Peak Aridity Research Articles

Response of the Akrotiri Marsh, island of Cyprus, to Bronze Age climate change

Here we present two multiproxy records covering the last 5000 years from the Akrotiri Marsh in southern Cyprus. Pollen and diatom analysis of radiocarbon dated marsh sediments with an average chronological resolution of one date every thousand years, reveal expansion and contraction of the marsh in response to mid-late Holocene climate events, with peak aridity reconstructed in the early Bronze Age, inferred between 4.3 and 4.1 cal ka BP, and repeated dry intervals in the Late Bronze Age, inferred between 3.4 and 3.1 cal ka BP. The record provides important contextual climate data to the debate surrounding reported Early and Late Bronze Age societal collapse events present in numerous archaeological archives throughout the Mediterranean and Near Eastern region. This is the first multiproxy record from the island of Cyprus potentially displaying the 4.2 ka BP event. The characteristics of the inferred 3.2 ka BP event are very similar to the manifestation of the event in the east of Cyprus and on the southern Levantine mainland. These results contribute to the regional understanding of Bronze Age climates on Cyprus, give insight into the expression of global climate forcing mechanisms such as the North Atlantic Oscillation and the Siberian High, and provide potential evidence for reduced anthropogenic land-use during the 4.2 ka BP and 3.2 ka BP Events supporting what is documented in archaeological archives. • Two 5000-year-old multiproxy records from the Akrotiri Marsh, southern Cyprus • Both the 4.2 K and 3.2 K climate events had an impact on the island's water balance. • Pollen & diatoms infer Early Bronze Age peak aridity between 4.3 & 4.1 cal ka BP • Repeat dry intervals in Late Bronze Age from 3.4 to 3.1 cal ka BP, W-Shaped event • Insight into the expression of the North Atlantic Oscillation and the Siberian High

Holocene Hydroclimate Variability and Vegetation Response in the Ethiopian Highlands (Lake Dendi)

Northern Africa’s past climate is characterized by a prolonged humid period known as the African Humid Period (AHP), giving origin to the “Green Sahara” and supporting human settlements into areas that are now desert. The spatial and temporal extent of climate change associated with the AHP is, however, subject to ongoing debate. Uncertainties arise from the complex nature of African climate, which is controlled by the strength and interactions of different monsoonal systems, resulting in meridional shifts in rainfall belts and zonal movements of the Congo Air Boundary. Here, we examine a ∼12,500-years record of hydroclimate variability from Lake Dendi located in the Ethiopian highlands based on a combination of plant-wax-specific hydrogen (δD) and carbon (δ13C) isotopes. In addition, pollen data from the same sediment core are used to investigate the response of the regional vegetation to changing climate. Our δD record indicates high precipitation during peak AHP (ca. 10 to 8 ka BP) followed by a gradual transition toward a drier late Holocene climate. Likewise, vegetation cover changed from predominant grassland toward an arid montane forest dominated by Juniperus and Podocarpus accompanied by a general reduction of understory grasses. This trend is corroborated by δ13C values pointing to an increased contribution of C3 plants during the mid-to late Holocene. Peak aridity occurred around 2 ka BP, followed by a return to a generally wetter climate possibly linked to enhanced Indian Ocean Monsoon strength. During the last millennium, increased anthropogenic activity, i.e., deforestation and agriculture is indicated by the pollen data, in agreement with intensified human impact recorded for the region. The magnitude of δD change (40‰) between peak wet conditions and late Holocene aridity is in line with other regional δD records of East Africa influenced by the CAB. The timing and pace of aridification parallels those of African and Indian monsoon records indicating a gradual response to local insolation change. Our new record combining plant-wax δD and δ13C values with pollen highlights the sensitive responses of the regional vegetation to precipitation changes in the Ethiopian highlands.

