Discerning the interactions between environmental parameters reflected in d13C and d18O of recent fluvial tufas: Lessons from a Mediterranean climate region

d13C and d18O of recent, continuous tufa records, obtained during a monitoring period spanning 3 to 13 years, are compared with the corresponding, known environmental conditions. Three rivers in NE Iberia (located along a 200-km N–S transect) are used for this comparison. The isotopic variations through space and time are discussed in terms of the environmental and geological parameters that operate on different scales, focusing on discerning the interactions between these parameters and providing examples of possible misinterpretation of climatic conditions, which is important to past climate studies based on isotopic data. The calculation of the actual isotopic fractionation coefficients, and the comparison with the literature-derived coefficients, demonstrates that the studied tufa formation was close to isotopic equilibrium to reflect the water temperature. The difference between mean measured water temperature (Tw) and mean calculated Tw (based on d18Ocalcite and measured d18Owater) is less than 2.7 °C. Tendencies of these calculated Tw are similar to the regional air temperature (Tair) tendencies through time, in particular in the case of the 13-year record, although certain deviations exist over shorter time spans. The best agreement between measured and calculated Tw and between d18Ocalcite-based Tw tendencies and Tair tendencies corresponds to the tufa stromatolite facies. Differences between the d18Ocalcite records of the three rivers cannot be attributed to temperature changes, but to the varying influences of groundwater inputs and isotopic rainfall composition in each river.Without considering these parameters, d18Ocalcite-based Tw calculations yield inaccurate results when comparing the study sites. d13Ccalcite values do not exhibit distinct patterns over time, and d13Ccalcite variations are likely caused by local processes that do not reflect general environmental changes. These findings underscore the significance of accounting for both groundwater behaviour and rainfall stable isotope composition when interpreting climate parameters in carbonate systems, particularly when differences between the isotopic signatures of deposits exist in the same region

New insights into the climate of northern Iberia during the Younger Dryas and Holocene: The Mendukilo multi-speleothem record

Recent hydroclimate studies on the Iberian Peninsula have shown a complex regional pattern in timing and intensity of climate change spanning the Younger Dryas and the Holocene. These changes are due to multifaceted interactions between climate variability that characterizes the Atlantic Ocean region and hydroclimatic processes associated with the Mediterranean climate, thus making it difficult to reconstruct centennial- and millennial-scale variability in rainfall. In this study we present a composite and continuous isotopic record (δ13C and δ18O) consisting of four stalagmites from Mendukilo cave (MEN composite) in the western Pyrenees covering the Younger Dryas and the entire Holocene. This record reveals millennial-scale shifts in carbon isotopes in response to changes in the hydroclimate in the northern part of Iberia. The MEN oxygen isotopes show little variation on millenial time scales but reveal centennial changes that correlate with North Atlantic events (e.g., the 8.2 kyr BP cooling event). We observe a delay in the onset of humid conditions in the early Holocene and a subsequent trend towards drier and colder conditions between 6.0 and 2.5 kyr BP. This new, high-resolution and replicated speleothem record denotes the complex connection that exists between the North Atlantic and Western Europe during last millennia and the strong regional heterogeneity of the hydroclimate of Iberia during this time.We acknowledge the Spanish projects PID 2019–106050RB-I00 (PYCACHU) and CGL 2016-77479-R (SPYRIT), the National Natural Science Foundation of China (NSFC) grants 41888101 and 42050410317, and the Postdoctoral Science Foundation of China (2020M683452) for funding. J.L. Bernal-Wormull was supported by an FPI grant (ref. BES-2017–081125).Peer reviewe

Geochemical differentiation of «Weald» materials of Cameros Basin (Soria - La Rioja)

The Cameros Basin ( N W o f the Iberian Range) is m a in ly composed o f very homogeneous silicic d e tr ita l m aterials in Weald facies. The occurrence o f c h lo rito id , cookeite, p y rite an d muscovite/p aragonite is related to a cretacic very low grade metamorphism. The geochemical analysis of this materials displays differences linked to lithologic features; comparison between metamorphic and no metamorphic materials shows no main differences in the chemical contents, but in the relationships between element

Controls on Mg/Ca Ratios in Recent Stromatolites: Insights from Fluvial Systems in the Iberian Range (Spain)

The utility of the Mg/Ca elemental ratio of calcite ((Mg/Ca)calcite) as a temperature indicator in continental carbonate deposits is a matter of debate due to the different results obtained by diverse authors. In this study, we aimed to test the reliability of the (Mg/Ca)calcite in fluvial carbonates. We selected the recent tufa stromatolite records of four rivers on the Iberian Peninsula for the trace element analysis based on six-monthly sampling. Previous sedimentary and hydrological studies on these fluvial basins provided the information for this work. The water temperature estimates for the stromatolite (Mg/Ca)calcite substantially differed from the measured water temperatures in most of the studied cases. We thus assessed other factors that participate in the control of the Mg partitioning between water and calcite. The correction of the detrital Mg content yielded water temperatures that matched the measured ones in one of the rivers. The (Mg/Ca)water, water discharge and calcite precipitation rates may also occasionally influence the (Mg/Ca)calcite. The six-month behaviour of some of these parameters could interfere with the relationship between the (Mg/Ca)calcite and water temperature. According to these results, and their comparison with other non-marine carbonates, the wide variety of parameters that are involved in the (Mg/Ca)calcite limit it as a geochemical thermometer in continental sedimentary environments

d13C and Mg/Ca dripwater response to environmental conditions in the Ortigosa caves (La Rioja, Spain)

Rainfall on Ortigosa de Cameros (La Rioja), dripping rate and drip water d13C, and Mg/Ca from the caves, as well as d13C and Mg/Ca from a close river and spring, were monitored during a hydrological year. Dripping rate follows local rainfall, excepting for an autumn delay, due to the drying of the epikarst after summer. The general more slowly response of La Viña Cave is likely due to the thicker vadose zone above the cave. d13C and Mg/Ca patterns are consistent with the dripping rate, showing the dripping autumn delay, related to the water decrease in the epikarst during summer and the subsequent decline of the biological activity. The spring d13C and Mg/Ca minimum values correspond to the rainfall maximum and dripping resume after winter, and are linked to the spring biological activity surge. d13C, similar in dripping caves, river and spring, reflects clearly the general spring humidity and the accompanying biological activity, whereas Mg/Ca values are more variable and more sensitive to the summer drought, delayed to autumn

Dinámica aluvial reciente en Bardenas Reales de Navarra.

An approach to alluvial dynamics from Little Ice Age to present time, in Bardenas Reales of Navarra (Ebro Basin), is presented based on geomorphological, sedimentological and chronological (14C, 210Pb and dendrochronology) data. Sedimentation and incision processes show a high degree of geomorphic effectiveness as well as a very quick response to centennial-decadal scale climatic variability, in a context of land use change.Peer Reviewe