Desiccation Events Research Articles

Lake Kumphawapi revisited – The complex climatic and environmental record of a tropical wetland in NE Thailand

Kumphawapi, which is Thailand’s largest natural freshwater lake, contains a >10,000-year-long climatic and environmental archive. New data sets (stratigraphy, chronology, hydrogen isotopes, plant macrofossil and charcoal records) for two sedimentary sequences are here combined with earlier multi-proxy studies to provide a comprehensive reconstruction of past climatic and environmental changes for Northeast Thailand. Gradually higher moisture availability due to a strengthening of the summer monsoon led to the formation of a large shallow lake in the Kumphawapi basin between >10,700 and c. 7000 cal. BP. The marked increase in moisture availability and lower evaporation between c. 7000 and 6400 cal. BP favoured the growth and expansion of vegetation in and around the shallow lake. The increase in biomass led to gradual overgrowing and infilling, to an apparent lake level lowering and to the development of a wetland. Multiple hiatuses are apparent in all investigated sequences between c. 6500 and 1400 cal. BP and are explained by periodic desiccation events of the wetland and erosion due to the subsequent lake level rise. The rise in lake level, which started c. 2000 cal. BP and reached shallower parts c. 1400 cal. BP, is attributed to an increase in effective moisture availability. The timing of hydroclimatic conditions during the past 2000 years cannot be resolved because of chronological limitations.

Desiccation frequency drives local invasions of non-native gibel carp (Carassius gibelio) in the catchment of a large, shallow lake (Lake Balaton, Hungary)

Although the problem of non-indigenous species and biological invasions has been widely discussed, knowledge is still limited on their prevention and elimination for the successful management of this problem. In this study, we tested relationships between fish community composition, local environmental parameters and habitat management practice in 11 lentic habitats in the catchment of Lake Balaton (Hungary). The frequency of desiccation events (related to fish pond management) proved to be highly important in increasing the dominance of non-indigenous Carassius gibelio. We suggest that high frequency of desiccation events and the robustness of this species (tolerance to low oxygen levels, gynogenetic reproduction) can contribute to local invasion cycles in wetlands and fish ponds resulting in their continuously high abundance. Our study suggests that ensuring more controlled and stable water level in these habitats can be a successful tool to manage C. gibelio invasions.

The biota of the Upper Cretaceous site of “Lo Hueco” (Cuenca, Spain)

The Late Cretaceous (Campanian-Maastrichtian) fossil site of Lo Hueco was recently discovered close to the village of Fuentes (Cuenca, Spain) during the cutting of a little hill for installation of the railway of the Madrid-Levante high-speed train. To date, it has yielded a rich collection of well-preserved Cretaceous macrofossils, including plants, invertebrates, and vertebrates. The recovered fossil assemblage is mainly composed of plants, molluscs (bivalves and gastropods), actinopterygians and teleosteans fishes, amphibians, panpleurodiran (bothremydids) and pancryptodiran turtles, squamate lizards, eusuchian crocodyliforms, rhabdodontid ornithopods, theropods (mainly dromaeosaurids), and titanosaur sauropods. This assemblage was deposited in a near-coast continental muddy floodplain crossed by distributary sandy channels, exposed intermittently to brackish or marine and freshwater flooding as well as to partial or total desiccation events. The Konzentrat-Lagerstatt of Lo Hueco constitutes a singular accumulation of fossils representing individuals of some particular lineages of continental tetrapods, especially titanosaurs, eusuchians and bothremydid turtles. In the case of the titanosaurs, the site has yielded multiple partial skeletons in anatomical connection or with a low dispersion of their skeletal elements. A combination of new taxa, new records of taxa previously known in the Iberian Peninsula, and relatively common taxa in the European record compose the Lo Hueco biota. The particular conditions of the fossil site of Lo Hueco and the preliminary results indicate that the analysis of the geological context, the floral and faunal content, and the taphonomical features of the site provide elements that will be especially useful for reassess the evolutionary history of some lineages of European Late Cretaceous reptiles.

