Warm Pliocene Research Articles

Carbonate leaching processes in the Red Clay Formation, Chinese Loess Plateau: Fingerprinting East Asian summer monsoon variability during the late Miocene and Pliocene

AbstractHigh‐resolution variations in carbonate minerals from the Jiaxian Red Clay section, located at the northern limit of the present East Asian summer monsoon (EASM) on Chinese Loess Plateau were quantified using Fourier transform infrared spectroscopy. We analyzed a large quantity of sediments dated from the late Miocene to Pliocene (8.2–2.6 Ma). The carbonates in this interval show high‐frequency variations alternating between leached and calcareous horizons. The low carbonate contents and high values of magnetic susceptibility and high Rb/Sr ratios were found in the leached zones, a pattern that is consistent with that observed in the overlying Quaternary loess‐paleosol sequences. This pattern suggests that East Asian Monsoon (EAM) rainwater enhanced leaching and accumulation processes of carbonate minerals in the Red Clay Formation in a way similar to the loess‐paleosol sequence. Seven alternating leached and calcareous zones are identified, suggesting oscillations of the EASM and East Asian winter monsoon intervals. The calcareous zones were also found to have high Zr/Rb ratio. These indications of shifts from a strong EASM to East Asian winter monsoon dominance correlate well with the cooling transition indicated by deep sea δ18O isotopes. This evidence suggests that the EAM was active during the late Miocene and Pliocene and was similar to the Quaternary monsoon. The presence of a strong EAM during the Pliocene Warm Period also raises questions about the hypothesis that past and future warm climate conditions could produce a permanent El Niño‐like state.

Significance of pre-Quaternary climate change for montane species diversity: Insights from Asian salamanders (Salamandridae: Pachytriton)

Despite extensive focus on the genetic legacy of Pleistocene glaciation, impacts of earlier climatic change on biodiversity are poorly understood. Because amphibians are highly sensitive to variations in precipitation and temperature, we use a genus of Chinese montane salamanders (Salamandridae: Pachytriton) to study paleoclimatic change in East Asia, which experienced intensification of its monsoon circulation in the late Miocene associated with subsequent Pliocene warming. Using both nuclear and mitochondrial DNA sequences, we reconstruct the species tree under a coalescent model and demonstrate that all major lineages originated before the Quaternary. Initial speciation within the genus occurred after the summer monsoon entered a stage of substantial intensification. Heavy summer precipitation established temporary water connectivity through overflows between adjacent stream systems, which may facilitate geographic range expansion by aquatic species such as Pachytriton. Species were formed in allopatry likely through vicariant isolation during or after range expansion. To evaluate the influence of Pliocene warming on these cold-adapted salamanders, we construct a novel temperature buffer-zone model, which suggests widespread physiological stress or even extinction during the warming period. A significant deceleration of species accumulation rate is consistent with Pliocene range contraction, which affected P. granulosus and P. archospotus the most because they lack large temperature buffer zones. In contrast, demographic growth occurred in species for which refugia persist. The buffer-zone model reveals the Huangshan Mountain as a potential climatic refugium, which is similar to that found for other East Asian organisms. Our approach can incorporate future climatic data to evaluate the potential impact of ongoing global warming on montane species (particularly amphibians) and to predict possible population declines.

A deep Eastern Equatorial Pacific thermocline during the early Pliocene warm period

During the early Pliocene warm period (∼4.6–4.2Ma) in the Eastern Equatorial Pacific upwelling region, sea surface temperatures were warm in comparison to modern conditions. Warm upwelling regions have global effects on the heat budget and atmospheric circulation, and are argued to have contributed to Pliocene warmth. Though warm upwelling regions could be explained by weak winds and/or a deep thermocline, the temporal and spatial evolution of the equatorial thermocline is poorly understood. Here we reconstruct temporal and spatial changes in subsurface temperature to monitor thermocline depth and show the thermocline was deeper during the early Pliocene warm period than it is today. We measured subsurface temperature records from Eastern Equatorial Pacific ODP transect Sites 848, 849, and 853 using Mg/Ca records from Globorotalia tumida, which has a depth habitat of ∼50–100m. In the early Pliocene, subsurface temperatures were ∼4–5°C warmer than modern temperatures, indicating the thermocline was relatively deep. Subsurface temperatures steeply cooled ∼2–3°C from 4.8 to 4.0Ma and continued to cool an additional 2–3°C from 4.0Ma to present. Compared to records from other regions, the data suggests the pronounced subsurface cooling between 4.8 and 4.0Ma was a regional signal related to restriction of the Isthmus of Panama, while continued cooling from 4.0Ma to present was likely related to global processes that changed global thermocline structure. Additionally, the spatial evolution of the equatorial thermocline along a N–S transect across ODP Sites 853, 849 and 848 suggests an intensification of the southeast trades from the Pliocene to present. Large-scale atmospheric and oceanographic circulation processes link high and low latitude climate through their influence on equatorial thermocline source water regions and consequently the equatorial thermocline. Through these low latitude/high latitude linkages, changes in the equatorial thermocline and thermocline source water played an important role in the transition from the warm Pliocene to the cold Pleistocene.

