Geng Liu

The stability of contemporary ice shelves is under threat due to global warming, and the geological records in the Ross Sea offer such an opportunity to test the linkage between them. However, the absence of calcareous microfossils in the sediments of the Ross Sea results in uncertainties in establishing a precise chronology for studies. Hence, three sediment cores were collected and studied in terms of radiocarbon dating, magnetic susceptibility, and sediment grain size to reconstruct the environmental processes in the Ross Sea since the last glacial period. The main results are as follows: (1) two grain-size components were identified for the studied cores, which can be correlated to ice-shelf and sea-ice transport, respectively; (2) due to old-carbon contamination and an inconsistent carbon reservoir, the radiocarbon dates were generally underestimated, and as an alternative, changes in magnetic susceptibility of the studied cores can be tuned to the ice-core records to establish a reliable age–depth model and; (3) integrating sediment grain-size changes and comparisons with other paleoenvironmental proxies in the Antarctic, a process from a sub-ice sheet in the last glacial period to a sub-ice shelf in the glacial maximum, and, finally, to a glaciomarine state since the last deglacial period was identified in the western Ross Sea. Integrating these findings, the warming processes in the Antarctic were highlighted in the retreat processes of the Ross Ice Shelf in the past.

Reconstructing changes in deep/bottom-water redox conditions are critical for understanding the role of the deep ocean in global carbon and metals cycling; nevertheless, the quantitative relationships between redox proxies and abyssal dissolved oxygen are poorly investigated. In this work, we studied the rock magnetic properties of surficial sediments in the western Pacific to investigate their relationship with regional redox conditions. Our results reveal a consistent sedimentary magnetic mineral assemblage in the western Pacific, dominated by pseudo-single-domain magnetite (Fe₃O₄), while the ratio of detrital and biogenic magnetite particles in different sites varies substantially. Detailed analyses identified two major magnetic-coercivity components, with modal coercivity values of 13.1 ± 1.6 mT and 54.7 ± 5.3 mT, respectively. All the magnetic parameters we measured, including both concentration-dependent and grainsize-dependent parameters, and the magnetic coercivities, are generally correlated to sedimentary redox conditions; however, the coercivities obtained by mathematical unmixing exhibit a stronger linkage, explaining about a quarter of variance of redox changes. Our findings confirm the potential of magnetic properties for tracing abyssal redox changes in the western Pacific, while the observed magnetic-redox relationships are complex and need further investigation.

The Philippine Sea is a typical region of aeolian dust reposition and is located within the Western Pacific Warm Pool. Here, we use the paleomagnetic stratigraphy and the grain‐size distributions of Quaternary abyssal deposits in the Central Philippine Sea to investigate the factors controlling regional sedimentary and paleoenvironmental changes. Our principal results are as follows: (a) A reliable geochronologic framework for Quaternary sediments in the Central Philippine Sea is established. (b) An eastward expansion of the regional depocenter in the Middle Pleistocene is observed. (c) The mean grain size of the abyssal sediments is 7–8 µm, and there are only minor differences between the sites. Comparison of the geochronological framework with various paleoenvironmental events during the Mid‐Pleistocene Transition shows that sedimentary processes can be correlated to a major transition in global climate which affected regions from the Asian interior to the tropical Pacific, and that changes in aeolian sedimentation are likely the predominant factor responsible. A derived grain‐size proxy of the sedimentary dynamics and its comparison with various paleoenvironmental proxies show that the relative contributions are roughly estimated as 23%, 9%, and 68% for aeolian inputs, oceanic circulation, and the tropical Pacific zonal SST gradient, respectively, in the studied region. The relative importance of tropical processes in abyssal sedimentary dynamics highlights the possibility of the long‐term influence of (sub)mesoscale eddies in the upper ocean, via regional upwelling and unique submarine topography, on the deepest part (>5,000 m) of the Central Philippine Sea, from meteorological to geological timescales.