mid-Pliocene Warm Period Research Articles

Southern African precipitation changes in a warmer world: insights from the PlioMIP2 mid-Pliocene Warm Period (∼3.3–3.0 Ma) ensemble

Near-modern geography and atmospheric carbon dioxide concentrations (∼400 ppmv) coupled with temperatures ∼3°C warmer than the pre-Industrial era are suggested to make the mid-Pliocene warm period (mPWP; 3.264–3.025 Ma) an important near-future climate change analogue. To date, however, few studies explore mPWP hydroclimatic characteristics for the full southern Africa area using proxy records and/or Pliocene Model Intercomparison Project (PlioMIP) climate projections. Hence, we analyse precipitation outputs from 17 PlioMIP phase 2 models to explore southern African mPWP precipitation changes compared to pre-Industrial outputs. Despite diverse inter-model changes, robust signals exist. Most models project annual precipitation declines, up to 0.5 mm/day in the ensemble median. Drying of a similar magnitude for the summer (October-March) and winter (April-September) half-year periods contribute to this change, with models more consistently projecting winter drying. Consequently, the summer and winter precipitation zones (SRZ and WRZ) are projected to shift poleward by ∼1°. For WRZ regions, relatively stable summer precipitation and reduced winter precipitation is projected to result in reduced seasonality. Over SRZ regions, early (late) summer precipitation declines (increases) projected for October–December (January–March) re-organise the summer wet-season to be more concentrated in late summer. Qualitatively good consistency with future projections highlights the mPWPs relevance considering southern Africa’s future climate changes, however, limited model-proxy agreement suggests a need to further (re)assess Pliocene (mPWP) proxy records and/or the PlioMIP2 model boundary conditions towards better capturing mechanisms driving mPWP climatic changes.

Shallow-water clastic carbonates of the southwestern margin of Valdelsa Neogene Basin. Preliminary data on mid-Pliocene Warm Period in Southern Tuscany (Italy)

Shallow-water clastic carbonates of the southwestern margin of Valdelsa Neogene Basin. Preliminary data on mid-Pliocene Warm Period in Southern Tuscany (Italy)

Aerosol uncertainties in tropical precipitation changes for the mid-Pliocene warm period

Abstract. The mid-Pliocene Warm Period (mPWP, 3.3–3.0 Ma) was characterised by an atmospheric CO2 concentration exceeding 400 ppmv with minor changes in continental and orbital configurations. Simulations of this past climate state have improved with newer models but still show some substantial differences from proxy reconstructions. There is little information about atmospheric aerosol concentrations during the Pliocene, but previous work suggests that it could have been quite different from the modern period. Here we apply idealised aerosol scenario experiments to examine the importance of aerosol forcing on mPWP tropical precipitation and the possibility of aerosol uncertainty explaining the mismatch between reconstructions and simulations. The absence of industrial pollutants leads to further warming, especially in the Northern Hemisphere. The Intertropical Convergence Zone (ITCZ) becomes narrower and stronger and shifts northward after removal of anthropogenic aerosols. Though not affecting the location of monsoon domain boundary, removal of anthropogenic aerosol alters the amount of rainfall within the domain, increasing summer rain rate over eastern and southern Asia and western Africa. This work demonstrates that uncertainty in aerosol forcing could be the dominant driver in tropical precipitation changes during the mid-Pliocene: causing larger impacts than the changes in topography and greenhouse gases.

