Past Climate Change Research Articles

Reconstructing carbonate alteration histories in orogenic sedimentary basins: Xigaze forearc, southern Tibet

Abstract Carbonate clumped isotope thermometry (T( Δ 47 )) and the oxygen stable isotope record ( δ 18 O ) provide critical constraints on the temperature of carbonate mineral formation and isotopic composition of ancient waters used in reconstructions of past climate, tectonics, and ecological and environmental change. The robust use of these proxies requires that carbonate minerals in the rock record retain primary isotopic compositions through often complex post-depositional thermal histories. New carbonate clumped isotope thermometry and sedimentology data are paired with existing thermochronology and isotope exchange reaction modeling to provide unique constraints on the alteration history of the carbon and oxygen isotopes in Tethyan marine carbonates (Jialazi Fm, Tso Jianding Group) of the Xigaze forearc, southern Tibet. Within the framework of the textural and isotopic data, the effects of early and late burial alteration on Δ 47 and δ 18 O values of marine rocks that were buried to 4 km above sea level are modeled. The alteration products are considered within two well-studied mechanistic frameworks: water-rock recrystallization and solid-state reordering of 13 C 18 O bonds at high temperature. The proposed alteration model is as follows: (1) shallow, early diagenesis with water of similar composition and temperature to formation waters infills primary porespace with microspar; (2) high-temperature, rock-buffered water-rock exchange and partial solid-state reordering at >3–4 km depth; and (3) near-surface, low-temperature water-rock exchange on the exhumation pathway. The Δ 47 heterogeneity within individual samples (0.456 to 0.721) requires significant differential alteration on the retrograde path (high to low temperature, low water-rock ratio) in which primary compositions and compositions inherited during early burial diagenesis are overprinted with modern meteoric values. A low T( Δ 47 ) value is often assumed to record the primary temperature of the depositional environment. However, samples yielding low T( Δ 47 ) values in the Jialazi Fm have undergone extensive high-temperature water-rock alteration, and therefore, require a mechanism for increasing 13 C 18 O bond ordering on the retrograde pathway while preserving many primary biogenic structures and micritic textures. This study highlights the potential significance of late-stage, low-temperature alteration of carbonates derived from orogenic sedimentary basins for studies of terrestrial paleoenvironments and tectonics. This study also provides an example framework for combining observational and analytical data to reconstruct a carbonate alteration history of a buried sedimentary package.

The paleolimnologist's guide to compound-specific stable isotope analysis – An introduction to principles and applications of CSIA for Quaternary lake sediments

The stable isotope composition of key chemical elements for life on Earth (e.g., carbon, hydrogen, nitrogen, oxygen, sulfur) tracks changes in fluxes and turnover of these elements in the biogeosphere. Over the past 15–20 years, the potential to measure these isotopic compositions for individual, source-specific organic molecules (biomarkers) and to link them to a range of environmental conditions and processes has been unlocked and amplified by increasingly sensitive, affordable and wide-spread analytical technology. Paleoenvironmental research has seen enormous step-changes in our understanding of past ecosystem dynamics. Vital to these paradigm shifts is the need for well-constrained modern and recent analogues. Through increased understanding of these environments and their biological pathways we can successfully unravel past climatic changes and associated ecosystem adaption.With this review, we aim to introduce scientists working in the field of Quaternary paleolimnology to the tools that compound-specific isotope analysis (CSIA) provides for the gain of information on biogeochemical conditions in ancient environments. We provide information on fundamental principles and applications of novel and established CSIA applications based on the carbon, hydrogen, nitrogen, oxygen and sulfur isotopic composition of biomarkers. While biosynthesis, sources and associated isotope fractionation patterns of compounds such as n-alkanes are relatively well-constrained, new applications emerge from the increasing use of functionalized alkyl lipids, steroids, hopanoids, isoprenoids, GDGTs, pigments or cellulose. Biosynthesis and fractionation are not always fully understood. However, although analytical challenges remain, the future potential of deeper insights into ecosystem dynamics from the study of these compounds is also emerging.

