Last Glacial Maximum Conditions Research Articles

Late Pleistocene glacial advances, equilibrium-line altitude changes and paleoclimate in the Jakupica Mts (North Macedonia)

In the Jakupica Mts a plateau glacier was reconstructed (max. area ∼45 km2, max thickness: ∼260 m). The study area comprises six formerly glaciated valleys, five of which were fed by the plateau glacier and one had an independent cirque when local glaciation reached its maximum ice extent (MIE). The equilibrium line altitude (ELA) of the most extended glacial phase was at 2075+37/-25 m asl. The 10Be cosmic ray exposure (CRE) age of this phase was estimated at 19.3+1.7/-1.3 ka, conformable with the Last Glacial Maximum (LGM). CRE ages from the next moraine generation placed the first phase of deglaciation to 18.2+1.0/-3.0 ka. The samples from the moraine of the penultimate deglaciation phase provided CRE ages with large scatter and biased towards old ages, which is probably the result of inherited cosmogenic nuclide concentrations within the rock.Glacio-climatological modelling was performed for the MIE, which has a well-established LGM age. The degree-day model was used to calculate the amount of accumulation required to sustain the glaciological equilibrium assuming a certain temperature drop at the ELA. The degree-day model constrained by the pollen-based July paleo-temperature reconstructions yielded an annual total melt at the LGM ELA comparable to or slightly higher than the current mean annual precipitation at the same elevation. These wetter LGM conditions inferred from the paleo-glaciological evidence in Jakupica Mts suggest an enhanced moisture advection in the region.

The form, distribution and palaeoclimatic implications of cirques in southwest Turkey (Western Taurus)

The Taurus Mountains of southwest Turkey are split into numerous separated ranges, of which eleven supported former glaciers. We describe cirques and related moraines in four new locations, as well as those in seven ranges where glaciation was previously known. This gives a complete inventory of the 85 cirques in southwest Turkey. These are comparable in size to those elsewhere, but narrower and often less developed. Lengths averaging 672 m are high relative to widths of 542 m. Overall axial gradients average 22.4°. Cirque floor altitudes are controlled largely by altitudes of the mountains above, but they also vary in relation to precipitation, in sympathy with ELAs (Equilibrium Line Altitudes) of former glaciers. In most ranges where glaciers were short (extending little beyond cirques), ELA can be predicted from mean mid-floor altitude. Our observations demonstrate lower ELAs than in previous literature. Both ELAs and cirque floors rise eastward in the west, and northward inland from the coast. This supports the importance of winds from the west and southwest, off the Mediterranean Sea, bringing LGM (Last Glacial Maximum) conditions wetter than present to mountains near the coast. Cirques face on average a little east of north, showing the effects of shade and differential solar radiation receipt.

A Last Interglacial speleothem record from the Sieben Hengste cave system (Switzerland): Implications for alpine paleovegetation

A precisely dated speleothem isotope record from the Sieben Hengste cave system, Switzerland, reveals a Last Interglacial (LIG) climate optimum centred at 128.1 ± 1.2 ka. The oxygen isotope signal is consistent with a temperature-dominated record and shows a strong correlation with the modelled Greenland δ18O signal. The comparison with speleothems formed during the Last Glacial Maximum (LGM) in the same cave indicates a 4–5‰ difference in δ18O between peak LIG and peak LGM conditions, suggesting peak LIG temperatures being up to 3 °C higher than the Holocene average. Pollen extracted from the stalagmite indicates a vegetation response delayed by up to 3 ka with maximum pollen concentrations recorded at 125 ± 2.2 ka. Our results support a regional vegetation dominated by thermophile tree species including Corylus (hazel), Quercus robur-type (oak), Ulmus (elm), Tilia (lime tree) and Hedera (ivy), consistent with slightly warmer conditions than today. Despite the relatively low pollen concentration, the speleothem-based pollen spectra are consistent with regional pollen assemblage zones from paleolake sediments and provide the first direct paleovegetation evidence of thermophilization during the LIG at high altitudes in the Alps.

