The present study provides an example of how palaeopedology and facies analysis may be integrated for the interpretation of a cyclothemic succession in the Upper Pliocene (Piacenzian) of the Valdelsa ...Basin (central Italy). The stacking of facies and intervening bounding surfaces, including palaeosols, outline a hierarchy of elementary (EDS) and composite (CDS) depositional sequences within the unconformity-bounded stratigraphic units (S4-S6 synthems) which compose the succession. The focus of the study is on synthem S4 and the transition to synthem S5. Synthem S4 records the development of a distal alluvial plain dominated by floodbasin mudstone with subordinated channelized sandstone (S41), followed by the incision of a fluvial valley aggraded by the cyclical stacking of braided and low sinuosity channelized conglomerate and sandstone (S42). Synthem S5 includes lower shoreface sandstone and inner shelf mudstone related to a major transgression which affected the study area during the late Piacenzian. Evidence of soil-forming processes is well preserved within sub-unit S41 where five palaeosols (PS4a-e) are stacked within the facies architecture of EDS1c-d, both being defined as transgressive to high stand tracts. Increasing palaeosol development was observed within both EDSs, while palaeosols were generally thicker and more closely stacked within EDS1d. Palaeosols were interpreted as marking minor cycles of accommodation space creation within EDS1c, while marking a better defined high stand tract in EDS1d.
Increasing upward soil development was observed within each EDS, with generally better developed soils in EDS S41d. The unconformable transition from S4 to S5 is marked by a thin veneer of slope deposits, bearing pedogenic carbonates reworked from a missing PS4f palaeosol, formed during the shaping of the erosional surface separating sub-units S41 and S42. The results of this study indicate that: 1) the sedimentary and pedogenic processes recorded in the channelized facies and palaeosols in the floodbasin facies of sub-unit S41, are coherent with a palaeoenvironmental setting dominated by seasonal climate; 2) the facies-palaeosol architecture of S4 synthem corresponds to those described in sequence-stratigraphic models applied to continental successions. The pedo-sedimentary signature of the major sea-level fluctuation recorded in the transition between S4 and S5 synthem differs from these models. In this case a well-developed and drained palaeosol, expected to record the maximum regressive surface shaped during the falling stage of sea level, is missing. This difference is related to a rapid fall and subsequent rise of relative sea level which marked the transition between S4 and S5 synthems.
•Palaeosol and facies analysis coherently restore a Piacenzian fluvial system.•A seasonal climate controlled sediment dispersal and weathering.•Palaeosols are key-surfaces in the cyclical fluvial facies architecture.•Cyclothemic stack of palaeosols partially fits sequence-stratigraphic models.•Major sequence boundary lacks a well developed palaeosol.
Seagrass conservation is critical for mitigating climate change due to the large stocks of carbon they sequester in the seafloor. However, effective conservation and its potential to provide ...nature-based solutions to climate change is hindered by major uncertainties regarding seagrass extent and distribution. Here, we describe the characterization of the world's largest seagrass ecosystem, located in The Bahamas. We integrate existing spatial estimates with an updated empirical remote sensing product and perform extensive ground-truthing of seafloor with 2,542 diver surveys across remote sensing tiles. We also leverage seafloor assessments and movement data obtained from instrument-equipped tiger sharks, which have strong fidelity to seagrass ecosystems, to augment and further validate predictions. We report a consensus area of at least 66,000 km
and up to 92,000 km
of seagrass habitat across The Bahamas Banks. Sediment core analysis of stored organic carbon further confirmed the global relevance of the blue carbon stock in this ecosystem. Data from tiger sharks proved important in supporting mapping and ground-truthing remote sensing estimates. This work provides evidence of major knowledge gaps in the ocean ecosystem, the benefits in partnering with marine animals to address these gaps, and underscores support for rapid protection of oceanic carbon sinks.
The ability of the subtropical North Atlantic to sustain export production despite the lack of available nutrients is fascinating. Subtropical gyres are expected to expand under a global warming ...scenario, so it is important to understand the mechanisms supplying the required nutrients. Current issues for the region concern the nutrient and metabolic balance, the origin of excess nitrogen and phosphorus shortage, and the maintenance of nitrogen fixation. We report data on the allocation of nitrogen and phosphorus in dissolved and suspended pools, the isotopic δ15N of suspended nitrogen, and the lability of dissolved organic phosphorus (DOP) along a section crossing the eastern seasonally stratified North Atlantic and the western subtropical North Atlantic (NASW). We find extreme P‐deficiency in the NASW, with the highest dissolved inorganic N:P ratios located within the upperthermocline isopycnals (σϴ = 26.3–26.8). Our data indicate an important role of the midlatitude northeast seasonally stratified North Atlantic bringing dissolved organic matter (DOM) to the thermocline of the North Atlantic. The mineralization of N‐rich DOM contributes to the N excess (P deficit) of the upperthermocline of NASW. We find lower concentrations of more reactive DOP in the western than in the eastern part of the transect, indicating an active role of DOP in the nutrition of microbial communities. Our results support recent hypotheses concerning the environmental controls of marine nitrogen fixation identifying the key role of DOP utilization.
