scholarly journals Extreme deep-sea warmth supports high climate sensitivity in the early Eocene hothouse

2021 ◽  
Author(s):  
Tobias Agterhuis ◽  
Martin Ziegler ◽  
Lucas Lourens
Keyword(s):  
Climate Sensitivity ◽  
Deep Sea ◽  
Isotope Composition ◽  
Ph Effect ◽  
Deep Ocean ◽  
Early Eocene ◽  
Sea Temperature ◽  
Temperature Reconstructions ◽  
Hyperthermal Events ◽  
Clumped Isotope

The early Eocene (56–48 Ma) hothouse experienced the highest CO2 levels of the Cenozoic, as well as the occurrence of multiple transient global warming events, so-called hyperthermals. The deep ocean constitutes a stable and vast heat reservoir in the climate system, and hence compromises a robust setting to estimate past global mean temperatures. However, available deep-sea temperature reconstructions rely on uncertain assumptions of non-thermal influences. Here, we apply for the first time the carbonate clumped isotope paleothermometer (Δ47), a proxy not governed by these uncertainties, on early Eocene benthic foraminifera to evaluate South Atlantic deep-sea temperatures across two hyperthermal events (ETM2 and H2; ~54 Ma). In comparison to the conventional δ18O-based estimates, our new temperature reconstructions indicate two and a half degrees warmer deep water conditions, i.e. 13.2±1.9 °C (95% Confidence Interval) for background state, and average deep-sea warming of 3.3±2.9 °C (95% CI) during these hyperthermal events. These findings imply a reassessment of the assumed isotope composition of the ancient seawater and of a potential pH effect on foraminiferal oxygen isotopes. On a broad scale, our Δ47-based overall warmer deep-sea temperatures provide new evidence for high climate sensitivity during the early Eocene hothouse.

scholarly journals Marine temperatures underestimated for past greenhouse climate

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Madeleine L. Vickers ◽  
Stefano M. Bernasconi ◽  
Clemens V. Ullmann ◽  
Stefanie Lode ◽  
Nathan Looser ◽  
...  
Keyword(s):  
Surface Waters ◽  
Isotope Composition ◽  
Stable Oxygen Isotopes ◽  
Greenhouse Climate ◽  
Temperature Reconstructions ◽  
Stable Oxygen ◽  
Clumped Isotope ◽  
Earth’S Climate ◽  
Extinct Group

AbstractUnderstanding the Earth’s climate system during past periods of high atmospheric CO2 is crucial for forecasting climate change under anthropogenically-elevated CO2. The Mesozoic Era is believed to have coincided with a long-term Greenhouse climate, and many of our temperature reconstructions come from stable isotopes of marine biotic calcite, in particular from belemnites, an extinct group of molluscs with carbonate hard-parts. Yet, temperatures reconstructed from the oxygen isotope composition of belemnites are consistently colder than those derived from other temperature proxies, leading to large uncertainties around Mesozoic sea temperatures. Here we apply clumped isotope palaeothermometry to two distinct carbonate phases from exceptionally well-preserved belemnites in order to constrain their living habitat, and improve temperature reconstructions based on stable oxygen isotopes. We show that belemnites precipitated both aragonite and calcite in warm, open ocean surface waters, and demonstrate how previous low estimates of belemnite calcification temperatures has led to widespread underestimation of Mesozoic sea temperatures by ca. 12 °C, raising estimates of some of the lowest temperature estimates for the Jurassic period to values which approach modern mid-latitude sea surface temperatures. Our findings enable accurate recalculation of global Mesozoic belemnite temperatures, and will thus improve our understanding of Greenhouse climate dynamics.

scholarly journals Estimate of climate sensitivity from carbonate microfossils dated near the Eocene-Oligocene global cooling

2012 ◽  
Vol 8 (5) ◽  
pp. 4923-4939
Author(s):  
M. W. Asten
Keyword(s):  
Climate Sensitivity ◽  
Deep Ocean ◽  
Temperature Data ◽  
Global Temperature ◽  
Published Data ◽  
Sea Temperature ◽  
Central Value ◽  
Partial Pressure Of Co2 ◽  
Global Cooling ◽  
Temperature Proxy

Abstract. Climate sensitivity is a crucial parameter in global temperature modelling. An estimate is made at the time 33.4 Ma using published high-resolution deep-sea temperature proxy obtained from foraminiferal δ18O records from DSDP site 744, combined with published data for atmospheric partial pressure of CO2 (pCO2) from carbonate microfossils, where δ11B provides a proxy for pCO2. The pCO2 data shows a pCO2 decrease accompanying the major cooling event of about 4 °C from greenhouse conditions to icecap conditions following the Eocene-Oligocene boundary (33.7 My). During the cooling pCO2 fell from 1150 to 770 ppmv. The cooling event was followed by a rapid and huge increase in pCO2 back to 1130 ppmv in the space of 50 000 yr. The large pCO2 increase was accompanied by a small deep-ocean temperature increase estimated as 0.59 ± 0.063 °C. Climate sensitivity estimated from the latter is 1.1 ± 0.4 °C (66% confidence) compared with the IPCC central value of 3 °C. The post Eocene-Oligocene transition (33.4 Ma) value of 1.1 °C obtained here is lower than those published from Holocene and Pleistocene glaciation-related temperature data (800 Kya to present) but is of similar order to sensitivity estimates published from satellite observations of tropospheric and sea-surface temperature variations. The value of 1.1 °C is grossly different from estimates up to 9 °C published from paleo-temperature studies of Pliocene (3 to 4 Mya) age sediments. The range of apparent climate sensitivity values available from paleo-temperature data suggests that either feedback mechanisms vary widely for the different measurement conditions, or additional factors beyond currently used feedbacks are affecting global temperature-CO2 relationships.