Northeast Siberian Permafrost Ice‐Wedge Stable Isotopes Depict Pronounced Last Glacial Maximum Winter Cooling

AbstractStable isotopes (δ18O, δD) of wedge ice hold potential to reconstruct past winter climate conditions. Here, we present records of the marine isotope stages (MIS) 3 and 2 including the last Glacial maximum (LGM) from Bol’shoy Lyakhovsky Island (NE Siberia). MIS 3 wedge ice dated from 52 to 40 Kyr b2k varies between −32 and −29‰ in δ18O. Colder LGM conditions are implied by δ18O of −37‰ around 25 Kyr b2k. Similar Deuterium excess values indicate comparable moisture sources during MIS 3 and MIS 2. Regional LGM climate reconstructions depend on the seasonal resolution of the proxies and model simulations. Our wedge‐ice record reflects coldest winters during global minima in atmospheric CO2 and sea level. The extreme LGM winter cooling is not represented in model projections of global LGM climate where West Beringia shows noticeably little cooling or even warming in mean annual temperatures compared to the late Holocene.

Seasonal Variation of the Westerly Jet over Asia in the Last Glacial Maximum: Role of the Tibetan Plateau Heating

AbstractThe westerly jet (WJ) is an important component of atmospheric circulation, which is characterized by prominent seasonal variations in intensity and position. However, the response of the WJ over Asia during the Last Glacial Maximum (LGM) is still not clear. Using general circulation model experiments, the seasonal behaviors of the WJ over central Asia and Japan are analyzed in this paper. The results show that, compared to the present day (PD), the WJ presents a complicated response during the LGM, both in intensity and position. Over central Asia, it becomes weaker in both summer and winter. But over Japan, it is enhanced in summer but becomes diminished in winter. In terms of position, the WJ over central Asia shifts southward in both summer and winter, whereas the WJ over Japan moves southward in summer but does not change obviously relative to PD in winter. Such WJ changes are well explained by meridional temperature gradients in high troposphere, which is closely linked to seasonal thermal anomalies over the Tibetan Plateau (TP). Despite cooler LGM conditions, the anomalous warming center over the TP becomes stronger in summer. Derived from the heat budget equation, the stronger heating center is mainly caused by the weaker adiabatic cooling generated from ascending motion over the area south of the TP. In winter, the cooling over the TP is also strengthened, mostly owing to the subsidence-induced weaker adiabatic heating. Due to the importance of the WJ, the potential role of TP thermal effects should be a focus when explaining the East Asian climate change during the LGM.

Distribution shifts in habitat suitability and hotspot refugia of Andean tree species from the last glacial maximum to the Anthropocene

ABSTRACT Forecasting the effects of climate change on the distribution of Andean trees (Polylepis, Rosaceae) is important to understand how species respond to climate variability and to assess their resilience to the ongoing climate crisis. Here, paleodistribution modelling is used to assess distribution shifts of 17 Polylepis species during the Last Glacial Maximum (LGM), mid-Holocene (MH), and the Anthropocene in the central Andes. Species distribution models (SDMs) were computed by combining presence records and current climatic conditions using Maxent and projected onto three climatic scenarios for the LGM (~22,000 yr BP), the MH (~6,000 yr BP), and the Anthropocene (1,970–2,000). Subsequently, current refugia hotspots were identified by intersecting suitable habitat over the LGM, MH, and anthropogenic conditions for all the studied species. SDMs for the LGM and MH showed a contraction of climate suitable habitat for most of the species in comparison to the Anthropocene. Four current refugia hotspots were identified: central Cordillera of Peru, Lake Titicaca basin, western Cordillera of Bolivia, and northern Chile. In general, SDMs were consistent with patterns proposed with pollen records, and partially with available phylogeographic studies. Current hotspots are highly important areas for the conservation of Polylepis and associated biota. This study assists in understanding distribution shifts over millennia of Andean tree species in response to climate change and identifying key conservation areas for the delineation of future conservation strategies.

