Paleoenvironmental Proxies Research Articles

Body-size reductions in dacryoconarid tentaculitoids during Late Devonian warming

Body size is an essential factor in an organism’s survival, and when paired with paleoenvironmental proxies, size trends can provide insights into a lineage’s evolutionary responses to changing environmental conditions. This study explores the diversity and body-volume trends of dacryoconarid tentaculitoids, globally abundant marine zooplankton, in the Devonian of the Appalachian Basin (eastern United States), spanning the late Givetian through the middle Frasnian punctata carbon isotope excursion. Using statistical approaches to model trends, we find evidence of a gradual, within-lineage reduction in styliolinid adult body sizes starting at the Givetian-Frasnian boundary. This reduction is followed by a significant decrease in both adult and initial chamber volumes during the punctata excursion. At the Givetian-Frasnian boundary, annulated forms (nowakiids) become rare and smooth forms (styliolinids) begin to dominate the assemblage. Using pre-existing geological and geochemical data sets, we consider environmental factors, including sea level, anoxia, nutrient availability, and temperature, as potential drivers of body-size reductions. Bottom-water anoxia most likely did not influence body-size trends of this pelagic group, but frequent water-column overturning in the Frasnian or other exchange between deep and shallow water may have affected taxonomic composition, favoring styliolinids. Sea-surface temperature correlates inversely with body size, suggesting that warming beginning in the early Frasnian may have contributed to gradual, long-term size reductions. Rising temperatures through the middle Frasnian may have led to the disappearance of dacryoconarids in the northern Appalachian Basin after the excursion.

Depositional Environment and Ecological Response of Bioconstructions: A Case Study of Southern China (Guizhou Province) in Moscovian-Gzhelian.

From the late Carboniferous to the early Permian, multiple pulses of glaciation and deglaciation have been caused by the LPIA. The Pennsylvanian period experienced phases of recovery, proliferation, and decline, ultimately forming a reef system distinctly different from that of the Mississippian period. During the late Bashkirian to Moscovian, the metazoan reef experienced a limited resurgence, with reef predominantly formed by chaetetid developing in the United States, northern China, and Japan. During the Kasimovian to Gzhelian, the phylloid algal reef dominated the global reef systems. In the late Pennsylvanian, bioconstruction cases and paleoenvironmental proxies in southern Guizhou Province were studied to investigate the composition, recovery, and evolutionary processes of the bioconstructions as well as their response to environmental variations during this period. Several bioconstructions have been reported in the Lumazhai section of Houchang Town, Guizhou Province, southern China, from the Moscovian to the Gzhelian. The upper Carboniferous strata are well-preserved and continuously exposed. The continuous strata, abundant fossils, and diverse bioconstructions provide excellent research materials for exploring the mutual constraints between organisms and their environment. This study identified ten microfacies, whose vertical evolution indicated significant changes in the depositional environment related to relative sea-level fluctuations. Skeletal grains are widely present in these facies. Among them, foraminifera, algae, bryozoans, crinoids, and Tubiphytes are the most common and exhibit distinct distribution characteristics in various environments. Quantitative statistics, CCA and theoretical ecospace have been utilized to examine and interpret environmental impact factors. Quantitative analysis of their relative abundance and distribution patterns provides insights into the complex interactions between organisms and environmental factors. The relative abundances of different organisms and factors controlling their bioconstructions are influenced by relative sea-level changes. CCA analysis reveal that hydrodynamic conditions are the primary influencing factor. Variation trends in average tiering and motility reveal the characteristics of biological communities during environmental changes in phylloid algae and microbial bioconstructions. These bioconstructions are not directly correlated with changes in environmental factors, and the biological communities in phylloid algae mounds and biostromes exhibit similar organism compositions and ecological niches across different environments.

