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

Giorgioni, M.; Jovane, Luigi; Rêgo, Eric Siciliano; Rodelli, Daniel; Frontalini, Fabrizio; Coccioni, Rodolfo; Catanzariti, Rita; Özcan, Ercan

doi:10.1038/s41598-019-45763-2

Cited by 41 publications

(42 citation statements)

References 58 publications

(86 reference statements)

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“…This change induces a decrease in sedimentation rate, explaining why, by applying the value of 10 m/Myr estimated by ref. 26 , the duration of the MECO at this site results 172 kyr, instead of ~500 kyr observed in most of the records 10,27 . Such shorter duration is an artefact related to a relatively poorly constrained sedimentation rate in this interval, which is based only on magnetostratigraphy and radiolarian biostratigraphy, due to the absence of carbonate microfossils 26 .…”

Section: Discussionmentioning

confidence: 66%

“…In order to acidify the bottom waters over the TAP, a large amount of inorganic carbon must have entered into the SO, and kept stored in the deep environment, which requires a stratified water column, as observed at the studied site, and an efficient biologic pump 41 . Such configuration could have maintained low pH and warming conditions for hundreds of thousand years, so explaining in part the conundrum related to this event [14.] On the other hand, the source of carbon that triggered the acidification still remains uncertain and perhaps it is related to C-cycle instability induced by orbital forcing 27 . Even though the main trigger of the MECO is still unclear, we showed that oceanic circulation played a key role for the development of this event.…”

Section: Discussionmentioning

confidence: 99%

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Abyssal oceanic circulation and acidification during the Middle Eocene Climatic Optimum (MECO)

Cornaggia

Bernardini

Giorgioni

et al. 2020

Sci Rep

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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. The Eocene (~56-34 Ma) was characterized by a gradual climatic cooling, accompanied by decreasing atmospheric pCO 2 and culminating with the onset of the Antarctic glaciation in the early Oligocene (33 Ma) 1-5. This trend was interrupted during the middle Eocene by a warm period known as Middle Eocene Climatic Optimum (MECO), with duration of ~500 kyr and a warmth peak at ~40 Ma 6,7. The MECO has been identified in several sedimentary records around the globe, including the South Pacific Ocean 8,9. It is related to an increase in seawater temperature, from the surface to deep bathyal depths, and increasing pCO 2 in the atmosphere 10,11. Moreover, significant changes in atmospheric and oceanic circulation dynamics and in the patterns of continental rainfall are recorded 12,13. However, classic climatic models fail to explain how such conditions could persist for several hundreds of thousand years 14. Southern Ocean (SO) circulation is extremely important for understanding the climatic evolution during the Eocene, and particularly during the MECO. The separation of Australia from Antartica during the middle-late Eocene profoundly affected the circulation and made this region particularly sensitive to paleoceanographic changes 4,15. In this complex geological framework, the study of iron and manganese oxides in the sediments can provide important information, as they are strongly controlled by redox conditions and circulation 16. Manganese oxides typically occur as cryptocrystalline materials, in which Mn precipitates under different oxidation states: Mn 4+ , Mn 3+ and Mn 2+17. Moreover, Mn is more sensitive than Fe to pH, and requires more basic conditions to precipitate. Therefore, an environment may promote the oxidation and precipitation of iron and not of manganese, if the pH is not sufficiently high 18-21. Accordingly, relatively small shift in the redox conditions can change significantly the equilibrium solubility of these elements and thus their presence or absence in the geological record. Microorgani...

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Section: Discussionmentioning

confidence: 66%

Section: Discussionmentioning

confidence: 99%

Abyssal oceanic circulation and acidification during the Middle Eocene Climatic Optimum (MECO)

Cornaggia

Bernardini

Giorgioni

et al. 2020

Sci Rep

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“…The MECO event has been defined by a negative bulk OIE, followed by a peak interval of lowest δ 18 O values that ends with a rapid recovery to preexcursion values. This pattern is recurrent in records from different latitudes and ocean basins (Bohaty et al, ; Giorgioni et al, ; Jovane et al, ; Spofforth et al, ). At Site 702 in the South Atlantic Ocean, our high‐resolution isotopic analyses follow the same overall trend.…”

Section: Discussionmentioning

confidence: 75%

“…Estimations of MECO duration based on isotopic records vary from ~500 Kyr (Bohaty et al, ), ~600 Kyr (Bohaty & Zachos, ) to ~750 Kyr (Edgar et al, ). Robust age models are needed to better constrain the duration of this event, to discuss its mechanisms, and to assess its relation with orbital cycles (Giorgioni et al, ; Westerhold et al, , ).…”

Section: Introductionmentioning

confidence: 99%

Paleoenvironmental Changes at ODP Site 702 (South Atlantic): Anatomy of the Middle Eocene Climatic Optimum

