The Middle Miocene (15.99–11.65 Ma) of Europe witnessed major climatic, environmental, and vegetational change, yet we are lacking detailed reconstructions of Middle Miocene temperature and precipitation patterns over Europe. Here, we use a high‐resolution (∼0.75°) isotope‐enabled general circulation model (ECHAM5‐wiso) with time‐specific boundary conditions to investigate changes in temperature, precipitation, and δ18O in precipitation (δ18Op). Experiments were designed with variable elevation configurations of the European Alps and different atmospheric CO2 levels to examine the influence of Alpine elevation and global climate forcing on regional climate and δ18Op patterns. Modeling results are in agreement with available paleobotanical temperature data and with low‐resolution Middle Miocene experiments of the Miocene Model Intercomparison Project (MioMIP1). However, simulated precipitation rates are 300–500 mm/yr lower in the Middle Miocene than for pre‐industrial times for central Europe. This result is consistent with precipitation estimates from herpetological fossil assemblages, but contradicts precipitation estimates from paleobotanical data. We attribute the Middle Miocene precipitation change in Europe to shifts in large‐scale pressure patterns in the North Atlantic and over Europe and associated changes in wind direction and humidity. We suggest that global climate forcing contributed to a maximum δ18Op change of ∼2‰ over high elevation (Alps) and ∼1‰ over low elevation regions. In contrast, we observe a maximum modeled δ18Op decrease of 8‰ across the Alpine orogen due to Alpine topography. However, the elevation‐δ18Op lapse rate shallows in the Middle Miocene, leading to a possible underestimation of paleotopography when using present‐day δ18Op—elevation relationships data for stable isotope paleoaltimetry studies.

Abstract. The European Alps are hypothesized to have experienced diachronous surface uplift in response to post-collisional processes such as, e.g., slab break-off. Therefore, understanding the geodynamic and geomorphic evolution of the Alps requires knowledge of its surface uplift history. This study presents the simulated response of regional climate and oxygen isotopic composition of precipitation (δ18Op) to different along-strike topographic evolution scenarios. These responses are modeled to determine if diachronous surface uplift in the Western and Eastern Alps would produce δ18Op signals in the geologic record that are sufficiently large and distinct for stable isotope paleoaltimetry. This is tested with a series of sensitivity experiments conducted with the water isotope tracking atmospheric General Circulation Model (GCM) ECHAM5-wiso. The topographic scenarios are created from the variation of two free parameters, (1) the elevation of the West-Central Alps and (2) the elevation of the Eastern Alps. Results suggest significant changes in the spatial patterns of δ18Op, the elevation-dependent rate of change in δ18Op (“isotopic lapse rate”), near-surface temperatures, precipitation amounts, and atmospheric circulation patterns in response to the different scenarios. The predictions for the diachronous surface uplift experiments are distinctly different from simulations forced with present-day topography and for simulations where the entire Alps experience synchronous surface uplift. Topographic scenarios with higher elevations in the West-Central Alps produce higher magnitude changes and an expansion of the affected geographical domain surrounding the Alps when compared to present-day topography. Furthermore, differences in δ18Op values of up to −2 to −8 ‰ are predicted along the strike of the Alps for the diachronous uplift scenarios, suggesting that the signal can be preserved and measured in geologic archives. Lastly, the results highlight the importance of sampling far-field and low-elevation sites using the δ-δ paleoaltimetry approach to discern between different surface uplift histories.