Sediment flux variation as a record of climate change in the Late Quaternary deep‐water active Corinth Rift, Greece

AbstractThe value of deep‐water sedimentary successions as reliable records of environmental change has been questioned due to their long response times and sediment pathways leading to complex responses to climatic change and tectonic signals over differing timescales. We studied the Gulf of Corinth, Greece, to test the value of deep‐water stratigraphic successions as records of external controls on sediment flux in a setting with short response times and transport distances. The confinement of the rift basin allows for a near‐complete accounting of clastic sediment volumes. The recent acquisition of high‐resolution seismic reflection data, utilisation of International Ocean Discovery Programme Expedition 381 cores and a robust chronological framework, enable evaluation of the stratigraphy at a high temporal resolution. Combining borehole and high‐resolution seismic reflection data, distinct seismic units can be correlated to multiple paleoenvironmental proxies, permitting quantification of sediment flux variation across successive glacial–interglacial cycles at ca. 10 kyr temporal resolution. Trends in average sediment flux since ca. 242 ka show ca. 2–9 times greater sediment flux in cooler glacials compared to warmer interglacial conditions. The Holocene is an exception to low sediment flux for the interglacials, with ca. 5 times higher rates than previous interglacials. The short and steep configuration of the Sythas canyon and its fan at the base of an active submarine normal fault results in deep‐sea deposition at all sea‐level stands. In contrast, adjacent canyon systems shut down during warm intervals. When combined with palynology, results show that periods of distinct vegetation re‐organisation correlate to sediment flux changes. The temporal correlation of sediment flux to palynology in the Gulf of Corinth over the last ca. 242 kyr is evidence that variability of sediment supply is largely governed by climate‐related changes in hinterland catchments, with sea‐level and tectonics being second‐order controls on sediment flux variability.

Phytolith based paleoecological reconstruction from a loess-paleosol sequence in the Kashmir Himalaya, India

The temporal vegetation development provides vital information for understanding past climatic changes. In this study, we reconstruct vegetation dynamics from the last glacial period using phytoliths as a proxy from the Wanihama loess-paleosol sequence (LPS) near Srinagar in Kashmir Himalaya, India. Different phytolith assemblages and indices (Ic and Iw) revealed a series of warm and cold events documented in the LPS. The data indicate the predominance of broad-leaved and sparse conifer vegetation from ca. 42 ka to 39 ka, suggesting a comparatively warm and humid climate. After ca. 39 ka, conifers and grasses increased, indicating a transition to a cold climate. The cold climate, intervened by a short stadial, continued until ca. 31 ka with the predominance of conifers, grasses, and sedges. Subsequently, three other cold events were noted until ca. 14 ka, which resulted in vegetation disappearance and a substantial decrease in phytolith count. These cold events roughly coincide with the climatic instability in the Atlantic Ocean that caused severe cooling at high northern latitudes and likely impacted the Asian climate. Phytolith assemblages showed an overall increasing proportion of C4 grasses towards the top of the LPS, suggesting warm and dry climatic conditions. We also correlated the phytolith-based vegetation reconstruction with other paleoenvironmental proxies recorded from the same section, as well as with the last glacial climatic changes documented in different regions, to determine the reliability of phytoliths in LPSs as a proxy for past vegetation and climate reconstruction in the Kashmir Himalaya.

Five series of benzohopanes in early Cretaceous sediments from the Chaoyang Basin, NE China

Five series of benzohopanes were identified in a set of immature to early-oil-window early Cretaceous sediments from the ZK1006 well, Chaoyang Basin, NE China. Series a (C31-C35), b (C33-C35), and c (C31-C35) benzohopanes form by different pathways, while the newly-found series d (C31-C34, maybe to C35?) and e (C31-C32, maybe to C35?) benzohopanes have similar formation mechanisms. Series a is usually the predominant benzohopane series, but occasionally samples are dominated by series c benzohopanes. Series b benzohopanes may be associated with terrigenous organic matter. Series a and b benzohopanes are possibly influenced by redox properties, while paleosalinity more likely controls the formation and enrichment of series c benzohopanes. Two novel parameters (a benzohopane index, and the C35/C34 benzohopane ratio) are proposed to be useful paleoenvironmental proxies in the study area. A high benzohopane index and C35/C34 benzohopane ratio may indicate an anoxic environment.

