Wet Phases Research Articles

Paleoenvironmental and paleoclimatic changes of Engir Lake (Central Anatolia) and its surroundings during the last 1090 years: The fossil diatom record

The main aim of the study is to determine the paleoenvironmental and climatic changes in the Engir Lake (Central Anatolia Region of Türkiye) and its surroundings during the last 1090 years. A total of 63 sub-samples with a resolution of 4 cm were obtained from the 263 cm-long sediment core, which was taken from a site away from the current and where the deterioration was the least. Based on fossil diatoms, important data have been obtained about the Medieval Warm Period (MWP), the Little Ice Age (LIA), and the Industrial Period (IP). The MWP corresponds to between ca. AD 860–1240 cal yr in the Engir Lake and its surroundings. In this study, the MWP is generally described as a warm and wet period characterized by a relatively high water level recorded between ca. AD 1110–1240 cal yr. Although the first evidence of the onset of dry conditions occurs between ca. AD 1260–1320 cal yr, the first characteristic impact of the LIA on Engir Lake is generally observed between ca. AD 1350–1380 cal yr. This first dry period in Engir Lake corresponds to the global Wolf Minimum, while ca. AD 1490–1530 cal yr corresponds to the Spörer Minimum and ca. AD 1620–1690 cal yr corresponds to the Maunder Minimum. During these periods, low water levels were recorded in the lake with aerophile taxa dominating. Between these dry phases, the core also recorded relatively wet phases. These wet phases occurred at ca. AD 1390–1480, AD 1530–1620, and AD 1690–1760 cal yr, respectively. After ca. AD 1890 cal yr, the pollution of the lake increased due to the industrial activities in the vicinity of Engir Lake, and aquatic plants developed in the vicinity of the lake with increasing nutrient input. This study is an important record for understanding the past, as there has not yet been a relatively detailed study on LIA and MWP through fossil diatoms in Türkiye.

Middle-Late Pleistocene Eastern Mediterranean nutricline depth and coccolith preservation linked to Monsoon activity and Atlantic Meridional Overturning Circulation

The eastern Mediterranean Sea lies under the influence of high- and low-latitude climatic systems. The northern part of the basin is affected by Atlantic depressions and continental and polar air masses that promote intermediate and deep-water formation. The southern part is influenced by subtropical conditions and monsoon activity. Monsoon intensification results in enhanced freshwater discharge from the Nile River and other (now dry) systems along the North African margin. This freshwater influx into the Mediterranean Sea reduces surface water buoyancy loss. Disentangling the influences of these diverse climatic forcings is hindered by inherent proxy data limitations and by interactions between the climatic forcings. Here we use a wealth of published and new paleoclimate records across Termination II to understand the impacts of the higher latitude and subtropical/monsoon climate influences on coccolithophore ecology and holococcolith preservation in Aegean Sea sediment core LC21. We then use these findings to interpret coccolith assemblage variations at Ocean Drilling Program Site 967 (located nearby LC21, at the Eratosthenes Seamount) during multiple glacial-interglacial cycles across the Middle Pleistocene (marine isotopic stages 14–9). The LC21 analysis suggests that holococcolith preservation was enhanced during Heinrich Stadial 11 (∼133 ka) and cold spell C26 (∼119 ka). These two events have been previously linked to cold conditions in the North Atlantic and Atlantic Meridional Overturning Circulation weakening. We propose that associated atmospheric perturbations over the Mediterranean Sea promoted deep-water formation, and thus holococcolith preservation. Similarly, in the Middle Pleistocene (MIS 14-9) of Site 967, we observe temporal coincidence between ten episodes of enhanced holococcolith preservation and episodes of Atlantic Meridional Overturning Circulation slowdown. In Site 967, we also identified repeated fluctuations in placoliths and in Florisphaera profunda, which indicate nutricline depth variations. The development of a deep chlorophyll maximum is associated with the North Africa and wet phases, as recently observed using elemental proxy records at Site 967, during the deposition of sapropel layers. A further deep chlorophyll maximum development is identified during MISs 12 and 10, as a result of pycnocline and nutricline shoaling within the lower part of the photic zone due to glacial sea-level lowering and water mass transport reduction at both the Gibraltar and Sicily Straits. Finally, enhanced holococcolith preservation during cold/dry events is clearly correlated to weakened monsoon activity in both Africa and Asia.

