Quaternary Glacial-interglacial Cycles Research Articles

Precipitation variability and environmental change across late Quaternary glacial-interglacial cycles in lowland Central America: Insights from Lake Petén Itzá (Guatemala) sediments

Lowland Central America, a biodiversity hotspot in the northern Neotropics, is a region where the climate is influenced by the location and expansion-contraction of the Intertropical Convergence Zone (ITCZ) on seasonal to millennial timescales. Paleo-records from the Caribbean Sea and the eastern equatorial and subtropical Pacific Ocean illustrate the response of regional precipitation to fluctuations in global temperature, driven by glacial-interglacial cyclicity over the past 500 kyr. Here, we present a paleoclimate and paleoenvironment record from Lake Petén Itzá, lowland Guatemala, which spans the last ∼413 kyr. Sediment in the lake recorded lacustrine and terrestrial ecosystem responses to large-scale climate variability. Precipitation patterns during MIS11-9 (∼413-304 ka BP) align with the latitudinal position of the ITCZ, with superimposed effects from the strength of the Caribbean Low-Level Jet (CLLJ). A sediment hiatus, likely attributable to mass removal processes in the lake's shallower areas, spans the period from MIS8 (starting at 304 ka BP) to the end of MIS6 (at 149 ka BP). MIS6 was characterized by humid conditions, perhaps ascribable to a more southerly extension of cold fronts and intensification of the CLLJ. During MIS5, pronounced fluctuations among all sediment variables, accompanied by an abrupt decline in precipitation, may correspond with cold events inferred from North Atlantic Ocean sediment cores. Although discontinuous, the Lake Petén Itzá sediment record provides a window into late Quaternary climate and environmental change in lowland Central America.

Weathering and pedogenesis of the Holocene aeolian loess-paleosol sections in the Guanzhong Basin on the Chinese Loess Plateau

The aeolian loess-paleosol sections on the Chinese Loess Plateau (CLP) represent invaluable archives for elucidating the dynamics of the East Asian Monsoon (EAM) across Quaternary glacial-interglacial cycles. In this study, a Holocene aeolian loess-paleosol section in the Guanzhong Basin on the CLP was meticulously investigated to assess the intensity of weathering and pedogenesis, and to discern its paleoclimatic implications. Through comprehensive analysis of chemical element composition and micromorphology, it was revealed that the majority of stratigraphic units within the Holocene aeolian loess-paleosol section exhibit indications of weak weathering and pedogenesis, while the mid-Holocene paleosol approaches to moderate weathering and pedogenesis. Hierarchically, the intensity of weathering and pedogenesis among the stratigraphic units can be ranked as follows: paleosol > topsoil > recent loess > transitional loess. Furthermore, the chemical index of alteration (CIA) values of the mid-Holocene paleosol exhibit a gradient decline from southeast to northwest, aligning with present-day temperature and precipitation distributions under the predominant influence of the East Asian summer Monsoon (EASM). Thus, it can be inferred that the robust impact of the EASM on weathering and pedogenesis of paleosol was pronounced during the mid-Holocene Climatic Optimum. These results are of significance in exploring the Holocene weathering and pedogenesis and paleoenvironmental evolution on the CLP.

Elemental composition of smectite minerals in continental rise sediments from the Amundsen Sea, West Antarctica, as a tool to identify detrital input from various sources throughout late Quaternary glacial-interglacial cycles