Interlaboratory Comparison of Branched GDGT Temperature and pH Proxies Using Soils and Lipid Extracts

AbstractRatios of glycerol dialkyl glycerol tetraethers (GDGT), which are membrane lipids of bacteria and archaea, are at the base of several paleoenvironmental proxies. They are frequently applied to soils as well as lake‐ and marine sediments to generate records of past temperature and soil pH. To derive meaningful environmental information from these reconstructions, high analytical reproducibility is required. Based on submitted results by 39 laboratories from across the world, which employ a diverse range of analytical and quantification methods, we explored the reproducibility of brGDGT‐based proxies (MBT′5ME, IR, and #ringstetra) measured on four soil samples and four soil lipid extracts. Correct identification and integration of 5‐ and 6‐methyl brGDGTs is a prerequisite for the robust calculation of proxy values, but this can be challenging as indicated by the large inter‐interlaboratory variation. The exclusion of statistical outliers improves the reproducibility, where the remaining uncertainty translates into a temperature offset from median proxy values of 0.3–0.9°C and a pH offset of 0.05–0.3. There is no apparent systematic impact of the extraction method and sample preparation steps on the brGDGT ratios. Although reported GDGT concentrations are generally consistent within laboratories, they vary greatly between laboratories. This large variability in brGDGT quantification may relate to variations in ionization efficiency or specific mass spectrometer settings possibly impacting the response of brGDGTs masses relative to that of the internal standard used. While ratio values of GDGT are generally comparable, quantities can currently not be compared between laboratories.

Paleoenvironmental and chemostratigraphic implications of variations in geochemical proxies across the Upper Jurassic–Lower cretaceous boundary: a case study from the Flemish Pass Basin

The Jurassic–Cretaceous boundary is the only Phanerozoic period-level boundary that lacks a golden spike on the geological timescale despite significant global geological and environmental change during this time related to the opening of the Atlantic Ocean. Paleoenvironmental proxy profiles (total organic carbon, δ34S, δ15N, Fe, Mn, Ce/Ce*, Th/U, δ13Corg, P, Ni, Zn, Cu, and B/Ga) for core 3 of the Baccalieu I-78 well in the Flemish Pass Basin, offshore eastern Canada, exhibit a geochemical anomaly between 3288.5 and 3289 m, overlapping with the biostratigraphic placement of the Jurassic–Cretaceous boundary. Collectively the geochemical analyses are interpreted to indicate that the anomaly is associated with a fall in relative sea level, followed by a rise, which led to restricted circulation, stratification, and widespread anoxia. This anoxia, coupled with an arid climate, further resulted in reduced weathering, limited nutrient supply, and an overall reduction in primary productivity. The results of this study, in conjunction with previous biostratigraphic studies on core 3, suggest that the Jurassic–Cretaceous boundary in Baccalieu I-78 likely falls within the geochemical anomaly, specifically between 3228.5 and 3288.85 m. Furthermore, the paleoenvironmental interpretations derived in this study agree with published reports on global sea level and climate trends around the Jurassic–Cretaceous boundary, implying the influence of global, rather than regional, factors on deposition. This suggests that geochemical proxies may be useful in providing additional paleoenvironmental insights and helping to constrain stratigraphic boundaries, particularly in intervals that lack significant lithological or biological change.

A pre-Campanian Ignimbrite techno-cultural shift in the Aurignacian sequence of Grotta di Castelcivita, southern Italy