Biofilm resilience to desiccation in groundwater aquifers: A laboratory and field study

Groundwater is used as a precious resource for drinking water worldwide. Increasing anthropogenic activity is putting increasing pressure on groundwater resources. One impact of increased groundwater abstraction coupled with increasing dry weather events is the lowering of groundwater levels within aquifers. Biofilms within groundwater aquifers offer protection to the groundwater by removing contaminants entering the aquifer systems from land use activities. The study presented investigated the impact of desiccation events on the biofilms present in groundwater aquifers using field and laboratory experiments. In both field and laboratory experiments a reduction in enzyme activity (glucosidase, esterase and phosphatase) was seen during desiccation compared to wet controls. However, comparing all the data together no significant differences were seen between either wet or desiccated samples or between the start and end of the experiments. In both field and laboratory experiments enzyme activity recovered to start levels after return to wet conditions. The study shows that biofilms within groundwater systems are resilient and can withstand periods of desiccation (4months).

Late Holocene hydrology inferred from lacustrine sediments of Laguna Cháltel (southeastern Argentina)

Hydrological changes that occurred during the last 4700years have been reconstructed using multi-proxy analyses of sediment cores from the volcanic crater lake of Laguna Cháltel (50°S, 71°W). The chronology is based on AMS 14C age modeling constrained by paleomagnetic secular variations. Chemical and physical properties of the lake water together with results of lake-water surface-temperature monitoring, as well as sediment characteristics reveal conspicuous features archived as different sedimentary carbonate phases and morphologies which are attributed to lake-level changes.Sedimentological, geochemical and biological proxies together suggest the development from an initial playa lake-phase towards a system with progressively rising lake level. In detail, proxies indicate the existence of an ephemeral lake since 4700cal BP until a glauberite-bearing carbonate crust formed around 4040cal BP which probably is associated to the globally recognized 4.2ka event. This crust is interpreted as a desiccation event terminating the ephemeral lake phase. Following this desiccation a shift towards conditions with a positive hydrological balance of Laguna Cháltel occurs, which leads to the development of a saline lake with ooid formation between 4040 and 3200cal BP. Further lake-level increase with initially high minerogenic input until 2700cal BP resulted in a lake freshening which allowed the preservation of diatoms. Sigmoidal and star shaped carbonate crystals occurred until 1720cal BP indicating a syn- or post-depositional formation of ikaite. Anoxic conditions and increased deposition of clay and sand through fluvial and eolian input are interpreted as a further lake-level rise and/or a prolonged winter ice cover culminating during the Little Ice Age. The highest lake level was probably reached at that time and since then dropped to its present day height.Previous studies have shown that the southern hemisphere westerly winds (SWW) exert an oppositional control on hydrological regimes at the eastern and the western sides of the Patagonian Andes. At Laguna Cháltel SWW forcing is changing evaporation rates by varying wind intensities, air temperatures and lake ice coverages as well as by precipitation rates (easterly vs. westerly sources of moisture). Our data suggests that the lake-level history of Laguna Cháltel reflects changes in the SWW during the last 4.7ka on the eastern side of the Andes. However, the elevated location of Laguna Cháltel on an 800m high plateau at the leeward side of the Andes potentially leads to a local overprint of the SWW influence on the hydrological balance.

Last glacial hydrological variations at the southern margin of sub‐tropical North America and a regional comparison

ABSTRACTGeochemical and magnetic characteristics of sediments from paleolake La Salada provide information about the last glacial hydrological conditions at the southern margin of sub‐tropical North America. Proxy records of runoff, lake water salinity, brine composition and provenance of organic matter are based on multi‐element concentration, magnetic susceptibility, mineralogy, carbonate content and C/N relation. Runoff was higher than average during ca. 43–36k cal a BP and at ca. 33k cal a BP. A shift in mineralogical assemblage from calcite > protodolomite–halite to protodolomite–gaylussite suggests that the brine composition changed from Ca–(Mg–Na)–HCO3–(Cl) to Mg–Na–Ca–HCO3 because of more runoff after the desiccation event at ca. 28k cal a BP. In general, organic matter deposited during the intervals of more runoff and deeper lake conditions were sourced from lacustrine phytoplankton. The contribution of terrestrial vegetation dominates during the intervals of reduced runoff. Comparison with other records provides a regional perspective of moisture variability. Humid conditions at ca. 33k cal a BP could be due to more summer precipitation in northern Mexico as well as increased winter rainfall in the south‐western USA.

