Cal Yrs BP Research Articles

A late Pleistocene nest cave of Gymnogyps californianus (California Condor) in Texas: New radiocarbon and stable isotope analyses

ABSTRACT Fossil remains of Gymnogyps californianus (California Condor) from Mule Ears Peak Cave, Big Bend National Park, Texas, recovered in the 1930s were reexamined to determine a precise age for nesting condors in this region. Bones of at least 6 prefledged chicks account for most (15, or 65%) of the 23 skeletal elements from this cave and a new osteology collection of known-age condor chicks at the U.S. National Museum, Division of Birds, now allows accurate estimate of the age of death of these fossil condor chicks based on their bone development and porosity. Current and previous radiocarbon dates on juvenile and adult bones, respectively, indicate the presence of condors at this site beginning at ~15,000 calendar years before present (cal yrs BP), with definite nesting occurring at ~13,000 cal yrs BP. Stable isotope analysis (δ13C and δ15N) of bone collagen on 2 bones of adult condors reflects a diet similar to other fossil condors previously analyzed from the inland western U.S. The δ13C values in the Mule Ears Peak condors indicate a diet of megafauna that subsisted on C4 plants in a desert grassland ecosystem. These results support the hypothesis that condors were extirpated from the inland west with the loss of megafauna at the end of the Pleistocene. Further, Big Bend National Park with its vast open space and cliffs and canyons for nesting condors should be considered as an additional release site for captive-reared condors as part of the current Condor Recovery Program.

Millennial to centennial-scale climate oscillations since 15000 cal yrs BP from Kanwar wetland in the Central Ganga Plain, India

Millennial-scale climate cycles have been meagerly discussed in the terrestrial records from the Indian subcontinent, particularly the wetlands of the Ganga Plain. The mineral magnetic and textural analyses, along with chronology, distinctly record variation in the monsoon intensity since 15000 cal yrs BP in the sediment core collected from the Kanwar Lake in the Central Ganga Plain (CGP) of India. This unique high-resolution data allowed us to analyse monsoon fluctuation in the CGP with respect to changes in the North Atlantic process (internal) and external (solar cycles) forcing. During this period, several palaeoclimatic events, such as the Bølling-Allerød (B/A), Older and Younger Dryas, and the high-frequency fluctuations in the Holocene viz., Greenlandian, Northgrippian, and Meghalayan stages, were observed. The B/A event is correlated with the Indian Summer Monsoon (ISM) intensification period of the CGP. Eleven dry events are recorded at 13600–13200, 13000–11700, 11000, 10600, 9800–9000, 8200, 6100–5300, 4300–4200, 3800, 1800–900 and 300 cal yrs BP. During the Holocene, the sustained episodes of weaker monsoon centered around 10600, 9600, 8200, 6000, 4200, 2800, 1400 and 600 cal yrs BP, where the variability of the proxy data is mostly synchronous with the reduced upwelling intensity in the western Arabian Sea as well as roughly align with ∼1500 years cyclic signals in the drifted ice proxy recorded Bond Events indicating weakened ISM circulation during colder North Atlantic. Two distinct short cycles, spanning 172–344 and 172–688 years, are evident around 12,000 and 14,000 cal yrs BP with an additional occurrence from 86 to 344 years during 2000 and 6000 cal yrs BP, affirming the significance of external forcing, particularly solar activity. For the 1492 years cycle in ISM fluctuation, we postulate it may represent a combined forcing of external (solar) and internal (Atlantic Meridional Overturning Circulation (AMOC)) factors during the Holocene. This is the first high-resolution record available in the CGP, which brings out crucial monsoon reconstruction during the last 15000 years.

Paleoclimate changes and ecosystem responses of the Bulgarian Black Sea zone during the last 26000 years

