This study presents a methodological advancement in the field of clumped‐isotope (∆47) thermometry, specifically tailored for application to freshwater ostracods. The novel ostracod clumped isotope ...approach enables quantitative temperature and hydrological reconstruction in lacustrine records. The relationship between ∆47 and the temperature at which ostracod shell mineralized is determined by measuring ∆47 on different species grown under controlled temperatures, ranging from 4 ± 0.8 to 23 ± 0.5ºC. The excellent agreement between the presented ∆47 ostracod data and the monitored temperatures confirms that ∆47 can be applied to ostracod shells and that a vital effect is absent outside the uncertainty of measurements. Results are consistent with the carbonate clumped‐isotope unified calibration (Anderson et al., 2021, https://doi.org/10.1029/2020gl092069), therefore, an ostracod‐specific calibration is not needed. The ostracod clumped‐isotope thermometer represents a powerful tool for terrestrial paleoclimate studies all around the world, as lakes and ostracods are found in all climatic belts.
Plain Language Summary
In the framework of global warming, the reconstruction of past climatic conditions is important to understand the future evolution of climate and its impact. Lake sediments can be used as archives to quantify these effects. This study presents a novel paleo‐thermometer based on the application of clumped‐isotope technique (i.e., measurement of the number of 13C–18O bonds in carbonate minerals that depends on the temperature of carbonate precipitation) on carbonatic microcrustacea, named ostracods that commonly live in lakes. By using ostracods that formed their shells at known temperatures, we demonstrate that they can be easily used to reconstruct water temperature and hydrological conditions (precipitation/evaporation). The ostracod clumped‐isotope thermometer represents a powerful tool for terrestrial paleoclimate studies around the world, as lakes and ostracods are located in all climatic belts.
Key Points
∆47—ostracod signal accurately records the shell calcification temperature
∆47—ostracod signal is not affected by the so called “vital effect”
The unified calibration of Anderson et al. (2021) can be used to convert the ∆47—ostracod signal into accurate temperatures
Available DNA barcodes of freshwater zooplankton are scarce in regions like the Iberian Peninsula, which harbours many rare and endemic species and is considered a hotspot of crustacean biodiversity. ...Recently, a new species of Ceriodaphnia (Cladocera: Daphniidae) was described using morphological analysis of specimens in the Mediterranean region and molecular data on a single locality in southern Spain. In our study, we detected the presence of the newly discovered taxa and here, we provide new DNA sequences on the barcoding region mitochondrial cytochrome c oxidase I together with ecological information of the recently described Ceriodaphnia smirnovi. Additionally, we built a molecular phylogenetic tree and genetically compared these specimens with previously available mitochondrial DNA sequences and with new sequences of the genus recovered in Iberia. Our data suggest that this morphospecies might contain some cryptic taxa and might be more common than previously thought, occupying temporary to semi‐permanent ecosystems, with vegetation and highly variable pH and turbidity conditions. Moreover, the existence of a non‐identified clade within our phylogenetic tree requires additional morphological research. Our study highlights the need for further research on microcrustacean biota to better constrain its spatial boundaries, phylogenetic relationship and determine species hiding cryptic diversity.
Palaeoenvironmental reconstructions from fossil mammals are based on the straightforward relationship between the environment and the mammal assemblage living in the area. However, in some cases the ...environmental variables estimated from mammals are biassed by local influences. The palaeoenvironmental reconstruction of the Granada Basin (southern Spain) based on carbon and oxygen isotopes from enamel rodent teeth is compared with the palaeoenvironmental data from small mammal assemblages. Estimated temperatures from both proxies coincide, in general terms: cold-temperate conditions during the latest Tortonian (~16°C; cold-temperate climate), dry sub-tropical conditions during the Messinian (16.6°C–22°C), and dry sub-tropical conditions during the early Pliocene (16.6°C–17.2°C). Reconstructed humidity trends from both proxies only agree in the first part of the record, showing dry conditions during the Tortonian–Messinian boundary and an increase in humidity at the beginning of the Messinian. During the Messinian and earliest Pliocene, humidity trends in each proxy are frequently opposed: small mammal assemblages suggest a huge increase in humidity at the beginning of the Messinian, and a decreasing trend towards the Pliocene, whereas carbon isotopes from rodent teeth suggest moderate humidity conditions during the Messinian. It can be concluded that physical changes in the landscape would affect taxa with high dependence on humid conditions, and they are more likely to record local environmental humidity changes rather than regional or global humidity ones. However, the past reconstructions of temperatures are not biassed by this effect, as the general temperature trends deduced from the faunal assemblages as well as those deduced from the isotopic approaches coincide. The general climatic trends reconstructed from isotopic analyses in small mammal teeth agree with the general environmental change in the western Mediterranean region as well as with the global evolution of sea temperatures.