Constraining the application of hydrogen isotopic composition of alkenones as a salinity proxy using marine surface sediments

Abstract Sea surface salinity is an essential environmental parameter necessary to understand past changes in global climate. However, reconstructing absolute salinity of the surface ocean with high enough accuracy and precision remains a complicated task. Hydrogen isotope ratios of long-chain alkenones (δ2HC37) have been shown to reflect salinity in culture studies and have been proposed as a tool to reconstruct sea surface salinity in the geologic record. The correlation between δ2HC37 – salinity in culture is prominently caused by the relationship between δ2HH2O and salinity, as well as the increase in fractionation factor α with increasing salinity. The δ2HC37 – salinity relationship in the natural environment is poorly understood. Here, surface sediments from a variety of environments covering a wide range of salinities were analyzed to constrain the environmental relationship between salinity and hydrogen isotopes of alkenones. δ2HC37 correlates significantly (r = 0.75, p

Classifying past climate change in the Chew Bahir basin, southern Ethiopia, using recurrence quantification analysis

The Chew Bahir Drilling Project (CBDP) aims to test possible linkages between climate and evolution in Africa through the analysis of sediment cores that have recorded environmental changes in the Chew Bahir basin. In this statistical project we consider the Chew Bahir palaeolake to be a dynamical system consisting of interactions between its different components, such as the waterbody, the sediment beneath lake, and the organisms living within and around the lake. Recurrence is a common feature of such dynamical systems, with recurring patterns in the state of the system reflecting typical influences. Identifying and defining these influences contributes significantly to our understanding of the dynamics of the system. Different recurring changes in precipitation, evaporation, and wind speed in the Chew Bahir basin could result in similar (but not identical) conditions in the lake (e.g., depth and area of the lake, alkalinity and salinity of the lake water, species assemblages in the water body, and diagenesis in the sediments). Recurrence plots (RPs) are graphic displays of such recurring states within a system. Measures of complexity were subsequently introduced to complement the visual inspection of recurrence plots, and provide quantitative descriptions for use in recurrence quantification analysis (RQA). We present and discuss herein results from an RQA on the environmental record from six short (< 17 m) sediment cores collected during the CBDP, spanning the last 45 kyrs. The different types of variability and transitions in these records were classified to improve our understanding of the response of the biosphere to climate change, and especially the response of humans in the area.

A Window into Africa’s Past Hydroclimates: The SISAL_v1 Database Contribution

Africa spans the hemispheres from temperate region to temperate region and has a long history of hominin evolution. Although the number of Quaternary palaeoclimatic records from the continent is increasing, much of the history of spatial and temporal climatic variability is still debated. Speleothems, as archives of terrestrial hydroclimate variability, can help reveal this history. Here we review the progress made to date, with a focus on the first version of the Speleothem Isotopes Synthesis and AnaLysis (SISAL) database. The geology of Africa has limited development of large karst regions to four areas: along the northern coast bordering the Mediterranean, eastern Africa and the Horn of Africa, southwestern Africa and southern Africa. Exploitation of the speleothem palaeoclimate archives in these regions is uneven, with long histories of research, e.g., in South Africa, but large areas with no investigations such as West Africa. Consequently, the evidence of past climate change reviewed here is irregularly sampled in both time and space. Nevertheless, we show evidence of migration of the monsoon belt, with enhanced rainfall during interglacials observed in northeast Africa, southern Arabia and the northern part of southern Africa. Evidence from eastern Africa indicates significant decadal and centennial scale rainfall variability. In northwestern and southern Africa, precession and eccentricity influence speleothem growth, largely through changing synoptic storm activity.

Genesis, morphology and mineralogy of Planosols developed from different parent materials in southern Brazil

The genesis of Planosols is a complex process since it can involve multiple cycles of soil formation, deposition of allochthonous materials and also past climate changes. Furthermore, this subject is still poorly studied in the humid tropics, thus hindering a proper appraisal of the potentials and limitations of Planosols. The objective of this research was to study pedogenetic processes and properties of Planosols formed from different parent materials in southern Brazil. Four soils were sampled: (P1) Hypereutric Luvic Albic Planosol, developed on lagoon plain sediments; (P2) Orthoeutric Luvic Albic Planosol, on Holocene alluvial deposits; (P3) Hypereutric Luvic Albic Planosol, on granite; and (P4) Orthoeutric Luvic Albic Planosol, on gneiss. All Planosols presented sandy horizons A and E, with low pH (<5.0), CEC (<5cmolckg−1 soil) and base saturation (<50%), despite having high-activity clays. The Planosols presented high levels of amorphous aluminum hydroxides at the top of Bt horizons, suggesting Al mobilization by the pedogenetic process of ferrolysis. Micromorphological observation of clay coatings also confirmed the pedogenetic process of lessivage in all Planosols, in accord with strong texture gradients between E/Bt horizons. Quartz is practically the only primary mineral present in sand fractions and thin sections, suggesting a strong weathering. The X-ray diffraction showed small feldspar and quartz peaks in the clays, which were dominated by interstratified kaolinite-smectite, probably stabilized by strongly restricted drainage, and which imparted the high clay activity, unusual in nearby soils. Although the Planosols studied differed in parent material, the composition of the clays was strikingly similar, suggesting the predominance of ferrolysis, illuviation and associated processes in producing Albic Planosols.

