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Abstract Reconstructing past oxygen fluctuations in oxygen minimum zones (OMZs) is crucial for understanding their response to climate change. Numerous studies suggest better oxygenation in the Arabian Sea OMZ during the Last Glacial Maximum (LGM) compared to the Holocene. However, bottom water oxygen (BWO) variability during the Penultimate Glacial Cycle (Marine Isotope Stage [MIS] 6 to MIS 5e, ∼140–115 ka B.P.) remains poorly constrained. This study reconstructs BWO variations during this period from sediment core TN041‐8JPC in the western Arabian Sea OMZ, utilizing proxies including benthic foraminiferal surface porosity, redox‐sensitive trace metal enrichment factors (e.g., U_EF), and U/Ba ratios. Bottom water oxygen concentrations were 24.4 ± 5.9 μmol/kg during MIS 6 and 16.8 ± 6.5 μmol/kg during MIS 5e, with all proxies indicating higher BWO in MIS 6 than in MIS 5e. However, these proxies show different patterns within MIS 5e, indicating that U_EFand U/Ba ratios may be limited to recording average BWO in glacial and interglacial (quasi)steady states. We propose that the intensified OMZ during MIS 5e, relative to MIS 6, was driven by higher productivity, temperature‐induced reductions in oxygen solubility, and reduced delivery of Southern‐sourced intermediate waters. In contrast, the intensified OMZ during the Holocene, compared to the LGM, was likely influenced by lower oxygen solubility, reduced Southern water delivery, and winter convective mixing rather than productivity. This study highlights a general trend of weaker OMZs in glacial than interglacial periods, though the mechanisms may not be identical, offering insights into OMZ dynamics under climate change in the past. 

Abstract. The equatorial Pacific is a nexus of key oceanic and atmospheric phenomena, and its regional climate has critical implications for hydroclimate, the partitioning of CO2, and temperature on a global scale. The spatial complexity of climate signals across the basin has long posed a challenge for interpreting the interplay of different climate phenomena including changes in the Intertropical Convergence Zone (ITCZ) and El Niño–Southern Oscillation (ENSO). Here, we present new, millennially resolved sediment core chronologies and stable isotope records from three sites in the equatorial Pacific's Line Islands region, as well as updated chronologies for four previously studied cores. Age constraints are derived from 14C (n=17) and δ18O (n=610), which are used as inputs to a Bayesian software package (BIGMACS: Bayesian Inference Gaussian Process regression and Multiproxy Alignment of Continuous Signals) that constructs age models and uncertainty bounds via correlation with the global benthic δ18O stack (Lee et al., 2023). We also make use of the new planktonic δ18O data to draw inferences about surface water salinity and to infer a southward-shifted position for the ITCZ at the Last Glacial Maximum (18–24 ka) and Marine Isotope Stage 6 (138–144 ka). These new chronologies and related datasets improve our understanding of equatorial Pacific climate and show strong promise for further surface and deep ocean paleoclimate reconstructions over the last several glacial cycles. 

A compilation of radiocarbon measurements is used to characterize deep-sea overturning since the last ice age. 

Abstract ²³⁰Th normalization is a valuable paleoceanographic tool for reconstructing high‐resolution sediment fluxes during the late Pleistocene (last ~500,000 years). As its application has expanded to ever more diverse marine environments, the nuances of²³⁰Th systematics, with regard to particle type, particle size, lateral advective/diffusive redistribution, and other processes, have emerged. We synthesized over 1000 sedimentary records of²³⁰Th from across the global ocean at two time slices, the late Holocene (0–5,000 years ago, or 0–5 ka) and the Last Glacial Maximum (18.5–23.5 ka), and investigated the spatial structure of²³⁰Th‐normalized mass fluxes. On a global scale, sedimentary mass fluxes were significantly higher during the Last Glacial Maximum (1.79–2.17 g/cm²kyr, 95% confidence) relative to the Holocene (1.48–1.68 g/cm²kyr, 95% confidence). We then examined the potential confounding influences of boundary scavenging, nepheloid layers, hydrothermal scavenging, size‐dependent sediment fractionation, and carbonate dissolution on the efficacy of²³⁰Th as a constant flux proxy. Anomalous²³⁰Th behavior is sometimes observed proximal to hydrothermal ridges and in continental margins where high particle fluxes and steep continental slopes can lead to the combined effects of boundary scavenging and nepheloid interference. Notwithstanding these limitations, we found that²³⁰Th normalization is a robust tool for determining sediment mass accumulation rates in the majority of pelagic marine settings (>1,000 m water depth).