A new quantitative approach to identify reworking in Eocene to Miocene pollen records from offshore Antarctica using red fluorescence and digital imaging

Antarctic palaeoclimate evolution and vegetation history after the formation of a continent-scale cryosphere at the Eocene–Oligocene boundary, 33.9 million years ago, has remained a matter of controversy. In particular, the reconstruction of terrestrial climate and vegetation has been strongly hampered by uncertainties in unambiguously identifying non-reworked as opposed to reworked sporomorphs that have been transported into Antarctic marine sedimentary records by waxing and waning ice sheets. Whereas reworked sporomorph grains over longer non-successive geological timescales are easily identifiable within younger sporomorph assemblages (e.g. Permian sporomorphs in Pliocene sediments), distinguishing non-reworked from reworked material in palynological assemblages over successive geological time periods (e.g. Eocene sporomorphs in Oligocene sediments) has remained problematic. This study presents a new quantitative approach to identifying non-reworked pollen assemblages in marine sediment cores from circum-Antarctic waters. We measured the fluorescence colour signature, including red, green, and blue fluorescence; brightness; intensity; and saturation values of selected pollen and spore taxa from Eocene, Oligocene, and Miocene sediments from the Wilkes Land margin Site U1356 (East Antarctica) recovered during Integrated Ocean Drilling Program (IODP) Expedition 318. Our study identified statistically significant differences in red-fluorescence values of non-reworked sporomorph taxa against age. We conclude that red fluorescence is a reliable parameter for identifying the presence of non-reworked pollen and spores in Antarctic marine sediment records from the circum-Antarctic realm that are influenced by glaciation and extensive reworking. Our study provides a new tool to accurately reconstruct Cenozoic terrestrial climate change on Antarctica using fossil pollen and spores

Glaucony authigenesis, maturity and alteration in the Weddell Sea: An indicator of paleoenvironmental conditions before the onset of Antarctic glaciation

This research used samples from the ODP. We thank the staff at the Gulf Coast core repository for assistance in ODP Leg 113 core handling and shipping.We acknowledge the help of Dr. María del Mar Abad, Dr. Isabel Sánchez Almazo, Dr. Miguel Angel Hidalgo, Dr. Miguel Angel Salas, and Isabel Nieto (Scientific Instrumentation Center of the University of Granada, CIC) for their help along different phases of the laboratory work. We also acknowledge the constructive comments of two anonymous reviewers that have helped to improve this paper. We wish to thank Prof. C. Hans Nelson for their constructive comments and improvement of our English, which contributed greatly toward clarification of the text. Thanks are also given to Dr. Francisco J. Lobo and Dr. Fernando Bohoyo for their helpful comments related to the study area and regional tectonics.Three types of glaucony grains were identified in the late Eocene (~35.5–34.1 Ma) sediments from Ocean Drilling Program (ODP) Hole 696B in the northwestern Weddell Sea (Antarctica). The grains are K2O-rich (~7 wt%) and formed by smectite-poor interstratified ~10 Å glauconite-smectite with flaky/ rosette-shaped surface nanostructures. Two glaucony types reflect an evolved (types 1 and 2 glaucony; less mature to mature) stage and long term glauconitization, attesting to the glaucony grains being formed in situ, whereas the third type (type 3 glaucony) shows evidences of alteration and reworking from nearby areas. Conditions for the glaucony authigenesis occurred in an open-shelf environment deeper than 50 m, under sub-oxic conditions near the sediment-water interface. These environmental conditions were triggered by low sedimentation rates and recurrent winnowing action by bottomcurrents, leading to stratigraphic condensation. The condensed glaucony-bearing section provides an overview of continuous sea-level rise conditions pre-dating the onset of Antarctic glaciation during the Eocene-Oligocene transition. Sediment burial, drop of O2 levels, and ongoing reducing (postoxic to sulphidic) conditions at Hole 696B, resulting in iron-sulphide precipitation, were a key limiting factor for the glauconitization by sequestration of Fe2+.Funding for this research is provided by the Spanish Ministry of Science and Innovation (grants CTM2014-60451-C2-1-P and CTM2017-89711-C2-1-P, CGL2016-75679P) cofunded by the European Union through FEDER funds and RNM-208 group (Discontinuidades estratigráficas, Junta de Andalucía, Spain)

