Interglacial Climate Change Research Articles

The Influence of Paleoclimate on Present-Day Patterns in Biodiversity and Ecosystems

Earth's climate has experienced strong changes on timescales ranging from decades to millions of years. As biodiversity has evolved under these circumstances, dependence on these climate dynamics is expected. In this review, we assess the current state of knowledge on paleoclimatic legacies in biodiversity and ecosystem patterns. Paleoclimate has had strong impacts on past biodiversity dynamics, driving range shifts and extinctions as well as diversification. We outline theory for how these dynamics may have left legacies in contemporary patterns and review the empirical evidence. We report ample evidence that Quaternary glacial–interglacial climate change affects current patterns of species distributions and diversity across a broad range of organisms and regions. We also report emerging evidence for paleoclimate effects on current patterns in phylogenetic and functional diversity and ecosystem functioning and for legacies of deeper-time paleoclimate conditions. Finally, we discuss implications for Anthropocene ecology and outline an agenda to improve our understanding of paleoclimate's role in shaping contemporary biodiversity and ecosystems.

A high-resolution record of Southern Ocean intermediate water radiocarbon over the past 30,000 years

The circulation of intermediate waters plays an important role in global heat and carbon transport in the ocean and changes in their distribution are closely tied to glacial–interglacial climate change. Coupled radiocarbon and U/Th measurements on deep-sea Desmophyllum dianthus corals allow for the reconstruction of past intermediate water ventilation. We present a high-resolution time series of Antarctic Intermediate Water radiocarbon from 44 corals spanning 30 ka through the start of the Holocene, encompassing the transition into the Last Glacial Maximum (LGM) and the last deglaciation. Corals were collected south of Tasmania from water depths between 1430 and 1950 m with 80% of them between 1500 and 1700 m, giving us a continuous record from a narrow depth range. The record shows three distinct periods of circulation: the MIS 3–2 transition, the LGM/Heinrich Stadial 1 (extending from ∼22 to 16 kyr BP), and the Antarctic Cold Reversal (ACR). The MIS 3–2 transition and the ACR are characterized by abrupt changes in intermediate water radiocarbon while the LGM time period generally follows the atmosphere at a constant offset, in support of the idea that the LGM ocean was at steady state for its 14C distribution. Closer inspection of the LGM time period reveals a 40‰ jump at ∼19 ka from an atmospheric offset of roughly 230‰ to 190‰, coincident with an observed 10–15 m rise in sea level and a southward shift of the Subantarctic and Polar Fronts, an abrupt change not seen in deeper records. During the ACR time period intermediate water radiocarbon is on average less offset from the atmosphere (∼110‰) and much more variable. This variability has been captured within the lifetimes of three individual corals with changes of up to 35‰ over ∼40 yr, likely caused by the movement of Southern Ocean fronts. This surprising result of relatively young and variable intermediate water radiocarbon during the ACR seems to go against the canonical idea of reduced circulation and ventilation in the south during this time period. However comparisons with other records from the Southern Ocean highlight zonal asymmetries, which can explain the deviation of our Tasmanian record from those in Drake Passage and the eastern Pacific. These signals seen in Tasmanian intermediate water Δ14C can also be found in Greenland ice core δ18O and East Asian monsoon strength. Throughout the LGM and the deglaciation, our Tasmanian intermediate water record is sensitive to times when the upper and lower cells of the meridional overturning circulation are more or less interconnected, which has important implications for the global climate system on glacial–interglacial time scales.

Vegetation and climate changes during the late Pliocene and early Pleistocene in SW Anatolia, Turkey

Pollen analysis was done on lacustrine sedimentary sequences dated by micromammals as late Pliocene–early Pleistocene that outcrop in two Neogene graben basins from SW Turkey. This study shows vegetation changes from steppe-like to more forested environments, very similar to the cyclic oscillations related to late Pleistocene glacial–interglacial climate changes. Artemisia was abundant during cold–arid periods, indicating that this species was already widespread in this area during the latest Pliocene and the beginning of the Pleistocene. A review of pollen records from Anatolia agrees with this study, suggesting that the spreading of this arid species occurred during a major climatic change: the beginning of the first glaciations and probably a change in seasonality towards summer aridity. Artemisia temporarily disappeared from the region during warm–wet periods and thus we suggest that glacial–interglacial-type oscillations already occurred in the area during the late Pliocene–early Pleistocene.