Quaternary Landform Development in the Central segment of tectonically active Kachchh Mainland Fault zone, Western India

The landform aggradation in an arid climatic region is often regulated by external forces, that provide signatures of climate and tectonic perturbations. The landforms in the central segment of Northern Hill Range (NHR), which marks the surface expression of Kachchh Mainland Fault (KMF), are investigated in this study to understand the role of climatic changes and tectonic activity during the time of aggradation and incision. Geomorphologically, the KMF is expressed by the presence of ∼80–150 m high E-W trending escarpment. The central segment of KMF preserves the alluvial fan surfaces which have been truncated at several places with anomalous incision. Conventional morphometric analyses indicate that the KMF is affected by tectonic activity in recent times. The optical chronology of oldest alluvial fan dated from back limb and forelimb of an anticline was around 28 ka (with gradual onset of aridity) and 25 ka (with peak aridity). This arid phase is correlated with enhanced tectonic uplift along the KMF, which is manifested in the form of strath terraces and incision of river valleys. The oldest activity pre-dated to 25 ka and continued till 14 ka and there was a tectonic stability between 14 and 8 ka. The younger activity began soon after 8 ka and continuous till today, which is most likely caused by the manifestation of the Early Holocene climatic optima that lead to severe erosional processes. The younger Middle Holocene (4.3 ka) event is correlated with enhanced uplift and was accountable for the down cutting of the fill sediments and the Mesozoic bedrock. The study suggests that the deformation pattern close to KMF is the result of localized compressive stress generated between two fault segments.

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.

Sedimentology, geochemistry and OSL dating of the alluvial succession in the northern Gujarat alluvial plain (western India) - A record to evaluate the sensitivity of a semiarid fluvial system to the climatic and tectonic forcing since the late Marine Isotopic Stage 3

The alluvial successions in the northern Gujarat alluvial plain (western India) have been investigated for reconstructing the climatic fluctuations during the last 40ka. Alluvial architecture and geochemical proxies indicate prevalence of a strengthened Indian Summer Monsoon (ISM) with fluctuations between the late Marine Isotopic Stage 3 (MIS 3; 37ka) to the early MIS 2 (27ka). A gradual onset of aridity (declining ISM) after 27ka with peak aridity at ~22ka is observed. A gradual strengthening of ISM at around 18 and >12ka followed by a short reversal in ISM intensity between 12 and 11ka, is attributed to the Younger-Dryas (YD) cooling event. The aeolian sand sheet dated to 6 and 3.5ka represents the onset of regional aridity. Following this, a short-lived humid phase was observed after ~2ka, which includes the Medieval Warm Period (MWP). The study suggests that the variability in the ISM to the latitudinal migration of the Inter Tropical Convergence Zone was caused by insolation-driven cooling and warming events in the North Atlantic.The incision of the valley fill alluvium occurred in two distinct phases. The older incision phase occurred after 11ka and before 6ka, whereas the younger incision phase that led to the development of present day topography is bracketed between 3.5ka and before 1ka. The older incision phase is ascribed to the early to mid-Holocene enhanced ISM (climatically driven), whereas the younger incision seems to be modulated by the activation of basement faults (tectonically driven).

Reconstruction of Indian monsoon precipitation variability between 4.0 and 1.6 ka BP using speleothem δ18O records from the Central Lesser Himalaya, India

The present study documents the monsoon precipitation variability spanned ~ 2500 years, between 4.0 and 1.6 ka BP (before 1950 AD), from the Central Lesser Himalaya, India, using δ18O measurements of Tityana cave stalagmite (hereafter referred as TC1). At present, the cave receives precipitation from both Indian Summer Monsoon (ISM) and Western Disturbances (WDs). The δ18O variation between − 8.04 and − 10.46‰ through growth axis of the TC1 and five 14C AMS dates (due to large age uncertainty by 230Th/U method) have allowed us to identify the mid to late Holocene multi-decadal to centennial scale climatic oscillations. The higher δ18O values indicate the weakening of the monsoon precipitation, while the lighter values represent the stronger monsoon precipitation strength. Based on the fluctuations in δ18O values, three distinct phases of the precipitation variability are distinguished as, declined/decreased precipitation between ~ 4.0 and 3.4 ka BP with peak aridity around ~ 3.4 ka BP, followed by slightly improved conditions from ~ 3.4 to ~ 2.7 ka BP. Subsequently, the climate was reduced from ~ 2.7 ka BP onwards until the end of stalagmite growth, around ~ 1.6 ka BP with spikes of two major drought events centred at ~ 1.9 and ~ 1.6 ka BP. In general, the droughts, centred at ~ 3.4, ~ 1.9 and ~ 1.6 ka BP, are characterized by abrupt drop (from − 8.12 to − 8.04‰) in the δ18O values and point to the weakening of the monsoon. One of the major drought events at ~ 3.4 ka BP can be correlated with the collapse of the Indus valley civilization in the NW India. A close correspondence of the TC1 data set with other WDs influenced regimes likely indicates a relative impact of mid-latitude WDs after transition of the mid-late Holocene around 3.5–3.4 ka BP.

