Demise of the planktic foraminifer genus Morozovella at ODP Site 1258 (Demerara Rise, west Equatorial Atlantic); understanding biological responses during the early Eocene climatic optimum

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Author(s): Luciani, Valeria; D'Onofrio, Roberta; Dickens, Gerald R.; Wade, Bridget; Kirtland-Turner, Sandra
Author Affiliation(s): Primary:
Ferrara University, Department of Physics and Earth Sciences, Ferrara, Italy
Rice University, United States
University College London, United Kingdom
University of California at Riverside, United States
Volume Title: European Geosciences Union general assembly 2019
Source: Geophysical Research Abstracts, Vol.21; European Geosciences Union general assembly 2019, Vienna, Austria, April 7-12, 2019. Publisher: Copernicus GmbH on behalf of the European Geosciences Union (EGU), Katlenburg-Lindau, Germany. ISSN: 1029-7006
Note: In English
Summary: The Early Eocene Climatic Optimum (EECO) expresses the multi-million year interval of peak Cenozoic global warmth and high atmospheric CO2 concentrations that occurred sometime between 54 and 48 million years ago. An outstanding issue is how life evolved during this crucial interval, and planktic foraminifera represent an excellent class in which to examine such links. Here we present new data on planktic foraminferal response to the EECO from the equatorial Atlantic ODP Site 1258 (Demerara Rise). Our main result reveals that the relative abundance of the surface-dweller symbiont-bearing genus Morozovella, that dominated early Paleogene planktic foraminiferal assemblages from tropical-subtropical regions, markedly and permanently declined at the beginning of the EECO moving from mean percentage of 34% to less than 10%. This distinct decrease in abundance occurred within 20 kyr before a negative δ13C excursion known as the "J" event (∼53.3 Ma), which marks the onset of the EECO. The permanent decrease of morozovellids is associated with reduction in species diversity, but an increase in the abundance and diversity of another symbiont-bearing foraminifera genus, Acarinina. The remarkable turnover from Morozovella to Acarinina was geographically widespread, as it is now recorded at the start of the EECO in the subtropical Pacific (Site 577), and elsewhere in the subtropical Atlantic (Sites 1051 and 1263). Interestingly, the timing of the drop in abundance is close but different at each site. Our new data from Demerara Rise further a notion that the morozovellid decline began first with unfavourable environmental conditions near the equatorial Atlantic Ocean and then extended to higher latitudes. The triggering mechanism for the striking planktic foraminiferal turnover remains elusive, because both Morozovella and Acarinina existed in the mixed-layer. Most of the morozovellid species that became extinct within the EECO reduced their maximum size. Recent culturing and open ocean observations indicate that omega-calcite saturation state can affect variably sized foraminifera differently, such that larger planktic foraminifera preferentially reduce their calcification. The two dominant genera, Morozovella and Acarinina, may have had different tolerances to temperature and ocean chemistry. This would explain why anti-phase variations in their abundances occurred during several early Paleogene hyperthermals that happened before the EECO. The EECO interval may represent the time when optimal conditions for morozovellids diminished for a sufficiently long time, such that acarininids dominated surface water habitats afterward. [Copyright Author(s) 2019. CC Attribution 4.0 License:]
Year of Publication: 2019
Research Program: DSDP Deep Sea Drilling Project
IPOD International Phase of Ocean Drilling
ODP Ocean Drilling Program
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Acarinina; Atlantic Ocean; Biostratigraphy; Blake Nose; Blake Plateau; C-13/C-12; Carbon; Cenozoic; Chemostratigraphy; Cores; DSDP Site 577; Deep Sea Drilling Project; Demerara Rise; Eocene; Equatorial Atlantic; Extinction; Foraminifera; IPOD; Isotope ratios; Isotopes; Leg 171B; Leg 207; Leg 208; Leg 86; Lower Eocene; Marine sediments; Microfossils; Morozovella; North Atlantic; North Pacific; Northwest Atlantic; Northwest Pacific; ODP Site 1051; ODP Site 1258; ODP Site 1263; Ocean Drilling Program; Pacific Ocean; Paleo-oceanography; Paleoclimatology; Paleogene; Planktonic taxa; Rotaliina; Sediments; Shatsky Rise; South Atlantic; Stable isotopes; Tertiary; Truncorotaloididae; Walvis Ridge; West Atlantic; West Pacific
Coordinates: N092600 N092600 W0544400 W0544400
N322628 N322632 E1574324 E1574323
N300311 N300311 W0762128 W0762128
S283200 S283200 E0024700 E0024700
Record ID: 2019050565
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from European Geosciences Union, Munich, Germany