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How stable are our ocean fronts?

SAFI research into Sea Surface Temperature (SST) has revealed some of the many complexities of water mass convergence zones: areas critically important to maintaining our ocean’s fisheries and ecological systems. These zones frequently represent areas where colder, nutrient rich water mixes with warmer waters. This interaction fuels increased plant growth at the bottom of the ocean food chain, feeding the system that produces the fish we eat.

A prime example concerns tuna, and research being undertaken in ACRI-ST computes SST fronts from daily, weekly and monthly SST data. These products are used for a range different applications in SAFI, one of the latest being an analysis of Bluefin tuna migration routes in the Gulf of Cadiz with IFAPA. Spatial analysis of SST isotherms and fronts is delivering interesting information to determine the tuna migration corridor. The first results in 2015 from SAFI research captured an excellent year in the South east part of the gulf (near Gibralter) (see fig.1); these results show that the exceptional catches of this year are related to a well-established 18°C isotherm in the fishing areas, as tuna migration routes are constrained by the 19°C isotherm. 

Meanwhile, researchers at University College Cork are currently trialling and refining novel hyper-temporal Earth Observation image analysis techniques and have discovered a surprising amount of variability in the strength and permanency of fronts between water masses of different temperatures (see fig. 2). Some regions have a strong and stable interaction zones between water masses (e.g. Eastern Coast of Iceland), while others (such as the waters surrounding the Straits of Gibraltar) are more variable from year to year in terms of location and strength. Fluctuations such as these could affect local fishery recruitment, with young fish and larvae facing unsuitable conditions with a frontal shift, or adults facing a need to modify their migration routes.

“This is really exciting”, says Rory Scarrott, UCC researcher leading the analysis, “we’re working closely with our colleagues in Portugal (IPMA) to see if these front destabilisations could be a factor in fisheries fluctuations, and with ACRI-ST to see how closely our method is comparable with standard front extraction approaches. We’re also chatting to colleagues in Marine Ecology to see if these variabilities are percolating through to seabird and whale movements”.

SAFI’s ventures into ocean research are certainly opening some exciting doors for science and EO applications and illustrate the truly collaborative nature of the SAFI initiative.

Sophie Power (UCC), Rory Scarrott (UCC), Jesus Morales (IFAPA), Phillipe Bryère (ACRI-ST)




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