Biomarker and Pollen Evidence for Late Pleistocene Pluvials in the Mojave Desert

AbstractThe climate of the southwestern North America has experienced profound changes between wet and dry phases over the past 200 Kyr. To better constrain the timing, magnitude, and paleoenvironmental impacts of these changes in hydroclimate, we conducted a multiproxy biomarker study from samples collected from a new 77 m sediment core (SLAPP‐SRLS17) drilled in Searles Lake, California. Here, we use biomarkers and pollen to reconstruct vegetation, lake conditions, and climate. We find that δD values of long chain n‐alkanes are dominated by glacial to interglacial changes that match nearby Devils Hole calcite δ18O variability, suggesting both archives predominantly reflect precipitation isotopes. However, precipitation isotopes do not simply covary with evidence for wet‐dry changes in vegetation and lake conditions, indicating a partial disconnect between large scale atmospheric circulation tracked by precipitation isotopes and landscape moisture availability. Increased crenarchaeol production and decreased evidence for methane cycling reveal a 10 Kyr interval of a fresh, productive, and well‐mixed lake during Termination II, corroborating evidence for a paleolake highstand from shorelines and spillover deposits in downstream Panamint Basin and Death Valley during the end of the penultimate (Tahoe) glacial (140–130 ka). At the same time brGDGTs yield the lowest temperature estimates (mean months above freezing = 9°C ± 3°C) of the 200 Kyr record. These limnological conditions are not replicated elsewhere in the 200 Kyr record, suggesting that the Heinrich stadial 11 highstand was wetter than the last glacial maximum and Heinrich 1 (18–15 ka).

Droughts Are Not the Likely Primary Cause for Abies sibirica and Pinus sibirica Forest Dieback in the South Siberian Mountains

Background. Since the mid-20th century, massive dieback of coniferous forests has been observed in the temperate and boreal zones across North America and Northern Eurasia. The first hypotheses explaining forest dieback were associated with industrial air pollution (acid rain). At the end of the century, new hypotheses emerged that supported critical climate-induced aridization to explain forest dieback. Many studies were based on the SPEI (Standardized Precipitation Evapotranspiration Index) drought index. Our goals were to investigate if the SPEI drought index was a suitable metric to reflect drought conditions in wet and moist dark-needled forests in the South Siberian Mountains (Mts) and if droughts trigger the dieback of those forests. Methods. We calculated the SPEI drought index, the annual moisture index AMI, potential evapotranspiration PET, and water balance dynamics for the period 1961–2019 for four transects in the South Siberian Mts. where decline/dieback of dark-needled Siberian pine and fir forests were identified in situ. Climate data from nine weather stations located at lower and upper elevations of each transect were used to calculate climatic index dynamics for the 1961–2019 period to identify dry and wet phases of the period. Results. Our findings showed that climatic moisture/dryness indices have rarely gone down to high risk levels during the last 60 years (1961–2019). AMI did not reach the critical limit, 2.25, characteristic of the lower border for the dark-needled taiga. SPEI values < −1.5 represent drought stress conditions for dark-needled conifers at the lower border, and these conditions occurred 3–4 times during the 60-year period. However, the annual water balance stayed positive in those years in wet and moist forests at mid-to-high elevations. Trees are known to survive occasional (1–2) dry years. We found that dark-needled conifer dieback often occurs in wet years with plentiful rain rather than in drought years. We found forest dieback was associated with the westerlies that bring atmospheric pollution from the west at 50–56 N latitudes, where the air masses cross populated regions that have widespread industrial complexes. Conclusions. We concluded that the observed decline of dark-needled conifers at middle-to-high elevations across the South Siberia’s Mts was conditioned by several plausible causes, among which air pollution seems to be more credible, rather than dry climatic conditions, as cited in recent literature. Results are essential for understanding these ecosystems and others as our planet changes. Other causes and mechanisms should be further investigated, which would necessitate creating infrastructure that supports multi-disciplinary, inter-agency teamwork of plant physiologists, foresters, chemists, etc.