Multi-proxy analysis (spore-pollen, dinoflagellate cysts, other non-pollen palynomorphs (NPPs), radiocarbon dating and lithology) was performed on marine sediments from three new cores retrieved during the two cruise expeditions on board the Research Vessel “Akademik” in 2009 and 2011. The Varna transect comprises three cores extending from the outer shelf, continental slope and deep-water zone. The record spans the last 26000 years (all ages obtained in this study are given in calendar years BP (cal. yrs BP)). The pollen record reveals the spreading of steppe vegetation dominated by Artemisia and Chenopodiaceae, suggesting cold and dry environments during the Late Pleniglacial – Oldest Dryas (25903–15612 cal. yrs BP). Stands of Pinus and Quercus reflect warming/humidity increase during the melting pulses (19.2–14.5 cal. ka BP) and the Late Glacial interstadials Bølling and Allerød. The Younger Dryas (13257–11788 cal. yrs BP) coldest and driest environments are clearly demonstrated by the maximum relative abundance of Artemisia and Chenopodiaceae. During the Early Holocene (Preboreal and Boreal chronozones, 11788–8004 cal. yrs BP), Quercus appeared as a pioneer species and, along with other temperate deciduous arboreal taxa, formed open deciduous forests as a response to the increased temperature. The rapid expansion of these taxa indicates that they survived in Glacial refugia in the coastal mountains. During the Atlantic chronozone (8004–5483 cal. yrs BP), optimal climate conditions (high humidity and increased mean annual temperatures) stimulated the establishment of species-rich mixed temperate deciduous forests. During the Subboreal chronozone (5483–2837 cal. yrs BP), Carpinus betulus and Fagus expanded simultaneously and became more important components of mixed oak forests and probably also formed separate communities. During the Subatlantic chronozone (2837 cal. yrs BP to pre-industrial time), climate-driven changes (an increase of humidity and a cooling of the climate) appear to be the main drivers of the specific vegetation succession expressed by increased abundance of Alnus, Fraxinus excelsior and Salix along with lianas, suggesting formation of flooded riparian forests (so called ‘Longoz’) lining the river valleys along the Black Sea coast. The first indicators of farming and other human activities have been recorded since 7074 cal. yrs BP. The dinoflagellate cyst (dinocyst) assemblages have been analysed to assess the changes in the Black Sea environment over the last 26000 years in terms of fluctuation in paleoproduction and surface water conditions related to changes in climate, freshwater input and Mediterranean water intrusion. Two major dinocyst assemblages were distinguished: one dominated by stenohaline freshwater/brackish-water species and a successive one dominated by euryhaline marine species. The changes in the composition of the assemblages occurred at 7668 cal. yrs BP. The abrupt decrease of stenohaline freshwater/brackish-water species Pyxidinopsis psilata and Spiniferites cruciformis was followed upwards by a gradual increase in euryhaline marine species, such as Lingulodinium machaerophorum, Spiniferites belerius, S. bentorii and acritarch Cymatiosphaera globulosa. The first occurrence of euryhaline marine species took place synchronously with the onset of sapropel deposition. Modern marine conditions were established after 6417 cal yrs BP when an abundance of Mediterranean-related species, such as Operculodinium centrocarpum and Spiniferites mirabilis, along with other heterotrophic species, occurred. After the stable cold and dry environment during the Last Glacial Maximum, the phytoplankton record of core AKAD 11-17 shows that Pediastrum boryanum var. boryanum has a cyclical abundance associated with the deposition of four red-brown clay layers between 19.2 and 14.5 cal. ka BP. This event is associated with the major melting phase of European Ice drained by the Danube and Dnieper Rivers in response to climate warming observed after the end of the Last Glacial Maximum. During the Early Holocene, P. psilata, characterised by a preference to warmer temperatures, demonstrates its ecological optimum for growth concerning SST reaching maximum relative abundance of 94% between 11072 and 8638 cal. yrs BP. This maximum was interrupted by an abrupt significant short-term decrease in the relative abundance of P. psilata centred between 8500 and 8300 cal. yrs BP reflecting cold conditions similar to those of Younger Dryas. This finding, also confirmed by the rapid significant decrease of arboreal pollen, particularly of Quercus in the same studied core, is considered a regional expression of the well-known ‘8.2 ka cold event’ which is commonly linked to a meltwater-related perturbation of the Atlantic Meridional Overturning Circulation (AMOC) and associated collapse of oceanic northward heat transport. Our fossil pollen and dinocyst data confirm that the high amplitude temperature anomaly associated with ‘the 8.2 ka cold event’ may have also occurred in south-eastern Europe, at lower latitudes of the western Black Sea coastal area, most probably due to atmospheric transition and/or river discharge.