Paleohydrology of Lake Turkana and its influence on the Nile River system

The detailed paleohydrological record of Lake Turkana, the largest lake in the eastern branch of the East African Rift, is necessary for determining the connectivity between adjacent watersheds in tropical Africa. The migration of both the Intertropical Convergence Zone (ITCZ) and the Congo Air Boundary (CAB) constrains rainfall amount and duration for most of East Africa. Lake Turkana, in northern Kenya, is the world's largest desert lake and experiences two ITCZ-associated rainy seasons annually, with cumulative rainfall of ~200mm/yr. Evidence from new continuous, high-fidelity sediment core records and high-resolution CHIRP seismic reflection data suggests that Lake Turkana received enough rainfall during the African Humid Period (AHP) to fill the lake to its sill (100m above current lake level) and spilled over into the White Nile River system. An atmospheric configuration with an eastward-shifted CAB over the Turkana region and the northern Kenya Rift is invoked as an additional source of rainfall for the catchment. This configuration began abruptly at ~11ka and lasted until ~5ka when Lake Turkana became a closed basin and was cut off from the White Nile. Prior to the AHP, Lake Turkana experienced at least two desiccation events following the Last Glacial Maximum at 18.5 and 17ka when the lake was at least 100m lower than modern, as evidenced by basin-wide, high amplitude reflections and 14C-dated shallow water facies in sediment cores. Lake level fluctuations generally follow trends in mean solar insolation, however the onset of lake level extremes are much more abrupt than rates of insolation change. Lake Turkana's location in relation to atmospheric convergence and dynamic rainfall patterns makes its susceptible to extreme climate change over relatively short timescales.

Unraveling Regulation of the Small Heat Shock Proteins by the Heat Shock Factor HvHsfB2c in Barley: Its Implications in Drought Stress Response and Seed Development

The rapid increase in heat shock proteins upon exposure to damaging stresses and during plant development related to desiccation events reveal their dual importance in plant development and stress tolerance. Genome-wide sequence survey identified 20 non-redundant small heat shock proteins (sHsp) and 22 heat shock factor (Hsf) genes in barley. While all three major classes (A, B, C) of Hsfs are localized in nucleus, the 20 sHsp gene family members are localized in different cell organelles like cytoplasm, mitochondria, plastid and peroxisomes. Hsf and sHsp members are differentially regulated during drought and at different seed developmental stages suggesting the importance of chaperone role under drought as well as seed development. In silico cis-regulatory motif analysis of Hsf promoters showed an enrichment with abscisic acid responsive cis-elements (ABRE), implying regulatory role of ABA in mediating transcriptional response of HvsHsf genes. Gene regulatory network analysis identified HvHsfB2c as potential central regulator of the seed-specific expression of several HvsHsps including 17.5CI sHsp. These results indicate that HvHsfB2c is co-expressed in the central hub of small Hsps and therefore it may be regulating the expression of several HvsHsp subclasses HvHsp16.88-CI, HvHsp17.5-CI and HvHsp17.7-CI. The in vivo relevance of binding specificity of HvHsfB2C transcription factor to HSE-element present in the promoter of HvSHP17.5-CI under heat stress exposure is confirmed by gel shift and LUC-reporter assays. Further, we isolated 477 bp cDNA from barley encoding a 17.5 sHsp polypeptide, which was predominantly upregulated under drought stress treatments and also preferentially expressed in developing seeds. Recombinant HvsHsp17.5-CI protein was expressed in E. coli and purified to homogeneity, which displayed in vitro chaperone activity. The predicted structural model of HvsHsp-17.5-CI protein suggests that the α-crystallin domain is evolutionarily highly conserved.

Predictions of climate change infer increased environmental harshness and altered connectivity in a cluster of temporary pools

Summary Future moderate changes in evaporation and precipitation regimes could have pronounced effects on zooplankton populations in small and temporary aquatic habitats, by causing higher salinity and a shorter wet phase and by reducing passive dispersal via hydrological connections between pools and increasing it by exposing propagules to the wind. Using a hydrological model, we simulated various climate change scenarios in a natural cluster of temporary rock pools in South Africa. In our simulations, a shift towards a drier climate was associated with reduced permanence and increased conductivity, resulting in a lower percentage of inundations sufficient for the hatching, growth and reproduction of aquatic organisms (up to a 21% decline for a fairy shrimp). Connections between pools by overflowing occurred less frequently (by up to 28%). However, more frequent desiccation events (by up to 15%) led to increased exposure of dormant propagules to wind, possibly promoting dispersal within the pool cluster but also leading to losses from the propagule bank. Our results suggest that environmental change might not only affect local (within‐pool) selection pressures but also regional dynamics in rock pool metapopulations and communities.

