Mid Pliocene Research Articles

West African Monsoon Dynamics and Its Control on the Stable Oxygen Isotopic Composition of Precipitation in the Late Cenozoic

AbstractThis study presents an overview of the Late Cenozoic evolution of the West African Monsoon (WAM), and the associated changes in atmospheric dynamics and oxygen isotopic composition of precipitation (δ18Op). This evolution is established by using the high‐resolution isotope‐enabled GCM ECHAM5‐wiso to simulate the climatic responses to paleoenvironmental changes during the Mid‐Holocene (MH), Last Glacial Maximum (LGM), and Mid‐Pliocene (MP). The simulated responses are compared to a set of GCM outputs from Paleoclimate Model Intercomparison Project Phase 4 (PMIP4) to assess the added value of a high resolution and model consistency across different time periods. Results show WAM magnitudes and pattern changes that are consistent with PMIP4 models and proxy reconstructions. ECHAM5‐wiso estimates the highest WAM intensification in the MH, with a precipitation increase of up to 150 mm/month reaching 25°N during the monsoon season. The WAM intensification in the MP estimated by ECHAM5‐wiso (up to 80 mm/month) aligns with the mid‐range of the PMIP4 estimates, while the LGM dryness magnitude matches most of the models. Despite an enhanced hydrological cycle in MP, MH simulations indicate a ∼50% precipitation increase and a greater northward extent of WAM than the MP simulations. Strengthened conditions of the WAM in the MH and MP result from a pronounced meridional temperature gradient driving low‐level westerly, Sahel‐Sahara vegetation expansion, and a northward shift of the Africa Easterly Jet. The simulated δ18Op values patterns and their relationship with temperature and precipitation are non‐stationarity over time, emphasizing the implications of assuming stationarity in proxy reconstruction transfer functions.

Contrasting faulting styles of salt domes and volcanoes: Can unsupervised learning techniques differentiate fault styles?

An attractive feature seen on seismic data, also known as funny-looking thing (FLT), has a wide range of interpretations, from noise patterns to amplitude anomalies. An example of an FLT is the similar faulting patterns between a volcanic intrusion and a salt intrusion from the point of view of a machine learning (ML) algorithm. Oftentimes, seismic interpreters do not have a complete data set or geologic background to determine the genesis of the observed features. This can be particularly perplexing when trying to determine if an intrusion is volcanic or halokinetic in origin because they exhibit similar geomorphologies. Examining the differences in these features in the Gulf of Mexico, a well-documented salt basin, and the Taranaki Basin in New Zealand, which is igneous prone, can help to understand the differences. The analysis aims to discern geologic features based on the geometries and attributes shared by seismic data and remote sensing tools. Seismic attributes and ML techniques highlight differences and similarities between the intrusions, including the discussion of using ML techniques, such as self-organized maps (SOMs), an unsupervised ML technique, and cluster fault systems, without regard to the geologic context. The attributes used in the SOM are fault probability, fault dip azimuth, fault dip magnitude, and thin-bed detector. Fault probability is performed through a combination of convolutional neural network fault prediction and a skeletonization process. Once the faults are clustered using SOM, the visualization of fault architecture due to the existing mount (either volcano or salt dome) is done considering high fault probabilities (>75%). The methodology consists of selecting the neurons from the SOM grid corresponding to the presence of faults and combining them with fault probability and a fault dip azimuth using a crossplot. The crossplot product assists in the automatic extraction of the fault planes using: (1) a voxel representation of the fault planes and (2) fault patches representing the fault planes. Moreover, the visualization technique defined demonstrates that the crossplot product yields better-defined fault planes. With the fault system characterized, compared horizon slices using coherence, fault dip magnitude, and azimuth against remote sensing images with similar attributes. In conclusion, our methodology combines technologies to differentiate the genesis of intrusion — salt or igneous — using the fault presence and could be helpful in frontier exploration or planetary exploration. Geologic feature: Comparison of extensional faults due to salt and igneous intrusions Seismic appearance: In the symmetric salt dome, crown faulting style with a set of synthetic and antithetic faults around the salt dome; for the igneous systems, symmetric radial faults Formation: Upper and Lower Wilcox (Gulf of Mexico); Ariki Formation — Mo hakatino Formation (Taranaki) Age: Upper Miocene and Lower Pliocene (Gulf of Mexico); Mid Pliocene (Taranaki) Location: Offshore Gulf of Mexico and Offshore Northeast New Zealand Seismic data: From the Gulf of Mexico: B-78-89-LA-3D, B-69-94-LA-3D, B-54d-94-LA-3D, and B-69a-94-LA-3D. From New Zealand: Nimitz and Kora 3D Analysis tools: Structural-oriented filter, Sobel similarity, fault dip magnitude and azimuth, CNN automatic fault prediction, and SOM classification