Detrital smectite is a ubiquitous clay mineral in marine sediments and has a variable total Fe, Al, and Mg composition depending on the source, i.e., bedrock or unconsolidated sedimentary strata, the smectite is derived from. Analyses of elemental composition of smectite minerals in marine sediments can help to differentiate the smectite sources and, thus, sediment provenance, with potentially far-reaching paleo-environmental implications. In this study, we investigated the smectite compositions of modern-latest Holocene seafloor surface sediments deposited offshore from the Amundsen Sea drainage sector, where the West Antarctic Ice Sheet is currently unstable and losing mass due to ocean-forced melting, to detect and understand the variabilities of their elemental composition and geographical distribution. The smectite composition in continental rise sediments was compared to that of potential source areas on the Amundsen Sea continental shelf and in the sub-Antarctic South Pacific basin. Furthermore, we analyzed the smectite composition of sediments in continental rise cores deposited during the last glacial and last interglacial periods to reconstruct source variations over glacial-interglacial cycles. In particular, high contents of Al–Fe-rich smectite indicate that the glacial sediments had been supplied from the coastal region around Pine Island Bay by the cross-shelf advance of the West Antarctic Ice Sheet during the last glacial period. This clearly contrasts with the smectite minerals in rise sediments deposited during the present and the last interglacial periods that are composed of two distinct smectite types (Mg-rich and Al-rich, respectively), indicating their supply from multiple sources. During interglacials, Mg-rich smectite is probably transported by Circumpolar Deep Water from the sub-Antarctic South Pacific basin to the continental rise, while Al-rich smectite is supplied as part of ice rafted debris and by marine currents from the coasts around the Amundsen Sea embayment. Our research demonstrates that analysis of the elemental composition of smectite minerals on the Amundsen Sea continental margin provides a valuable tool to trace variations in sources for detrital sediment components and their pathways throughout glacial-interglacial cycles.

Geologically calibrated mammalian tree and its correlation with global events, including the emergence of humans.

A robust timetree for Mammalia was constructed using the time calibration function of BEAST v1.10.4 and MEGA 11. The analysis involved the application of times of the most recent common ancestors, including a total of 19 mammalian fossil calibration ages following Benton etal. (Palaeontologia Electronica, 2015, 1-106) for their minimum ages. Additionally, fossil calibration ages for Gorilla, Pan, and a geologic event calibration age for otters were incorporated. Using these calibration ages, I constructed a geologically calibrated tree that estimates the age of the Homo and Pan splitting to be 5.69 Ma. The tree carries several significant implications. First, after the initial rifting at 120 Ma, the Atlantic Ocean expanded by over 500 km around Chron 34 (84 Ma), and vicariant speciation between Afrotheria (Africa) and Xenarthra (South America) appears to have commenced around 70 Ma. Additionally, ordinal level differentiations began immediately following the K-Pg boundary (66.0 Ma), supporting previous hypothesis that mammalian radiation rapidly filled ecological niches left vacant by non-avian dinosaurs. I constructed a diagram depicting the relationship between base substitution rate and age using an additional function in BEAST v1.10.4. The diagram reveals an exponential increase in the base substitution rate approaching recent times. This increased base substitution rate during the Neogene period may have contributed to the expansion of biodiversity, including the extensive adaptive radiation that led to the evolution of Homo sapiens. One significant driving factor behind this radiation could be attributed to the emergence and proliferation of C4 grasses since 20 Ma. These grasses have played a role in increasing carbon fixation, reducing atmospheric CO2 concentration, inducing global cooling, and initiating Quaternary glacial-interglacial cycles, thereby causing significant climatic changes.

Global biome patterns of the Middle and Late Pleistocene

AbstractOur primary aim was to assess the hypothesis that distinctive features of the patterns of vegetation change during successive Quaternary glacial–interglacial cycles reflect climatic differences arising from forcing differences. We addressed this hypothesis using 207 half‐degree resolution global biome pattern simulations, for time slices between 800 and 2 ka, made using the LPJ‐GUESS dynamic global vegetation model. Simulations were driven using ice‐core atmospheric CO2 concentrations, Earth's obliquity, and outputs from a pre‐industrial and 206 palaeoclimate experiments; four additional simulations were driven using projected future CO2 concentrations. Climate experiments were run using HadCM3. Using a rule‐based approach, above‐ground biomass and leaf area index of LPJ‐GUESS plant functional types were used to infer each grid cell's biome. The hypothesis is supported by the palaeobiome simulations. To enable comparisons with the climatic forcing, multivariate analyses were performed of global vegetation pattern dissimilarities between simulations. Results showed generally similar responses to glacial–interglacial climatic variations during each cycle, although no two interglacials or glacials had identical biome patterns. Atmospheric CO2 concentration was the strongest driver of the dissimilarity patterns. Dissimilarities relative to the time slice with the lowest atmospheric CO2 concentration show the log‐linear relationship to atmospheric CO2 concentration expected of an index of ecocarbon sensitivity. For each simulation, extent and total above‐ground biomass of each biome were calculated globally and for three longitudinal segments corresponding to the major continental regions. Mean and minimum past extents of forest biomes, notably Temperate Summergreen Forest, in the three major continental regions strongly parallel relative tree diversities, hence supporting the hypothesis that past biome extents played an important role in determining present diversity. Albeit that they reflect the climatic consequences only of the faster Earth system components, simulated potential future biome patterns are unlike any during the past 800 ky, and likely will continue to change markedly for millennia if projected CO2 concentrations are realised.

