Drift pumice at Christmas Island and Hawaii: evidence of oceanic dispersal patterns

The use of pumice as a geological tracer for oceanic dispersal patterns was evaluated by comparing the elemental signatures of drift pumice collected from Christmas Island and Hawaii in relation to prevailing oceanic currents and pumice source areas. Both sites lie in the middle of the Pacific Ocean, far from sources of volcanic pumice. Hawaii lies in the persistent westward-flowing North Equatorial Current. Christmas Island, in contrast, is influenced by the highly variable westward-flowing South Equatorial Current and the eastward-flowing Equatorial Counter Current. Pumice is very abundant at Christmas Island in the beach drift. Pumice from Christmas Island is derived from the western Pacific Ocean (Krakatau), southwestern Pacific Ocean (Tonga Trench), east Pacific Ocean (Mexico), South Atlantic Ridge and an unknown source. In contrast, pumice is rare in Hawaii. Pumice from Hawaii originates primarily from the South Sandwich Islands, Mexico (Isla San Benedicto) and Krakatau. The currents that control dispersal of pumice also control dispersal of larvae and rafted organisms. Christmas Island has a higher coral diversity (31 genera, 81 species) than Hawaii (17 genera, 50 species). Hawaii receives only small amounts of pumice drift from a limited area to the east and has a more restricted coral diversity, while Christmas receives massive amounts of pumice (and presumably larvae and rafted organisms) from the area of high coral diversity to the west.