Rivero-Cuesta

Westerhold

Agnini

et al. 2019

Paleoceanog and Paleoclimatol

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The Middle Eocene Climatic Optimum (MECO) was an unusual global warming event that interrupted the long-term Eocene cooling trend ca. 40 Ma. Here we present new high-resolution bulk and benthic isotope records from South Atlantic ODP Site 702 to characterize the MECO at a high latitude setting. The MECO event, including early and peak warming as well as recovery to background levels, had an estimated~300 Kyr duration (~40.51 to~40.21 Ma). Cross-plots (δ 18 O vs. δ 13 C) suggest that the mechanisms driving coupled changes in O and C isotope values across the MECO were weaker or absent before the event. The paleoecological response has been evaluated by quantitative analysis of calcareous nannofossils and benthic foraminifera assemblages. We document a shift in the biogeographical distribution of warm and temperate calcareous nannoplankton taxa, which migrated toward higher latitudes due to increased temperatures during the MECO. Conversely, changes in the organic matter flux to the seafloor appear to have controlled benthic foraminifera dynamics at Site 702. Benthic phytodetritus exploiting taxa increased in abundance coinciding with a positive δ 13 C excursion,~150 Kyr before the start of the δ 18 O negative excursion that marks the start of MECO warming. Our data suggest that paleoecological disturbance in the deep sea predates MECO δ 18 O excursion and that it was driven by changes in the type and/or amount of organic matter reaching the seafloor rather than by increased temperature.

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“…Black diamonds are the tuning tie points to the orbital solution (Table S2). Ages are shown on the Gradstein et al (2012) timescale. Abbreviations of datums are T, B, or Bc for Top, Base, or Base of common occurrence, respectively, followed by the first letter of the genus and species name.…”

Section: Planktic Foraminiferal Biostratigraphymentioning

confidence: 99%

New composite bio- and isotope stratigraphies spanning the Middle Eocene Climatic Optimum at tropical ODP Site 865 in the Pacific Ocean

Edgar

Bohaty

Coxall

et al. 2020

J. Micropalaeontol.

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Abstract. The Middle Eocene Climatic Optimum (MECO) at ca. 40 Ma is one of the largest of the transient Eocene global warming events. However, it is relatively poorly known from tropical settings since few sites span the entirety of the MECO event and/or host calcareous microfossils, which are the dominant proxy carrier for palaeoceanographic reconstructions. Ocean Drilling Program (ODP) Pacific Ocean Site 865 in the low-latitude North Pacific (Allison Guyot) has the potential to provide a useful tropical MECO reference, but detailed stratigraphic and chronological constraints needed to evaluate its completeness were previously lacking. We have addressed this deficit by generating new high-resolution biostratigraphic, stable isotope, and X-ray fluorescence (XRF) records spanning the MECO interval (∼38.0–43.0 Ma) in two holes drilled at Site 865. XRF-derived strontium ∕ calcium (Sr∕Ca) and barium ∕ strontium (Ba∕Sr) ratios and Fe count records allow correlation between holes and reveal pronounced rhythmicity, enabling us to develop the first composite section for Holes 865B and 865C and a preliminary cyclostratigraphy for the MECO. Using this new framework, the sedimentary record is interpreted to be continuous across the event, as identified by a pronounced transient benthic foraminiferal δ18O shift of ∼0.8 ‰. Calcareous microfossil biostratigraphic events from widely used zonation schemes are recognized, with generally good agreement between the two holes, highlighting the robustness of the new composite section and allowing us to identify planktic foraminiferal Zones E10–E15 and calcareous nannofossil Zones NP15–18. However, discrepancies in the relative position and ordering of several primary and secondary bioevents with respect to published schemes are noted. Specifically, the stratigraphic highest occurrences of planktic foraminifera, Acarinina bullbrooki, Guembelitrioides nuttalli, and Morozovella aragonensis, and calcareous nannofossils, Chiasmolithus solitus and Sphenolithus furcatolithoides, and the lowest occurrence of Reticulofenestra reticulata all appear higher in the section than would be predicted relative to other bioevents. We also note conspicuous reworking of older microfossils (from planktic foraminiferal Zones E5–E9 and E13) into younger sediments (planktic foraminiferal Zones E14–15) within our study interval consistent with reworking above the MECO interval. Regardless of reworking, the high-quality XRF records enable decimetre-scale correlation between holes and highlight the potential of Site 865 for constraining tropical environmental and biotic changes, not just across the MECO but also throughout the Palaeocene and early-to-middle Eocene interval.

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

Cited by 41 publications

References 58 publications

Abyssal oceanic circulation and acidification during the Middle Eocene Climatic Optimum (MECO)

Abyssal oceanic circulation and acidification during the Middle Eocene Climatic Optimum (MECO)

Paleoenvironmental Changes at ODP Site 702 (South Atlantic): Anatomy of the Middle Eocene Climatic Optimum

New composite bio- and isotope stratigraphies spanning the Middle Eocene Climatic Optimum at tropical ODP Site 865 in the Pacific Ocean

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