Paleoceanographic changes in the Eastern Equatorial Pacific over the last 10 Myr

To examine the Late Neogene evolution of tropical Pacific oceanography, we determined multiple geochemical proxy records for temperature (U37K′and TEX86Hindices) and primary productivity (algal biomarkers and diol indices) in sediments recovered at ODP Site 1241 in the East Equatorial Pacific (EEP) spanning a record of the last 10 Myr. The TEX86Htemperatures are lower than those recorded by U37K′indices, exhibiting large fluctuations and suggesting strong warming during the Mid Pliocene Warm Period (MPWP; 4.5–3.2 Ma) and significantly colder temperature during the Late Miocene cooling period (7–5 Ma) and after the Middle Pliocene Warm Period (MPWP). Such variations could reflect changes in the EEP thermocline temperatures, but we suggest that they instead reflect changes in the depth of export production of glycerol dialkyl glycerol tetraether lipids in response to changes in the upper ocean structure. A combination of temperature records, inferred to represent different and likely varying depths in the water column, as well as algal biomarker records for export production and ecosystem structure, suggest that both productivity and inference upwelling were reduced in the EEP during warmer periods, such as the MPWP and prior to 7 Ma. In contrast, stronger upwelling conditions and associated increased productivity likely prevailed from 7 to 5 Ma and for the past 3 Myr, both corresponding to globally cool intervals. A further increase in EEP productivity occurred at ca 1.8 Ma, coincident with the development of the E‐W Pacific SST gradient. These results confirm previous work that protracted El Niño–like conditions prevailed during warmer intervals of the Pliocene before ultimately descending into the current climate state.

Paleoceanographic significance of deep-sea benthic foraminiferal species diversity at southeastern Indian Ocean Hole 752A during the Neogene

Diversity parameters of Neogene deep-sea benthic foraminifera were measured at Ocean Drilling Program (ODP) Hole 752A, southeastern Indian Ocean (water depth of 1086.3m) using Information Function (H), Equitability (E), number of species (S) and Sander's rarefaction values. These parameters combined with population abundance of dominant benthic foraminifera (Bulimina macilenta, Nuttallides umbonifera, Cibicides wuellerstorfi, Cibicides lobatulus, Bolivina pusilla, Ehrenbergina carinata, Gavelinopsis lobatulus, Cassidulina laevigata, Globocassiulina subglobosa) reveal significant paleoceanographic changes in the southeastern Indian Ocean during the Neogene. The values of all the diversity parameters show a decrease from 25 to 23Ma and thereafter an increase with peak values at ~13.5Ma. The Late Oligocene to Earliest Miocene was an interval of more unstable conditions at Hole 752A dominated by species characteristic of low organic carbon, well-ventilated, carbonate corrosive high energy conditions. The highest values of diversity parameters coincide with the early Middle Miocene climatic optimum. All these parameters show a declining trend and gradual decrease from 13.5 to 4.5Ma coinciding with the major build up of ice sheets in the Antarctic region. Major increase in B. pusilla and E. carinata population during this time suggests high nutrient levels and low oxygen conditions at Hole 752A. This interval corresponds with the so-called “biogenic bloom” and an intense Oxygen Minimum Zone as observed throughout the Indo-Pacific region. Deep waters were warmer from 4.5 to 3Ma marked by an increase in species diversity values, coinciding with the early middle Pliocene warmth. The species diversity values abruptly decreased in the younger interval, contemporaneous with the major Northern Hemisphere glaciation. During this time species characteristics of high-energy bottom currents and relatively cold deep water were dominant.

