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Aradhna Tripati - One of the best experts on this subject based on the ideXlab platform.
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Evidence for ephemeral Middle Eocene to early Oligocene Greenland glacial ice and pan-Arctic sea ice
Nature Communications, 2018Co-Authors: Aradhna Tripati, Dennis DarbyAbstract:Earth's modern climate is defined by the presence of ice at both poles, but that ice is now disappearing. Therefore understanding the origin and causes of polar ice stability is more critical than ever. Here we provide novel geochemical data that constrain past dynamics of glacial ice on Greenland and Arctic sea ice. Based on accurate source determinations of individual ice-rafted Fe-oxide grains, we find evidence for episodic glaciation of distinct source regions on Greenland as far-ranging as similar to 68 degrees N and similar to 80 degrees N synchronous with ice-rafting from circum-Arctic sources, beginning in the Middle Eocene. Glacial intervals broadly coincide with reduced CO2, with a potential threshold for glacial ice stability near similar to 500 p.p.m.v. The Middle Eocene represents the Cenozoic onset of a dynamic cryosphere, with ice in both hemispheres during transient glacials and substantial regional climate heterogeneity. A more stable cryosphere developed at the Eocene-Oligocene transition, and is now threatened by anthropogenic emissions.
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constraints on glaciation in the Middle Eocene 46 37 ma from ocean drilling program odp site 1209 in the tropical pacific ocean
Paleoceanography, 2011Co-Authors: Caroline F Dawber, Aradhna TripatiAbstract:The presence of glacial ice in the late Middle Eocene has been vigorously debated. Recently published sedimentary data from the high latitudes is suggestive of episodic cooling events and near-freezing sea surface temperatures during parts of the late Middle Eocene. Constraints on ice volumes and the significance of excursions in open ocean foraminifera and seawater δ 18O reconstructions are less clear, and there are few high-resolution δ 18O records. We present a new detailed record of benthic foraminiferal δ 18O from Site 1209 that exhibits variations (Δ δ 18O benthic) of 0.6‰–1.3‰. Different approaches have previously been used to interpret Δ δ 18O benthic, including (1) an a priori assumption of a 50% contribution of temperature, similar to what is reconstructed for the Last Glacial Maximum–recent change; (2) applying Oligocene calibrations between apparent sea level (ASL) and Δ δ 18O benthic; or (3) assuming temperature and seawater δ 18O contributions can be partitioned through comparison with benthic Mg/Ca. Using assumption 1, the record from Site 1209 indicates changes in seawater δ 18O of 0.3‰–0.7‰, equivalent to ∼33–72 m (m) of ASL (assuming mean ice δ 18O of ∼−45‰). Using assumption 2 and two different end-member calibrations, the δ 18O benthic record implies changes in ASL of 23–50 m or 50–108 m. The third approach yields changes in seawater δ 18O of up to 0.6‰ to 1.4‰. We explore the compatibility of the results of each of these approaches with other studies that discuss evidence for ephemeral glaciations during the Middle Eocene with variable ice storage at one or both poles.
Steven M Bohaty - One of the best experts on this subject based on the ideXlab platform.