The Interaction of Climate Change and Agency in the Collapse of Civilizations ca. 2300–2000 BC

Human history has been marked by major episodes of climate change and human response, sometimes accompanied by independent innovations. In the Bronze Age, the sequencing of causes and reactions is dependent in part on dendrochronology and radiocarbon dating. This paper explores the interaction of a major, prolonged desiccation event between c. 2300 and 2000 BC and human agency including migrations, the displacement of trading networks, warfare, the appearance of weapons made of bronze, and the first appearance of sailing vessels in the Mediterranean.

The Interaction of Climate Change and Agency in the Collapse of Civilizations ca. 2300–2000 BC

Human history has been marked by major episodes of climate change and human response, sometimes accompanied by independent innovations. In the Bronze Age, the sequencing of causes and reactions is dependent in part on dendrochronology and radiocarbon dating. This paper explores the interaction of a major, prolonged desiccation event between c. 2300 and 2000 BC and human agency including migrations, the displacement of trading networks, warfare, the appearance of weapons made of bronze, and the first appearance of sailing vessels in the Mediterranean.

<b>Desiccation and recovery of periphyton biomass and density in a subtropical lentic ecosystem</b> - doi: 10.4025/actascibiolsci.v35i3.14022

This study assessed the desiccation effects on biomass and algal density of periphyton in a subtropical lentic ecosystem. This experiment was conducted with only one in situ experimental desiccation event for 15 hours in a mature periphytic community. The periphyton after desiccation was distinct in density and biomass estimators (dry weight and chlorophyll a) when compared to the control periphyton. After the tenth day of desiccation, the community presented similar values for biomass estimators when compared to the control periphyton. The density and biomass estimators of the periphyton community was affected by the desiccation event and required about ten days to recover to pre-disturbance conditions.

Survival and behavior of Chinese mystery snails (Bellamya chinensis) in response to simulated water body drawdowns and extended air exposure

Nonnative invasive mollusks degrade aquatic ecosystems and induce economic losses worldwide. Extended air exposure through water body drawdown is one management action used for control. In North America, the Chinese mystery snail (Bellamya chinensis) is an invasive aquatic snail with an expanding range, but eradication methods for this species are not well documented. We assessed the ability of B. chinensis to survive different durations of air exposure, and observed behavioral responses prior to, during, and following desiccation events. Individual B. chinensis specimens survived air exposure in a laboratory setting for > 9 weeks, and survivorship was greater among adults than juveniles. Several B. chinensis specimens responded to desiccation by sealing their opercula and/or burrowing in mud substrate. Our results indicate that drawdowns alone may not be an effective means of eliminating B. chinensis. This study lays the groundwork for future management research that may determine the effectiveness of drawdowns when combined with factors such as extreme temperatures, predation, or molluscicides.

Present-day variability and Holocene dynamics of permafrost-affected lakes in central Yakutia (Eastern Siberia) inferred from diatom records

Thermokarst lakes are assumed to develop cyclically, driven by processes that are triggered by climate and maintained by internal feedbacks that may trigger lake drainage. However, the duration of these cycles remains uncertain, as well as whether or not they affect the stabilization of lake ecosystems in permafrost regions over millennial time scales. Our research has combined investigations into modern lake-to-lake variability with a study of the long-term development of individual lakes. We have investigated the physico-chemical and diatom compositions of a set of 101 lakes with a variety of different origins in central Yakutia (Eastern Siberia), including thermokarst lakes, fluvial-erosion thermokarst lakes, fluvial-erosion lakes, and dune lakes. We found a significant relationship between lake genesis and the present-day variability in environmental and diatom characteristics, as revealed by multi-response permutation procedures, indicator species analyses, and redundancy analyses. Environmental parameters also exhibit a significant correlation with variations in the diatom data, for which they may have been to a substantial extent responsible. Mg and SO4 concentrations, together with pH and water depth, were identified as the most important parameters, influencing the variations in the diatom data almost as much as the entire environmental parameter set. We were therefore able to establish a robust Mg-diatom transfer function, which was then applied to three Holocene lake records. From these reconstructions, together with a general interpretation of the diatom record (including, e.g., the ratio between benthic/epiphytic and planktonic taxa), we have been able to infer that all three of these lakes show (1) a continuous record with no desiccation events, (2) high lake water-levels during the early Holocene, (3) centennial to millennial scale variability, and (4) high levels of variability during the early Holocene but rather stable conditions during the late Holocene (a feature that is also known from other sites around the world). We therefore concluded that the development of these three lakes was mainly driven directly by the climate, rather than by thaw lake cycling.

