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Abstract Fully and accurately reconstructing changes in oceanic productivity and carbon export and their controls is critical to determining the efficiency of the biological pump and its role in the global carbon cycle through time, particularly in modern CO₂source regions like the eastern equatorial Pacific (EEP). Here we present new high-resolution records of sedimentary²³⁰Th-normalized opal and nannofossil carbonate fluxes and [²³¹Pa/²³⁰Th]xs ratios from site MV1014-02-17JC in the Panama Basin. We find that, across the last deglaciation, phytoplankton community structure is driven by changing patterns of nutrient (nitrate, iron, and silica) availability which, in turn, are caused by variability in the position of the Intertropical Convergence Zone (ITCZ) and associated changes in biogeochemical cycling and circulation in the Southern Ocean. Our multi-proxy work suggests greater scrutiny is required in the interpretation of common geochemical proxies of productivity and carbon export in the EEP. 

Abstract The dynamics shaping the El Niño‐Southern Oscillation's (ENSO) response to present and future climate change remain unclear, partly due to limited paleo‐ENSO records spanning past abrupt climate events. Here, we measure Mg/Ca ratios on individual foraminifera to reconstruct east Pacific subsurface temperature variability, a proxy for ENSO variability, across the last 25,000 years, including the millennial‐scale events of the last deglaciation. Combining these data with proxy system model output reveals divergent ENSO responses to Northern Hemisphere stadials: enhanced variability during Heinrich Stadial 1 (H1) and reduced variability during the Younger Dryas (YD), relative to the Holocene. H1 ENSO likely intensified through meltwater‐induced changes to ocean/atmospheric circulation, a response observed in models, but the lack of a similar response during the YD challenges model simulations. We suggest the tropical Pacific mean state during H1 primed ENSO for larger fluctuations under meltwater forcing, whereas the YD mean state likely buffered against it. 

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).