Coupled Southern Ocean cooling and Antarctic ice sheet expansion during the middle Miocene

Leutert, Thomas Jan; Auderset, Alexandra; Martínez‐García, Alfredo; Modestou, Sevasti; Meckler, Anna Nele

doi:10.1038/s41561-020-0623-0

Cited by 51 publications

(122 citation statements)

References 60 publications

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“…This allowed for the most direct comparison possible between Mg/Ca and Δ 47 temperatures, although we could not use the same species of foraminifera (all Oridorsalis umbonatus were previously removed for Mg/Ca analysis). The age model is based on biostratigraphy following Holbourn et al (2004) with ages updated to GTS 2012 (Hilgen et al, 2012), and additional isotope stratigraphy (supporting information Table S2 of Leutert et al, 2020).…”

Section: Samplingmentioning

confidence: 99%

Warm Middle Miocene Indian Ocean Bottom Water Temperatures: Comparison of Clumped Isotope and Mg/Ca‐Based Estimates

Modestou

Leutert

Fernández

et al. 2020

Paleoceanog and Paleoclimatol

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102

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The middle Miocene is an important analogue for potential future warm climates. However, few independent deep ocean temperature records exist, though these are important for climate model validation and estimates of changes in ice volume. Existing records, all based on the foraminiferal Mg/Ca proxy, suggest that bottom water temperatures were 5–8°C warmer than present. In order to improve confidence in these bottom water temperature reconstructions, we generated a new record using carbonate clumped isotopes (Δ47) and compared our results with Mg/Ca‐based estimates for the Indian Ocean at ODP Site 761. Our results indicate temperatures of 11.0 ± 1.7°C during the middle Miocene Climatic Optimum (MCO, 14.7–17 Ma) and 8.1 ± 1.9°C after the middle Miocene Climate Transition (MCT, 13.0–14.7 Ma), values 6 to 9°C warmer than present. Our record also indicates cooling across the MCT of 2.9 ± 2.5°C (uncertainties 95% confidence level). The Mg/Ca record derived from the same samples indicates temperatures well within uncertainty of Δ47. As the two proxies are affected by different non‐thermal biases, the good agreement provides confidence in these reconstructed temperatures. Our Δ47 temperature record implies a ~0.6‰ seawater δ18O change over the MCT, in good agreement with previously published values from other sites. Our data furthermore confirm overall high seawater δ18O values across the middle Miocene, at face value suggesting ice volumes exceeding present‐day despite the warm bottom water temperatures. This finding suggests previously underappreciated additional influences on seawater δ18O and/or a decoupling of ice volume and ocean temperature.

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Section: Samplingmentioning

confidence: 99%

Warm Middle Miocene Indian Ocean Bottom Water Temperatures: Comparison of Clumped Isotope and Mg/Ca‐Based Estimates

Modestou

Leutert

Fernández

et al. 2020

Paleoceanog and Paleoclimatol

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102

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“…boron isotope and alkenone records, suggesting a coupling of pCO2 and benthic foraminiferal δ 18 O during this interval (Sosdian et al, 2018;Super et al, 2018). Atmospheric pCO2 also appears to be coupled to upper ocean temperatures in the North Atlantic and Southern Ocean (Leutert et al, 2020;Super et al, 2018). Conversely, several studies propose a degree of decoupling between BWT and global ice volume during the middle Miocene (Billups and Schrag, 2002;Lear et al, 2010Lear et al, , 2015Shevenell et al, 2008).…”

Section: Introductionmentioning

confidence: 93%

“…We note that the individual datasets in this compilation (Meinicke et al, 2020;Peral et al, 2018;Piasecki et al, 2019) are all in good agreement with a travertine-based calibration (Kele et al (2015), recalculated by Bernasconi et al (2018)) spanning a wider temperature range (6-95°C). For consistency, previously published ∆47-based ocean temperatures from ODP Sites 761 (Modestou et al, 2020) and 1171 (Leutert et al, 2020) originally based on the travertine calibration were recalculated with the calibration equation of Meinicke et al (2020). We propagated analytical and calibration uncertainties in ∆47-based temperatures (as described in the supporting information of Huntington et al (2009)), and report combined uncertainties as 68 % and 95 % confidence intervals.…”

Section: Stable Isotope Measurements and Data Processingmentioning

confidence: 99%

“…Consequently, the ∆47 thermometer holds great promise for reconstructing accurate BWTs from benthic foraminiferal tests (e.g., Leutert et al, 2019). The ∆47 thermometer has been previously applied to middle Miocene benthic foraminifera from ODP Site 761 in the Indian Ocean yielding results that are in good agreement with Mg/Ca BWTs from the same site (Lear et al, 2010;Modestou et al, 2020). However, there are intervals with very low data density in the middle Miocene record from Site 761, limiting its informative value for understanding the drivers of the MMCT.…”

