Surface-circulation change in the Southern Ocean across the Middle Eocene Climatic Optimum: inferences from dinoflagellate cysts and biomarker paleothermometry

Cramwinckel, Margot J.; Woelders, Lineke; Huurdeman, Emiel P; Peterse, Francien; Gallagher, Stephen; Pross, Jörg; Burgess, Catherine E; Reichart, Gert‐Jan; Sluijs, Appy; Bijl, Peter K.

doi:10.5194/cp-2019-35

Cited by 8 publications

(12 citation statements)

References 127 publications

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“…is not unique to only the MECO interval at Site 647. Similar poleward range expansion of plankton species from lower latitudes has been recorded in southern Indian Ocean calcareous nannofossils (Villa et al, 2008) and in Southwest Pacific dinocyst assemblages (Bijl et al, 2010;Cramwinckel et al, 2020) during the MECO.…”

Section: The Signature Of the Meco In The Labrador Seasupporting

confidence: 72%

A Warm, Stratified, and Restricted Labrador Sea Across the Middle Eocene and Its Climatic Optimum

Cramwinckel

Coxall

Śliwińska

et al. 2020

Paleoceanog and Paleoclimatol

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Several studies indicate that North Atlantic Deep Water (NADW) formation might have initiated during the globally warm Eocene (56-34 Ma). However, constraints on Eocene surface ocean conditions in source regions presently conducive to deep water formation are sparse. Here we test whether ocean conditions of the middle Eocene Labrador Sea might have allowed for deep water formation by applying (organic) geochemical and palynological techniques, on sediments from Ocean Drilling Program (ODP) Site 647. We reconstruct a long-term sea surface temperature (SST) drop from~30°C to~27°C between 41.5 to 38.5 Ma, based on TEX 86. Superimposed on this trend, we record~2°C warming in SST associated with the Middle Eocene Climatic Optimum (MECO;~40 Ma), which is the northernmost MECO record as yet, and another, likely regional, warming phase at~41.1 Ma, associated with low-latitude planktic foraminifera and dinoflagellate cyst incursions. Dinoflagellate cyst assemblages together with planktonic foraminiferal stable oxygen isotope ratios overall indicate low surface water salinities and strong stratification. Benthic foraminifer stable carbon and oxygen isotope ratios differ from global deep ocean values by 1-2‰ and 2-4‰, respectively, indicating geographic basin isolation. Our multiproxy reconstructions depict a consistent picture of relatively warm and fresh but also highly variable surface ocean conditions in the middle Eocene Labrador Sea. These conditions were unlikely conducive to deep water formation. This implies either NADW did not yet form during the middle Eocene or it formed in a different source region and subsequently bypassed the southern Labrador Sea.

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Section: The Signature Of the Meco In The Labrador Seasupporting

confidence: 72%

A Warm, Stratified, and Restricted Labrador Sea Across the Middle Eocene and Its Climatic Optimum

Cramwinckel

Coxall

Śliwińska

et al. 2020

Paleoceanog and Paleoclimatol

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“…Post-MECO cooling seems more gradual than MECO warming, although this might be the result of sedimentation rate changes (Bijl et al, 2010), which are not accounted for in our age model. SSTs are almost identical to those for the MECO at nearby Site 1170 on the South Tasman Rise (Cramwinckel et al, 2020 (Houben et al, 2019).…”

Section: Sstmentioning

confidence: 54%

“…Palynological evidence confirms that the Proto-Ross Gyre influence persisted at the ETP until the late Eocene (Bijl et al, 2011;Warnaar et al, 2009). This means that despite northward tectonic drift, the same strong western boundary current bathed the site during the Maastrichtian to early Eocene (Sijp et al, 2016), with perhaps some intermittent influence of East Australian Current waters from the north (Bijl et al, 2010;Cramwinckel et al, 2020). This ended when the proto-Leeuwin Current started to flow through the progressively widening TG ( Fig.…”

