Cal Yrs BP Research Articles

Phytoliths and seeds in fluvial island paleoenviroment reconstruction (interaction with pollen analysis)

We tested the use of phytoliths and seeds as bioindicators in the paleoenvironmental reconstruction of fluvial islands and compared the results with those of facies and pollen analyses. The studied material was taken from a 215 cm core drilled in Mutum Island. The study included a) the quantification and identification of phytoliths and seeds, b) the determination of the distribution of biological material in the island sediment and sedimentary facies, c) the determination of organic material contents, and d) a chronological analysis with three 14C dates. This study also determined the distribution of seeds and phytoliths over the sedimentary environment succession. We identified the following distributions of seeds and phytoliths over the paleoenvironmental hydrach succession. 1) Channel paleoenvironment (eupotamic stage): the sediment was deposited under lotic flow conditions, with the occurrence of Podostemaceae phytoliths and a predominance of Poliygonaceae seeds. 2) Blind channel paleoenvironment (parapotamic stage): this environment, which occurred 725–935 cal yrs BP., demonstrated an increase in the quantity of Podostemaceae phytoliths and seed quantity alternations. 3) Lake paleoenvironment (paleopotamic stage): a change from the blind channel to lake environment occurred at 631–797 cal yrs BP. An increase in the phytolith concentration was associated with a saddle morphology peak and general decrease in seeds, except for over the 110-100 cm interval, with a high occurrence of Cecropiaceae and Lentibulariaceae seeds. 4) Present swamp environment (paleopotamic to terrestrial stage): the present environment was settled approximately 300 cal yrs BP. (uncertainties range) with phytoliths. The seed assemblage in the sediment resembles the current vegetation on the island. The variation in the types of phytoliths and seeds from the base to the top of the sedimentary column reflect changes in the vegetation with changes in the environmental conditions and the great potential for these structures to be paleoindicators in fluvial systems. The seed and phytolith data were compared with the pollen analysis results.

New Holocene pollen records from the Brazilian Caatinga.

We present two pollen diagrams from the semi-arid Caatinga of the Catimbau National Park, in Pernambuco and from a Mauritia palm forest in the Caatinga/Cerrado ecotone of southern Piauí, NE Brazil, spanning the last 10,000 cal. yrs BP and the last 1,750 cal yrs BP, respectively. These two records contain a signature of the local vegetation and permit the correlation of the pollen signal with regional climatic changes. The Catimbau record shows Zizyphus sp., a typical Caatinga taxon, in all three pollen zones indicating regional Caatinga vegetation and the predominance of local arboreal taxa adapted to high humidity from 10,000 to ca. 6,000 cal. yrs BP with a gradual tendency towards drier conditions revealed by a deposition hiatus between 6,000 to ca. 2,000 cal. yrs BP. This abrupt loss of sediments in both localities is interpreted as a consequence of the establishment of modern semi-arid climates. The subsequent return of humidity is signaled by increased sedimentation rates and 14C date inversions in agreement with high precipitation, revealed by σ18O ratios in speleothems from NE Brazil. Modern sediments deposited in the last 500 years reflect local conditions with the maintenance of humidity by geological faulting and surfacing water tables.

Complementary medicine use in community-based Australians with type 2 diabetes: The Fremantle Diabetes Study Phase II (FDS2)

To investigate the Lateglacial and early Holocene climatic and environmental dynamics in the Eastern Baltic we analysed chironomid and pollen data from Lieporiai palaeolake, North Lithuania. The first quantitative mean July air temperature reconstruction from Lithuania based on fossil chironomid assemblages was performed using expanded Fennoscandian calibration model. Our study suggests that sedimentation started at about 14 600 cal yrs BP and lasted until the early Holocene. The mean July air temperature for Lateglacial and early Holocene from studied site ranged between 13 °C−16 °C which was ~ 2–4 °C lower than the present. Rapidly after the deglaciation during Bølling (GI-1e) interstadial reconstructed July air temperature reached ~ 15 °C. The marked temperature decrease to 13.2 °C was recorded during the Older Dryas (GS-1d). Temperature reached its highest values (up to 16 °C) during the Allerød (GI-1a). The Younger Dryas (GS-1) was relatively cold with the mean July air temperature ~ 14 °C and this was 3.9 °C colder than the present. The pattern of the Lateglacial temperature changes from Lieporiai Lake shows both similarities and some differences from the other chironomid based regional and European reconstructions. Chironomid inferred palaeoenvironmental changes are in positive correlation with changes in the development of vegetation.

