Comparison and Synthesis of Sea‐Level and Deep‐Sea Temperature Variations Over the Past 40 Million Years

Abstract

Understanding ice-volume (sea-level) and deep-sea temperature variations over the past 40 million years is important for many lines of research. For example, it will lead to (a) a better understanding of ice sheet (in-)stability under different climate conditions, with implications for sea-level responses to anthropogenic warming (e.g.,

Reconciling equatorward migration of Southern Ocean fronts with minor ice volume change during Miocene cooling

“…Thus, our Δ47-based record is different from previous far-field sea-level and deep-sea temperature syntheses based on global δ 18 O stack 19,69 , one of which recently deconvolved the mid-Miocene δ 18 Obf decline into in 2.5°C deep-sea cooling and 25 m of concurrent global average sea-level drop 19 . The discrepancy in δ 18 Osw between the study by Rohling et al 19 and the clumped isotope data is driven by the difference in absolute BTWs and the magnitude of BWT decline. The uncertainty of the Δ47based BWT (from 9.9±4°C to 5±2.5°C) may allow for some ice volume change (0.3±0.5‰).…”

“…The 5±2.5°C BWT in the 10-9 Ma interval is based on most replicates, and thus has the smallest uncertainty. Only when the 10-9 Ma BWT is at the high end of its 95% confidence interval, can the global 25m RSL (Relative Sea Level) ice volume build-up of Rohling et al 19 be replicated with our Δ47 data. Given the low probability of that scenario, we conclude that the clumped isotope data imply a stronger cooling and thus less ice volume build-up during MMCT than in the model of Rohling et al 19 .…”

“…Throughout the Neogene (23-2.58 Ma), pCO2 declined from 800 to 300 ppmv 17 , global temperatures dropped 18,19 , latitudinal SST gradients increased 20 and global ice volume 19,[21][22][23] and sea ice expanded 24 . The current paradigm assigns pCO2 decline as the primary driver, which, through polar amplification of cooling, stimulates ice growth and cooling in the regions of deepwater formation 18,25,26 .…”

Antarctic Ice Sheet tipping in the last 800 kyr warns of future ice loss

“…Meanwhile, the East Antarctic ice core record [34,41], and radiostratigraphy [42,43], testify to this region's stability for several glacial cycles. Our simulated sea-level equivalent ice volume is also consistent with the imposed GMSL reconstruction [36] (which is not inevitable, given the ŕexibility in modelling choices). Speciőcally, we őnd peak ice sheet contributions of 5 to 6 m sea-level equivalent (SLE) during interglacials 11, 9 and 5, reasonably close to reconstructed GMSL high-stands of 3 to 5 m [36].…”

“…Our simulated sea-level equivalent ice volume is also consistent with the imposed GMSL reconstruction [36] (which is not inevitable, given the ŕexibility in modelling choices). Speciőcally, we őnd peak ice sheet contributions of 5 to 6 m sea-level equivalent (SLE) during interglacials 11, 9 and 5, reasonably close to reconstructed GMSL high-stands of 3 to 5 m [36]. Overall, consistent with our simulations, geological evidence supports a persistent East Antarctica PISM sims 800ka but intermittent West Antarctica during successive interglacials with relatively modest ocean warming in comparison to IPCC projections [44].…”