Pliocene Warm Period Research Articles

Forest or grassland? Late Pliocene vegetation and climate of the Yushe Basin, Northern China

The Pliocene warm period is regarded as an analogue of future warming, and quantitative reconstruction of palaeovegetation and palaeoclimate during this period is helpful for predicting vegetation and climate changes in the future. Here, we quantitatively reconstructed the late Pliocene vegetation and climate based on phytolith assemblages from the Upper Zhangcun Formation in the Yushe Basin, Northern China. The results show that the vegetation was dominated by grasses with few trees, which conflicts with the pollen assemblage results. The possible reason for this contradiction is that phytoliths tend to mirror local, shoreline vegetation (grasses with few aquatic plants), while pollen tend to mirror both local and regional vegetation (trees in surrounding mountains and piedmont, grasses on lakeshores and aquatic plants in wetlands) in a small structurally confined lake. The phytolith-based quantitative reconstruction of mean annual precipitation (812–1673 mm) and warm season precipitation (417–1197 mm) provides values that are higher than those at present, revealing an increase in Asian monsoon rainfall during the late Pliocene, which is consistent with the pollen results, although the reconstructed vegetation is different. This study highlights the usefulness of phytoliths in reconstructing Cenozoic vegetation and climate and underlines the importance of landforms in determining phytolith and pollen assemblages in sediments.

How changing the height of the Antarctic ice sheet affects global climate: a mid-Pliocene case study

Abstract. Warming-induced topographic changes of the East Antarctic ice sheet (EAIS) during the Pliocene warm period could have a significant influence on the climate. However, how large changes in the EAIS height could theoretically affect global climate have yet to be studied. Here, the influence of possible height changes of the EAIS on climate over the East Antarctic ice sheet region versus the rest of the globe is investigated through numerical climate modeling using the Pliocene as a test case. As expected, the investigation reveals that the reduction of ice sheet height leads to a warmer and wetter East Antarctica. However, unintuitively, both the surface air temperature and the sea surface temperature decrease over the rest of the globe. These temperature changes result from the higher air pressure over Antarctica and the corresponding lower air pressure over extra-Antarctic regions with the reduction of EAIS height. This topography effect is further confirmed by energy balance analyses. These findings could provide insights into future climate change caused by warming-induced height reduction of the Antarctic ice sheet.

Nature and origin of variations in pelagic carbonate production in the tropical ocean since the mid-Miocene (ODP Site 927)

Abstract. Marine plankton is an important component of the global carbon cycle. Whereas the production and seafloor export of organic carbon produced by the plankton, the biological pump, has received much attention, the long-term variability in plankton calcification, controlling the carbonate counter pump, remains less well understood. However, it has been shown that changes in pelagic calcification (biological compensation) could affect the ocean's buffering capacity and thus regulate global carbon budget on geological timescales. Here we use Neogene pelagic sediments deposited on the Ceara Rise in the tropical Atlantic to characterize the variability in pelagic carbonate production with a focus on warm climates. A re-evaluation of published records of carbonate accumulation at the Ceara Rise reveals a systematic increase in sedimentation rates since the late Miocene, but the carbonate accumulation rate does not show a clear trend. Instead, we observe substantial orbital timescale variability in carbonate accumulation, combined with a trend towards less carbonate on average at sites located below 4 km, likely due to the effect of carbonate dissolution. To evaluate long-term changes against possible orbital-scale variability, we generated new high-resolution records of carbonate accumulation rate at Ocean Drilling Program (ODP) Site 927 across two Quaternary interglacials (MIS 5 and MIS 9), the Pliocene warm period (MIS KM5) and the Miocene Climatic Optimum (MCO). We observe that the highest carbonate accumulation rates occurred during the Pliocene but that each of the studied intervals was characterized by large-magnitude orbital variability. Prominent variations in carbonate accumulation prior to the Quaternary preservation cycles appear to follow Earth obliquity and eccentricity. These results imply that pelagic carbonate accumulation in the tropical ocean, buffered from large temperature changes, varied on orbital timescales. The magnitude of the orbital-scale variability was similar or even higher than the long-term mean differences among the studied intervals. Since preservation can be excluded as a driver of these changes prior to the Quaternary, the observed variations must reflect changes in the export flux of pelagic biogenic carbonate. We conclude that the overall carbonate production by pelagic calcifiers responded to local changes in light, temperature, and nutrients delivered by upwelling, which followed long orbital cycles, as well as to long-term shifts in climate and/or ocean chemistry. The inferred changes on both timescales were sufficiently large such that when extrapolated on a global scale, they could have played a role in the regulation of the carbon cycle and global climate evolution during the transition from the Miocene warm climates into the Quaternary icehouse.