Foraging habitats and niche partitioning of European large herbivores during the Holocene – Insights from 3D dental microwear texture analysis

Environmental changes related to forest expansion and later to agricultural development and deforestation during the Holocene in Europe have strongly shaped herbivore distribution and habitat selection, leading to species extinction. In this paper, we examine, through dental microwear textural analysis, the foraging habitats, dietary flexibility and niche partitioning of large herbivores (100 to 1000 kg) including two bovids (European bison Bison bonasus and aurochs Bos primigenius) and two cervids (moose Alces alces and red deer Cervus elaphus). The study focuses on northeast (NE) and south central (SC) Europe during three periods of the Holocene: Neolithic (6500–3500 cal yrs BP), Roman Period and Middle Ages (~2000–450 cal yrs BP) and Recent times (1963–2014). Our study highlights differences in diet between species only in the Neolithic SC Europe. This may have resulted from diversified habitats and dietary niche separation in SC Europe. The absence of differences in NE Europe may suggest more homogeneous habitat conditions in combination with lower densities of large herbivores in forested habitats. Analysis shows that during the Neolithic, in the bison diet there was more herbaceous monocotyledons in SC Europe than in NE Europe. We also found temporal changes in microwear texture variables for the bison in SC Europe suggesting a more herbaceous diet in the Neolithic than during the Roman Period and Middle Ages. However, neither spatial nor temporal differences in microwear texture variables were found in the aurochs. Thus, the diet of the European bison has likely changed, which may indicate a greater plasticity that promoted survival in refuge habitats.

Ultra-distal fine ash occurrences of the Icelandic Askja-S Plinian eruption deposits in Southern Carpathian lakes: New age constraints on a continental scale tephrostratigraphic marker

Here we present the results of the first cryptotephra investigation of two Late glacial-Holocene lake records from the Southern Carpathian Mountains in Romania, Lake Brazi and Lake Lia. The discovery of an important Icelandic tephrostratigraphic marker, the Askja-S, in the sedimentary records of both sites significantly extends the known ash dispersal from this Plinian eruption. Bayesian age-depth modelling of available radiocarbon (14C) data from both sedimentary records allows us to further refine the depositional age of this ultra-distal tephra. In combination with age constraints on the tephra from other well-dated European sites, we produce an updated age for this key tephrostratigraphic marker of 10,824 ± 97 cal yrs BP (95.4% range). The Askja-S tephra is stratigraphically positioned after the palaeoenvironmental proxy response to the Preboreal Oscillation at both sites. The widespread distribution of this tephra across Europe offers the potential to assess spatio-temporal variability of this climatic signal. The discovery of the Askja-S in lake records from the Southern Carpathians highlights the likelihood of finding other ultra-distal (Icelandic) cryptotephra marker layers within the region. Additionally, given the location of the Carpathian region, it offers the opportunity to further enhance and integrate tephrostratigraphic frameworks of north-western Europe with those of the Mediterranean and Anatolia regions, which will enable a more precise comparison of palaeoenvironmental archives across Europe.

Drought in the northern Bahamas from 3300 to 2500 years ago

Intensification and western displacement of the North Atlantic Subtropical High (NASH) is projected for this century, which can decrease Caribbean and southeastern American rainfall on seasonal and annual timescales. However, additional hydroclimate records are needed from the northern Caribbean to understand the long-term behavior of the NASH, and better forecast its future behavior. Here we present a multi-proxy sinkhole lake reconstruction from a carbonate island that is proximal to the NASH (Abaco Island, The Bahamas). The reconstruction indicates the northern Bahamas experienced a drought from ∼3300 to ∼2500 Cal yrs BP, which coincides with evidence from other hydroclimate and oceanographic records (e.g., Africa, Caribbean, and South America) for a synchronous southern displacement of the Intertropical Convergence Zone and North Atlantic Hadley Cell. The specific cause of the hydroclimate change in the northeastern Caribbean region from ∼3300 to 2500 Cal yrs BP was probably coeval southern or western displacement of the NASH, which would have increased northeastern Caribbean exposure to subsiding air from higher altitudes.