Genomic insights of evolutionary divergence and life history innovations in Antarctic brittle stars.

Understanding the drivers of evolutionary innovation provides a crucial perspective of how evolutionary processes unfold across taxa and ecological systems. It has been hypothesised that the Southern Ocean provided ecological opportunities for novelty in the past. However, the drivers of innovation are challenging to pinpoint as the evolutionary genetics of Southern Ocean fauna are influenced by Quaternary glacial-interglacial cycles, oceanic currents and species ecology. Here we examined the genome-wide single nucleotide polymorphisms of the Southern Ocean brittle stars Ophionotus victoriae (five arms, broadcaster) and O. hexactis (six arms, brooder). We found that O. victoriae and O. hexactis are closely-related species with interspecific gene flow. During the late Pleistocene, O. victoriae likely persisted in a connected deep water refugium and in situ refugia on the Antarctic continental shelf and around Antarctic islands; O. hexactis persisted exclusively within in situ island refugia. Within O. victoriae, contemporary gene flow linking to the Antarctic Circumpolar Current, regional gyres and other local oceanographic regimes was observed. Gene flow connecting West and East Antarctic islands near the Polar Front was also detected in O. hexactis. A strong association was detected between outlier loci and salinity in O. hexactis. Both O. victoriae and O. hexactis are associated with genome-wide increase in alleles at intermediate-frequencies; the alleles associated with this peak appear to be species specific, and these intermediate-frequency variants are far more excessive in O. hexactis. We hypothesise that the peak in alleles at intermediate frequencies could be related to adaptation in the recent past, linked to evolutionary innovations of increase in arm number and a switch to brooding from broadcasting, in O. hexactis.

Phylogeography of Falagoniamexicana Sharp, 1883 (Coleoptera, Staphylinidae, Aleocharinae).

Falagoniamexicana is an aleocharine distributed from northern Mexico to Guatemala and El Salvador. It is associated with Attamexicana ants and lives within their piles of waste or external debris. The phylogeography and historical demography of 18 populations from Mexico, Guatemala, and El Salvador were studied. The data set encompasses a 472 bp fragment of the COI. Results suggest that F.mexicana was originated during Middle Pliocene (ca. 0.5 Mya), starting its diversification at the Upper Pleistocene and Holocene. Populations were recovered forming at least four main lineages, with a significant phylogeographic structure. Evidence of contemporary restricted gene flow was found among populations. The historical demography suggests that the geographic structure is due to recent physical barriers (e.g., Isthmus of Tehuantepec) rather than ancient geological events. Also, recent geological and volcanic events in the east of the Trans-Mexican Volcanic Belt and the Sierra Madre Oriental might be responsible for the restricted gene flow among populations. Skyline-plot analyses suggested that a demographic expansion event took place at the end of the Late Quaternary glacial-interglacial cycles.

Late Quaternary Ponto-Caspian dinoflagellate cyst assemblages from the Gulf of Corinth, Central Greece (eastern Mediterranean Sea)

We present here the first long Quaternary record of organic-walled dinoflagellate cyst assemblages analysed from sediment cores retrieved during the International Ocean Discovery Program (IODP) Expedition 381 in the Gulf of Corinth. Site M0078A is located in the central part of the Gulf of Corinth (GoC), a semi-isolated marine basin that was repeatedly isolated and reconnected to the Mediterranean Sea during the Quaternary glacial/interglacial cycles. Our results show that dinoflagellate cysts are sorted in two major ecogroups, each group alternating between marine and isolated/brackish conditions. The marine intervals are characterised by high dinocyst diversity whereas the isolated intervals are dominated by taxa thriving in low-salinity conditions such as Spiniferites cruciformis and Pyxidinopsis psilata. In several of these assemblages, S. cruciformis is so prevalent that it forms almost monospecific assemblages. The low salinity dinocyst assemblages are reported for the first time outside the Ponto-Caspian region and they show a close affinity to modern assemblages from the Black Sea, Caspian Sea and Marmara Sea. The alternations between marine and brackish conditions recorded in the Gulf of Corinth reflect changes in surface water salinity (SSS) and temperature (SST), in response to the Quaternary glacial-interglacial cycles. These seem to be in good agreement with regional and global marine isotope and sea-level records. Our findings suggest that the study region sensitively responds to climate forcing at orbital time scales and that local factors most likely drive shifts in dinoflagellate species composition and diversity.

