Paleoenvironmental implications of high-density records in Co-rich seamount crusts from the Pacific Ocean

Abstract

Co-rich seamount crusts have been shown to possess great potential for providing information on paleoceanographic and paleoclimatic changes. High resolution data are essential to decipher and correctly understand such high-density records. With the development of modern micro-probe techniques, detailed sampling of crusts can be performed and it is possible to retrieve detailed information about environmental changes recorded in the seamount crusts. We report here geochemical results of more than 40 elements (including all rare earth elements) of four Co-rich seamount crust samples, which were collected from seamounts in the central and western Pacific Ocean. These data were obtained with two micro-probe techniques: Electron Probe Micro Analyzer and Laser Ablation Inductively Coupled Plasma Mass Spectrometry. The chronological framework of the seamount crust samples was determined using the cosmogenic 10 Be and the Co-chronometer. Records of elemental composition, P, and Al/(Fe + Mn) and Y/Ho ratios across the sections of the four samples are used to identify paleoceanographic and paleoclimatic events over the past ~30 Ma. These data show that: (1) Al/(Fe + Mn) in the western Pacific seamount crust is a useful proxy for the assessment of changes of source materials related to the variability of the Asian monsoon; (2) P and Y/Ho can be used as proxies to infer biogenic episodes. Finally we discuss the methodology related to dating and micro-probe analysis used in crust study.Co-rich seamount crust, micro-probe, chronology, geochemical record, paleo-oceanic environment During the last ten years' investigation on marine geology and mineral resources in deep oceans, marine ferro-manganese oxides, especially Co-rich seamount crusts, laminated mineral deposits, have been shown to have great potential for obtaining information on long-term paleoceanographic and paleoclimatic changes and have attracted the attention of the scientists around the world. The formation of Fe-Mn crust by deposition of ions or molecules is an extremely slow process at an average growth rate of only one atomic layer per year [1] . Therefore, Co-rich seamount crusts are virtually condensed stratigraphic sections in which several millimeters can represent one million years of oceanic history [2,3] .Great progress has been made in the study of the

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