This study updates the lithostratigraphic and chronostratigraphic framework of the marine carbonate-dominated Paleogene strata of northwestern Saudi Arabia within the Sirhan–Turayf Basin by integrating detailed field observations and high-resolution calcareous nannofossil biostratigraphy. Previous studies assigned these strata to the Middle–Upper Eocene Rashrashiyah Formation but lacked precise chronostratigraphic constraints. New biostratigraphic and lithostratigraphic data from three measured sections (Rash1–Rash3) reveal that these strata comprise two distinct formations: the Middle–Upper Eocene Rashrashiyah Formation and the newly defined Lower Oligocene Qurayyat Formation, separated by a prominent erosional disconformity at the Eocene–Oligocene boundary (EOB). The revised framework highlights the role of local tectonics, including block faulting and differential subsidence, in preserving the Oligocene strata. Calcareous nannofossil assemblages suggest that the Rashrashiyah Formation corresponds to Zones NP17–NP20, while the Qurayyat Formation is assigned to Zone NP21, collectively spanning the Bartonian–Rupelian interval. The documentation of marine Oligocene strata in NW Saudi Arabia for the first time, with erosional disconformity at the base, challenges previous interpretations of continuous sedimentation across the Eocene-Oligocene transition. The findings suggest that depositional architecture and stratal distribution in the study area are significantly controlled by regional tectonics and global sea-level fluctuations. The proposed lithostratigraphic scheme and chronostratigraphic constraints improve regional correlations across the Arabian Plate.

The Oligocene–Miocene Transition (OMT) includes a pronounced ~1‰ positive excursion in benthic oxygen isotope records (δ18O), reflecting Antarctic ice sheet expansion and/or deep ocean cooling, commonly referred to as the Mi-1 glaciation. At present, limited reconstructions of sea surface temperature (SST) evolution across the OMT have been published, leaving the magnitude of global cooling during Mi-1 uncertain. Here we present high-resolution (~10 kyr) SST reconstructions from IODP Site U1406 on the Newfoundland Margin (North Atlantic) using the lipid biomarker TEX86 proxy, based on isoGDGT distributions. Our record shows TEX86 values ranging from 0.64 to 0.76, with a ~0.04 decrease during the Mi-1 event. To assess potential non-thermal overprints on the TEX86 data, we calculated GDGT-based indices, including the Branched-to-Isoprenoid Tetraether (BIT) index. BIT values are relatively high (0.4–0.8), suggesting significant input of terrestrial GDGTs that could bias TEX86. However, TEX86 and BIT show weak correlation (R2 = 0.124), indicating limited terrestrial overprint on the TEX86 signal. Furthermore, a ternary plot of brGDGT compositions shows that the Newfoundland samples differ from modern soils and peats, suggesting marine production of brGDGTs as the source of the high BIT values. These findings suggest that the Newfoundland Margin was not influenced by substantial terrestrial organic matter input across the OMT, and that TEX86 provides a reliable record of SST. Translating TEX86 into temperature, our record indicates warm SSTs ranging from 25 to 31 °C, with a cooling of ~2 °C during the Mi-1 event, consistent with published low-resolution alkenone-derived (UK’37) estimates (Guitián et al., 2019). Future work will focus on determining whether the observed SST cooling at Site U1406 reflects a global climate signal or is driven by latitudinal shifts in the North Atlantic SST gradient. This could be addressed using seawater oxygen isotope (δ18Osw) reconstructions based on the combination of SST proxies and planktic foraminiferal δ18O to infer changes in surface ocean circulation, alongside comparisons with Earth System Model simulations.