Effects of orbital forcing, greenhouse gases and ice sheets on Saharan greening in past and future multi-millennia

Abstract. Climate archives reveal alternating arid and humid conditions in North Africa during the last several million years. Most likely the dry phases resembled current hyper-arid landscapes, whereas the wet phases known as African humid periods (AHPs) sustained much more surface water and greater vegetated areas that “greened” large parts of the Sahara region. Previous analyses of sediment cores from the Mediterranean Sea showed the last five AHPs differed in strength, duration and rate of change. To understand the causes of such differences we perform transient simulations of the past 190 000 years with the Earth system model of intermediate complexity CLIMBER-2. We analyse the amplitude and rate of change of the modelled AHP responses to changes in orbital parameters, greenhouse gases (GHGs) and ice sheets. In agreement with estimates from Mediterranean Sea sapropels, we find the model predicts a threshold in orbital forcing for Sahara greening and occurrence of AHPs. Maximum rates of change in simulated vegetation extent at AHP onset and termination correlate strongly with the rate of change of the orbital forcing. As suggested by available data for the Holocene AHP, the onset of modelled AHPs usually happens faster than termination. A factor separation analysis confirms the dominant role of the orbital forcing in driving the amplitude of precipitation and vegetation extent for past AHPs. Forcing due to changes in GHGs and ice sheets is only of secondary importance, with a small contribution from synergies with the orbital forcing. Via the factor separation we detect that the threshold in orbital forcing for AHP onset varies with GHG levels. To explore the implication of our finding from the palaeoclimate simulations for the AHPs that might occur in a greenhouse-gas-induced warmer climate, we extend the palaeoclimate simulations into the future. For the next 100 000 years the variations in orbital forcing will be smaller than during the last 100 millennia, and the insolation threshold for the onset of late Quaternary AHPs will not be crossed. However, with higher GHG concentrations the predicted threshold drops considerably. Thereby, the occurrence of AHPs in upcoming millennia appears to crucially depend on future concentrations of GHGs.

Effects of Relative Humidity and Paper Geometry on the Imbibition Dynamics and Reactions in Lateral Flow Assays

Lateral flow assays and paper microfluidics have the potential to replace benchtop instrumented medical diagnostic systems with instrument-free systems that rely on passive transport of liquid through micro-porous paper substrates. Predicting the imbibition dynamics of liquid through dry paper substrates is mostly modeled through the Lucas-Washburn (LW) equations. However, the LW framework assumes that the fluid front exhibits a sharp boundary between the dry and wet phases across the liquid imbibition interface. Additionally, the relative humidity in the environment results in moisture trapped within the pores of the paper substrates as the paper attains an equilibrium with the ambient air. Here, we apply a two-phase transport framework based on Brooks and Corey's model to capture imbibition dynamics on partially saturated paper substrates. The model is experimentally validated and is then used to predict the liquid-paper imbibition dynamics in simulated environments with 1-70% relative humidity. The model was also used to determine the saturation gradient of liquid along the imbibition interface of the paper substrate. Insights from these studies enabled us to determine the mechanism of the liquid transport in partially saturated porous paper substrates. The model also enabled us to evaluate the optimal paper shapes and relative humidity of the environment that maximize imbibition rates and minimize imbibition front broadening. Finally, we evaluate the effect of moisture content of paper on the rate of paper-based biochemical reaction by amplifying a sequence of the SARS-CoV-2 RNA target via reverse transcriptase loop-mediated isothermal amplification. Taken together, this study provides some important guidelines to academic and applied researchers working in point-of-care diagnostics to develop paper-based testing platforms that are capable of functioning in a robust manner across multiple environmental conditions.

Tufas indicate prolonged periods of water availability linked to human occupation in the southern Kalahari.