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).

Paleoclimatic and palaeoceanographic changes coupled to the Panama Isthmus closing (13–4 Ma) using organic proxies

This study reconstructs the climatic and oceanographic changes from 13 to 4 Ma at Ocean Drilling Program (ODP) Sites 999 (Caribbean) and 1241 (East Pacific) during Panama Isthmus closure. We used lipid biomarkers as marine production indicators and organic proxies (U37K´ and TEX86H) to estimate ocean surface and thermocline temperatures. Enhanced terrestrial input during the first 3 Ma of the record, possibly coupled to tectonic processes, may have triggered higher surface productivity at both sides of the Isthmus. Even though marine production is generally higher in the tropical Pacific, a peak in alkenone production at 12.4–10.6 Ma indicates unrestricted inflow of nutrient-rich waters into the Caribbean. Higher production is observed during the global late Miocene biogenic bloom (LMBB 8–4.5 Ma) coupled to enhanced nutrients from terrestrial sources and/or upwelling. We find a good correspondence between U37K´ and modern sea surface temperature (SST). The TEX86H is a good tracer for thermocline values, however, the deeper Thaumarchaeota distribution in the Caribbean may result in an underestimation of absolute temperatures at ODP Site 999. None the less, temperature records at both Sites show similar trends coupled to global climate dynamics, therefore Isthmus build up did not significantly affect surface or thermocline temperatures at a regional level. Globally reported decreasing temperatures during the late Miocene and early Pliocene coupled to decreasing CO2 levels are registered at both Sites down to at least 200 m. The late Miocene warm period (LMWP 9.5–7 Ma), late Miocene cold period (LMC 7–5.4 Ma) and the Pliocene warm period (PWP 4–3.5 Ma) are reflected by our temperature records confirming global climate is the main driver of temperature evolution in the study area. The reconstructed temperatures are mainly coupled to atmospheric forcing in the Caribbean, with a deviation possibly due to inflow of colder Pacific intermediate waters. While at ODP Site 1241 temperatures are mainly controlled by global climate, the Site also reflects changes in the water column as it migrates interacting with the complex current structure of the tropical Pacific. Decoupled temperature patterns at both Sites are related with differential changes in water column structure partially masking the climatic signal. Therefore, we could establish that while tectonic processes and related terrestrial input increases as well as upwelling control production and water column structure, climate in the study area remained tuned to global patterns regardless of Isthmus closure stage.

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.

Global warming-induced Asian hydrological climate transition across the Miocene\u2013Pliocene boundary

Across the Miocene–Pliocene boundary (MPB; 5.3 million years ago, Ma), late Miocene cooling gave way to the early-to-middle Pliocene Warm Period. This transition, across which atmospheric CO2 concentrations increased to levels similar to present, holds potential for deciphering regional climate responses in Asia—currently home to more than half of the world’s population— to global climate change. Here we find that CO2-induced MPB warming both increased summer monsoon moisture transport over East Asia, and enhanced aridification over large parts of Central Asia by increasing evaporation, based on integration of our ~1–2-thousand-year (kyr) resolution summer monsoon records from the Chinese Loess Plateau aeolian red clay with existing terrestrial records, land-sea correlations, and climate model simulations. Our results offer palaeoclimate-based support for ‘wet-gets-wetter and dry-gets-drier’ projections of future regional hydroclimate responses to sustained anthropogenic forcing. Moreover, our high-resolution monsoon records reveal a dynamic response to eccentricity modulation of solar insolation, with predominant 405-kyr and ~100-kyr periodicities between 8.1 and 3.4 Ma.