Multiple Equilibria in a Coupled Climate–Carbon Model

Abstract Multiple stable equilibria are intrinsic to many complex dynamical systems, and have been identified in a hierarchy of climate models. Motivated by the idea that the Quaternary glacial–interglacial cycles could have resulted from orbitally forced transitions between multiple stable states mediated by internal feedbacks, this study investigates the existence and mechanisms of multiple equilibria in an idealized, energy-conserving atmosphere–ocean–sea ice general circulation model with a fully coupled carbon cycle. Four stable climates are found for identical insolation and global carbon inventory: an ice-free Warm climate, two intermediate climates (Cold and Waterbelt), and a fully ice-covered Snowball climate. A fifth state, a small ice cap state between Warm and Cold, is found to be barely unstable. Using custom radiative kernels and a thorough sampling of the model’s internal variability, three equilibria are investigated through the state dependence of radiative feedback processes. For fast feedbacks, the systematic decrease in surface albedo feedback from Cold to Warm states is offset by a similar increase in longwave water vapor feedback. At longer time scales, the key role of the carbon cycle is a dramatic lengthening of the adjustment time comparable to orbital forcings near the Warm state. The dynamics of the coupled climate–carbon system are thus not well separated in time from orbital forcings, raising interesting possibilities for nonlinear triggers for large climate changes. Significance Statement How do carbon cycle and other physical processes affect the physical and mathematical properties of the climate system? We use a complex climate model coupled with a carbon cycle to simulate the climate evolution under different initial conditions. Four stable climate states are possible, from the Snowball Earth, in which ice covers the whole planet, to the Warm state, an ice-free world. The carbon cycle drives the global climate change at an extremely slower pace after sea ice retreats. Sea ice and water vapor, on the other hand, constitute the major contributing factors that accelerate faster climate change.

Palaeoceanographic and palaeoenvironmental controls on late Quaternary benthic foraminifera of the western continental slope of South Africa

Benthic foraminifera from two gravity cores recovered on the western continental slope (3522 and 3631 m water depth) of South Africa were studied to determine bottom water conditions and benthic environments over late Quaternary glacial-interglacial cycles. Benthic foraminifera assemblages and the carbon isotopic composition (δ13C) of Cibicidoides wuellerstorfi and Globoconella inflata were used to reconstruct palaeoenvironmental conditions. The assemblages reflect influences from substrate, productivity (seasonal and annual variations in the flux of organic matter, such as phytodetritus to the seafloor) and bottom water oxygenation. Uvigerinid forms were found to be distributed along bathymetric depths that also reflect oxygenation of bottom waters, where hispid and hispidocostate forms were more abundant at depths of oxygen-enriched bottom waters on the lower slope. These uvigerinids and other benthic species such as Epistominella exigua were also found to benefit from periods of high productivity. Palaeoproductivity increased during glacial periods but decreased sharply by a difference of ∼1‰ in δ13C during glacial terminations, reflecting a less nutrient-rich bottom water signal. During interglacial periods, epifaunal foraminifera and taxa adapted to oxygen-enriched environments, such as Cibicidoides spp. and high oxygen assemblages increased in abundance and were correlated to the less radiogenic regional εNd signals, while the abundance of high-productivity fauna and assemblages, associated with the nutrient-rich Southern Component Water, and that are adapted to a high organic matter flux and low oxygen conditions, decreased. Interglacial periods were reflected to exhibit benthic environments that are more oligotrophic, while glacial periods were interpreted to reflect more eutrophic conditions.

