EGU2020-21576
https://doi.org/10.5194/egusphere-egu2020-21576
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Dominant dextral to sinistral coiling change in planktic foraminifera Morozovella during the Early Eocene Climatic Optimum in the Atlantic Ocean

Valeria Luciani1, Roberta D'Onofrio1, Wade Bridget S.3, and Dickens Jerry R.2
Valeria Luciani et al.
  • 1Ferrara University, Physics and Earth Sciences, Ferrara, Italy (lcv@unife.it)
  • 2Department of Earth Sciences, University College London, London, United Kingdom
  • 3Department of Earth Science, Rice University, Houston, TX 77005, USA,

Coiling direction is a basic characteristic of trochospiral planktic foraminifera. However, although modifications in the coiling direction within ancient planktic foraminiferal populations may reflect important changes in evolution or environment, they remain scarcely discussed. Here we present data on fluctuations in the coiling direction within morphologically defined Morozovella species from successions that span the interval of peak Cenozoic warmth, the Early Eocene Climatic Optimum (EECO; ~53-49 Ma). We selected three widely separated Ocean Drilling Program (ODP) sites in the Atlantic Ocean: the subtropical Site 1051, the equatorial Site 1258 and the temperate south Atlantic Site 1263. The surface-dwelling genus Morozovella is of particular interest because it dominated tropical-subtropical early Paleogene assemblages and  suffered an abrupt and permanent decline in abundance and taxonomic diversity at the start of the EECO. At all ODP sites investigated, morozovellids display a dominant dextral coiling preference during the interval preceding the EECO. However, all species became at all sites prevailing sinistral within the EECO. Specifically, the switch from dominant dextral to sinistral coiling occurred at all sites ~ 300 Kyr after the K/X event (~52.8 Ma). The coiling switch occurred ~550 kyr to ~650 kyr after a distinct drop in abundance. We provide therefore evidence of a coiling variation during the warmest interval of the early Paleogene. Our records highlight that the recorded coiling variations might provide a biostratigraphic tool for correlation of early Eocene marine strata. In order to establish whether this coiling switch was related to changes in morozovellid ecological niche we estimated stable carbon isotopes on dextral and sinistral species from samples located below and above the recorded coiling change. Results suggest that sinistral species moved higher in the mixed-layer after the coiling switch. It is thus possible that only species sinistrally coiled were able to keep the optimal environmental conditions for their survivorship. We need however more effort to understand the meaning of these modifications, such to verify whether variations in sea surface temperature or other parameters directly corresponded to the coiling change. Coiling switches can relate to ecophenotypic adaption (when a single species changes morphology in response to variation in environmental parameters, such as temperature) or genetic variance (when two almost identical morphotypes have different genetic signatures so they represent ‘cryptic’ species from a morphological point of view). Previous interpretations of coiling flips in planktic foraminifera in the early Eocene, especially including morozovellids, have favoured a genetic explanation rather than an ecological response. Our present data cannot validate or disprove this idea, but should stimulate renewed thought on the matter.

How to cite: Luciani, V., D'Onofrio, R., Bridget S., W., and Jerry R., D.: Dominant dextral to sinistral coiling change in planktic foraminifera Morozovella during the Early Eocene Climatic Optimum in the Atlantic Ocean, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21576, https://doi.org/10.5194/egusphere-egu2020-21576, 2020

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Presentation version 1 – uploaded on 05 May 2020
  • CC1: Comment on EGU2020-21576, Flavia Fiorini, 06 May 2020

    Dear Valeria,

    Thanks for participating to our session.

    I have a question related to the drop in abundance that happened before the switch from dominant dextral to sinistral coiling of morozovellids ( ~ 300 Kyr after the K/X event). How do you explain this drop of abundance? What can be the ecological factors that triggered the decrease of abundance?

    Thanks.

    • AC1: Reply to CC1, Valeria Luciani, 06 May 2020

      Dear Flavia,

      actually we don't know the true cause(s) of the morozovellid crash. We suppose that ther is a relationship with the EECO warming and its consequences on the morozovellis habitat. We thought on a possible bleaching that we tested at Site 1051 but results documented only a transitory bleaching. The crash was coupled with a decrease in size so it appears clear that stressors related to the EECO were involved. Possible acidification? You can give a look to our papers Luciani et al. 2016 Climate of the Past, Luciani et al. 2017a Paleoceanography,  Luciani et al 2017 b Global and Planetary Change and D'Onofrio et al.2020 Geosciences

    • AC2: Reply to CC1, Gerald Dickens, 06 May 2020

      As a co-author, but a mere chemist, I have the same question. When Valeria and Roberta first showed me the data I found it one of the more fascinating things I have seen -- why woud multiple morphologically defined species change their coiling direction collectively and across a time of modest environmental change? It seems to me that there must be some genetic link across "species" so that when some environmental  threshold is crossed a similar rssponse happens. Exactly how and why seems to me at the cutting edge of paleo-biology (for which Valeria and Roberta hopefully can give much better answers, and which may reqquire some really clever biogeochemsitry). Right now, I think just cool and interesting.