Interdecadal Pacific Oscillation Drives Enhanced Greenland Surface Temperature Variability During the Last Glacial Maximum

AbstractStable oxygen isotope records from central Greenland suggest disproportionally large long‐term surface air temperature (SAT) variability during the Last Glacial Maximum (LGM) relative to preindustrial times. Large perturbations in mean atmospheric circulation and its variability forced by extensive Northern Hemisphere ice sheet coverage have been suggested as cause for the enhanced Greenland SAT variability. Here, we assess the factors driving Greenland SAT variability during the LGM by means of dedicated climate model simulations and find remote forcing from the Pacific of critical importance. Atmospheric teleconnections from the Interdecadal Pacific Oscillation (IPO), a multidecadal oscillation of sea surface temperature in the Pacific Ocean, strongly intensify under LGM conditions, driving enhanced surface wind variability over Greenland, which in turn amplifies SAT variability by anomalous atmospheric heat transport. A major role of the IPO in forcing Greenland SAT variability also is supported by a number of models from the Paleoclimate Modeling Intercomparison Project Phase III.

Climate Conditions on the Tibetan Plateau During the Last Glacial Maximum and Implications for the Survival of Paleolithic Foragers

Environmental conditions on the Tibetan Plateau (TP) during the last glacial maximum (LGM) are poorly known. Existing studies of environmental proxies and climate model simulations are contradictory, with interpretations varying between cold-dry and cold-wet environmental conditions which differentially influenced lake volumes, loess deposition and vegetation communities across the TP. Genetic and archaeological studies suggest anatomically modern paleolithic foragers initially occupied the TP between 60 and 30 ka, and may have seasonally occupied the TP during the LGM. Hence, a better understanding for LGM environmental conditions is needed in order to estimate whether paleolithic foragers could have survived on the TP during the extreme LGM cold stage. Here we report the investigation of lacustrine sediments and beach deposits within two paleoshorelines around Dagze Co on the southern TP, ∼22 and ∼42 m higher than the present lake level. Optical age estimates suggest the sediments were deposited during the LGM and mid-Holocene, respectively. TraCE-21 climate model simulation results suggest that net annual LGM precipitation in the Dagze Co basin was lower than the mid-Holocene, but about the same as that of the past 1,000 years. Combining the optical age estimates with TraCE-21 and CAM4 climate model simulation results, we deduce that increased summer precipitation and glacier meltwater supply, combined with decreased lake surface evaporation, produced LGM lake levels ∼22 m higher than present. We also synthesized paleoenvironmental records reported across the TP spanning the LGM. This synthesis suggests that the LGM climate in the northern TP was cold and dry, but that some of the southern TP was cold and wet. These relatively wetter LGM conditions in the southern TP may have favored the growth of cold-resistant plants which, in turn, may have supported larger herbivore populations, and provided food for paleolithic foragers. We conclude that seasonal or short-term human occupation of the TP during the LGM was thus more likely in the southern TP than in the north.

A new bias-correction method for precipitation over complex terrain suitable for different climate states: a case study using WRF (version 3.8.1)

Abstract. This work presents a new bias-correction method for precipitation over complex terrain that explicitly considers orographic characteristics. This consideration offers a good alternative to the standard empirical quantile mapping (EQM) method during colder climate states in which the orography strongly deviates from the present-day state, e.g. during glacial conditions such as the Last Glacial Maximum (LGM). Such a method is needed in the event that absolute precipitation fields are used, e.g. as input for glacier modelling or to assess potential human occupation and according migration routes in past climate states. The new bias correction and its performance are presented for Switzerland using regional climate model simulations at 2 km resolution driven by global climate model outputs obtained under perpetual 1990 and LGM conditions. Comparing the present-day regional climate model simulation with observations, we find a strong seasonality and, especially during colder months, a height dependence of the bias in precipitation. Thus, we suggest a three-step correction method consisting of (i) a separation into different orographic characteristics, (ii) correction of very low intensity precipitation, and (iii) the application of an EQM, which is applied to each month separately. We find that separating the orography into 400 m height intervals provides the overall most reasonable correction of the biases in precipitation. The new method is able to fully correct the seasonal precipitation bias induced by the global climate model. At the same time, some regional biases remain, in particular positive biases over high elevated areas in winter and negative biases in deep valleys and Ticino in winter and summer. A rigorous temporal and spatial cross-validation with independent data exhibits robust results. The new bias-correction method certainly leaves some drawbacks under present-day conditions. However, the application to the LGM demonstrates that it is a more appropriate correction compared to the standard EQM under highly different climate conditions as the latter imprints present-day orographic features into the LGM climate.