An absolutely dated record of climate change over the last three glacial–interglacial cycles from Chinese loess deposits

Abstract Chinese loess-paleosol sequences have long been regarded as the continental counterpart of deep-sea sediments in terms of their record of the Quaternary glacial–interglacial cycles. However, absolute chronologies for loess-paleosol sequences older than ca. 130 ka on the Chinese Loess Plateau are scarce. We conducted the first high-resolution luminescence dating, extending back to 350 ka, of the classical Luochuan loess section of the central Chinese Loess Plateau. Bacon age-depth modeling of the luminescence ages was used to obtain an age framework. The results indicate that on orbital timescales, loess accumulation at Luochuan was continuous over the last three glacial–interglacial cycles. The new age framework resolves discrepancies between orbitally tuned age models at several boundaries and provides new evidence supporting the reassignment of the Marine Isotope Stage 8/9 boundary age from 300 ka to ca. 280 ka. Our results also suggest that published astronomical timescales for the loess deposits of the Chinese Loess Plateau over the last ~2.6 m.y. are probably broadly reliable, as are the related regional and global climatic interpretations.

Early Oligocene—Late Miocene Wildfire History in the Northern Tibetan Plateau and Links to Temperature-Driven Precipitation Changes

Late Cenozoic wildfire evolution in Inner Asia has been attributed to both ice-volume modulating precipitation changes and surface uplift of the Tibetan Plateau. Whether this is the case or not requires additional research and wildfire records from older periods. In this study, 251 microcharcoal samples from the Huatugou section in the western Qaidam Basin are used to reconstruct the early Oligocene-middle Miocene wildfire history of the northern Tibetan Plateau. The results show that wildfires remained relatively frequent before ∼26 Ma, then reduced gradually until ∼14 Ma, and finally increased slightly but still at low level between 14 and 12 Ma. The wildfire variations can be correlated to the steppe-based dryness changes, and both of which are coincident with global temperature changes. We infer that mean annual temperature might have played a dominant role in controlling wildfire frequencies in the northern Tibetan Plateau through modulating atmospheric moisture content. This conclusion is in line with previous studies including microcharcoal-based wildfire records of 18–5 Ma successions from the Qaidam Basin as well as soot-based wildfire records from Quaternary glacial–interglacial cycles of the Chinese Loess Plateau.

Biogeographic and metabolic studies support a glacial radiation hypothesis during Chrysanthemum evolution.

Chrysanthemum (Chrysanthemum morifolium Ramat.) is an economically important plant species growing worldwide. However, its origin, especially as revealed by biogeographic and metabolomics research, remains unclear. To understand the geographic distribution of species diversity and metabolomics in three genera (Chrysanthemum, Ajania, and Phaeostigma), geographic information systems and gas chromatography–mass spectrometry were used in 19, 15, and 4 species respectively. China and Japan were two potential panbiogeographic nodes and diverse hotspots of Chrysanthemum, with species richness ratios of 58.97 and 33.33%. We studied different species from two hotspots which in similar geographical environments had closer chemotaxonomic relationships under the same cultivation conditions based on a cluster of 30 secondary metabolites. The average distribution altitude (ADA) differed significantly among Chrysanthemum, Ajania, and Phaeostigma in which it was 1227.49, 2400.12, and 3760.53 m.a.s.l. respectively, and the presence/absence of ray florets (RF) was significantly correlated with ADA (−0.62). Mountain landform was an important contributor to global Chrysanthemum diversity, playing a key role in the divergence and distribution pattern of Chrysanthemum and its allies. The Hengduan Mountains–Qinling Mountains (HDQ) in China was a potential secondary radiation and evolution center of Chrysanthemum and its related genera in the world. During the Quaternary glacial–interglacial cycles, this region became their refuge, and they radiated and evolved from this center.

