Iceland-Scotland Ridge Exchange Flow Seaglider Surveys

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The scientific goal of the project is to document and understand the seasonal and interannual variability of both Atlantic inflow to and deep overflow from the Nordic Seas over the Iceland-Scotland Ridge, a region where meridional overturning circulation deep branches are formed and important shallow branches concentrate. Currently, the most reliable estimates of exchange across the Iceland-Scotland Ridge are based on currents and hydrography sampled with different spatial and temporal resolution, with different techniques, and with debatable values for reference temperature and salinity. The detailed spatial structure and seasonal and interannual variability of circulation in this region has yet to be resolved. In the context of global climate change, decline of the meridional overturning circulation is widely predicted. Climate models are very sensitive to these transports and resolution of them is crucial to understanding ocean climate variability, past, present and future. New observations (primarily physical) will be used to infer entrainment sites and to quantify transports by water mass type for use in improving climate models, whose predictions under global warming are sensitive to the physics of the high-latitude ocean. The intense biological productivity of the region, which depends on these circulations and water masses, will also be profiled optically. Long-range autonomous underwater vehicles (Seagliders) will be used to collect full-depth hydrography and estimate absolute geostrophic velocity sections simultaneously of both shallow northward inflow and dense southward overflow across the Iceland-Faroe Ridge and the Faroe-Shetland Channel. This domain is thought to account for about 90% of the Atlantic transport poleward and about half of the deep water transport equatorward (the remaining portion passes through the Denmark Strait). Seagliders will collect high-resolution sections of temperature, salinity, dissolved oxygen, fluorescence and optical backscatter as well as depth-averaged horizontal velocity. The sections will resolve seasonal variations and begin to detect prominent interannual variations. One Seaglider will traverse the Faroe-Shetland Channel weekly while a pair of Seagliders will survey the southwestern flank of the Iceland-Faroe Ridge, repeating a ~1000 km track monthly. The vehicles will be deployed in 4-month missions continuously for 3 years, using vessels in the Faroe Islands for launch and recovery. The plan is to collect about 30,000 full-depth (500-1000m) profiles with 3-6 km horizontal resolution across nearly 60,000 km of track during the three year project, all delivered in near real-time via satellite. Real-time command of the Seagliders will allow mapping of finescale water masses and frontal features. The observations will be carried out in conjunction with mooring/ship observations of on-going projects, and with Norwegian, Icelandic and Faroese collaborating scientists The study is a contribution to the U.S. CLIVAR (CLImate VARiability and predictability) program..Intellectual Merit. The most basic dynamic balances of the global overturning circulation of the oceans are under debate. Global change may alter the overturning circulation and with it, global climate and ecosystems. High resolution climate observations with radically new platforms, sustained in time, can guide the numerical climate models which are increasingly relied upon in matters of policy and planning Broader Impacts. Beyond physical science, this work relates to ecosystems in one of the most biologically productive sites on Earth, and a region of strong uptake of carbon from the atmosphere. The work will provide bio-optical profiles and sections at high resolution in regions of unusually high biological productivity. The interdependence of fisheries and physical oceanography in this region is extremely strong, as primary productivity is associated with buoyant, low-salinity layers which trap phytoplankton. The research contributes to our undergraduate teaching in environmental studies, in which the methods and results of science are put before young students who are the beneficiaries and custodians of the environment.