Reconstruction of seasonal SST from the combination of sediment trap and sediments in the central North Pacific

Sediment trap experiments were conducted and one sedimentary core was taken in the mid-latitude of the central North Pacific. The combination of both results can lead to more precise reconstruction of seasonal change of paleo-marine environments. The duration period of the trap experiments was 1 year beginning in July 1993. Each planktonic foraminifer showed definite seasonality in this area. G. bulloides, G. quinqueloba, and N. dutertrei were observed only May- July, summer season. In contrast, G. inflata, G. falconensis, and G. foliata were observed from December to February, winter season. G. ruber and G. scitula occurred only in August - October and in October - February. Regarding one sedimentary core, a 5 m long core (NP36) was collected from 2,664 m water depth in the same area and yielded a continuous record for the last 370-kyr. We analyzed the abundance of planktonic foraminifera and 32 species were identified. MAR of planktonic foraminifera increased during glacial periods such as OIS 2, 4, 6, 8, and 10, relative to values in adjacent interglacial periods. Five major components include N. pachyderma, G. inflata, G. truncatulinoides, G. foliata and G. bulloides. We analyzed stable isotope of planktonic foraminifera through the core. A part of the results were shown here, which demonstrated that delta 18O of G. ruber were on average -0.07 permil in OIS 1 and 0.58 permil in OIS 2. Also these values of G. inflata were +0.79 permil in OIS 1 and 1.67 permil in OIS 2. Right-coiling of N. pachyderma showed mean delta 18O of +0.52 permil in OIS 1 and 1.71 permil in OIS 2. The differences of delta 18O between OIS 1 and 2 were 0.65 permil for G. ruber, 0.88 permil for G. inflata and 1.19 for right-coiling of N. pachyderma. Although these have been traditionally explained by the change of seawater temperature at different depths in the surface water, they can be ascribed more to seasonal change of temperature because G. ruber and G. inflata were found in the trap samples only during summer and winter, respectively.