The late Miocene and Pliocene were periods characterized by warmer-than-present climatic conditions and are therefore commonly used to investigate the possible effects of ongoing global warming. The Atlantic meridional overturning circulation (AMOC) is a crucial component of the climate system, since it involves oceanic currents and controls the redistribution of heat around the globe. Specifically, warm and saline water from the low-latitudes reaches the high-latitude North Atlantic, where it loses heat and sinks to form deep-water masses. This sinking generates strong bottom currents, which flow southwards, powering what is known as the global ocean conveyor belt. Understanding the generation and evolution of these water masses during past warm periods provides valuable insights into their potential response to ongoing increases in ocean temperatures. Recently, International Ocean Discovery Program (IODP) expeditions 395 and 395C made such investigations possible by recovering deep sea sedimentary sequences spanning the late Miocene and Pliocene in the high latitude North Atlantic region (60°N; Parnell-Turner et al., 2025). In this study, we investigate sediment samples from IODP Site U1562 (60°06.3006′N, 26°30.1044′W; ~2003m water depth), located at the edge of a sediment body deposited under the influence of deep-water currents (Björn Drift). This site exhibits continuous sedimentation and excellent microfossil preservation during the latest Miocene to Pliocene (~6.5–3.6 Ma). For our investigation, we use a combination of micropaleontological and geochemical proxies, including X-Ray fluorescence (XRF) core scanning, isotopic analysis of foraminiferal shells, and microfossil species identification and morphometrics. Combining these proxies allows for reconstructing the evolution of temperature, primary productivity, and ocean circulation in the region. Pronounced cyclic variations in calcium carbonate (CaCO₃) preservation indicate a highly dynamic depositional environment, likely controlled by changes in export production and bottom ocean dissolution related to deep-sea currents. These cycles are accompanied by distinct isotopic signatures, with intervals of high CaCO₃ content broadly corresponding to lighter δ¹⁸O values, and vice versa. The occurrence of planktonic foraminifera Orbulina universa, as well as calcareous nannofossils belonging to the genus Discoaster reveal periodically warmer conditions, driven by an overall increase in upper-ocean temperature or enhanced influence of warm currents associated with stronger AMOC. Further analyses will aim to better characterize these cyclic changes, link them to orbital cycles, and combine them with other sedimentological observations to reconstruct the evolution of AMOC during past warm intervals of the late Neogene.ReferencesParnell-Turner, R.E., Briais, A., LeVay, L.J., and the Expedition 395 Scientists, 2025. Reykjanes Mantle Convection and Climate. Proceedings of the International Ocean Discovery Program, 395: College Station, TX (International Ocean Discovery Program). https://doi.org/10.14379/iodp.proc.395.2025

To understand Earth's history, a comprehensive time scale integrating available stratigraphic information is crucial. The middle Eocene to late Oligocene offers abundant stratigraphic information, including foraminiferal and magnetostratigraphic data. However, traditional biostratigraphy uses only a small fraction (1-10 %) of foraminifera as markers, reducing the time scale's temporal resolution and lacking a quantitative method to assess the chronologic significance of both mearker and non-marker biotic events. This study employs the quantitative stratigraphic method, Constrained Optimization (CONOP), using 11 reference sections to create a high-resolution magneto-foraminiferal time scale for the middle Eocene-late Oligocene. The new composite sequence improves temporal resolution by nearly tenfold over traditional methods, incorporating 409 additional biotic events while aligning closely with established markers. Two evaluation factors, diachrony and centrality, were developed to assess the temporal consistency of events among different locations and geographic ranges. Findings reveal that the chronological significance of small benthic foraminifera, planktonic foraminifera, and foraminiferal zonal species events increases sequentially. Conversely, larger benthic foraminiferal events are affected by endemism, complicating their evaluation. Incorporating magnetostratigraphic data into CONOP enhances the robustness and accuracy of stratigraphic correlation. Our approach offers a way to apply CONOP for high-resolution time scales, allowing for a comprehensive assessment of biotic events beyond the use of zonal fossils.