Early Pliocene (Zanclean) stratigraphic framework for PRISM5/PlioMIP3 time slices

Global reconstructions of Pliocene climate provide important insights into how the climate system operates under elevated temperatures and atmospheric CO2 levels. These reconstructions have been used extensively in paleoclimate modeling experiments for comparison to simulated conditions, and as boundary conditions. Most previous work focused on the Late Pliocene interval known as the mid Piacenzian Warm Period (mPWP), the interval originally identified by the U.S. Geological Survey Pliocene Research, Interpretation and Synoptic Mapping Project (PRISM) as the PRISM interval or Mid Pliocene Warm Period. The term Mid Pliocene Warm Period is a misnomer due to changes to the geological time scale, and its use should be discontinued. The Pliocene Model Intercomparison Project (PlioMIP), now in its third phase, is expanding to include a focus on the Early Pliocene (Zanclean). PlioMIP3 experiments will allow comparison of environmental and climatic conditions before and after closure of the Central American Seaway (CAS). PlioMIP3 used the annual insolation pattern at the top of the atmosphere to determine time slices in the Zanclean that have orbital configurations that are most similar to modern. Two have been selected by PlioMIP and adopted by PRISM for inclusion in future studies: PRISM5.1 (4.474 Ma) and PRISM5.2 (4.870 Ma). Here we establish the stratigraphic framework for these Early Pliocene time slices and furnish information to help locate these intervals in proxy records of paleoenvironmental data using oxygen isotope stratigraphy, paleomagnetic stratigraphy, biostratigraphy, and biochronology (calibrated planktic foraminifer and calcareous nannofossil events).

Same place, different stories: Disparate evolutionary trends of mygalomorph spiders from the Peripampasic orogenic arc

AbstractAimComparative phylogeography aims to unravel similarities in the population structure and evolutionary processes undergone by co‐distributed taxa, under the assumption that they will have experienced the same geoclimatic events. However, small differences in functional traits, particularly those related to dispersal abilities, may translate into incongruent evolutionary histories. Here, we used a sequence target multi‐locus approach to infer and compare the phylogeographical patterns of three sympatric mygalomorph spiders in the Argentinean Peripampasic orogenic arc.LocationThe mountainous systems of central and northern Argentina.TaxonAcanthogonatus centralis, Grammostola vachoni and Plesiopelma longisternale (Araneae: Mygalomorphae).MethodsWe inferred mitochondrial gene trees (16S + L1 + nad1) and nuclear (ITS2) networks of three species of mygalomorph spiders from 159 individuals using Bayesian and Maximum likelihood approaches, and estimated divergence times in a Bayesian framework. Based on our time‐stamped gene trees, we reconstructed ancestral areas using the Bayesian Binary MCMC method.ResultsDeeply divergent and highly geographically structured populations, isolated since the Late Miocene to mid Pliocene, were obtained in the pycnothelid Acanthogonatus centralis. Conversely, the theraphosids Plesiopelma longisternale and Grammostola vachoni showed slightly divergent and poorly geographically structured populations, tracing back to the Late Pliocene to Early Pleistocene.Main conclusionsWe propose that differences in dispersion rates and time of colonization between the theraphosids and the pycnothelid species led to divergent lineage history despite common environmental conditions. We corroborate the key role played by the Plio‐Pleistocene geoclimatic events in shaping the present‐day diversity of mygalomorph spiders along the Peripampasic orogenic arc. Additionally, we uncovered potentially overlooked species diversity within G. vachoni.