Geological Oceanography of the Pliocene Warm Period: A Review with Predictions on the Future of Global Warming

Atmospheric carbon dioxide reached a record concentration of 419 parts per million in May 2021, 50% higher than preindustrial levels at 280 parts per million. The rise of CO2 as a heat-trapping gas is the principal barometer tracking global warming attributed to a global average increase of 1.2 °C over the last 250 years. Ongoing global warming is expected to perturb extreme weather events such as tropical cyclones (hurricanes/typhoons), strengthened by elevated sea-surface temperatures. The melting of polar ice caps in Antarctica and Greenland also is expected to result in rising sea levels through the rest of this century. Various proxies for the estimate of long-term change in sea-surface temperatures (SSTs) are available through geological oceanography, which relies on the recovery of deep-sea cores for the study of sediments enriched in temperature-sensitive planktonic foraminifera and other algal residues. The Pliocene Warm Period occurred between ~4.5 and 3.0 million years ago, when sea level and average global temperatures were higher than today, and it is widely regarded as a predictive analog to the future impact of climate change. This work reviews some of the extensive literature on the geological oceanography of the Pliocene Warm Period together with a summary of land-based studies in paleotempestology focused on coastal boulder deposits (CBDs) and coastal outwash deposits (CODs) from the margin of the Pacific basin and parts of the North Atlantic basin. Ranging in age from the Pliocene through the Holocene, the values of such deposits serve as fixed geophysical markers, against which the micro-fossil record for the Pliocene Warm Period may be compared, as a registry of storm events from Pliocene and post-Pliocene times.

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.

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.

Combined high- and low-latitude forcing of East Asian monsoon precipitation variability in the Pliocene warm period.

East Asian monsoon variability in the Pliocene warm world has not been sufficiently studied because of the lack of direct records. We present a high-resolution precipitation record from Pliocene fluvial-lacustrine sequences in the Weihe Basin, Central China, a region sensitive to the East Asian monsoon. The record shows an abrupt monsoon shift at ~4.2 million years ago, interpreted as the result of high-latitude cooling, with an extratropical temperature decrease across a critical threshold. The precipitation time series exhibits a pronounced ~100-thousand year periodicity and the presence of precession and half-precession cycles, which suggest low-latitude forcing. The synchronous phase but mismatched amplitudes of the East Asian monsoon precipitation proxy and eccentricity suggest a nonlinear but sensitive precipitation response to temperature forcing in the Pliocene warm world. These observations highlight the role of high- and low-latitude forcing of East Asian monsoon variations on tectonic and orbital time scales.

Polar amplification of Pliocene climate by elevated trace gas radiative forcing

Warm periods in Earth's history offer opportunities to understand the dynamics of the Earth system under conditions that are similar to those expected in the near future. The Middle Pliocene warm period (MPWP), from 3.3 to 3.0 My B.P, is the most recent time when atmospheric CO2 levels were as high as today. However, climate model simulations of the Pliocene underestimate high-latitude warming that has been reconstructed from fossil pollen samples and other geological archives. One possible reason for this is that enhanced non-CO2 trace gas radiative forcing during the Pliocene, including from methane (CH4), has not been included in modeling. We use a suite of terrestrial biogeochemistry models forced with MPWP climate model simulations from four different climate models to produce a comprehensive reconstruction of the MPWP CH4 cycle, including uncertainty. We simulate an atmospheric CH4 mixing ratio of 1,000 to 1,200 ppbv, which in combination with estimates of radiative forcing from N2O and O3, contributes a non-CO2 radiative forcing of 0.9 [Formula: see text] (range 0.6 to 1.1), which is 43% (range 36 to 56%) of the CO2 radiative forcing used in MPWP climate simulations. This additional forcing would cause a global surface temperature increase of 0.6 to 1.0 °C, with amplified changes at high latitudes, improving agreement with geological evidence of Middle Pliocene climate. We conclude that natural trace gas feedbacks are critical for interpreting climate warmth during the Pliocene and potentially many other warm phases of the Cenezoic. These results also imply that using Pliocene CO2 and temperature reconstructions alone may lead to overestimates of the fast or Charney climate sensitivity.

