Nonlinear increase in seawater 87Sr ∕  86Sr in the Oligocene to early Miocene and implications for climate-sensitive weathering

Stoll, Heather M.; Pena, Leopoldo D.; Hernandez-Almeida, Ivan; Guitián, José; Tanner, Thomas; Pälike, Heiko

The inline-formula87Sr inline-formula M8inlinescrollmathml / 8pt14ptsvg-formulamathimgfb147fccdcf98a9911cf3d26a8f6dc33 cp-20-25-2024-ie00004.svg8pt14ptcp-20-25-2024-ie00004.png inline-formula86Sr of marine carbonates provides a key constraint on the balance of continental weathering and hydrothermal Sr fluxes to the ocean, and the mid-Oligocene to mid-Miocene period features the most rapid rates of increase in the inline-formula87Sr inline-formula M11inlinescrollmathml / 8pt14ptsvg-formulamathimg165b352473919034209a9d51d0eaf41d cp-20-25-2024-ie00005.svg8pt14ptcp-20-25-2024-ie00005.png inline-formula86Sr of the Cenozoic. Because previous records of the inline-formula87Sr inline-formula M14inlinescrollmathml / 8pt14ptsvg-formulamathimg539a58614ea8688159b8effbc6d3da8d cp-20-25-2024-ie00006.svg8pt14ptcp-20-25-2024-ie00006.png inline-formula86Sr increase with time were based on biostratigraphically defined age models in diverse locations, it was difficult to unambiguously distinguish million-year-scale variations in the rate of inline-formula87Sr inline-formula M17inlinescrollmathml / 8pt14ptsvg-formulamathimga3a809672b156f3719eee3cbaf593ee5 cp-20-25-2024-ie00007.svg8pt14ptcp-20-25-2024-ie00007.png inline-formula86Sr change from variations in sedimentation rate. In this study, we produce the first inline-formula87Sr inline-formula M20inlinescrollmathml / 8pt14ptsvg-formulamathimg78c74280a32911099c6aadbec3864e34 cp-20-25-2024-ie00008.svg8pt14ptcp-20-25-2024-ie00008.png inline-formula86Sr results from an Oligocene to early Miocene site with a precise age-model-derived orbital tuning of high-resolution benthic inline-formulaδ18O at Equatorial Pacific Ocean Drilling Program (ODP) Site 1218. Our new dataset resolves transient decreases in inline-formula87Sr inline-formula M24inlinescrollmathml / 8pt14ptsvg-formulamathimgcdb097d754d0791f99b194a2a037445d cp-20-25-2024-ie00009.svg8pt14ptcp-20-25-2024-ie00009.png inline-formula86Sr, as well as periods of relative stasis. These changes can be directly compared with the high-resolution benthic inline-formulaδ18O at the same site. We find that slowing of the rate of inline-formula87Sr inline-formula M28inlinescrollmathml / 8pt14ptsvg-formulamathimg6e9042c80619a800f49fe8d9da77f107 cp-20-25-2024-ie00010.svg8pt14ptcp-20-25-2024-ie00010.png inline-formula86Sr increase coincides with the onset of Antarctic ice expansion at the beginning of the mid-Oligocene glacial interval, and a rapid steeping in the inline-formula87Sr inline-formula M31inlinescrollmathml / 8pt14ptsvg-formulamathimgcde794723cf5af95a282a8ea7937b694 cp-20-25-2024-ie00011.svg8pt14ptcp-20-25-2024-ie00011.png inline-formula86Sr increase coincides with the benthic inline-formulaδ18O evidence for rapid ice retreat. This pattern may reflect either northward shifts in the Intertropical Convergence Zone precipitation to areas of nonradiogenic bedrock and/or lowered weathering fluxes from highly radiogenic glacial flours on Antarctica. We additionally generate the first inline-formula87Sr inline-formula M35inlinescrollmathml / 8pt14ptsvg-formulamathimg07d7a1dd05fd1823c5d4d7644fe5a26c cp-20-25-2024-ie00012.svg8pt14ptcp-20-25-2024-ie00012.png inline-formula86Sr data from ODP Site 1168 on the Tasman Rise and Integrated Ocean Drilling Program (IODP) Site 1406 of the Newfoundland Margin during the Oligocene to early Miocene to improve the precision of age correlation of these Northern Hemisphere and Southern Hemisphere midlatitude sites and to better estimate the duration of early Miocene hiatus and condensed sedimentation.

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Stoll, Heather M. / Pena, Leopoldo D. / Hernandez-Almeida, Ivan / et al: Nonlinear increase in seawater 87Sr ∕ 86Sr in the Oligocene to early Miocene and implications for climate-sensitive weathering. 2024. Copernicus Publications.

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