Detrital apatite is a promising accessory mineral for reliable fingerprinting of the protolith composition of detrital sediment. Here, we present the geochemical compositions of detrital apatites from four sections of a high-resolution (~140 cm/kyr) sedimentary archive from the southern Okinawa Trough (SOT) for constraining sediment source rock types and establishing changes in provenance. A series of diagrams based on the geochemical data show that apatites in Section 1 derived mainly from mafic/intermediate rocks, while apatites in the three younger sections largely originated from mafic/intermediate rocks and acid rocks. Further, the four sections included a few contributions of apatites from alkaline rocks and metamorphic rocks. Through a comprehensive analysis of controlling factors and regional stratigraphy in the study area, we concluded that sediments in the SOT are the weathering/erosion products of sedimentary and meta-sedimentary rocks in the western and northeastern Taiwan Island, with ultimate sources containing a wide variety of rock types. The sediment from rivers in eastern Taiwan did not significantly contribute to deposition in the SOT. Apatites in Sections 2–4 showed strong geochemical similarity but differed from those in Section 1, indicating that the types of weathered/eroded sedimentary rocks in the weathering profile of river drainage basins of Taiwan Island changed in Section 2 (2010–1940 cal. yr BP) and have remained stable since then.

Large explosive volcanic eruptions from island volcanoes deliver vast quantities of ash to the marine environment. While many of the transport pathways are understood, those from shoreline-crossing or submarine pyroclastic currents, and their transformation into water-supported gravity flows, remain poorly constrained. We report the discovery by International Ocean Discovery Program (IODP) deep drilling of a 200-meter-thick ash megabed buried in rift basins of the South Aegean Volcanic Arc. The >73–cubic kilometer ash deposit originates from the Kos Plateau Tuff caldera-forming eruption, which occurred 161 thousand years ago, >120 kilometers to the east. The ash forms a chemically uniform, graded megabed lacking bioturbation, interpreted as having been emplaced by a stream of eruption-fed turbidity currents. Bioclastic debris within the ash provides evidence of widespread destruction of marine ecosystems. Large volcanic eruptions can remodel the seafloor landscape, deposit thick ash turbidites, and destroy marine biota on island arc–wide scales in short-lived, catastrophic events.

Tomographic images of the Ryukyu subduction zone suggest upwelling of asthenospheric mantle through slab tears; this can affect the genesis of arc magma. However, geochemical evidence testing this hypothesis is lacking. Here, we analyzed magnesium (Mg) isotopes of volcanic rocks from various regions in the Ryukyu subduction zone and combined these with trace element and Sr-Nd isotopes to understand how heterogeneous mantle contributed to arc magmas. The δ26Mg values of Okinawa Trough samples (−0.30‰ to −0.09‰) are sometimes slightly higher than those of typical mantle; we think this reflects the role of slab-derived fluids. Kueishantao lavas exhibit radiogenic Sr-Nd isotopes and mantle-like δ26Mg values (−0.27‰ to −0.19‰), which are primarily contaminated by the continental crust. Notably, samples from the northern Taiwan volcanic zone display lower δ26Mg values in basalts (−0.45‰ to −0.28‰) and higher values in andesitic rocks (−0.18‰ to −0.14‰). We postulate that elevated δ26Mg values stem from the contribution of slab-derived fluids. Conversely, the heat and material transported by upwelling of subslab asthenosphere around the slab edge or tear may induce melting of carbonate sediment at subarc depths to yield low-δ26Mg melts, explaining the lower δ26Mg values in basalts. This study provides direct geochemical evidence underscoring the involvement of subslab asthenospheric material in the formation of arc magma and helps elucidate the causes of arc mantle heterogeneity.