The Early Eocene Climatic Optimum (EECO; ~53–49 Ma) represents the prolonged interval with the highest temperatures and CO₂ levels of the Cenozoic with superimposed transient peak warming events (hyperthermals). The geological record provides a long-term perspective to current observations of marine ecosystem response to global warming. The EECO interval offers the opportunity to evaluate how global climatic shifts have influenced the resilience of planktic foraminifera, a key component of marine ecosystem.Planktic foraminifera morphologic traits, including shifts in coiling direction - the ability to grow their chambers either clockwise (dextral) or counterclockwise (sinistral) - serve as highly sensitive indicators of environmental changes. This underscores their pivotal role in the study of past climate conditions. Previous studies highlighted a permanent decline in the symbiont-bearing Morozovella abundance and diversity near the EECO onset and a coiling shift from dextral to sinistral during the K/X event in the Atlantic Ocean.Here, we extend the coiling direction record to tropical Pacific (Shatsky Rise, Sites 1209–1210), southern Pacific (Tasman Sea, Site U1510), and Indian Ocean locations (Exmouth Plateau, Hole 762C). Our results reveal that the switch to sinistral coiling in Morozovella occurred at all the studied sites thus it appears globally recorded within the last ~200 kyrs after the K/X event. This evidence emphasizes the utility of this coiling shift as a valuable biostratigraphic tool. The Morozovella species-specific analysis discloses that the dominant M. aragonensis and M. crater significantly contributed to the coiling switch in the Atlantic, tropical Pacific, and Indian Oceans. Regardless sinistral and dextral Morozovella forms indicate cryptic speciation or morphotypes within the same species, our record implies that this interval favoured sinistral forms, so that he morozovellid decline in abundance can be largely read as the decline of dextral morphotypes. Notably, Acarinina exhibits no coiling preference.Stable isotope analysis on dextral and sinistral Acarinina and Morozovella morphotypes can shed light on the intricate ecological dynamics of planktic foraminifera during the EECO. Sinistral Morozovella have lower δ 13C values across the EECO with respect to the pre-EECO interval, with both dextral and sinistral Acarinina showing even lower values. This suggests that Acarinina occupied a deeper habitat within the mixed layer and/or had reduced symbiotic activity. This ecological strategy may have ensured the Acarinina success, allowing it to thrive during the EECO, but only partially advantaged the sinistral morozovellids forms, which survived with respect to dextral morphotypes but only in small abundance.Within the first ~600 kyr of the EECO, morozovellids declined in abundance and changed their coiling direction. The scenario recorded in this research delineates on how planktic foraminifera adapted—or struggled— in response to extreme warmth, a crucial result for a future climatic perspective.

The Early Eocene Climatic Optimum (EECO; ~53–49 million years ago, Ma), that represents the Cenozoic peak of temperature and atmospheric CO2 concentrations, significantly affected planktic foraminiferal (PF) assemblages. The main change documented is the permanent decline in abundance and diversity of the symbiont-bearing mixed-layer dweller genus Morozovella, coupled with an increase in abundance and diversity of the genus Acarinina at the beginning of the EECO in the tropical Pacific Ocean (Sites 1209-1210), similar to the previously documented record from the Atlantic Ocean. A second significant variation is the change in coiling direction of morozovellids that moved from dominantly dextral to sinistral close to the K/X event (52.85 Ma), in contrast to Acarinina which does not show any preferential coiling direction throughout. In addition, the deep-dweller genus Chiloguembelina virtually disappeared at the K/X event. Even though a link between these PF changes and EECO climatic change appears evident, the driving causes are still unknown. With the aim of evaluating whether a possible temperature increase may have impacted the observed PF changes, we performed Mg/Ca analysis to derive paleotemperatures from diverse species of Morozovella and Acarinina, and on the thermocline-dweller Subbotina from tropical Pacific sites 1209-1210 using laser ablation (LA)-ICP-MS. Our B/Ca and Sr/Ca results in all the examined samples/species, along with the observed low PF test-fragmentation allow us to exclude a significant influence of contamination or diagenesis on the reconstructed temperatures. As uncertainties in the interpretation of Mg/Ca data remain when working with extinct species, the temperatures were evaluated with both a ‘Trilobatus sacculifer-like’ calibration (no pH correction) and with a ‘Globigerinoides ruber-like’ calibration (pH-correction).In both cases a mixed-layer mean temperature increase of at least 1°C is recorded, with much warmer absolute temperature resulting from the former calibration approach.We hypothesize that the temperature rise may have impacted the morozovellid symbiotic relationship that, in turn, can represent a reason for their decline in abundance, given the many examples of the evolutionary benefits of symbiosis in modern oligotrophic mixed-layer habitats. Although there may have been several contributing factors resulting in photosymbiont bleaching at this time, increased temperature is considered a primary factor of bleaching in modern tropical larger benthic foraminifera. Our assumption appears supported by the lower δ13C values exhibited by the surviving sinistral morozovellids (Luciani et al. 2021 GloPlaCha) while the new dominant genus, Acarinina that does not record lower δ13C values displays greater ecological adaptability. Our evidence appears in line with the hypothesis of Davis et al. (2022 PlosOne) that acarininids changed their symbiotic associations in response to the extreme warming of the PETM (~56 Ma) (but not the subsequent smaller hyperthermals), resulting in long term evolutionary success.

