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. 2019 Jun 27;9(1):9357.
doi: 10.1038/s41598-019-45763-2.

Carbon cycle instability and orbital forcing during the Middle Eocene Climatic Optimum

Martino Giorgioni  1   2 , Luigi Jovane  3 , Eric S Rego  3   4 , Daniel Rodelli  3 , Fabrizio Frontalini  5 , Rodolfo Coccioni  5 , Rita Catanzariti  6 , Ercan Özcan  7
Affiliations

Carbon cycle instability and orbital forcing during the Middle Eocene Climatic Optimum

Martino Giorgioni et al. Sci Rep. .

Abstract

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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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
(a) Geographic maps showing the location of the studied area. The base of the terrain map is from Google Maps (Map data©2019 Google; https://www.google.com/maps/@38.6360375,38.9277941,10z/data=!5m1!1e4); the satellite map of Turkey at the top right corner is from Google Earth (Map data©2018 Google; https://www.google.com/maps/); the globe at the top left corner was made using Python 3.4.3-0 with Matplotlib. (b) Paleogeographic map of the eastern part of the Neo Tethys at 40 Ma, showing the paleogeographic location of the studied area (generated with the ODSN Plate Tectonic Reconstruction Service, 2011; http://www.odsn.de/odsn/services/paleomap/paleomap.html).
Figure 2
Figure 2
Magnetobiostratigraphy, lithological log, and stable isotopes curves of the Baskil section. Litho-, magneto-, and biostratigraphic data are from ref.. Carbon (δ13C) and oxygen (δ18O) isotopes are shown for three individual genera of foraminifera, representing surface (Acarinina), thermocline (Subbotina) and bottom (Cibicidoides) conditions. Diamonds represent individual data points, whereas solid lines represent curves smoothed by 3pts moving average. The yellow shaded bar highlights the position of the MECO based on its isotopic signatures.
Figure 3
Figure 3
∆18O and abundance of calcite, quartz, palygorskite, smectite and illite throughout the Baskil section. ∆18O is the difference between the δ18O measured on Subbotina and Acarinina, and is related to the temperature difference between the sea surface and the thermocline. The thin grey line represents the raw ∆18O curve, whereas the thick blue line represents the 3pts moving average smoothed curve. Minerals abundance is from ref., note that quartz and calcite are respect to bulk minerals abundance, whereas clays are respect to bulk phyllosilicates abundance. The intervals I, II, and III represent the climatic phases described in ref.. The yellow shaded bar highlights the position of the MECO isotopic signatures shown in Fig. 2.
Figure 4
Figure 4
Bottom and upper water column carbon and oxygen stable isotopes records from the middle Eocene. The lower pale yellow bar highlights where the δ13C starts increasing, corresponding also to the onset of the warming in the Southern Ocean. The dark yellow bar highlights the MECO warming peak, defined as the negative δ18O anomaly at around 40 Ma. The upper pale yellow bar highlights the interval with highest δ13C values. Data are from this study and refs, (see methods for more details).
Figure 5
Figure 5
Middle Eocene carbon isotope curves from six representative regions, correlated according to the base of the magnetochron C18n and calibrated respect to the age model of ref.. The yellow bar highlights the position of the MECO and the grey one the co-occurring minima of 400 kyr and 2.4 Myr eccentricity cycles. Data are from this study, and refs,,,, (see methods for more details).
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