High tide of the warm Pliocene: Implications of global sea level for Antarctic deglaciation

We obtained global sea-level (eustatic) estimates with a peak of ∼22 m higher than present for the Pliocene interval 2.7–3.2 Ma from backstripping in Virginia (United States), New Zealand, and Enewetak Atoll (north Pacific Ocean), benthic foraminiferal δ18O values, and Mg/Ca-δ18O estimates. Statistical analysis indicates that it is likely (68% confidence interval) that peak sea level was 22 ± 5 m higher than modern, and extremely likely (95%) that it was 22 ± 10 m higher than modern. Benthic foraminiferal δ18O values appear to require that the peak was <20–21 m. Our estimates imply loss of the equivalent of the Greenland and West Antarctic ice sheets, and some volume loss from the East Antarctic Ice Sheet, and address the long-standing controversy concerning the Pliocene stability of the East Antarctic Ice Sheet.

Cold tongue/Warm pool and ENSO dynamics in the Pliocene

Abstract. It has been suggested that a "permanent" El Niño climate state has existed in the warm Pliocene. One of the main pieces of evidence of such conditions is the small east-west sea surface temperature (SST) difference that is found in proxy temperature records of the equatorial Pacific. Using a coupled version of the Zebiak-Cane model of intermediate complexity for the tropical Pacific, we study the sensitivity of the time-mean Pacific background state and El Niño/Southern Oscillation (ENSO) variability to Pliocene climate changes. The parameters varied in this sensitivity study include changes in the trade wind strength due to a reduced equator-to-pole temperature gradient, higher global mean temperatures and an open Panama gateway. All these changes lead to a westward shift of the position of the cold tongue along the equator by up to 2000 km. This result is consistent with data from the PRISM3D Pliocene SST reconstruction. Our model further suggests that ENSO variability is present in the Pliocene climate with only slight changes as compared to today. A background climate that would resemble a "permanent" El Niño with weak to no east-west temperature difference along the equator is only found for very weak trade winds which seem unrealistic for the Pliocene climate.

El Niño in the Pliocene

Whether interannual variability in the Pacific Ocean was a feature of the warm Pliocene climate is debated. Variance in reconstructed eastern tropical Pacific surface temperatures provides strong support for persistent El Nino activity at this time.

Climate and environment of a Pliocene warm world

The Pliocene Epoch, 5.33–2.58 million years ago (Ma), was a generally warmer and wetter interval with atmospheric CO 2-concentrations at or slightly above modern levels. This paper provides an overview of Pliocene vegetation, sea surface temperatures and climate modelling outcomes. Most prominent changes in Pliocene biome distribution compared to today include a northwards shift of temperate and boreal vegetation zones in response to a warmer and wetter climate as well as an expansion of tropical savannas and forests at the expense of deserts. Faunal analysis techniques and modelling experiments using the Hadley Centre climate model identified significantly higher Pliocene sea surface temperatures at mid and high latitudes of the northern hemisphere with cooling or unchanged sea surface temperatures at low latitudes. Global mean annual surface temperatures (MAT) are estimated to have been 2 to 3 °C higher during the Piacenzian (3.6–2.58 Ma) than today with a reduced equator to pole gradient. The marine realm during the Pliocene was characterised by a reconfiguration of ocean gateways, particularly the narrowing of the Indonesian Seaway and closure of the Central American Isthmus, which produced essentially a modern pattern of ocean circulation. In the Southern Ocean a warm early Pliocene gave way to late Piacenzian cooling. Proxy data indicate a reduced east to west sea surface temperature gradient in the tropical Pacific during the Pliocene warmth. The Pliocene is one of the most intensively studied geological intervals of the pre-Quaternary. No other warm period in the geological past yields such a unique combination of near modern atmospheric CO 2-concentrations, palaeogeography and palaeobiology. However, this paper also identifies data gaps and shortcomings in the reconstruction of Pliocene environments using proxy data and climate models on which future research should focus.