Late Pliocene continental climate and vegetation variability in the Arctic-Atlantic gateway region prior to the intensification of Northern Hemisphere glaciations

We describe Pliocene palynological assemblages from ODP Hole 910C on the Yermak Plateau, Arctic Ocean. Analysis of high-resolution (~10 ± 3 ka) sampling allows us to detect changes in late Pliocene vegetation biomes corresponding to climatic variability between ~3.4 to 2.6 Ma. Findings show that a cool temperate and mixed boreal forest ( Pinus-Tsuga-Picea-Alnus-Ulmus community) initially dominated the Arctic-Atlantic gateway region. Following the onset of Marine Isotope Stage M2 cooling, ~3.3 Ma, there was a marked decline in vegetation coverage (low abundance of Pinus, Abies community). The mid Pliocene warm period that followed at ~3.2 to 3.0 Ma showed an increase in percentage of thermophilic and moist boreal taxa ( Tsuga-Thuja- Cupressaceae -Betula-Ilex community) suggesting influx of warm Atlantic Current. The dominance of Pinus-Ulmus persisted until ~3.0 Ma. Intermittent cooler and warmer periods occurred after 2.9 Ma, with an increase in herbaceous pollen and cryptogamic spores. This was followed by an abrupt change at ~2.73–2.64 Ma marked by a prominent shift from taiga to tundra-steppe vegetation, and coinciding with the intensification of Northern Hemisphere Glaciation ~2.65 Ma. Occurrences of Impatiens pollen indicates frost-free conditions in the region until ~2.7 Ma. Our high resolution analysis of palynological assemblages synchronizes closely with the Marine Isotope record, in general; however, we show that the mid Pliocene warm period was interrupted by short spells of intermittent cooler periods. • Palynological succession ~3.40 to 2.62 Ma indicate biome change in ODP Hole 910C, Yermak Plateau. • Mixed boreal forest dominated until Marine Isotope Stage (MIS) M2 (~3.30 Ma ago). • During 3.21 to 3.02 Ma pollen taxa indicate warmer period obstructed by two cooling phases. • A shift from Taiga to Tundra-steppe vegetation was recorded between ~2.73–2.64 Ma and Impatiens pollen shows frost-free climate. • The intensification before Northern Hemisphere Glaciation was characterised by intermittent short-term interstadials.

Enhanced Arctic Stratification in a Warming Scenario: Evidence From the Mid Pliocene Warm Period

AbstractGlobal warming is most pronounced in the Arctic as evident from the massive sea ice loss during the past few decades. The Mid‐Pliocene Warm Period (MPWP), 3.264 – 3.025 million years ago with similar CO2 levels, is the nearest analogue for understanding the impacts of future global warming. High‐resolution studies of relative nutrient utilization and productivity from the Atlantic‐Arctic Gateway (AAG) can provide insight into the nutrient availability governed by stratification strength during past warm climates. Here, we present relative nutrient utilization and productivity variability during the MPWP using sediments collected during the Ocean Drilling Program (ODP) Leg 151 from Fram Strait, AAG. We find that the relative nutrient utilization was high (low) implying stronger (weaker) stratification during warm (cold) periods during the MPWP. Stronger stratification inhibits the nutrient influx from intermediate water depths into the surface leading to higher utilization of available nutrients. It existed during warm periods likely due to enhanced summer sea ice melt and river discharge from the hinterland. As a consequence, the freshened surface layer could have stored more heat and accelerated the sea ice melt further implying that in the present‐day warm scenario, stronger stratification and upper layer freshening may lead to more sea ice melt in the Arctic Ocean.

Submarine landslides along the Siberian termination of the Lomonosov Ridge, Arctic Ocean

