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  1. This study examines Holocene phreatic overgrowths on speleothems (POS) found in brackish pools of Mallorca Island’s coastal caves. It traces the evolution of knowledge about these deposits, beginning with initial morphogenetic observations in the late 1970s. Recent research, involving 138 U-Th datings from eight caves, reconstructs the late Holocene sea-level history over the last 4,000 years. Findings include a sea level position at 25 cm below the pre-industrial times ‒occurring between 3.89 and 3.26 ka BP‒, followed by a rapid rise to current levels, remaining stable from 2.84 ka BP until the early 20th century. The paper also discusses glacial isostatic adjustment models, one of which is similar with the obtained POS data, linking sea-level rise to West Antarctica’s ice melt. Today, these crystallizations are partially submerged in the coastal phreatic waters, due to the gradual rise in sea level linked to modern (industrial) global warming; since 1900 the sea-level has risen by about 17.3 cm, with the rate of rise accelerating to 2.05 mm/year in the recent decades. 
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    Free, publicly-accessible full text available March 25, 2025
  2. Abstract

    We examined a Late Holocene sea-level stillstand using phreatic overgrowths on speleothems (POS) recovered from Medvjeđa Špilja [Bear Cave] (northern Adriatic Sea) from −1.28 ± 0.15 m below present mean sea level. Different mineralogical analyses were performed to characterize the POS and better understand the mechanisms of their formation. Results reveal that the fibrous overgrowth is formed of calcite and that both the supporting soda straw and the overgrowth have very similar trace element compositions. This suggests that the drip-water and groundwater pool from which the POS formed have similar chemical compositions. Four subsamples were dated by means of uranium-series. We found that ca. 2800 years ago, the relative sea level was stable for about 300 years at a depth of approximately −1.28 ± 0.15 m below the current mean sea level. This finding roughly corresponds with the end of a relatively stable sea-level period, between 3250 and 2800 cal yr BP, previously noted in the southern Adriatic. Our research confirms the presence of POS in the Adriatic region and establishes the Medvjeđa Špilja pool as a conducive environment for calcite POS formation, which encourages further investigations at this study site.

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    Free, publicly-accessible full text available March 1, 2025
  3. Coupled partial differential equations (PDEs) are key tasks in modeling the complex dynamics of many physical processes. Recently, neural operators have shown the ability to solve PDEs by learning the integral kernel directly in Fourier/Wavelet space, so the difficulty for solving the coupled PDEs depends on dealing with the coupled mappings between the functions. Towards this end, we propose a coupled multiwavelets neural operator (CMWNO) learning scheme by decoupling the coupled integral kernels during the multiwavelet decomposition and reconstruction procedures in the Wavelet space. The proposed model achieves significantly higher accuracy compared to previous learning-based solvers in solving the coupled PDEs including Gray-Scott (GS) equations and the non-local mean field game (MFG) problem. According to our experimental results, the proposed model exhibits a 2ˆ „ 4ˆ improvement relative L2 error compared to the best results from the state-of-the-art models. 
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  4. In this paper, we study the structural state and input observability of continuous-time switched linear time-invariant systems and unknown inputs. First, we provide necessary and sufficient conditions for their structural state and input observability that can be efficiently verified in O((m(n+p))2), where n is the number of state variables, p is the number of unknown inputs, and m is the number of modes. Moreover, we address the minimum sensor placement problem for these systems by adopting a feed-forward analysis and by providing an algorithm with a computational complexity of O((m(n+p)+α)2.373), where α is the number of target strongly connected components of the system’s digraph representation. Lastly, we apply our algorithm to a real-world example in power systems to illustrate our results. Keywords: Structural systems; Unknown inputs; Observability 
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  5. Time-evolution of partial differential equations is fundamental for modeling several complex dynamical processes and events forecasting, but the operators associated with such problems are non-linear. We propose a Pad´e approximation based exponential neural operator scheme for efficiently learning the map between a given initial condition and the activities at a later time. The multiwavelets bases are used for space discretization. By explicitly embedding the exponential operators in the model, we reduce the training parameters and make it more data-efficient which is essential in dealing with scarce and noisy real-world datasets. The Pad´e exponential operator uses a recurrent structure with shared parameters to model the non-linearity compared to recent neural operators that rely on using multiple linear operator layers in succession. We show theoretically that the gradients associated with the recurrent Pad´e network are bounded across the recurrent horizon. We perform experiments on non-linear systems such as Korteweg-de Vries (KdV) and Kuramoto–Sivashinsky (KS) equations to show that the proposed approach achieves the best performance and at the same time is data-efficient. We also show that urgent real-world problems like epidemic forecasting (for example, COVID- 19) can be formulated as a 2D time-varying operator problem. The proposed Pad´e exponential operators yield better prediction results (53% (52%) better MAE than best neural operator (non-neural operator deep learning model)) compared to state-of-the-art forecasting models. 
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  6. Modern global sea-level rise is anomalous relative to any natural variability over the past 4000 years. 
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  7. null (Ed.)
    Abstract Water availability for Native Americans in the southwestern United States during periods of prolonged droughts is poorly understood as regional hydroclimate records are scant or contradicting. Here, we show that radiocarbon-dated charcoal recovered from an ice deposit accumulated in Cave 29, western New Mexico, provide unambiguous evidence for five drought events that impacted the Ancestral Puebloan society between ~ AD 150 and 950. The presence of abundant charred material in this cave indicates that they periodically obtained drinking water by using fire to melt cave ice, and sheds light on one of many human–environment interactions in the Southwest in a context when climate change forced growing Ancestral Puebloan populations to exploit water resources in unexpected locations. The melting of cave ice under current climate conditions is both uncovering and threatening a fragile source of paleoenvironmental and archaeological evidence of human adaptations to a seemingly marginal environment. 
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  8. Abstract

    Sea-level reconstructions are important for understanding past ice sheet variability and its response to past and future warming. Here we present Neogene and Quaternary sea-level snapshots using phreatic overgrowths on speleothems (POS) from caves on Mallorca, Spain. POS are excellent sea level index points because of their clear relationship to sea level and precise U–Pb chronology. We find that local sea-level before and at the onset of the Messinian Salinity Crisis was at 33.3 ± 0.25 m (6.54 ± 0.37 Ma) and 31.8 ± 0.25 m (5.86 ± 0.60 Ma) above present levels, respectively. We further present global mean sea level (GMSL) estimates, i.e. local sea level corrected for glacial isostatic adjustment and long-term uplift, for three other POS. The results show that GMSL during the Pliocene–Pleistocene Transition was 6.4 m (− 2.0–8.8 m) at 2.63 ± 0.11 Ma and during the beginning and the end of the Mid-Pleistocene Transition was − 1.1 m (− 5.6–2.4 m) and 5 m (1.5–8.1 m), respectively. These estimates provide important constraints for the past evolution of sea level and show that local sea level prior to the MSC was similar to the highest stand during the Pliocene, with markedly lower position afterwards.

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