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the early to Middle Eocene transition an integrated calcareous nannofossil and stable isotope record from the northwest atlantic ocean integrated ocean drilling program site u1410
Paleoceanography and Paleoclimatology (2019) (In press)., 2019Co-Authors: C Cappelli, Paul R Bown, Steven M Bohaty, Claudia Agnini, Thomas Westerhold, M De Riu, V Lobba, Yuhji YamamotoAbstract:The early to Middle Eocene is marked by prominent changes in calcareous nannofossil assemblages coinciding both with long‐term climate changes and modification of the North Atlantic deep‐ocean circulation. In order to assess the impact of Eocene climate change on surface‐water environmental conditions of the Northwest Atlantic, we developed calcareous nannoplankton assemblage data and bulk stable isotope records (δ18O and δ13C) across an early to Middle Eocene interval (~52–43 Ma) at IODP Site U1410 (Southeast Newfoundland Ridge, ~41°N). At this site, early Eocene sediments are pelagic nannofossil chalk, whereas Middle Eocene deposits occur as clay‐rich drift sediments reflecting the progressive influence of northern‐sourced deep currents. Between the end of Early Eocene Climatic Optimum and the Ypresian/Lutetian boundary, calcareous nannofossils switched from an assemblage mainly composed of warm‐water and oligotrophic taxa (Zygrhablithus, Discoaster, Sphenolithus, Coccolithus) to one dominated by the more temperate and eutrophic reticulofenestrids. The most prominent period of accelerated assemblage change occurred during a ~2 Myr phase of relatively high bulk δ18O values possibly related to the post‐EECO cooling. Although the dominance of reticulofenestrids persisted unvaried throughout the Middle Eocene interval, early Lutetian (~47.4 to 47 Ma) stable isotope records indicate a reversal in the paleoenvironmetal trends suggesting a potential restoration of warmer conditions. Importantly, our data indicate that the ~2 Myr‐interval immediately following the EECO was crucial in establishing the modern calcareous nannofossil assemblage structure and also reveal that the establishment of Reticulofenestra‐dominated assemblage occurred prior to the onset of persistent deep‐current system in the Northwest Atlantic.
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Middle Eocene greenhouse warming facilitated by diminished weathering feedback
Nature Communications, 2018Co-Authors: Robin Van Der Ploeg, Steven M Bohaty, David Selby, Margot J Cramwinckel, Jack J Middelburg, Appy SluijsAbstract:The Middle Eocene Climatic Optimum (MECO) represents a ~500-kyr period of global warming ~40 million years ago and is associated with a rise in atmospheric CO2 concentrations, but the cause of this CO2 rise remains enigmatic. Here we show, based on osmium isotope ratios (187Os/188Os) of marine sediments and published records of the carbonate compensation depth (CCD), that the continental silicate weathering response to the inferred CO2 rise and warming was strongly diminished during the MECO—in contrast to expectations from the silicate weathering thermostat hypothesis. We surmise that global early and Middle Eocene warmth gradually diminished the weatherability of continental rocks and hence the strength of the silicate weathering feedback, allowing for the prolonged accumulation of volcanic CO2 in the oceans and atmosphere during the MECO. These results are supported by carbon cycle modeling simulations, which highlight the fundamental importance of a variable weathering feedback strength in climate and carbon cycle interactions in Earth’s history.
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astronomical calibration of the geological timescale closing the Middle Eocene gap
Climate of The Past, 2015Co-Authors: Thomas Westerhold, Steven M Bohaty, Ursula Röhl, Thomas Frederichs, James C ZachosAbstract:Abstract. To explore cause and consequences of past climate change, very accurate age models such as those provided by the astronomical timescale (ATS) are needed. Beyond 40 million years the accuracy of the ATS critically depends on the correctness of orbital models and radioisotopic dating techniques. Discrepancies in the age dating of sedimentary successions and the lack of suitable records spanning the Middle Eocene have prevented development of a continuous astronomically calibrated geological timescale for the entire Cenozoic Era. We now solve this problem by constructing an independent astrochronological stratigraphy based on Earth's stable 405 kyr eccentricity cycle between 41 and 48 million years ago (Ma) with new data from deep-sea sedimentary sequences in the South Atlantic Ocean. This new link completes the Paleogene astronomical timescale and confirms the intercalibration of radioisotopic and astronomical dating methods back through the PalEocene–Eocene Thermal Maximum (PETM, 55.930 Ma) and the Cretaceous–Paleogene boundary (66.022 Ma). Coupling of the Paleogene 405 kyr cyclostratigraphic frameworks across the Middle Eocene further paves the way for extending the ATS into the Mesozoic.
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a Middle Eocene carbon cycle conundrum
Nature Geoscience, 2013Co-Authors: Appy Sluijs, Richard E Zeebe, Peter K Bijl, Steven M BohatyAbstract:A 500,000-year-long period of warmth in the Middle Eocene was marked by high atmospheric carbon dioxide concentrations and prolonged dissolution of carbonate in the deep oceans. Numerical simulations attempting to capture these features identify gaps in our understanding of the causes of this and similar perturbations.