Acoustic and detailed swath bathymetry data revealed a systematic picture of submarine landslides on the Siberian part of Lomonosov Ridge. Whereas numerous studies on mass movement exist along the margin of the Arctic Ocean less is known from central Arctic. A regional survey comprising swath bathymetry, sediment echo sounder and multichannel seismic profiling was performed on the southeastern Lomonosov Ridge. The data provide constraints on the present-day morphology of the Siberian part of Lomonosov Ridge, between 81°–84°N and 140°–146°E. We mapped twelve crescent-shaped escarpments located on both flanks on the crest of Lomonosov Ridge. The escarpments are 2.1 to 10.2 km wide, 1.7 to 8.2 km long and 125 to 851 m high from which 58 to 207 m are occupied by crescent-shaped headscarps. Subbottom data show chaotic reflections within most of the escarpment areas. The unit is overlain by ~110–340 m of semi-coherent parallel reflections. At its bottom the chaotic reflections are limited by a partly eroded high-amplitude reflection sequence that is inclined with <1° basinwards. We find the escarpments to be remnants of submarine landslide events that mobilized 0.09 to 7.58 km3 of sediments between mid Pliocene and mid Miocene. The relatively small amounts of mobilized sediments seem to be typical for the Lomonosov Ridge. The epoch corresponds to the ongoing subsidence of the Lomonosov Ridge below sea level. During that time deposition and the load of sediments changed. We suggest that changes in sediment type preconditioned, and co-occurring earthquakes finally triggered the submarine landslides.

Life history patterns of modern and fossil Mercenaria spp. from warm vs. cold climates

Recent work projects significant increases in sea surface temperature by the end of the 21st century. The biological consequences of such temperature increases are poorly understood. Study designs using a conservation paleobiology approach combined with sclerochronology methods can provide a powerful framework in which to assess these consequences. This study focuses on the ecological and economically important hard clam, Mercenaria, from modern and fossil settings that grew during climates that were warmer than or comparable to today. We compared lifespans and growth rates (von Bertalanffy k) of modern Mercenaria spp. populations to those from the Mid Pliocene Warm Period (MPWP) and early Pleistocene to better understand the influences of temperature on life history. We found that growth rates tend to increase with increasing temperature both through space and time. However, the relationship between lifespan and climate state is not as clear. Further, we observe that mid-to high-latitude individuals seem to be more impacted by changes in climate state than low latitude individuals. We suggest in response to increased seawater temperatures, mid- and high-latitude individuals might experience significant shifts towards faster growth rates whereas low latitude individuals might not see as much change. These findings provide insight to how growth rates and lifespans of Mercenaria might shift in response to future increases in seawater temperature. Understanding such impacts are critical for the development of management strategies and policies for future environmental change.

Genetic and toxinological divergence among populations of Tityus trivittatus Kraepelin, 1898 (Scorpiones: Buthidae) inhabiting Paraguay and Argentina.

Envenoming by scorpions in genus Tityus is a public health problem in Tropical America. One of the most medically significant species is Tityus trivittatus, which is known to occur from southwest Brazil to central-northern and eastern Argentina. In this work, we studied the lethality, composition, antigenicity, and enzymatic activity of venom from a T. trivittatus population found further north in urban areas of eastern Paraguay, where it has caused serious envenomation of children. Our results indicate that the population is of medical importance as it produces a potently toxic venom with an LD50 around 1.19 mg/kg. Venom neutralization in preliminary mouse bioassays was complete when using Brazilian anti-T. serrulatus antivenom but only partial when using Argentinean anti-T. trivittatus antivenom. Venom competitive solid-phase enzyme immunoassays and immunoblotting from Argentinean and Paraguayan T. trivittatus populations indicated that antigenic differences exist across the species range. SDS-PAGE showed variations in type and relative amounts of venom proteins between T. trivitattus samples from Argentina and Paraguay. MALDI-TOF mass spectrometry indicated that while some sodium channel toxins are shared, including β-toxin Tt1g, others are population-specific. Proteolytic activity by zymography and peptide identification through nESI-MS/MS also point out that population-specific proteases may exist in T. trivitattus, which are postulated to be involved in the envenoming process. A time-calibrated molecular phylogeny of mitochondrial COI sequences revealed a significant (8.14%) genetic differentiation between the Argentinean and Paraguayan populations, which appeared to have diverged between the mid Miocene and early Pliocene. Altogether, toxinological and genetic evidence indicate that T. trivitattus populations from Paraguay and Argentina correspond to distinct, unique cryptic species, and suggest that further venom and taxonomic diversity exists in synanthropic southern South American Tityus than previously thought.