Vegetation diversity in response to monsoonal variability in the Eastern Himalaya, India over the past ~13 000 yrs

Monsoon precipitation plays a crucial role in shaping the diversity of vegetation in the Himalayas, both in terms of temporal and spatial distribution. While palynology has traditionally been employed to reconstruct the past climate of the Himalaya, there has been limited understanding of how monsoon-related changes affect the structure and distribution of vegetation. To address this, we analysed pollen data from a 3 m deep sedimentary profile in the higher Sikkim Himalaya to reconstruct monsoon driven changes in vegetation diversity. Our results show a highly fluctuating trend of pollen and diversity parameters at late-Pleistocene-Holocene transition for which fluctuating hydroclimatic conditions and differential pollen preservation in coarser sediments is attributed. During the Early Holocene (10,438–7934 cal yrs BP) favourable hydroclimatic conditions led to a rapid expansion of mixed broad-leaved forests, marked by higher values of richness and alpha diversity. Between 7934 and 5481 cal yrs BP, the region experienced moderate hydroclimatic conditions that facilitated expansion and diversification of woody taxa, and correlated with the global Holocene Climate Optimum (HCO). Conversely, from 5481 to3949 cal yrs BP, declining total pollen count (TPC), species richness, and alpha diversity indicates significant shifts in vegetation composition under deteriorating climatic conditions, which corresponds with the 4.2 ka event worldwide. From 3949 to 2049 cal yrs BP, an increasing yet variable trend in TPC and diversity indices, suggests warm-humid conditions prevailed in the region. During the last 1086 cal yrs, an increasing trend is recorded in the palyno assemblage and diversity parameters suggesting ameliorating climate, matches well with the Mediaeval Climate Anomaly (MCA). Our inferences suggest that the palyno assemblage and diversity parameters are quiet sensitive to warm and humid conditions.

Late-Holocene environmental conditions revealed by a small mammal assemblage in mountain areas of Northwestern Argentina

Based on a diverse Late-Holocene (1889–1743 cal yrs BP) small mammal assemblage (14 species, 204 individuals) resulting from the trophic activity of owls, we reconstruct the paleoenvironmental conditions of Las Chacritas area, Catamarca Province, northwestern Argentina. Twenty modern and one additional Late-Holocene samples from the region were used as comparative parameters in the paleoenvironmental reconstruction. Through direct comparison with a present-day assemblage from Las Chacritas, and using Nonmetric Multidimensional Scaling, spatial and temporal beta diversity (employing the Sorensen dissimilarity index), and the temporal beta diversity index (TBI) including all the small mammal samples, we quantitatively reconstruct the relationships among modern and Late-Holocene assemblages. Direct comparison showed significant differences, with relative abundances changing markedly over time, with several species of the Late-Holocene assemblage absent in the modern sample whereas many species frequent in the modern community absent in the Late-Holocene. NMDS analysis associated the Late-Holocene assemblage with modern samples of western drier environments. Beta diversity was low for presence-absence and moderate for abundance data, with higher contribution of turnover than nestedness, although for abundance data the proportion of nestedness was higher. TBI showed high variation among both Holocene sites and their present-day counterparts, whereas species gains dominated in modern samples. Our results suggest that the habitats surrounding Las Chacritas have modified markedly since the Late-Holocene. Presence of species today frequent in arid environments and absence of forest-dwelling species suggest that open, dry and relatively rocky habitats characterized this area in that interval.

COBERTURA VEGETAL, AÇÃO ANTROPOGÊNICA E PALEOCLIMAS NA CAATINGA

The Caatinga is dominated by a semiarid climate and a high plant biodiversity dealing with anthropogenic disturbance and climate change. Previous studies suggest that Caatinga became a completely soil‐water pulse-dominated forest in response to reduced water availability at the end of the last ice age, around 10 cal kyr BP. This work aimed to identify vegetative and climatic evolution, and the human influence in the Cariri region, one of the driest parts of Brazil. We sampled soil in a temporal pond to identify pollen. The testimony is 170 cm in lenght and achieves 6,216 cal yr BP at the base. Pollen analysis indicates the presence of taxa representative of humid climates, between 6,216 and ca. 5000 cal yr BP, like Azolla, followed by implantation of Caatinga's modern configuration from ca. 4,900 cal yrs BP. After 2,700 cal yr BP, humid episodes occurred, possibly related to the El Niño - La Niña variation across the region, marked by increased algae and aquatic herbs concentrations. The occurrence of human activity species like Caryocar, Dioscorea, Spondias, and Licania suggest possibly landscape manipulation by pre – Columbian populations, and exotic Pinus and Prosopis reveal changes in the tree cover caused by European colonization in the Caatinga. Keywords: Anthropocene; Dry Forest; Paleogeography; Semiarid Region; Sedimentology, Lakes, Lagoons & Swamps.

