Sea Technology

MAY 2018

The industry's recognized authority for design, engineering and application of equipment and services in the global ocean community

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Page 11 of 44 May 2018 | ST 11 as the tag bobbed on the waves. Fast forward in the ob- servation record a year and a half, with the tag having completed most of its Atlantic journey and now west of Ireland, several pronounced depth spikes were apparent. Desert Star Systems' SeaTag is equipped with a float, but sometimes an animal will ingest the floating tag and dive with it until regurgitating it some period later. This was not the case here. Upon reaching depths consistent with bathymetry at each site, the tag would remain still, at near constant or just slowly drifting depth for hours to a few days before suddenly surfacing again. Other sen- sor readings confirmed the validity of these square dives and ruled out causes such as heavy biofouling or float body loss until the seemingly most unlikely of explana- tions remained: The water encountered by the tag must have suddenly become lighter, causing it to sink to the seafloor. After some time, the tag must have returned to normal density, prompting the tag to rise from the seas again; a real-life enactment of old sailors' lore of ships suddenly and inexplicably sinking beneath the waves. One explanation would be a methane seep, the mix- ture of gas and water being light enough to overcome the minimal flotation of the tag. As research showed, these events all happened within the bounds of a recent off- shore exploration. The tiny explorer, commissioned to track a shark, had inadvertently "discovered" the Porcu- pine Basin of Ireland, a large hydrocarbon field only re- cently explored. It had probed potential methane or gas seeps known in the area from the surface to the seafloor at depths up to 600 m. A 'Smartphone' for Ocean Exploration SeaTag-MOD somewhat resembles the fundamental design concepts of a smartphone specifically optimized for ocean exploration. At 145 g, weighing somewhat lighter than a smartphone, its cylindrical body is termi- nated with a syntactic float rated for service depth to 2,000 m through which runs the antenna for satellite re- porting. A thin-film solar panel covers the tag's body, and solar energy is stored in an internal ultracapacitor for use both in satellite reporting and ongoing sensor operation at night or during deep dives. A primary battery for extend- ed operation in darkness is integrated in an exchangeable plug-in payload section. The solar and capacitor design has an unlimited recharge endurance. Thus, some users A tiger shark is tagged with a SeaTag-MOD PSAT.

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