Increased Climate Response and Earth System Sensitivity From CCSM4 to CESM2 in Mid‐Pliocene Simulations

AbstractThree new equilibrium mid‐Pliocene (MP) simulations are implemented with the Community Climate System Model version 4 (CCSM4) and Community Earth System Model versions 1.2 (CESM1.2) and 2 (CESM2). All simulations are carried out with the same boundary and forcing conditions following the protocol of Pliocene Model Intercomparison Project Phase 2 (PlioMIP2). These simulations reveal amplified MP climate change relative to the preindustrial going from CCSM4 to CESM2, seen in global and polar averages of surface warming, sea ice reduction in both the Arctic and the Antarctic, and weakened Hadley circulation. The enhanced global mean warming arises from enhanced Earth system sensitivity (ESS) to not only CO2 change but also changes in boundary conditions primarily from vegetation and ice sheets. ESS is amplified by up to 70% in CCSM4 and up to 100% in CESM1.2 and CESM2 relative to the equilibrium climate sensitivity of respective models. Simulations disagree on several climate metrics. Different from CCSM4, both CESM1.2 and CESM2 show reduction of cloud cover, and weakened Walker circulation accompanied by an El Niño‐like mean state of the tropical Pacific in MP simulations relative to the preindustrial. This El Niño‐like mean state is consistent with paleo‐observational sea surface temperatures, suggesting an improvement upon CCSM4. The performances of MP simulations are assessed with a new compilation of observational MP sea surface temperature. The model‐data comparison suggests that CCSM4 is not sensitivity enough to the MP forcings, but CESM2 is likely too sensitive, especially in the tropics.

Message in a bottle: the Mediterranean Sea currents acted as protagonists in shaping the distribution of the sea daffodil (Pancratium maritimum, Amaryllidaceae)

AbstractThe Mediterranean Basin can be considered as a natural laboratory with which to study the effects of sea currents in the dispersal of coastal plant species that use hydrochory. Pancratium maritimum is a perennial geophyte, with a wide distribution along Mediterranean coasts. We aim to provide a timeframe for the origin of the diversification of this plant, to clarify its phylogeographical structure and to investigate the role of currents in the Mediterranean Sea in influencing spatial patterns of its genetic distribution. The phylogeographic history was analysed using 50 populations. A genetic structure analysis and divergence time estimation was performed using plastid sequences. Five haplotypes were detected, of which two were the most abundant; a third was observed in the central Mediterranean, and two rare haplotypes were present in the eastern Mediterranean. The genetic breaks were concordant with the direction of the major Mediterranean currents. The divergence time estimation for the origin of P. maritimum was located at the end of the Neogene (mid Pliocene to mid Pleistocene). We showed the importance of sea currents in the Mediterranean in acting both as a means of dispersal and as a barrier to the distribution and evolution of P. maritimum due to the special adaptations of its seeds.

Pliocene short-term climate changes preserved in continental shallow lacustrine-palustrine carbonates: Western Opache Formation, Atacama Desert, Chile

AbstractMultiple climate proxies indicate episodic changes in moisture levels within an ∼1 Ma duration (early–mid Pliocene) interval. Limestones within the Opache Formation, Calama Basin, Atacama Desert region, Chile, contain evidence for wetter and drier periods on short time scales. Proxies include carbonate lithological changes, paleontology (stromatolites, oncolites, gastropods, ostracods and diatoms), O and C stable isotopes, geochemistry, and mineralogical changes (aragonite, calcite, Mg-calcite, dolomite and gypsum) throughout a 30 m stratigraphic section. Stromatolite fossil cyanobacteria dark and light laminations and mesohaline to hypersaline diatom species suggest Pliocene annual seasonality. Short-term changes between wetter and drier conditions indicate that at least this part of the Atacama region was experiencing relatively rapid early–mid Pliocene climate instability. The predominance of limestone in the Opache Formation, in contrast to the 1500 m of Oligocene-Miocene siliciclastic conglomerates and sandstones, interpreted as arid climate alluvium, that underlie it, indicates a shift from arid or hyperarid climate to a semi-arid climate. Semi-arid conditions promoted limestone deposition in a shallow lacustrine-palustrine environment. In this setting, events such as storms with associated surface water flow, erosion, siliciclastic sand, gravel, and intraclast deposition, coupled with significant biological activity, represent sedimentation during more humid periods in a shallow lacustrine depositional environment. In contrast, limestone characterized by mudcracks, Navicula diatoms, and vadose syndepositional cementation, reflect periods of enhanced evaporation, water shallowing, and episodic desiccation, characteristic of a palustrine depositional system. These facies shifts, in conjunction with geochemical and isotopic proxy evidence, yield a sedimentary record of wetter and drier climate shifts.