Disentangling the impacts of climate and human colonization on the flora and fauna of the Australian arid zone over the past 100 ka using stable isotopes in avian eggshell

Abstract Throughout the Quaternary, the flora and fauna of Australia evolved and adapted to the high-amplitude, low- and high-frequency climate changes that characterized the ice-age cycles. However, during the last glacial cycle, between ∼120 and 15 ka, unprecedented irreversible changes in flora and fauna occurred, and in that same interval modern humans established their first firm presence in the landscape. Disentangling the impacts of the first-order trend toward a colder, drier planet through the Late Quaternary from the impacts of human colonization has been challenging, from both the chronological and paleoenvironmental perspectives. We utilize the stable isotopes of carbon and oxygen preserved in near-continuous time series of Dromaius (emu) eggshell from five regions across Australia to provide independent reconstructions of ecosystem status and climate over the past 100 ka. Carbon isotopes are determined by the diet consumed by the female bird, whereas oxygen isotopes record the status of local moisture balance in the months prior to breeding. Together, δ13C and δ18O provide ecosystem status and climate from the same dated sample, reducing correlation uncertainties between proxies. Combined with recent improvements in the chronologies of Late Quaternary shorelines fringing inland lake basins and deflation during arid times, these data collectively reaffirm that Australia generally became increasingly, albeit irregularly, drier from the last interglaciation through to the last glacial maximum. Dromaius eggshell δ18O documents peak aridity between 30 and 15 ka, but shows no evidence of exceptional climate change between 60 and 40 ka. In contrast, Dromaius δ13Cdiet documents an irreversible loss of the majority of palatable summer-rainfall-related C4 grasses across the Australian arid zone between 50 and 45 ka, about the same time that the giant megafaunal bird, Genyornis, became extinct, and coincident with human dispersal across the continent. Our data indicate that changes unique to Australia occurred between 50 and 45 ka that led to a new climate-vegetation relationship and an overall reduction in effective moisture across much of the continent. The large summer-rainfall-dominated lakes of interior Australia failed to re-fill subsequently, despite a wide range of global climate states. A full explanation for the mechanisms behind these changes remains elusive, but they are almost certainly related to human agency. Plausible explanations include a change in fire regime resulting from human-lit fires, a change in fire regime following extinction of megafaunal browsers, and/or a threshold response to increasing aridity. Of these, the climate change explanation is least likely, given the lack of evidence for unprecedented aridity between 60 and 40 ka, and the successful adaptation of Australian ecosystems to 2.5 Ma of similar changes.

Andean microrefugia: testing the Holocene to predict the Anthropocene.

Microrefugia are important for supporting populations during periods of unfavourable climate change and in facilitating rapid migration as conditions ameliorate. With ongoing anthropogenic climate change, microrefugia could have an important conservation value; however, a simple tool has not been developed and tested to predict which settings are microrefugial. We provide a tool based on terrain ruggedness modelling of individual catchments to predict Andean microrefugia. We tested the predictions using nine Holocene Polylepis pollen records. We used the mid-Holocene dry event, a period of peak aridity for the last 100000yr, as an analogue climate scenario for the near future. The results suggest that sites with high terrain rugosity have the greatest chance of sustaining mesic conditions under drier-than-modern climates. Fire is a feature of all catchments; however, an increase in fire is only recorded in settings with low rugosity. Owing to rising temperatures and greater precipitation variability, Andean ecosystems are threatened by increasing moisture stress. Our results suggest that high terrain rugosity helps to create more resilient catchments by trapping moisture through orographic rainfall and providing firebreaks that shelter forest from fire. On this basis, conservation policy should target protection and management of catchments with high terrain rugosity.