Sediment biomarkers elucidate the Holocene ontogeny of a shallow lake.

We carried out geochemical analyses on a sediment core from Lake Harris, Florida (USA) to identify sources of organic matter to the sediment throughout the Holocene, and relate changes in those sources to shifts in past climate and environmental conditions. We hypothesized that the sources of organic matter changed in response to regional hydrologic shifts following de-glaciation, and to human population expansion in the state during the 20th century. Hydroclimate shifts in Florida were related to: 1) a steady rise in relative sea level and the fresh water table that began in the early Holocene, 2) wetland formation and expansion ca. 5,000 cal yrs BP, and 3) the onset of the modern El Niño (ENSO) cycle ~3,000 cal yrs BP. Stratigraphic changes in sediment variables from Lake Harris reflect each of these hydroclimate periods. Early in the Holocene, Lake Harris was a marsh-like system in a relatively dry, open-prairie environment. Organic sediments deposited at that time were derived largely from terrestrial sources, as inferred from high TOC/TN ratios, a dominance of longer-chain of n-alkanes (n-C29-31), relatively negative organic carbon isotope values (δ13CTOC), and low biogenic silica concentrations. In the middle Holocene, a positive shift in δ13CTOC coincided with the onset of wetter conditions in Florida. Submerged macrophyte biomarkers (n-C21-23) dominated, and during that period bulk organic carbon isotope values were most similar to δ13C values of mid-chain-length n-alkanes. In the late Holocene, δ13CTOC values declined, CaCO3 levels decreased to trace amounts, organic carbon concentrations increased and diatom biogenic silica concentrations increased from 10 to 120 mg g-1. Around 2,900 cal yrs BP, the effects of ENSO intensified and many Florida lakes deepened to their current limnetic state. Concentrations of algal and cyanobacterial biomarkers in the Lake Harris core increased by orders of magnitude after about AD 1940, in response to human-induced eutrophication, an inference supported by values of δ15N that fluctuate around zero.

Pollen based vegetation and climate change records deduced from the lacustrine sediments of Kikar Tal (Lake), Central Ganga Plain, India

A 2.0 m thick sediment profile from Kikar Tal, Raebareli District is studied for the pollen assemblage to infer the vegetation and climate variability scenario during the Holocene period. Four distinct palynozones were demarcated based on the palynological succession in the core sediment. However, the radiocarbon dates for the profile could not be procured; therefore, the lake profile is corroborated with the chronology of adjacent lake ‘Chaudhary–Ka–Tal’, Raebareli District. It is envisaged that during 8,000–7,200 cal yrs BP, (Pollen Zone KT–I), forest groves with Holoptelea, Acacia, Madhuca indica, Syzygium and Prosopis as major tree taxa were present in the adjoining area of the lake. The forest groves were interspersed with wider stretches of open vegetation comprising grasses, Tubuliflorae, Liguliflorae, Chenopodiaceae/Amaranthaceae, etc. and shrubs of Adhatoda vasica and Acanthaceae. This vegetation scenario reflects that the region was under a warm and humid climate during that time. The existence of lake is also envisaged by the presence of aquatic elements, Lemna and Typha. Subsequently, during 7,200–4,200 cal yrs BP (Pollen Zone KT–II), the forest groves became more diversified and dense in composition as evidenced by the expansion of most of the existing trees as well as presence of Emblica officinalis, Aegle, Adina cordifolia, Symplocos and Sapotaceae and thickets of Adhatoda vasica and Mimosa pudica. This significant change in the vegetation mosaic as a whole implies the initiation of a warm and more–humid climatic condition, owing to climate amelioration. The encounter of Cerealia and concomitant cropland weeds, viz. Cheno/Am. Cannabis sativa, Brassica, etc. suggests that the vicinity of the lake was under agrarian practice and other anthropogenic activities. The ground flora was still dominated by grasses; however, it also turned more profuse than before. The increasing trend of Cerealia coupled with concomitant cropland weeds signifies the augmentation in Cereal–based agrarian practice owing to favourable climatic condition. The lake expanded as manifested by the increase in aquatic elements, such as Typha, Potamogeton and Lemna during this period. During the time bracket of 4,200–1,800 cal yrs BP (Pollen Zone KT–III), the arboreals reveal a decrease in their frequency and diversity of major tree taxa with incursion of Moringa and Bombax ceiba suggesting warm and moderately humid climate with reduced monsoon. The last zone (Pollen Zone KT–IV), from 1,800 cal yrs BP–Present, elucidates open grassland vegetation corresponding to reduced monsoon precipitation, with the shrinkage of lake area. The presence of Cerealia and other culture pollen taxa suggests the prevalence of intense agrarian practice in the vicinity of the lake.