Detailed, well-dated palaeoclimate and archaeological records are critical for understanding the impact of environmental change on human evolution. Ga-Mohana Hill, in the southern Kalahari, South Africa, preserves a Pleistocene archaeological sequence. Relict tufas at the site are evidence of past flowing streams, waterfalls, and shallow pools. Here, we use laser ablation screening to target material suitable for uranium-thorium dating. We obtained 33 ages covering the last 110 thousand years (ka) and identify five tufa formation episodes at 114-100 ka, 73-48 ka, 44-32 ka, 15-6 ka, and ~3 ka. Three tufa episodes are coincident with the archaeological units at Ga-Mohana Hill dating to ~105 ka, ~31 ka, and ~15 ka. Based on our data and the coincidence of dated layers from other local records, we argue that in the southern Kalahari, from ~240 ka to ~71 ka wet phases and human occupation are coupled, but by ~20 ka during the Last Glacial Maximum (LGM), they are decoupled.

Dry-Wet Cycles Affect Nitrous Oxide Emissions Across Aquatic-Terrestrial Interfaces: A Mesocosms Study

Aquatic-terrestrial interfaces may act as biogeochemical hotspots for greenhouse gas emissions, especially when exposed to frequent transitions between wet and dry phases. The study aimed to analyze the dynamics of nitrogen (N) processing along an inundation gradient from floodplain soils to river sediments and identify environmental factors affecting net nitrous oxide (N2O) production from different microbial sources. Intact soil and sediment cores were subject to two consecutive drying-rewetting cycles in laboratory experiments. The 15N isotope pairing technique was used to quantify N2O emissions sourced from denitrification and nitrification. We observed enhanced N2O emissions from both nitrification and denitrification following drying events. Sites exposed to frequent drying-rewetting cycles appear less affected by drying than hydrologically more stable habitats. Fluxes from nitrification were related to the organic matter content, while fluxes from denitrification were controlled by dissolved organic matter quality changes during the drying-rewetting cycles. This study shows the potential link between carbon metabolism and N2O production, combining the effect of drying-rewetting cycles.

The late Holocene hydroclimate variability in the Northwest Himalaya: Sedimentary clues from the Wular Lake, Kashmir Valley

• Wular Lake levels, redox conditions , and organic matter supply significantly altered over the last ∼4.2 kyr BP. • Hydroclimate varied from early wetter to relatively drier conditions and severe drought before the wet Little Ice Age. • Latitudinal migration of inter-tropical convergence zone drove seasonal precipitation turnover in Kashmir Valley. • A spatially coherent hydroclimate is found in the Northwest Himalaya during the late Holocene . This study focuses on the immensely debated pre-instrumental centennial–millennial scaled forcing of the late Holocene hydroclimate variability in the Northwest Himalaya (NWH). The Wular Lake is ideally situated close to the modern intertropical convergence zone (ITCZ) in the NWH and fed by the Jhelum River draining the vast Kashmir Valley, which receives seasonal precipitations from the Indian Summer Monsoon (ISM) and Western Disturbances (WD). In this study, size segregated lithic fractions (sand, silt, and clay) and elemental concentrations (TOC, TN, Ba, Al, Mn, and Fe) have been measured in the 14 C-AMS dated NWC sediment core collected from this lake. The continuous NWC sedimentary records reveal temporal environmental changes (water level, organic detritus supply, and redox conditions) in this open mega-lake system suggesting prevailed hydroclimate variations in the valley during the late Holocene. The captured hydroclimate variations are a wetter phase (∼4.2–3.4 cal kyr BP) followed by relatively drier conditions and extreme drought before the wet Little Ice Age (LIA). The plausible forcing seems to be the latitudinal ITCZ migration regulated seasonal precipitations from the tropical/subtropical moisture sources. The ISM to WD moisture turnover dominated winter over summer precipitations in the valley during the former warm and wet phase but unequivocally reflected during the cold and wet LIA. Additional hydroclimate control comes from permafrost ice melting episodes of a few centuries duration during high solar activity events (sunspot number ≥50). A comparison with the regional studies further indicates that NWC records capture hydroclimate signatures widespread in the NWH.

