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Dominant dextral to sinistral coiling change in planktic foraminifer Morozovella during the Early Eocene Climatic Optimum in the Atlantic Ocean Roberta D’Onofrio Department of Physics and Earth Sciences, Ferrara University, Italy [email protected] Valeria Luciani Department of Physics and Earth Sciences, Ferrara University, Italy [email protected] Bridget Wade Department of Earth Sciences, University College London, UK [email protected] Gerald R. Dickens Department of Earth Sciences, Rice University Houston, USA [email protected] 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 (Figs. 4, 5). 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 Coiling direction is a basic characteristic of trochospiral planktic foraminifera (Fig. 1). 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 (Fig. 2). 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 (Luciani et al., 2016 ClimPast; 2017 Paleoceanography; 2017b GloPlaCha; D’Onofrio et al. 2020 Geosciences (Fig. 3). Figure 1. Examples of sinistral and dextral coiling within the same morphospecies of Morozovella from the early Eocene sediments of the Site 1051. A-B: cartoons showing spiral view of sinistral (A) and dextral (B) coiled Morozovella crater. C-D: sinistral and dextral Morozovella formosa. E-F: sinistral and dextral Morozovell aragonensis. G-H: Cartoons of sinistral (G) and dextral (H) coiled Morozovella aragonensis in umbilical view where chambers increase appears in the opposite direction with respect to the dorsal view. I-J: sinistral and dextral coiled Morozovella marginodentata. K-L: sinistral and dextral coiled Morozovella crater. Scale bar: 100 µm. -60° -30° 60° 30° 0° -60° -30° 60° 30° 0° 1051 1263 1258 PALEOMAP AT ca 50 MA http://www.odsn/de/services/paleomap.html Figure 2. EECO I-1 I-2 H-1 = ETM2 K/X = ETM3 J H-2 N L-2 L-1 Q O T P R S M U 40 50 30 20 Acarinina (%) 40 10 50 0 30 20 Morozovella (%) 4 10 0 30 20 Subbotinids (%) 90 70 80 60 bulk δ C (‰) 0.8 2 1.6 1.2 13 0.4 0.8 1.2 0.4 0 -0.4 -0.8 13 N. truempyi δ C (‰) E6 / E7a E5 E4 Chronostratigraphy E-Zonation LOWER EOCENE Depth (rmcd) 240 260 280 300 250 270 290 1263 B Recovery 20 - H 21 - H 22 - H 23 - H 24 - H 25 - H Blake Nose (ODP Site 1051) Figure 3. In order to establish whether the observed coiling switch was related to changes in morozovellid ecological niche we estimated stable carbon isotopes on dextral (DX) and sinistral (SN) species from samples located below and above the coiling change at sites 1258 and 1263 (Fig. 6). At Site 1263, in the interval pre-shift (Fig. 6A) dominated by DX forms, SN morphotypes occupied a lower position in the mixed-layer with respect to the DX forms. Interestingly, during the coiling switch (Fig. 6B) we observe a reversal situation, i.e., SN morphotypes moved higher in the mixed-layer. After the coiling shift, in the interval of dominant SN morphotypes (Fig. 6C), the position of the two morphotypes in the mixed-layer changes according to the different species. Specifically, M. formosa SN is higher at Site 1263 whereas M. crater SN results in a lower position with respect to DX