Global late Quaternary megafauna extinctions linked to humans, not climate change.

The late Quaternary megafauna extinction was a severe global-scale event. Two factors, climate change and modern humans, have received broad support as the primary drivers, but their absolute and relative importance remains controversial. To date, focus has been on the extinction chronology of individual or small groups of species, specific geographical regions or macroscale studies at very coarse geographical and taxonomic resolution, limiting the possibility of adequately testing the proposed hypotheses. We present, to our knowledge, the first global analysis of this extinction based on comprehensive country-level data on the geographical distribution of all large mammal species (more than or equal to 10 kg) that have gone globally or continentally extinct between the beginning of the Last Interglacial at 132 000 years BP and the late Holocene 1000 years BP, testing the relative roles played by glacial–interglacial climate change and humans. We show that the severity of extinction is strongly tied to hominin palaeobiogeography, with at most a weak, Eurasia-specific link to climate change. This first species-level macroscale analysis at relatively high geographical resolution provides strong support for modern humans as the primary driver of the worldwide megafauna losses during the late Quaternary.

Sensitivity simulations with direct shortwave radiative forcing by aeolian dust during glacial cycles

Abstract. Possible feedback effects between aeolian dust, climate and ice sheets are studied for the first time with an Earth system model of intermediate complexity over the late Pleistocene period. Correlations between climate and dust deposition records suggest that aeolian dust potentially plays an important role for the evolution of glacial cycles. Here climatic effects from the dust direct radiative forcing (DRF) caused by absorption and scattering of solar radiation are investigated. Key elements controlling the dust DRF are the atmospheric dust distribution and the absorption-scattering efficiency of dust aerosols. Effective physical parameters in the description of these elements are varied within uncertainty ranges known from available data and detailed model studies. Although the parameters can be reasonably constrained, the simulated dust DRF spans a~wide uncertainty range related to the strong nonlinearity of the Earth system. In our simulations, the dust DRF is highly localized. Medium-range parameters result in negative DRF of several watts per square metre in regions close to major dust sources and negligible values elsewhere. In the case of high absorption efficiency, the local dust DRF can reach positive values and the global mean DRF can be insignificantly small. In the case of low absorption efficiency, the dust DRF can produce a significant global cooling in glacial periods, which leads to a doubling of the maximum glacial ice volume relative to the case with small dust DRF. DRF-induced temperature and precipitation changes can either be attenuated or amplified through a feedback loop involving the dust cycle. The sensitivity experiments suggest that depending on dust optical parameters, dust DRF has the potential to either damp or reinforce glacial–interglacial climate changes.

Climate refugia: joint inference from fossil records, species distribution models and phylogeography.

Climate refugia, locations where taxa survive periods of regionally adverse climate, are thought to be critical for maintaining biodiversity through the glacial-interglacial climate changes of the Quaternary. A critical research need is to better integrate and reconcile the three major lines of evidence used to infer the existence of past refugia - fossil records, species distribution models and phylogeographic surveys - in order to characterize the complex spatiotemporal trajectories of species and populations in and out of refugia. Here we review the complementary strengths, limitations and new advances for these three approaches. We provide case studies to illustrate their combined application, and point the way towards new opportunities for synthesizing these disparate lines of evidence. Case studies with European beech, Qinghai spruce and Douglas-fir illustrate how the combination of these three approaches successfully resolves complex species histories not attainable from any one approach. Promising new statistical techniques can capitalize on the strengths of each method and provide a robust quantitative reconstruction of species history. Studying past refugia can help identify contemporary refugia and clarify their conservation significance, in particular by elucidating the fine-scale processes and the particular geographic locations that buffer species against rapidly changing climate.