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transient Middle Eocene atmospheric co2 and temperature variations
Science, 2010Co-Authors: Peter K Bijl, Steven M Bohaty, Jaap Sinninghe S Damste, Gertjan Reichart, Appy Sluijs, Alexander J P Houben, Stefan Schouten, Henk BrinkhuisAbstract:The long-term warmth of the Eocene (~56 to 34 million years ago) is commonly associated with elevated partial pressure of atmospheric carbon dioxide (pCO2). However, a direct relationship between the two has not been established for short-term climate perturbations. We reconstructed changes in both pCO2 and temperature over an episode of transient global warming called the Middle Eocene Climatic Optimum (MECO; ~40 million years ago). Organic molecular paleothermometry indicates a warming of southwest Pacific sea surface temperatures (SSTs) by 3° to 6°C. Reconstructions of pCO2 indicate a concomitant increase by a factor of 2 to 3. The marked consistency between SST and pCO2 trends during the MECO suggests that elevated pCO2 played a major role in global warming during the MECO.
Gertjan Reichart - One of the best experts on this subject based on the ideXlab platform.
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transient Middle Eocene atmospheric co2 and temperature variations
Science, 2010Co-Authors: Peter K Bijl, Steven M Bohaty, Jaap Sinninghe S Damste, Gertjan Reichart, Appy Sluijs, Alexander J P Houben, Stefan Schouten, Henk BrinkhuisAbstract:The long-term warmth of the Eocene (~56 to 34 million years ago) is commonly associated with elevated partial pressure of atmospheric carbon dioxide (pCO2). However, a direct relationship between the two has not been established for short-term climate perturbations. We reconstructed changes in both pCO2 and temperature over an episode of transient global warming called the Middle Eocene Climatic Optimum (MECO; ~40 million years ago). Organic molecular paleothermometry indicates a warming of southwest Pacific sea surface temperatures (SSTs) by 3° to 6°C. Reconstructions of pCO2 indicate a concomitant increase by a factor of 2 to 3. The marked consistency between SST and pCO2 trends during the MECO suggests that elevated pCO2 played a major role in global warming during the MECO.
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modeling the influence of a reduced equator to pole sea surface temperature gradient on the distribution of water isotopes in the early Middle Eocene
Earth and Planetary Science Letters, 2010Co-Authors: Eveline N Speelman, David Noone, Jacob O Sewall, Matthew Huber, Anna Von Der Heydt, Jaap Sinninghe S Damste, Gertjan ReichartAbstract:Proxy-based climate reconstructions suggest the existence of a strongly reduced equator-to-pole temperature gradient during the Azolla interval in the Early/Middle Eocene, compared to modern. Changes in the hydrological cycle, as a consequence of a reduced temperature gradient, are expected to be reflected in the isotopic composition of precipitation (δD, δ18O). The interpretation of water isotopic records to quantitatively reconstruct past precipitation patterns is, however, hampered by a lack of detailed information on changes in their spatial and temporal distribution. Using the isotope-enabled version of the National Center for Atmospheric Research (NCAR) atmospheric general circulation model, Community Atmosphere Model v.3 (isoCAM3), relationships between water isotopes and past climates can be simulated. Here we examine the influence of an imposed reduced meridional sea surface temperature gradient on the spatial distribution of precipitation and its isotopic composition in an Early/Middle Eocene setting. As a result of the applied forcings, the Eocene simulation predicts the occurrence of less depleted high latitude precipitation, with δD values ranging only between 0 and −140‰ (compared to Present-day 0 to −300‰). Comparison with Early/Middle Eocene-age isotopic proxy data shows that the simulation accurately captures the main features of the spatial distribution of the isotopic composition of Early/Middle Eocene precipitation over land in conjunction with the aspects of the modeled Early/Middle Eocene climate. Hence, the included stable isotope module quantitatively supports the existence of a reduced meridional temperature gradient during this interval.