Situation maps and comparison between the temperature reconstruction from isotopic data and that based on the palaeoecology of the small mammal associations in the Granada Basin (García-Alix et al., 2008b), the humidity reconstruction from isotopic data and those based on the palaeoecology of the small mammal associations in the Granada Basin, as well as the sedimentary and environmental evolution of the Granada Basin according to García-Alix et al. (2008b). The estimated absolute age of the studied fossil localities has been taken from García-Alix et al. (2008a, 2008b). Fossil locality acronyms are the same as in Table 1. Display omitted
•Isotopic data of Mio–Pliocene fossil rodent teeth were obtained in southern Spain.•Dry cold temperature and dry subtropical climates were recognized through time.•The deduced palaeoenvironments were compared with those of the fossil assemblages.•Fossil small mammals as a humidity proxy might be biassed by local environmental factors.•Temperature from fossil remains and isotopic data coincide suggesting regional trends.
Tierra del Fuego in Argentina is a unique location to examine past Holocene wind variability since it intersects the core of the Southern Hemisphere Westerly Winds (SHWW). The SHWW are the most ...powerful prevailing winds on Earth. Their variation plays a role in regulating atmospheric CO2 levels and rainfall amounts and distribution, both today and in the past. We obtained a piston core (LF06‐PC8) from Bahía Grande, a protected sub‐basin at the southern margin of Lago Fagnano, the largest lake in Tierra del Fuego. This article focuses on the uppermost 185 cm of this core, corresponding to laminated sediment from the last ~6.3 ka. Laminations consist of millimetre‐scale paired dark and light layers. Previous studies and new geochemical analysis show that the dark and light layers are characterized by differing concentrations of Mn and Fe. We attribute the distribution of Mn and Fe to episodic hypolimnic oxic–anoxic variations. The age model suggests an approximately bidecadal timescale for the formation of each layer pair. We propose a new model of these redox changes with the SHWW variations. The most likely phenomenon to produce complete water‐column mixing is thermobaric instability, which occurs in colder winters with low‐intensity SHWW (El Niño‐like conditions). In contrast, windier winters are characterized by higher temperatures and reduced mixing in the water column, facilitating a decline in oxygen concentration. Laminations, and the inferred presence of periodic hypolimnion redox changes, are common features of the past ~6.3 ka. Geochemical proxy variability is compatible with an intensification of El Niño/Southern Oscillation activity during the past ~2 ka.
Aim: The Messinian salinity crisis (MSC) was an extraordinary geological event that affected the whole Mediterranean region as well as the global marine circulation between 5.97 and c. 5.33 Ma. One ...of its most direct effects was the emersion of land masses and the subsequent establishment of land bridges that led to common terrestrial faunal exchanges. However, the details of the onset of these exchanges have been a matter of controversy. New findings from southern Iberia of small mammal remains with African similarities have enabled us to review the Messinian faunal exchanges in the Mediterranean region. Location: Mediterranean region. Methods: Small mammal remains with African similarities from two new southern Iberian sites were studied. The small mammal associations of eight Miocene-Pliocene North African sites were also reviewed. Results: Two taxa with African similarities were identified at the Iberian study sites: Debruijnimys almenarensis and a Ruscinomys-like form (cf. Ruscinomys) with a strong spur in the lingual lobe of the anterocone in the M¹, a feature observed in North African Ruscinomys and eastern Mediterranean Byzantinia. The taxonomic status of some North African species and/or genera, such as Castillomys, Occitanomys and Prolagus, should be revised according to the new phylogenetic relationships established in European faunas. Main conclusions: Two hypotheses can be proposed for the origin of the African Ruscinomys: (1) among the Iberian Ruscinomys or (2) from the eastern Mediterranean Byzantinia. Our data, currently from only a few, albeit significant, taxa, tend to support an Iberian origin. The discussion presented in this paper suggests an age near the closure of the last Betic Gateway (c. 6.18 Ma) for the first small mammal exchange between Africa and Europe, as well as a single migratory wave of small mammals, filtered by their ecological preferences from this point until the end of the MSC.