Highly stratified mid-Pliocene Southern Ocean in PlioMIP2

Abstract. During the mid-Pliocene warm period (mPWP; 3.264–3.025 Ma), atmospheric CO2 concentrations were approximately 400 ppm, and the Antarctic Ice Sheet was substantially reduced compared to today. Antarctica is surrounded by the Southern Ocean, which plays a crucial role in the global oceanic circulation and climate regulation. Using results from the Pliocene Model Intercomparison Project (PlioMIP2), we investigate Southern Ocean conditions during the mPWP with respect to the pre-industrial period. We find that the mean sea surface temperature (SST) warming in the Southern Ocean is 2.8 °C, while global mean SST warming is 2.4 °C. The enhanced warming is strongly tied to a dramatic decrease in sea ice cover over the mPWP Southern Ocean. We also see a freshening of the ocean (sub)surface, driven by an increase in precipitation over the Southern Ocean and Antarctica. The warmer and fresher surface leads to a highly stratified Southern Ocean that can be related to weakening of the deep abyssal overturning circulation. Sensitivity simulations show that the decrease in sea ice cover and enhanced warming is largely a consequence of the reduction in the Antarctic Ice Sheet. In addition, the mPWP geographic boundary conditions are responsible for approximately half of the increase in mPWP SST warming, sea ice loss, precipitation, and stratification increase over the Southern Ocean. From these results, we conclude that a strongly reduced Antarctic Ice Sheet during the mPWP has a substantial influence on the state of the Southern Ocean and exacerbates the changes that are induced by a higher CO2 concentration alone. This is relevant for the long-term future of the Southern Ocean, as we expect melting of the western Antarctic Ice Sheet in the future, an effect that is not currently taken into account in future projections by Coupled Model Intercomparison Project (CMIP) ensembles.

Range-Wide Phylogeography and Ecological Niche Modeling Provide Insights into the Evolutionary History of the Mongolian Racerunner (Eremias argus) in Northeast Asia.

The Mongolian racerunner, Eremias argus, is a small lizard endemic to Northeast Asia that can serve as an excellent model for investigating how geography and past climate change have jointly influenced the evolution of biodiversity in this region. To elucidate the processes underlying its diversification and demography, we reconstructed the range-wide phylogeographic pattern and evolutionary trajectory, using phylogenetic, population genetic, landscape genetic, Bayesian phylogeographic reconstruction and ecological niche modeling approaches. Phylogenetic analyses of the mtDNA cyt b gene revealed eight lineages that were unbounded by geographic region. The genetic structure of E. argus was mainly determined by geographic distance. Divergence dating indicated that E. argus and E. brenchleyi diverged during the Mid-Pliocene Warm Period. E. argus was estimated to have coalesced at~0.4351 Ma (Marine Isotope Stage 19). Bayesian phylogeographic diffusion analysis revealed out-of-Inner Mongolia and rapid colonization events from the end of the Last Interglacial to the Last Glacial Maximum, which is consistent with the expanded suitable range of the Last Glacial Maximum. Pre-Last Glacial Maximum growth of population is presented for most lineages of E. argus. The Glacial Maximum contraction model and the previous multiple glacial refugia hypotheses are rejected. This may be due to an increase in the amount of climatically favorable habitats in Northeast Asia. Furthermore, E. argus barbouri most likely represents an invalid taxon. The present study is the first to report a range-wide phylogeography of reptiles over such a large region in Northeast Asia. Our results make a significant contribution towards understanding the biogeography of the entire Northeast Asia.

Evaluating the climatic state of Indian Summer Monsoon during the mid-Pliocene period using CMIP6 model simulations

The Indian Summer Monsoon Rainfall (ISMR) plays a critical role in agriculture, thereby significantly affecting the economy of India. Yet, there is a large spread in the ISMR variability for future projections (by the end of 21st century) as simulated by coupled general circulation models. Gaining insight into the variations of the ISMR during warm periods could enhance our ability to understand ISMR variability in the future. In this study, we have selected the mid-Pliocene warm period from 3.0 to 3.3 million years ago (Ma), which has similar external forcing (orbital parameters) comparable to the end of the 21st century. To evaluate the ISMR mean state during the mid-Pliocene, we have used six available Coupled Model Intercomparison Project phase 6 (CMIP6) model simulations and their multi-model ensemble mean. Our analysis suggests that the ensemble of CMIP6 models is better than individual models in capturing the ISM rainfall patterns and its characteristics for the historical period of 1914–2013. During the mid-Pliocene, we find an increase in the JJAS rainfall over most parts of India in comparison to the pre-industrial period with an increase of 34% in seasonal precipitation. This higher precipitation conditions during the mid-Pliocene is accompanied by thermo dynamical (higher CO2 forcing led to higher tropospheric temperature and higher precipitable water) and dynamical (larger tropospheric temperature gradient between Indian landmass and southern Indian Ocean corresponds to enhanced moisture transport, enhanced low-level cross-equatorial flow and intensified Monsoon Hadley Circulation) aspects.

