Sarah J. Feakins

The Miocene epoch (~23 to 5.3 million years ago) was a period when global mean temperatures were warmer than today, with estimated atmospheric CO2 levels similar to those expected in coming centuries. Climate models generally underestimate reconstructed Miocene global mean and high-latitude ocean temperatures, a persistent discrepancy that raises questions about both the reliability of proxy reconstructions and the ability of climate models to represent warm climate states. Resolving this discrepancy requires a critical, unified reevaluation of the existing proxy record. Here we compile and reevaluate existing ocean temperature records reconstructed using the TEX86 paleothermometer. The TEX86 paleothermometer, which derives upper ocean temperatures from the distribution of the membrane lipids of marine archaea, has been widely used to reconstruct past sea surface and shallow subsurface (0–200 m) temperatures. Here, we introduce MioTEX, a global compilation of Miocene ocean temperature records based on the TEX86 proxy. This effort, developed within the MioOcean initiative, applies uniform screening criteria and calibration methods to published records from 46 sites spanning multiple ocean basins. We find distinct temperature variations among different latitudinal bands and ocean basins, as well as absolute temperature differences arising from the choice of calibration. Compared with previous SST reconstructions suggesting an Early to Middle Miocene collapse and Late Miocene establishment of the modern meridional SST gradient, our standardised, multi‑site synthesis quantifies when and where such gradient changes occurred across ocean basins, with the strongest cooling recorded at high-latitude sites in the South Atlantic and Southwest Pacific. The MioTEX dataset is publicly available at Zenodo (https://doi.org/10.5281/zenodo.22258386, Sosdian et al., 2026) and presented on an interactive Streamlit-based web platform, allowing users to explore data, apply different calibrations, and test screening criteria.

To reconstruct Iberian Margin paleoclimate and the effects of Mediterranean gateway restriction during the late Miocene, International Ocean Discovery Program Expedition 401 drilled Site U1609 on the southwestern Portuguese Margin (37º22.6259’N, 9º35.9120’W; 1660 m water depth) in the path of Mediterranean Overflow Water (MOW). We present a multiproxy study of plant waxes, lignin phenols, palynomorphs, and X-ray fluorescence. From 11.5–9.5 Ma, hemipelagic sediments have high Ca and dinoflagellate:pollen ratios. Between 9.5 and 6 Ma plant proxies (e.g., alkanes and lignin) and terrigenous elements (e.g., Ti) become more abundant, with more land-based flux attributed to tectonic uplift and the initiation of MOW. Sediments from 6–2.5 Ma indicate relatively stable elemental proportions, although precessional pacing of Ti/Ca occurs throughout the record. Plant wax n -alkane δ ¹³ C and δD values indicate C ₃ vegetation and Atlantic storm tracks, like modern, occurred throughout the warmer Tortonian–Zanclean climates. In contrast, lignin indicates greater variability across the record. High lignin transport and low syringyl/vanillyl ratio suggest riverine export from high-elevation conifer forests in the SE Iberian Peninsula, followed by lateral ocean current transport transport, with fluxes increasing as MOW strengthened at 4.5 Ma. During the Messinian Salinity Crisis, when MOW ceased, lignin delivery was reduced and restricted to lowland riverine inputs from SW Iberia, where angiosperms today dominate the exported woody biomass. We find river-exported gymnosperm lignin to be a valuable tracer of distal advection tracking the history of MOW across the Messinian gateway reorganization.