A multiproxy approach to reconstruct the Late Holocene environmental dynamics of the semiarid Andes of central Chile (29°S)

Mountain ecosystems located in the Andes cordillera of central Chile (29–35°S) have been strongly affected by the ongoing Mega Drought since 2010, impacting the snow cover, the surficial water resources (and thereby water storage), as well as the mountain biota and ecosystem services. Paleoenvironmental records in this part of the semiarid Andes are key to estimating the effects of past climate changes on local communities helping to forecast the ecological and biological responses under the aridification trend projected during the 21st century. Here we present a 2400-year multiproxy paleoenvironmental reconstruction based on pollen, diatoms, chironomids, sedimentological and geochemical data (XRF and ICP-MS data) of Laguna El Calvario (29°S; 3994 m a.s.l), a small and shallow Andean lake. Four main hydrological phases were established based on changes in the lithogenic and geochemical results associated with allochthonous runoff input and the subsequent response of the biological proxies. Between 2400 and 1400 cal yrs BP, wetter than present conditions occurred based on the intense weathering of the lake basin and the dominance of upper Andean vegetation. A decrease in moisture along with sub-centennial discrete wet pulses and lake-level changes occurred until ~800 cal yrs BP followed long-term stable climate conditions between 1850 and 1950 AD as suggested by a drop in vegetation productivity and low lake levels. From 1950 AD to the present, a decline in moisture with a severe trend to drier conditions occurring in the last decades occurred as reflected by an upward vegetation belt displacement around Laguna El Calvario along with a turnover of diatom assemblages and high productivity in the water column.

Permafrost-thaw lake development in Central Yakutia: sedimentary ancient DNA and element analyses from a Holocene sediment record

In Central Yakutia (Siberia) livelihoods of local communities depend on alaas (thermokarst depression) landscapes and the lakes within. Development and dynamics of these alaas lakes are closely connected to climate change, permafrost thawing, catchment conditions, and land use. To reconstruct lake development throughout the Holocene we analyze sedimentary ancient DNA (sedaDNA) and biogeochemistry from a sediment core from Lake Satagay, spanning the last c. 10,800 calibrated years before present (cal yrs BP). SedaDNA of diatoms and macrophytes and microfossil diatom analysis reveal lake formation earlier than 10,700 cal yrs BP. The sedaDNA approach detected 42 amplicon sequence variants (ASVs) of diatom taxa, one ASV of Eustigmatophyceae (Nannochloropsis), and 12 ASVs of macrophytes. We relate diatom and macrophyte community changes to climate-driven shifts in water level and mineral and organic input, which result in variable water conductivity, in-lake productivity, and sediment deposition. We detect a higher lake level and water conductivity in the Early Holocene (c. 10,700–7000 cal yrs BP) compared to other periods, supported by the dominance of Stephanodiscus sp. and Stuckenia pectinata. Further climate warming towards the Mid-Holocene (7000–4700 cal yrs BP) led to a shallowing of Lake Satagay, an increase of the submerged macrophyte Ceratophyllum, and a decline of planktonic diatoms. In the Late Holocene (c. 4700 cal yrs BP–present) stable shallow water conditions are confirmed by small fragilarioid and staurosiroid diatoms dominating the lake. Lake Satagay has not yet reached the final stage of alaas development, but satellite imagery shows an intensification of anthropogenic land use, which in combination with future warming will likely result in a rapid desiccation of the lake.

Assessment the Impacts of Sea-Level Changes on Mangroves of Ceará-Mirim Estuary, Northeastern Brazil, during the Holocene and Anthropocene.

Predictions of the effects of modern Relative Sea-Level (RSL) rise on mangroves should be based on decadal-millennial mangrove dynamics and the particularities of each depositional environment under past RSL changes. This work identified inland and seaward mangrove migrations along the Ceará-Mirim estuary (Rio Grande do Norte, northeastern Brazil) during the mid-late Holocene and Anthropocene based on sedimentary features, palynological, and geochemical (δ13C, δ15N, C/N) data integrated with spatial-temporal analysis based on satellite images. The data indicated three phases for the mangrove development: (1°) mangrove expansion on tidal flats with estuarine organic matter between >4420 and ~2870 cal yrs BP, under the influence of the mid-Holocene sea-level highstand; (2°) mangrove contraction with an increased contribution of C3 terrestrial plants between ~2870 and ~84 cal yrs BP due to an RSL fall, and (3°) mangrove expansion onto the highest tidal flats since ~84 cal yr BP due to a relative sea-level rise. However, significant mangrove areas were converted to fish farming before 1984 CE. Spatial-temporal analysis also indicated a mangrove expansion since 1984 CE due to mangrove recolonization of shrimp farming areas previously deforested for pisciculture. This work mainly evidenced a trend of mangrove expansion due to RSL rise preceding the effects of anthropogenic emissions of CO2 in the atmosphere and the resilience of these forests in the face of anthropogenic interventions.