Oligocene to Pleistocene mudwhelks (Gastropoda: Potamididae, Batillariidae) of the Eurasian Paratethys Sea – Diversity, origins and mangroves

Potamidids (Potamididae, Batillariidae) are today typical inhabitants of coastal mudflats in tropical and warm temperate seas. From the Oligocene to the Early Pleistocene, the Eurasian Paratethys Sea harbored a striking diversity of mudwhelks as well. Based on occurrences from 466 localities covering an area of about 3 million km2 we trace range expansions of potamidids from the Western Tethys and the Proto-Mediterranean Sea into the Eurasian Paratethys Sea, coinciding with global warming trends, such as the Miocene Climate Optimum, the Tortonian Thermal Maximum and the Mid-Pliocene Warm Period. For several species and genera, the stratigraphically oldest occurrences are documented from Rupelian localities south of the Paratethys, which indicates a northward migration over time. A hypothetical refuge along western Africa is hypothesized to explain the 9 Myr long gap between Oligocene and Sarmatian occurrences of Potamides in Europe. Highest potamidid diversities in the Central Paratethys coincided with the Miocene Climate Optimum. The second diversity peak is observed during the Sarmatian when the Volhynian flooding united the Central and Eastern Paratethys in a “Mega-Paratethys”. This event appears to have boosted potamidid diversity at least in the western part of the Paratethyan basin. About 25% of the species belong to Paratethyan lineages, which partly passed the Badenian/Sarmatian Extinction Event.A close relation with mangrove environments is documented for Mesohalina, Ptychopotamides and Terebralia and is assumed for Tiarapirenella. The retreat of mangroves from the Paratethys following the Miocene Climate Optimum is reflected by the loss of large species. Latest Middle Miocene to Late Miocene (Sarmatian) potamidid faunas were dominated by species of Tiaracerithium and Potamides, which were adapted to mudflats devoid of mangroves. Maeotian and Akchagylian potamidid faunas were low diverse, comparatively small and indicate two last phases of immigrations from the Mediterranean region. An influx from the Arctic region during the “Akchagylian marine incursion” can be excluded as explanation for the exotic occurrence of Akchagylian potamidids.

A thicker Antarctic ice stream during the mid-Pliocene warm period

Ice streams regulate most ice mass loss in Antarctica. Determining ice stream response to warmer conditions during the Pliocene could provide insights into their future behaviour, but this is hindered by a poor representation of subglacial topography in ice-sheet models. We address this limitation using a high-resolution model for Dronning Maud Land (East Antarctica). We show that contrary to dynamic thinning of the region’s ice streams following ice-shelf collapse, the largest ice stream, Jutulstraumen, thickens by 700 m despite lying on a retrograde bed slope. We attribute this counterintuitive thickening to a shallower Pliocene subglacial topography and inherent high lateral stresses at its flux gate. These conditions constrict ice drainage and, combined with increased snowfall, allow ice accumulation upstream. Similar stress balances and increased precipitation projections occur across 27% of present-day East Antarctica, and understanding how lateral stresses regulate ice-stream discharge is necessary for accurately assessing Antarctica’s future sea-level rise contribution.

Enhanced summer extreme precipitation over the Asian-African land monsoon regions during past warm periods: A modelling perspective from CESM2

