Demise of the Planktic Foraminifer Genus Morozovella during the Early Eocene Climatic Optimum: New Records from ODP Site 1258 (Demerara Rise, Western Equatorial Atlantic) and Site 1263 (Walvis Ridge, South Atlantic)

Abstract

Here we present relative abundances of planktic foraminifera that span the Early Eocene Climatic Optimum (EECO) at Ocean Drilling Program (ODP) Site 1258 in the western equatorial Atlantic. The EECO (~53.3−49.1 Ma) represents peak Cenozoic warmth, probably related to high atmospheric CO2, and when planktic foraminifera, a dominant component of marine sediment, exhibit a major biotic response. Consistent with previous work, the relative abundance of the genus Morozovella, which dominated early Paleogene tropical-subtropical assemblages, markedly and permanently declined from a mean percentage of ~32% to less than ~7% at the beginning of the EECO. The distinct decrease in Morozovella abundance occurred at Site 1258 within ~20 kyr before a negative excursion in δ13C records known as the J event and which defines the beginning of EECO. Moreover, all morozovellid species except M. aragonensis dropped in abundance permanently at Site 1258, and this is related to a reduction in test-size. Comparing our data with that from other locations, the remarkable switch in planktonic foraminifera assemblages appears to have begun first with unfavourable environmental conditions near the Equator and then extended to higher latitudes. Several potential stressors may explain observations, including some combination of algal photosymbiont inhibition (bleaching), a sustained increase in temperature, or an extended decrease in pH.

Which was the habitat of early Eocene planktic foraminifer Chiloguembelina? Stable isotope paleobiology from the Atlantic Ocean and implication for paleoceanographic reconstructions

“…Our new record from Site 1051 shows that the relative abundance of chiloguembelinids decreased their relative abundance from ~8% of total foraminifera assemblages to virtually and permanently absence near the K/X event. Similarly, chiloguembelinids decrease within the EECO at sites 1263 (Luciani et al, 2017a) and 1258 (D'Onofrio et al, 2020). Specifically, at Site 1263, chiloguembelinids move from ~10 % in relative abundance to virtually absence above the K/X event (Luciani et al, 2017a) and, at Site 1258, move from ~5% below the EECO to 0% below the K/X event.…”

“…Specifically, at Site 1263, chiloguembelinids move from ~10 % in relative abundance to virtually absence above the K/X event (Luciani et al, 2017a) and, at Site 1258, move from ~5% below the EECO to 0% below the K/X event. (D'Onofrio et al, 2020). Results are shown in figure 2, percentage data are available in Table S1.…”

“…1) that have good sedimentary J o u r n a l P r e -p r o o f recovery and complete lower Eocene successions (Norris et al, 1998;Shipboard Scientific Party, 1998;Shipboard Scientific Party, 2004;Sexton et al, 2006a;Zachos et al, 2004;Kennet and Stott, 1990). In addition, most of these sites have been extensively studied thus providing a very solid stratigraphic framework, included bulk stable isotope curves for the early Eocene and data on abundance of planktic foraminiferal genera across the EECO (Zachos et al, 2004;Lauretano et al, 2015;Westerhold et al, 2007Westerhold et al, , 2015Luciani et al, 2016Luciani et al, , 2017aLuciani et al, , 2017bD'Onofrio et al, 2020). All these evidences make these sites truly appropriate for our investigation.…”

Size‐Fraction‐Specific Stable Isotope Variations as a Framework for Interpreting Early Eocene Bulk Sediment Carbon Isotope Records

“…2017), which was characterized by a 'hothouse' climate and was the warmest interval of the Cenozoic (e.g., Westerhold et al., 2020; Zachos et al., 2001, 2008). Temporal variations in bulk carbonate δ 13 C values from widely separated ocean sites show remarkable consistency during the early Paleogene, thus forming a robust tool for chemostratigraphic correlation between marine sedimentary sections (e.g., Agnini et al., 2016; Barnet et al., 2019; D'Onofrio et al., 2020; Slotnick et al., 2012; Westerhold et al., 2018). However, bulk carbonate stable isotope values are largely offset from one site to another, depending on location, latitude and paleodepth of sediment deposition.…”

“…show remarkable consistency during the early Paleogene, thus forming a robust tool for chemostratigraphic correlation between marine sedimentary sections (e.g., Agnini et al, 2016;Barnet et al, 2019;D'Onofrio et al, 2020;Slotnick et al, 2012;Westerhold et al, 2018). However, bulk carbonate stable isotope values are largely offset from one site to another, depending on location, latitude and paleodepth of sediment deposition.…”