Phylogeography of Ixiolirion songaricum, a spring ephemeral species endemic to Northwest China

Past geological and climatic changes have promoted shifts in both intraspecific differentiation and distribution ranges for many desert plants, though little is known about the effects of these changes specifically on spring ephemerals in Northwest China. In the present study, we aimed to survey the population structure and phylogeographic history of an endemic spring ephemeral species, Ixiolirion songaricum P. Yan in Northwest China. We sequenced the nITS and two ptDNA fragments (psbB–psbH and ycf6–psbM) for 265 individuals from 15 populations across the entire range. Eight nITS ribotypes and eleven plastid chlorotypes were identified, with three of them dominant. A significant phylogeographic structure was detected for the species in which two larger, distinct phylogeographic lineages were identified. A high proportion of the total genetic variation existed between populations and between the two lineages. The species had undergone a sudden range expansion in the late Quaternary, which might have been driven by an interglacial warm, humid climate following the largest Pleistocene glaciation period in Northwest China. The ecological niche modeling suggested the species experienced continuous shrinkage of potential range since the last interglacial, which is distinct from other desert plants. Overall, our results indicated that climate change associated with the Quaternary greatly promoted differentiation of I. songaricum. The shift in population distribution was likely driven by increasing aridity in Xinjiang during the Quaternary.

Altitudinal patterns of wind transport and deposition of Yungas tree pollen in northwestern Argentina: Implications for interpreting the Quaternary fossil record

The presence of pollen from Yungas tree species in fossil sequences located above the tree-line has led to alternative interpretations of past climate changes in tropical and subtropical Andes. We studied atmospheric and surface pollen deposition rates of Yungas trees along an altitudinal gradient (1700–3800 m a.s.l.) to understand the role of local wind patterns in modern pollen transport to mountain regions. Pollen from the Montane forest (Alnus and Juglans) and the Montane rainforest (Anadenanthera, Celtis and Myrtaceae) becomes airborne and is transported upslope well above the tree-line. The resulting patterns of pollen deposition show a secondary maximum in the Montane grassland, consistent with the development of a mountain-valley breeze system during the flowering period of the pollen producer species. Given that the pattern is also preserved in the surface sediment, we propose that these tree pollen types are good indicators of mesoscale atmospheric circulation and could provide a proxy for this circulation system in Quaternary records. This alternative approach to interpreting fossil pollen records of Yungas species in highlands of the Central Andes has implications for regional reconstructions of past climate.

Modeling and estimating aboveground biomass of Dacrydium pierrei in China using machine learning with climate change

Accurate estimations of the aboveground biomass (AGB) of rare and endangered species are particularly important for protecting forest ecosystems and endangered species and for providing useful information to analyze the influence of past and future climate change on forest AGB. We investigated the feasibility of using three developed and two widely used models, including a generalized regression neural network (GRNN), a group method of data handling (GMDH), an adaptive neuro-fuzzy inference system (ANFIS), an artificial neural network (ANN) and a support vector machine (SVM), to estimate the AGB of Dacrydium pierrei (D. pierrei) in natural forests of China. The results showed that these models could explain the changes in the AGB of the D. pierrei using a limited amount of meteorological data. The GRNN and ANN models are superior to the other models for estimating the AGB of D. pierrei. The GMDH model consistently produced comparatively poor estimates of the AGB. Three climate scenarios, including the representative concentration pathway (RCP) 2.6, RCP 4.5, and RCP 8.5, were compared with the climate situation of 2013–2017. Under these scenarios, the AGB of D. pierrei females with the same diameter at breast height (DBH) would increase by 13.0 ± 31.4% (mean ± standard deviation), 16.6 ± 30.7%, and 18.5 ± 30.9% during 2041–2060 and 15.6 ± 32.1%, 21.2 ± 33.2%, and 24.8 ± 32.7% during 2061–2080; the AGB of males would increase by 16.3 ± 32.3%, 21.7 ± 32.5%, and 22.9 ± 32.6% during 2041–2060 and 22.3 ± 30.8%, 27.2 ± 31.8%, and 30.1 ± 34.4% during 2061–2080. The R2 values of all models range from 0.82 to 0.95. In conclusion, this study suggests that these advanced models are recommended to estimate the AGB of forests, and the AGB of forests would increase in 2041–2080 under future climate scenarios.