The evolution of the Antarctic Circumpolar Current in the SouthwestPacific sector of the Southern Ocean throughout the Cenozoic era

EGU General Assembly in Viena, Austria, 7–12 April 2019The establishment and evolution of the Antarctic Circumpolar Current (ACC) throughout the Cenozoic remainspoorly known, mainly because of the lack of continuous long-term records at strategic locations. Here we presentnew records from marine sediments collected by the Deep Sea Drilling Project (DSDP) Site 278, located in theSouthwestern Pacific sector of the Southern Ocean (Southern Emerald Basin), spanning from the mid-Oligoceneto the Pleistocene (ie. the∼28-2 Ma). Our site is ideally situated to reconstruct changes in the ACC sincethe mid-Oligocene as it remained along the polar frontal zone as shown by paleolatitude reconstructions andmicrofossil assemblage data. To track its evolution, we combined (i) mean grain size of sortable silt (SS) datawith (ii) primary productivity proxies including biogenic silica (BSi), calcium carbonate (CaCO3) and organicmatter, and (iii) neodymium isotope ratios (εNd) generated from fossil fish teeth and debris. Our results documenta significant increase in SS, enhanced marine productivity and a decrease inεNd values towards present-dayCircumpolar deep waterεNd values, suggesting a progressive strengthening of the proto-ACC flow over the last28 Ma. However, we find that the development of a modern-like, homogenous and deep-reaching current wasfully established solely during the Pliocene-Pleistocene transition, concomitantly with the onset of the NorthernHemisphere glaciation

Absence of a strong, deep-reaching Antarctic Circumpolar Current zonal flow across the Tasmanian gateway during the Oligocene to early Miocene

The vigorous eastward flow of the Antarctic Circumpolar Current (ACC) connects all major ocean basins and plays a prominent role in the transport of heat, carbon and nutrients around the globe. However, the establishment of a deep circumpolar flow, similar to the present-day ACC, remains controversial thereby obscuring our understanding of its climatic impact. Deciphering the chemical composition of Circumpolar Deep Water (CDW) within the ACC can provide critical insights about its development and evolution. Here we present new fossil fish teeth/bone debris neodymium isotope (ε) records from Deep Sea Drilling Project (DSDP) Sites 278 and 274 in the southwest Pacific Ocean, with the aim to trace changes in deep water masses across the Tasmanian Gateway between the early Oligocene and early Miocene (~ 33–22 Ma). Site 274 provides the first Nd isotope record proximal to the Ross Sea during the Oligocene (33.5–23.4 Ma). Its Nd isotope composition shows excursions to very radiogenic values, ε = −3.1 and ε − 3.7, at 33.5 Ma and 23.8 Ma, respectively, in response to major steps in Antarctic ice sheet expansion. A shift to lower, more unradiogenic ε values between 29.7 and 29.1 Ma is linked to an increased influence of proto-CDW upwelling at the site. In contrast, the Nd isotope record from Site 278 in the southern Emerald Basin shows little variability (ε = −6.0 to −6.7) throughout the Oligocene and early Miocene (30.9–21.8 Ma). Comparison with published data north of the ACC path, demonstrates the presence of two deep water masses in the South Pacific prior to the inferred onset of the ACC (33–30 Ma), one occupying depths between ~2500 and 3000 m (ε ~ −3 to −5) and a deep/bottom water mass (> 3000 m) with a more unradiogenic Nd isotope composition (ε ~ −6). Site 278 located close to the proto-polar front (proto-PF) indicates that following the inferred onset of the ACC, deep waters bathing the southern Emerald Basin remained more radiogenic in the Southwest Pacific compared to sites along the proto-PF in the South Atlantic and Indian Ocean (ε ~ −8.1). This indicates a provinciality in Nd isotope compositions of deep waters along the proto-PF across the Tasmanian Gateway. Our data are incompatible with the existence of a modern-like homogenous (lateral and vertical) Nd isotope composition of CDW along the main flow path of the ACC in all oceanic basins in the Oligocene to early Miocene. We attribute distinct Nd isotope compositions of deep waters across the Tasmanian Gateway to reflect a less deep reaching and weaker ACC (proto-ACC) than today. Our findings suggest that the modern strong and deep-reaching ACC flow must have been developed at a later point in the Neogene.Funding to this research is provided by the Alexander S. Onassis Public Benefit Foundation Ph.D. research grant: F ZL 016-1/2015-2016; the Spanish Ministry of Economy, Industry and Competitivity (grants CTM2017-89711-C2-1/2-P), co-funded by the European Union through FEDER funds; and an ECORD Research grant awarded to DE. PKB and FH acknowledge funding through the European Research Council starting grant #802835 OceaNice and NWO polar programme grant ALWPP2016.001. This paper is a contribution to the SCAR PAIS Programme