Lake level changes and paleo-precipitation estimations based on colluvial stratigraphy of Holocene sediments in West Anatolia (Simav Graben)

Time-controlled quantitative climate data are crucial for reconstructing past environmental contexts of human history. In west Anatolia, the Simav Graben used to be occupied by a lake. However, today it is drained and associated with Holocene sediments that record lake level changes. An initial drill-core at the lake's centre reveals an arid phase before ca. 14 ka (i.e. prior to the Late Glacial warming) followed by a wet phase (marshes and lake) throughout the Holocene. Along the lake's margin, two additional sediment sequences contain a detailed Holocene record of changes in humidity throughout the Simav Graben's watershed. Classification of the shoreline facies from these sequences records drought events marked by colluvium prograding towards the lake. Using 13 radiocarbon dates, sedimentary facies suggest rapid lake contraction phases grossly around 8.0, 3.9, 2.9, 2.4 and 2.0 ka. After the drier periods, recorded by phases of terrestrial progradation, lake level increase is marked by retrogradational lake muds and peats onlapping the colluvium, consistent with increases in total lake volume. Based on modern lake morphology, climate and runoff data, and the elevations recorded by the shoreline facies identified within the marginal Holocene sedimentary sequence, we constructed a paleohydrologic balance model and a precipitation curve. According to the model, annual precipitation may have been fallen below 460 mm during the 8.2 ka event, and 468–478 mm during the 4.2 ka and 3.2 ka events – demonstrating an extreme decrease in precipitation compared to the earlier wet phases. In turn, Holocene Archaeology in West Anatolia outlines (i) a widespread abandonment and/or notable fire events at the end of the Early Bronze Age III (ca. 4.2 ka), and (ii) a high level of social instability at the beginning of the Early Iron Age (ca. 3.2 ka). The correlation between the timing of lake level falls at Simav (water volume depletion caused by drying trends) at 8.0 ka, 3.9 ka and 2.8 ka and cultural fluctuations suggest that drought events may have played a major role in these socio-political changes in western Anatolia. Furthermore, the high lake-level stages (associated with precipitation >500 mm) coincide with the Late Chalcolithic to Early Bronze Age I transition as well as the Hellenistic and Roman periods, both times of economic stability and growth in the region.

Modulation of East African Boreal Fall Rainfall: Combined Effects of the Madden–Julian Oscillation (MJO) and El Niño–Southern Oscillation (ENSO)

Abstract Climate variabilities can have significant impacts on rainfall in East Africa, leading to disruption in natural and human systems and affecting the lives of tens of millions of people. Subseasonal and interannual variabilities are critical components of total rainfall variability in the region. The goal of this study is to examine the combined effects of the Madden–Julian oscillation (MJO), operating at a subseasonal time scale, and El Niño–Southern Oscillation (ENSO), operating at an interannual scale, on the modulation of East African boreal fall [October–December (OND)] rainfall, commonly called the short rains. Composite analysis shows that daily rainfall responses depend on MJO phase and its interaction with ENSO state. In particular, MJO modulation of rainfall is generally stronger under El Niño conditions relative to ENSO neutral and La Niña conditions, leading to increased potential for daily precipitation excesses during wet MJO phases under El Niño. There is evidence for both dynamic and thermodynamic mechanisms associated with these impacts, including an increase in westerly moisture transport and easterly advection of temperature and moist static energy. Seasonal analysis shows that the frequency and intensity of wet MJO phases during an El Niño contribute notably to the seasonal total precipitation anomaly. This suggests that the MJO can mediate El Niño’s impact on OND rainfall in East Africa.

The terrestrial and semi-aquatic invertebrates of intermittent rivers and ephemeral streams.

ABSTRACTIntermittent rivers and ephemeral streams (IRES), which cease flow and/or dry at some point, are the most abundant waterways on earth, and are found on every continent. They can support a diverse, and often abundant, terrestrial and semi‐aquatic invertebrate (TSAI) fauna, which has been poorly explored due to its position at the fringe between aquatic and terrestrial disciplines. TSAIs can inhabit a variety of habitat types, including the shoreline, the surface of exposed gravel bars, unsaturated gravels, dry riverbeds, riparian zones, and floodplains. Much less is known about the species composition and ecological roles of TSAIs of IRES than their aquatic counterparts, with TSAIs being largely overlooked in conceptual models, legislation, policy, and ecological monitoring. Herein we review the TSAI literature that has increased substantially over the last decade and present conceptual models describing how TSAIs respond to hydrological changes in IRES. Then, we test these models with data collected during wet and dry phases in IRES from Australia and France. These generic models can be utilised by water managers and policy makers, ensuring that both wet and dry phases are considered in the management and protection of IRES. IRES should be viewed as a habitat continuum through time, with taxa from a pool of aquatic, semi‐aquatic and terrestrial invertebrates inhabiting at any hydrological stage. We call for collaboration among terrestrial and aquatic ecologists to explore these invertebrates and ecosystems further.