Glacial–interglacial dynamics of Antarctic firn columns: comparison between simulations and ice core air-δ<sup>15</sup>N measurements

Abstract. Correct estimation of the firn lock-in depth is essential for correctly linking gas and ice chronologies in ice core studies. Here, two approaches to constrain the firn depth evolution in Antarctica are presented over the last deglaciation: outputs of a firn densification model, and measurements of δ15N of N2 in air trapped in ice core, assuming that δ15N is only affected by gravitational fractionation in the firn column. Since the firn densification process is largely governed by surface temperature and accumulation rate, we have investigated four ice cores drilled in coastal (Berkner Island, BI, and James Ross Island, JRI) and semi-coastal (TALDICE and EPICA Dronning Maud Land, EDML) Antarctic regions. Combined with available ice core air-δ15N measurements from the EPICA Dome C (EDC) site, the studied regions encompass a large range of surface accumulation rates and temperature conditions. Our δ15N profiles reveal a heterogeneous response of the firn structure to glacial–interglacial climatic changes. While firn densification simulations correctly predict TALDICE δ15N variations, they systematically fail to capture the large millennial-scale δ15N variations measured at BI and the δ15N glacial levels measured at JRI and EDML – a mismatch previously reported for central East Antarctic ice cores. New constraints of the EDML gas–ice depth offset during the Laschamp event (~41 ka) and the last deglaciation do not favour the hypothesis of a large convective zone within the firn as the explanation of the glacial firn model–δ15N data mismatch for this site. While we could not conduct an in-depth study of the influence of impurities in snow for firnification from the existing datasets, our detailed comparison between the δ15N profiles and firn model simulations under different temperature and accumulation rate scenarios suggests that the role of accumulation rate may have been underestimated in the current description of firnification models.

Using modern models to test Poynton's predictions

In his seminal work ‘The Amphibia of southern Africa: a faunal study’, Poynton identified and contrasted two centres of amphibian importance, the temperate south-western Cape (“Cape”) and tropical northeast (“Tropical”). With reference to the dominant role of climate fluctuations resulting from Milankovitch forcing since the Pliocene, Poynton hypothesised: “These climatic fluctuations must have altered the faunal patterning very considerably, and they have probably left an impression on present distribution”. In this study we use modern methods of species distribution and palaeoclimatic models not available in the 1960s to further investigate Poynton's predictions on the importance of glacial–interglacial climatic changes on the distributions of southern Africa's amphibian assemblages. We constructed current distribution models based on presence data for 20 representative endemic anuran taxa from the two centres. We then used two paleoclimatic models (Model for Interdisciplinary Research on Climate: MIROC and Community Climate System Model: CCSM) to project the species’ current niches back to 6 and 21 Kya (Last Glacial Maximum: LGM) to reconstruct hypothetical historical distributions. Our results predict that 65% or 75% of species experienced a range reduction since the LGM, using MIROC and CCSM respectively, but this shrinking was significantly greater in the Cape (mean reduction since LGM = 18 099.6 ±5 894.27 km2 MIROC) than Tropical areas, most of which expanded (mean = − 5 990.3±8 801.80 km2 MIROC; F1,18=5.074; P = 0.037. CCSM; F1,18=15.65; P = 0.001.). Our results are discussed with reference to Poynton's predictions.