Late Quaternary deep marine sediment records off southern Africa

Abstract High-resolution mapping, sampling and analysis of upper Quaternary southern African continental margin sediments recovered from beyond the Last Glacial Maximum shoreline (>130 m water depth) have expanded our understanding of how marine and terrestrial records are linked over glacial-interglacial climatic cycles. This paper synthesises data currently available from the deep seafloor around southern Africa and, specifically, core sites that demonstrate terrestrial sedimentological connectivity. Several proxies and case studies reveal the evolution of depositional systems, palaeoceanography and palaeoclimate over the last 191 kyr. Hydroacoustic mapping and investigations of submarine canyons have been carried out primarily on the eastern and southwestern margins, while palaeoceanographic productivity and microfossil assemblages have been applied most extensively on the western marine and southern Agulhas Bank. Studies on the western margin indicate that enhanced productivity, less oxygenated bottom waters and reduced marine faunal diversity in the transition to glacial periods, while glacial terminations are associated with reduced productivity and more oxygenated bottom waters. These changes, linked to palaeoceanography and late Quaternary sea-level fluctuations, influence the sedimentary record and sedimentation rates. On the eastern margin, sediment fluxes applied as proxies for rainfall offshore of the Great Kei, Umzimvubu, Limpopo and Zambezi rivers indicate that the southern African climate responds to changes in orbitally-modulated insolation and in particular, to the ~23 kyr precessional cycle, where the proxy records keep pace with this and then diverge at ~80 to 70 kyr. Since the penultimate glacial (Marine Isotope Stage/MIS 6), more humid conditions observed in southern Africa, as the Northern Hemisphere entered phases of rapid cooling, were potentially driven by a combination of warming in the Agulhas Current and shifts of the subtropical anticyclones. Broadly, the sedimentary records reviewed suggest fluctuations in climate and oceanographic circulation that are strongly correlated with the global benthic δ18O record, suggesting sensitivity to high-latitude forcing, and a strong influence of late Quaternary glacial-interglacial cycles despite these marine sites being far-removed from terrestrial environments.

On the significance of periglacial conditions in active mountain belts for chemical weathering processes: Insights from the Chayu area, SE Tibet

Chemical weathering is a key player of the long-term (Ma) timescale carbon cycle. Weathering processes under alpine periglacial environment could be important during the Quaternary glacial-interglacial cycles, but such timescale is difficult to fully apprehend for the weathering impact on C cycles. The Chayu river catchment in SE Tibet spans a geographical gradient from a periglacial environment in the north to a monsoonal environment in the south and we have investigated the various chemical weathering along this climatological gradient. The lithology of the catchment is dominated by granitoid rocks. Due to the active tectonic activity and the periglacial environment, mass wasting deposits including landslide deposits, talus and rock glaciers are found in the catchment. In order to figure out the influence of mass wasting process on water chemistry, we sampled seepage water from the mass wasting deposits and nearby stream water for comparison. Cyclic input contributes 5.7 to 8.2% to the dissolved load of the water samples, suggesting the dominance of weathering contribution within this granitoid catchment. The contributions from sulfuric acid and carbonate to chemical weathering are estimated based on the elemental data and the oxidation of sulfide as the source of dissolved sulfate. In the monsoonal South Chayu, the K*/Si, Ca*/Si ratios of the bedrock landslide seepages are higher than the streams by 265% and 117%, respectively. Together with the high contribution of carbonate (~80%) and sulfuric acid (20 to 40%), the results indicates that landslide deposits have strong influences on local water chemistry by processes identical to bedrock landslides of greywacke and carbonate lithology in active mountain belts, suggesting that the enhanced weathering by landslide process can apply to granitoid regions as well. In the North Chayu with periglacial environment, the chemistry of the seepages and streams are nearly identical, and are similar to the landslide seepage water in the south. Such result highlights the role of the periglacial critical zone without the influence of mass wasting deposits that possibly enhances chemical weathering. The high porosity created by repeat freeze-thaw cycles provides more fresh mineral surfaces for water-rock interaction. But, the low temperature and the partial availability of water, restricted to thaw periods, provide strong kinetic limitations that inhibit the silicate weathering. Such features of the alpine periglacial critical zone led to the preferential weathering of the most reactive mineral phases including calcite, sulfide, and the interlayer K+ of sheet silicates (biotite, chlorite), resulting in the characteristic periglacial water chemistry. The influence of periglacial environment on local water chemistry may apply beyond the North Chayu and may play an important role in modulating the chemical weathering within the transition between Quaternary glacial and interglacial period.

