Sediment-magnetic signature of the mid-Holocene paleoenvironmental change in the central Okinawa Trough

摘要

The Kuroshio Current (KC) has strong effects on local paleoclimate fluctuations and the paleoenvironmental evolution of the East China Sea (ECS). In the Okinawa Trough, the changes in the spatial position of its long axis and/or current strength since the last glacial stage have been a controversial topic. 'A multi-proxy study, including both magnetic and non-magnetic (grain-size measurements and AMS ~(14)C dating) approaches, has been carried out on samples from core Y179 (2.53 m long) recovered from the central Okinawa Trough to investigate the possible KC-related Holocene paleoenvironmental changes in the trough. The core spans about the last 12,000 years and comprises dominantly clayey silt and silt. Magnetic measurements indicate that pseudo-single domain (PSD) magnetite of terrigenous origin is the main magnetic carriers with no apparent alteration due to early diagenesis. Based on physical properties, the core can be divided into three zones: I (0-1.05 m, <7.0 cal kyr BP), II (1.05-1.10 m, between 7.0 and 7.2 cal kyr BP) and III (1.10-2.53 m, >7.2 cal kyr BP). Compared with zone III, zone I contains less abundant but coarser magnetite particles and shows notable differences in magnetic and non-magnetic mineral components. Zone II shows transitional features between zones I and III in terms of magnetic properties. Constrained by ~(14)C ages, zone II coincides with the middle-Holocene paleoenvironmental event in the Okinawa Trough (approx 7.3-7.0 cal kyr BP) which was either previously identified to be associated with the re-entering of the KC into the trough after its shifting away during the Last Glacial Maximum (LGM) or interpreted as the KC strengthening at the same time. The down-core variations of magnetic properties in core Y179 agree well with the environmental changes caused by the middle-Holocene KC-related event in the Okinawa Trough. Therefore, our new results provide environmental magnetic evidence for the middle-Holocene event in the trough.