Sea-level changes controlled detrital sediment inputs to the Bicol Shelf in the western Philippine Sea since 150 ka

Detrital sediments derived from the Philippine Islands are one of the main sources of deep-sea sediments in the western Philippine Sea. However, systematic research on their characteristics and transport mechanisms are lacking. We used parametric end-member analysis to quantitatively partition the grain size of detrital sediments in core MD06-3052 from the Bicol Shelf in the western Philippine Sea; three end-members EM1, EM2, and EM3, whose respective modes were at 2, 10, and 45 µm, were separated. We also measured the Sr and Nd isotopic compositions of different size fractions (20 µm) of the detrital sediments and the results showed that the detrital sediments mainly originate from the Philippine Islands. Components EM1 and EM2 are transported to the Bicol Shelf mainly by surface and bottom currents from the islands, and component EM3 is delivered by gravity flow from the exposed shelf during low sea-level stands. The content of the total detrital fraction and the three end-members, as well as the mass accumulation rates (MARs) of the coarse detritus (EM2 and EM3), were considerably higher during glacial periods (40–14 ka and 150–130 ka) than during other intervals; the glacials corresponded to a low sea level, while the MAR of the fine detritus (EM1) did not increase remarkably during 40–14 ka. We therefore concluded that the input of coarse detritus to the Bicol Shelf from the islands was mainly controlled by sea-level change. Variations of the input of fine-grained detritus (EM1) was influenced not only by sea level but also by ocean currents and regional precipitation. Overall, our results help understand “source-to-sink” processes in the western Pacific marginal seas and their response to global change.