Continental Shelf Research 23 (2003) 991–1003 Eddies around Guam, an island in the Mariana Islands group

Near-surface currents around Guam, a 35 km long, slab-shaped island in the Mariana Islands group, were estimated from current meters, satellite-derived surface topography, and a numerical model. A dominant northwestward-flowing North Equatorial Current prevailed from June to December 2000, with speeds typically 0.1–0.2m s1, generating unsteady eddies in the lee of Guam. A number of transient eddies off the tips of the island were apparent, the smallest eddies were at the scale of local topographic features such as headlands and embayments, while other eddies were island size. In addition to eddies off the tips of the island, a large (200 km in diameter) cyclonic oceanic eddy was advected eastward past Guam during the last 2 weeks of August 2000. Centered on Guam for a few days, this eddy formed elsewhere and impinged on the island generating anticlockwise currents around the island of up to 0.5m s1. It is suggested that these eddies are sufficiently energetic to return fish and coral eggs and larvae to their natal reefs in Guam, thereby enabling self-seeding of coral reefs in Guam. The numerical model also predicts that large (up to 30m amplitude) island-generated internal waves may occur around Guam; however, no observations are presently available to support this prediction