Investigation of summer extreme precipitation during past warm periods may deepen our understanding of its behavior in current and future warmer climates. In this study, we investigate the variation of summer (June-July-August) extreme precipitation and the associated dynamic mechanisms over the Asian and African land monsoon regions during the mid-Pliocene warm period (mPWP) and the Last Interglacial (LIG), using six extreme indices defined by the Expert Team on Climate Change Detection and Indices. Model results indicate that summer extreme precipitation becomes more intense and frequent over the African land monsoon region during both the mPWP and LIG relative to the pre-industrial, together with longer wet spell and shorter dry spell, though the magnitudes are relatively larger during the LIG than the mPWP. Based on the moisture budget equation, the vertical thermodynamic term and the vertical dynamic term largely account for the increased summer precipitation over the African land monsoon region during the mPWP and LIG, respectively. Over the Asian land monsoon region, summer extreme precipitation is also generally intensified and occurs more frequently during the mPWP and LIG, but with large regional differences. The main contributing factors to precipitation change hence vary greatly with sub-regions and periods. Although the modeled variations of extreme precipitation remain hard to be constrained by geological evidence, our results highlight an intensification of extreme precipitation in a warmer world, though the dominating factors (i.e., thermodynamic vs. dynamic) for precipitation change may vary with the external forcing that induces the warmth.

Highly restricted near‐surface permafrost extent during the mid-Pliocene warm period

Accurate understanding of permafrost dynamics is critical for evaluating and mitigating impacts that may arise as permafrost degrades in the future; however, existing projections have large uncertainties. Studies of how permafrost responded historically during Earth's past warm periods are helpful in exploring potential future permafrost behavior and to evaluate the uncertainty of future permafrost change projections. Here, we combine a surface frost index model with outputs from the second phase of the Pliocene Model Intercomparison Project to simulate the near-surface (~3 to 4 m depth) permafrost state in the Northern Hemisphere during the mid-Pliocene warm period (mPWP, ~3.264 to 3.025 Ma). This period shares similarities with the projected future climate. Constrained by proxy-based surface air temperature records, our simulations demonstrate that near-surface permafrost was highly spatially restricted during the mPWP and was 93 ± 3% smaller than the preindustrial extent. Near-surface permafrost was present only in the eastern Siberian uplands, Canadian high Arctic Archipelago, and northernmost Greenland. The simulations are similar to near-surface permafrost changes projected for the end of this century under the SSP5-8.5 scenario and provide a perspective on the potential permafrost behavior that may be expected in a warmer world.

Response of East Asian summer monsoon to precession change during the mid-Pliocene warm period

Numerous palaeoclimatic records have shown that precession plays a dominant role in the Asian monsoon precipitation. However, the impact and mechanism of precession change on the East Asian summer monsoon (EASM) under high CO2 conditions have yet to be studied. The mid-Pliocene (∼3.3–3.0 Ma) was the most recent warm interval during which atmospheric CO2 concentrations were similar to the present level of ∼400 ppmv. Therefore, it is often regarded as an analog for a near-future climate scenario. Here, the influence of precession change on EASM is investigated through numerical climate modeling using the mid-Pliocene as a test case. The results show that from the minimum to maximum of the precession, the summer temperature maximum zone shifted northward from ∼30°N to ∼45°N and the summer precipitation increased by ∼60% over the mainland East Asia. The simulations also show that the top-of-atmosphere insolation increased significantly in the Northern Hemisphere summer over mid- and high-latitudes and increased slightly over low latitudes from the precession minimum to maximum, leading to a substantial increase in the thermal contrast between the mainland East Asia and the equatorial western North Pacific. In this scenario, the western North Pacific subtropical high intensified and expanded, and the ITCZ migrated northward over South and Southeast Asia and was shifted southward over the area between the 110°E and 130°E, thereby leading to the rain belt penetration into northern China.

Amplified surface warming in the south-west Pacific during the mid-Pliocene (3.3–3.0 Ma) and future implications