morphotypes at both sites. M. aragonensis SN and DX proved to be at similar position at Site 1258. Intriguingly, SN M. crater and SN M. aragonensis show higher degrees of resilience because in the post-shift interval (Fig. 6C) they returned to stay deeper with respect to the DX forms. By contrast, M. formosa, that disappeared during the EECO, probably had lower degrees of flexibility as SN coiled forms maintained a higher mixed-layer habitat during the post-shift interval. It is thus possible that only morphotypes sinistrally coiled had enough flexibility to keep the optimal environmental conditions for their survivorship across the EECO. We need however more effort to understand the meaning of these modifications, such as 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. EECO M (C23r-H2) I-1 (C24n.3n-H1) H-1 = ETM2 (C24r-H8) K/X = ETM3 (C24n.1n-H1) J L-1 (C23r-H1) L-2 I-2 (C24n.3n-H2) H-2 (C24r-H9) Q (C22r-H1) P (C23n.1n-H1) R (C22r-H2) T (C22r-H4) S (C22r-H3) N (C23r-H3) O (C23n.2n-H1) M (C23r-H2) I-1 (C24n.3n-H1) H-1 = ETM2 (C24r-H8) K/X = ETM3 (C24n.1n-H1) J L-1 (C23r-H1) L-2 I-2 (C24n.3n-H2) H-2 (C24r-H9) Q (C22r-H1) P (C23n.1n-H1) R (C22r-H2) T (C22r-H4) S (C22r-H3) N (C23r-H3) O (C23n.2n-H1) M (C23r-H2) I-1 (C24n.3n-H1) H-1 = ETM2 (C24r-H8) K/X = ETM3 (C24n.1n-H1) J L-1 (C23r-H1) L-2 I-2 (C24n.3n-H2) H-2 (C24r-H9) U Blake Nose ODP Site 1051 Sinistral within Morozovella (%) 0 60 20 80 40 100 Sinistral within Morozovella (%) 0 60 20 80 40 100 Demerara Rise ODP Site 1258 Sinistral within Morozovella (%) 0 60 20 80 40 100 Walvis Ridge ODP Site 1263 Dextral within Morozovella (%) 0 60 20 80 40 100 Dextral within Morozovella (%) 0 60 20 80 40 100 Dextral within Morozovella (%) 0 60 20 80 40 100 Dextral Sinistral 0.8 0.6 0.2 0.0 N. truempyi δ C (‰) 13 1.2 1.0 0.4 -0.8 -0.6 -0.2 -1.0 -0.4 0.8 0.6 2.0 1.2 1.0 0.4 1.8 1.6 1.4 bulk δ C (‰) 13 0.8 0.6 0.2 1.2 1.0 0.4 1.8 1.6 1.4 bulk δ C (‰) 13 -0.20.0 1.4 0.8 0.6 0.2 1.6 0.0 bulk δ C (‰) 13 1.2 1.0 0.4 E-Zonation Chronostratigraphy 54.2 54.0 53.8 53.6 53.4 53.2 53.0 52.8 52.6 52.4 52.2 52.0 51.8 LOWER EOCENE E6 / E7a E5 E4 51.6 51.4 51.2 51.0 50.8 50.6 50.4 Age (Ma) Polarity Chron E-Zonation C24r C23r C24n.1n C24n.3n C23n.1n C22r C23n.2n E7a E6 E5 E4 C24n.1n C24n.2n 53.8 53.6 53.4 53.2 53.0 52.8 52.6 52.4 52.2 52.0 51.8 51.6 51.4 51.2 51.0 50.8 50.6 50.4 50.2 50.0 49.8 49.6 E-Zonation Polarity Chron Chronostratigraphy 54.2 54.0 53.8 53.6 53.4 53.2 53.0 52.8 52.6 52.4 52.2 52.0 51.8 C23n C24n.1n C24n.3n C24r C23r LOWER EOCENE E6 / E7a E5 E4 Chronostratigraphy LOWER EOCENE Age (Ma) Age (Ma) Figure 5. = Coiling shift bulk δ C (‰) 0.4 1.6 1.2 0.8 13 0 80 20 100 0 60 40 80 20 100 0 60 40 80 20 100 0 60 40 80 20 100 0 60 40 80 20 100 0 60 40 80 20 100 0 60 40 80 20 100 0 60 40 80 20 100 0 60 40 80 20 100 0 60 40 Sinistral within M. aequa (%) Sinistral within M. subbotinae (%) Sinistral within M. gracilis (%) Sinistral within M. marginodentata (%) Sinistral within M. lensiformis (%) Sinistral within M. formosa (%) Sinistral within M. crater (%) Sinistral within M. aragonensis (%) Sinistral within M. caucasica (%) I-1 I-2 EECO H-1 = ETM2 K/X = ETM3 J H-2 