Disentangling regional and global signatures from benthic foraminifera records during the Late Miocene-Early Pliocene Biogenic Bloom (IODP Site U1506 and ODP Site 1085)

Abstract

<p>The Late Miocene-Early Pliocene Biogenic Bloom (~ 9-3.5 Ma) is a paleoceanographic event defined by anomalously high marine biological productivity and associated with changes in the marine carbon cycle. Marine sedimentary records in the Indian, Pacific, and Atlantic oceans, point to a significant increase in primary productivity across low-latitude oceanic regions maintained for several millions of years. Surface primary productivity is typically limited by the availability of nutrients; whose residence times are fairly short in the global ocean. Therefore, the global nature and the multimillion years duration of the Biogenic Bloom make this event a paleoceanographic puzzle. Two main explanations for these anomalously high productivity conditions have been proposed: a major redistribution of nutrients triggering an intensification of regional upwelling; or an absolute increase of nutrients delivery to the oceans. We investigated the Biogenic Bloom at IODP Site U1506 (Tasman Sea, southwest Pacific Ocean, 1505 m water depth) and at ODP Site 1085 (Cape Basin, southeast Atlantic Ocean, 1713 m water depth). For these sites we generated implemented age models and quantitative benthic foraminiferal records across an interval spanning from the Tortonian (Late Miocene) to the Zanclean (Early Pliocene). The benthic foraminiferal assemblage analysis shows that the Biogenic Bloom was a complex, multiphase event rather than a single uniform period of sustained high marine water productivity. Both sites record changes that can be interpreted in terms of modification of productivity conditions. Intervals with low diversity and abundant opportunistic and phytodetritus exploiting taxa (PET) are indicative of transient pulsed food supply, high oxygen levels, and oligotrophic conditions. Intervals characterized by increased diversity, higher relative abundance of uvigerinids and buliminids, and relative lower abundance of PET instead suggest lower oxygen and /or more eutrophic conditions. However, the two sites show a different taxonomic composition of the benthic foraminiferal assemblages. The dominating PET comprise distinct species at different the study sites, with <em>Globocassidulina crassa</em> and <em>Globocassidulina subglobosa</em> displaying high abundance at Site U1506, and <em>Epistominella exigua</em> and <em>Alabaminella weddellensis </em>at Site 1085. While showing common features, the Biogenic Bloom is also characterized by unique regional responses at different study sites which highlight the need for further high-resolution records to provide global mechanisms and dynamics for the Biogenic Bloom event.</p><p><strong>Acknowledgments</strong></p><p>The authors acknowledge funding from University of Padova DOR grant, CARIPARO Foundation Ph.D. scholarship, Fondazione Ing. Aldo Gini scholarship, and Spanish Ministry of Economy and Competitiveness and FEDER funds (PID2019-105537RB-I00).<strong> </strong></p>

Ocean bottom-water oxygenation across the Late Miocene–Early Pliocene biogenic bloom

“…The Upper Miocene-Lower Pliocene interval consists of a 140 m thick interval of nannofossil ooze and chalk (from 82.01 to 221.75 m; Sutherland et al, 2019). The biogenic bloom was identified across this interval, and the palaeoenvironmental turnover was documented through quantitative analyses of benthic foraminiferal assemblages, integrated with other independent proxies (Gastaldello et al, 2023a(Gastaldello et al, , 2024a. The palaeoenvironmental reconstruction in those publications is here compared with the EBFOI calculated for the first time at Site U1506.…”

“…INTRODUCTION Gastaldello, M. E. et al -Miocene-Pliocene benthic foraminifera -Spanish Journal of Palaeontology 39, 2024 2 Farrell et al, 1995;Nomura, 1995;Dickens & Owen, 1999;Gupta & Thomas, 1999;Grant & Dickens, 2002;Lyle et al, 2019;Gastaldello et al, 2023a). Despite the extensive documentation of the biogenic bloom globally, our understanding of its driving mechanisms, consequences, and biotic response remains limited.…”

“…Benthic foraminifera serve as a proxy of bottom water oxygenation and food supply to the seafloor, mostly based on morphological similarities with modern benthic foraminifera (Corliss, 1985;Jones & Charnock, 1985) and the strong relationship between their morphology and microhabitats (Corliss, 1985;Jorissen et al, 1995). Palaeoenvironmental reconstructions across the biogenic bloom reveal variability in the seafloor conditions, switching from low oxygen eutrophic conditions with a fairly constant food supply, to well-oxygenated oligotrophic conditions associated with seasonal phytodetritus inputs (Gastaldello et al, 2023a(Gastaldello et al, , 2024b. The possible link between changes in benthic foraminiferal abundance taxa and bottom-water oxygenation was highlighted by Kaiho (1991Kaiho ( , 1994, who defined oxic, suboxic, and dysoxic indicators and introduced the Benthic Foraminifera Oxygen Index (BFOI) to evaluate changes in bottom-water oxygenation.…”

The Late Miocene‐Early Pliocene Biogenic Bloom: An Integrated Study in the Tasman Sea

“…Data generated in this study are available in the Supporting Information S1 and archived in PANGAEA database (Gastaldello et al, 2023). Funding provided by Universita degli Studi di Padova within the CRUI-CARE Agreement.…”

“…Data generated in this study are available in the Supporting Information and archived in PANGAEA database (Gastaldello et al., 2023).…”