Sea Technology

FEB 2013

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Deep NINJA Collects Profles Down to 4,000 Meters Deep-Float Project Aims to Fill in Gaps in Ocean Observations By Taiyo Kobayashi ��� Kazuhiro Watanabe ��� Michihiko Tachikawa I n recent years, the deep ocean has been increasingly recognized as one of the important components of the global climate system. This is due to changes and variations of temperature and salinity that were detected in the deep ocean, the subsequent infuences of which may be much larger on the global climate than what had been previously expected. For example, comparisons between accurate hydrographic surveys conducted in the 1990s and 2000s showed signifcant warming in the deep and bottom layers of the Pacifc Ocean at frst and then others. The heat that accumulated in layers deeper than 3,000 meters of the ocean was estimated as 15 percent of the total heat accumulated in the entire Earth. However, such estimates of the deep ocean include larger errors than other components of the global climate system and thus are recognized as bottlenecks in understanding the anthropogenic global change and predicting its future accurately. The largest cause of these errors is the sparseness of deep-ocean observations. Therefore, more deep-ocean observations are required for not only scientifc reasons, but for the environmental security of human society as well. The efforts to increase the number of deep-ocean observaA schematic comparison between present Argo foat and deep-foat tions, however, are almost limited since a majority of observations. the observations are conducted by research vessels. Thus, establishing a monitoring network with numerous Two comprehensive feld tests were conducted with JAMfoats in the deep ocean, called Deep Argo, was proposed STEC research vessels in Sagami Bay in August 2011 and to the international community of ocean science. the Sea of Japan in May. Then, in the summer of 2012, a Floats have several advantages over existing devices for feld test was carried out in the Pacifc Ocean. Deep proocean observations. They can operate in severe conditions, fles from the depth of 4,000 meters were obtained by the e.g., at high latitudes during winter, and as a result, obtain foats. The successfully developed deep foat was named data without seasonal limitations. After deployment, the Deep NINJA. foat can continue to perform observations for long periods Deep NINJA can measure oceanic profles from the sea automatically, which provides oceanic data in inaccessible surface to a depth of 4,000 meters. It can obtain measureregions, such as the Southern Ocean. The higher cost-perments throughout the global ocean, from the tropics to the formance is another advantage of foat observations. high-latitude waters seasonally covered with sea ice. The development of Deep Argo, however, has not started This suggests that approximately 90 percent of the ocean���s yet because most foats cannot reach depths greater than 2,000 volume is measurable by Deep NINJA, whereas existing meters. Therefore, the Japan Agency for Marine-Earth Science foats, which can only submerge to 2,000 meters, can meaand Technology (JAMSTEC) and Tsurumi Seiki Co. Ltd. (Yokosure about 50 percent of the ocean���s volume. It has a height hama, Japan), began to develop the deep-ocean foat in 2009. of 210 centimeters (including the antenna) and a weight of approximately 50 kilograms in air. The First Deep Float: Deep NINJA The pressure hull is made of aluminum-alloy and has a The frst deep-foat prototype was assembled in March diameter of 20 centimeters for the cylindrical components 2011, and its control module was tested in coastal waters. and 25 centimeters for the central bulge. www.sea-technology.com FEBRUARY 2013 / st 41

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