23 million years of productivity reconstructed in the Central Pacific Ocean using past and modern proxies

28 November 2025

Using a wide range of geochemical proxies, Chu and co-workers (2025, see reference below) analysed an iron-manganese (Fe–Mn) crust (173.2°E, 19.9°N) to reconstruct central Pacific Ocean productivity over the past 23 million years. Magnetic scanning and beryllium (Be) isotopes were used for dating, while major and trace elements—including phosphorus (P), calcium (Ca), bioactive trace metals, barium (Ba), and manganese (Mn)—together with comparisons to δ¹³C data, were used to trace productivity. Mineralogical and elemental changes across the phosphatization interface were also documented. In addition, the authors compared their results with the modern distributions of the same tracers using data from the GEOTRACES Intermediate Data Product.

The authors showed that long-term trends in Ba/Mn ratios show a decrease from 23 Ma to the present, consistent with an overall decline in paleoproductivity as the studied crust was transported northwestward with the Pacific Plate. Co-variations between Ba, benthic δ¹³C, and other bioactive trace metals (copper (Cu), nickel (Ni), zinc (Zn)) indicate that Ba content in Fe–Mn crusts is closely linked to biological processes rather than large-scale ocean circulation. However, an interplay between climate conditions and the origin of deep waters in the Pacific may explain the observed productivity variations over this interval.

**Figure:** (a) Ba concentrations in surface Fe-Mn crusts (Mizell et al., 2020) overlaid on modern surface chlorophyll-a distributions (NASA Earth Observations, https://neo.gsfc.nasa.gov/). The star marks crust CXD31. (b) Depth section of Ba in crust surfaces and seawater along 20°S–25°N from GEOTRACES IDP (GEOTRACES Intermediate Data Product Group, 2023; Le Roy et al., 2024), with CXD31 highlighted. (c) Schematic illustrating the three-stage evolution of high-productivity events (Koschinsky et al., 1997).

Reference:

Chu, Y., Li, X., Yi, L., Dong, Y., Xie, R. C., Fan, Z., Hein, J. R., Little, S. H., Liu, Y., Matsuzaki, H., Zhang, W., Meng, X., Ma, W., Li, Z., Wang, H., & Li, J. (2025). A shift in ocean circulation drives variations in paleoproductivity in the North Pacific Ocean. Earth and Planetary Science Letters, 671, 119669. Access the paper: 10.1016/j.epsl.2025.119669

Koschinsky, A., Stascheit, A., Bau, M., Halbach, P., 1997. Effects of phosphatization on the geochemical and mineralogical composition of marine ferromanganese crusts. Geochim. Cosmochim. Acta 61, 4079-4094. Access the paper: 10.1016/s0016-7037(97)00231-7

Le Roy, E., Charette, M. A., Henderson, P. B., Shiller, A. M., Moore, W. S., Kemnitz, N., et al. (2024). Controls on dissolved barium and radium-226 distributions in the Pacific Ocean along GEOTRACES GP15. Glob. Biogeochem. Cycles, 38, e2023GB008005. Access the paper: 10.1029/2023GB008005

Mizell, K., Hein, J.R., Lam, P.J., Koppers, A.A.P., Staudigel, H., 2020. Geographic and Oceanographic Influences on Ferromanganese Crust Composition Along a Pacific Ocean Meridional Transect, 14°N to 14°S. Geochem. Geophys. Geosyst. 21, e2019GC008716. Access the paper: 10.1029/2019gc008716

GEOTRACES Intermediate Data Product Group (2023). The GEOTRACES Intermediate Data Product 2021 version 2 (IDP2021v2). NERC EDS British Oceanographic Data Centre NOC. DOI:10.5285/ff46f034-f47c-05f9-e053-6c86abc0dc7e

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