Section: Depositional Settingmentioning

confidence: 60%

Maastrichtian-Rupelian paleoclimates in the southwest Pacific – a critical evaluation of biomarker paleothermometry and dinoflagellate cyst paleoecology at Ocean Drilling Program Site 1172

Bijl¹,

Frieling²,

Cramwinckel³

et al. 2021

Preprint

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Abstract. Sea surface temperature (SST) reconstructions based on isoprenoid glycerol dialkyl glycerol tetraether (isoGDGT) distributions from the Eocene southwest (sw) Pacific Ocean are unequivocally warmer than can be reconciled with state-of-the-art fully coupled climate models. However, the SST signal preserved in sedimentary archives can be affected by contributions of additional isoGDGT sources. Methods now exist to identify and possibly correct for overprinting effects on the isoGDGT distribution in marine sediments. We here use the current proxy insights to assess the reliability of the isoGDGT-based SST signal in 69 newly analysed and 242 re-analysed sediments ODP Site 1172 (East Tasman Plateau, Australia) following state-of-the-art chromatographic techniques, in context of paleo-environmental and paleoclimatologic reconstructions based on dinoflagellate cysts. The resulting ~130 kyr-resolution Maastrichtian-Oligocene TEX86-based SST record confirms previous conclusions of anomalous warmth in the early Eocene sw Pacific and remarkably cool conditions during the mid-Paleocene. Dinocyst diversity and assemblages show a strong response to the local SST evolution, supporting the robustness of the TEX86 record. Soil-derived branched GDGTs stored in the same sediments are used to reconstruct mean annual air temperature (MAAT) of the nearby land using the MBT'5me proxy. MAAT is consistently lower than SST during the early Eocene, independent of the calibration chosen. General trends in SST and MAAT are similar, except for: 1) an enigmatic absence of MAAT rise during the Paleocene-Eocene Thermal Maximum and Middle Eocene Climatic Optimum, and 2) a subdued middle–late Eocene MAAT cooling relative to SST. Both dinocysts and GDGT signals suggest a mid-shelf depositional environment with strong river-runoff during the Paleocene-early Eocene, progressively becoming more marine thereafter. This trend reflects gradual drying and more pronounced wet/dry seasons in the northward drifting Australian hinterland, which may also explain the subdued middle Eocene MAAT cooling relative to that of SST. The overall correlation between dinocyst assemblages, marine biodiversity and SST changes suggests that temperature exerted a strong influence on the surface-water ecosystem, probably in part through sea level changes caused by steric effects. Finally, we find support for a potential temperature control on compositional changes of branched glycerol monoalkyl glycerol tetraethers (brGMGTs) in marine sediments. It is encouraging that a critical evaluation of the GDGT signals confirms the vast majority of the generated data is reliable. However, this also implies the high TEX86-based SSTs for the Eocene sw Pacific, and the systematic offset between absolute TEX86-based SST and MBT'5me-based MAAT estimates remain unexplained.

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“…The changes described represent the response of the complex oceanographic circulation of the SO to the MECO climatic warming 4,38 . Major circulation changes have been described in previous studies associated with the MECO climatic warming, at surface to bathyal depths 4,10,11,26,39,40 . Here we show that modifications occurred also in the abyssal circulation of the SO, with the inflow of more acid bottom water.…”

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 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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Surface-circulation change in the Southern Ocean across the Middle Eocene Climatic Optimum: inferences from dinoflagellate cysts and biomarker paleothermometry

Cited by 8 publications

References 127 publications

A Warm, Stratified, and Restricted Labrador Sea Across the Middle Eocene and Its Climatic Optimum

A Warm, Stratified, and Restricted Labrador Sea Across the Middle Eocene and Its Climatic Optimum

Maastrichtian-Rupelian paleoclimates in the southwest Pacific – a critical evaluation of biomarker paleothermometry and dinoflagellate cyst paleoecology at Ocean Drilling Program Site 1172

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

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