Conservation and Conventional Vegetable Cultivation Increase Soil Organic Matter and Nutrients in the Ethiopian Highlands

Agriculture in Africa is adversely affected by the loss of soil fertility. Conservation agriculture (CA) was introduced to curb the loss of soil fertility and water shortages and improve crop productivity. However, information on how CA practices enhance soil quality and nutrients is scarce in the sub-Saharan Africa context. The objective of this study was to investigate the effects of CA and conventional tillage (CT) on soil organic matter and nutrients under irrigated and rainfed vegetable on-farm production systems. During the dry and wet monsoon phases in the northern Ethiopian Highlands, a four-year experiment with CA and CT was carried out on ten vegetable farms under rainfed and irrigated conditions. Although the increase in concentration of organic matter in CA was generally slightly greater than in CT, the difference was not significant. The average organic matter content in the top 30 cm for both treatments increased significantly by 0.5% a−1 from 3% to almost 5%. The increase was not significant for the 30–60 cm depth. The total nitrogen and available phosphorus concentrations increased proportionally to the organic matter content. Consequently, the extended growing season, applying fertilizers and livestock manure, and not removing the crop residue increased the nutrient content in both CA and CT. The increase in CA was slightly greater because the soil was not tilled, and hay was applied as a surface cover. Although CA increased soil fertility, widespread adoption will depend on socioeconomic factors that determine hay availability as a soil cover relative to other competitive uses.

Holocene Monsoonal Variations Over Southern India: Looking Into Its Antecedents

A proper understanding of the paleoclimatic variability in the Southern Peninsular India demands a high-resolution paleoclimate reconstruction record. Hence, in this paper, we compiled all the available paleoclimate records from various locations across the Southern India that receives the southwest and the northeast monsoon. We delineated the southwest monsoon (SWMR) and Northeast monsoon (NEMR) variations within the Holocene Period based on the existing paleoclimatic record from this region. Paleoclimate records are primarily based on various paleoclimate archives and proxies. A detailed study of these variations unravels, (i) that SWMR gradually intensified since the younger dryas during the Early Holocene period. On the contrary, NEMR records indicate a dry phase during the same period. (ii) During the mid-late Holocene, precipitation in SWMR-dominated regions decreased, whereas precipitation in NEMR-dominated regions shows an increasing trend. (iii) Then, in the late Holocene Period, SWMR exhibits an overall wet phase with a few drier periods, and NEMR shows an intense dry period with shorter wet phases, which can be correlated to the demise of Chola dynasty, in the Southern India.

Break Events of the Western North Pacific Summer Monsoon during 1979–2018

Abstract The monsoon break is a typical phenomenon representing the monsoon’s subseasonal variability, but our understanding of it is still limited for the western North Pacific (WNP) area. This study identifies all break events of the WNP summer monsoon (WNPSM) from 1979 to 2018. The statistical analysis suggests that break events occur from late June to late October and peak at the end of August. The occurrence frequency of break events decreases as the duration increases, with 74% of events persisting for 3–7 days and merely 26% lasting longer (8–15 days). During the break period, which is characterized by significant suppression of convection, there is an extensive anticyclonic anomaly in the lower troposphere, corresponding to a notable westward retreat of the monsoon trough and a southwestward shift of the subtropical high. Meanwhile, an anomalous cyclone and convergence in the upper troposphere are also conducive to inhibiting convection. The composite results indicate that both 10–25- and 30–60-day oscillations contribute to the break, with their dry phases explaining 49.6% and 37.5% of the original suppression of convection, respectively. Around the break, the phase alternation of the 10–25-day oscillation causes convection fluctuation, while the 30–60-day oscillation maintains a stable dry phase that favors the establishment and maintenance of the break. A further case-by-case diagnosis suggests that 46 (51) out of the 61 break events occur in dry phases of the 10–25-day (30–60-day) oscillation, whereas only 10 (4) events occur in wet phases, indicating that the phase of the two oscillations significantly modulates the occurrence of the monsoon break.