Simulated regional dust cycle in the Carpathian Basin and the Adriatic Sea region during the Last Glacial Maximum

The climate and environmental conditions in the Carpathian Basin and the adjacent northern Italy/Adriatic region during the Last Glacial Maximum (LGM) exhibit some major differences, as compared to present-day conditions. For instance, high accumulation rates recorded in loess deposits point to an active dust cycle during the LGM. Here, we investigate the climate conditions and provide new insights into the regional dust cycle based on regional climate simulations for both LGM and present-day boundary conditions. The high-resolution model output (grid spacing of ~8.5 km) is in good agreement with available proxy data, showing much colder (particularly during winter) and drier conditions during the LGM over the model domain. Further, the simulated aeolian dust cycle of small grain size particles (<20 μm) is investigated in more detail for LGM conditions. Highest dust emissions are simulated to the east of the Alpine ice sheet and in the Kvarner Bay region. In the northern Carpathian Basin, dust deposition plumes indicate prevailing northerly (NW, N and NE) winds. Strong Bora winds flowing down the slopes of the Dinaric Alps appear to play a major role in the local to regional dust cycle in the northern Adriatic region. From a seasonal perspective, the dust cycle is most active during winter and spring. A closer look at climate and environmental conditions at key areas reveals that high mean wind speeds and low precipitation rates correlate well with the high dust emissions during winter and spring. In contrast, lower wind speeds, increasing precipitation and the greening of vegetation prevent high dust emissions during summer and autumn. An additional analysis of the occurrence frequency of cyclonic circulation patterns in the Adriatic shelf region reveals that individual passing cyclones played an important role in the transport of dust particles from the alluvial Po plain towards the eastern Adriatic loess stacks.

Stability of the Atlantic overturning circulation under intermediate (MIS3) and full glacial (LGM) conditions and its relationship with Dansgaard-Oeschger climate variability

Paleoclimatic records reveal that millennial-scale climate variability during the Pleistocene was most pronounced during intermediate glacial conditions, like Marine Isotope Stage 3 (MIS3), rather than during interglacial and fully glaciated climates, like the Last Glacial Maximum (LGM). The rapid transitions between cold stadials and warm interstadials recorded in Greenland ice cores during MIS3, referred to as Dansgaard–Oeschger (D-O) events, have been correlated with millennial-scale climate variations worldwide. Although the origin of D-O events is a matter of controversy, striking evidence shows that variations in the strength of the Atlantic meridional overturning circulation (AMOC) were involved. Therefore, understanding the stability properties of the ocean circulation under different background climate conditions is key to understanding D-O millennial-scale climate variability. In the present study, the stability of the AMOC to northern high-latitude freshwater perturbations under MIS3 and LGM boundary conditions is investigated by using the coupled climate model CCSM3. Stability diagrams constructed from a large set of equilibrium experiments reveal a nonlinear dependence of AMOC strength on freshwater forcing under both MIS3 and LGM conditions. The MIS3 baseline state is close to an AMOC stability threshold, which makes the MIS3 climate unstable with respect to minor perturbations. A similar threshold behavior in AMOC stability is observed under LGM conditions; however, larger freshwater perturbations are necessary to pass the threshold and weaken the AMOC. The threshold’s displacement relative to the MIS3 background climate is attributable to differences in the atmospheric hydrologic cycle and North Atlantic sea ice transport. Different atmospheric moisture transports are attributable to thermodynamic and dynamic processes related to differences in greenhouse gas forcing and ice-sheet height between MIS3 and the LGM. We conclude that the higher stability of the AMOC during the LGM is a physically plausible explanation for millennial-scale D-O-type climate variability being suppressed under full glacial conditions, whereas minor perturbations in freshwater fluxes could have triggered D-O climate shifts during MIS3.

East Atlantic Pattern Drives Multidecadal Atlantic Meridional Overturning Circulation Variability During the Last Glacial Maximum

AbstractThe variability of the Atlantic meridional overturning circulation (AMOC) and its governing processes during the Last Glacial Maximum (LGM) is investigated in the Kiel Climate Model. Under LGM conditions, multidecadal AMOC variability is mainly forced by the surface heat flux variability linked to the East Atlantic pattern (EAP). In contrast, the multidecadal AMOC variability under preindustrial conditions is mainly driven by the surface heat flux variability associated with the North Atlantic Oscillation. Stand‐alone atmosphere model experiments show that relative to preindustrial conditions, the change in AMOC forcing under LGM conditions is tightly linked to the differences in topography.

