997 / 2024-09-20 00:02:45

Geochemical records of changing redox conditions in the western Philippine Sea over the past 26,000 years

Deep Water Oxygenation, Paleo-Redox Proxies, Global Thermohaline Circulation, Philippine Sea

Global ocean circulation plays a pivotal role in shaping the world's climate. Significant changes in the large-scale ocean circulation have occurred since the last glacial period, affecting the oxygenation of the different water masses. While changes in the different water masses have been extensively studied in the Atlantic Ocean, changes in deep water oxygenation have been less well studied in the Pacific Ocean, particularly in the Philippine Sea region.Taiwan lies at the intersection of two key tectonic systems, the Ryukyu Arc, and the Luzon-Manila arc-trench systems. The Ryukyu Arc formed due to the subduction of the Philippine Sea Plate. In the forearc region, there are several distinct depocenters at depths of 3000 to 4500 meters below sea level, such as the Hoping, Nanao, East Nanao, and Hateruma Basins. These basins thus offer an ideal area for long-term varied studies. It is imperative to reconstruct the long-term paleo-redox conditions of the bottom water in this area. To address this research issue, core MD18-3532 was retrieved from an intra-slope basin of the Ryukyu accretionary prism presently less influenced by the Pacific bottom water. According to the age model, the sediment core covers the last 26 kyr BP and is primarily composed of dark grey clay, devoid of turbiditic sediment sequences. Notably, distinct features such as multiple black dots, black silty lines, and prominent black color lines were identified during the last glacial period. These features are attributed to the formation of pyrite (FeS₂) under bottom water dysoxic conditions, and may be linked to a slowdown in the ventilation in the North Pacific Deep Water, with implications for the global carbon cycle during the last glacial period.