The Aurignacian is the first European technocomplex assigned to Homo sapiens recognized across a wide geographic extent. Although archaeologists have identified marked chrono-cultural shifts within the Aurignacian mostly by examining the techno-typological variations of stone and osseous tools, unraveling the underlying processes driving these changes remains a significant scientific challenge. Scholars have, for instance, hypothesized that the Campanian Ignimbrite (CI) super-eruption and the climatic deterioration associated with the onset of Heinrich Event 4 had a substantial impact on European foraging groups. The technological shift from the Protoaurignacian to the Early Aurignacian is regarded as an archaeological manifestation of adaptation to changing environments. However, some of the most crucial regions and stratigraphic sequences for testing these scenarios have been overlooked. In this study, we delve into the high-resolution stratigraphic sequence of Grotta di Castelcivita in southern Italy. Here, the Uluzzian is followed by three Aurignacian layers, sealed by the eruptive units of the CI. Employing a comprehensive range of quantitative methods—encompassing attribute analysis, 3D model analysis, and geometric morphometrics—we demonstrate that the key technological feature commonly associated with the Early Aurignacian developed well before the deposition of the CI tephra. Our study provides thus the first direct evidence that the volcanic super-eruption played no role in this cultural process. Furthermore, we show that local paleo-environmental proxies do not correlate with the identified patterns of cultural continuity and discontinuity. Consequently, we propose alternative research paths to explore the role of demography and regional trajectories in the development of the Upper Paleolithic.

Sulfur Isotope Geochemistry of Ice‐Wedges in Yakutia, East Siberia

ABSTRACTSulfur, with its highly varying stable isotope ratio and involvement in numerous biogeochemical processes, is one of the most widely used elements as an isotopic paleoenvironmental proxy, yet the sulfur isotope ratios of ice‐wedges and their insoluble fraction remain unexplored. This study first presents the sulfur isotopic compositions of soluble sulfate, particulate organic matter (POM), and lithic particles recovered from East Siberian ice‐wedges. Soluble sulfate, primarily representing atmospheric sulfate deposition, shows comparable sulfur isotope ranges in Zyryanka and Batagay, while in Central Yakutia, ice‐wedge sulfate is more enriched in 34S, consistent with the orogenic and cratonic terranes in East Siberia. Given the wedge growth during the inland winter, it is likely that sulfate aerosols were derived mainly from erosion and weathering of regional basement rocks rather than from sea salt spray or biogenic emissions. Within individual ice‐wedges, however, the sulfur isotopic composition of soluble sulfate varies by as much as 7‰, possibly reflecting changes in the relative contributions of sulfur‐isotopically distinct source regions. Beyond the origin of sulfate, greater sulfur isotope fractionations between POM and sulfate during the last glaciation suggest that sulfate may have been anaerobically reduced to sulfide and vice versa in the adjacent root zone.

Uncovering Holocene climate fluctuations and ancient conifer populations: Insights from a high-resolution multi-proxy record from Northern Finland

A series of abrupt climate events linked to circum-North Atlantic meltwater forcing have been recognised in Holocene paleoclimate data. To address the paucity of proxy records able to characterise robustly the regional impacts of these events, we retrieved a sub-centennial resolution, well-dated core sequence from Lake Kuutsjärvi, northeast Finland. By analysing a range of paleo-environmental proxies (pollen, plant sedimentary ancient DNA, plant macrofossils, conifer stomata, and non-pollen palynomorphs), and supported with proxy-based paleotemperature and moisture reconstructions, we unravel a well-defined sequence of vegetation and climate dynamics over the early-to-middle Holocene. The birch-dominated pioneer vegetation stage was intersected by two transient tree-cover decrease events at 10.4 and 10.1 thousand years ago (ka), likely representing a two-pronged signal of the 10.3 ka climate event. Our data also show a clear signal of the 8.2 ka climate event, previously not well recorded in the European Arctic, with a collapse of the pine-birch forest and replacement by juniper developing in tight synchrony with Greenland isotopic proxies over 8.4–8.0 ka. Supported by climate modelling, severe winter cooling rather than summer might have been driving vegetation disruptions in the early Holocene. The Kuutsjärvi data indicate an early arrival of Norway spruce (Picea abies) by 9.2 ka (pollen, DNA, and stoma finds), as well as the first evidence for Holocene presence of larch (Larix) in Finland, with pollen finds dating to 9.6–5.9 ka.