How likely was a green Antarctic Peninsula during warm Pliocene interglacials? A critical reassessment based on new palynofloras from James Ross Island

The question of whether Pliocene climate was warm enough to support a substantial vegetation cover on Antarctica is of great significance to the ongoing and controversial debate on the stability or dynamism of Antarctic ice sheets during warm periods with high atmospheric greenhouse gas concentrations. Here we present a systematic palynological comparison of pollen and dinoflagellate cyst assemblages from Early Pliocene diamictites and underlying late Cretaceous sediments collected from James Ross Island, northern Antarctic Peninsula. The diamictites are dated using a combination of 40Ar/ 39Ar and 87Sr/ 86Sr isotope ages on interbedded lavas and pristine bivalves. Well preserved pectinid shells and cheilostome bryozoans suggest that the palynomorph-bearing sediments were probably deposited during warmer Pliocene interglacials and later amalgamated into a diamictite formed by a major ice advance during cold glacial cycle. The palynological analyses presented herein do not identify any in-situ pollen and spores which indicate the presence of a substantial vegetation cover. Our study suggests a local (i.e. James Ross Island) provenance for most of the diamictites, whilst sediments from the western coast might have been delivered by ice sheets from the Antarctic Peninsula. Whilst the acritarch Leiosphaeridia might imply the presence of sea-ice and near-modern climate conditions during the Late Neogene, the presence of the dinoflagellate cyst Bitectatodinium tepikiense at one location suggests that sea surface temperatures might have been substantially warmer during some interglacials. The absence of in-situ pollen and spores in the James Ross Island diamictites cannot be taken as proof of non-existence of vegetation. However, the combined palynological and geological evidence presented in this paper makes the presence of a substantial Pliocene vegetation cover on James Ross Island unlikely and supports previous reconstructions of a permanent ice sheet on the Antarctic Peninsula throughout the Late Neogene.

Bathymetric controls on Pliocene North Atlantic and Arctic sea surface temperature and deepwater production

The mid-Pliocene warm period (MPWP; ~ 3.3 to 3.0 Ma) is the most recent interval in Earth's history in which global temperatures reached and remained at levels similar to those projected for the near future. The distribution of global warmth, however, was different than today in that the high latitudes warmed more than the tropics. Multiple temperature proxies indicate significant sea surface warming in the North Atlantic and Arctic Oceans during the MPWP, but predictions from a fully coupled ocean–atmosphere model (HadCM3) have so far been unable to fully predict the large scale of sea surface warming in the high latitudes. If climate proxies accurately represent Pliocene conditions, and if no weakness exists in the physics of the model, then model boundary conditions may be in error. Here we alter a single boundary condition (bathymetry) to examine if Pliocene high latitude warming was aided by an increase in poleward heat transport due to changes in the subsidence of North Atlantic Ocean ridges. We find an increase in both Arctic sea surface temperature and deepwater production in model experiments that incorporate a deepened Greenland–Scotland Ridge. These results offer both a mechanism for the warming in the North Atlantic and Arctic Oceans indicated by numerous proxies and an explanation for the apparent disparity between proxy data and model simulations of Pliocene northern North Atlantic and Arctic Ocean conditions. Determining the causes of Pliocene warmth remains critical to fully understanding comparisons of the Pliocene warm period to possible future climate change scenarios.

Teleconnections in a warmer climate: the pliocene perspective

Migrations toward altered sea surface temperature (SST) patterns in the Indo-Pacific region are present in the recent observational record and in future global warming projections. These SSTs are in the form of “permanent” El Nino-like (herein termed “El Padre”) and Indian Ocean Dipole (IOD)-like patterns. The Early Pliocene Warm Period, which bears similarity to future warming projections, may have also exhibited these Indo-Pacific SST patterns, as suggested by regional terrestrial paleo-climatic data and general circulation model studies. The ability to corroborate this assessment with paleo-data reconstructions is an advantage of the warm Pliocene period that is not afforded by future warming scenarios. Thus, the Pliocene period provides us with a warm-climate perspective and test bed for understanding potential changes to future atmospheric interactions given these altered SST states. This study specifically assesses how atmospheric teleconnections from El Padre/IOD SST patterns are generated and propagate to create the regional climate signals of the Pliocene period, as these signals may be representative of future regional climatic changes as well. To do this, we construct a holistic diagnostic rubric that allows us to examine atmospheric teleconnections, both energetically and dynamically, as produced by a general circulation model. We incorporate KE′, a diagnostic adapted from the eddy kinetic energy generation field, to assess the available energy transferred to these teleconnections. Using this methodology, we found that relative to our Modern Control experiments, weaker atmospheric teleconnections prevail under warm Pliocene conditions, although pathways of propagation still appear directed toward the southwestern United States from our tropical Pacific sector forcing. Propagation directly emanating from the Indian Ocean forcing sector appears to be largely blocked, although indirect teleconnective pathways appear traversing the Asian continent toward the North Pacific. The changes in the atmospheric circulation of Indian Ocean region in response to the underlying specified SST forcing (and indicated by Pliocene paleo-data) may have a host of implications for energy transfer out of and into the region, including interactions with the Asian jet stream and changes to the seasonal monsoon cycle. These interactions warrant further study in both past and future warm climate scenarios.