Middle Pleistocene dynamics of southern Africa's winter rainfall zone from δ13C and δ18O values of Hoedjiespunt faunal enamel

Stable carbon and oxygen isotopes of fossil fauna have become important tools in linking palaeoecology and palaeoclimate. In the case of grazing ungulates, enamel δ13C reflects C3/C4 grass abundance, which in turn is primarily a reflection of minimum growing season temperature. The south-western Cape is today a winter rainfall area where grasses are almost entirely C3. Other parts of the country, in contrast, have summer rainfall and C4 grass flora. In palaeoenvironmental studies, the presence of C3 grasses serve as an important proxy for the presence of a winter rainfall regime, and as a test of regional models of glacial–interglacial climate change. However, evidence for the extent and intensity of the winter rainfall regime beyond the last glacial period is currently thin, and a coherent picture of the long-term evolution of this system has not yet emerged.Here we present a set of δ13C and δ18O values of fauna from paleontological layers at Hoedjiespunt 1 (HDP1), a fossilised brown hyaena (Parahyaena brunnea) lair dating to between 200 and 350ka on the west coast of South Africa. The assemblage is dominated by large grazing species which were resident during a glacial period when sea levels were lower and grasslands were widespread and productive. Grazers had predominantly C3 diets, an indication of the dominance of C3 grass taxa. Comparison with other sites shows an extended picture of C3 grass dominance, and hence winter rainfall regime on the west coast of South Africa throughout the Pleistocene. However, a positive shift in δ13C values relative to those expected for pure C3 consumers is noted across all species. In part this may reflect fluctuations in the global carbon isotopic content of the atmosphere, but most likely indicates a small but significant intrusion of C4 grasses into the vegetation mosaic. This phenomenon is most consistent with models which predict that C4 grasses should be favoured over C3 species at very low pCO2, and reveals a hitherto unknown subtlety in our understanding of the evolution of this important biome.

Preface: Geoscience dynamics in the Patagonia Archipelago^|^mdash;Southern Pacific Ocean

ports carbon from the surface to the deep ocean, sea-surface temperatures, and understanding of the ventila-tion rate of the intermediate water, which are related toglacial and inter-glacial climate changes. The MR08-06cruise was intended also to elucidate the influence of sub-duction of young and hot oceanic crust and subductedsediments on the composition of magma that had intrudedinto the overriding continental crust.While the current global warming has been occurring,understanding the enhancement or reduction of glaciersin association with climate change during the geologicalpast would be thought-provoking. Aniya (2013) reviewedHolocene glaciations at Hielo Patagonico (PatagoniaIcefield) and proposed the new scheme of fiveNeoglaciations: I at 4.5–4 kilo year before present (kyrBP), II at 3.6–3.3 kyr BP, III at 2.7–2 kyr BP, IV at 1.6–0.9 kyr BP, and V at the 17th–19th centuries, the LittleIce Age (LIA). A study of the isolated temperate glaciersprovides direct and important implications for paleo-climate changes in the Southern Hemisphere.The sequential record for paleo-climate changes areusually best recorded in marine and/or lake sedimentcores. Sediment cores obtained using the R/V

The magnesium isotope record of cave carbonate archives

Abstract. Here we explore the potential of magnesium (δ26Mg) isotope time-series data as continental climate proxies in speleothem calcite archives. For this purpose, a total of six Pleistocene and Holocene stalagmites from caves in Germany, Morocco and Peru and two flowstones from a cave in Austria were investigated. These caves represent the semi-arid to arid (Morocco), the warm-temperate (Germany), the equatorial-humid (Peru) and the cold-humid (Austria) climate zones. Changes in the calcite magnesium isotope signature with time are compared against carbon and oxygen isotope records from these speleothems. Similar to other proxies, the non-trivial interaction of a number of environmental, equilibrium and disequilibrium processes governs the δ26Mg fractionation in continental settings. These include the different sources of magnesium isotopes such as rainwater or snow as well as soil and host rock, soil zone biogenic activity, shifts in silicate versus carbonate weathering ratios and residence time of water in the soil and karst zone. Pleistocene stalagmites from Morocco show the lowest mean δ26Mg values (GDA: −4.26 ± 0.07‰ and HK3: −4.17 ± 0.15‰), and the data are well explained in terms of changes in aridity over time. The Pleistocene to Holocene stalagmites from Peru show the highest mean value of all stalagmites (NC-A and NC-B δ26Mg: −3.96 ± 0.04‰) but only minor variations in Mg-isotope composition, which is consistent with the rather stable equatorial climate at this site. Holocene stalagmites from Germany (AH-1 mean δ26Mg: −4.01 ± 0.07‰; BU 4 mean δ26Mg: −4.20 ± 0.10‰) suggest changes in outside air temperature was the principal driver rather than rainfall amount. The alpine Pleistocene flowstones from Austria (SPA 52: −3.00 ± 0.73‰; SPA 59: −3.70 ± 0.43‰) are affected by glacial versus interglacial climate change with outside air temperature affecting soil zone activity and weathering balance. Several δ26Mg values of the Austrian and two δ26Mg values of the German speleothems are shifted to higher values due to sampling in detrital layers (Mg-bearing clay minerals) of the speleothems. The data and their interpretation shown here highlight the potential but also the limitations of the magnesium isotope proxy applied in continental climate research. An obvious potential lies in its sensitivity for even subtle changes in soil-zone parameters, a hitherto rather poorly understood but extremely important component in cave archive research. Limitations are most obvious in the low resolution and high sample amount needed for analysis. Future research should focus on experimental and conceptual aspects including quantitative and well-calibrated leaching and precipitation experiments.