The Miocene epoch has been highlighted as containing reference intervalsfor near future warmer climates; however, to realize the full potential of this analogue, discrepancies must be addressed, including those between model predictions and proxy data for ocean temperatures. Over recent years, new insights into ocean temperature proxy systematics have come to light, thus providing robust Miocene ocean temperature estimates requires re-evaluation of available data. In tandem, collaboration between stratigraphers and geochemists emphasises the importance of refining and synchronising age models to ensure robust comparisons of temperature patterns across space and time. Here, we compiled published Miocene temperature proxy records from 101 publications and 94 sites into the new MioOcean database, recalculated temperatures using state of the art proxy constraints, and revised and/or verified age models for 38 key sites. The MioOcean database includes upper and bottom ocean temperature records from organic (UK’37 and TEX86) and inorganic (Mg/Ca, δ18O, and Δ47) marine geochemical proxies. To improve confidence in, and comparability between, datasets, we convert proxies into temperature in an internally consistent manner, including updating all associated input variables. To aid usability, the database provides propagated numerical uncertainty estimates encompassing as many sources of error as possible. The MioOcean database improves accessibility of proxy-based Miocene ocean temperature reconstructions to non-specialists, simplifies model-data comparison and validation, and provides the necessary groundwork for in-depth inter-proxy comparison studies. The data compilation (https://doi.org/10.5281/zenodo.22258386, Sosdian et al., 2026) is also hosted on www.mioocean.com, including interactive data visualization, enabling interrogation and comparison of re-evaluated MioOcean records.

The Miocene Epoch has emerged as an important paleoclimate model intercomparison target due to its dynamic nature, global warmth, and reconstructed atmospheric CO₂ concentrations. Miocene CO₂ estimates range from as low as 300–600 ppmv to as high as 800–1100 ppmv. The formalized Miocene Model Intercomparison Project (MioMIP2) aims to address questions about the mechanisms driving the climatic changes and tipping points seen in the geological record and improve confidence in the ability of climate models to predict future climates and constrain climate sensitivity. Through alignment with PlioMIP and DeepMIP-Eocene efforts, a coordinated MioMIP (DeepMIP-Miocene) effort will allow for cross-time-period studies that sample the full range of Shared Socioeconomic Pathway paleo analogues. Building on the MioMIP1 “MIP of opportunity”, the Miocene community has been developing the experimental design for MioMIP2. The MioMIP1 effort was an ensemble of opportunity that leveraged existing Miocene simulations run with different models, boundary conditions, and reference datasets. MioMIP2 will be the first formal Miocene MIP with common boundary conditions and will target the Miocene Climatic Optimum (MCO; 16.75–14.5 Ma). We present the experimental design for coordinated “CORE” MCO simulations and sensitivity studies. This community effort synthesizes paleogeography, ice sheet, CO₂, and vegetation boundary conditions based on the latest available literature and will use geological data from companion proxy synthesis efforts to evaluate the simulations.

The Miocene Epoch has emerged as an important paleoclimate model intercomparison target due to its dynamic nature, global warmth, and reconstructed atmospheric CO₂ concentrations. Miocene CO₂ estimates range from as low as 300–600 ppmv to as high as 800–1100 ppmv. The formalized Miocene Model Intercomparison Project (MioMIP2) aims to address questions about the mechanisms driving the climatic changes and tipping points seen in the geological record and improve confidence in the ability of climate models to predict future climates and constrain climate sensitivity. Through alignment with PlioMIP and DeepMIP-Eocene efforts, a coordinated MioMIP (DeepMIP-Miocene) effort will allow for cross-time-period studies that sample the full range of Shared Socioeconomic Pathway paleo analogues. Building on the MioMIP1 “MIP of opportunity”, the Miocene community has been developing the experimental design for MioMIP2. The MioMIP1 effort was an ensemble of opportunity that leveraged existing Miocene simulations run with different models, boundary conditions, and reference datasets. MioMIP2 will be the first formal Miocene MIP with common boundary conditions and will target the Miocene Climatic Optimum (MCO; 16.75–14.5 Ma). We present the experimental design for coordinated “CORE” MCO simulations and sensitivity studies. This community effort synthesizes paleogeography, ice sheet, CO₂, and vegetation boundary conditions based on the latest available literature and will use geological data from companion proxy synthesis efforts to evaluate the simulations.