Ant megadiversity and its origins in arid Australia

AbstractIt is widely recognised that arid Australia (including semi‐ and seasonally arid regions) supports an extremely diverse ant fauna. However, the truly remarkable extent of its diversity is not well appreciated, even among myrmecologists, and the reasons for such diversity are poorly understood. The vast majority of ant species in arid Australia are undescribed, and I argue that a recognition of the true diversity of the fauna would re‐define the conventional understanding of global ant diversity patterns. For example,MonomoriumMayr andTetramoriumMayr are formally recognised as widespread but essentially Afrotropical genera, whereas the large majority of species actually occur in arid Australia. The Australian fauna includes many genera each with >100 arid‐adapted species, and several of these have >300 species.MelophorusLubbock is likely to have well over 1000 species, making it one of the world's richest ant genera despite being endemic to Australia. I estimate that the total size of the ant fauna of arid Australia is as much as 7500 species, which would make it rival, if not surpass, that of the Amazon basin. I argue that the phenomenal ant diversity of arid Australia is a product of its unique history of aridity and associated patterns of speciation and extinction over the past few million years. I propose that the Pleistocene glaciations that caused waves of mass extinctions throughout the northern hemisphere actually promoted speciation in Australia. Australia remained relatively warm during glacial periods, but there was massive movement of sand during these times of peak aridity, with up to 85% of the continent covered by desert dunes. This would have resulted in a highly fragmented biota confined to a very large number of isolated refugia, providing the perfect storm for speciation.

An 8700 year paleoclimate reconstruction from the southern Maya lowlands

Analysis of a sediment core from Lago Puerto Arturo, a closed basin lake in northern Peten, Guatemala, has provided an ∼8700 cal year record of climate change and human activity in the southern Maya lowlands. Stable isotope, magnetic susceptibility, and pollen analyses were used to reconstruct environmental change in the region. Results indicate a relatively wet early to middle Holocene followed by a drier late Holocene, which we interpret as reflecting long-term changes in insolation (precession). Higher frequency variability is more likely attributable to changes in ocean/atmosphere circulation in both the North Atlantic and the Pacific Oceans. Pollen and isotope data show that most of the period of prehispanic agricultural settlement, i.e. ∼5000–1000 cal yr BP, was characterized by drier conditions than previous or subsequent periods. The presence of Zea (corn) pollen through peak aridity during the Terminal Classic period (∼1250–1130 cal yr BP) suggests that drought may not have had as negative an impact as previously proposed. A dramatic negative shift in isotope values indicates an increase in precipitation after ∼950 cal yr BP (hereafter BP).

Late Pleistocene monsoon variability in northwest Thailand: an oxygen isotope sequence from the bivalve Margaritanopsis laosensis excavated in Mae Hong Son province

Long, continuous records of Late Quaternary environmental change are rare in Southeast Asia, yet they are crucial for understanding the nature of early human dispersal and occupation in the Australasian region. We present a new record of palaeomonsoon activity extending back to 35,000 BP (years before the present), based on the analysis of oxygen isotope ratios (δ 18O) in the freshwater bivalve Margaritanopsis laosensis excavated from the Tham Lod and Ban Rai rockshelters in Mae Hong Son Province, northwest Thailand. Long-term changes in the M. laosensis δ 18O record reflect changes in the δ 18O of the river water in which these organisms grew, and correlate well with changes in speleothem δ 18O records of east Asian monsoon rainfall from Hulu Cave and Dongge Cave in China. The new northwest Thailand δ 18O sequence indicates wetter and relatively unstable climatic conditions from 35,000 to 20,000 BP, followed by drier conditions from 20,000 to 11,500 BP. A period of peak aridity occurred around 15,600 BP during Heinrich Event 1, suggesting that the intertropical convergence zone shifted southward when the North Atlantic region cooled. However, there is little evidence for the Younger Dryas event at ∼12,800–11,500 BP. After 9,800 BP, precipitation increased substantially and climatic variability declined. Our findings provide an improved baseline against which to gauge interactions between early humans and climate change in Southeast Asia. For example, there was no significant change in the prehistoric flake stone technology used at Tham Lod and Ban Rai despite the bivalve δ 18O evidence for substantial climate change in the region. Also, the climatic impact of the Younger Dryas event appears to have been less intense in northwest Thailand compared to the cooling and drying observed in China, and may explain why agriculture made a relatively late appearance in Thailand, possibly involving migrants from China.