Following the announcement of the retirement of the JOIDES Resolution drilling platform, it has become even more important to efficiently utilise the finite resource of marine sediment stored in IODP repositories. Marine sediments processed for inorganic geochemical analysis are often separated into fine (0.63 µm) fractions to help isolate benthic and planktonic foraminifera. However, organic matter can be associated with different particle size fractions and may have experienced different transport and diagenetic processes. Previous studies have suggested that sieving sediments into different size fractions does not affect the distribution of isoprenoidal [1,2] and branched glycerol dialkyl glycerol tetraethers (GDGTs) [3]. However, this has never been systematically investigated across a wide range of sample types (e.g., age, depositional environment, thermal maturity). It is also unclear whether size processing affects other lipid biomarker proxies (e.g., leaf waxes, alkenones).Here we test whether processing marine sediments into different size fractions influences lipid distributions by separating sediments into fine ( 0.63 µm) fractions and comparing these to corresponding bulk un-sieved sediments. Temperature reconstruction using the marine sea surface temperature proxy TEX86 shows relatively minimal deviation (average ±0.12 TEX86 units, or ~2-3 °C) between the bulk un-sieved sediment (i.e,. control) and fine (10 °C). We also analysed leaf wax derived n-alkanes extracted from the marine sediment to evaluate the impact on terrestrial biomarkers. The average chain length shows similar deviation in both the fine (±0.21 units) and coarse (±0.21 units) fractions relative to the bulk sediment, suggesting that either fraction is suitable for interpreting first-order changes in vegetation type. Moving forward, our results suggest that the fine fraction of grain size-sorted sediment yield similar lipid distributions compared to the bulk un-washed sediment. However, coarse fractions often show large deviations from the bulk sediment across different proxies, perhaps making these unsuitable for biomarker-based climate reconstruction.References[1] Zachos et al., Geology, 34, 9, pp 737-740 (2006)[2] Xiao et al., Global Biogeochemical Cycles, 37, e2022GB007648 (2023)[3] Peterse and Eglinton, Frontiers in Earth Science, 5, 49 (2017)

The larger-scale oceanic gyre circulation regulates temperature, salinity and nutrient flow throughout the ocean, profoundly influencing the biological environment and climate. Here, we investigate the response of the Pacific gyre circulation during the warm climate of the early Eocene in eight models from the Deep-Time model intercomparsion project (DeepMIP). Our DeepMIP results suggest a northward expansion of the North Pacific subtropical gyre by up to 10 degrees latitude in the Eocene, maintaining a similar strength to the present day. This simulated poleward expansion of the North Pacific gyre circulation is corroborated by proxy evidence, including poleward shifts in low sedimentation rate and high clay concentration during the Eocene. In the southern Pacific, the super subtropical gyre is much stronger during the Eocene due to the southward position of Australia that leads to a wide-open Indonesian gateway. The poleward shifted boundary between the subtropical and subpolar gyre in North Pacific occurs as a result of the northward shifted westerly winds maxima, as also corroborated by an analysis of the Sverdrup transport. The Sverdrup transports describes the upper circulation during the Eocene further poleward than modern day mainly due to their continental differences. The upper circulation corresponds to Sverdrup transport up to ~53°N for the North Pacific, slightly further north than modern day of 50°N, and up to ~55°S for the South Pacific that is much further south than in the modern ocean and continents (~45°S).

