Topographic zonation and polycyclic pedogenesis in the northern atolls of the Chagos Archipelago, Indian Ocean

We conducted soil surveys on two islands in the Peros Banhos and Salomon atolls of northern Chagos Archipelago, Indian Ocean. found muted but consistent topographic zonation from ocean shores to lagoons. The main elements are: berms coral boulders rubble along heads ocean-side beaches; rubble-strewn soils inland berm; pale sands with shallower topsoils few clasts slight rises declivities over rest islands. rubbly have interstitial coarse sand are most fertile islands, dense tangled stands unmanaged coconuts, profuse litter, deep humic topsoils. Topsoils less inland. Sand size decreases lagoon, increases depth profiles. Water tables often <2 m deep, many faint brownish mottling lower subsoils. There is a low tabular outcrop bare Holocene sandstone one It incised by shallow grikes that partly infilled silty muck, as some small depressions central parts both pedogenic environment appears be dynamic, storm surges depositing fresh sand, eroding coastlines, infilling inter-island channels. Some buried topsoils, stone layers, inversions, changes colour, which attributed polycyclic pedogenesis. elevated levels total Zn, thought derived long distance volcanic ash. Our data indicate nutrient fertility. Total N available P do not attain strikingly eutric atoll soils. fertility predation seabirds inadvertently introduced black rats. This precludes enrichment marine-derived nutrients guano deposition. • Archipelago. vary consistently topography lagoon. landscape modified appear polycyclic. Elevated Zn may come Rat limits enhancement guano.