Sediment focusing in the central equatorial Pacific Ocean

At four sites in the central equatorial Pacific Ocean the flux of extraterr estrial He-3, determined using the excess Th-230 profiling method, is 8 x 1 0(-13) cm(3) STP cm(-2) ka(-1). This supply rate is constant to within 30%. At these same sites, however the burial rate of He-3, determined using chr onostratigraphic accumulation rates, varies by more than a factor of 3. The lowest burial rates, which occur north of the equator at 1 degreesN, 139 d egreesW are lower than the global average rate of supply of extraterrestria l He-3 by 20% and indicate that sediment winnowing may have occurred. The h ighest burial rates, which are recorded at the equator and at 2 degreesS. a re higher than the rate of supply of extraterrestrial He-3 by 100%, and the se provide evidence for sediment focusing. By analyzing several proxies mea sured in core PC72 sediments spanning the past 450 kyr we demonstrate that periods of maximum burial rates of (230) Th, He-3, Be-10, Ti, and barite, w ith a maximum peak-to-trough amplitude of a factor of 6, take place systema tically during glacial time. However, the ratio of any one proxy to another is constant to within 30% over the entire length of the records. Given tha t each proxy represents a different source (U-234 decay in seawater, interp lanetary dust, upper atmosphere, continental dust, or upper ocean), our pre ferred interpretation for the covariation is that the climate-related chang es in burial rates are driven by changes in sediment focusing.