SEDIMENT SUPPLY FOR COASTAL DUNES CONTROLLED BY SEA-LEVEL HISTORY: AN EXAMPLE FROM THE SOUTHERN CHANNEL ISLANDS, CALIFORNIA

The aeolian system state of coastal dune fields is a function of climate and vegetation history, but also sediment supply and availability. On islands with limited drainages, sea level may play a major role in aeolian supply dynamics. We tested this on the southern Channel Islands of California (San Nicolas Island [SNI] and San Clemente Island [SCI]), where Holocene dunes are limited, but Pleistocene dunes are extensive. On SNI, initial deposition occurred after ~80 ka (U-series on coral), but before ~32 ka (calibrated radiocarbon ages of land snails). A second phase of deposition occurred from ~32 ka and ~19-16 ka. On SCI, aeolian deposition also began after ~80 ka, and continued in pulses (as indicated by paleosols) between ~80-44 ka, ~42-39 ka, and ~33-23 ka. Based on modeled southern California sea-level history, the chronology indicates that aeolian deposition commenced after the end of the last interglacial complex, following marine isotope stage (MIS) 5a (~80 ka). Sea level lowered after this time, providing high-carbonate shelf sediments as an aeolian source, during the early, last-glacial period (MIS 4). Aeolian deposition likely diminished during interstadial sea stands of MIS 3, but continued when sea level lowered during the latter part of the last-glacial period (MIS 2). After sea level lowered to its minimum position in the last glacial period, dunes apparently stabilized, as no new sediment supplies were available. The results indicate that sediment supply from insular shelves, as controlled by sea-level history, plays a large role in the timing of coastal dune formation on islands.