The role of sediment compaction and groundwater withdrawal in local sea-level rise, Sandy Hook, New Jersey, USA

The rate of relative sea-level (RSL) rise at Sandy Hook, NJ (4.0 ± 0.5 mm/yr) was higher than The Battery, NY (3.0 ± 0.3 mm/yr) from 1900 to 2012 despite being separated by just 26 km. The difference cannot be explained by differential glacial isostatic adjustment (GIA; 1.4 ± 0.4 and 1.3 ± 0.4 mm/yr RSL rise, respectively) alone. We estimate the contribution of sediment compaction to subsidence at Sandy Hook using high-resolution grain size, percent organic matter, and porosity data from three upper Quaternary (≤13,350 cal yr) cores. The organic matter content (<2%) is too low to contribute to local subsidence. However, numerical modeling of the grain size-depth-age-porosity relationship indicates that compaction of deglacial silts likely reduced the column thickness by 10–20% over the past 13,350 cal yrs. While compaction rates were high immediately after the main silt deposition (13,350–13,150 cal yrs BP), rates decreased exponentially after deposition to an average 20th century rate of 0.16 mm/yr (90% Confidence Interval (C.I.), 0.06–0.32 mm/yr). The remaining ∼0.7 mm/yr (90% C.I. 0.3–1.2 mm/yr) difference in subsidence between Sandy Hook and The Battery is likely due to anthropogenic groundwater withdrawal. Historical data from Fort Hancock wells (2 km to the southeast of the Sandy Hook tide gauge) and previous regional work show that local and regional water extraction lowered the water levels in the aquifers underlying Sandy Hook. We suggest that the modern order of contribution to subsidence (highest to lowest) appears to be GIA, local/regional groundwater extraction, and compaction of thick Quaternary silts.

The usefulness of subfossil Cladocera remains in Younger Dryas climatic reconstructions in central Poland

Abstract Cladoceran-based paleotemperature estimates for the Younger Dryas for ten sections of paleo-oxbow lakes, valley mires, and lacustrine sediments from central Poland are presented, and their potential usefulness to climatostratigraphy is described. Most of the changes observed in the cladoceran assemblages are responses to climate changes. The cladoceran-based temperature reconstructions reflect cold conditions during the Younger Dryas (YD) and allow a division of this period into two phases: an older colder phase, between 12,800 and 12,000 cal yrs BP, and a younger, warmer phase, between ca. 12,000 and 11,500 cal yrs BP. The geomorphological features of the study sites and local environmental forces are also taken into consideration. The cladoceran-inferred summer temperature estimates from all of the study sites correspond closely with the available climate reconstruction for the YD in central Europe.

Late Holocene palynology of a saline lake in the Pantanal of Nhecolândia, Brazil

ABSTRACTThis work presents the first description of a palynological assemblage preserved in sediments deposited in a saline lake (salina) in the Nhecolândia area of the Brazilian Pantanal. Pollen studies from salinas have been underappreciated due to inferred taphonomic issues related to elevated alkalinity. We have found a well-preserved assemblage that allowed the reconstruction of the history of local vegetation. Radiocarbon dating revealed a constant deposition since ∼3760 calibrated years before present (cal yrs BP), and pollen analyses suggested two main phases of vegetation and environmental development. From 3760 to 1510 cal yrs BP, the site was a swamp to shallow lake dominated by cattails (Typha domingensis) and Poaceae. From 1510 cal yrs BP to the present the herbaceous community is enriched with Cyperaceae and Bromeliaceae, and with tree taxa such as the Arecaceae (palm trees), evidencing the local development of a fringe vegetation. These two phases were interpreted as a change from drier to wetter settings, largely in agreement with regional lake and speleothem records, as well as pollen and carbon isotope studies from other locations in central South America during the latest Holocene. Given that salinas are non-floodable and pollen was found to be well preserved, we highlight the potential of palaeopalynology in these environments as a source of palaeoecological information for the Pantanal Basin.

