Atmospheric carbon dioxide concentrations and climate are regulated on geological timescales by the balance between carbon input from volcanic and metamorphic outgassing and its removal by weathering feedbacks; these feedbacks involve the erosion of silicate rocks and organic-carbon-bearing rocks. The integrated effect of these processes is reflected in the calcium carbonate compensation depth, which is the oceanic depth at which calcium carbonate is dissolved. Here we present a carbonate accumulation record that covers the past 53 million years from a depth transect in the equatorial Pacific Ocean. The carbonate compensation depth tracks long-term ocean cooling, deepening from 3.0-3.5 kilometres during the early Cenozoic (approximately 55 million years ago) to 4.6 kilometres at present, consistent with an overall Cenozoic increase in weathering. We find large superimposed fluctuations in carbonate compensation depth during the middle and late Eocene. Using Earth system models, we identify changes in weathering and the mode of organic-carbon delivery as two key processes to explain these large-scale Eocene fluctuations of the carbonate compensation depth.

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Dust transport to the tropical/subtropical northwestern Pacific over the past 600 kyr was investigated using radiogenic isotopes ( 87 Sr/ 86 Sr and ε Nd ), together with the clay mineral composition, of eolian dust preserved in a sediment core obtained from the Philippine Sea (12°30′N, 134°60′E). These data revealed the influence of two prevailing dust sources, namely, the Asian deserts and nearby volcanic arcs (e.g., the Luzon Arc), with average contributions of around 70% and 30%, respectively, from each. The clay mineral composition of the core resembled dust from the central Asian deserts (CADs; e.g., the Taklimakan Desert) as in the north-central Pacific, but published aerosol data collected near the study site during winter/spring have the mineralogical signature of dust originating from the East Asian deserts (EADs). These data indicate that the relative contribution of EAD dust increases with the northeasterly surface winds associated with the East Asian Winter Monsoon (EAWM) during winter/spring, but the Prevailing Westerlies and Trade Winds that carry dust from the CADs is the dominant transport agent in the overall dust budget of the study site. The results of this study contradict the prevailing view that direct dust transport by the EAWM winds in spring dominates the annual flux of eolian dust in the northwest Pacific.

[1] Eolian components of a 328-cm-long piston core collected from the northeast equatorial Pacific at 16°12 0 N and 125°59 0 W were investigated for mineral and geochemical compositions in order to constrain the sources of dust and determine the latitudinal position of the Intertropical Convergence Zone (ITCZ) recorded in the core. The eolian components below 250 cm are characterized by smectite-and phillipsite-rich mineral composition, depleted rare earth elements (REEs), and high Eu/Sm ratios, indicative of volcanic-rich composition. These characteristics are found in equatorial and south Pacific surface sediments, of which eolian particles are supplied from Central and South America. In contrast, eolian components above 250 cm are characterized by quartz-and illite-rich mineralogy, and more shale-like REE and trace element compositions, which are common in surface sediments of the central Pacific north of the ITCZ, where eolian particles are sourced from the Asia and North America. The observed changes are attributed to the shifting of its eolian sources from the Central and South America to the China and North America across the hemispheric dust barrier of the ITCZ. This result suggests that smectite-illite transition, a phenomenon that smectite amount increases over illite at a depth, can be used as a tracking tool for the paleolocation of the ITCZ in the northeast and central Pacific. Backtrack path construction of Pacific plate indicates paleolocation of the ITCZ north of 12°N (±2°) prior to late Miocene.