A high-resolution multi-proxy approach, integrating pollen, inorganic and organic geochemical and sedimentological analyses, has been carried out on the Holocene section of the Padul sedimentary ...record in the southern Iberian Peninsula reconstructing vegetation, environment and climate throughout the last ~ 11.6 cal kyr BP in the western Mediterranean. The study of the entire Holocene allows us to determine the significant climate shift that occurred during the middle-to-late Holocene transition. The highest occurrence of deciduous forest in the Padul area from ~ 9.5 to 7.6 cal kyr BP represents the Holocene humidity optimum probably due to enhanced winter precipitation during a phase of highest seasonal anomaly and maximum summer insolation. Locally, insolation maxima induced high evaporation, counterbalancing the effect of relatively high precipitation, and triggered very low water table in Padul and the deposition of peat sediments. A transitional environmental change towards more regional aridity occurred from ~ 7.6 to 4.7 cal kyr BP and then aridification enhanced in the late Holocene most likely related to decreasing summer insolation. This translated into higher water levels and a sedimentary change at ~ 4.7 cal kyr BP in the Padul wetland, probably related to reduced evaporation during summer in response to decreased in seasonality. Millennial-scale variability is superimposed on the Holocene long-term trends. The Mediterranean forest regional climate proxy studied here shows significant cold-arid events around ~ 9.6, 8.5, 7.5, 6.5 and 5.4 cal kyr BP with cyclical periodicities (~1100 and 2100 yr) during the early and middle Holocene. A change is observed in the periodicity of these cold-arid events towards ~1430 yr in the late Holocene, with forest declines around ~ 4.7–4, 2.7 and 1.3 cal kyr BP. The comparison between the Padul-15-05 data with published North Atlantic and Mediterranean paleoclimate records suggests common triggers for the observed climate variability, with the early and middle Holocene forest declines at least partially controlled by external forcing (i.e. solar activity) and the late Holocene variability associated with internal mechanisms (oceanic-atmospheric).
•We carried out a multi-proxy analysis for the last 11.6 cal kyr BP from a new sedimentary record from Padul (Sierra Nevada, Spain).•This record shows a long-term climate pattern mostly forced by insolation, showing a significant climate and environmental shift at 4.7 cal kyr BP.•Millennial-scale climate oscillations are also characterized in this study by the decrease in Mediterranean forest and local response in the lake level, showing possible atmospheric and climate links between the western Mediterranean and North Atlantic areas.
