Quaternary radiolarian biostratigraphy of IODP Site 341-U1417A

Expedition 341 of the Integrated Ocean Drilling Program (IODP) retrieved sediment cores spanning the time interval between the Pleistocene and Miocene from the southern Gulf of Alaska. Onboard Pleistocene radiolarian biostratigraphy is hereby refined by increasing the sampling resolution. The 178 core samples from the upper 190 m CCSF-B of Site U1417 contained faunal elements similar to the Northwest Pacific; for example, the three biozones in the Northwest Pacific (i.e., Eucyrtidium matuyamai, Stylatractus universus and Botryostrobus aquilonaris) were also recognized in the Gulf of Alaska, spanning 1.80-1.13 Ma, 1.13-0.45 Ma, and the last 0.45 Myr, respectively. Based on the age model that we used in this study and the shipboard paleomagnetic reversal events, the first occurrences (FOs) of Amphimelissa setosa and Schizodiscus japonicus in the Northeast Pacific were preliminarily determined to be 1.48 and 1.30 Ma, respectively. The last occurrence (LO) of Eucyrtidium matuyamai and the FO of Lychnocanoma sakaii, both well-established bioevents in the Northwest Pacific, were dated at 0.80 Ma and 1.13 Ma, respectively. The LO of E. matuyamai is a synchronous event at 1.05±0.1 Ma in the North Pacific, while the FOs of A. setosa and S. japonicus are significantly older than what found elsewhere at 1.48 Ma and 1.30 Ma, respectively

Middle Miocene Climate-Carbon Cycle Dynamics: A Key to Understand Future Trends on a Warmer Earth?

Benthic foraminiferal stable isotopes from ODP Sites 1146A/1146C and 1237B/1237C, and IODP sites U1337A/U1337C/U1337D, U1338A-C and U1443A-C with revised downcore depths and ages (early to middle Miocene)

Counts of radiolarians at Hole C9001C

The Northwest Pacific Ocean is characterized by a strong mixing of water masses, due to the interplay of three distinct currents, i.e., the Kuroshio, the Tsugaru, and the Oyashio. The C9001C drill core site, located east of the Shimokita Peninsula and directly influenced by the Tsugaru warm current and the Oyashio subarctic current was used here to reconstruct the paleoceanographical history of this region, especially focusing on the Mid-Brunhes Event (MBE) and its consequences. This core provides a continuous record from marine isotope stage (MIS) 18 (740 ka) to the present. Polycystine radiolarian assemblages were analyzed to highlight paleoceanographic and sea surface temperature changes at this site. Based on the radiolarian fauna, seven time periods are defined, which coincide with changes in the dynamics of the Tsugaru and Oyashio currents, respectively. The oldest time interval covered by our analysis (i.e., VII: 740-621 ka) was marked by generally sluggish ocean circulation. The Tsugaru Current influence increased during the following Interval VI (621-478 ka) which encompasses interglacials MIS 15 and 13, while the Oyashio Current strengthened during the Interval V (478-337), i.e. from glacials MIS 12 to 10. These latter intervals (VI to V) constitute a long climatic transitional period where Tsugaru Current and Oyashio Current influences are strengthened. In the time period from Interval IV to Interval I (0-337 ka), the warming intensity of interglacials (MIS 9, MIS 5) appears to be close to the modern one. However, several unusually warm glacials, associated with a relatively strong Tsugaru Current flow, were identified during this interval (e.g., MIS 8 and MIS 6). Radiolarian productivity data suggest that during Intervals VII to V, deep water masses are rich in nutrient content. However, a high vertical mixing event is recorded after Interval IV, when high nutrient concentrations appear to shift to the surface layer