Calcite raft geochemistry as a hydrological proxy for Holocene aquifer conditions in Hoyo Negro and Ich Balam (Sac Actun Cave System), Quintana Roo, Mexico

Two cores from calcite rafts deposits located in Cenote Ich Balam and Hoyo Negro were dated and analyzed for 87Sr/86Sr, δ18O, δ13C, Sr/Ca and Cl/Ca. The geochemical records show changing aquifer salinity spanning the last ∼ 8.5 cal kyrs BP and interrelationships with Holocene climate trends (wet and dry periods). During the wet mid-Holocene, the salinity of the meteoric Water Mass (WM; at 7.8–8.3 cal kyrs BP) was relatively high at 1.5–2.7 ppt and then became less saline (1.0–1.5 ppt) during the last ∼ 7000 yrs as climate became progressively drier. High salinity of the meteoric WM during the wet mid-Holocene is attributed to increased turbulent mixing between the meteoric and underlying marine WM. Increased precipitation, in terms of amount, frequency, and intensity (e.g. hurricanes) causes higher flow of meteoric water towards the coast and mixing at the halocline, a phenomenon recorded with recent instrumental monitoring of the aquifer. Conversely, during dry periods reduced precipitation and flow in the meteoric WM would result in lower salinity. Karst properties and Holocene sea-level rise also seem to have an effect on the aquifer. When the regionally extensive network of shallow cave passages (∼ 10–12 m water depth) are flooded at ∼ 8000 cal yrs BP, there is a rapid shift in salinity. This study demonstrates that calcite raft deposits can be used as paleo-environmental recorders documenting the effects of sea level and climate change on aquifer condition.

Baltic Sea Holocene evolution based on OSL and radiocarbon dating: evidence from a sediment core from the Arkona Basin (the southwestern Baltic Sea)

Abstract The paper presents the chronology of the Holocene evolution of the Baltic Sea based on the optically stimulated luminescence (OSL) and radiocarbon dating methods applied to a core taken from the Arkona Basin. The dating results were supplemented by grain size and geochemical analysis. The obtained results of OSL and radiocarbon dating enabled the construction of an age-depth model and confirmed the continuous sedimentation since 9900 cal yrs BP. One of the most interesting findings of this study is a clear relationship between the rate of sedimentation and fluctuations in the energy of depositional environment. The analyzed sediment core revealed two sections of different accumulation rates. The bottom section was deposited until 2700 cal yrs BP when the Ancylus Lake and the Littorina Sea were present, characterized by the accumulation rate estimated at around 0.46 mm year-1 and the dynamic sedimentation environment confirmed by grain size parameters. The accumulation rate at the top section deposited during the Post-Littorina Sea stage was estimated at around 1 mm year-1. This stage, characterized by more stable deposition and lower-energy environment conditions, was confirmed by small grain size, symmetric skewness and increasing content of organic matter.

Sources and characteristics of terrestrial carbon in Holocene-scale sediments of the East Siberian Sea

Abstract. Thawing of permafrost carbon (PF-C) due to climate warming can remobilise considerable amounts of terrestrial carbon from its long-term storage to the marine environment. PF-C can be then be buried in sediments or remineralised to CO2 with implications for the carbon–climate feedback. Studying historical sediment records during past natural climate changes can help us to understand the response of permafrost to current climate warming. In this study, two sediment cores collected from the East Siberian Sea were used to study terrestrial organic carbon sources, composition and degradation during the past ∼ 9500 cal yrs BP. CuO-derived lignin and cutin products (i.e., compounds solely biosynthesised in terrestrial plants) combined with δ13C suggest that there was a higher input of terrestrial organic carbon to the East Siberian Sea between ∼ 9500 and 8200 cal yrs BP than in all later periods. This high input was likely caused by marine transgression and permafrost destabilisation in the early Holocene climatic optimum. Based on source apportionment modelling using dual-carbon isotope (Δ14C, δ13C) data, coastal erosion releasing old Pleistocene permafrost carbon was identified as a significant source of organic matter translocated to the East Siberian Sea during the Holocene.