Planktonic foraminifera, single-celled protists, are extensively used in biostratigraphy and biochronology thanks to their abundance in marine sediments, widespread distribution and extensive fossil record in the Cretaceous and Cenozoic. We present an overview of planktonic foraminiferal taxonomy, and evolutionary trends that are relevant to the practice and application of biostratigraphy. Additionally, we present the key features in planktonic foraminiferal paleoecology and paleogeography that characterise Cretaceous-Cenozoic species diversity and geographic distributions. The types of bioevents and biozone definitions, morphologic terminology and species identification in evolutionary lineages are illustrated through examples. Planktonic foraminifera are crucial in the development of geological timescales and their value and reliability in chronostratigraphic correlations is demonstrated by the identification of 14 primary and secondary boundary events applied in the definition of the Global Stratotype Section and Points (GSSP). The presentation of the methodologies used in biochronological studies is aimed to describe the significance of planktonic foraminifera for correlation and integration with magnetostratigraphy, chemostratigraphy and orbital tuning. Calibration difficulties such as diachroneity of species occurrences are discussed, and examples of astronomical calibrations are provided for the Late Cretaceous and Late Miocene.

Globigerina bollii Cita and Premoli Silva was described from the historical Langhian-type section in Langhe, Piedmont (Italy). Due to its peculiar compact morphology, it was set apart from all the other globigerinids typical of the coeval Mediterranean fauna, and it was only reported for a short and limited stratigraphic range. The taxon became a first-order marker for the local biostratigraphy with its own Globigerina bollii Zone within the Langhian stage. However, the species was later synonymised with Globigerina falconensis Blow, ending its use in biostratigraphic schemes, and it was no longer utilised by authors working in the Mediterranean area and Paratethys. We present a reassessment of Globigerina bollii, showing for the first time a full collection of high-quality scanning electron and optical microscope images of the type series of specimens and a comparative study with Mediterranean individuals from the Langhian of the Cretaccio Section (Italy) and extra-Mediterranean individuals from Ocean Drilling Program Site 747 in the Kerguelen Plateau (Indian Ocean). The stratigraphic ranges of all the occurrences cited in the scientific literature from 1960 to the present day and all the references including images of the taxon are compiled. We compare G. bollii to other four-chambered morphospecies inhabiting the oceans during the Miocene, providing a detailed discussion of their morphological differences, which allows us to retain G. bollii as a valid taxon and to disclaim its synonymy with Globigerina falconensis. Our taxonomical observations also allow us to reassign Globigerina bollii to the genus Globoturborotalita, due to its strong affinities with other members of that genus, such as G. eolabiacrassata Spezzaferri and Coxall, and G. ouachitaensis (Howe and Wallace). We present a direct visual comparison with the other representatives of middle Miocene globoturborotaliids. An additional comparison is also discussed with Globigerina bollii lentiana Rögl, a species endemic in the Paratethys. We conclude that the presence of G. bollii in the Mediterranean Basin during such a confined stratigraphic interval (Mediterranean Subzone MMi4c–MMi4d), might be a palaeogeographical indicator of the intermittent opening of the eastern gateway with the Paratethys, affecting the Mediterranean faunas during the Langhian and their migration from oceanic realms into the Paratethys and Mediterranean.

Abstract. The ratio of the trace element Mg over Ca (Mg/Ca) and the oxygen isotopic composition (δ18O) of foraminiferal calcite are widely employed for reconstructing past ocean temperatures, although geochemical signals are also influenced by several other factors that vary temporally and spatially. Here, we analyze a global dataset of Mg/Ca and δ18O data of 59 middle Miocene to Holocene species of planktonic foraminifera from a wide range of depth habitats, many of which have never been analyzed before for Mg/Ca. We investigate the extent to which Mg/Ca and δ18O covary through time and space, and identify several sources of mismatch between the two proxies. Once the data are adjusted for long term non-thermal factors, Mg/Ca and δ18O are overall positively correlated in a way consistent with temperature being the dominant controller of both through space and time and across many different species, including deep-dwellers. However, we identify several species with systematic offsets in Mg/Ca values, to which multispecies calibrations should be applied with caution. We can track the appearance of such offsets through ancestor-descendent species over the last 15 million years and propose that the emergence of these offsets may be the geochemical expression of evolutionary innovations. We find virtually all of the Mg/Ca and δ18O-derived temperatures from the commonly used genera Globigerinoides and Trilobatus are within uncertainty of each other, highlighting the utility of these species for paleoceanographic reconstructions. Our results highlight the potential of leveraging information from species lineages to improve sea surface temperature reconstruction from planktonic foraminifera over the Cenozoic.