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modeling the influence of a reduced equator to pole sea surface temperature gradient on the distribution of water isotopes in the early Middle Eocene
Earth and Planetary Science Letters, 2010Co-Authors: Eveline N Speelman, David Noone, Jacob O Sewall, Matthew Huber, Jaap Sinninghe S Damste, Gertjan Reichart, Anna Von Der HeydtAbstract:Proxy-based climate reconstructions suggest the existence of a strongly reduced equator-to-pole temperature gradient during the Azolla interval in the Early/Middle Eocene, compared to modern. Changes in the hydrological cycle, as a consequence of a reduced temperature gradient, are expected to be reflected in the isotopic composition of precipitation (δD, δ18O). The interpretation of water isotopic records to quantitatively reconstruct past precipitation patterns is, however, hampered by a lack of detailed information on changes in their spatial and temporal distribution. Using the isotope-enabled version of the National Center for Atmospheric Research (NCAR) atmospheric general circulation model, Community Atmosphere Model v.3 (isoCAM3), relationships between water isotopes and past climates can be simulated. Here we examine the influence of an imposed reduced meridional sea surface temperature gradient on the spatial distribution of precipitation and its isotopic composition in an Early/Middle Eocene setting. As a result of the applied forcings, the Eocene simulation predicts the occurrence of less depleted high latitude precipitation, with δD values ranging only between 0 and −140‰ (compared to Present-day 0 to −300‰). Comparison with Early/Middle Eocene-age isotopic proxy data shows that the simulation accurately captures the main features of the spatial distribution of the isotopic composition of Early/Middle Eocene precipitation over land in conjunction with the aspects of the modeled Early/Middle Eocene climate. Hence, the included stable isotope module quantitatively supports the existence of a reduced meridional temperature gradient during this interval.
Luigi Jovane - One of the best experts on this subject based on the ideXlab platform.
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abyssal oceanic circulation and acidification during the Middle Eocene climatic optimum meco
Scientific Reports, 2020Co-Authors: Flaminia Cornaggia, Simone Bernardini, Martino Giorgioni, Gabriel L X Silva, Andre Istvan M Nagy, Luigi JovaneAbstract:The Middle Eocene Climatic Optimum (MECO) is a global warming event that occurred at around 40 Ma and lasted about 500 kyr. We study this event in an abyssal setting of the Tasman Sea, using the IODP Core U1511B-16R, collected during the expedition 371. We analyse magnetic, mineralogical, and chemical parameters to investigate the evolution of the sea bottom conditions at this site during the Middle Eocene. We observe significant changes indicating the response to the MECO perturbation. Mn oxides, in which Mn occurs under an oxidation state around +4, indicate a high Eh water environment. A prominent Mn anomaly, occurring just above the MECO interval, indicates a shift toward higher pH conditions shortly after the end of this event. Our results suggest more acid bottom water over the Tasman abyssal plain during the MECO, and an abrupt end of these conditions. This work provides the first evidence of MECO at abyssal depths and shows that acidification affected the entire oceanic water column during this event.
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carbon cycle instability and orbital forcing during the Middle Eocene climatic optimum
Scientific Reports, 2019Co-Authors: Martino Giorgioni, Luigi Jovane, Rodolfo Coccioni, E S Rego, Daniel Rodelli, Fabrizio Frontalini, Rita Catanzariti, Ercan OzcanAbstract:The Middle Eocene Climatic Optimum (MECO) is a global warming event that occurred at about 40 Ma. In comparison to the most known global warming events of the Paleogene, the MECO has some peculiar features that make its interpretation controversial. The main peculiarities of the MECO are a duration of ~500 kyr and a carbon isotope signature that varies from site to site. Here we present new carbon and oxygen stable isotopes records (δ13C and δ18O) from three foraminiferal genera dwelling at different depths throughout the water column and the sea bottom during the Middle Eocene, from eastern Turkey. We document that the MECO is related to major oceanographic and climatic changes in the Neo-Tethys and also in other oceanic basins. The carbon isotope signature of the MECO is difficult to interpret because it is highly variable from site to site. We hypothesize that such δ13C signature indicates highly unstable oceanographic and carbon cycle conditions, which may have been forced by the coincidence between a 400 kyr and a 2.4 Myr orbital eccentricity minimum. Such forcing has been also suggested for the Cretaceous Oceanic Anoxic Events, which resemble the MECO event more than the Cenozoic hyperthermals.