Successions of Quaternary mollusc fauna in easternmost continental Europe (southern Urals, Russia)

The evolution of the mollusc fauna found in the easternmost part of Europe was affected by three main stages of development during the Quaternary. The Early Eopleistocene mollusc assemblage consists of rare terrestrial and numerous freshwater species with numerous thermophilic (Pliocene) species. The Late Eopleistocene – Early Neopleistocene is characterized by terrestrial and freshwater molluscs with few warm stenothermic Pliocene species. The Early Neopleistocene – Holocene assemblage is characterized by terrestrial and freshwater molluscs of modern affinities.

Workshop on Pliocene Climate

The warm Pliocene epoch (5–3 million years ago) is often cited as a good analog for the near future climate because of its striking resemblance to the predictions of the “Intergovernmental Panel on Climate Change” for the next decades. Indeed, relative to today, during the Pliocene epoch, surface temperatures were 3–4°C warmer, sea level was about 5–40 meters higher, atmospheric CO2 concentrations were relatively similar or slightly higher (~400 ± 50 ppmv), and ice sheets were restrained to Antarctica. However, since 3.0 Ma ago, the Earth’s climate has undergone a major transition from a warm and relatively stable state towards cold conditions marked by amplified glacial/interglacial cycles and widespread ice sheets in the Northern Hemisphere (NHG), and to a lesser extent over Antarctica. The causes and consequences of this global climate transition— driving warm periods to “icehouse” conditions marked by “Quaternary-style” glacial/interglacial cycles—are still uncertain. Yet, they may include the interaction of several mechanisms tied to oceanic and atmospheric circulations, tectonic-, greenhouse gases-, and biological activity, biogeo

Alkenone and boron-based Pliocene pCO 2 records

The Pliocene period is the most recent time when the Earth was globally significantly (∼ 3 °C) warmer than today. However, the existing pCO 2 data for the Pliocene are sparse and there is little agreement between the various techniques used to reconstruct palaeo- pCO 2. This disagreement, coupled with the general low temporal resolution of the published records, does not allow a robust assessment of the role of declining pCO 2 in the intensification of the Northern Hemisphere Glaciation (INHG) and a direct comparison to other proxy records are lacking. For the first time, we use a combination of foraminiferal ( δ 11B) and organic biomarker (alkenone-derived carbon isotopes) proxies to determine the concentration of atmospheric CO 2 over the past 5 Ma. Both proxy records show that during the warm Pliocene pCO 2 was between 330 and 400 ppm, i.e. similar to today. The decrease to values similar to pre-industrial times (275–285 ppm) occurred between 3.2 Ma and 2.8 Ma — coincident with the INHG and affirming the link between global climate, the cryosphere and pCO 2.

Cooling upwelling regions along the California margin during the early Pliocene: evidence for a shoaling thermocline