Thermochronological insights into the thermotectonic evolution of Mishmi hills across the Dibang Valley, NE Himalayan Syntaxis

Eastern Himalayan Syntaxis (EHS) that forms the northeastern termination of the Himalaya consists of three broad zones; Namche Barwa massif, Siang antiform and Mishmi Hills. The present work provides new in-situ apatite fission track (AFT), zircon (U-Th)/He (ZHe) and 40Ar/39Ar multi-thermochronometric ages across the Dibang valley in the Mishmi hills. The study constrains the structure, emplacement time of major thrusts and initiation of Lesser Himalayan Duplex (LHD). Biotite 40Ar/39Ar ages of the Lohit batholith suggest late Oligocene cooling. ZHe ages indicate late Miocene (~8–9 Ma) foreland directed duplex initiation in the Dibang valley. The AFT cooling ages (~5–3 Ma) suggest LHD continued into Mid Pliocene. Confined track lengths and thermal modelling indicate that the northeastern samples from the study area underwent a phase of rapid exhumation around 10 Ma, followed by slow cooling. It is in contrast to the south-western samples from the Dibang valley that have cooled and uplifted rapidly only after around 4 Ma, due to accelerated phase of LHD. Our 3D thermo-kinematic modelling of the data indicates less mass removal around Hunli than other parts of Dibang valley. The result is in contrast to previously estimated ~16 km uplift near Hunli and mass removal. AFT ages from the Hunli window indicate that the region witnessed modest uplift of ~4–5 km since ca. 4 Ma. Brittle duplexing of the lower LHS at Hunli and Mayodia caused the warping of the overlying litho-units. Hunli duplex alone accommodated ~86% of the total shortening.

Estimating Modern Elevations of Pliocene Shorelines Using a Coupled Ice Sheet‐Earth‐Sea Level Model

AbstractA coupled ice sheet‐Earth‐sea level model is used to estimate the modern elevations of shoreline features that were formed at high sea level stands during the warm mid Pliocene ~3 million years ago. Knowledge of global mean sea level during this period is important as an indicator of possible future ice sheet retreat and sea level rise. However, local shoreline elevations can deviate from the eustatic mean by various geologic processes over the last 3 million years, including glacial isostatic adjustment of the solid Earth and gravitational field due to both Pliocene ice‐cover changes and more recent glacial cycles. Our coupled model includes glacial isostatic adjustment processes and simulates Antarctic ice sheet, global sea level, and solid Earth variations in the warmest mid‐Pliocene and over the last 40,000 years. Global maps of estimated modern elevations of Pliocene shoreline markers are produced for a standard radial profile of Earth viscosity and lithospheric thickness. Results are compared to an earlier study with an uncoupled Earth‐sea level model and a different methodology (Raymo et al., Nature Geoscience, 2011, https://doi.org:/10.1038/ngeo1118). As in that study, Pliocene shoreline elevations diverge significantly from the eustatic value in widespread regions, especially in the vicinity of present and former ice sheets. In some other regions, elevations are close to eustatic. The results emphasize that care should be taken in interpreting elevations of paleo‐shoreline markers.

Using tetraether lipids archived in North Sea Basin sediments to extract North Western European Pliocene continental air temperatures