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Great Salt Lake (GSL), Utah, USA, is a large hypersaline lake, but during short‐lived (∼10–20 kyr) pluvials, it was an expansive freshwater lake. We update the age model of GLAD1‐GSL00‐4, a 120‐m sediment core recovered by the Global Lakes Drilling (GLAD) project, with new U‐series measurements dating evaporites representing the driest times in lake history and providing a new basal age of 236.3 ka (2 σ uncertainty = 6.7 kyr) during the penultimate interglacial. We measure microbial membrane lipid abundances, dialkyl glycerol diethers and glycerol dialkyl glycerol tetraethers (GDGT), to reconstruct salinity over the last two glacial cycles. High and variable salinity precludes use of GDGTs as a proxy for temperature. The freshwater, deep, expanded lake phases “Bonneville” and “Little Valley,” here dated to 30.3–16.1 ka (2 σ = 1.0–1.4 kyr) and 140.4–134.6 ka (2 σ = 5.5–5.7 kyr) respectively, occur during deglacial pluvials and briefly interrupt the hypersaline conditions which dominate the record. The salinity rise following the last pluvial agrees with water balance reconstructions from well‐dated lacustrine carbonates. However, evaporite (thenardite) deposition dated to 16.1–12.2 ka (2 σ = 0.8–1.0 kyr) contrasts with Holocene timing elsewhere in the basin. After the Little Valley highstand, a salinity increase culminates in halite precipitation. Despite four disparate halite dates spanning 90–160 ka, age model assignment agrees with U‐series dating of Little Valley shoreline tufa. This continuous salinity record provides context for lake expansion/contraction followed by evaporite deposition across two glacial terminations, consistent with regional pluvials.

The modern Amazon Basin is covered by a wet, tropical rainforest and drained by the Amazon River system flowing from the Andes eastward to the Atlantic Ocean. To better understand Amazonian stratigraphic and vegetation history during the Cenozoic, an 870-m drill core was collected from the Acre Basin in western Amazonia by the International Continental Scientific Drilling Program’s Trans-Amazon Drilling Project (TADP) in 2023. We analyze the hydrocarbon components of solvent extractible lipids along with coaly fragments to characterize plant producers and the paleoenvironment. Coaly fragments at depths below 767m reveal no heating above 71 °C, sufficient to promote microbial degradation but insufficient for thermal cracking, consistent with a plant wax n-alkane carbon preference index (CPI) of mostly >4. n-Alkanoic acid δ13C values average –32.2±1.5‰, broadly consistent with a C3 rainforest, with progressive enrichment with depth hypothesized to result from heterotrophic enrichment. n-Alkanoic acid-reconstructed precipitation δD averages –61±14‰, broadly consistent with values for modern precipitation associated with moisture recycling over a forested landscape, although heterogeneity may indicate pulsed deposition with differences in provenance. PAHs are variably abundant and include pyrogenic PAHs and retene, the latter likely from bryophytes given gymnosperm scarcity. Overall, the biomarker record supports sustained rainforest conditions and similar-to-modern precipitation patterns, with complexity associated with depositional environment and diagenetic changes. This biomarker evidence will be tested by additional proxy evidence (e.g., carbonates, pollen) in forthcoming work on the continental drill cores.

This special collection celebrates the 40th anniversary of Paleoceanography and Paleoclimatology and highlights the breadth, impact, and frontiers in paleoenvironmental research. Since the journal's founding in 1986 as Paleoceanography , the field has expanded from its early emphasis on marine sedimentary archives to an increasingly integrated Earth system perspective encompassing the oceans, atmosphere, cryosphere, biosphere, and terrestrial environments. The papers in this collection are selected from the recent archives since the expansion to Paleoceanography and Paleoclimatology in 2018. The topics span timescales from the Cretaceous to the Common Era and showcase advances in reconstructing past climates, understanding Earth system processes, developing innovative analytical and computational methods, and synthesizing observations and testing mechanisms with numerical models. Together, they illustrate how studies of past environmental change provide fundamental insights into climate sensitivity, carbon‐cycle dynamics, ocean circulation, abrupt climate change, and hydroclimate variability. They also demonstrate the importance of past climate for evaluating climate models, contextualizing modern environmental change, and informing projections of Earth's future under continued anthropogenic forcing. This anniversary collection celebrates four decades of scientific discovery, with a curated selection of articles that illustrate recent themes in the journal, from greenhouse to icehouse climates, and cutting‐edge methods, to reveal how the past informs our future.