Environmental controls on the distribution of brGDGTs and brGMGTs across the Seine River basin (NW France): implications for bacterial tetraethers as a proxy for riverine runoff

Abstract. Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are bacterial lipids that have been widely used as environmental proxies in continental paleorecords. Another group of related lipids, branched glycerol monoalkyl glycerol tetraethers (brGMGTs), has recently been proposed as a potential paleotemperature proxy. Nevertheless, the sources and environmental dependencies of both brGDGTs and brGMGTs along the river–sea continuum are still poorly understood, complicating their application as paleoenvironmental proxies in some aquatic settings. In this study, the sources of brGDGTs and brGMGTs and the potential factors controlling their distributions are explored across the Seine River basin (NW France), which encompasses the freshwater-to-seawater continuum. BrGDGTs and brGMGTs were analyzed in soils, suspended particulate matter (SPM), and sediments (n=237) collected along the land–sea continuum of the Seine basin. Both types of compounds (i.e., brGDGTs and brGMGTs) are shown to be produced in situ, in freshwater and saltwater, based on their high concentrations and distinct distributions in aquatic settings (SPM and sediments) vs. soils. Redundancy analysis further shows that both salinity and nitrogen dominantly control the brGDGT distributions. Furthermore, the relative abundance of 6-methyl vs. that of 5-methyl brGDGTs (the IR6Me ratio), the total nitrogen (TN), the δ15N, and the chlorophyll a concentration co-vary in a specific geographical zone with low salinity, suggesting that 6-methyl brGDGTs are preferentially produced under low-salinity and high-productivity conditions. In contrast to brGDGTs, the brGMGT distribution appears to be primarily regulated by salinity, with a distinct influence on the individual homologues. Salinity is positively correlated with homologues H1020a and H1020b and negatively correlated with compounds H1020c and H1034b in SPM. This suggests that bacteria living in freshwater preferentially produce compounds H1020c and H1034b, whereas bacteria that primarily grow in saltwater appear to be predominantly responsible for the production of homologues H1020a and H1020b. Based on the abundance ratio of the freshwater-derived compounds (H1020c and H1034b) vs. their saltwater-derived homologues (H1020a and H1020b), a novel proxy, the Riverine IndeX (RIX), is proposed to trace riverine organic matter inputs, with high values (>0.5) indicating a higher riverine contribution. We successfully applied RIX to the Godavari River basin (India) and a paleorecord across the upper Paleocene and lower Eocene from the Arctic Coring Expedition at Lomonosov Ridge, showing its potential applicability to both modern samples and paleorecords.

The where, when, and how of ooid formation: What ooids tell us about ancient seawater chemistry

Ooids are a common constituent of carbonate rock throughout the last 3.2 billion years. The chemical and physical characteristics of ooids record essential details of the carbonate chemistry and hydrodynamic conditions of their depositional environment. As a result, ooids may be a powerful tool for reconstructing Earth's ancient climates and environments. However, lack of constraints on fundamental aspects of ooid formation, such as the role of abrasion, underscores the potential for additional discoveries utilizing ooids as paleoenvironmental proxies. Here, we use three-dimensional models built by serially grinding and imaging ooids to show how ooid shape changes during growth. We find that ooid abrasion plays only a small role in the formation of ooids, even in giant ooids, where the mass should cause abrasion to be most intense. A lack of abrasion during ooid formation suggests a greater sensitivity of ooid distribution and size to the chemistry of depositional environments. This insight enables us to harmonize our understanding of ooid formation with longstanding questions regarding their spatial and temporal distribution, as well as size variations. With a new database of ooid occurrences, we analyze the influence of seawater chemistry, carbonate shelf area, and evolutionary developments on ooid abundance in the Modern, Last Glacial Period, and throughout the Phanerozoic. Finally, we leverage our new understanding of ooid growth to show how ooid size, including giant ooids, can shed light on relative changes in alkalinity throughout the Phanerozoic.