Chronological reconstruction of eolianites and transversal mobile dunes of northwest coast of Ceará State – Brazil, in the last 3000 cal yrs BP

Abstract Dunefields are very common in the northern coastal zone of northeast Brazil. They have the potential to yield important information about paleoclimate, paleo-winds and regional winds and their response to sea-level fluctuations during the Holocene. We reconstructed the coastal dunes geochronological evolution of northwest Ceara State – Brazil, in the last 3000 cal yrs BP, using detailed analyses of lithostratigraphy, microfossil (foraminifera), wind regime, dune monitoring and 8 radiocarbon dates. The chronology was based on 14 C dating in eolianites and monitoring transversal mobile dunes movement processes. Radiocarbon date results indicated that the dunes corresponding to eolianites revealed ages between 2760–2480 and 980–750 cal yrs BP, suggesting that the vast transversal mobile dunefields were formed after this period in similar condition to the current sea-level. We considered that the material transportation by the prevailing east winds towards the transversal dunes is estimated in the order of 11.0 m/year, thus the current aeolian system is less than 1000 yrs BP.

Palaeohydric balance variations in eastern Andean environments in southern Patagonia (48°–52.5° S): Major trends and forcings during the last ca. 8000 cal yrs BP

The core of the storm track flow intersects the landmass of Southern Patagonia providing a unique opportunity for palaeo-reconstructions. Most of the palaeo-reconstructions are based on records from sites where the relationship between precipitation and wind flow intensity, can be reconstructed from the impact on vegetation communities. Seven sites were selected for this study. The importance relies on their location in relation to vegetation communities; two sites lie within forest communities, two are from the forest-steppe ecotone and the other three from steppe communities in Southern Patagonia, Argentina, between 48° and 52.5° S and between 70° and 72° W. To compare the past palaeohydric balance based on the seven pollen records from these different vegetation communities along the precipitation gradient, we constructed a Palaeohydric Balance Index (PBI). The PBI is based on the water requirement of the main plant taxa represented by the pollen types analyzed in the records. The information provided by this index improves the understanding of the hydric balance variability in relation to the storm track behavior. During the last 8000calyrsBP we observed out-of-phase behavior in PBI variations between forest, forest-steppe ecotone and steppe PBIs, a greater amplitude of forest versus steppe environments and low amplitude of the forest-steppe ecotone variability. This out-of-phase behavior appears to have been replaced by in-phase palaeohydric changes between 700 and 500calyrsBP interpreted as related to an equatorward migration of the storm tracks.

HOLOCENE CLOSURE OF A BARRIER BEACH IN SEPETIBA BAY AND ITS ENVIRONMENTAL IMPACT (RIO DE JANEIRO, BRAZIL)

Core T4 (with 286 cm long) collected in the inner part of Sepetiba Bay is a record of late Holocene evolution of Sepetiba Bay. This core was described and sampled every 2 cm. Textural, geochemical and foraminifera data were analyzed, and two radiocarbon dates were obtained. Estimated ages indicate that core T4 represents the last ≈4,000 years calibrated before present (yrs cal BP). Results of this core suggest that coarse sediments, recorded in the period between ≈4,000-3,400 yrs cal BP, were probably associated with high hydrodynamic conditions in the study area. These sediments should be deposited at an incipient phase of the Marambaia Beach Barrier evolution; the development of this sand barrier resulted in the confinement of the inner region of Sepetiba Bay, leading to the deposition of muddy sediments rich in organic matter. Organic matter enrichment increased especially in the last ≈500 yrs cal BP. Foraminifera assemblages and carbonates content indicate that the studied region should have been affected in the last ≈3,400 yrs cal BP by changes in the water depth column. An increase of the water column depth was recorded for example between ≈850-350 yrs BP. The results obtained in the core T4 show that the confinement and eutrophication process of the internal zone of Sepetiba Bay, has been occurring since ≈3,400 yrs cal BP and is being caused by other factors such as geomorphological and climatic changes and human activities.