Key Points
Upperthermocline isopycnals import excess organic nitrogen
Lateral transport of subsurface waters with high N:P ratio reinforces the P deficit of the western subtropical North Atlantic
Nitrogen fixation can be maintained by the highly reactive DOP despite the high N:P ratio of inorganic supply
Rationale
Stable carbon isotope ratios have many applications in natural sciences. In the first worldwide interlaboratory proficiency test, the discrepancies in measured δ13CDIC values of natural ...waters were up to σ = ±3‰. Therefore, we continued the investigation on the analytical data quality assurance of individual laboratories and internal consistency among laboratories worldwide.
Methods
We designed and performed an interlaboratory comparison exercise for δ13C analyses of ten water and two solid samples (Na2CO3, CaCO3), including two synthetic samples prepared by dissolving the carbonates individually. Three laboratories analyzed an additional sample set to assess solution stability, at least one month after the first set analysis period. The δ13C values were measured using dual inlet isotope ratio mass spectrometry (DI‐IRMS) or continuous flow (CF)‐IRMS.
Results
The δ13C values of solid Na2CO3 and its aqueous solution were −5.06 ± 0.21‰ and 5.32 ± 0.24‰, respectively, while the δ13C value of solid CaCO3 was −4.49 ± 0.93‰. Similarly, the lake water has a consistent value (2.45 ± 0.19‰). The δ13C values of geothermal water have a wide dispersion among individual laboratory measurements and among those of different laboratories; however, a trend exists in the δ13C values measured at the three sampling points of each well.
Conclusions
The δ13C values of solid Na2CO3 and its solution, and lake water (i.e. DIC concentration samples >100 mg/L carbon) are consistent among all the participating laboratories. The dispersion in the δ13C values of solid CaCO3 is associated with its lower chemical affinity than that of Na2CO3. The poor reproducibility in the δ13C values of geothermal fluids, collected at three points of a geothermal well, despite overall consistent trends regarding their collection points suggests inadequate sample handling (atmospheric CO2 exchange) and/or inappropriate analytical approaches (incomplete H3PO4 acid reaction).
Recent studies have proved that high elevation environments, especially remote wetlands, are exceptional ecological sensors of global change. For example, European glaciers have retreated during the ...20
century while the Sierra Nevada National Park in southern Spain witnessed the first complete disappearance of modern glaciers in Europe. Given that the effects of climatic fluctuations on local ecosystems are complex in these sensitive alpine areas, it is crucial to identify their long-term natural trends, ecological thresholds, and responses to human impact. In this study, the geochemical records from two adjacent alpine bogs in the protected Sierra Nevada National Park reveal different sensitivities and long-term environmental responses, despite similar natural forcings, such as solar radiation and the North Atlantic Oscillation, during the late Holocene. After the Industrial Revolution both bogs registered an independent, abrupt and enhanced response to the anthropogenic forcing, at the same time that the last glaciers disappeared. The different response recorded at each site suggests that the National Park and land managers of similar regions need to consider landscape and environmental evolution in addition to changing climate to fully understand implications of climate and human influence.
Rising temperatures in the Arctic Ocean are causing sea ice and glaciers to melt at record breaking rates, which has consequences for carbon cycling in the Arctic Ocean that are yet to be fully ...understood. Microbial carbon cycling is driven by internal processing of in situ produced organic carbon (OC), however recent research suggests that melt water from sea ice and glaciers could introduce an allochthonous source of OC to the microbial food web with ramifications for the metabolic balance of plankton communities. In this study, we characterized autochthonous and allochthonous sources of OC to the Western Svalbard fjord system using stable isotopes of carbon. We quantified δ
13C of eukaryotic and prokaryotic planktonic groups using polar lipid-derived fatty acids as biomarkers in addition to measuring δ
13C of marine particulate OC and dissolved OC from glacial runoff. δ
13C of bacteria (-22.5&) was higher than that of glacial runoff OC (-28.5&) and other phytoplankton groups (-24.7 to -29.1&), which suggests that marine bacteria preferentially use a third source of OC. We present a Bayesian three-source δ
13C mixing model whereby ~ 60% of bacteria carbon is derived from OC in sea ice, and the remaining carbon is derived from autochthonous production and glacial-derived OC. These results suggest that subsidies of OC from melting glaciers will not likely influence microbial carbon cycling in Svalbard fjords in the future and that further research is needed to determine the effects of melting sea ice on microbial carbon cycling in fjord systems and elsewhere in the Arctic Ocean.