The early Pliocene is the most recent time in Earth history when average global temperatures were warmer than they are today. Previous work has shown that coastal upwelling regions had a particularly strong response to early Pliocene warmth, with sea surface temperature records in the southern California margin indicating SST was 9-10°C warmer compared to today. Warmer SST in upwelling regions could have been an important factor in maintaining Pliocene warmth. However, the cause for the warmer conditions in upwelling regions and the transition to colder SST has remained elusive. We present alkenone derived SST estimates from a northern California margin location, ODP Site 1022 (40°N, 125°W, 1950m water depth), from the early Pliocene (4. 2-2.8 Ma). The 2.8°C cooling during this time interval is similar to that observed at two southern California margin sites (ODP Sites 1014 and 1012), indicating the three sites were responding to the same forcing. However, SST was only 3°C warmer than today at ODP Site1022 while the southern sites were 9-10°C warmer than today, thereby increasing the latitudinal temperature gradient along the California margin dramatically during the early Pliocene compared to today. This indicates that the tropical warm pool expansion during the early Pliocene was not felt along the Northern California margin. We quantified diatom assemblages at ODP Site 1022 to constrain changes in oceanographic conditions during early to middle Pliocene. The percent of diatoms indicative of subarctic waters is unchanged from 4.2 to 3 Ma, suggesting that a change in the strength of the California current cannot explain the cooling SST trend. We also found no trend in the percent of upwelling-indicative diatoms, which is consistent with records of alkenone mass accumulation rate, diatom preservation, biosilica, and total organic carbon, none of which show evidence that the upwelling of nutrient-rich subsurface water increased as SST cooled. The fact that upwelling of nutrient-rich water was occurring even when SST were warmer can be explained by a deeper early Pliocene thermocline.

Early to mid-Pliocene environmentally constrained diatom assemblages from the AND-1B drillcore, McMurdo Sound, Antarctica

In extended lower to mid-Pliocene stratigraphic record of near-shore environmental variation in the southwestern Ross Sea, Antarctica is preserved in ANDRILL’s McMurdo Ice Shelf Project AND-1B drillcore.A94meter-thick sequence of three diatomite and diatomaceous mudstone intervals represents the highest latitude record (78° S) of persistent open-marine conditions on the Antarctic continental shelf, in response to a protracted period of Pliocene warmth. This core provides new chronostratigraphic control for Antarctic paleoclimatic events, and describes a sequence of distinct diatom assemblages comprised of both extant and extinct species that are unknown on the Antarctic shelf today. Common taxa include those with modern distributions close to the Polar Frontal Zone (e.g. Shionodiscus tetraoestrupii, Stellarima stellaris, Thalassionema nitzschioides), suggesting marine temperatures in the southwestern Ross Sea warmer than at present. Representatives of the modern sea-ice assemblage (e.g. Fragilariopsis curta, Stellarima microtrias) and cold open-marine species associated with the retreating sea-ice front (e.g. Eucampia antarctica var. recta) are also present, but in much lower abundance than in the Ross Sea today as suggested by core top and surface sample data. The co-occurrence of species from these three distinct modern environments in Pliocene sediments, in close proximity to the continent, suggests that modern ecological zonal concepts cannot be applied directly in Pliocene paleoenvironmental analyses. Species present in the 4 m-thick lowest diatomite unit (~4.5 Ma) indicate a cold openmarine environment,with the period of deposition likely comprising the length of one interglacial period. The middle diatomite unit (~4.1-4.3 Ma; 14m) records warmer and perhaps seasonally mixed conditions with often abundant Thalassionema nitzschioides and Shionodiscus tetraoestrupii and little evidence of sea-ice associated species. Documentation of changes in diatom assemblages through the upper 75m-thick diatomite interval (~3.3-3.6Ma) offers the opportunity to resolve environmental limits of Pliocene diatom species thatwill serve as a guide to diatom-based paleoenvironmental interpretations for other Pliocene deposits. This upper unit records deposition during several glacial/interglacial cycles indicating an extended interval with open marine productivity during the mid-Pliocene. In addition, environmental associations for extinct species are inferred by their co-occurrence with extant taxa. Persistent intervals of pure diatomite suggest high productivity in an open-marine setting and minimal to no influence of sea ice. Commonly occurring species can be placed in five ecological cateories; Neritic/Stratified, Warm, Cold/Sea Ice, Heavy/Wind Mixed and Mixed. Comparison of this long diatom-bearing interval with coeval Antarctic deposits presents a regional and continental picture of Pliocene warmth, suggesting East Antarctic Ice Sheet was smaller with sub-polar marginal conditions.