Selective transport of palynomorphs in marine turbiditic deposits: An example from the Ascension-Monterey Canyon system offshore central California

The pollen assemblage of a deep-sea core (15G) collected at lower bathyal depths (3491 m) on a levee of Monterey Canyon off central California was investigated to gain insights into the delivery processes of terrigenous material to submarine fans and the effect this transport has on the palynological record. Thirty-two samples were obtained down the length of the core, 19 from hemipelagic and mixed mud deposits considered to be the background record, and 13 others from displaced flow deposits. The pollen record obtained from the background samples documents variations in the terrestrial flora as it adapted to changing climatic conditions over the last 19,000 cal yrs BP. A Q-mode cluster analysis defined three pollen zones: a Glacial Pollen Zone (ca. 20,000–17,000 cal yr BP), an overlying Transitional Pollen Zone (ca. 17,000–11,500 cal yr BP), and an Interglacial Pollen Zone (ca. 11,500 cal yr BP to present). Another Q-mode cluster analysis, of both the background mud and flow deposits, also defined these three pollen zones, but four of the 13 turbiditic deposits were assigned to pollen zones older than expected by their stratigraphic position. This was due to these samples containing statistically significant fewer palynomorphs than the background muds as well as being enriched (∼10–35% in some cases) in hydraulically-efficient Pinus pollen. A selective bias in the pollen assemblage, such as demonstrated here, may result in incorrect interpretations (e.g., climatic shifts or environmental perturbations) based on the floral record, indicating turbiditic deposits should be avoided in marine palynological studies. Particularly in the case of fine-grained flow deposits that may not be visually distinct, granulometry and grain size frequency distribution curves may not be enough to identify these biased deposits. Determining the relative abundance and source of displaced shallow-water benthic foraminifera entrained in these sediments serves as an excellent additional tool to do so.

Late Pleistocene-Holocene variability in the southern Gulf of Mexico surface waters based on planktonic foraminiferal assemblages

Abstract Planktonic foraminiferal assemblages are used as proxies of surface ocean variations, as documented in five marine sediment cores from the Bay of Campeche (BoC), Gulf of Mexico (GoM), spanning the last 34,000 cal yrs BP. This paper seeks to better understand the regional history by studying cores taken in the poorly studied Southern GoM. Multivariate factor analyses calculated five assemblages at millennial to glacial–interglacial scales. During the last glacial period, including the Last Glacial Maximum (LGM), the assemblage contained G. inflata , and T. sacculifer which suggests the presence of colder and less saline waters than younger times; although during the LGM, saltier waters and weaker ocean circulation may have occurred. During the deglaciation, the deep-dweller G. crassaformis suggest a reorganization of deep-thermocline waters and the establishment of transitional conditions, where mild to warm waters entered the Gulf. During the early to mid-Holocene, the tolerant tropical species G. ruber pink suggests salinity variations and warmer conditions than the previous interval. During the late-Holocene, only warm species comprise the assemblage, where the group G. menardii and G. truncatulinoindes suggest warm and stratified conditions, with an oxygen decrease in the thermocline, and rather high salinity levels linked to reduced moisture exported from the Pacific due to the progressively more influential ENSO-like conditions. Prominently, all the assemblages include the species G. ruber white chromotype, suggesting that the environmental conditions are continuously favorable to this abundant species. These scenarios show agreement to previous reconstructions in northern and western GoM, the Caribbean, as well as paleoclimate on land, which are mostly regulated by the position of the ITCZ, changes in the expansion of the Atlantic Warm Pool, the tropical circulation, and teleconnections with nearby regions.

Shallow Subsurface Evidence for Postglacial Holocene Lakes at Ivanpah Dry Lake: An Alternative Energy Development Site in the Central Mojave Desert, California, USA

Dry lakes, or playas, in the American Southwest have become important locations for alternative energy solar electric generation systems. Many of these playas have not been investigated for past environmental conditions prior to their development, causing alterations to the shallow sediment profile and altering subsurface chemical and physical data important to recent geologic and hydrologic histories of these areas. Recent studies of these features commonly have focused on surficial data with little or no subsurface geologic data to delineate wet and dry cycles of playa lakes. Many of the playa margins are covered with a surficial layer of alluvial and/or aeolian sands varying in thickness, which could interfere with correct interpretations of data gathered only on the surface material on these lands. Over the past 13,000 years Ivanpah Dry Lake has had at least three episodes of lake highstands up to ~10m in response to climate changes, based on data in this study with the oldest episode dates to ~13,000 cal yrs BP. This study has a link to other sites as many other playas are slated for energy development and could endure subsurface data alteration during site reworking and occupation, resulting in a loss in their collective historical geologic and hydrologic records if more complete studies of important sites are not carried out before developments begin.