<p><span>Reconstructions of topography and surface uplift histories of mountain ranges over geological time help constrain the geodynamic evolution of collisional domains and improve our understanding of the interactions between climate, tectonics, and surface processes. Stable isotope palaeoaltimetry is a powerful tool to estimate past surface elevations. However, recent studies suggest that knowledge of climate conditions is needed to accurately interpret the isotopic composition of water recorded in geologic archives. Furthermore, the geodynamic history of the European Alps is hypothesized to have resulted from the eastward propagation of surface uplift that could be reflected in palaeoaltimetry data. In this study we apply high-resolution isotope-tracking ECHAM5-wiso General Circulation Model (GCM) to forward-model the climate and water isotopes in meteoric water for different surface uplift histories of the Alps. Our emphasis is on understanding the climate and topographic signals preserved in the isotopic composition of precipitation (δ</span><sup><span>18</span></sup><span>O</span><sub><span>p</span></sub><span>) which is eventually recorded in paleosol carbonates. More specifically, we test the hypothesis that different topographic configurations for Eastern and Western Alps result in significantly different regional climates and spatial distributions of δ</span><sup><span>18</span></sup><span>O</span><sub><span>p</span></sub><span>. We present sensitivity experiments with two free parameters: the height of the Western/Central Alps and the height of the Eastern Alps. Results indicate a different response of δ</span><sup><span>18</span></sup><span>O</span><sub><span>p</span></sub><span>, precipitation, surface temperature, low level wind patterns and isotopic lapse rate for the different topographic scenarios. In addition, we find δ</span><sup><span>18</span></sup><span>O</span><sub><span>p</span></sub><span> locally increases up to 2‰ when the Eastern Alps are reduced to 0% of their current height, and decreases up to -8% when uplifted to 200%. The precipitation amount increases by ~60 mm/month in response to surface uplift due to orographic effects. The surface temperature locally decreases by -4°C in response Eastern Alps uplift due to both adiabatic and non-adiabatic cooling and increases by -8°C for reduced elevation scenario. The results of our study suggest that the hypothesized west-to-east surface uplift should be reflected in the isotopic composition of meteoric water. Furthermore, our simulated isotopic response to different uplift scenarios provides a basis for the interpretation of isotopic composition derived from geological archives in a stable isotope palaeoaltimetry approach.</span></p>

<p>Stable isotope ratios of oxygen (δ<sup>18</sup>O<sub>p</sub>) and hydrogen (δD<sub>p</sub>) record information about the hydrological cycle. These signals are preserved in natural archives, such as speleothems, stalagmites, ice cores, and pedogenic carbonates. Recent studies have used these proxy records of water isotopologues to reconstruct the evolution of paleoclimates, paleoenvironments, and even tectonic-related changes in surface elevations. However, such reconstructions require information about the atmospheric dynamics that drive the spatial variability of isotopic ratios. δ<sup>18</sup>O<sub>p</sub> and δD<sub>p</sub> are known to reflect the history of air masses, surface temperature, precipitation, and synoptic-scale atmospheric teleconnection patterns like the North Atlantic Oscillation (NAO). Climate-driven variations in these data can complicate their interpretation of geologic processes. The NAO is the predominant mode of inter-annual and seasonal variability that controls the weather and climate system across the North Atlantic region and continental Europe. The influence of the NAO on the Global Network of Isotopes in Precipitation (GNIP) stations records of δ<sup>18</sup>O<sub>p</sub> and δD<sub>p</sub> across Europe was previously studied in the winter season when the NAO impacts are well defined. </p> <p>Here we build upon previous work by (1) investigating the present-day NAO-δ<sup>18</sup>O<sub>p</sub> and -δD<sub>p</sub> relationships and their associated atmospheric dynamics and causal mechanism in all seasons, and (2) studying the NAO’s influence on the δ<sup>18</sup>O and δD in precipitation in the late Cenozoic. We focus on the latter since many δ<sup>18</sup>O<sub>p</sub>- and δD<sub>p</sub>-based studies tackle problems in the Late Cenozoic. In addition, important characteristics of such pressure systems (e.g., the location of the centers of maximum and minimum pressures and axis of polarity) may change over longer (centennial to geological) time scales in response to different forcings such as atmospheric CO<sub>2</sub>, paleogeography, orbital changes, and land-surface cover. To achieve the study’s first goal, we explore the NAO-δ<sup>18</sup>O<sub>p</sub> and -δD<sub>p</sub> link by tracking the NAO in the ERA5 reanalysis data and relating its variability with GNIP observational data across Europe. For the second goal, we use the isotope-enabled Atmospheric General Circulation Model ECHAM5-wiso to perform time-specific, high spatial resolution (paleo)climate simulations with (paleo)environmental conditions of the middle Miocene (~14 Ma), the mid-Pliocene (~3 Ma), the Last Glacial Maximum (~21 ka), the mid-Holocene (~6.5 ka), the pre-industrial (the reference year 1850) and the present-day (1979-2000). We then transfer the analyses from the first step to our paleoclimate simulation output, using the present-day simulation for calibration. Our results help reconstruct the NAO from proxy archives and provide context for more refined interpretations of the isotopic ratios of rainwater in proxy archives.</p>

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