Isotopic Evidence for Degradation of Particulate Black Carbon in the Ocean

AbstractBlack carbon (BC) has emerged as an integral part of the global carbon (C) cycle, constituting 12% ± 5% of the organic C pool in rivers and soils, with the potential to generate negative climate feedback. However, its ability to sequester C depends on the recalcitrant nature of BC in the environment, which is under debate. Using CTO‐375 method and by measuring concentrations and isotopic compositions of particulate BC (δ13CPBC), we explore the transformation of particulate black carbon (PBC) along the atmosphere‐river‐ocean continuum. Significantly high δ13CPBC in the ocean compared to rivers and atmospheric particulate matter indicates (a) degradation of PBC, potentially through photodegradation and leaching, and/or (b) availability of an enriched source other than fluvial or aeolian inputs. This evidence for degradation of PBC in aquatic systems warrants rethinking on its C sequestration potential and role in aquatic C biogeochemistry and further raises concerns regarding the use of sedimentary BC as a paleoenvironmental proxy.

Paleoenvironment reconstruction of the eastern Tethys during the pre-onset excursion preceding the PETM

A rapid warming event known as the pre-onset excursion (POE) occurred prior to the Paleocene-Eocene Thermal Maximum (PETM). It is less well studied compared to the PETM due to the limited number of well-resolved records globally despite its importance in shaping the subsequent PETM. Shallow marine environments, particularly in low latitudes, are insufficiently documented despite their significant influence on heat and moisture distribution. Here we report high temporal resolution geochemical and magnetic susceptibility records from a well-preserved shallow marine Kuzigongsu section in the Tarim Basin in China to reconstruct the paleoenvironment of the eastern Tethys during the POE. Changes in chemical weathering proxies (e.g., chemical index of alteration [CIA] and Rb/Sr) suggest chemical weathering intensification occurred after the POE. Higher enrichment factors of P, Ba, Ni, and Cu support increased primary productivity due to enhanced river runoff and nutrient input, which aligns with the observed rise in magnetic susceptibility. Concurrently, the eastern Tethys experienced bottom water deoxygenation, which is supported by redox-sensitive proxies (e.g., elevated enrichment factors of U and V, and low Mn* values). Increased δ15Norg values provide additional evidence of enhanced reduction processes due to increased productivity, attributed to enhanced denitrification and 15N enrichment in seawater's NO3− reservoir. The carbon isotope excursion during the POE recovers significantly faster than that during the PETM yet coincides with lingering environmental impacts that are also globally reported for the PETM. These paleoenvironmental proxies reflect notable changes in chemical weathering, ocean productivity, and redox conditions of the eastern Tethys region, potentially setting the stage for the anomalously impactful PETM.

Variability of leaf wax n-alkanes across gradients of environment and plant functional type in China

The abundance and distribution of long-chain n-alkanes in sedimentary archives have been proposed as plant-derived paleoenvironmental proxies. The reliable application of these proxies hinges on comprehensive understandings drawn from investigations of living plants. However, previous studies have predominantly relied on narrow environmental gradients and limited datasets sourced from local and regional sampling. As a result, our comprehension of how n-alkanes in living plants respond to climate factors on larger spatial scales remains unclear, especially across different plant functional types (PFTs). In this study, we analyzed the abundance and distribution of n-alkanes in the leaves of 552 plant samples from diverse regions in China and explored the variability of leaf wax n-alkanes across gradients of climate and PFTs. Average chain length (ACL) and carbon preference index (CPI) exhibit statistically significant differences between various PFTs, and the ratio of C33/(C31 + C33) holds the potential to distinguish between C3 and C4 vegetation types. The n-alkane concentration (Σalk) is primarily controlled by precipitation, with a notable negative correlation between Σalk and mean annual precipitation (MAP) that is independent of PFTs. Overall, ACL is negatively related to MAP and positively to mean annual temperature (MAT), but the relationship varies across PFTs. MAT is a stronger driver of ACL for C4 herbs and woody plants, while MAP exerts a more pronounced influence on C3 herbs. CPI in most PFTs shows no correlation with environmental variables. These findings indicate Σalk is a good indicator of precipitation, and ACL is indicative of precipitation or temperature depending on the specific PFT; CPI appears unsuitable as a climate indicator and great caution should be exercised in using CPI records in paleoclimate research.