Characterisation of aeolian sediments from the Strzelecki and Tirari Deserts, Australia: Implications for reconstructing palaeoenvironmental conditions

In arid environments dominated by desert dunes, aeolian sediments represent a major source of potential palaeoenvironmental information. However, the extent to which dune sedimentology can be used for past environmental reconstruction is unclear. This paper assesses the value of dune sediments as palaeoenvironmental indicators by investigating the sedimentological characteristics of linear dunes in the Strzelecki and Tirari Deserts of central Australia. We use thin section microscopy, particle size analysis and X-ray Diffractometry (XRD) mineralogy to characterise the sediments occurring within the dunefields of the region, and examine the stratigraphic record in the context of dune preservation and sediment reworking. We find that it is rarely possible to reconstruct past environmental change within desert dunefields purely on the basis of sedimentological evidence. However, limited palaeoenvironmental information is preserved within dune sediments which can be combined with additional arid zone proxies and geochronological techniques to enable the most reliable reconstruction of past conditions. Paleosols provide the most informative and unambiguous palaeoenvironmental indicators within dune sediments, acting as markers of relative environmental stability. Paleosols are characterised by pedogenic carbonates and gypsum, and illuviated clays in the form of intact grain coatings. The potential for incomplete stratigraphic preservation within dunes is a critical consideration for reconstructing palaeoenvironments, however the preservation of paleosols indicates that the dunes in this region have not been completely reworked. Grain coatings provide important evidence both for pedogenesis when they are intact, and for aeolian reworking when they are partially abraded. Abraded cutans are ubiquitous across the region studied. Linear dune mineralogy of the Strzelecki and Tirari Deserts is dominated by quartz, with minor feldspar and clay minerals, the latter in the form of grain coatings and aggregates. The occurrence of intact sand-sized aggregates composed of clay and silt particles at several sites indicates incipient rather than peak aridity, and may, within this geomorphic context, indicate reduced stream discharges. Grain size shows a regional bias, although silt-sized material is most likely to have been deposited as long-travelled dust. The regional grain size characteristics, combined with local occurrences of rock fragments and high feldspar content, suggest that sediments are mostly derived from local sources.

Upper Permian vertebrates and their sedimentological context in the South Urals, Russia