The impact of dehydration rate on the production and cellular location of reactive oxygen species in an aquatic moss.

The aquatic moss Fontinalis antipyretica requires a slow rate of dehydration to survive a desiccation event. The present work examined whether differences in the dehydration rate resulted in corresponding differences in the production of reactive oxygen species (ROS) and therefore in the amount of cell damage. Intracellular ROS production by the aquatic moss was assessed with confocal laser microscopy and the ROS-specific chemical probe 2,7-dichlorodihydrofluorescein diacetate. The production of hydrogen peroxide was also quantified and its cellular location was assessed. The rehydration of slowly dried cells was associated with lower ROS production, thereby reducing the amount of cellular damage and increasing cell survival. A high oxygen consumption burst accompanied the initial stages of rehydration, perhaps due to the burst of ROS production. A slow dehydration rate may induce cell protection mechanisms that serve to limit ROS production and reduce the oxidative burst, decreasing the number of damaged and dead cells due upon rehydration.

Desiccation Tolerance and Global Change: Implications for Tropical Bryophytes in Lowland Forests

AbstractGlobal change puts an increasing pressure on tropical forests and their inherent diversity by the risk of longer droughts and drier microclimatic conditions within the forest. How organisms will respond is uncertain, especially for organisms highly depending on their microclimatic environment such as bryophytes. An adequate tolerance to desiccation is important to face these changes, however, little is known for tropical bryophytes. We investigated for the first time the desiccation tolerance of epiphytic bryophytes from contrasting microsites at the tropical lowland forest in French Guiana. Using chlorophyll‐fluorescence (Fv/Fm) as an indicator of recovery, we tested: (1) desiccation tolerance for short (3 d) and long (9 d) desiccation events; (2) different desiccation intensities; and (3) recovery by rehydration with water vapor. Species from the canopy were well adapted to desiccation events. Thirteen of 18 species maintained more than 75 percent of their photosynthetic capacity after recovery at the strongest desiccation treatment of 9 d at 43 percent relative humidity (RH). In contrast, species from the understory were sensitive and withstood desiccation only at humid conditions of 75 percent RH and higher. The photosystem of the studied bryophytes was reactivated efficiently in equilibration with water vapor only—a yet neglected phenomenon in bryology. A novel introduced desiccation tolerance index allows global comparison of desiccation tolerances and highlights the sensitivity of understory species. Our results suggest that decreasing humidity caused by climate change and forest degradation could be a concerning threat for understory species.

Interazioni tra clima, ambiente e uomo nell'evoluzione olocenica del delta del Tevere: dati paleobotanici e ritrovamenti archeologici

Climate, environment and man interactions in the Holocene evolution of the Tiber delta: palaeobotanical and archaeological data.The integration of palaeobotanical and archaeological data from recent studies carried out in the Tiber delta allows reconstructing the Holocene landscape evolution of the coastal area near Rome, revealing a long history of climate, environment and man interactions (Manfredini, 2002; D'Ambrogi et alii, 2009; Di Rita et alii, 2010; Bellotti et alii, 2011).The geomorphological, sedimentological, palaeobotanical and archaeological data from sites located in the northern and southern sides of the Tiber delta clearly document major environmental changes, including eustatic sea-level variations, geomorphologic processes, groundwater fluctuations, desiccation events and micro-climatic processes, which have produced dramatic and repeated landscape transformations, with inevitable repercussions on the local plant biodiversity and human communities.Human activity, documented in the area since the Neolithic and characterized by significant Eneolithic and Bronze Age settlements, appears to have had a marginal role in the landscape evolution. Only the Etruscan and Roman exploitation of the area for salt extraction produced an important impact on the landscape, becoming a major factor for environmental instability.When considered within the last thousands of years, the modern environmental situation appears a snap-shot, destined to new, abrupt and dramatic future changes.