Alpine regions of the Mediterranean realm are among the most climatically sensitive areas in the world. Thus, alpine wetlands from the southern Iberian Peninsula, in the westernmost part of the ...Mediterranean region, are highly sensitive sensors of environmental changes. Difficulties have surfaced in separating controls by temperature and/or precipitation in previous paleoenvironmental studies from alpine environments in this area. We present a Holocene biomarker record (n-alkanes and long-chain diols) from a high elevation lake, Laguna de Río Seco (LdRS), in the south of the Iberian Peninsula, which contributes to the identification of these forcing mechanisms. The hydrological history of the area, primarily water availability and evapotranspiration, is reconstructed by means of the n-alkane record, including the indices of average chain length, portion aquatic, and carbon preference index, as well as hydrogen isotopes (δD) of aquatic (δDaq) and terrestrial (δDwax) n-alkanes. Temperatures are also estimated using the algae derived long-chain diols. We interpret δDaq and δDwax fluctuations as showing changes in the source and amount of precipitation throughout the LdRS record. An Atlantic precipitation source appears to have predominated during the early-middle Holocene, but an occasional Mediterranean influence with an isotopic enrichment in precipitation is detected in the middle-late Holocene that is likely related to the setting of the current atmospheric pattern in southeastern Iberia under the joint control of the North Atlantic Oscillation (NAO) and the Western Mediterranean dynamics, such as the Western Mediterranean Oscillation (WeMO). Our new record from LdRS is consistent with a generalized trend of a humid early-middle Holocene with low temperature variability, evolving towards an arid middle-late Holocene with abrupt temperature changes. In addition to these long-term trends during the last ∼10,500 years, two phases of climate instability, evidenced by abrupt depletions in δDaq, have been identified at the end of these periods, one between ∼6500 and 5500 cal yr BP and another in the last ∼500 years. These episodes would represent strengthened winter cold conditions that favoured the persistence of snowpack and frozen soil in the catchment, causing reduced terrestrial plant growth and low lake evaporation. According to the long-chain diol record, temperatures during these phases were relatively low, but experienced abrupt increases at the end of each period.
•Algal and plant lipids reconstruct Holocene environments in South Iberia alpine wetlands.•First reconstruction of Holocene temperatures and hydrology in South Iberia alpine wetlands.•Wet climate and Atlantic precipitation sources predominate in the early-middle Holocene.•Arid climate and occasional Mediterranean moisture sources lead the middle-late Holocene.•Climate instability phases have been identified in both middle and latest Holocene.
Abstract
The Muslim expansion in the Mediterranean basin was one the most relevant and rapid cultural changes in human history. This expansion reached the Iberian Peninsula with the replacement of ...the Visigothic Kingdom by the Muslim Umayyad Caliphate and the Muslim Emirate of Córdoba during the 8th century CE. In this study we made a compilation of western Mediterranean pollen records to gain insight about past climate conditions when this expansion took place. The pollen stack results, together with other paleohydrological records, archaeological data and historical sources, indicate that the statistically significant strongest droughts between the mid-5th and mid-10th centuries CE (450–950 CE) occurred at 545–570, 695–725, 755–770 and 900–935 CE, which could have contributed to the instability of the Visigothic and Muslim reigns in the Iberian Peninsula. Our study supports the great sensitivity of the agriculture-based economy and socio-political unrest of Early Medieval kingdoms to climatic variations.
A combination of microfossil assemblages, abundance of fossil ephippia and mean body size provides the longest paleoclimatic reconstruction based on cladoceran subfossils in the Iberian Peninsula. ...Species turnover in Laguna de Río Seco (Sierra Nevada, southern Spain) was controlled by changes in lake levels in response to fluctuations in hydroclimatic variability over the last ∼8600 years. Our archive documents a wet period in the Early and Middle Holocene (∼8600–5000 cal yr BP), characterized by eurytopic and plant-associated species. A drier stage occurred from ∼5000 cal yr BP and implied a reduction in lake level and higher occurrence of species highly adapted to more ephemeral environments. Proportions of total chydorid ephippia (TCE), indicating rates between asexual and sexual reproduction, are well-correlated with a progressive trend towards aridification. Lower TCE was registered before ∼5000 cal yr BP as a result of a favourable environment under higher lake level, while higher TCE started with the upcoming arid stage (∼5000 cal yr BP) due to environmental stress. Besides these hydrological signatures, data on Daphnia size broadly indicate a warmer period ∼8600–4000 cal yr BP and a colder stage ∼4000–255 cal yr BP. Further investigations using this indicator in the Sierra Nevada will provide more precise reconstructions of past climatic conditions in southern-latitude and alpine ecosystems.
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•Precipitation and temperature were reconstructed in southern Spain for the Holocene.•Cladoceran assemblages indirectly respond to variables modulated by precipitation.•Daphnia size was used as an indicator of the ice-free season length.•The Early and Middle Holocene were relatively wet and warm.•Cladoceran gamogenesis increased from ∼5000 cal yr BP coinciding with a drier stage.
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