Regional difference of grain production potential change and its influencing factors: a case-study of Shaanxi Province, China

AbstractGrain production potential (GrPP) is the maximum production in 1 year that can be achieved by land use under the limitations of climate conditions and in the absence of pests and diseases and other factors. Regional GrPP can change over time and there is an urgent need to identify the main factors affecting regional differences in such changes. Therefore, changes in GrPP were studied for six geographical units in Shaanxi Province, with summer maize and winter wheat as the main grain crops. Changes of GrPP during 2000–2015 were simulated by the global aro-ecological zone model. Analysis of modelled GrPP driven by observed changes in climate and land use suggest that over this period GrPP increased to the north but declined to the south of the Qinling Mountains. This is driven mainly by past changes in climate, with modelled GrPP more sensitive to changes in precipitation than temperature in all geographical units except one. Climate change was the main factor affecting GrPP in all geographical units except one; however, model prediction suggests that land use changes had a clear yield-reducing effect in three of the units. It is the conversion from cultivated land to construction land, grassland and woodland that led to the greatest declines in GrPP in these three geographical units. In order to ensure the stable development of regional agriculture and food security, Shaanxi Province should focus on tapping GrPP north of the Qinling Mountains and increasing the conversion rate of GrPP to actual production.

Predicting spatial and temporal effects of climate change on the South American lizard genus Teius (Squamata: Teiidae)

Abstract The consequences of past or future climate change have been studied in many physical and biological systems, and their effects could change the ecology and spatial distribution of suitable areas for a wide variety of organisms. We analyzed the environmental and geographic space of the current suitable area projecting these conditions into Mid-Holocene and 2050 RCP8.5 scenarios to quantify whether climate change would affect the distribution and size of environmental and geographic space for lizard species of the genus Teius. The potentially suitable geographic area for the Mid-Holocene was found to be smaller than today for T. oculatus (−29.55%) and for T. teyou (−6.82%), but for T. suquiensis it was inferred as a larger suitable area (+26%). For the future scenario all species showed a decrease in the potentially suitable area compared to the present (T. oculatus = − 9.30%, T. teyou = − 0.79%, T. suquiensis = − 37.58%). The PCA axes that in the environmental space showed a higher contribution for PC1-2 in Mid-Holocene and Present were mostly related to temperature and for PC3 with altitude variables, for the 2050 scenario were temperature for PC1, precipitation for PC2 and altitude-temperature for PC3. The current Teius’ potentially suitable geographic space results versus the other temporal forecasts, showed specific differences in magnitude changes. This work illustrates how ectothermic organisms might have to face major changes in their environmental and geographic space as a consequence of the effect of climate changes.

Global warming and other climate change phenomena on the geological time scale

Global warming and other climate change phenomena became a worldwide exploited subject over recent decades. World science has made enormous progress in understanding past climate change and its causes, and continues to study current and potential impacts that will affect people in the future. All scientists agree that the Earth's climate is changing due to natural phenomena, and most of them argue that human activities are increasing the greenhouse effect, while some scientists attribute climate changes exclusively to the natural causes. Though there still is, and always will be, need for multiple lines of research on an extremely complex system like Earth's climate is, an immediate consensus is crucial for decision-makers to place climate change in the context of other large challenges facing the world today. This paper discusses the existing body of evidence on climate changes in the past, and uncertainties that prevent scientists to reach full consensus on how climate might change in the future. It extends the time scale of climate changes over the entire history of Earth to help better understanding of hypothetical changes and their consequences that could be expected both in the near and in a very distant future.