The Pliocene is often regarded as a suitable analogue for future climate, due to an overall warmer climate (2–3 °C) coupled with atmospheric CO2 concentrations largely similar to present values (∼400 ppmv). Numerous Pliocene sea surface temperature (SST) records are available, however, little is known about climate in the terrestrial realm. Here we generated a Pliocene continental temperature record for Northwestern Europe based on branched glycerol dialkyl glycerol tetraether (brGDGT) membrane lipids stored in a marine sedimentary record from the western Netherlands. The total organic carbon (TOC) content of the sediments and its stable carbon isotopic composition (δ13Corg) indicate a strong transition from primarily marine derived organic matter (OM) during the Pliocene, to predominantly terrestrially derived OM after the transition into the Pleistocene. This trend is supported by the ratio of branched and isoprenoid tetraethers (BIT index). The marine–terrestrial transition indicates a likely change in brGDGT sources in the core, which may complicate the applicability of the brGDGT paleotemperature proxy in this setting. Currently, the application of the brGDGT-based paleothermometer on coastal marine sediments has been hampered by a marine overprint. Here, we propose a method to disentangle terrestrial and marine sources based on the degree of cyclization of tetramethylated brGDGTs (#rings) using a linear mixing model based on the global soil calibration set and a newly developed coastal marine temperature transfer function. Application of this method on our brGDGT record resulted in a ‘corrected’ terrestrial temperature record (MATterr). This latter record indicates that continental temperatures were ∼12–14 °C during the Early Pliocene, and 10.5–12 °C during the Mid Pliocene, confirming other Pliocene pollen based terrestrial temperature estimates from Northern and Central Europe. Furthermore, two colder (Δ 5–7 °C) periods in the Pliocene MATterr record show that the influence of Pliocene glacials reached well into NW Europe.

A Robustness Analysis of CMIP5 Models over the East Asia-Western North Pacific Domain

Abstract The Coupled Model Intercomparison Project (CMIP) is an international community-based infrastructure that supports climate model intercomparison, climate variability, climate prediction, and climate projection. Improving the performance of climate models over East Asia and the western North Pacific has been a challenge for the climate-modeling community. In this paper, we provide a synthesis robustness analysis of the climate models participating in CMIP-Phase 5 (CMIP5). The strengths and weaknesses of the CMIP5 models are assessed from the perspective of climate mean state, interannual variability, past climate change during the mid-Pliocene (MP) and the last millennium, and climate projection. The added values of regional climate models relative to the driving global climate models are also assessed. Although an encouraging increase in credibility and an improvement in the simulation of mean states, interannual variability, and past climate changes are visible in the progression from CMIP3 to CMIP5, some previously noticed biases such as the ridge position of the western North Pacific subtropical high and the associated rainfall bias are still evident in CMIP5 models. Weaknesses are also evident in simulations of the interannual amplitude, such as El Nino-Southern Oscillation (ENSO)-monsoon relationships. Coupled models generally show better results than standalone atmospheric models in simulating both mean states and interannual variability. Multi-model intercomparison indicates significant uncertainties in the future projection of climate change, although precipitation increases consistently across models constrained by the Clausius-Clapeyron relation. Regional ocean-atmosphere coupled models are recommended for the dynamical downscaling of climate change projections over the East Asia-western North Pacific domain.

Cooling and drying in northeast Africa across the Pliocene

Terrestrial records suggest that Northeast Africa experienced drying during the Pliocene; however, these records are often incomplete in time and space, and questions about this shift in climate remain. Here, we use marine sediments from Deep Sea Drilling Project (DSDP) Site 231 in the Gulf of Aden to generate a multi-proxy organic geochemical record of northeast African climate spanning 5.3–2 Ma. This new record provides a regional perspective on climate and serves as context for the fossil record of early hominin evolution. We measured leaf wax carbon (δ13Cwax) and hydrogen (δDwax) isotopic composition and TEX86 (tetraether index of 86 carbons) to investigate past changes in vegetation, aridity, and ocean temperature, respectively. In the earliest Pliocene, we infer warm subsurface ocean temperatures from TEX86, semi-arid conditions on land and extensive C4 grasslands based on δDwax, δ13Cwax and previously published pollen. After 5 Ma, ocean temperatures gradually cooled, and at 4.3 Ma there was a transition to arid conditions on land based on δDwax and pollen. Grasslands yielded to a mid Pliocene landscape of dry shrublands. This drying appears to be an atmospheric response to cooling ocean temperatures, which may reflect changes in tropical ocean circulation, the intensification of Indian Monsoon winds or perhaps other changes associated with Pliocene cooling.