Abstract. Based on Nationally Determined Contributions concurrent with Shared Socioeconomic Pathways (SSPs) 2-4.5, the IPCC predicts global warming of 2.1–3.5 ∘C (very likely range 10–90th percentile) by 2100 CE. However, global average temperature is a poor indicator of regional warming and global climate models (GCMs) require validation with instrumental or proxy data from geological archives to assess their ability to simulate regional ocean and atmospheric circulation, and thus, to evaluate their performance for regional climate projections. The south-west Pacific is a region that performs poorly when GCMs are evaluated against instrumental observations. The New Zealand Earth System Model (NZESM) was developed from the United Kingdom Earth System Model (UKESM) to better understand south-west Pacific response to global change, by including a nested ocean grid in the south-west Pacific with 80 % greater horizontal resolution than the global-scale host. Here, we reconstruct regional south-west Pacific sea-surface temperatures (SSTs) for the mid-Pliocene warm period (mPWP; 3.3–3.0 Ma), which has been widely considered a past analogue with an equilibrium surface temperature response of +3 ∘C to an atmospheric CO2 concentration of ∼350–400 ppm, in order to assess the warming distribution in the south-west Pacific. This study presents proxy SSTs from seven deep sea sediment cores distributed across the south-west Pacific. Our reconstructed SSTs are derived from molecular biomarkers preserved in the sediment – alkenones (i.e. U37K′ index) and isoprenoid glycerol dialkyl glycerol tetraethers (i.e. TEX86 index) – and are compared with SSTs reconstructed from the Last Interglacial (125 ka), Pliocene Model Intercomparison Project (PlioMIP) outputs and transient climate model projections (NZESM and UKESM) of low- to high-range SSPs for 2090–2099 CE. Mean interglacial equilibrium SSTs during the mPWP for the south-west Pacific sites were on average 4.2 ∘C (1.8–6.1 ∘C likely range) above pre-industrial temperatures and show good agreement with model outputs from NZESM and UKESM under mid-range SSP 2–4.6 conditions. These results highlight that not only is the mPWP an appropriate analogue when considering future temperature change in the centuries to come, but they also demonstrate that the south-west Pacific region will experience warming that exceeds that of the global mean if atmospheric CO2 remains above 350 ppm.

Geochemical characterization evidence for the climate variability of the Mid-Pliocene warm period in the Nihewan Basin, North China

The mid-Pliocene warm period (mPWP) is regarded as an important geological analogue for predicting future climate characteristics and trends, due to its similar atmospheric CO2 concentration to that of the modern period. Within a chronologic framework provided by magnetostratigraphy, we analyzed the carbonate δ18O and geochemical element contents of 243 sediment samples from the NHA drill core in the Nihewan Basin, and combined them with grain size and magnetic susceptibility records. Our results revealed the paleoclimatic characteristics in the Nihewan Basin during 3.66–2.89 Ma for the first time. The interval of 3.58–3.31 Ma had the warmest and most stable climate during this interval, with low-amplitude fluctuations in all proxies, and with the following general characteristics: δ18O < −8‰, CIA > 40%, Rb/Sr > 0.3, ∑REE > 180 μg/g, and TiO2 > 0.7%). The climate remained warm overall during 3.31–3.10 Ma, but there were three pronounced cold events (at ∼3.30 Ma, ∼3.23 Ma, and ∼ 3.14 Ma) with the following general characteristics: δ18O > −7‰, CIA < 35%, Rb/Sr < 0.2, ∑REE < 160 μg/g, TiO2 < 0.6%). These events are correlative with increases in global ice volume, corresponding respectively to Marine Isotope Stage (MIS) M2, KM6, and KM2. The climate cooled substantially after 3.10 Ma, and most of the proxy index values were close to those during the three previous cold events. We ascribe this to increases in global ice volume and the strengthening of the East Asian winter monsoon.

Causes of the weak emergent constraint on climate sensitivity at the Last Glacial Maximum

Abstract. The use of paleoclimates to constrain the equilibrium climate sensitivity (ECS) has seen a growing interest. In particular, the Last Glacial Maximum (LGM) and the mid-Pliocene warm period have been used in emergent-constraint approaches using simulations from the Paleoclimate Modelling Intercomparison Project (PMIP). Despite lower uncertainties regarding geological proxy data for the LGM in comparison with the Pliocene, the robustness of the emergent constraint between LGM temperature and ECS is weaker at both global and regional scales. Here, we investigate the climate of the LGM in models through different PMIP generations and how various factors in the atmosphere, ocean, land surface and cryosphere contribute to the spread of the model ensemble. Certain factors have a large impact on an emergent constraint, such as state dependency in climate feedbacks or model dependency on ice sheet forcing. Other factors, such as models being out of energetic balance and sea surface temperature not responding below −1.8 ∘C in polar regions, have a limited influence. We quantify some of the contributions and find that they mostly have extratropical origins. Contrary to what has previously been suggested, from a statistical point of view, the PMIP model generations do not differ substantially. Moreover, we show that the lack of high- or low-ECS models in the ensembles critically limits the strength and reliability of the emergent constraints. Single-model ensembles may be promising tools for the future of LGM emergent constraint, as they permit a large range of ECS and reduce the noise from inter-model structural issues. Finally, we provide recommendations for a paleo-based emergent constraint and notably which paleoclimate is ideal for such an approach.