Exploring the effects of the quaternary glacial–interglacial cycles on the geographic distributions of tropical Andean rodents: species in the genus Aepeomys Thomas, 1898 (Thomasomyini: Sigmodontinae: Cricetidae) as a case study

ABSTRACT The Quaternary glaciations had great impacts on the historical biogeography of small mammal species. Recent studies have showed the effects of these climatic cycles on the diversification of several Neotropical rodents, but these have focused on species whose distributions do not encompass the tropical Andes. Thus, the influences of these climatic dynamics on the evolutionary history of tropical Andean rodent species remain unknown. The effects of these climatic changes were addressed on Aepeomys lugens and A. reigi, two Thomasomyine endemics from the Cordillera de Mérida in the Venezuelan Andes. The past potential geographic distribution of both species was inferred using an ecological niche modeling approach. The estimations obtained indicated that the availability of the suitable climatic conditions for these taxa has varied in size and location during the last 140,000 years. The spatial projection of the niche models onto the climatic scenarios explored indicates that the effects over the historical distributions were smaller in A. lugens than in A. reigi. These results show that the current geographic distribution of both Andean rodents conceals complex biogeographic histories, and characterizations of the demographic history and genetic diversity will be required to understand the evolution of the genus Aepeomys in the Andes.

Late Quaternary high-resolution seismic stratigraphy and core-based paleoenvironmental reconstructions in Ona Basin, southwestern Scotia Sea (Antarctica)

The variability of sedimentation patterns and processes driven by late Quaternary glacial-interglacial paleoclimatic and paleoceanographic changes are investigated in Ona Basin, southwestern Scotia Sea. The interest of this area lies in the fact that the nearby Antarctic Peninsula has recorded extreme climatic variability, and the Drake Passage-Scotia Sea oceanic domain is influenced by two major Southern Ocean water masses, the eastward-flowing Antarctic Circumpolar Current (ACC) and the westward-flowing Weddell Sea Deep Water (WSDW). These goals are achieved through the examination of a grid of very high-resolution sub-bottom profiles and two gravity cores collected in Ona Basin. Multi-proxy data derived from the gravity cores include 14C-derived ages, descriptions of sedimentary units and diatom assemblages, and continuous logging of physical properties and micro-XRF core scanning.The sub-surface seismic stratigraphy is composed of four seismic units (U4 to U1) with a dominant sub-parallel configuration, with local occurrence of wavy facies and intercalations of transparent seismic facies. Additionally, four sedimentary units were recognized through sediment core analysis from bottom to top: Unit IV is composed of slightly bioturbated diatom-rich mud and silty mud with sparse ice-rafted debris (IRDs); Unit III is composed of gravelly silty to sandy mud with large amounts of IRDs; Unit II mostly contains bioturbated diatomaceous mud; and Unit I is composed of diatom-rich silty to sandy mud. The highest diatom abundances are found in Unit II, whereas highly variable abundances are found in Unit IV. The most common diatoms are Fragilariopsis kerguelensis and Chaetoceros subg. Hyalochaete. Overall, these characteristics document a change in the depositional style from terrigenous during the Last Glacial Maximum (LGM) to hemipelagic sedimentation during the deglaciation.The high-resolution seismic stratigraphy analysis reveals significant fluctuations in the regional bottom-current patterns during the late Quaternary (i.e., after 0.4 Ma) glacial-interglacial cycles. An overall strengthening of the westward-flowing WSDW is postulated in relation to latitudinal displacements of the interphase between the deeper ACC and the WSDW, together with enhanced interactions between along- and downslope processes. In addition, sedimentological, geochemical, and micropaleontological analyses revealed two distinctive phases during the late Pleistocene, in terms of paleoenvironments and paleoceanographic conditions. During the LGM, extensive sea-ice coverage limited biogenic productivity in the ocean. Increased terrigenous input was largely supplied by the westward-flowing WSDW, under a reduced ACC influence due to the northward location of fronts. During deglaciation, the sediment record indicates reduced sea-ice cover and increased open-ocean conditions and surface water productivity, as well as a long-term intensification of the WSDW flow. We postulate bottom-current strengthening was driven by an increased Weddell Sea water export and the southward migration of fronts as a consequence of major retreat of sea ice, enhancing the ACC influence in the southern Ona Basin, and thus, affecting the sloping interphase between the deeper ACC and the WSDW.

