Cycladophora davisiana abundances as a paleoceanographic and stratigraphic tool in high latitude siliciceous sediments

Like the oxygen isotope curve, the relative abundance curve for Cycladophora davisiana (hereafter, c-curve) exhibits synchronous fluctuations between high-latitude regions. It was also thought that high abundances of C. davisiana indicated glacial periods. Although numerous short c-curves have been calibrated to oxygen isotope curves (spanning the last 100. kyr), only two longer c-curves have been associated with oxygen isotopes (spanning the last 0.425. Myr in the Southern Ocean and 1.1. Myr in the Sea of Okhotsk). This lack of well-established long c-curve calibrations to the oxygen isotope curve decreases the reliability of the c-curve for periods beyond 100. ka. Furthermore, recent work indicates that high abundances of C. davisiana do not necessary indicate glacial conditions. This study sought, to establish a long C. davisiana curve by directly calibrating the c-curve to oxygen isotope records measured from benthic foraminifera in the North Pacific over the last 740. kyr, to discuss the paleoceanographic significance of the c-curve and to check the suitability of the c-curve as a stratigraphic tool. Samples were obtained from Core C9001C, which was recovered at a water depth of 1180. m, east of the Shimokita Peninsula in the Tohoku region of Japan. The core contained a continuous stratigraphic succession down to marine isotope stage 18 (740. ka). Abundance peaks exceeding 5% of the total radiolarian fauna were defined as Davisiana event (DAE), and a total of 20 DAEs were observed over the last 740. kyr. The DAEs were generally near interglacial/glacial period boundary whereas peaks in the radiolarian total abundance, reflecting warm surface radiolarian productivity, occur mainly within the interglacial intervals. The DAEs appear to reflect hydrological and productivity events in the intermediate water masses of the studied site during climatic transition. We correlated the occurrence of 20 DAEs in Shimokita area with c-curve Davisiana events identified in previous studies. The c-curve fluctuations appear to be generally synchronized in the North Pacific, Sea of Okhotsk and Southern Ocean, supporting the interpretation that DAEs are intermediate water changes possibly caused by ice cover fluctuations in high latitude regions on the background of the glacial/interglacial cycling.