AbstractTwo distinct extraterrestrial impacts events struck the Earth less than 25,000 years apart in the late Eocene, approximately 35.65 million years ago. These resulted in the Popigai (northern Siberia) and Chesapeake Bay (eastern North America) impacts structures, the largest of the Cenozoic era. To examine the paleoclimatic consequences attributed to the late Eocene Chesapeake and Popigai extraterrestrial impact events, we present multispecies planktonic and benthic foraminiferal oxygen (δ18O) and carbon (δ13C) isotope records. Here we generate data from the Gulf of Mexico, Deep Sea Drilling Project Site 94 covering 35.85 to 35.49 million years ago. No isotopic anomalies or excursions were recorded across the impact horizons. However, ~100,000 years before the impacts, a negative 0.75‰ δ18O shift occurs in planktonic foraminifera, coincident with a 0.25‰ positive change in benthic foraminifera. We interpret this as a warming of ~2 °C in the surface ocean, accompanied by 1 °C deep water cooling, but these modifications are before and not coeval with the impact horizons. Despite the close succession of two or more large extraterrestrial impact events within a short space of time (less than 25,000 years), our study from the Gulf of Mexico indicates no detectable paleoclimatic response.

The functioning of the Pacific Ocean—the world's largest ocean—during a warmer‐than‐present paleoclimate state remains underexplored. We present planktonic and benthic foraminiferal stable oxygen (δ18O) and carbon (δ13C) isotope records from Integrated Ocean Drilling Program (IODP) Site U1334 that span the Oligocene‐Miocene Transition (OMT) interval, from 24.15 to 21.95 million years ago (Ma). We reconstruct (sub‐)surface and deep‐water conditions and provide better constraints on the physical and chemical oceanography of the eastern equatorial Pacific Ocean (EEP). Positive trends in planktonic and benthic foraminiferal δ18O values, mark a largely uniform imprint of increased land‐ice volume/global cooling on surface‐ and deep‐waters. We document a delayed planktonic foraminiferal δ18O increase across the OMT as well as an increase in the amplitude variability of planktonic foraminiferal δ18O values on eccentricity timescales during the early Miocene. We interpret this as an enhanced glacioeustatic sea‐level control on Atlantic‐Pacific salinity exchange through the Central American Seaway (CAS) or as the onset of more variable surface currents and oceanic fronts in the EEP. Positive trends in planktonic and benthic foraminiferal δ13C values characterize the whole‐ocean depletion in 12C linked to organic carbon burial during the Oligocene‐Miocene carbon maximum (CM‐OM). However, this depletion is more pronounced in the planktonic foraminiferal δ13C record, especially during ∼400 Kyr eccentricity minima, reflecting an increase in nutrient upwelling and the efficacy of the biological carbon pump (BCP) when global temperatures decreased across the OMT and during the early Miocene. Our study highlights the dynamic behavior of the EEP in a warmer‐than‐present unipolar icehouse state.

We conducted a morphometric study and wall texture analysis on extant and fossil specimens of the planktonic foraminifera Globigerina falconensis plexus. Our global data reveal morphological inconsistencies between fossil and extant populations. Our results are significant as G. falconensis is widely used in palaeoceanographic studies in conjunction with its sister taxon G. bulloides . Morphologically these two species are similar, with the main difference being the distinctive apertural lip present in G . falconensis . We selected cores covering the entire stratigraphic range of G . falconensis , from the early Miocene to current day, spanning sites from high latitudes in the North Atlantic Ocean and the southern Indian Ocean to sites in equatorial regions. The morphology found in the modern ocean is not consistent with the Miocene holotype of Globigerina falconensis Blow described from lower Miocene sediments in Venezuela. A more lobate morphology evolved in the late Miocene, thus, a new name is required for this morphotype, coexisting in the modern oceans with G . falconensis s.s . We thus describe the new morphospecies, G . neofalconensis for the more lobate forms which evolved in the late Miocene and inhabit the modern oceans. Additionally, we report a pseudocancellate wall texture present in the G . falconensis plexus. We use the molecular sequences from the PR 2 database to explore the generic attribution of the G . falconensis lineage, confirming its close relationship with G . bulloides and its retention in the genus Globigerina .