Late-Quaternary speleothem records from the Balkan Peninsula: potential, objectives and first results

Mid-latitude speleothems often contain detailed, high-resolution records of local and regional interglacial climate changes. Many speleothem records of Holocene (MIS 1) and Eemian (MIS 5e) climate evolution have been investigated, but there is very little work being done in the Balkan region, despite the fact that the area is very rich in limestone caves with speleothems. We are investigating speleothems from the Western Balkan Peninsula that are likely to contain one of the most detailed, high-resolution records of local and regional interglacial climate changes in Southeast Europe. By example of a stalagmite collected in Vernjikica Cave, Serbia (Carpatho-Balkans), the project’s potential to address important aspects of paleoclimatic research in the Mediterranean realm is discussed.

Centennial- to millennial-scale climate shifts in continental interior Asia repeated between warm–dry and cool–wet conditions during the last three interglacial states: evidence from uranium and biogenic silica in the sediment of Lake Baikal, southeast Siberia

We observed timescale-dependent changes in the correlations between biogenic silica (bioSi) and uranium concentrations of bulk sediment from the Buguldeika Saddle, Lake Baikal. There was a positive correlation for the glacial–interglacial (100 kyr) scales over the 180 kyr, with inverse correlations for centennial- to-millennial scales during the last three interglacial states (MIS 5, 3, and 1). The distinction of these correlations between the time scales suggests that the sedimentation processes of bioSi and U differ from each other. The Baikal bioSi concentration record is generally regarded as a paleotemperature proxy, reflecting the diatom production of the lake. On the other hand, we concluded that the temporal variation of the U concentration in the sediment reflected the weathering intensity in the south of Lake Baikal watershed associated with changes in the rainfall/moisture levels.Based on the paleoclimate proxies from Lake Baikal, climates in continental interior Asia are identified as having dry and wet conditions during the glacial and interglacial periods, respectively. This accounts for the rhythms in growth and retreat of ice sheets in Eurasia on glacial–interglacial scales. In the interglacial periods (MIS 5, 3, and 1), the continental interior is, contrary to the glacial–interglacial climate changes, characterized by alternating warm–dry and cool–wet climates with periods in tens of thousands years. In particular, such shifts in the climate stand out prominently at the beginning of MIS 5d. The detrended U record for the last 5.2 kyr shows wet events at 4.3–3.7, 3.2–2.3, 1.8–1.2, and 0.8–0.3 kyr. These events coincide with the timing of the North Atlantic ice-rafted debris events, which were possibly related to solar activity. All this evidence suggests that climate in the continental interior followed significantly different fluctuation patterns in the glacial–interglacial and shorter time scales.