A decrease in the number and the timing shift of the bird arrival in the North-Eastern Baikal Region

The article deals with the main results of a long-term study of birds in the Barguzin State Nature Biosphere Reserve (Russia). Phenological observations of the bird spring arrival have been carried out from 1938 to 2020. Monitoring of bird communities has been carried out from 1984 to 2020 on permanent counting routes in the valleys of three rivers in the area from the Lake Baikal coast to the highlands of the Barguzin Range (460–1700 m a.s.l.). We detected shifts and cyclical changes in the timing of the bird arrival and revealed a steady decrease in the abundance of the bird population after 1997–1998. The long-term series of observations (taking into account of model bird groups) made it possible to identify some responses of the biota to climatic changes in the Lake Baikal Region. Twenty-six species (40.0%) began to arrive in spring statistically significantly earlier, seven species (10.8%) significantly later, and for 32 species (49.2%) the arrival timing did not change statistically significantly. In contrary to Europe and North America, in the Baikal Region, the proportion of distant migrants in the group of early arriving bird species is higher than in the group of nearby migrants. We suggest that these differences may be associated with different wintering areas of long-distance migrants (species of the Baikal Region winter in South and Southeast Asia in contrast to African wintering areas of European birds). In the Baikal Region, the periods of high and low abundance in background species populations are probably associated with the passage of wet and dry phases of a long climatic cycle. We have identified positive trends in long-term changes in abundance for seven background species (14.0%), and a steady decline in abundance for 17 species (34.0%). In addition, we noted an equal ratio of species with a positive and negative trend in native species abundance. Negative trends of changes in the number of distant and nearby migrants prevailed over positive (increase) trends. So, we found 14 species with negative and four species with positive trends. An increase in the duration of observations makes it possible to give a more reliable assessment of processes in population dynamics, and identify mechanisms of the influence of meteorological and phenological factors on the dynamics of the abundance of bird species. This makes it possible to predict some biota responses to long-term climate changes in the absence of anthropogenic transformations of the natural environment.

Establishing a Luminescence-Based Chronostratigraphy for the Last Glacial-Interglacial Cycle of the Loess-Palaeosol Sequence Achajur (Armenia)

The loess-palaeosol section Achajur is part of the Sevkar loess area in north-eastern Armenia and comprises three prominent pedocomplexes with intercalated loess units, probably spanning at least three glacial-interglacial cycles. With its central position between the Black Sea and the Caspian Sea, the Sevkar loess area serves as important bridge between loess sections in southeastern Europe and Central Asia. Establishing a numerical chronology of the Achajur loess section enables correlation with other loess-palaeosol sections and a palaeoenvironmental reconstruction of the region. In this paper, we focus on the chronology of the last glacial-interglacial cycle using luminescence dating on fine grain (4–11 µm) material. We compare two post-IR-IRSL protocols on polymineral fine grain using different stimulation temperatures, in order to evaluate the influence of fading and potential unbleachable residuals on our samples. For a backup of the younger ages (<50 ka), we also applied a single aliquot protocol on the quartz fine grain fraction. The results indicate that the upper loess unit was deposited during MIS3 and 4, while MIS2 ages are not present. The underlying pedocomplex and loess unit fall into MIS5 and MIS6, respectively. This confirms that the loess was deposited during dry phases and pedocomplexes formed during wetter phases, as is also shown by comparison with other palaeoenvironmental proxies from the area.