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environmental magnetic implications of magnetofossil occurrence during the Middle Eocene climatic optimum meco in pelagic sediments from the equatorial indian ocean
Palaeogeography Palaeoclimatology Palaeoecology, 2016Co-Authors: Jairo F Savian, Martino Giorgioni, Luigi Jovane, Fabio Florindo, Andrew P Roberts, Daniel Rodelli, Francesco Iacoviello, Liao Chang, Mario SprovieriAbstract:Abstract Magnetic properties of pelagic marine sediments that record the Middle Eocene Climatic Optimum (MECO) at ~ 40 Ma provide information about major environmental changes. The main variations observed during this transient warming event reflect a bacterial magnetofossil signal, but the cause of the linkage between bacterial production and climate remains unclear. We present an environmental magnetic study of Middle Eocene deep-sea sediments from the northern edge of Madingley Rise (Ocean Drilling Program Hole 711A, equatorial Indian Ocean) to investigate the origin of the increased magnetic mineral concentration concomitant with subchron C18n.2n, which corresponds to the MECO interval in ODP Hole 711A. This magnetic mineral peak also coincides with a change in lithofacies from calcareous nannofossils to radiolarian ooze, and a slight increase in clay concentration. Magnetite is the main magnetic mineral in the MECO sediments, which occurs as magnetically non-interacting single domain biogenic particles. The increased magnetic mineral concentration across the MECO event is likely to have been caused by increased eolian iron fertilization. This is interpreted to have given rise to increased surface ocean productivity, where increased delivery of iron and nutrients to the seafloor enhanced magnetotactic bacterial populations during the MECO event.
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the Middle Eocene climatic optimum event in the contessa highway section umbrian apennines italy
Geological Society of America Bulletin, 2007Co-Authors: Luigi Jovane, Jaume Dinaresturell, Fabio Florindo, Rodolfo Coccioni, Andrea Marsili, Simonetta Monechi, Andrew P Roberts, Mario SprovieriAbstract:We report a high-resolution paleomagnetic investigation constrained by new qualitative and semiquantitative analyses of planktic and benthic foraminifera, nannofossil assemblages, integrated with oxygen and carbon isotope measurements, for the Middle Eocene Scaglia limestones of the Contessa Highway section, central Italy. Calcareous plankton assemblages enable recognition of several biostratigraphic events from planktic foraminiferal zone P11 to the lower part of zone P15 and from calcareous nannofossil zone NP15 to the upper part of zone NP17, which results in refi nement of the magnetobiostratigraphy of the Contessa Highway section. Correlation of the paleomagnetic polarity pattern with the geomagnetic polarity time scale provides a direct age interpretation for strata around the Middle Eocene Scaglia limestones of the Contessa Highway section, from chrons C21n (47 Ma) through to subchron C18n.1n (38.5 Ma). Bulk carbon isotope values indicate a distinct carbon isotopic shift at 40 Ma that is interpreted to represent the fi rst evidence in the Northern Hemisphere of the Middle Eocene climatic optimum, which has recently been observed as a stable isotope anomaly in multiple records from the Indian-Atlantic sector of the Southern Ocean. This demonstrates a global response of the carbon cycle to the proposed transient increased pCO 2 levels during the late Middle Eocene and consequent global CO 2 -driven climate change.
Martino Giorgioni - One of the best experts on this subject based on the ideXlab platform.