scholarly journals First absolute seasonal temperature estimates for greenhouse climate from clumped isotopes in bivalve shells

2021 ◽  
Author(s):  
Niels de Winter ◽  
Inigo Müller ◽  
Ilja Kocken ◽  
Nicolas Thibault ◽  
Clemens Ullmann ◽  
...  
Keyword(s):  
Seasonal Variability ◽  
Climate Model ◽  
Sea Water ◽  
Isotope Composition ◽  
Seasonal Temperature ◽  
Deep Time ◽  
Temperature Reconstructions ◽  
Climate Model Simulations ◽  
Clumped Isotope ◽  
Bivalve Shells

Abstract Seasonal variability in sea surface temperatures plays a fundamental role in climate dynamics and species distribution. As such, it is essential to better understand seasonal variability in climates of the past. Previous reconstructions of seasonality in deep time are poorly constrained, relying on controversial assumptions such as estimates of seawater composition and neglect seasonal bias. This work presents the first absolute seasonal temperature reconstructions based on clumped isotope measurements in bivalve shells which, critically, do not rely on these assumptions. Our new approach reconstructs highly precise higher mid-latitude (~50°N) monthly temperatures from individual oyster and rudist shells of the Campanian (78 million years ago) greenhouse period (15—27 °C seasonal range). Our analysis demonstrates that seasonal bias and previous assumptions about sea water oxygen isotope composition can lead to highly inaccurate temperature reconstructions, distorting our understanding of the behavior of greenhouse climates and our ability to model them. Our results agree with fully coupled climate model simulations showing greenhouse climates outside the tropics were warmer and more seasonal than previously thought.

scholarly journals First absolute seasonal temperature estimates for greenhouse climate from clumped isotopes in bivalve shells

2020 ◽  
Author(s):  
Niels de Winter ◽  
Inigo Müller ◽  
Ilja Kocken ◽  
Nicolas Thibault ◽  
Clemens Vinzenz Ullmann ◽  
...  
Keyword(s):  
Seasonal Variability ◽  
Climate Model ◽  
Sea Water ◽  
Isotope Composition ◽  
Seasonal Temperature ◽  
Deep Time ◽  
Temperature Reconstructions ◽  
Climate Model Simulations ◽  
Clumped Isotope ◽  
Bivalve Shells

Abstract The seasonal variability of sea surface temperatures plays a fundamental role in climate dynamics and species distribution. As such, it is essential to better understand seasonal variability in warm climates of the past. Previous reconstructions of seasonality in deep time are relatively unconstrained, relying on unsupported assumptions such as estimates of seawater composition and negligible seasonal bias. This work presents the first absolute seasonal temperature reconstructions based on clumped isotope measurements in bivalve shells which, critically, do not rely on these assumptions. Our new approach reconstructs highly precise mid-latitude (~50°N) monthly temperatures from individual oyster and rudist shells of the Campanian (78 million years ago) greenhouse period (15—27 °C seasonal range). Our analysis demonstrates that seasonal bias and previous assumptions about sea water oxygen isotope composition can lead to highly inaccurate temperature reconstructions, distorting our understanding of the behavior of greenhouse climates and our ability to model them. Our results agree remarkably well with fully coupled climate model simulations showing greenhouse climates outside the tropics were warmer with higher seasonality than previously thought.

scholarly journals Cenozoic evolution of deep-sea temperature from clumped isotope thermometry

2021 ◽  
Author(s):  
Anna Nele Meckler ◽  
Philip Sexton ◽  
Alison Piasecki ◽  
Thomas Leutert ◽  
Johanna Marquardt ◽  
...  
Keyword(s):  
Deep Sea ◽  
Sea Temperature ◽  
Clumped Isotope

scholarly journals First absolute seasonal temperature estimates for greenhouse climate from clumped isotopes in bivalve shells

2020 ◽  
Author(s):  
Niels de Winter ◽  
Inigo Müller ◽  
Ilja Kocken ◽  
Nicolas Thibault ◽  
Clemens Vinzenz Ullmann ◽  
...  
Keyword(s):  
Seasonal Variability ◽  
Climate Model ◽  
Sea Water ◽  
Isotope Composition ◽  
Seasonal Temperature ◽  
Deep Time ◽  
Temperature Reconstructions ◽  
Climate Model Simulations ◽  
Clumped Isotope ◽  
Bivalve Shells

Abstract The seasonal variability of sea surface temperatures plays a fundamental role in climate dynamics and species distribution. As such, it is essential to better understand seasonal variability in warm climates of the past. Previous reconstructions of seasonality in deep time are relatively unconstrained, relying on unsupported assumptions such as estimates of seawater composition and negligible seasonal bias. This work presents the first absolute seasonal temperature reconstructions based on clumped isotope measurements in bivalve shells which, critically, do not rely on these assumptions. Our new approach reconstructs highly precise mid-latitude (~50°N) monthly temperatures from individual oyster and rudist shells of the Campanian (78 million years ago) greenhouse period (15—27 °C seasonal range). Our analysis demonstrates that seasonal bias and previous assumptions about sea water oxygen isotope composition can lead to highly inaccurate temperature reconstructions, distorting our understanding of the behavior of greenhouse climates and our ability to model them. Our results agree remarkably well with fully coupled climate model simulations showing greenhouse climates outside the tropics were warmer with higher seasonality than previously thought.

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