Summary
Plant–plant interactions shape the structure and composition of plant communities, but shifts in interaction outcomes might occur in the face of ongoing climate change.
We assessed the ...influence of Pinus halepensis plantations on the long‐term ecophysiological performance of understorey vegetation, by conducting a retrospective comparison (1989–2007) of growth‐ring widths, δ13C and δ18O between Rhamnus lycioides shrubs from two contrasting vegetation types: P. halepensis plantations vs. open woodlands. We also measured the leaf δ13C, δ18O, δ15N, and nutrient concentrations of understorey R. lycioides shrubs growing at varying distances from planted trees within pine plantations.
Dendroecological and stable isotope data revealed strong competitive effects of planted P. halepensis trees on R. lyciodies. Shrubs in pine plantations showed lower radial growth and higher growth ring δ13C and δ18O than those in open woodlands, indicating lower stomatal conductance and photosynthesis in the former. The strong competitive effects of P. halepensis on understorey R. lycioides were most evident in wet, productive years. Conversely, in very dry years, there were indications of a facilitative effect of planted P. halepensis canopies on understorey shrubs.
Within pine plantations, understorey R. lycioides shrubs growing at shorter distances from planted trees were forced to rely on more superficial and ephemeral soil water sources, which reduced their stomatal conductance (higher leaf δ18O) and interfered with nutrient uptake (lower leaf N and P concentrations and more negative δ15N).
The intrinsic water use efficiency of R. lycioides shrubs growing in open woodlands has increased during recent decades as a result of their ability to adjust their stomatal conductance in response to increasing temperature and atmospheric CO2. However, this adaptive response was much weaker or absent in the severely drought‐stressed shrubs from pine plantations.
Pine afforestation strongly reduces water and nutrient availability for understorey shrubs in drylands, with potential long‐term consequences for ecosystem biodiversity, structure and functioning. Competition by P. halepensis on R. lycioides clearly outweighed facilitation in the long‐term, thus compromising the ability of understorey shrubs in semi‐arid pine plantations to cope with climate change.
Lay Summary
Isotopic values of two Caribbean sharpnose shark Rhizoprionodon porosus litters (Poey, 1861) with two and three embryos and one litter of 11 smalltail shark Carcharhinus porosus embryos showed ...enriched 15N and 13C compared to their mothers. In R. porosus, embryonic isotope values were 3.06 ± 0.07‰ and 0.69 ± 0.15‰ greater than their mothers' for δ15N and δ13C, respectively, whereas in C. porosus, δ15N and δ13C were 1.79 ± 0.09‰ and 1.31 ± 0.17‰ greater in embryos than their mothers.
Lead poisoning is not a new threat for wild birds, but it is now playing an important role in shaping raptor populations. Studies have been focused mainly on Europe, North-America, and Japan, but ...little is known about the situation in South-America. Lead is a serious threat for wildlife, especially for long-lived species. Nevertheless, no information is available for wild Andean condor (
Vultur gryphus) populations. This species, which lives throughout the Andes Mountains, is endangered mainly in the north though it is having problems throughout its distribution. We evaluated lead exposure in the Andean condor by a non-destructive method using feathers. We determined lead concentration from 152 feathers, collected in 15 communal roosts distributed throughout almost all condor’s range in Patagonia (ca. 1500
km north–south). We also looked for the origin of this lead through the analysis of lead isotope composition of feathers and ammunition. We present here the first reference data on lead concentration for a raptor population from Argentina. Lead concentrations were generally low, however, some individuals had concentrations several times above the overall mean (up to 21
μg/g). Our results suggest that lead might come from a mix of two types of ammunition sources, one used for big game and another for hare hunting. Andean condors are at the top of the food chain, thus all the other medium-to-large sized scavengers and predators from this area can be also exposed to this threat. We highlight the need to change hunting policies in Argentina, and in other South-American countries, including the banning of lead ammunitions to protect carnivores consuming hunted animals.
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