How to survive a glaciation: the challenge of estimating biologically realistic potential distributions under freezing conditions

Correlative ecological niche models are increasingly used to estimate potential distributions during the Last Glacial Maximum (LGM) for biogeographical research. In the case of presence‐background/pseudoabsences techniques, cold environments that are poorly represented in existing geography can complicate the process of model calibration and transfer into more extreme cold environments that were very common during the LGM (non‐analog conditions). This may lead to biologically unrealistic estimations. Using one cold‐adapted North American mammal, we explore a real scenario to better understand the effect of restricting the range of environmental conditions over which niche models are calibrated and then transferred to LGM conditions. We performed two sets of experiments in Maxent: 1) we calibrated models in the context of only present‐day climate conditions, which is the most common practice, and compared predictions under LGM conditions based on two extrapolation methods (clamping versus unconstrained); 2) we calibrated single models using both present‐day and LGM conditions as part of the same background in order to include more extreme environments in the model calibration. Our experiments led to dramatically different estimates of species’ potential distributions, showing notable differences with respect to latitudinal and elevational shifts during the LGM. Models calibrated using present‐day climates yielded biologically unrealistic estimations, suggesting that species survived in the glaciers during the LGM. Even more unrealistic estimations were achieved when clamping was enforced as the method to extrapolate. Models calibrated in the context of both modern and past climates reduced the required degree of extrapolation and allowed more realistic potential distributions, suggesting that the species avoided extremely cold conditions during the LGM. This study alerts to the possibility of obtaining implausible potential distributions during the LGM due to restricted background datasets and offers recommendations that should promote better strategies to estimate distributional changes during glaciations.

Evolutionary history of the scorpionfly Dicerapanorpa magna (Mecoptera, Panorpidae)

AbstractClimate changes can have fundamental impacts on the distributional patterns of montane species, and range shifts frequently lead to allopatric divergence followed by the establishment of secondary contact zones. Many European and North American organisms have retreated to southern refugia during glacial periods and colonized northward during postglacial periods, but little is known about the evolutionary response of cold‐adapted insects to Pleistocene climate changes in eastern Asia. The scorpionfly Dicerapanorpa magna (Chou), with cold temperate habitat preference and weak dispersal ability, provides a good model system to explore how climate changes have influenced the distribution and divergence of cold‐adapted insects in eastern Asia. This study reconstructed the demographic dynamics and evolutionary history of D. magna with phylogeographic approaches, and predicted the species’ suitable areas under the Last Glacial Maximum (LGM) and current scenarios with the ecological niche modelling analysis. The mitochondrial cytochrome c oxidase subunit I resolved three phylogenetic lineages in D. magna dating back to Pleistocene, corresponding well with the geographically isolated Qinling, Bashan and Minshan Mountains. The ecological niche modelling recovered the suitable habitats for D. magna were the Qinling and Bashan Mountains under LGM and current conditions. The three lineages of D. magna might be in a process of incipient speciation, and likely derived their current distribution from separate glacial origins, followed by vicariance and divergence.

Understanding biogeographical patterns in the western Balkan Peninsula using environmental niche modelling and geostatistics in polymorphic Edraianthus tenuifolius.

The Balkan Peninsula represents one of the three southern European glacial refugia where biodiversity persisted throughout the climatically unstable Quaternary. This study considered the ‘refugia within refugia’ model, which assumes the environmental heterogeneity over time and space in larger refugia. To better understand patterns shaped during the Quaternary climatic oscillations, the present and last glacial maximum (LGM) environmental conditions and current morphological variability of Edraianthus tenuifolius, an endemic plant of the western Balkans with a well-known therphical structure, were considered. Potential present and LGM distributions were studied through environmental niche modelling using 161 data of occurrences and six bioclimatic variables, hindcasting the model to LGM conditions using three different global circulation models. To test the geographical variability of the reproductive region, 41 characters of 667 inflorescences from 35 populations within the distribution range were measured. Geographical patterns, using geostatistics together with univariate and multivariate statistical approaches, were analysed. The environmental niche model suggested the current potential distribution in correspondence to its known occurrences. The hindcast to LGM conditions suggested two separate areas of environmental suitability, one in the present-day northern Adriatic coast of Croatia (Istrian Peninsula, Kvarner) and another on the present-day south-eastern Adriatic coast (southern Dalmatia, Montenegro and northern Albania). Morphological variability showed a similar pattern, where southern populations separated from northern populations according to a major split in the central part of its distribution range (central Dalmatia). On other levels, stronger barriers were predicted to separate northern populations from the eastern Istrian Peninsula and the Kvarner area. The results suggested congruent biogeographical patterns to the already known phylogeographical structure. Both environmental niche modelling and the geographical variability of morphological characters suggested spatial partitioning, indicating the potential presence of two separate refugia during the LGM.