Late Oligocene-Miocene proto-Antarctic Circumpolar Current dynamics off the Wilkes Land margin, East Antarctica

At present, the Southern Ocean plays an important role in the global climate system and in modern Antarctic ice sheet dynamics. Past Southern Ocean configurations are however poorly understood. This information is yet important as it may provide important insights into the climate system and past ice-sheet behavior under warmer than present day climates. Here we study Southern Ocean dynamics during the Oligocene and Miocene when reconstructed atmospheric CO2 concentrations were similar to those expected during this century. We reconstruct snapshots of late Oligocene to earliest Miocene (~24.2–23 Ma) paleoceanographic conditions in the East Antarctic Wilkes Land abyssal plain. For this, we combine marine sedimentological, geochemical (X-ray fluorescence, TEX86,), palynological and isotopic (εNd) records from ocean sediments recovered at Deep Sea Drilling Project (DSDP) Site 269. Overall, we find that sediments, delivered to the site by gravity flows and hemipelagic settling during glacial-interglacial cycles, were persistently reworked by a proto-Circumpolar Deep Water (CDW) with varying strengths that result from climatically controlled frontal system migrations. Just prior to 24 Ma, terrigenous input of predominantly fine-grained sediments deposited under weak proto-CDW intensities and poorly ventilated bottom conditions dominates. In comparison, 24 Ma marks the start of episodic events of enhanced proto-CDW current velocities, associated with coarse-grained deposits and better-ventilated bottom conditions. In particular, the dominance of P-cyst and low Calcium (Ca) in the sediments between ~ 24.2 Ma and 23.6 Ma indicate the presence of an active open ocean upwelling associated with high nutrient conditions. This is supported by TEX86-derived sea surface temperature (SST) data pointing to cool ocean conditions. From ~ 23.6 to 23.2 Ma, our records reveal an enrichment of Ca in the sediments related to increased calcareous microfossil preservation, high amounts of G-cysts and increasing TEX86-SSTs. This implies warmer water masses reaching the Antarctic margin as the polar front migrated southward. Together with the radiogenic Nd isotope data indicating modern-like CDW values, our records suggest a prominent poleward expansion of proto-CDW over our study site and reduced AABW formation during the latest Oligocene (i.e. ~23.2 Ma ago). Our findings support the notion of a fundamentally different Southern Ocean, with a weaker proto-ACC than present during the late Oligocene and the earliest Miocene

Oligocene - Miocene Ice Sheet and Paleoceanographic Evolution of the Eastern Wilkes Land Margin