白馬岳東麓，長走沢・金山沢の地すべり地形と堆積物

This paper describes landslide features observed in the Nagashirisawa Basin and Kanayamazawa Basin east of Mount Shiroumadake (central Japan), where mid- to late-Pleistocene mountain glaciers are thought to have developed. Geomorphological analyses accompanied by a study of airphoto interpretation and a geological survey show gentle slopes, low-relief ridges and mounds in the basins. In most cases, angular gravels in major deposits of these landforms comprise either one or a few kinds of bedrocks exposed near the slopes. No gravels originating from any other geology in the basins are found. Jigsaw-brecciated clasts and folded-elongated silt patches in the major deposits can also be distinguished. Landslide processes, including the gravitational deformation of bedrock (i.e., mass rock creep), are probable causes of these features. Chronological information suggests that a major landslide occurred during the period from late Pleistocene to late Holocene. The triggers of these landslides remain incompletely understood, glacial–interglacial climate changes along with precipitation variations, as well as paleoearthquakes originating from nearby active faults, might be important. Some landslides found in the basins overlap moraines identified by previous research. Historical geomorphology of this area requires further study.

Quaternary and pre‐Quaternary historical legacies in the global distribution of a major tropical plant lineage

ABSTRACTAim The relative importance of current climate and past historical legacies is hotly debated. Here, we assess their role in determining the global distribution and diversity patterns of palms (Arecaceae), a widespread, species‐rich group of keystone ecological importance in tropical ecosystems.Location Global.Methods We assembled country‐level species lists world‐wide and compiled associated data on potential contemporary environmental drivers (current climate, habitat heterogeneity, area, and insularity), Quaternary glacial–interglacial climate change and major biogeographic regions to evaluate to what extent the global distribution and species richness patterns in palms reflect Quaternary climatic oscillations or regional effects reflecting pre‐Quaternary legacies. We also assessed for the first time if historical legacies differ between continents and islands, providing novel insights into determinants of insular species richness.Results Palm species richness was significantly affected by Quaternary climate changes and further differed between biogeographic regions even when both current environmental conditions and Quaternary climate changes were accounted for. In contrast, global limits to the distribution of the palm family were best explained by current temperature while biogeographic regional differences were unimportant and Quaternary climate change caused only a small constraint. Historical legacies were weak on islands, with only a small regional effect and no effect of Quaternary climate changes.Main conclusions Strong historical legacies supplement current environment as determinants of palm species richness. These primarily comprise pre‐Quaternary historical effects, reflected in low African species richness (possibly linked to pre‐Quaternary extinctions) and outstandingly high Neotropical and Indomalayan palm species richness (possibly linked to these regions' long‐term climatic suitability for palms). In contrast to species richness, the global distribution of the family range is largely in equilibrium with current climate. The small historical effects on islands are consistent with climatic buffering from their oceanic environment.

Last interglacial climate changes and environments of the Lesser Kuril arc, north-western Pacific

Last Interglacial Age deposits were studied in detail with radiocarbon and 230Th/ 232Th and 234U/ 232Th-dating on Zelenyi and Tanfil’ev Islands. The deposits of two transgressions were distinguished (MIS 5e and 5a). The deposits of maximal transgression include warm marine diatom assemblages with subtropical species. The climate was warmer than modern. On Tanfil’ev Island, marine deposits were deposited under cooler conditions (MIS 5a), covered by lacustrine and peat bog deposits. 230Th/ 232Th and 234U/ 232Th-data (interval of 69.4 + 8.2–7.0 ka and 73.0 + 5.3–4.8 ka) were obtained from this terrestrial unit. Pollen spectra established some stages of vegetation development that reflect progressive cooling. The surface peat record shows pronounced cooling that correlates with the Late Pleistocene Glacial (MIS 4). During warming in the second half of the Late Pleistocene (MIS 3), the climate was similar to modern or slightly cooler, and forest vegetation occupied the land bridge that connected the Lesser Kurils with surrounding islands. The Last Interglacial Maximum caused considerable changes to landscape zones on the Southern Kurils. The specific paleolandscape changes on small islands depended upon significant changes in the configurations of land during oscillations in sea level. Volcanic activity was another regional factor influencing different landscape components.

