Information and images from GNS website which includes images by JAMSTEC
The Japanese submersible Shinkai 6500 was busy in New Zealand waters in the final months of 2004 assisting scientists to study undersea volcanoes, hot seafloor vents and the strange lifeforms at depths of 1,850 metres where water temperatures can exceed 300 degrees celsius!
This expedition, SWEEP VENTS, is the culmination of several yearsâ work involving the mapping of the final part of the Kermadec arc within New Zealandâs Economic Exclusive Zone and into Tongan territorial waters. The scientists at the Institute of Geological and Nuclear Sciences (GNS) led by project leader, chief scientist Cornell De Ronde in conjunction with their international partners started the project in 1999. The recent expedition was conducted in conjunction with the Japanese Government owned, Japan Agency for Marine-Earth Science and Technology (JAMSTEC). In that year they systematically surveyed a 360km stretch of the submarine arc looking for hot springs. The results were spectacular with seven of the 13 volcanoes hosting hot spring vents.
In 2002 a further 550km was surveyed.
With the completion of NZAP PLUME III which joins on to a segment mapped during the Australian 2002 TELVE cruise meant that approximately 1,800 km had been surveyed for hydrothermal venting.
The Japanese are funding most of the projectâs $10 million cost.
During the October/November 2004 expedition the submersible dived two of the Kermadec Arc volcanoes: Brothers and Healy.
On the GNS web site Gary Massoth a chemical oceanographer, describes a dive on the Brothers volcano. Following is part of Garyâs description of the dive. The full details can be viewed on GNSâs web site, address listed at the end of this article.
Dive date: 28 October 2004:
âWe began our descent at 0952hrs. By 250m all surface light appeared to be absorbed as we continued down into the blackness, interrupted only by the occasional bioluminescent creatures passing our viewing ports. Position âfixesâ passed to us from the mother ship Yokosuka indicated we were about 300m west of our intended landing point, so we began a slow drive to the east while we descended. At 1300m depth we dropped our two descent weights and trimmed the submersible. We observed bottom at 1034hrs. The manipulator arm was used to close a 2.2L water sampling bottle for comparison as âbackground waterâ to vent fluids we would collect later.
After 48 minutes of descending we landed on a rocky bottom at a depth of 1379m, about 150m NE of our first sampling target, which was the summit of the lower of two peaks that cap the strato-cone which we were to explore. The high-resolution swath bathometry data upon which terrain models were produced for viewing this area prior to our dives suggested a smooth 30Â°+ slope would rise to the summit peak. What we saw was quite different: a metre to several-metres-high steps composed of precariously poised slabs and smaller rocks angularly chiselled by previous tectonic bashing.
Cross-cutting these steps were metre to several-metre wide ravines that radiated from the summit like spokes on a wheel providing patches of smooth relief due to extensive infilling by grey, flow wave-rippled volcanic ash that in most instances completely buried the underlying talus. At our initial landing point a 15cm blue translucent fish and one 2cm-long shrimp were the only fauna observed. We ascended to about 1335m when a remarkable transition occurred: almost everywhere we observed a rather vigorous, clear discharge visible as schlieren that bathed the bottom to an average height of about 30cm. This depth also demarcated a biological transition boundary, as associated particularly with the white surface covering. Apparently grazing on it was a ubiquitous population of shrimp, appearing to be of two distinct sizes: the small 2cm and less size seen deeper and, in less abundance, larger individuals greater than 4-5cm in length. As the submarine passed, the effect was like being in a shrimp snowstorm with hundreds if not thousands of âshrimp-flakesâ swarming about the submarine. An observation that struck me was the eyes of the red coloured shrimp appeared to have a bright yellow illumination, like wolves in the dark when spotted by a torch. On elevated outcrops, just above the layer of shimmering water, there were abundant (20-40 individuals per square metre) clusters of stalked barnacles with white-puffed plumes blowing in the current. Spiny/hairy crabs about 7cm in girth were foraging in moderate abundance. The translucent blue fish observed deeper was also in some abundance, but not so great as the slightly larger (up to about 30cm-long) flesh-coloured semi-translucent fish that mingled with the shrimp in the shimmering water. Up to six of these fish could be seen out the porthole at one time.
Our second and final target, the upper summit peak at a chart depth of 1210m, lay 500m to our northwest. We quickly flew above the seafloor taking 20 minutes to reach the 1300m depth on the southwest flank of the cone. We landed on a slightly steep slope, which was again heavily sedimented by grey volcanic ash interrupted by occasional outcrops of well-weathered volcanic rock. No glassy rock surfaces were observed and neither sessile nor motile fauna were abundant, only the occasional small shrimp. The peak summit was characterized by a 40m diameter pit crater about 10m in relief with a minimum rim depth of 1196m. We rigorously explored the pit crater and the southern side of the summit peak down to a depth of about 1260m and did not observe active or relic sulfide structures or high-temperature venting, only very sporadic diffuse fluid discharge. Vibrant, visually observable biological communities were missing.
Our sampling activity at this summit comprised of: 1) collection of pieces of a 1m tall chimney that looked like massive sulfide, but upon sampling this proved to be a sulfur chimney with an oxidized (by microbial activity?) brown surface; 2) collection of top-pieces from one of about five relic chimney structures. Some being greater than 6m in height.
Deployment of a temperature sensor/recorder within the flowstream of a vent for recovery on a subsequent dive programme (data reordered every 2.5hrs for 185 days). We departed the bottom at 1656 hrs.â
The programme is to continue in March/April 2005 with the American research vessel, Kaâimikai-o-Kanaloa and its submersible Pisces Visit:
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