Geological effects influence population genetic connectivity more than Pleistocene glaciations in the water strider Metrocoris sichuanensis (Insecta: Hemiptera: Gerridae)

AbstractAimPalaeoclimatic and palaeogeological events have been identified as two main factors that influence the genetic structuring of extant organisms. We studied a montane stream‐dwelling insect, Metrocoris sichuanensis, to explore the relative roles played by these two factors in population genetic connectivity.LocationSichuan Basin, China.MethodsMitochondrial (COI, COII, Cytb, 16S) and nuclear (EF‐1α, ITS1) markers were sequenced from 208 individuals. Suitable habitat shifts from the Last Glacial Maximum (LGM) to the present were predicted through fine‐tuned ecological niche modelling (ENM). Phylogenetic and phylogeographical analyses were conducted to reveal the population genetic structure. Intraspecific divergence and expansion times were estimated using beast. Finally, the least cost path (LCP) method coupled with migrate analysis was used to identify possible dispersal corridors and estimate the asymmetric gene flow.ResultsOur ENM results suggested that population habitat connectivity did not change both in the LGM and current conditions. Whole haplotypes were separated into four highly supported clades/haplogroups that exhibited strong geographical structure. The splitting events between the four lineages likely date back to the Early Pleistocene. Bayesian skyline plot (BSP) indicated a moderate demographic growth from the LGM to the present. A putative dispersal corridor was detected along the Longmen Mountains thrust belt, with unidirectional gene flow from north to south.Main conclusionOur findings support the geographical isolation of the genetic lineages and a deep early Pleistocene split in M. sichuanensis. Landscape connectivity analysis incorporating the genetic data and the ENM prediction revealed that population genetic connectivity was strongly associated with stable climatic habitats shaped by complex topography. The drainage system might have assisted the rapid movement of populations along the Longmen Mountains thrust belt. A strategy for researching the population genetic connectivity of narrow endemics, such as M. sichuanensis, in global biodiversity hotspots is proposed and discussed in this paper.

On the Reduced North Atlantic Storminess during the Last Glacial Period: The Role of Topography in Shaping Synoptic Eddies

AbstractThe North Atlantic storminess of Last Glacial Maximum (LGM) fully coupled climate simulations is generally less intense than that of their preindustrial (PI) counterparts, despite having stronger baroclinicity. An explanation for this counterintuitive result is presented by comparing two simulations of the IPSL full climate model forced by Paleoclimate Modelling Intercomparison Project Phase 3 (PMIP3) LGM and PI conditions. Two additional numerical experiments using a simplified dry general circulation model forced by idealized topography and a relaxation in temperature provide guidance for the dynamical interpretation. The forced experiment with idealized Rockies and an idealized Laurentide Ice Sheet has a less intense North Atlantic storm-track activity than the forced experiment with idealized Rockies only, despite similar baroclinicity. Both the climate and idealized runs satisfy or support the following statements. The reduced storm-track intensity can be explained by a reduced baroclinic conversion, which itself comes from a loss in eddy efficiency to tap the available potential energy as shown by energetic budgets. The eddy heat fluxes are northeastward oriented in the western Atlantic in LGM and are less well aligned with the mean temperature gradient than in PI. The southern slope of the Laurentide Ice Sheet topography forces the eddy geopotential isolines to be zonally oriented at low levels in its proximity. This distorts the tubes of constant eddy geopotential in such a way that they tilt northwestward with height during baroclinic growth in LGM while they are more optimally westward tilted in PI.

Genetic and ecological insights into glacial refugia of walnut (Juglans regia L.).

