DRIFT PUMICE AT NEW CALEDONIA: IMPLICATIONS FOR POLLUTANT DISTRIBUTION IN A REEF SYSTEM

Drift pumice was collected from eight beaches around the Pacific island of New Caledonia during the summer of 2008. The pumice clasts are generally 1 to 2 cm in diameter, with none exceeding 5 cm. They range in color from a light tan to grey. Biological traces such as attached surpulids are evident. Preliminary geochemical analyses show that most of the pumice has similar characteristics to pumice reportedly originating from volcanism along the Tonga-Kermadec Arc. Most of the analyzed samples show evidence of alteration. Two samples show evidence of aluminum oxide enrichment due to diagenesis. The rest exhibit lower major element compositions than expected, likely related to NaCl enrichment from sea water.

As recently as 2006, undersea volcanic eruptions have been observed along the Tonga-Kermadec Arc producing large pumice rafts subject to trans-oceanic transport. Pumice from these eruptions has been reported on islands along the South Equatorial Current (SEC) from Fiji to Vanuatu to Australia. The island chain of New Caledonia runs nearly parallel to and lies about 300 miles southwest of Vanuatu. It sits between Tonga and Australia in the path of the SEC, so is an obvious stranding point for Tongan pumice.

New Caledonia's largest island, Grand Terre, is surrounded by one of Earth's longest reef systems, that in 2008 was named a UNESCO world heritage site. Protecting the reefs is vital to maintaining the biological diversity of our planet, but pollution is a constant threat. Nickel mining is one of the island's most important industries, yet its effects on the lagoon are mostly unknown.

Previous studies have shown that coral is particularly susceptible to sediment overload, such as from mining waste. The timing and extent of the distribution of exotic clastic sediment such as Tongan pumice around New Caledonia may give insight into the vectors for intra-lagoonal transport, and lead to methods for protecting the reefs from pollution.