Paleoecology and evolutionary response of planktonic foraminifera to the mid-Pliocene Warm Period and Plio-Pleistocene bipolar ice sheet expansion

Abstract. The Pliocene-Recent is associated with many important climatic and paleoceanographic changes, which have shaped the biotic and abiotic nature of the modern world. The closure of the Central American Seaway and the development and intensification of Northern Hemisphere ice sheets had profound global impacts on the latitudinal and vertical structure of the oceans, triggering the extinction and radiation of many marine groups. In particular, marine calcifying planktonic foraminifera, which are highly sensitive to water column structure, exhibited a series of extinctions as global temperatures fell. By analyzing high-resolution (∼ 5 kyr) sedimentary records from the Eastern Equatorial Pacific Ocean, complemented with global records from the novel Triton dataset, we document the biotic changes in this microfossil group, within which three species displayed isochronous co-extinction, and species with cold-water affinity increased in dominance as meridional temperature gradients steepened. We suggest that these changes were associated with the terminal stages of the closure of the Central American Seaway, where following the sustained warmth of the mid-Pliocene Warm Period, bipolar ice sheet expansion initiated a world in which cold- and deep-dwelling species became increasingly more successful. Such global-scale paleoecological and macroevolutionary variations between the Pliocene and the modern icehouse climate would suggest significant deviations from pre-industrial baselines within modern and future marine plankton communities as anthropogenic climate forcing continues.

Unraveling the mechanisms and implications of a stronger mid-Pliocene Atlantic Meridional Overturning Circulation (AMOC) in PlioMIP2

Abstract. The mid-Pliocene warm period (3.264–3.025 Ma) is the most recent geological period in which the atmospheric CO2 concentration was approximately equal to the concentration we measure today (ca. 400 ppm). Sea surface temperature (SST) proxies indicate above-average warming over the North Atlantic in the mid-Pliocene with respect to the pre-industrial period, which may be linked to an intensified Atlantic Meridional Overturning Circulation (AMOC). Earlier results from the Pliocene Model Intercomparison Project Phase 2 (PlioMIP2) show that the ensemble simulates a stronger AMOC in the mid-Pliocene than in the pre-industrial. However, no consistent relationship between the stronger mid-Pliocene AMOC and either the Atlantic northward ocean heat transport (OHT) or average North Atlantic SSTs has been found. In this study, we look further into the drivers and consequences of a stronger AMOC in mid-Pliocene compared to pre-industrial simulations in PlioMIP2. We find that all model simulations with a closed Bering Strait and Canadian Archipelago show reduced freshwater transport from the Arctic Ocean into the North Atlantic. This contributes to an increase in salinity in the subpolar North Atlantic and Labrador Sea that can be linked to the stronger AMOC in the mid-Pliocene. To investigate the dynamics behind the ensemble's variable response of the total Atlantic OHT to the stronger AMOC, we separate the Atlantic OHT into two components associated with either the overturning circulation or the wind-driven gyre circulation. While the ensemble mean of the overturning component is increased significantly in magnitude in the mid-Pliocene, it is partly compensated by a reduction in the gyre component in the northern subtropical gyre region. This indicates that the lack of relationship between the total OHT and AMOC is due to changes in OHT by the subtropical gyre. The overturning and gyre components should therefore be considered separately to gain a more complete understanding of the OHT response to a stronger mid-Pliocene AMOC. In addition, we show that the AMOC exerts a stronger influence on North Atlantic SSTs in the mid-Pliocene than in the pre-industrial, providing a possible explanation for the improved agreement of the PlioMIP2 ensemble mean SSTs with reconstructions in the North Atlantic.