Dampened El Niño in the Early Pliocene Warm Period

AbstractEl Niño‐Southern Oscillation (ENSO) is the strongest mode of interannual climate variability, and its predicted response to anthropogenic climate change remains unclear. Determining ENSO's sensitivity to climatic mean state and the strength of positive and negative feedbacks, notably the thermocline feedback, will help constrain its future behavior. To this end, we collected ENSO proxy data from the early and mid‐Pliocene, a time during which tropical Pacific zonal and vertical temperature gradients were much lower than today. We found that El Niño events had a reduced amplitude throughout the early Pliocene, compared to the late Holocene. By the mid‐Pliocene, El Niño amplitude was variable, sometimes reduced and sometimes similar to the late Holocene. This trend in Pliocene ENSO amplitude mirrors the long‐term strengthening of zonal and vertical temperature gradients and verifies model results showing dampened ENSO under reduced gradients due to a weaker thermocline feedback.

Vertical and horizontal distribution of sedimentary facies and hydromorphic paleosols around paleo-lake in the Pliocene sediments in southwest Japan

The collaborative study between descriptive paleopedology and sedimentology for the Pliocene sediments in southwest Japan clarified the paleo-groundwater table at lake margins and the change of the paleoclimatic conditions in the coastal region of eastern Asia during the Pliocene period (3–4 Ma). Some hydromorphic paleosols were formed in the proximal floodplain and the natural levee, which are generally located in a high-topographic position, and these paleosols finally reached a similar maturity to ultisol and inceptisol. The vertical variation of the sedimentary facies suggests the increased sedimentation rates and increased volume of sediment supply during this period. The stratigraphic distribution of the hydromorphic paleosols in the Pliocene formation implies the rising of the paleo-groundwater table and to become considerably fluctuating of the paleo-groundwater table. The temporal change in weathering conditions implies that precipitation increased during the middle Pliocene warm period.

Intense chemical weathering in southwest Japan during the Pliocene warm period

Bulk chemical composition and mineral composition of the Pliocene sediments in southwest Japan reveal the effects of source rock compositions and grain sizes, as well as the relationship between sedimentary environments and the degree of chemical weathering in the Pliocene warm period. A wide variation in the degree of chemical weathering, source rock compositions and grain sizes was observed with vertical and spatial changes in the sedimentary environment. Coarse-grained sediments, deposited in sandy channels and their floodplains, indicate a lower but wide range of CIA values. This result suggests that the degree of chemical weathering can be modified by changes in grain size due to hydrologic processes. In contrast, stagnant water sediments, composed of homogeneous fine-grained sediments, display a wide variety of REE compositions and Al2O3/SiO2 ratios mainly caused by variation in source rock compositions and grain sizes. However, the CIA values of the stagnant water sediments are over 90, such that these sediments display a tight cluster near the Al2O3 apex on the Al2O3-(CaO + Na2O)-K2O ternary diagram. This study demonstrates CIA values are generally above 90, which is due to the increased leaching of Ca, Na, and K with exposure to under intense chemical weathering conditions even if the source rocks and grain sizes are variable. Regardless of the wide variety of source rock compositions and grain sizes, REE and kaolinite-rich clay mineral concentrations in these sediments are indicative of the intense weathering conditions that prevailed in the Pliocene period (3–4 Ma) in southwest Japan.