Late Glacial palaeoenvironmental changes in the southern part of the Holy Cross Mountains based on the “Białe Ługi” peatland record

This paper presents the Late Glacial stage of the development of the Białe Ługi peatland in the southern Holy Cross Mountains, based on a comprehensive palaeoenvironmental data. A complex analysis of palynology, Cladocera, sed imentology, geochemistry and 14C dating were used. Organic deposition was initiated during the Oldest Dryas. The sedimentary record of the aquatic and terrestrial ecosystems reflects considerable difference between cooler (Oldest, Older and Younger Dryas) and warmer phases (Břlling and Allerřd). Periods of intensified interaction between aeolian processes and peatland are related to stages of disappearing vegetation and changes in aquatic invertebrate communities. We therefore suggest that peatlands were created as a result of local lithological-structural, tectonic, hydrogeological and morphological conditions, and the peatland development rate was largely influenced by changing climatic conditions, which determined local vegetation development, intensity of denudation processes and water level changes. The results validate significance of selection and use of several methods, as well as value of biogenic deposits from the Białe Ługi peatland as archives of past climate change in the Małopolska Upland. Relatively stable water conditions and uninter rupted biogenic sedimentation in the Late Glacial that were provided by the geological structure and relief suggest the studied peatland is a leading one in the region.

Has past climate change affected cold‐specialized species differentially through space and time?

AbstractQuaternary climate change has been strongly linked to distributional shifts and recent species diversification. Montane species, in particular, have experienced enhanced isolation and rapid genetic divergence during glacial fluctuations, and these processes have resulted in a disproportionate number of neo‐endemic species forming in high‐elevation habitats. In temperate montane environments, a general model of alpine population history is well supported, where cold‐specialized species track favourable climate conditions downslope during glacial episodes and upslope during warmer interglacial periods, which leads to a climate‐driven population or species diversification pump. However, it remains unclear how geography mediates distributional changes and whether certain episodes of glacial history have differentially impacted rates of diversification. We address these questions by examining phylogenomic data in a North American clade of flightless, cold‐specialized insects, the ice crawlers (Insecta: Grylloblattodea: Grylloblattidae: Grylloblatta). These low‐vagility organisms have the potential to reveal highly localized refugia and patterns of spatial recolonization, as well as a longer history of in situ diversification. Using continuous phylogeographic analysis of species groups, we show that all species tend to retreat to nearby low‐elevation habitats across western North America during episodes of glaciation, but species at high latitude exhibit larger distributional shifts. Lineage diversification was examined over the course of the Neogene and Quaternary periods, with statistical analysis supporting a direct association between climate variation and diversification rate. Major increases in lineage diversification appear to be correlated with warm and dry periods, rather than with extreme glacial events. Finally, we identify substantial cryptic diversity among ice crawlers, leading to high endemism across their range. This diversity provides new insights into highly localized glacial refugia for cold‐specialized species across western North America.

Regional paleoclimates and local consequences: Integrating GIS analysis of diachronic settlement patterns and process-based agroecosystem modeling of potential agricultural productivity in Provence (France).

Holocene climate variability in the Mediterranean Basin is often cited as a potential driver of societal change, but the mechanisms of this putative influence are generally little explored. In this paper we integrate two tools–agro-ecosystem modeling of potential agricultural yields and spatial analysis of archaeological settlement pattern data–in order to examine the human consequences of past climatic changes. Focusing on a case study in Provence (France), we adapt an agro-ecosystem model to the modeling of potential agricultural productivity during the Holocene. Calibrating this model for past crops and agricultural practices and using a downscaling approach to produce high spatiotemporal resolution paleoclimate data from a Mediterranean Holocene climate reconstruction, we estimate realistic potential agricultural yields under past climatic conditions. These serve as the basis for spatial analysis of archaeological settlement patterns, in which we examine the changing relationship over time between agricultural productivity and settlement location. Using potential agricultural productivity (PAgP) as a measure of the human consequences of climate changes, we focus on the relative magnitudes of 1) climate-driven shifts in PAgP and 2) the potential increases in productivity realizable through agricultural intensification. Together these offer a means of assessing the scale and mechanisms of the vulnerability and resilience of Holocene inhabitants of Provence to climate change. Our results suggest that settlement patterns were closely tied to PAgP throughout most of the Holocene, with the notable exception of the period from the Middle Bronze Age through the Early Iron Age. This pattern does not appear to be linked to any climatically-driven changes in PAgP, and conversely the most salient changes in PAgP during the Holocene cannot be clearly linked to any changes in settlement pattern. We argue that this constitutes evidence that vulnerability and resilience to climate change are strongly dependent on societal variables.

