Postcruise science from ODP Leg 191 consists mainly of data recovery and initial study of seismic data from the observatory and studies of the sedimentary and igneous sections cored in Site 1179. A study of diatoms defined a nearly continuous biostratigraphy that is similar to shipboard biostratigraphies based on radiolarians and dinoflagellates. Studies of several anomalous carbonate-rich layers in the Pliocene–Pleistocene section suggest that terrigenous dust from Asia caused plankton blooms by supplying nutrients that caused high productivity and sedimentation during several glacial periods. The rapid sequestration of carbonate in seafloor sediments at this time may have augmented global cooling. The conclusion that Site 1179 sediments contain a terrigenous component is bolstered by a sedimentary geochemistry study that shows element ratios that are between true pelagic and continental values. This same study also shows that Mn is depleted downsection by diagenesis and that Mn abundance ratios, sometimes used to infer sediment provenance, may not be reliable. Other sedimentary studies show the effects of the downsection decrease in diatom content and increase in compaction on permeability, porosity, and magnetic grain orientation. 40Ar/39Ar dating of vitric shards in discrete ash layers provides a new combined 40Ar/39Ar and magnetostratigraphic chronology at Site 1179 for the past 6.2 m.y. The 14 ash layers correspond to 14 major volcanic episodes on land since late Miocene (Messinian) time. The increase in sedimentation rates at ~2.5–3.0 Ma, coinciding with maximum frequency of volcanic events and with peaks in cumulative ash thickness, is interpreted to result from increased dust and ash transport by stronger winds to Site 1179, likely associated with cool climates. Tephras within the sediment column to be subducted in the Kurile Trench are chemically bimodal (i.e., rhyolitic and basaltic), with a total thicknesses of ash in discrete ash layers estimated to be ~1 m (~0.5%) of the total sediment at Site 1179. The total thickness of volcanigenic material is estimated to be 3–13 m (1.5%–6.5%) if the mass fraction of dispersed ash in the background sediment is also considered. Natural gamma ray logs in the sedimentary section show the utility of a new high-resolution logging tool. Igneous section geochemistry and isotope ratios imply that Site 1179 basalts have higher Sr isotope ratios than normal MORB, perhaps owing to the influence of a plume that was building Shatsky Rise near the ridge when the crust at Site 1179 was formed. Paleomagnetic data from the igneous section indicate that the lower basalts were emplaced rapidly and that the crust formed near the equator.
Because the main objective of Leg 191 was to emplace a seismometer and to conduct engineering tests, the results from research in samples and data from this site are not geared to solve a particular scientific problem or to test a hypothesis but are nonetheless relevant to the understanding of the paleoceanographic evolution, history of volcanic arc volcanism, subduction factory studies, and formation and evolution of the oceanic crust, among other topics. In addition, the sedimentary section at Site 1179 is very similar to the one recovered from Site 1149, located just east of the Izu-Bonin Trench. Both Sites 1149 and 1179 are locations where the two most complete sedimentary sections have been recovered from the northwestern Pacific. Future comparative studies between these two sites thus have the potential to augment the results presented in this synthesis.