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).

A proxy-model comparison for mid-Pliocene warm period hydroclimate in the Southwestern US

Hydroclimate proxy reconstructions and paleoclimate models of the mid-Pliocene warm period provide insight into the forcings and feedbacks that impacted regional hydroclimate in a world moderately warmer than present. However, in the Southwestern United States, there is discord between proxies and climate models: proxy data have been interpreted to indicate much wetter conditions, while the most recent generation of mid-Pliocene warm period climate models simulates drying. We use a water and energy balance framework to directly compare paleoclimate model output to a refined compilation of proxies recording the presence and areal extent of mid-Pliocene lakes. Within this framework, we quantify uncertainties in the proxy system model parameters and in the interpretation of available proxy records. We find that despite these significant uncertainties, most paleoclimate models simulate a regional balance between precipitation and evaporative demand that could not have sustained the extent of recorded lakes from this time. Moreover, the extensive lakes included as boundary conditions in mid-Pliocene warm period climate models are inconsistent with the regional climate simulated by those same models. This study identifies and quantifies the remaining unknowns in our picture of regional mid-Pliocene warm period hydroclimate, with implications for analyses of climate dynamics during this time.

Mid-Pliocene El Niño/Southern Oscillation suppressed by Pacific intertropical convergence zone shift

The El Niño/Southern Oscillation (ENSO), the dominant driver of year-to-year climate variability in the equatorial Pacific Ocean, impacts climate pattern across the globe. However, the response of the ENSO system to past and potential future temperature increases is not fully understood. Here we investigate ENSO variability in the warmer climate of the mid-Pliocene (~3.0–3.3 Ma), when surface temperatures were ~2–3 °C above modern values, in a large ensemble of climate models—the Pliocene Model Intercomparison Project. We show that the ensemble consistently suggests a weakening of ENSO variability, with a mean reduction of 25% (±16%). We further show that shifts in the equatorial Pacific mean state cannot fully explain these changes. Instead, ENSO was suppressed by a series of off-equatorial processes triggered by a northward displacement of the Pacific intertropical convergence zone: weakened convective feedback and intensified Southern Hemisphere circulation, which inhibit various processes that initiate ENSO. The connection between the climatological intertropical convergence zone position and ENSO we find in the past is expected to operate in our warming world with important ramifications for ENSO variability. Suppressed El Niño/Southern Oscillation variability during the mid-Pliocene Warm Period was caused mainly by a northward displacement of the intertropical convergence zone, according to an analysis of a large ensemble of climate model simulations.

Intensification of Asian dust storms during the Mid-Pliocene Warm Period (3.25–2.96 Ma) documented in a sediment core from the South China Sea

Dust storms are an important component of the global climate system. At the same time, they also bear a risk for human health by causing pulmonary diseases. Today, East Asian dust storms account for as much as half of the global dust emissions and temporarily affect highly populated areas. Therefore, understanding their mechanisms and predicting their evolution under warmer near-future climate conditions is of major interest. The mid-Pliocene Warm Period (mPWP; 3.264–3.025 Ma) is considered one of the best analogues from the past for anthropogenic climate change. Consequently, understanding the climate dynamics and associated environmental change during the mPWP can help with predicting the environmental effects of warmer-than-present climates. In order to reconstruct Asian dust storm evolution during the mPWP we have analyzed a sediment core from the northern South China Sea (SCS) for its elemental composition, grain-size variations and radiogenic isotope signature for the interval spanning from 3.69 to 2.96 Ma. We show that shortly after the first strong northern hemisphere glaciation (Marine Isotope Stage [MIS] M2; 3.25 Ma) atmospherically transported dust appeared in the northern SCS and this dust deposition prevailed throughout the mPWP. Atmospheric dust input further intensified with the onset of the MIS KM2 glaciation at 3.15 Ma, with distinct and strong dust storms occurring periodically from that time onwards. The increase in atmospherically transported dust can be attributed to the cooling and drying of interior Asia over the course of the mPWP along with an intensification of the East Asian Winter Monsoon and a potential southward shift of the westerlies.