100‐kyr Paced Climate Change in the Pliocene Warm Period, Southwest Pacific

AbstractThe mid to late Pliocene (~4.2–2.8 Ma.) represents an experiment in climate sensitivity to orbital pacing in which nearly all continental ice was confined to the Southern Hemisphere. Most studies have emphasized the dominant role of obliquity in determining changes in ice volume and temperature at this time, although most records come from the Northern Hemisphere, instead of the hemisphere where the bulk of ice resided. We present the first orbitally‐resolved, mid to late Pliocene Southern Hemisphere paired records of surface and subsurface variability from two deep ocean archives from the Southwest Pacific Ocean (Sites 594 and 1125). These records indicate dominance of low frequencies centered at ~100 kyr for this time period. Because these signatures extend coherently and synchronously from middepth water properties (δ13C, δ18O of benthic foraminifera), which have their chemistry set in the subantarctic belt, to the surface (alkenone‐derived surface temperature estimates, color reflectance, and magnetic susceptibility), we infer that the fingerprint of the ~100‐kyr cycles must have extended over a large region of the Southern Hemisphere. We propose that nonlinearities in climate response to precessional forcing—most likely through ice sheet and/or carbon cycle behavior—generated the observed low frequency. A review of published mid to late Pliocene time series suggests that the ~100‐kyr pacing may be a widespread phenomenon and that major approximately 100‐kyr excursions in Pliocene climate were an important overlay to the underlying 41‐kyr glacial‐interglacial rhythm. These results caution against uncritical use of existing Pliocene isotopic templates to construct high‐resolution age models.

Reexamination of the Late Pliocene Climate over China Using a 25-km Resolution General Circulation Model

Simulations of past warm climate provide an opportunity to better understand how the climate system may respond to increased greenhouse gas emissions. Using the ~25-km-resolution Community Atmosphere Model, version 4 (CAM4), we examine climate change over China in the Late Pliocene warm period (3.264–3.025 Ma) and further explore the influences of different sea surface temperature (SST) forcings and model horizontal resolutions. Initial evaluation shows that the high-resolution CAM4 performs well in capturing the climatological distribution of present-day temperature, precipitation, and low-level monsoon circulations over China. Based on the standard Pliocene Research, Interpretation and Synoptic Mapping (version 4; PRISM4) boundary conditions, CAM4 predicts an increase of annual mean temperature by ~0.5°C over China in the Late Pliocene relative to the preindustrial era, with the greatest warming in northwest China but cooling in southwest China. Enhanced annual mean precipitation is observed in the Late Pliocene over most of China except for northwest China where precipitation is decreased. The East Asian summer (winter) monsoon is intensified (weakened) in the Late Pliocene as suggested by geological evidence, which is attributed to the enhanced (reduced) land–sea thermal contrast. The East Asian monsoon domain exhibits a northwestward expansion in the Late Pliocene, especially over the Tibetan Plateau. Additionally, our results indicate that the modeled climate change is sensitive to the Late Pliocene SST forcings and model resolution. Particularly, different SST forcings [PRISM4-based vs Pliocene Model Intercomparison Project (PlioMIP)-based SSTs] affect the modeled phase change of summer monsoon and the associated precipitation change, while model resolution (~25 vs 400 km) mainly impacts precipitation change.

Investigating Sensitivity of East Asian Monsoon to Orbital Forcing During the Late Pliocene Warm Period

