Climate and sea level changes and the role of shelf morphology in recording in Sibuyan Sea Basin, Philippines during the last 14 kyBP

Abstract:

In this study, we reconstruct changes in precipitation using geochemical and grain size proxies and we look at how shelf morphology can influence the nature of sedimentary record of climate and oceanographic events. A 9.6m long sediment core from Sibuyan Sea basin within the internal seas of the Philippines, was raised from a water depth of 1660m. It was analyzed using an XRF core scanner at 1 cm resolution. Grain size was determined using a laser particle analyzer. Thirteen AMS radiocarbon dates from bulk organics provide age control spanning back to 14 kyBP. Overall, the trends of precipitation proxies Ti, Al and Al/Ti follow the 10^o N insolation curve. A 1.4 ky periodicity rides on this general trend. But a stepwise decrease of these precipitation proxies occur at about 9ka and 4ka. The former correpond to the melt water pulse 1-c rapid sea level rise of about 15m while the latter correlates time-wise to a period of aridification. The Younger Dryas period, ca. 12.9-11.6 ka, another known dry period, does not show a shift or decrease in sediment input. Similarly, MWP -1B does no register a distinct signal in the core. The insensitivity of the core in reflecting the older climate and sea level events is attributed to the steep morphology of the sea floor where shoreline translations took place during the earlier sea level events; with a steeper sea floor, sediment sequestration near the shoreline will be low and therefore the basin will not feel much change in sediment input. For the younger climate and sea level events, the shoreline positions were already adjacent to sea floor with relatively gentler gradient where sediment sequestration is greater and where a sea level rise of a certain magnitude will translate the shoreline much farther.