Remnant peat deposit provides clues to the inundated cultural landscapes of Kepa Kurl, southwestern Australia

In early 2021 several tree stumps embedded in a remnant peat deposit were found in the intertidal zone of Wharton Beach, southwestern Australia by Esperance Tjaltjraak Rangers. Attempts were made to identify the tree using both dendrochronological and anthracological methods but were limited by the lack of reference information from tree species in the southwestern Australia. Radiocarbon dates from one stump indicates the tree lived for approximately 200 years, growing into the peaty sediments sometime before ca. 7340 cal yrs BP and died directly or indirectly as a result of marine transgression. The peat deposit is dated to 7608–7429 cal yrs BP but its exposed seaward edge was unconformably underlain by younger sand, dated by OSL to around 3550 years, which may have intruded as a result of a storm event. An OSL age of 12,600 years was obtained from the base of a laminated dune sequence behind the exposed peat deposit, and is significant given a similar age for a previously documented infant burial site in the area. Together these records provide a rare insight into the former wetland landscape and a cultural and scientific link to the drowned coastal plain. A need for more integrative research along this cultural corridor is clear but this preliminary study has demonstrated the value of combining Cultural Knowledge Systems and Western Science, for Tjaltjraak Healthy Country Program and analogous Aboriginal ‘caring for country’ programmes throughout Australia.

Precipitation variability, vegetation turnover, and anthropogenic disturbance over the last millennium in the Atacama highlands of northern Chile (19°S)

The Late-Holocene history of hydroclimatic variability in the Atacama Desert offers insights into the effects of precipitation and humans on ecosystems in one of the most extremely arid regions of the world. However, understanding the effects of regional precipitation variability in relation to local ecological stressors remains to be fully resolved. Here, we present a pollen-based qualitative precipitation reconstruction derived from fossil rodent middens recovered from two sites near Laguna Roja (LRO; n = 25) and Isluga (ISL; n = 15) in the Atacama highlands (19°S) of northern Chile. At LRO, the fossil pollen record shows multi-centennial hydroclimatic anomalies during the last millennium, with wetter than present phases at 1155–1130, 865–670, and 215–80 cal yrs BP, and similar to present conditions between 1005 and 880 cal yrs BP. In contrast, the ISL record shows a wet phase during 1115–840 cal yrs BP, suggesting that meso-ecological processes were as important in vegetation turnover as regional hydroclimate anomalies. Wetter conditions derived from LRO partially overlap with the Medieval Climate Anomaly (865–670 cal yrs BP) and with the latest part of the Little Ice Age (215–80 cal yrs BP). Furthermore, no strong anthropogenic signal was identified possibly related to the remote location of the records. Palynological diversity analyses evidence increasing diversification of plant communities during wet events at both sites. In correlation to existing regional hydroclimatic records from the Western Andes, our precipitation reconstruction verifies that centennial-scale changes in the strength of the South American Summer Monsoon (SASM) and partial influence of El Niño-like (ENSO) conditions drove vegetation turnover in the Atacama Desert during the last millennium.

Setting the stage: How abrupt climate change, geomorphic thresholds, and drought control flood response in the lower Tennessee River, USA