Proposal for Pliocene and Pleistocene land–sea correlation in the Italian area

The present study attempts a correlation between calcareous plankton (foraminifera and nannofossils) and terrestrial (pollen and mammal fauna) bioevents in Italy and Mediterranean Sea, through the last 3.3 million years, within a standard chronostratigraphical time scale. The approach was basically interdisciplinary and considered biochronological, biostratigraphical, chronostratigraphical, climatostratigraphical, and tephrochronological data. Despite different timing and mode characterised evolution of marine and continental organisms in relation to their ecology and relationships with environment, the main biota changes seem related with severe climate changes. The short interval of the known global scale Pliocene warmth (∼3.0 Ma) has been documented by the last significant expansion of the warm subtropical forest before the progressive disappearance of its main components and possibly by the paracme of some nannofossil species. The first evidence of cooler conditions near 2.8 Ma has been mainly indicated by both the progressive decrease of subtropical to warm temperate pollen taxa and by the notable change in the ecological structure of mammalian faunal complexes as well as by the first incursion of left-coiled cold N. pachyderma into the Mediterranean. The first glacial phases related to Northern Hemisphere ice-sheet growth (∼2.5 Ma) are indicated by the drastic drop of Discoaster spp. and by the first (cyclical) expansion of steppe or cooler coniferous forests, as well as by the progressive dispersal of mammalian taxa dwelling in open landscapes. The most significant biotical changes have been observed during the Calabrian–Ionian transition; several calcareous plankton appearances and extinctions occurred across marine isotope stages 25–20, together with the expansion of cold steppes (glacials) and the progressive disappearance of the most thermophilous arboreal and non-arboreal taxa. The late Early to Middle Pleistocene terrestrial faunal “revolution” actually was not an “abrupt” phenomenon, which started from about 1.3 Ma giving rise to a progressive reconstruction of mammalian faunal complexes, which ended during the early Ionian. The last node of 1.2 Ma obliquity cycles, centred at about 0.9 Ma, significantly influenced changes in the structure and composition of palaeocommunities. After the Ionian, fluctuations in biota assemblages, without any significant appearance–extinction events, testify that the new oceanographical and climate system is related to dominant periodicity of 100 ky in glacial–interglacial cycles. Although the changes observed in fossil assemblages do not always correspond to the standard chronostratigraphical boundaries, the data suggest that the Piacenzian–Gelasian and Calabrian–Ionian transitions are also noticeable by large, even if gradual, biota modifications.

From the warm Pliocene to the cold Pleistocene: A tale of two oceans

What drove the transition from a warm Pliocene to a cold Pleistocene, dominated by widespread Northern Hemisphere glaciation? This has become one of the most intriguing questions in the earth sciences. Although we can constrain each of these individual global climate states via continental and

History of the Antarctic Peninsula Ice Sheet since the early Pliocene—Evidence from cosmogenic dating of Pliocene lavas on James Ross Island, Antarctica

Knowledge of the thickness, extent and basal thermal conditions of ice cover on Antarctica during past climatic fluctuations is essential if we are to accurately predict the contribution from the Antarctic ice sheets to future global sea level rise. When combined with geomorphological evidence, terrestrial cosmogenic nuclides are a powerful tool for palaeo-ice sheet reconstructions. Here we present results from the first terrestrial cosmogenic nuclide study on James Ross Island, northern Antarctic Peninsula. We measured cosmogenic 3He concentrations in primary flow surface features of Pliocene basalt lavas which are exposed more than 600 m above present-day sea level. Our results suggest that the lava surfaces have been ice-free for no more than 15 kyr since their eruption at 4.69 Ma. This implies that a glacial cover has persisted on James Ross Island since 4.69 Ma, even during interglacial periods, and much (if not all) of the warm Pliocene (5–3 Ma, when average global temperatures were up to 3 °C higher than today). This is consistent with results of recent modelling studies, but contradicts General Circulation Models that suggest an ice-free Antarctic Peninsula during that time. Field observations of striated lava surfaces found adjacent to primary volcanogenic features, such as ropy textures, combined with cosmogenic 3He data suggest that the ice cover was locally wet-based, and relatively thin (not exceeding 45–200 m) for the majority of the past 4.69 Myr. The ice temporarily reached a thickness sufficient to cause some localised erosion in hollows, but this erosion was not widespread. Although the pristinely-preserved lavas found on upstanding tumuli appear never to have been eroded, our exposure age data show that they were covered by ice for most of their history, and therefore could not have been refugia for terrestrial organisms during glacial periods.