Paleoenvironmental variations during the Late Cambrian: Implications from Zn isotopes, I/(Ca+Mg) ratios, and other elemental proxies

The Upper Cambrian at the Martin Point section (∼110 m-thick) in western Newfoundland is a part of the Cow Head Group and partially spans the coeval Tuckers Cove and the Martin Point members of the Shallow Bay and Green Point formations, respectively. These units comprise alternating shale, minor conglomerate beds, and limestone rhythmites of a toe-of-slope apron. Earlier studies of the C-isotope profile, based on the lime mudstone interbeds, documented global negative δ13Ccarb shifts (from old to young: NL1, NL2, HERB) correlated with the lowermost Proconodontus posterocostatus, Proconodontus muelleri and base of Eoconodontus notchpeakensis conodont zones, respectively (post-Steptoean Positive Carbon Isotope Excursion NL1 and NL2 and Hellnmaria-Red Tops Boundary-HERB). Samples were extracted from the most preserved spots of micritic to near-micritic grain size (≤4 μm−10 μm). Fabric retention confirms petrographic preservation and insignificant correlations (R2 ≤ 0.1) of diagenetic proxies (e.g., Sr) with their environmental counterparts support the preservation of at least near-primary geochemical signatures. The paleoenvironmental proxies (TOC, Zn, P, Cu, Al/Ti, Mn, Fe, V, Mo) support dominant dysoxic conditions. The δ66Zn values (0.09–0.73 ‰ JMC Lyon) and (I/(Ca + Mg)) ratios (0.02–0.48 μmol/mol) vary consistently throughout the studied events. The minor decreases in δ66Zn values seem to denote inhibition of bioproductivity in a dysoxic water column, consistent with warm and humid climate during general transgressive settings and shoaling of organic-rich water into the shallow environment. The low I/(Ca + Mg) ratios (<0.5 μmol/mol) reinforce this interpretation, suggesting general dysoxic settings throughout the entire section.

δ18O variability in guanaco bone bioapatite in Southern Patagonia: Implications for paleoecological and paleoenvironmental studies

The guanaco (Lama guanicoe) is the largest and the most widely distributed ungulate in South America since the Pleistocene and constituted the main prey for hunter-gatherers in Southern Patagonia (Argentina) in the past. An isomorphic relationship has been suggested between the mobility of these animals and that of human groups that inhabited the region, which presents altitudinal differences. On the one hand, we seek to understand the spatial dynamics of guanaco populations and their interaction with hunter-gatherer societies. On the other hand, to evaluate the utility of archaeological herbivores' values as paleoenvironmental proxies that allow addressing the environmental variations during the Holocene in the region. We present the results of the analysis of δ18O in bioapatite of Lama guanicoe bone specimens from the area located in the central-western area of the province of Santa Cruz, between 70 and 72 degrees west longitude. We analyzed 41 samples. 22 of them correspond to modern individuals, while the remaining 19 were recovered from Holocene archaeological sites. The carbonate-phosphate and estimated water equations will be used to compare with pre-existing data of δ18O in the waters of the region. Results showed that the mean value of δ18O of the pooled samples was −6.5 ‰ ± 1 ‰. Even though some differences were detected, both, between archaeological vs. modern and between highlands vs. lowlands samples, no statistically significant differences were obtained in either case. In general terms, the data respond to what was expected regarding the complex nature of the water intake behaviors of these animals. The data presented in this paper constitutes a first approximation to the expected values of δ18O for guanacos in the region, its relationship with the hydrological cycle and human populations.