Pollen evidence for Late Pliocene – Early Pleistocene vegetation and climate change in the North Caucasus, North-Western Caspian Region

Pollen and spores have been analysed in deposits of the Akchagylian–Apsheronian in the north-western Caspian Sea region, providing a picture of past vegetation and climate change for the late Pliocene to early Pleistocene. On the basis of pollen assemblages in sediment cores and outcrops from the North Caucasus (the Caucasus Mineral'nyye Vody region, the Tersko-Sunzhensky area and the foothills of Dagestan), climatic fluctuations, and related changes in vegetation can be recognized for the time from 3.6 to 0.8 Ma. The lower Akchagylian is characterized at first by an open landscape dominated by steppe vegetation. In the middle of the lower Akchagylian, the transgression of the palaeo-Caspian spread, and the treeless landscapes of the earliest Akchagylian were replaced by forests with thermophilic relicts. During the middle-upper Akchagylian and Apsheronian periods, the vegetation cover of the North Caucasus gradually changed: forests were replaced with steppe and semi-desert vegetation in response to episodes of aridification, and changes were evident in the structure of the dendroflora. The vegetation of the North Caucasus shows changes consistent with climatic warming at around 3.2 Ma which coincides with a period of warming in the Mediterranean and probable represents the “Mid Pliocene Warm Period”.

Lake George revisited: New evidence for the origin and evolution of a large closed lake, Southern Tablelands, NSW, Australia

Lake George contains the longest continuous sedimentary record of any Australian lake basin, but previous age models are equivocal, particularly for the oldest (pre-Quaternary) part of the record. We have applied a combination of cosmogenic nuclide burial dating, magnetostratigraphy and biostratigraphy to determine the age of the basal (fluvial) unit in the basin, the Gearys Gap Formation. Within the differing resolutions achievable by the three dating techniques, our results show that (i) the Gearys Gap Formation, began accumulating at ca 4 Ma, in the early Pliocene (Zanclean), and (ii) deposition had ceased by ca 3 Ma, in the mid late Pliocene (Piacenzian). Whether the same age control provides an early Pliocene (Zanclean) age for the formation of the lake basin is uncertain. During the Piacenzian, the vegetation at the core site was a wetland community dominated by members of the coral fern family Gleicheniaceae, while the surrounding dryland vegetation was a mix of sclerophyll and temperate rainforest communities, with the latter including trees and shrubs now endemic to New Guinea–New Caledonia and Tasmania. Mean annual rainfall and temperatures are inferred to have been ∼2000–3000 mm, although probably not uniformly distributed throughout the year, and within the mesotherm range (>14°C <20°C), respectively. Unresolved issues are: (1) Does the basal gravel unit predate uplift of the Lake George Range and therefore provide evidence that one of the proposed paleo-spillways of Lake George, that above Geary's Gap, has been elevated up to 100–200 m by neotectonic activity over the past 4 million years? (2) Did a shallow to deepwater lake exist elsewhere in the lake basin during the Pliocene?

The Slanicul de Buzau section, a unit stratotype for the Romanian stage of the Dacian Basin (Plio-Pleistocene, Eastern Paratethys)

Climatic changes cause large paleoenvironmental responses in semi-isolated basins. We analyze here the sedimentary successions of the Dacian Basin (Romania) to evaluate Late Pliocene and Early Pleistocene paleoenvironmental changes through macro- and micropaleontology. These changes are dated by creating a magnetostratigraphic time frame for two long and continuous sections with a combined total thickness of 2850m. The studied succession spans the time interval between 4.7Ma and 1.6Ma and records both the mid Pliocene Warm Period (3.3–2.9Ma) and the onset of large-scale glaciations on the Northern Hemisphere (~2.7Ma). Due to progressive basin infill, the paleoenvironment changes from brackish to fluvio-lacustrine with a major extinction event of lymnocardiine bivalves around 4.15Ma. Rich and dominantly freshwater mollusk and ostracod faunas develop from this moment onwards. Between 3.2Ma and 2.95Ma, the reappearance of lymnocardiines identifies a short moment of higher salinities, the previously identified Plescoi event. In time, this correlates closely to the warmest interval of the Pliocene, and is therefore most likely related to connectivity to the Black Sea during maximum sea-level. After the climatic optimum, deposition continues in a fluvio-deltaic setting with only scarce finds of fauna. Increasing amounts of coarse grained fluvial sediments show a close relationship with the progressive cooling during the Pleistocene.