Arctic Ocean stratification set by sea level and freshwater inputs since the last ice age

Abstract Salinity-driven density stratification of the upper Arctic Ocean isolates sea-ice cover and cold, nutrient-poor surface waters from underlying warmer, nutrient-rich waters. Recently, stratification has strengthened in the western Arctic but has weakened in the eastern Arctic; it is unknown if these trends will continue. Here we present foraminifera-bound nitrogen isotopes from Arctic Ocean sediments since 35,000 years ago to reconstruct past changes in nutrient sources and the degree of nutrient consumption in surface waters, the latter reflecting stratification. During the last ice age and early deglaciation, the Arctic was dominated by Atlantic-sourced nitrate and incomplete nitrate consumption, indicating weaker stratification. Starting at 11,000 years ago in the western Arctic, there is a clear isotopic signal of Pacific-sourced nitrate and complete nitrate consumption associated with the flooding of the Bering Strait. These changes reveal that the strong stratification of the western Arctic relies on low-salinity inflow through the Bering Strait. In the central Arctic, nitrate consumption was complete during the early Holocene, then declined after 5,000 years ago as summer insolation decreased. This sequence suggests that precipitation and riverine freshwater fluxes control the stratification of the central Arctic Ocean. Based on these findings, ongoing warming will cause strong stratification to expand into the central Arctic, slowing the nutrient supply to surface waters and thus limiting future phytoplankton productivity.info:eu-repo/semantics/publishe

Sea level and climate control the Arctic Ocean halocline over the last 35,000 years

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The Bering Strait Was Flooded During Marine Isotope Stage 3: Evidence from Foraminifera-bound Nitrogen Isotopes and Glacial Isostatic Adjustment Modeling

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The Bering Strait was flooded 10,000 years before the Last Glacial Maximum

The cyclic growth and decay of continental ice sheets can be reconstructed from the history of global sea level. Sea level is relatively well constrained for the Last Glacial Maximum (LGM, 26,500 to 19,000 y ago, 26.5 to 19 ka) and the ensuing deglaciation. However, sea-level estimates for the period of ice-sheet growth before the LGM vary by > 60 m, an uncertainty comparable to the sea-level equivalent of the contemporary Antarctic Ice Sheet. Here, we constrain sea level prior to the LGM by reconstructing the flooding history of the shallow Bering Strait since 46 ka. Using a geochemical proxy of Pacific nutrient input to the Arctic Ocean, we find that the Bering Strait was flooded from the beginning of our records at 46 ka until [Formula: see text] ka. To match this flooding history, our sea-level model requires an ice history in which over 50% of the LGM's global peak ice volume grew after 46 ka. This finding implies that global ice volume and climate were not linearly coupled during the last ice age, with implications for the controls on each. Moreover, our results shorten the time window between the opening of the Bering Land Bridge and the arrival of humans in the Americas.ISSN:0027-8424ISSN:1091-649

Arctic Ocean 50 ka foram-bound nitrogen isotope data, core age models, and Bering Strait sea level simulations

The cyclic growth and decay of continental ice sheets can be reconstructed from the history of global sea level. Sea level is relatively well-constrained for the Last Glacial Maximum (LGM, 26,500-19,000 years ago, 26.5-19 ka) and the ensuing deglaciation. However, sea-level estimates for the period of ice-sheet growth before the LGM vary by > 60 m, an uncertainty comparable to the sea-level equivalent of the contemporary Antarctic Ice Sheet. Here we constrain sea level prior to the LGM by reconstructing the flooding history of the shallow Bering Strait since 46 ka. Our data constraint on Bering Strait flooding are nitrogen isotope measurements in organic matter bound in the planktonic foraminifer Neogloboquadrina pachyderma from four sediment cores in the Arctic Ocean, dating back to ~50,000 years before present. These data extend the previous measurements of Farmer et al., 2021 (https://doi.org/10.1038/s41561-021-00789-y). We additionally provide new Bayesian age-depth models for each sediment core based on existing radiocarbon (14C) measurements on N. pachyderma. The nitrogen isotope data are compared with a suite of reconstructions of global mean sea-level and relative sea level at the Bering Strait from glacial isostatic adjustment modeling covering the last 120,000 years

The connectivity of the Bering Strait as a tool for reconstructing past sea level and ice sheets

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