M L-2 L-1 360 380 400 420 440 460 Depth (mbsf) Recovery Polarity Chron Chronostratigraphy E - Zonation C21n C21r C23n C24n C24n MIDDLE EOCENE LOWER EOCENE E7b / E8 E6 / E7a E5 E4 Blake Nose ODP Site 1051 40 10 50 0 30 20 Morozovella (%) 80 20 100 0 60 40 Sinistral within Morozovella (%) 20 80 0 100 40 60 Dextral within Morozovella (%) Dextral Sinistral Base Base Top Top Top Top 135 125 115 105 95 85 65 75 C24r C23r C24n.1n C24n.3n C23n C22r 55 Demerara Rise ODP Site 1258 Depth (rmcd) Polarity Chron E-Zonation E7a E6 E5 E4 1.4 1.0 0.6 0.2 1.8 -0.2 bulk δ C (‰) 13 Q (C22r-H1) P (C23n.1n-H1) R (C22r-H2) T (C22r-H4) S (C22r-H3) N (C23r-H3) O (C23n.2n-H1) M (C23r-H2) I-1 (C24n.3n-H1) H-1 = ETM2 (C24r-H8) K/X = ETM3 (C24n.1n-H1) J-1 L-1 (C23r-H1) L-2 I-2 (C24n.3n-H2) H-2 (C24r-H9) J-2 0 60 20 80 40 100 Sinistral within Morozovella (%) Sinistral within M. aequa (%) Sinistral within M. subbotinae (%) Sinistral within M. gracilis (%) Sinistral within M. marginodentata (%) Sinistral within M. formosa (%) Sinistral within M. lensiformis (%) Sinistral within M. crater (%) Sinistral within M. aragonensis (%) Sinistral within M. caucasica (%) 0 60 20 80 40 100 0 60 20 80 40 100 0 60 20 80 40 100 0 60 20 80 40 100 0 60 20 80 40 100 0 60 20 80 40 100 0 60 20 80 40 100 0 60 20 80 40 100 0 60 20 80 40 100 0 30 10 40 20 50 Morozovella (%) 0 60 20 80 40 100 Dextral within Morozovella (%) Dextral Sinistral Base Top Top Top Top Top Base EECO I-1 I-2 H-1 = ETM2 K/X = ETM3 J H-2 N L-2 L-1 Q O T P R S M U 80 20 100 0 60 40 Sinistral within Morozovella (%) 80 20 100 0 60 40 Sinistral within M. aequa (%) 80 20 100 0 60 40 Sinistral within M. subbotinae (%) 80 20 100 0 60 40 Sinistral within M. marginodentata (%) 80 20 100 0 60 40 Sinistral within M. gracilis (%) 80 20 100 0 60 40 Sinistral within M. crater (%) 80 20 100 0 60 40 Sinistral within M. lensiformis (%) 80 20 100 0 60 40 Sinistral within M. formosa (%) 80 20 100 0 60 40 Sinistral within M. aragonensis (%) 80 20 100 0 60 40 Sinistral within M. caucasica (%) 80 20 100 0 60 40 Dextral within Morozovella (%) Dextral Sinistral bulk δ C (‰) 0.8 2 1.6 1.2 13 0.4 0.8 1.2 0.4 0 -0.4 -0.8 13 N. truempyi δ C (‰) E6 / E7a E5 E4 Chronostratigraphy E-Zonation LOWER EOCENE Depth (rmcd) 1263 B Recovery 240 250 260 270 280 290 300 20 - H 21 - H 22 - H 23 - H 24 - H 25 - H 10 20 0 Morozovella (%) 40 30 5 15 35 25 45 Walvis Ridge ODP Site 1263 Top Top Top Top Base Base Figure 4. Walvis Ridge (ODP Site 1051) 1.5 2.0 2.5 3.0 δ C (‰) 13 3.5 1.5 2.0 2.5 3.0 δ C (‰) 13 3.5 1.5 2.0 2.5 3.0 δ C (‰) 13 3.5 ODP Site 1258 Demerara Rise -2.6 -2.2 -2.4 -3.0 -2.8 -2.0 -2.6 -2.2 -2.4 -3.0 -2.8 -2.0 δ O (‰) 18 -2.6 -2.2 -2.4 -1.8 -2.8 -2.0 1.0 1.5 2.0 2.5 δ C (‰) 13 3.0 1.0 1.5 2.0 2.5 δ C (‰) 13 3.0 1.0 1.5 2.0 2.5 δ C (‰) 13 3.0 -0.8 -0.4 -0.6 -1.2 -1.0 -0.2 δ O (‰) 18 -0.8 -0.4 -0.6 -1.2 -1.0 -0.2 -0.8 -0.4 -0.6 -1.2 -1.0 -0.2 ODP Site 1263 Walvis Ridge PRE SHIFT COILING SHIFT POST SHIFT M. aequa M. subbotinae M. marginodentata M. formosa M. aragonensis M. crater M. caucasica M. aequa M. subbotinae M. formosa M. aragonensis M. crater Dextral morphotypes Sinistral morphotypes Fig. 6. C) B) A)