Section: Introductionmentioning

confidence: 99%

“…On the basis of current knowledge, other environmental variables such as pH and salinity appear to be of minor importance for measured ∆47 values over the range of natural variation (Tripati et al, 2015;Watkins and Hunt, 2015). When applied to foraminiferal calcite, the method also does not show detectable species-specific vital effects (Grauel et al, 2013;Meinicke et al, 2020;Modestou et al, 2020;Peral et al, 2018;Piasecki et al, 2019;Tripati et al, 2010). Consequently, the ∆47 thermometer holds great promise for reconstructing accurate BWTs from benthic foraminiferal tests (e.g., Leutert et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

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Southern Ocean bottom water cooling and ice sheet expansion during the middle Miocene climate transition

Leutert

Modestou

Bernasconi

et al. 2020

Preprint

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Abstract. The middle Miocene climate transition (MMCT, ~14.5–13.0 Ma) was associated with a significant expansion of Antarctic ice, but the mechanisms triggering the event remain enigmatic. We present a new clumped isotope (∆47) bottom water temperature (BWT) record from 16.0 Ma to 12.2 Ma from Ocean Drilling Program (ODP) Site 747 in the Southern Ocean, and compare it to existing BWT records. We show that BWTs in the Southern Ocean were ~8–10 °C during the middle Miocene greenhouse, and thus considerably warmer than today. Nonetheless, bottom water δ18O (calculated from foraminiferal δ18O and ∆47) suggests substantial amounts of land ice throughout the interval of the study. Our dataset demonstrates that BWTs at Site 747 decreased by ~3–5 °C across the MMCT. This cooling preceded the stepped main increase in global ice volume, and appears to have been followed by a transient bottom water warming starting during or slightly after the main ice volume increase. We speculate that a regional freshening of the upper water column at this time may have increased stratification and reduced bottom water heat loss to the atmosphere, counteracting global cooling in the bottom waters of the Southern Ocean and possibly even at larger scales. Additional processes and feedbacks required for substantial ice growth may have contributed to the observed decoupling of Southern Ocean BWT and global ice volume.

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Assessing the effects of embedding resins on carbonate stable and clumped isotope analyses

Guo

Zong

Winter

et al. 2023

Rapid Comm Mass Spectrometry

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RationaleEmbedding resins are widely used to fix carbonates for high‐precision sample preparation and high‐resolution sampling. However, these embedding materials are difficult to remove after sample preparation and are known to affect the accuracy of carbonate stable isotope analyses. Nevertheless, their impact on clumped isotope analysis, which is particularly sensitive to contamination artifacts, has so far not been tested. The observation that running resin‐containing samples decreased the reproducibility of clumped isotope values for internal laboratory carbonate standards and increased the external standard deviation (SD 0.061–0.088‰) compared to the long‐term observations (0.034‰), prompted us to set up an experiment to test the influence of resin addition on instrument performance.MethodsHere we analyzed the stable and clumped isotope composition of a pure calcium carbonate standard (ETH‐4) mixed with three types of embedding resins in 2:1 and 1:1 proportions. Our aim was to assess how resin addition affects isotope analyses.ResultsWe found that none of the stable isotopic values were significantly different. The δ13C values were −10.22 ± 0.07‰ (mean ± SD) for pure ETH‐4, while the δ13C values of ETH‐4 mixed with embedding resins in 2:1 and 1:1 proportions were −10.21 ± 0.06‰ and −10.18 ± 0.06‰, respectively (p > 0.05). The δ18O values were −18.82 ± 0.11‰ for pure ETH‐4 versus −18.81 ± 0.09‰ and −18.82 ± 0.08‰ for 2:1 and 1:1 ETH‐4:resin mixtures, respectively (p > 0.05). Given the large uncertainty in our results, we did not find significant differences between different mixtures in the carbonate clumped isotope values (Δ47), with 0.458 ± 0.107‰, 0.464 ± 0.086‰, and 0.417 ± 0.089‰ in pure ETH‐4 and ETH‐4 with 2:1 and 1:1 resin mixtures, respectively (p > 0.05). However, a resin‐related bias in the results might be masked by the large uncertainty. The measured ETH‐4 values in our study are similar to the InterCarb values (δ13C = −10.20‰, δ18O = −18.81‰, Δ47 = 0.450‰, InterCarb‐Carbon Dioxide Equilibrium Scale). However, the external SD of Δ47 in sessions measuring ETH‐4 with resins is higher than in sessions without deliberate resin addition for the same measuring period.ConclusionsWe find that the potential contamination from the resin addition leads to a larger variability for Δ47 values in sessions measuring ETH‐4 including resins. We therefore recommend purification of embedded samples using a contamination trap with Porapak prior to analysis, if possible, or avoiding resins during sample preparation and workup, as well as monitoring the measurement quality during and after sessions with samples containing embedding resins.

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Coupled Southern Ocean cooling and Antarctic ice sheet expansion during the middle Miocene

Cited by 51 publications

References 60 publications

Warm Middle Miocene Indian Ocean Bottom Water Temperatures: Comparison of Clumped Isotope and Mg/Ca‐Based Estimates

Warm Middle Miocene Indian Ocean Bottom Water Temperatures: Comparison of Clumped Isotope and Mg/Ca‐Based Estimates

Southern Ocean bottom water cooling and ice sheet expansion during the middle Miocene climate transition

Assessing the effects of embedding resins on carbonate stable and clumped isotope analyses

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