Sediment focusing in the central equatorial Pacific Ocean

At four sites in the central equatorial Pacific Ocean the flux of extraterrestrial ³He, determined using the excess ²30Th profiling method, is 8 x 10^-13 cm^-2 STP cm^-2 ka^-1. This supply rate is constant to within 30%. At these same sites, however, the burial rate of ³He, determined using chronostratigraphic accumulation rates, varies by more than a factor of 3. The lowest burial rates, which occur north of the equator at 1^cN, 139°W are lower than the global average rate of supply of extraterrestrial ³He by 20% and indicate that sediment winnowing may have occurred. The highest burial rates, which are recorded at the equator and at 2°S, are higher than the rate of supply of extraterrestrial ³He by 100%, and these provide evidence for sediment focusing. By analyzing several proxies measured in core PC72 sediments spanning the past 450 kyr we demonstrate that periods of maximum burial rates of ²30Th, ³He, ¹0Be, Ti, and barite, with a maximum peak-to-trough amplitude of a factor of 6, take place systematically 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 that each proxy represents a different source (²34U decay in seawater, interplanetary dust, upper atmosphere, continental dust, or upper ocean), our preferred interpretation for the covariation is that the climate-related changes in burial rates are driven by changes in sediment focusing.