Timing of past glaciation at the Sierra de Aconquija, northwestern Argentina, and throughout the Central Andes

Advances in cosmogenic nuclide exposure dating have made moraines valuable terrestrial recorders of palaeoclimate. A growing number of moraine chronologies reported from the Central Andes show that tropical glaciers responded sensitively to past changes in precipitation and temperature over timescales ranging from 103 to 105 years. However, the causes of past glaciation in the Central Andes remain uncertain. Explanations have invoked insolation-modulated variability in the strength of the South American Summer Monsoon, teleconnections with the North Atlantic Ocean, and/or cooling in the Southern Hemisphere. The driver for these past climate changes is difficult to identify, partly due to a lack of dated moraine records, especially in climatically sensitive areas of the southern Central Andes. Moreover, new constraints are needed on precisely where and when glaciers advanced. We use cosmogenic 10Be produced in situ to determine exposure ages for three generations of moraines at the Sierra de Aconquija, situated at 27°S on the eastern flank of the southern Central Andes. These moraines record glacier advances at approximately 22 ka and 40 ka, coincident with summer insolation maxima in the sub-tropics of the Southern Hemisphere, as well as at 12.5 ka and 13.5 ka during the Younger Dryas and the Antarctic Cold Reversal, respectively. We also identify minor glaciation during Bond Event 5, also known as the 8.2 ka event. These moraines register past climate changes with high fidelity, and currently constitute the southernmost dated record of glaciation on the eastern flank of the Central Andes. To contextualise these results, we compile 10Be data reported from 144 moraines in the eastern Central Andes that represent past glacier advances. We re-calculate exposure ages from these data using an updated reference production rate, and we re-interpret the moraine ages by taking the oldest clustered boulder age (after the exclusion of outliers attributed to nuclide inheritance) as closest to the timing of glacier advance—an approach for which we provide empirical justification. This compilation reveals that Central Andean glaciers have responded to changes in temperature and precipitation. We identify cross-latitude advances in phase with insolation cycles, the last global glacial maximum, and episodes of strengthened monsoonal moisture transport including the Younger Dryas and Heinrich Stadials 1 and 2. Our results from the Sierra de Aconquija allow us to constrain the southerly limit of enhanced precipitation associated with Heinrich Stadials at ∼25°S. More broadly, our findings demonstrate at both local and regional scales that moraines record past climate variability with a fine spatial and temporal resolution.

Cretaceous climatic reconstruction from Argentina based on palynological data

Paleoclimatic reconstructions have used different proxies as climate indicators. In this context, palynomorphs play a crucial role for making inferences about past climate changes because of their presence and distribution during the geologic history in almost all types of environments. Argentina has a wide latitudinal range in South America, with diverse cretaceous units yielding palynomorphs that represent different climatic conditions. The Cretaceous was a time when climate conditions showed some special variations. Different theories about the climate conditions at this time were postulated. The main aim of this contribution is to understand climate trends during the Cretaceous, based on the quantitative analysis of selected pollen and spores, considered as climate indicators, from different geological units in Argentina. The evaluation of the palynofloras has been undertaken mainly by reviewing published sources from cretaceous basins but also with our own unpublished data. The climatic trend during the Cretaceous showed that the Early Cretaceous is marked by aridity episodes with high values of Classopollis and Gnetales. In contrast, the Late Cretaceous showed warmer and more humid conditions indicated by increasing values of free-sporing plants (especially Bryophytes and ferns) and palm pollen grains, and the decrease until their absence of the aridity indicators.