Population dynamics and tolerance to desiccation in a crustacean ostracod adapted to life in small ephemeral water bodies

Given their small size, isolation and unpredictability, temporary rockpools present high environmental stress and impoverished communities of species that have adapted to such stressful conditions. Special adaptations of the invertebrates living in these habitats include tolerance to desiccation and fast ontogenetic development in order to maintain stable populations and face high risk of extinction. Dozens of small rockpools (mostly with Ø < 1 m) can be found in east Spain on limestone substrate, where the only known Iberian populations of Heterocypris bosniaca Petkovski et al. (2000) , an ostracod species with geographic parthenogenesis, have been recently found. In this survey, two of these rockpools have been monitored during the main hydroperiod between the fall of 2005 and summer 2006 to test the ability of H. bosniaca parthenogenetic populations to face unpredictable hydroperiod dynamics. Pools were visited weekly, and limnological data and ostracod samples were obtained from either water or substrate in dry periods. Ostracod individuals were counted and assigned to growth instars to monitor population changes. In the laboratory, experimental cultures allowed the estimation of survival dependence on the substrate desiccation rate. Throughout the hydrological cycle studied, several hatching periods were observed, usually preceded by desiccation, followed by substrate hydration and water dilution by rain. The demographic changes observed indicate that H. bosniaca populations are able to persist in intermittently inundated environments and produce several generations per annual hydrological cycle. In addition, adult individuals were able to survive in the wet mud of dry pools for longer than five weeks. The experimental data suggest a lower average survival time when exposed to desiccation processes, and that the velocity of substrate water loss is a determining factor for the survival rate of ostracods resisting dry events in temporary ponds. As shown by ostracods’ life histories in temporary aquatic environments undergoing unpredictable desiccation events, a combined strategy of adult tolerance to short periods of water scarcity and rapid hatching from resting egg banks can be advantageous for the monopolization of small-sized ephemeral habitats.

Physiological consequences of desiccation in the aquatic bryophyte Fontinalis antipyretica

The moss Fontinalis antipyretica, an aquatic bryophyte previously described as desiccation-intolerant, is known to survive intermittent desiccation events in Mediterranean rivers. To better understand the mechanisms of desiccation tolerance in this species and to reconcile the apparently conflicting evidence between desiccation tolerance classifications and field observations, gross photosynthesis and chlorophyll a fluorescence were measured in field-desiccated bryophyte tips and in bryophyte tips subjected in the laboratory to slow, fast, and very fast drying followed by either a short (30 min) or prolonged (5 days) recovery. Our results show, for the first time, that the metabolic response of F. antipyretica to desiccation, both under field and laboratory conditions, is consistent with a desiccation-tolerance pattern; however, drying must proceed slowly for the bryophyte to regain its pre-desiccation state following rehydration. In addition, the extent of dehydration was found to influence metabolism whereas the drying rate determined the degree of recovery. Photosystem II (PSII) regulation and structural maintenance may be part of the induced desiccation tolerance mechanism allowing this moss to recover from slow drying. The decrease in the photochemical quenching coefficient (qP) immediately following rehydration may serve to alleviate the effects of excess energy on photosystem I (PSI), while low-level non-photochemical quenching (NPQ) would allow an energy shift enabling recovery subsequent to extended periods of desiccation. The findings were confirmed in field-desiccated samples, whose behavior was similar to that of samples slowly dried in the laboratory.

The Holocene environmental history of Lake Hoare, Taylor Valley, Antarctica, reconstructed from sediment cores

AbstractUp to 2.3 m long sediment sequences were recovered from the deepest part of Lake Hoare in Taylor Valley, southern Victoria Land, Antarctica. Sedimentological, biogeochemical, and mineralogical analyses revealed a high spatial variability of these parameters in Lake Hoare. Five distinct lithological units were recognized. Radiocarbon dating of bulk organic carbon samples from the sediment sequences yielded apparently too old ages and significant age reversals, which prevented the establishment of reliable age-depth models. However, cross correlation of the sedimentary characteristics with those of sediment records from neighbouring Lake Fryxell indicates that the lowermost two units of the Lake Hoare sediment sequences were probably deposited during the final phase of proglacial Lake Washburn, which occupied Taylor Valley during the late Pleistocene and early Holocene. High amounts of angular gravel and the absence of fine-grained material imply a complete desiccation with subaerial conditions in the Lake Hoare basin in the middle of the Holocene. The late Holocene (&lt; c. 3300 calendar yr bp) is characterized by the establishment of environmental conditions similar to those existing today. A late Holocene desiccation event, such as proposed in former studies, is not indicated in the sediment sequences recovered.