Fossil fishes and tetrapods (amphibians and reptiles) have been discovered at 81 localities in the Upper Permian of the Southern Urals area of European Russia. The first sites were found in the 1940s, and subsequent surveys have revealed many more. Broad-scale stratigraphic schemes have been published, but full documentation of the rich tetrapod faunas has not been presented before. The area of richest deposits covers some 900,000 km 2 of territory between Samara on the River Volga in the NW, and Orenburg and Sakmara in the SW. A continental succession, some 3 km thick, of mudstones, siltstones, and sandstones, deposited on mudflats and in small rivers flowing off the Ural Mountain chain, span the last two stages of the Permian (Kazanian, Tatarian). The succession is divided into seven successive units of Kazanian (Kalinovskaya, Osinovskaya, and Belebey svitas, in succession) and Tatarian age, which is further subdivided into the early Tatatian Urzhumian Gorizont (Bolshekinelskaya and Amanakskaya svitas, in succession), and the late Tatarian Severodvinian (Vyazovskaya and Malokinelskaya svitas, of equivalent age) and Vyatkian gorizonts (Kulchumovskaya and Kutulukskaya svitas, of equivalent age). This succession documents major climatic changes, with increasing aridity through the Late Permian. The climate changes are manifested in changing sedimentation and the spread of dryland plants, and peak aridity was achieved right at the Permo–Triassic (PTr) boundary, coincident with global warming. Uplift of the Urals and extinction of land plants led to stripping of soils and massive run-off from the mountains; these phenomena have been identified at the PTr boundary elsewhere (South Africa, Australia) and this may be a key part of the end-Permian mass extinction. The succession of Late Permian fish and tetrapod faunas in Russia documents their richness and diversity before the mass extinction. The terminal Permian Kulchomovskaya and Kutulukskaya svitas have yielded respectively some 6 and 13 species of fishes (sharks, bony fishes, lungfishes) and 11 and 14 species of tetrapods (aquatic amphibians, herbivorous and carnivorous reptiles of all sizes up to the hippo-sized pareiasaurs and sabre-toothed gorgonopsians). Immediately following the end-Permian environmental catastrophe, earliest Triassic faunas consisted only of a few fish taxa and small, aquatic tetrapods, in low-diversity, low-abundance assemblages.

A Late Pleistocene vegetation history from the Australian semi-arid zone

Cuddie Springs is an ephemeral lake in central northern New South Wales, Australia. The upper 3 m of sediment consist of lacustrine clays containing a Late Pleistocene sequence of extinct and extant fauna, and in the upper 1.7 m, an associated archaeological record. Changes observed in the pollen sequence include: (i) a peak in charcoal values corresponding to a dramatic decline in Casuarina woodland to chenopod shrubland at 2.5 m, respresenting a climatic shift to more arid conditions; (ii) chenopod shrubland moved into decline with the spread of grasslands around 1.7 m, and the amelioration in climatic conditions persisted until approximately 28,000 BP. A regime emerged which resulted in extended lake dry periods and peak aridity by approximately 19,000 BP and (iii) at 1 m depth, around 19,000 BP a shift to peak arid conditions is observed with a return of Chenopodiaceae and a decline in grasses. The lake entered an ephemeral phase that has persisted until the present day. The broad palaeoenvironmental framework of lake history, climate and vegetation change spans the archaeological and faunal records from Cuddie Springs. The direct association enables a closer examination of causation in faunal extinctions and human subsistence activities in the Australian arid zone.

The ostracode record from Harris Lake, southwestern Saskatchewan: 9200 years of local environmental change

Holocene paleoenvironments of Harris Lake, southwestern Saskatchewan, are reconstructed from the ostracode stratigraphy of a 10.4 m sediment core. Twenty three taxa, representing nine genera, were identified and counted from 113 samples. At each depth, a theoretical faunal assemblage was derived from the raw counts. The mean and variance of chemical, climatic and physical variables were inferred from modern analogues of the fossil assemblages, using existing autecological data from 6720 sites, mostly in western Canada. These data suggest four paleoenvironments: an early-Holocene (9240–6400 years BP) variable climate supporting aspen parkland vegetation; the warm dry hypsithermal (6400–4500 years BP); a short transitional period of ameliorating climate and expanding subboreal forest (4500–3600 years BP); and the present environment since 3600 years BP. A change in regional climate with the draining of Glacial Lake Agassiz (ca. 8500 years BP) and landsliding in the watershed (ca. 4000 years BP) caused relatively rapid environmental change. The ostracode record generally corroborates the interpretations of other proxy data previously published for Harris Lake. Most of the discrepancy involves the timing and severity of maximum Holocene warmth and aridity. Peak aridity interpreted from the pollen data is earlier than in the other proxy records. Both the diatoms and ostracodes indicate highest paleosalinity between ca. 6500 and 5000 years BP, but maximum salinity in the diatom record occurs between ca. 6000–5700 years BP, whereas the ostracode-inferred salinity is relatively low at this time and peaks later at ca. 5000 years. Neither of these reconstructions suggests the short episodes of hypersalinity interpreted from the mineralogy.