Extreme floods, with multi-century to millennia recurrence intervals, arise from a combination of antecedent watershed characteristics and unusual or rare atmospheric circulations that occur too infrequently to discern drivers from instrumental records. Few stream gauge records in the United States contain 100 years or more of annual peak flow data, meaning rare extreme floods are underrepresented in the peak flow population. We synthesized approximately 8,000 years of paleoflood hydrologic data from multiple studies and various landforms (floodplains, rock shelters, and caves) conducted in the Tennessee River Valley between Chattanooga, Tennessee, and Florence, Alabama, to examine Holocene flood variability. Extreme floods (>11,000 m3/s) clustered around ∼7,900, 6,000–4,900, and ∼1,000–80 cal yrs BP. More moderate floods occurred between 4,800 and 2,000 cal yrs BP. We compared flood variability in the Tennessee Valley to Holocene paleorecords available in North America. All periods of extreme flooding occurred during large-scale, abrupt climate transitions that lacked a distinct directionality of temperature change (i.e., warm to cool or cool to warm). Our findings indicate that extreme floods clustered in times when (1) warm-season precipitation increased, (2) abrupt increases in precipitation followed episodes of drought, and (3) the rate of change in the hydroclimate regimes was greater than the rate of morphological change in response to increased moisture, thus, exceeded geomorphic thresholds. Internal river basin factors such as drought-induced watershed changes and river morphological changes are key flood drivers that set the stage for flood response to changes in precipitation. Our findings suggest that anticipated changes to drought and precipitation intensity due to modern climate change may increase extreme floods, particularly for urban and regulated rivers not given the space for adjusting to higher precipitation variability.

Carbon accumulation dynamics of the Klukva peatland at the southern boundary of broad-leaved forest zone in European Russia

The study is focused on reconstructing the carbon accumulation rate of the peatland Klukva (1 ha) situated at the southern boundary of broad-leaved forest zone within the Oka river basin in European Russia. The age of the peatland is about 9400 cal years BP and it is one of the oldest peatlands within the Central Russian Upland. The results of our experimental study showed that the rate of peat accumulation is ranged from 0.15 to 0.9 mm/year and it was strongly influenced by climatic factors. Two main stages were distinguished in the peatland genesis. The longest was the mesotrophic stage, which began in the Early Holocene at about 9400 cal years BP and ended in the Late Holocene at about 1500 cal years BP. Since 1500 cal years BP there has been a gradual transition of the peatland from mesotrophic to oligotrophic type. The mean carbon accumulation rate during the peatland Klukva development was about 20 gC/(m2yr). This process was most actively going between 2500 and 6300 cal yrs BP, when the rates of peat accumulation increased to 26-29 gC/(m2yr). Nowadays, the carbon stock in the peat deposit of the peatland Klukva is amounted to 175 kgC/m2 and it is comparable with the carbon stocks of boreal peatlands in Northern Eurasia. This means that the oligotrophic peatlands situated at the southern boundary of broad-leaved forest zone, despite the small areas, continue to be a large stock of atmospheric carbon.

Late Holocene fire regime reconstruction and vegetation dynamics of southern Monte desert region

This work presents the first Monte desert palaeofire record from an ephemeral northern Patagonia pond called Bajo de la Quinta (40° 55′ 42″S; 64° 20′ 19″W). The aims of this study are (1) to reconstruct past fire regime changes related to vegetation variability during the last 4000 cal yrs BP for the southern Monte region; (2) to discuss the importance of climatic versus anthropogenic control of fire regime at different periods; and (3) to integrate these results with other fossil pollen sequences located in North Patagonia (between 39° and 43°S), to infer centennial to millennial-scale changes in vegetation, linked to major palaeoclimatic variability. Long-scale fire-vegetation changes have characterised the southern Monte desert modifying vegetation intra-community patches distribution. The heterogeneous two-phase mosaic shrubland distribution is more resilient to fire at centennial to millennial scales than homogeneous high vegetation coverage. Southern Monte desert presents current fire regime characteristics since the last two centuries, which may be related to livestock introduction and the subsequent increase in human-induced- fires and changes in biomass availability. Also, the use of the composite Nothofagus pollen abundance index and the comparison between sequences located along the west-east precipitation gradient of North Patagonia (between 39° and 43°S), suggests synchronous but in opposite direction humidity availability long term changes affecting vegetation and fire behavior in Northern Patagonia during the Late Holocene.

Documenting the Evolution of a Southern California Coastal Lagoon during the Late Holocene

Coastal wetlands are declining globally, and although wetland restoration looks to offset these losses, its success relies on anticipating environmental response to external forces. The purpose of this study is to investigate the sedimentological record of Los Peñasquitos Lagoon to determine the processes that drive environmental transitions in a Southern California coastal wetland. For this project, we analyze three sediment cores from the wetland for grain size, total organic matter, and shell assemblages to reconstruct environmental change over the past ~4000 years. From the results, we find that the lagoon was initially an open embayment that persisted for >2000 years; however, at ~1000 cal yrs BP, a short-lived wet climatic period triggered a fluvial deltaic progradation at the head of the lagoon. As the wet period ended and drier conditions returned, the delta began to retreat, and the lagoon infilled as the estuarine mouth bar was permanently established. The permanent establishment of the mouth bar resulted in a transition to a marsh-dominated environment throughout the wetland. Ultimately, these environmental transitions were driven by climate variability, although evidence of human impacts was observed more recently in the record. Therefore, future restoration efforts must consider both natural climatic variability and anthropogenic influences if they intend to sustain coastal wetlands.