This thesis shows that before 28 Ma a single water mass flowing westward, the proto-AABW, occupied the seafloor in the studied region. The first evidence for the onset of a current flowing eastward, the proto-CDW, is found at 28 Ma. Between 26 and 25 Ma ice sheets were mainly continental-based and an oceanic frontal system already existed and migrated during glacial-interglacial cycles that were paced by obliquity. The late Oligocene frontal system was however weaker than today´s Polar Front because we find evidence for intrusion of warm north component waters close to the Antarctic margin. The latest Oligocene (24-23.4 Ma) witnessed at least eight times of ice sheet advancing into the continental shelf and retreats inland, pointing to a highly dynamic ice sheet during the cooling trend leading to the glacial Mi-1 event. During this period, we interpret that the EAIS in the WSB becomes marine-based as a consequence of the erosion and overdeepening of the Wilkes Subglacial Basin by the repeated advances and retreats of the EAIS since it was formed in the early Oligocene (33.6 Ma).Los resultados derivados de esta tesis muestran que antes de los 28 Ma una masa de agua, la AABW, circulaba hacia el oeste y ocupaba todo el fondo marino en la región estudiada. La primera evidencia de una corriente de agua hacia el este, la proto-CDW, es al comienzo del Oligoceno superior. Entre 26 y 25 Ma, los casquetes de hielo fundamentalmente eran continentales, y los sistemas oceánicos frontales ya existían y migraban durante los ciclos glaciares-interglaciares forzados por la oblicuidad. Sin embargo, la intrusión de aguas cálidas de componente norte cerca del margen Antártico muestra que dichos frentes eran más débiles que el Frente Polar actual. A finales del Oligoceno (24-23.4 Ma) el registro muestra al menos ocho avances de la EAIS a la plataforma continental y retrocesos hacia tierra, evidenciando un casquete de hielo muy dinámico durante la fase de enfriamiento que culmina en el evento glaciar Mi-1. Es en este periodo interpretamos que la EAIS pasa de estar anclado en tierra a estar anclado por debajo del nivel del mar (marine-based) como consecuencia de la erosión y la profundización de la Cuenca Subgacial de Wilkes durante avances repetidos de la EAIS desde su formación hace 33.6 MaTesis Univ. Granada.Spanish Ministerio de Economía y Competitividad with the grants CTM 2011-24079 and CTM2014-60451-C2-1-P

Oligocene-Miocene Ice sheet and paleoceanographic evolution of the eastern wilkes land margin

[EN] This thesis shows that before 28 Ma a single water mass flowing westward, the proto-AABW, occupied the seafloor in the studied region. The first evidence for the onset of a current flowing eastward, the proto-CDW, is found at 28 Ma. Between 26 and 25 Ma ice sheets were mainly continental-based and an oceanic frontal system already existed and migrated during glacial-interglacial cycles that were paced by obliquity. The late Oligocene frontal system was however weaker than today´s Polar Front because we find evidence for intrusion of warm north component waters close to the Antarctic margin. The latest Oligocene (24-23.4 Ma) witnessed at least eight times of ice sheet advancing into the continental shelf and retreats inland, pointing to a highly dynamic ice sheet during the cooling trend leading to the glacial Mi-1 event. During this period, we interpret that the EAIS in the WSB becomes marine-based as a consequence of the erosion and overdeepening of the Wilkes Subglacial Basin by the repeated advances and retreats of the EAIS since it was formed in the early Oligocene (33.6 Ma)

Paleoceanography and ice sheet variability offshore Wilkes Land, Antarctica - Part 2: Insights from Oligocene-Miocene dinoflagellate cyst assemblages

