacob's ladder and the water surface which now had 4-to 5-ft. waves. While we opened the sample bag for the photographers, the anchor was brought up. The ship changed course to 080o and moved into deeper water to prepare for a deeper dredge haul along the flank of the seamount.

"The second dredge haul (Dredge No. 2) from Seahorse Shoal was successful. Between 1550 and 1650, the ship had moved 1.15 nm on a course of 276o. As nearly as we could tell, the samples were obtained from depths of 250 to 400 fms on the flanks of the seamount. There were four chunks of black rock--not coral. One piece about 6 by 4 by 2 inches, was yellowish brown, but one of the 2-inch sides was dense white. It was limestone, and contained circular fossils about 1/8-inch in diameter. One side had a borehole of some organism, possibly of a Pholad or Lithophaga of the boring mollusk type. A clear break along one side indicated that the rock had been in place until broken loose by the dredge. The largest of the other pieces was 11 by 5 by 3 inches, irregularly shaped, and covered with a heavy encrustation of manganese. Even an attached shell had a patina of manganese. The encrusting layer was as much as 1/4-inch thick in places and followed the shape of the rock, even lining the numerous cavities. Where the sample had broken from the outcrop, the surface had the appearance of igneous rock, including what appeared to be fairly large phenocrysts. When broken, and exposed cavity appeared to be filled with sediment. The second dredge also was fabricated aboard ship from lightweight material and was damaged beyond repair."

The second SCUBA dive was made in Invisible Bank off the Andaman Islands on April 17, 1964. The ship arrived here about 1400 local time. A good swell was running and great white breakers formed, crested, and rolled off the rock awash. The Pioneer anchored in 9 to 10 fms of water and one of the launches was put over the side. This dive, when compared with that at Seahorse Shoal, was a disappointment. Although the water looked clear from the ship and was clear in the top 30 or 50 ft, it was quite turbid below a very sharp thermocline and very minute suspended material limited underwater visibility to approximately 40 to 50 ft. The coral growth consisted only of occasional solitary forms. The bottom was paved with golf- to baseball-sized algal balls and broken algal material. Samples of this material and the coarse calcerous sand underneath were obtained. A sample broken from the bottom appeared to be either a dark limestone or a highly calcerous siltstone. As the divers moved back nearer to the ship, there were schools of small yellow-fin tuna, red snapper, and many variously colored small tropical fish. One large barracuda was seen. As the group headed for the launch, it was joined by a 3- to 4-ft shark. The three divers climbed the Jacob's ladder in "one bunch" and the dive was completed.