Phylogeographic analyses of Acacia karina (Fabaceae) support long term persistence of populations both on and off banded iron formations

Understanding the response of species to past climatic changes and whether particular areas acted as refugia is critical both to our understanding of the distribution of genetic variation, and for the conservation and/or restoration of species. We used phylogeographical analyses of Acacia karina, a Banded Iron Formation (BIF) associated species, to better understand historical processes in the semiarid midwest region of Western Australia. We specifically examined whether BIF acted as refugia for the species during the colder, dryer periods of the Quaternary. The genetic structure over the entire range of A. karina was assessed using seven nuclear microsatellites (19 populations; n=371) and 3196bp of chloroplast sequence (19 populations; n=190). We found high levels of nuclear and chloroplast genetic diversity and high levels of chloroplast haplotype differentiation. Genetic diversity was higher than expected for such a geographically restricted species, and similarly high levels of nuclear and chloroplast diversity were observed in BIF and non-BIF populations. The chloroplast and nuclear data suggest that BIFs have not acted as climate refugia for A. karina. Instead, long-term persistence of both BIF and non-BIF populations is supported.

Tracking Host Trees: The Phylogeography of EndemicPsittacanthus sonorae(Loranthaceae) Mistletoe in the Sonoran Desert

The host dependence of mistletoes suggests that they track the distributions of their hosts. However, the factors that determine the geographic distribution of mistletoes are not well understood. In this study, the phylogeography of Psittacanthus sonorae was reconstructed by sequencing one nuclear (ITS) and two plastid (trnL-F and atpB-rbcL) regions of 148 plants from populations separated by the Sea of Cortez. Divergence time and gene flow were estimated to gain insight into the historical demography and geographic structuring of genetic variation. We also described and mapped the spatial distribution of suitable habitat occupied by P. sonorae and its most common host Bursera microphylla in the Sonoran Desert, along with their responses to Quaternary climate fluctuations using environmental data and ecological niche modeling (ENM). We detected environmental and genetic differentiation between the peninsular and continental P. sonorae populations. Population divergence occurred during the Pleistocene, around the time of the Last Glacial Maximum. No signals of population growth were detected, with net gene flow moving from the continent to the peninsula. ENM models indicate decoupled responses by the mistletoe and its main host to past climate changes. For the Last Interglacial to the present, most models produce only partial areas of overlap on both the peninsula and the continent. Our results support a scenario of Late-Pleistocene isolation and divergence with asymmetrical gene flow between peninsular and continental P. sonorae populations. Continental populations migrated to the peninsula and the spatial isolation probably produced genetic differentiation under different environmental conditions.

Paleoclimatic and archaeological evidence from Lake Suches for highland Andeanrefugiaduring the arid middle-Holocene

Severe aridity during the mid-Holocene, ca. 8.0–4.0 kyr BP, led to extreme ecological stress in the tropical Andes. Here, we report paleolimnological and archeological data from Lake Suches in southern Peru (70° 24’ 12” W, 16° 55’ 35” S) spanning 13.6–4.4 kyr BP. Integrated paleoclimate and archeological data reveal that moisture was locally available and the basin served as an ecological refugium throughout the mid-Holocene. Mid-Holocene aridity was established no later than 7.2 kyr BP, with maximum aridity ca. 5.5–4.8 kyr BP. However, water levels in Lake Suches were sustained throughout peak middle-Holocene aridity, even as other systems desiccated. Isotopic enrichment of water in Lake Suches (δ18Olake) and extensive wetlands (δ18Obofedal) surrounding the lake indicate prolonged residence time. These reservoirs, combined with elevation-linked hydrographic factors, mitigated mid-Holocene net decreases in atmospheric moisture. Archeological data from Suches indicate successive population increases beginning ca. 11.0–9.8 kyr BP as drier but more stable early Holocene conditions were established regionally. Population maxima in Suches during the mid-Holocene/mid-Archaic period ca. 9.0–7.0 kyr BP coincide with peak aridity in the Titicaca and Atacama systems, as well as documented archeological hiatuses in these regions. Population decreases coincide with peak aridity recorded in Lake Suches ca. 6.0–5.0 kyr BP, but the basin was never fully abandoned. Evidence for refugial microenvironments is key to understanding the persistence of human populations and other endemic Andean flora and fauna during the highly adverse climates of the middle-Holocene. We outline several mechanisms which likely explain the formation of refugia linked to bofedales and hydrographic characteristics of Suches. Understanding refugial dynamics will be key to understanding the effects of past climatic change, as well as addressing current warming and decreased precipitation trends in the tropical Andes.