Next to atmospheric CO concentrations, ice-proximal oceanographic conditions are a critical factor for the stability of Antarctic marine-terminating ice sheets. The Oligocene and Miocene epochs (∼ 34-5 Myr ago) were time intervals with atmospheric CO concentrations between those of present-day and those expected for the near future. As such, these past analogues may provide insights into ice-sheet volume stability under warmer-than-present-day climates. We present organic-walled dinoflagellate cyst (dinocyst) assemblages from chronostratigraphically well-constrained Oligocene to mid-Miocene sediments from Integrated Ocean Drilling Program (IODP) Site U1356. Situated offshore the Wilkes Land continental margin, East Antarctica, the sediments from Site U1356 have archived the dynamics of an ice sheet that is today mostly grounded below sea level. We interpret dinocyst assemblages in terms of paleoceanographic change on different timescales, i.e. with regard to both glacial-interglacial and long-term variability. Our record shows that a sea-ice-related dinocyst species, Selenopemphix antarctica, occurs only for the first 1.5 Myr of the early Oligocene, following the onset of full continental glaciation on Antarctica, and after the Mid-Miocene Climatic Optimum. Dinocysts suggest a weaker-than-modern sea-ice season for the remainder of the Oligocene and Miocene. The assemblages generally bear strong similarity to present-day open-ocean, high-nutrient settings north of the sea-ice edge, with episodic dominance of temperate species similar to those found in the present-day subtropical front. Oligotrophic and temperate surface waters prevailed over the site notably during interglacial times, suggesting that the positions of the (subpolar) oceanic frontal systems have varied in concordance with Oligocene-Miocene glacial-interglacial climate variability.This research used data and samples from the Integrated Ocean Drilling Program (IODP). IODP was sponsoredbytheUSNationalScienceFoundationandparticipating countries under management of Joined Oceanographic Institutions Inc. Peter K. Bijl and Francesca Sangiorgi thank NWO-NNPP grant no. 866.10.110 and NWO-ALW VENI grant no. 863.13.002 for funding and Natasja Welters for technical support. Jörg Pross acknowledges support through the IODP priority program of the German Research Foundation (DFG). Carlota Escutia and Ariadna Salabarnada thank the Spanish Ministerio de Economía y Competitividad for grant CTM2014-60451-C2-1-P. We thank Kasia ´Sliwi´nska, Stephen Gallagher and the anonymous reviewer for their constructive comments that considerably improved our paper

A new quantitative approach to identify reworking in Eocene to Miocene pollen records from offshore Antarctica using red fluorescence and digital imaging

Antarctic palaeoclimate evolution and vegetation history after the formation of a continent-scale cryosphere at the Eocene-Oligocene boundary, 33.9 million years ago, has remained a matter of controversy. In particular, the reconstruction of terrestrial climate and vegetation has been strongly hampered by uncertainties in unambiguously identifying non-reworked as opposed to reworked sporomorphs that have been transported into Antarctic marine sedimentary records by waxing and waning ice sheets. Whereas reworked sporomorph grains over longer non-successive geological timescales are easily identifiable within younger sporomorph assemblages (e.g. Permian sporomorphs in Pliocene sediments), distinguishing non-reworked from reworked material in palynological assemblages over successive geological time periods (e.g. Eocene sporomorphs in Oligocene sediments) has remained problematic. This study presents a new quantitative approach to identifying non-reworked pollen assemblages in marine sediment cores from circum-Antarctic waters. We measured the fluorescence colour signature, including red, green, and blue fluorescence; brightness; intensity; and saturation values of selected pollen and spore taxa from Eocene, Oligocene, and Miocene sediments from the Wilkes Land margin Site U1356 (East Antarctica) recovered during Integrated Ocean Drilling Program (IODP) Expedition 318. Our study identified statistically significant differences in red-fluorescence values of non-reworked sporomorph taxa against age. We conclude that red fluorescence is a reliable parameter for identifying the presence of non-reworked pollen and spores in Antarctic marine sediment records from the circum-Antarctic realm that are influenced by glaciation and extensive reworking. Our study provides a new tool to accurately reconstruct Cenozoic terrestrial climate change on Antarctica using fossil pollen and spores.This study was funded by the Faculty of Engineering and Environment Research Studentship from Northumbria University. The samples used for this research were provided by the Integrated Ocean Drilling Program (IODP). Ulrich Salzmann acknowledges funding received from the Natural Environment Research Council (NERC grant NE/H000984/1). Francesca Sangiorgi thanks the Netherlands Organisation for Scientific Research (NWO) for NNPP Polar 866.10.110. Peter K. Bijl acknowledges the Dutch National Organisation for Scientific Research(NWO)for VENI grant no. 863.13.002. Carlota Escutia thanks the MINECO for scientific research grant CTM2014-60451-C2-1-P. Jörg Pross acknowledges support through the German Science Foundation (DFG; grant PR 651/10). We would finally like to thank the anonymous reviewer and Michael Hannah for their useful comments, which helped us to further improve this paper