AbstractThe Late Pliocene climate (3.264–3.025 Ma) is thought to be relatively warm and stable compared with the Pleistocene, but with clear orbital‐scale climate variability. Using the Community Earth System Model, we investigate the sensitivity of East Asian monsoon to realistic orbital forcing during the Late Pliocene. Initial evaluation shows that the Community Earth System Model broadly captures modern East Asian monsoon climatology and reproduces the reconstructed stronger (weaker) East Asian summer (winter) monsoon in the Late Pliocene under the PRISM3D (Pliocene Research, Interpretation and Synoptic Mapping) boundary conditions that use present‐day orbital configurations. Sensitivity experiments indicate that summer and winter temperatures averaged over the East Asia continent remain higher for different orbital configurations in the Late Pliocene than the preindustrial, but with different warming magnitude. Variation of East Asian summer monsoon is significantly modulated by orbital forcing in the Late Pliocene. Under several extreme orbital configurations, the summer monsoon becomes weaker relative to the preindustrial. This is attributed to the fact that the orbitally induced decrease in land‐sea thermal contrast exceeds the increase arising from the PRISM3D boundary conditions. East Asian winter monsoon exhibits a relatively stable feature and remains weaker in the Late Pliocene even with extreme orbital forcing, as the effect of PRISM3D boundary conditions that lead to reduced land‐sea thermal contrast overwhelms the influence of orbital forcing. Given limitations of snapshot time slab simulation and different model sensitivity, the orbital‐scale variability of East Asian monsoon in the Late Pliocene should be further explored using transient simulation and with other coupled models.

Growth of the Ballena fan delta on the Gulf of California (Mexico) at the close of the Pliocene Warm Period

Tectonic uplift on the shores of Bahia San Rafael in Mexico’s upper Gulf of California exposed a Pliocene delta system that covers a map area of 4 km2. Subaerial dissection by arroyos entrenched during Pleistocene and post-Pleistocene time carved cross-sectional slices through the delta, showing its dominant construction resulting from massive transfers of siliciclastic sand derived from the breakdown of igneous rocks (tonolite) in a well-defined terrestrial basin. Restoration of the sedimentary structure by elimination of Pleistocene arroyos and linkage of former topographic lines reveals a triangular shape recognizable as a classic fan delta. The complex includes an alluvial fan that emerges from a small opening in the landscape connected to a semi-circular, high-walled basin with a map area of 2.6 km2. Through a strictly longitudinal sequence, estimates of the excavated basin’s volume and the delta’s sedimentary volume were conducted as a mass-balance exercise that yielded a strong match. The lower central part of the delta features dense concentrations of sand dollars (Dendraster granti) that form a distinct limestone coquina not previously recognized elsewhere in Baja California. Through the regional biostratigraphy of concurrent range zones supplemented by absolute age dates from inter-bedded volcanics in other places, a later Pliocene age around 3–2 Ma is suggested for the sand dollars and the delta complex in which they are buried. Such timing corresponds to the close of the Pliocene Warm Period, during which a persistent El Nino climate brought tropical storms and excessive rainfall to the upper Gulf of California. Comparisons with other Pliocene deltas throughout the Gulf of California underscore the unique status of the complex named the Ballena fan delta.

Climate change and tectonic activity during the early Pliocene Warm Period from the ostracod record at Lake Qinghai, northeastern Tibetan Plateau

The Early Pliocene Warm Period (EPWP, 5–3Ma) is sometimes thought to be a useful analogue for a future warmer world, and thus the boundary conditions and drivers of climate in the EPWP may provide valuable lessons for understanding how a future warmer world might unfold. Lake Qinghai is located on the northeastern margin of the Tibetan Plateau (TP) and is affected by both Monsoon climate and Westerlies circulation. It is sensitive to the climate drivers of these systems. Its sediments, accumulated over the Cenozoic period, are a rich source of information for climate, tectonics and environmental changes of the period.We present a high-resolution ostracod record from a Lake Qinghai sediment core with a record of the period 5.10–2.60Ma, thus covering the EPWP. Ostracods appear at 4.63Ma and are most abundant until 3.58Ma, while a body of water was present at the core site. This suggests a phase of humid climate and an intensified Asian Summer Monsoon (ASM), which is consistent with a warmer and wetter climate in the early Pliocene. Within this period the ostracod record shows some variabilities in lake level with deeper periods suggesting more intense ASM compared to those with shallower water. The disappearance of ostracods at 3.58Ma may provide evidence for the uplift of Qinghai Nanshan (south of Qinghai Lake) since this is when the ASM intensified.