Evidence for ephemeral ring species formation during the diversification history of western fence lizards (Sceloporus occidentalis).

Divergence is often ephemeral, and populations that diverge in response to regional topographic and climatic factors may not remain reproductively isolated when they come into secondary contact. We investigated the geographical structure and evolutionary history of population divergence within Sceloporus occidentalis (western fence lizard), a habitat generalist with a broad distribution that spans the major biogeographical regions of Western North America. We used double digest RAD sequencing to infer population structure, phylogeny and demography. Population genetic structure is hierarchical and geographically structured with evidence for gene flow between biogeographical regions. Consistent with the isolation-expansion model of divergence during Quaternary glacial-interglacial cycles, gene flow and secondary contact are supported as important processes explaining the demographic histories of populations. Although populations may have diverged as they spread northward in a ring-like manner around the Sierra Nevada and southern Cascade Ranges, there is strong evidence for gene flow among populations at the northern terminus of the ring. We propose the concept of an "ephemeral ring species" and contrast S.occidentalis with the classic North American ring species, Ensatina eschscholtzii. Contrary to expectations of lower genetic diversity at northern latitudes following post-Quaternary-glaciation expansion, the ephemeral nature of divergence in S.occidentalis has produced centres of high genetic diversity for different reasons in the south (long-term stability) vs. the north (secondary contact).

Chronostratigraphic framework and paleoenvironmental interpretation of the Holocene loess-paleosol sequence in the Luoyang Basin, Central China

Abstract The loess-paleosol sequences in the Loess Plateau are major paleoclimatic archives which document the evolution of East Asian Monsoon (EAM) during the Quaternary glacial-interglacial cycles. A complete Holocene loess-paleosol sequence was identified by detailed field investigations in the Luoyang Basin, which is located at the southeastern margin of the Loess Plateau, Central China. Laboratory analysis including magnetic susceptibility, hygroscopic water, grain-size distribution, geochemical elements characteristics, AMS 14C dating, Bacon age-depth modelling and stratigraphic correlations have been carried out. Our results show that the stratigraphic sequence, from top to bottom, is topsoil (TS), recent loess (L0), mid-Holocene paleosol (S0), early Holocene transitional loess (Lt) and Malan loess (L1). The intensity of weathering and pedogenesis varies significantly in different layers and presents such a tendency of S0 > L0 > Lt > L1. This indicates four distinct stages in the EAM evolution: 1) an extreme dry-cold climate with strengthened East Asian winter monsoon (EAWM) during the last glacial period, 2) an episode of gradual transition to the warm-humid climate with intensive East Asian summer monsoon (EASM) in the early Holocene (11,500–8500 yr BP), 3) a warm-humid climate affected by intense EASM in the mid-Holocene (8500–3100 yr BP), and lastly 4) an episode of gradually shifting to dry-cool climate with weakened EASM (3100–0 yr BP). These results provide basic data for exploring the Holocene weathering and pedogenesis and paleoenvironmental evolution in Central China.

The Quaternary range dynamics ofNoccaea iberidea(Brassicaceae), a typical representative of subalpine/alpine steppe communities of Anatolian mountains

AbstractThe responses of Anatolian plants to global climate change have been poorly investigated. In this study, we aimed to understand how climatic oscillation during the Quaternary period helped to shape the current distribution patterns of the Anatolian endemic Noccaea iberidea, a typical representative of tragacanthic (thorny cushion) steppe communities of Anatolia. We used ecological niche modelling combined with statistical phylogeography, based on nuclear ribosomal ITS and plastidic trnL-F and trnS-ycf9 regions. Both the structure of the haplotype networks and the results of the extended Bayesian skyline plot analysis clearly indicated that N. iberidea has been through a recent population expansion. This interpretation was also supported by ecological niche modelling analysis, which showed that the availability of areas of high suitability expanded from the Last Interglacial to the Last Glacial Maximum, suggesting that N. iberidea might have expanded its range during the glacial periods. In conclusion, the study improves our understanding of the demographic history and responses of steppe plant communities of Anatolia to global climate changes through the Late Quaternary glacial–interglacial cycles, which in turn might aid in the development of future conservation strategies.