<p>Modern studies on marine ecosystems are limited in time so the evaluation of their stability under the ongoing CO<sub>2</sub> emissions and global warming remains uncertain and necessarily requires a long-term perspective. The dynamic early Paleogene climate offers the crucial opportunity to detect relationships among calcareous plankton, past carbon cycle perturbations and climate. Specifically, the EECO (~53-49 Ma) represents a key interval to investigate the planktic foraminiferal resilience on a long-term perspective as it records the peak temperature and <em>p</em>CO<sub>2</sub> of the entire Cenozoic. We investigated the Pacific Sites 1209-1210 and eastern Indian Ocean Site 762 following the evidence that the EECO marked impacted planktic foraminiferal assemblages at the Atlantic Oceans. Abrupt and permanent abundance decline (more than one-third) of the symbiont-bearing genus <em>Morozovella </em>occurred<em> </em>at the EECO beginning (J event, ~53 Ma) at sites 1209-1210, whereas <em>Acarinina</em> concomitantly increased, as from the Atlantic sites. Site 762 recorded the southern high-latitude migration of the warm <em>Acarinina</em> species coupled with the decline of the ‘cold’ subbotininds. Another major change documented at the Pacific and Indian Oceans revealed to be similar to the Atlantic record and involved the coiling direction (ability to add chambers clock- or counter-clockwise) of the genus <em>Morozovella.</em> Indeed, the morozovellid coiling direction is dominantly dextral below the EECO but became sinistral within the EECO, although this change is registered ~ 200 kyr later at the Pacific Ocean and ~ 200 kyr before at Site 762 where it occurred at the K/X event (~52.8 Ma). Therefore, the morozovellids crisis observed in the Atlantic and Pacific Oceans can be mainly read as the dextral forms decline. Searching for the driving causes of the observed modifications, we performed stable isotope analysis on sinistral and dextral morozovellids morphotypes (possibly cryptic species) from sites 1209-1210 and 762. Results show that the sinistral forms generally record lower d<sup>13</sup>C values, once again as recorded for the Atlantic Ocean. This evidence suggests a reduced symbiosis relationship and/or a slightly deeper habitat, probably a strategy to sustain the stressors induced by the EECO. Our record advises on a causal relationship to chemical-physical modifications in the surface waters, such as the temperature increase. The increased temperature of at least 1°C [Mg/Ca (LA)-ICP-MS] recorded by sinistral morozovellids within the EECO may have acted in the reduced photosymbiotic activity. Conversely, acarininids do not show preferential coiling nor below neither within the EECO and they reveal d<sup>13</sup>C values that imply major ecological flexibility, possibly enabling them to proliferate. The EECO also induced the virtual disappearance of the genus <em>Chiloguembelina</em> after the K/X event at all the Atlantic, Pacific and Indian sites investigated. This disappearance appears to be related to thermocline warming and Oxygen Minimum Zone enhanced oxygenation. Our records demonstrate the wide geographic and possibly global character of the striking modifications occurred in the planktic foraminiferal assemblages during the first ~800 kyr of the EECO. Our derived paleobiology gives new insights into planktic foraminiferal strategies adopted under long-term global warming.</p>

We describe Globigerinoides rublobatus n. sp., a new morphospecies of fossil planktonic foraminifera, from the Pleistocene sediments (∼810 ka) of the Indian Ocean and Pacific Ocean. We use image analysis and morphometry of 860 specimens from International Ocean Discovery Program Site U1483 in the tropical Indian Ocean to document morphological variability in the new morphospecies and related taxa, and we also report it from Pacific Ocean Site U1486 for the first time. The new morphospecies combines characteristics typical of Globigerinoides conglobatus (Brady, 1879) and Globigerinoides ruber (d'Orbigny, 1839), with which it co-occurs, but is distinct from both. Morphometric data indicate that G. rublobatus n. sp. is closer to G. conglobatus, potentially signalling an evolutionary affinity. We find that Globigerinoides rublobatus n. sp. occurs as two variants, a pigmented (pink) form and a non-pigmented (white) form. The non-pigmented forms are on average ∼50 % larger than the pigmented forms. This is so far only the third instance of fossil planktonic foraminifera known to exhibit this pink pigmentation. We regard the pink and white forms as variants of a single morphospecies and suggest the pink form may represent a later evolutionary adaptation.