The distribution and survival of trees during the last glacial maximum (LGM) has been of interest to paleoecologists, biogeographers, and geneticists. Ecological niche models that associate species occurrence and abundance with climatic variables are widely used to gain ecological and evolutionary insights and to predict species distributions over space and time. The present study deals with the glacial history of walnut to address questions related to past distributions through genetic analysis and ecological modeling of the present, LGM and Last Interglacial (LIG) periods. A maximum entropy method was used to project the current walnut distribution model on to the LGM (21–18 kyr BP) and LIG (130–116 kyr BP) climatic conditions. Model tuning identified the walnut data set filtered at 10 km spatial resolution as the best for modeling the current distribution and to hindcast past (LGM and LIG) distributions of walnut. The current distribution model predicted southern Caucasus, parts of West and Central Asia extending into South Asia encompassing northern Afghanistan, Pakistan, northwestern Himalayan region, and southwestern Tibet, as the favorable climatic niche matching the modern distribution of walnut. The hindcast of distributions suggested the occurrence of walnut during LGM was somewhat limited to southern latitudes from southern Caucasus, Central and South Asian regions extending into southwestern Tibet, northeastern India, Himalayan region of Sikkim and Bhutan, and southeastern China. Both CCSM and MIROC projections overlapped, except that MIROC projected a significant presence of walnut in the Balkan Peninsula during the LGM. In contrast, genetic analysis of the current walnut distribution suggested a much narrower area in northern Pakistan and the surrounding areas of Afghanistan, northwestern India, and southern Tajikistan as a plausible hotspot of diversity where walnut may have survived glaciations. Overall, the findings suggest that walnut perhaps survived the last glaciations in several refugia across a wide geographic area between 30° and 45° North latitude. However, humans probably played a significant role in the recent history and modern distribution of walnut.

Cryptic elevational zonation in trapdoor spiders (Araneae, Antrodiaetidae, Aliatypus janus complex) from the California southern Sierra Nevada

The relative roles of ecological niche conservatism versus niche divergence in promoting montane speciation remains an important topic in biogeography. Here, our aim was to test whether lineage diversification in a species complex of trapdoor spiders corresponds with riverine barriers or with an ecological gradient associated with elevational tiering. Aliatypus janus was sampled from throughout its range, with emphasis on populations in the southern Sierra Nevada Mountains of California. We collected multi-locus genetic data to generate a species tree for A. janus and its close relatives. Coalescent based hypothesis tests were conducted to determine if genetic breaks within A. janus conform to riverine barriers. Ecological niche models (ENM) under current and Last Glacial Maximum (LGM) conditions were generated and hypothesis tests of niche conservatism and divergence were performed. Coalescent analyses reveal deeply divergent genetic lineages within A. janus, likely corresponding to cryptic species. Two primary lineages meet along an elevational gradient on the western slopes of the southern Sierra Nevada Mountains. ENMs under both current and LGM conditions indicate that these groups occupy largely non-overlapping niches. ENM hypothesis testing rejected niche identity between the two groups, and supported a sharp ecological gradient occurring where the groups meet. However, the niche similarity test indicated that the two groups may not inhabit different background niches. The Sierra Nevada Mountains provide a natural laboratory for simultaneously testing ecological niche divergence and conservatism and their role in speciation across a diverse range of taxa. Aliatypus janus represents a species complex with cryptic lineages that may have diverged due to parapatric speciation along an ecological gradient, or been maintained by the evolution of ecological niche differences following allopatric speciation.

Impacts of surface boundary conditions on regional climate model simulations of European climate during the Last Glacial Maximum

AbstractWe examine the influences of North Atlantic sea surface temperatures (SSTs) and vegetation on regional climate simulations over Europe during the Last Glacial Maximum (LGM). Simulated regional temperature and precipitation patterns over Europe are considerably improved when using revised SSTs based on proxy data. Likewise, the simulated permafrost is more accurately reproduced with the SST modifications. These improvements are partially related to the changed regional atmospheric circulation due to the revised SSTs, leading to colder and drier conditions over Western Europe. Further sensitivity tests with prescribed vegetation for LGM conditions provide evidence of the sensitivity of the simulated glacial climate. This study reveals the importance of considering more realistic SST and vegetation boundary conditions for a more accurate representation of regional climate variability under glacial conditions.