The legacy of 1300 years of land use in Jamaica

Despite decades of archaeological research on Jamaica, little is known about how settlers influenced landscape change on the island over time. Here, we examine the impact of human occupation through a multi-proxy approach using phytolith, charcoal, and stratigraphic analyses. White Marl was a continuously inhabited village settlement (ca. 1050–450 cal yrs BP) with large mounded midden areas, precolonial house structures, and human landscape management practices. We have shown that the local vegetation at White Marl was directly affected by human settlement through the use of agroforestry and burning, and suggest that fire was used to modify vegetation. Manioc phytoliths were found throughout human occupation and are broadly associated with increases in evidence for burning, suggesting fire was used to modify the landscape and clear vegetation for crop cultivation. The phytolith assemblages relate to three distinct temporal vegetation phases: (1) the earliest occupation dominated by arboreal vegetation (pre-ca. 870 cal yrs BP); (2) a transition to palm-dominated vegetation (ca. 870–670 cal yrs BP); and (3) the latest occupation representing European colonization associated with a more open, grass-dominated landscape (after ca. 670 cal yrs BP). These transitions occur independent of changes in paleoclimate records, suggesting humans were the dominant driver of vegetation change.

Early-to-Middle Holocene environmental reconstruction in the southern Puna (26° S, Argentina) from camelid coprolite records

Paleoenvironmental records in the eastern Andes (16–26° S), broadly indicate a gradual trend towards aridity from the Early to the Middle Holocene with certain chronological discrepancies. Even under this adverse climatic scenario, the archaeological record suggests the presence of hunter-gatherers in the southern Argentinian Puna associated with the availability of resources for their subsistence, even during drier than present periods. Herbivore coprolites contain multiple proxies that provide independent records of paleovegetation and paleoenvironments. Among them, plant tissue fragments and pollen grains, offer a powerful and complementary insight on past vegetation changes and their relationship with climatic conditions during the Holocene, particularly in the southern Argentine Puna. Thus, in this work camelid coprolites recovered from the archaeological site Quebrada Seca 3 (QS3) were analyzed using microhistological and palynological techniques to reconstruct the diet of these herbivores but also to infer vegetation and environmental changes from the Early to Middle Holocene (ca. 9600–6100 cal yrs BP) in the southern Argentine Puna (26°S). Results of both records show similar patterns in the percentages and species richness (especially those growing in wetlands) within and between coprolites dating to the Early Holocene (9600-8000 cal yrs BP) which suggest an environmental stability during this period. Around 8000 cal yrs BP, an increased variability in the richness of grasses, shrubs, dwarf shrubs, annual herbs and sedges species shows the gradual establishment of dry conditions, peaking around 6100 cal yrs BP. By this time, variability in the plant content of coprolites reflects seasonality in the assemblages due to the presence/absence of annual herbs either in the pollen or microfragment records. Therefore, it is likely that coprolites were from different animals that were hunted at different times of the year, supporting the evidence that QS3 has been occupied for short intervals of time after 7200 cal yrs BP when environmental conditions were extremely arid. The complementary analysis of the microfragments and pollen records preserved in coprolites provide valuable, complementary and alternative archive for herbivorous diet and for vegetation and environmental reconstructions, reinforcing that multiproxy approaches are necessary to obtain maximum information from coprolite studies.

Holocene Environmental Dynamics of the Lago Cochrane/Pueyrredón Valley, Central West Patagonia (47°S)