Seven glacial cycles in the middle-late Pleistocene of northwest Europe: Geomorphic evidence from buried tunnel valleys

The deep-ocean marine isotope record and the Antarctic and Greenland ice caps record numerous glacial and interglacial cycles since the middle Pleistocene, and yet evidence for similar numbers of ice-sheet advances over the continent and shallow shelves of northwest Europe is absent. Here, we document seven generations of regionally correlatable subglacial tunnel valleys that record the geomorphic imprint of ice sheets traversing the North Sea basin between ca. 500 and 40 ka, consistent with that predicted by proxy records of glacial and interglacial climate change. Over 180 subglacial tunnel valleys that incise into Pleistocene sediments in the North Sea basin were mapped over ∼60,000 km 2 of three-dimensional seismic-reflection data. Using a subset of these data, we identified seven separate episodes of subglacial erosion that can be correlated regionally in the UK sector of the central North Sea. The characteristics of the valley morphologies, orientations, and infill stratigraphy indicate that each set of tunnel valleys formed during a separate ice-sheet advance and retreat cycle. Stratigraphic data suggest that the tunnel valleys formed significantly later than the Brunhes-Matuyama reversal event at 780 ka and before the Last Glacial Maximum (marine isotope stage [MIS] 2; 21 ka). These results imply a more complicated glacial history for northwest Europe and more glaciations than the three-glaciation model traditionally interpreted from the terrestrial record for the past 500 k.y. Our data provide the most complete documentary evidence for repeated advance and retreat of the northwest European ice sheets since the middle Pleistocene, and for the first time indicate that terrestrial ice-sheet advances in the North Sea can be matched in number with the cold events recorded in oceanic and/or ice-core proxies of climate change over the past 500 k.y.

Pleistocene and Holocene fluvial development of the Ecemiş Valley (Central Anatolia, Turkey)

The Ecemiş River developed during the Pleistocene and Holocene in the Ecemiş basin. The basin developed because of tectonic movement on the Ecemiş Fault, which is west of the Aladağ Mountains. In the Pleistocene, glacial–interglacial climate changes directly affected the regimes and discharges of rivers, causing changes in river levels along the Ecemiş channel. Fluvial formations became extremely complicated when active tectonic movements accompanied the changes resulting from the climatic conditions. The rivers embedded in their beds according to new local base levels in interglacials. Terraces formed due to interruptions in the cycle of morphological development along the Ecemiş River. From the morphologic structure of these terraces and their positions in the Ecemiş Valley two groups and five levels of terraces were defined. In the Ecemiş Valley, modern terraces (1–5 m) formed in the Holocene, while low terrace systems (5–10 m and 15–20 m) and high terrace systems (30–40 and 70–80 m) formed in the Pleistocene.

The structure and rate of late Miocene expansion of C4 plants: Evidence from lateral variation in stable isotopes in paleosols of the Siwalik Group, northern Pakistan