Copper and zinc isotopic compositions of methane-derived carbonates: Implications for paleo-methane seepage and paleoenvironmental proxies

Copper and zinc isotopic compositions of methane-derived carbonates: Implications for paleo-methane seepage and paleoenvironmental proxies

Potential impacts of cable bacteria activity on hard-shelled benthic foraminifera: implications for their interpretation as bioindicators or paleoproxies

Abstract. Hard-shelled foraminifera are protists able to build a calcareous or agglutinated shell (called a “test”). Here we study the impact of sediment acidification on calcareous test preservation. For this study, sediment cores were sampled in the macrotidal Auray estuary located on the French Atlantic coast. Living and dead foraminifera were quantified until 5 cm depth and discriminated using the Cell-Tracker™ Green vital marker. The pH and oxygen profiles combined with quantitative polymerase chain reaction (qPCR) suggested that cable bacteria were most likely to cause the acidifying process. Cable bacteria (CB) are filamentous bacteria coupling sulfide oxidation to oxygen reduction over centimetre distances, generating a strong pH gradient within the first few centimetres of the sediment that could affect the microhabitats occupied by benthic foraminifera. On two different intertidal mudflats, volumetric filament densities have been estimated. They were comparable to those observed in the literature for coastal environments, with 7.4 ± 0.4 and 74.4 ± 5.0 m cm−3 per bulk sediment, respectively. Highly contrasting sediment acidification (from low to very intense) was described from 1.0 to 2.4 ΔpH. This seems to lead to various dissolution stages of the foraminiferal calcareous test from intact to fully dissolved tests revealing the organic lining. The dissolution scale is based on observations of living Ammonia spp. and Haynesina germanica specimens under a scanning electronic microscope. Furthermore, dead foraminiferal assemblages showed a strong calcareous test loss and an organic lining accumulation throughout depth under low pH, hampering the test preservation in deep sediment. These changes in both living and dead foraminiferal assemblages suggest that cable bacteria must be considered in ecological monitoring and historical studies using foraminifera as bioindicators and paleoenvironmental proxies.

Bonneville basin critical zones

Playa margin wetlands in the Bonneville basin are sustained by groundwater-fed brackish springs, which transport salts and other solutes into the playa basin. These wetlands are sensitive to changing water availability and quality, which are impacted by changing climate and land use, and whose sediments also provide important records of changing environmental conditions. Gastropods building their shells in these springs provide important recorders of water chemistry and may reflect changing aqueous conditions. In this paper, we analyze spring water chemistry, gastropod ecology and gastropod shell chemistry of Blue Lake (BL) and Horseshoe Springs (HRS), two groundwater-fed wetlands in the Great Salt Lake watershed. We report the physical parameters including pH, temperature, and specific conductivity across the spring pond at Horseshoe springs. There was a slight but statistically significant variation in these physical characteristics between the deeper and shallower parts of the pool, providing evidence that there are different subsite microclimates, which may impact the populations and the isotopic composition of gastropod shells. We measured gastropod population diversity amongst nearly 12,000 shells sampled at Horseshoe springs, finding low population diversity (Shannon’s Diversity Index of 0.432), although the populations of shallow and deep snails are slightly different. The dominant snail at HRS is the Pyrgulopsis which is imperiled, and we also note that we did not find living snails here. We evaluated the bulk shell variation of stable carbonate isotopes (δ13C, and δ18O) across sites and genera. We show that there were no significant subsite-level differences in gastropod δ13C compositions, suggesting that water depth and productivity were not impacting the isotopic signal. We found subsite- and genera-specific differences in snail δ18O compositions, which we interpret to be more dependent on the geography and microclimate of where the snail lived rather than the genera’s physiology (pulmonate versus gil-breathing). We report concentrations of alkali metals (Li, Na, K, Rb, Cs), alkali earth metals (Be, Mg, Ca, Sr, Ba), and metals and metalloids (Al, Sc, Mn, Fe, Cu, Ni, Zn, As) at spring site waters and in bulk shells as potential baseline data for interpreting future or past environmental changes as recorded in shell material. We found trace element concentration and certain elemental ratio differences between genera at the same site (particularly of note were Li, Zn, Mn and Al) that will be important to constrain if these shells are to be applied as a paleoenvironmental proxy and are sometimes attributed to land use change.