Abstract The Eocene (56–34 million years ago) is characterized by declining sea surface temperatures (SSTs) in the low latitudes (∼4°C) and high southern latitudes (∼8–11°C), in accord with decreasing CO2 estimates. However, in the mid‐to‐high northern latitudes there is no evidence for surface water cooling, suggesting thermal decoupling between northern and southern hemispheres and additional non‐CO2 controls. To explore this further, we present a multi‐proxy (Mg/Ca, δ18O, TEX86) SST record from Bass River in the western North Atlantic. Our compiled multi‐proxy SST record confirms a net decline in SSTs (∼4°C) between the early Eocene Climatic Optimum (53.3–49.1 Ma) and mid‐Eocene (∼44–41 Ma), supporting declining atmospheric CO2 as the primary mechanism of Eocene cooling. However, from the mid‐Eocene onwards, east‐west North Atlantic temperature gradients exhibit different trends, which we attribute to incursion of warmer waters into the eastern North Atlantic and inception of Northern Component Water across the early‐middle Eocene transition.

Trochospiral planktonic foraminifera will coil either sinistral (left) or dextral (right). The prevalence of sinistral or dextral coiling can change through the stratigraphic range of morphospecies with a preference in coiling direction. A number of coiling shifts have been applied as secondary marker events through the Recent to late Miocene (similar to 0-7 Ma) biochronology. However, no such events have been applied beyond this age despite a number of species being known to adopt preferential coiling directions. Here we investigate selected Miocene species within the genus Paragloborotalia. Previous work in the tropical to subtropical realm has shown that the mayeri-siakensis group undergoes a shift from random to sinistrally dominated coiling in the mid Miocene (similar to 15 Ma). We extend the investigation to other Miocene paragloborotaliids in the low (IODP Sites U1337, U1338, ODP Sites 871 and 925), mid (JOIDES-3 hole) and high latitudes (ODP Site 747) in order to assess whether there is global synchronicity and if the change is unique to the mayeri-siakensis group. In addition, a number of outcrop samples from the Cipero and Lengua formations in southern Trinidad are quantitatively compared to previously published trends. Our results show that in the low-mid latitudes the coiling shift is at similar to 15.37 Ma within planktonic foraminiferal Zone M5 within both Paragloborotalia siakensis and Paragloborotalia continuosa. In the high latitudes the absence of paragloborotaliids through a portion of the mid Miocene interval prevents accurate dating of a shift from early forms showing random coiling to later paragloborotaliids adopting a sinistral preference. We also find two coiling changes in the genus Globorotalia at high latitude Site 747, from random to sinistral in the mid Miocene (15.14 Ma) and sinistral to dextral (10.02 Ma) in the late Miocene. We propose the recognition of a coiling change in Paragloborotalia as a secondary bioevent in the mid Miocene at 15.37 Ma, and a useful means for the recognition of the base of the Langhian. The coiling shift as a biostratigraphic marker is likely to be particularly useful in regions where the currently applied bioevents, namely the Praeorbulina-Orbulina lineage, is rare or poorly represented.

Pulleniatina is an extant genus of planktonic foraminifera that evolved in the late Miocene. The bottom and top occurrences of its six constituent morphospecies (P. primalis, P. praespectablis, P. spectabilis, P. praecursor, P. obliquiloculata, P. finalis) provide a series of more or less useful constraints for correlating tropical and subtropical deep-sea deposits, as do some prominent changes in its dominant coiling direction and a substantial gap in its record in the Atlantic Ocean. Biostratigraphic information about these events has accumulated over many decades since the development of systematic deep-sea drilling in the 1960s, during which time the geochronological framework has evolved substantially, as have taxonomic concepts. Here we present new data on the biochronology of Pulleniatina from International Ocean Discovery Program Site U1488, which has a record of its entire evolutionary history from the centre of its geographic range in the Western Pacific Warm Pool. We then present and compare revised calibrations of 183 published Pulleniatina bioevents worldwide, with stated sampling errors as far as they are known, using a consistent methodology and in the context of an updated evolutionary model for the genus. We comment on the reliability of the various bioevents; their likely level of diachrony; and the processes of evolution, dispersal, and extinction that produced them.