This study uses stable isotope variation within individual Mio-Pliocene paleosols to investigate subkilometer-scale phytogeography of late Miocene vegetation change in southeast Asia between ca. 8.1 and 5 Ma, a time interval that coincides with dramatic global vegetation change. We examine trends through time in the distribution of low-latitude grasses (C4 plants) and forest (C3 plants) on Indo-Gangetic floodplains using carbon (δ13C) and oxygen isotopic (δ18O) values in buried soil carbonates in Siwalik Series sediments exposed in the Rohtas Anticline, north-central Pakistan. Revised, high-resolution magnetostratigraphy and a new 40Ar/39Ar date provide improved age control for the 2020 m Rohtas section. Carbon isotope results capture lateral variability of C3 versus C4 plants at five stratigraphic levels, R11 (8.0 Ma), R15 (6.74–6.78 Ma), R23 (5.78 Ma), R29 (4.8–4.9 Ma), and upper boundary tuff (UBT; 2.4 Ma), using detailed sampling of paleosols traceable laterally over hundreds of meters. Paleosols and the contained isotopic results can be assigned to three different depositional contexts within the fluvial sediments: channel fill, crevassesplay, and floodplain environments. δ13C results show that near the beginning (8.0 Ma) and after (4.0 Ma) the period of major ecological change, vegetation was homogeneously C3 or C4, respectively, regardless of paleo-landscape position. In the intervening period, there is a wide range of values overall, with C4 grasses first invading the drier portions of the system (floodplain surfaces) and C3 plants persisting in moister settings, such as topographically lower channel swales. Although abrupt on a geologic timescale, changes in abundance of C4 plants are modest (∼2% per 100,000 yr) compared to rates of vegetation turnover in response to glacial and interglacial climate changes in the Quaternary. Earlier research documented a sharply defined C3 to C4 transition in Pakistan between 8.1 and 5.0 Ma, based on vertical sampling, but this higher-resolution study reveals a more gradual transition between 8.0 and 4.5 Ma in which C3 and C4 plants occupied different subenvironments of the Siwalik alluvial plain. δ18O values as well as δ13C values of soil carbonate increase up section at Rohtas, similar to isotope trends in other paleosol records from the region. Spatially, however, there is no correlation between δ13C and δ18O values at most stratigraphic levels. This implies that the changes in soil hydrology brought about by the shift from forest to grassland (i.e., an increase in average soil evaporation) did not produce the shift through time in δ18O values. We interpret the trend toward heavier soil carbonate δ18O values as a response to changes in external climatic factors such as a net decrease in rainfall over the past 9 Ma.

Palaeoclimatic inferences from upper Palaeozoic siltstone of the Earp Formation and equivalents, Arizona‐New Mexico (USA)

AbstractThe Late Palaeozoic configuration of Pangaea contributed to a palaeoclimatic extreme that was characterized by both icehouse and monsoonal conditions. This study uses sedimentological, geochemical, and provenance data from silty facies of the Earp and equivalent Supai Formations (Arizona, New Mexico) to shed light on atmospheric circulation and glacial–interglacial climate change in westernmost equatorial Pangaea. Five silt‐rich facies comprise both loessite and marine and fluvially reworked loessite. An initial aeolian origin for the silt is indicated by the remarkably invariant grain size and the laterally continuous, sheet‐like geometry of beds. The silt‐rich facies occur in repetitive facies associations (1–20 m scale) that form mixed continental‐marine (loess, marine‐reworked loess), shallow‐marine, and continental (loess, palaeosol) ‘sequences’. Facies repetitions of both mixed continental‐marine and shallow‐marine sequences reflect a linked glacioeustatic–glacioclimatic control, whereas the continental (loess–palaeosol) couplets reflect a primary glacial–interglacial climatic cyclicity linked to glacioeustasy. Stratigraphic interpretations suggest that aeolian silt flux maximized during glacial to incipient interglacial stages (lowstand to early transgression), and decreased significantly or ceased during interglacials (highstand to early falling stage). Detrital‐zircon geochronological data indicate a transition from dominantly north‐easterly winds during the Middle Pennsylvanian to north‐westerly and south‐easterly winds by the Early Permian, which trend is inferred to reflect the onset of monsoonal circulation in western Pangaea. Relative grain‐size data support the detrital‐zircon data, and exhibit a significant decrease from the Sedona arch/Central Arizona shelf (north) to the Pedregosa basin (south) sections. Whole‐rock geochemical data suggest a relatively unweathered source for the silt in the north, and detrital‐zircon data indicate significant silt was derived from the local basement. These large piles of silt(stone) preserve valuable information for reconstructing both long‐term evolution in atmospheric circulation and short‐term fluctuations in glacial–interglacial climate. Many such indicators for long have been applied to ‘recent’ (Plio‐Pleistocene) loess, but are equally applicable to ‘deep‐time’ strata.