Deglaciation modeling of the Patagonian Ice Field since the Last Glacial Maximum has been a topic of intensive research in Central West Patagonia (44°–49°S). However, the chronology of deglaciation onset, acceleration, and the subsequent thinning and recession of the different ice lobes as well as the timing and extension of large proglacial systems are still a matter of discussion. The maximum eastward extension the Lago Cochrane/Pueyrredón ice lobe was around ∼20,000–27,000 cal yrs BP; its associated proglacial lake drained toward the Pacific between 12,600 and 8,000 cal yrs BP. This study presents the first two pollen and charcoal records from the Lago Cochrane/Pueyrredón valley, spanning the last 11,650 cal yrs BP. The Laguna Maldonado record spans between 11,650 and 8,500 cal yrs BP, while the Laguna Anónima record the last 8,500 cal yrs BP, thereby overlapping chronologically. The lithological record of Laguna Maldonado shows that organic sedimentation began at the onset of the Holocene (11,650 cal yrs BP), once the site was free of glacio-lacustrine influence. Between 11,650 and 10,500 cal yrs BP, an open Nothofagus forest developed associated with high fire occurrence/frequency, followed by a transitional phase to a closer forest associated with a shift from low to high fire activity up to 9,400 cal yrs BP. Between 9,400 and 8,500 cal yrs BP, the Laguna Maldonado record suggests the development of an open forest or probably scattered patches of forest of variable size in a steppe matrix, probably related to geomorphological and paraglacial dynamics as well as climatic forcings, while the Laguna Anónima record indicates the development of a closed Nothofagus forest and high to low fire occurrence/frequency from 8,200 to 3,800 cal yrs BP. Since 3,800 cal yrs BP, a highly dynamic open forest or forest patches scattered in a grass/shrub–grass steppe matrix occurred around Laguna Anónima associated with high fire occurrence/frequency synchronous with an important increase in the presence of hunter-gatherers during the last 3,000 years. The results from the Lago Cochrane/Pueyrredón valley are integrated and discussed at the regional scale alongside other records from Central West Patagonia.

Termination of Little Ice Age in Northeastern Anatolia, A multi-proxy paleolimnology study of undisturbed sediments, Lake Aygır (Kars, NE Anatolia)

Sedimentary, geochemical and stable isotope analyses of a sediment core (core AY) recovered from Lake Aygır (NE Anatolia) provide evidence of the climatic shifts during the last ~500 yrs. Sediments in Lake Aygırare composed of silty clay with a modeled ~0.16 cm/yr sedimentation rate. Multi-proxy analyses of the downcore distribution of detritally-deposited proxy elements, total calcium carbonate, organic carbon and stable isotopes reveal climatic records of the Industrial Epoch (IE; 18th-19th centuries) and the termination of the Little Ice Age (LIA; AD 1350 to 1850), represented by fluctuating Total Organic Carbon (TOC), Ca, Sr and relatively low detrital precursors (Fe, Ti, K, Rb, Zr), indicating low chemical weathering and dry conditions. The upper part of the core (192 cal yrs BP to present), identified with high detrital input, contains an increasing trend of Fe, Ti, K, Rb, and Zr together with high δ 18 O and δ 13 C values, indicating warmer conditions during the IE.

Late Holocene palaeogeographic evolution of the Lihoura coastal plain, Pteleos Gulf, Central Greece

The present study aims to determine the Late Holocene palaeogeographic evolution of the coastal Lihoura plain located at the western part of Pteleos Gulf, in central-eastern Greece. The study area is a low-lying marsh, located at the mouth of an ephemeral stream. In order to determine the evolution of the plain, three cores (max. depth of 6 m) were drilled. Grain size analysis coupled with macro- and micro-palaeontological analyses were performed on sediment samples collected from the cores and six biosedimentary facies were identified corresponding to different depositional palaeoenvironments. The chronostratigraphy of the cores was established by 14C radiocarbon datings on three samples. Furthermore, detailed (at a scale 1:5000) geomorphological mapping was carried out, providing us with valuable information on the palaeogeographic evolution of the area. The results suggest that during the Mid-Holocene, the sea inundated the Lihoura Bay and created a transitional marine-brackish environment. The existence of an elongated (SW-NE) limestone peninsula along with the development of a sand bar shortly after 5027–5462 cal yrs BP, led to the formation of a protected lagoonal environment at the western part of the marshy plain, which at times was influenced by multiple terrestrial inputs induced by fluvial sediment supply. At the northern part of the marshy plain, a very recent high energy marine inundation event has been recorded in the sedimentary stratigraphy. Average rates of relative sea-level rise of 0.78 ± 0.24 mm/yr, 0.94 ± 0.24 mm/yr and 1.45 ± 0.77 mm/yr were estimated for the last 5244.5 ± 217.5 cal yrs BP, 5543 ± 196 cal yrs BP and 1901 ± 200 cal yrs BP respectively, which is in good agreement with previously published sea-level data for the broader area.