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abyssal oceanic circulation and acidification during the Middle Eocene climatic optimum meco
Scientific Reports, 2020Co-Authors: Flaminia Cornaggia, Simone Bernardini, Martino Giorgioni, Gabriel L X Silva, Andre Istvan M Nagy, Luigi JovaneAbstract:The Middle Eocene Climatic Optimum (MECO) is a global warming event that occurred at around 40 Ma and lasted about 500 kyr. We study this event in an abyssal setting of the Tasman Sea, using the IODP Core U1511B-16R, collected during the expedition 371. We analyse magnetic, mineralogical, and chemical parameters to investigate the evolution of the sea bottom conditions at this site during the Middle Eocene. We observe significant changes indicating the response to the MECO perturbation. Mn oxides, in which Mn occurs under an oxidation state around +4, indicate a high Eh water environment. A prominent Mn anomaly, occurring just above the MECO interval, indicates a shift toward higher pH conditions shortly after the end of this event. Our results suggest more acid bottom water over the Tasman abyssal plain during the MECO, and an abrupt end of these conditions. This work provides the first evidence of MECO at abyssal depths and shows that acidification affected the entire oceanic water column during this event.
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carbon cycle instability and orbital forcing during the Middle Eocene climatic optimum
Scientific Reports, 2019Co-Authors: Martino Giorgioni, Luigi Jovane, Rodolfo Coccioni, E S Rego, Daniel Rodelli, Fabrizio Frontalini, Rita Catanzariti, Ercan OzcanAbstract:The Middle Eocene Climatic Optimum (MECO) is a global warming event that occurred at about 40 Ma. In comparison to the most known global warming events of the Paleogene, the MECO has some peculiar features that make its interpretation controversial. The main peculiarities of the MECO are a duration of ~500 kyr and a carbon isotope signature that varies from site to site. Here we present new carbon and oxygen stable isotopes records (δ13C and δ18O) from three foraminiferal genera dwelling at different depths throughout the water column and the sea bottom during the Middle Eocene, from eastern Turkey. We document that the MECO is related to major oceanographic and climatic changes in the Neo-Tethys and also in other oceanic basins. The carbon isotope signature of the MECO is difficult to interpret because it is highly variable from site to site. We hypothesize that such δ13C signature indicates highly unstable oceanographic and carbon cycle conditions, which may have been forced by the coincidence between a 400 kyr and a 2.4 Myr orbital eccentricity minimum. Such forcing has been also suggested for the Cretaceous Oceanic Anoxic Events, which resemble the MECO event more than the Cenozoic hyperthermals.
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environmental magnetic implications of magnetofossil occurrence during the Middle Eocene climatic optimum meco in pelagic sediments from the equatorial indian ocean
Palaeogeography Palaeoclimatology Palaeoecology, 2016Co-Authors: Jairo F Savian, Martino Giorgioni, Luigi Jovane, Fabio Florindo, Andrew P Roberts, Daniel Rodelli, Francesco Iacoviello, Liao Chang, Mario SprovieriAbstract:Abstract Magnetic properties of pelagic marine sediments that record the Middle Eocene Climatic Optimum (MECO) at ~ 40 Ma provide information about major environmental changes. The main variations observed during this transient warming event reflect a bacterial magnetofossil signal, but the cause of the linkage between bacterial production and climate remains unclear. We present an environmental magnetic study of Middle Eocene deep-sea sediments from the northern edge of Madingley Rise (Ocean Drilling Program Hole 711A, equatorial Indian Ocean) to investigate the origin of the increased magnetic mineral concentration concomitant with subchron C18n.2n, which corresponds to the MECO interval in ODP Hole 711A. This magnetic mineral peak also coincides with a change in lithofacies from calcareous nannofossils to radiolarian ooze, and a slight increase in clay concentration. Magnetite is the main magnetic mineral in the MECO sediments, which occurs as magnetically non-interacting single domain biogenic particles. The increased magnetic mineral concentration across the MECO event is likely to have been caused by increased eolian iron fertilization. This is interpreted to have given rise to increased surface ocean productivity, where increased delivery of iron and nutrients to the seafloor enhanced magnetotactic bacterial populations during the MECO event.