The Stalagmite Record of Southern Arabia: Climatic Extremes, Human Evolution and Societal Development

The fluctuating climatic conditions of the Saharo-Arabian deserts are increasingly linked to human evolutionary events and societal developments. On orbital timescales, the African and Indian Summer Monsoons were displaced northward and increased precipitation to the Arabian Peninsula which led to favorable periods for human occupation in the now arid interior. At least four periods of climatic optima occurred within the last 130,000 years, related to Marine Isotope Stages (MIS) 5e (128–121 ka BP), 5c (104–97 ka BP), 5a (81–74 ka BP) and 1 (10.5–6.2 ka BP), and potentially early MIS 3 (60–50 ka BP). Stalagmites from Southern Arabia have been key to understanding climatic fluctuations and human-environmental interactions; their precise and high-resolution chronologies can be linked to evidence for changes in human distribution and climate/environment induced societal developments. Here, we review the most recent advances in the Southern Arabian Late Pleistocene and Early Holocene stalagmite records. We compare and contrast MIS 5e and Early Holocene climates to understand how these differed, benchmark the extremes of climatic variability and summarize the impacts on human societal development. We suggest that, while the extreme of MIS 5e was important for H. sapeins dispersal, subsequent, less intense, wet phases mitigate against a simplistic narrative. We highlight that while climate can be a limiting and important factor, there is also the potential of human adaptability and resilience. Further studies will be needed to understand spatio-temporal difference in human-environment interactions in a climatically variable region.

Different facets of dry–wet patterns in south-western China over the past 27 000 years

Abstract. Frequently occurring mega-droughts under current global climate change have attracted broad social attention. A paleoclimatic perspective is needed to increase our understanding of the causes and effects of droughts. South-western (SW) China has been threatened by severe seasonal droughts. Our current knowledge of millennial-scale dry and wet phases in this region is primarily based on the variability of the Indian summer monsoon. However, water availability over land does not always follow patterns of monsoonal precipitation but also depends on water loss from evaporation and transpiration. Here, we reconstructed precipitation intensity, lake hydrological balance and the soil water stress index (SWSI) for the last 27 000 years. Grain size, geochemical and pollen records from Yilong Lake reveal the long-term relationships and inconsistencies of dry–wet patterns in meteorological, hydrological and soil systems in the central Yunnan region, SW China. Our results show that the long-term trends among precipitation, hydrological balance and soil moisture varied through time. The hydrological balance and soil moisture were primarily controlled by temperature-induced evaporation change during periods of low precipitation such as the Last Glacial Maximum and Younger Dryas. During periods of high precipitation (the early to late Holocene), intensified evaporation from the lake surface offset the effects of increased precipitation on the hydrological balance. However, abundant rainfall and the dense vegetation canopy circumvented a soil moisture deficit that might have resulted from rising temperature. In conclusion, the hydrological balance in the central Yunnan region was more sensitive to temperature change while soil moisture could be further regulated by vegetation changes over millennial timescales. Therefore, under future climate warming, the surface water shortage in the central Yunnan region may become even more serious. Our study suggests that reforestation efforts may provide some relief to soil moisture deficits in this region.

Upper Pleistocene–Holocene in the continental slope of the Cará Basin: an integrated analysis based on planktic foraminifera, sedimentological and geochemical aspects

This research addresses paleoclimatic variations using sedimentological, geochemical, and planktic foraminifera. The study was carried out in a survey core (ANP 1011) collected on the continental slope of the Icaraí Sub-basin (Ceará Basin), on the coast of the Municipality of Itapipoca, CE, Brazil. Particle size analysis, CaCO3 content, Ti/Ca and Fe/Ca ratios, and the analysis of foraminifera associations for biostratigraphic purposes were performed. Based on the relative abundance of planktic foraminifera, with indicators of warm and cold water throughout the studied cores, two biozones (Y: Upper Pleistocene and Z: Holocene), and two subzones (Z2 and Z1) were recognized. The data of sedimentological markers obtained confirmed the occurrence of more wet phases in northeastern Brazil during the early stages of the Holocene. The Ti/Ca and Fe/Ca ratios, as well as the geochemical and micropaleontological proxies, indicated a farther north displacement of the Intertropical Convergence Zone (ITCZ) in the Pleistocene–Holocene transition. This may have caused greater precipitation in the Northeastern region of Brazil, effectuating the entry of a high volume of terrestrial sediments directly into the ocean basin. Keywords: Quaternary biostratigraphy, marine sedimentation, ITCZ mobility, paleoclimate.