Planktic foraminiferal response to early Eocene carbon cycle perturbations in the southeast Atlantic Ocean (ODP Site 1263)

Abstract

At low latitude locations in the northern hemisphere, striking changes in the relative abundances and diversity of the two dominant planktic foraminifera genera, Morozovella and Acarinina, are known to have occurred close to the Early Eocene Climatic Optimum (EECO; ~49–53 Ma). Lower Eocene carbonate-rich sediments at Ocean Drilling Program (ODP) Site 1263 were deposited on a bathymetric high (Walvis Ridge) at ~40° S, and afford an opportunity to examine such planktic foraminiferal assemblage changes in a temperate southern hemisphere setting. We present here quantified counts of early Eocene planktic foraminiferal assemblages from Hole 1263B, along with bulk sediment stable isotope analyses and proxy measurements for carbonate dissolution. The bulk sediment δ13C record at Site 1263 resembles similar records generated elsewhere, such that known and inferred hyperthermal events can be readily identified. Although some carbonate dissolution has occurred, the well-preserved planktic foraminiferal assemblages mostly represent primary changes in environmental conditions. Our results document the permanent decrease in Morozovella abundance and increase in Acarinina abundance at the beginning of the EECO, although this switch occurred ~165 kyr after that at low-latitude northern hemisphere locations. This suggests that unfavourable environmental conditions for morozovellids at the start of the EECO, such as sustained passage of a temperature threshold or other changes in surface waters, occurred at lower latitudes first. The remarkable turnover from Morozovella to Acarinina was widely geographically widespread, although the causal mechanism remains elusive. In addition, at Site 1263, we document the virtual disappearance within the EECO of the biserial chiloguembelinids, commonly considered as inhabiting intermediate water depths, and a reduction in abundance of the thermocline-dwelling subbotinids. We interpret these changes as signals of subsurface water properties, perhaps warming, and the associated contraction of ecological niches

Global Extent of Early Eocene Hyperthermal Events: A New Pacific Benthic Foraminiferal Isotope Record From Shatsky Rise (ODP Site 1209)

“…The new late Paleocene to early Eocene Site 1209 benthic isotope record clearly demonstrates the global extent of repeated hyperthermal events during the warmest period of the Cenozoic era, thus providing additional insight into the nature of these events and their relation to orbital and other forcing (Figure ). Multiple carbon isotope excursions are revealed over the course of the Ypresian and Lutetian that correspond in timing and magnitude to hyperthermal events previously observed, for example, in New Zealand, Italy, and the Atlantic realm (e.g., Cramer et al, ; Coccioni et al, ; D'Onofrio et al, ; Galeotti et al, ; Kirtland Turner et al, ; Lauretano et al, , ; Leon‐Rodriguez & Dickens, ; Littler et al, ; Luciani et al, , ; Sexton et al, ; Slotnick et al, , ; Westerhold et al, ; Zachos et al, ). As a consequence of carbonate dissolution, benthic foraminifera are rare in some intervals, and thus, not all hyperthermal layers can be identified by their characteristic paired negative benthic stable carbon and oxygen isotope excursions.…”

“…Planktic foraminiferal (Petrizzo, ) and calcareous nannofossil (Bralower, ) biohorizon zonations published for Site 1209 have to be updated to the revised schemes of Wade et al () and Agnini et al (). This updated biostratigraphic scheme would provide a further stratigraphic tool to correlate hyperthermals and, at the same time, evaluate the synchronicity of planktic foraminiferal and calcareous nannofossil events that show some diachrony in the early Eocene (Luciani et al, ; Luciani & Giusberti, ; Westerhold et al, ). Updating the biozonal scheme of Petrizzo () and Bralower () is beyond the objectives of this study, requiring investigations on well‐selected additional samples.…”

“…Starting at the J event a persistent change from limestone to marl at Mead Stream is interpreted to reflect enhanced terrigenous supply to a continental margin because of warming and an enhanced seasonal hydrological cycle (Dallanave et al, 2015;Slotnick et al, 2012Slotnick et al, , 2015. In addition, close to the J event, major permanent changes in planktic foraminiferal abundance and evolution have been documented in several sites (Luciani et al, , 2017. The termination of the EECO is tentatively placed using the base of calcareous nannofossil biohorizon Discoaster sublodoensis occurring in polarity Chron C22n (Agnini et al, 2014), at the same time when limestone deposition returns in the Mead Stream section (Dallanave et al, 2015).…”

Did Photosymbiont Bleaching Lead to the Demise of Planktic ForaminiferMorozovellaat the Early Eocene Climatic Optimum?

“…This major turnover further relates to taxonomic diversity, consisting of species reduction among Morozovella and species diversification among Acarinina (Aze et al, 2011;Pearson et al, 2006). This turnover occurred also in the temperate Southern Hemisphere setting of Atlantic Site 1263 (Luciani et al, 2017). Supporting Information:…”

“…This major turnover further relates to taxonomic diversity, consisting of species reduction among Morozovella and species diversification among Acarinina (Aze et al, ; Pearson et al, ). This turnover occurred also in the temperate Southern Hemisphere setting of Atlantic Site 1263 (Luciani et al, ). The timing of the Morozovella–Acarinina switch is interesting because the EECO (~49–53 Ma; Lauretano et al, ; Luciani et al, ; Slotnick et al, , ) represents the interval of peak sustained Cenozoic warmth (Bijl et al, ; Hollis et al, ; Huber & Caballero, ; Inglis et al, ; Pross et al, ; Zachos et al, ).…”