High Sr aragonite-rich carbonates (HSAC) from neritic settings were deposited in the Maldives Inner Sea during sea-level highstand intervals, increasing the
CLIMBER-X simulates a rapid increase in Northern Hemisphere ice sheet area through MIS5d, with ice sheets expanding over northern North America and Scandinavia, in broad agreement with proxy reconstructions. While most of the increase in ice sheet area occurs over a relatively short period between 119 and 117 ka, the larger part of the increase in ice volume occurs afterwards with an almost constant ice sheet extent.
We show that the vegetation feedback plays a fundamental role in controlling the ice sheet expansion during the last glacial inception. In particular, with prescribed present-day vegetation the model simulates a global sea level drop of only ∼ 20 m, compared with the ∼ 35 m decrease in sea level with dynamic vegetation response. The ice sheet and carbon cycle feedbacks play only a minor role during the ice sheet expansion phase prior to ∼ 115 ka but are important in limiting the deglaciation during the following phase characterized by increasing summer insolation.
The model results are sensitive to climate model biases and to the parameterization of snow albedo, while they show only a weak dependence on changes in the ice sheet model resolution and the acceleration factor used to speed up the climate component.
Overall, our simulations confirm and refine previous results showing that climate–vegetation–cryosphere feedbacks play a fundamental role in the transition from interglacial to glacial states characterizing Quaternary glacial cycles.
]]>This study demonstrates a novel method of identifying the dominant drivers of interannual variability in Laptev Sea dynamics within reanalysis products and testing if these relationships appear to hold in satellite-based SSS, sea surface temperature (SST) data, and in situ observations. The satellite SSS data firmly establish what is suggested by reanalysis products and what has previously been subject to debate due to the limited years and locations analysed with in situ data; the zonal wind is the dominant driver of offshore or onshore Lena River plume transport. The eastward wind confines the plume to the southern Laptev Sea and drives alongshore transport into the East Siberian Sea, and westward wind drives offshore plume transport into the northern Laptev Sea. This finding is affirmed by the strong agreement in SSS pattern under eastward and westward wind regimes in all reanalyses and satellite products used in this study, as well as with in situ data. The pattern of SST also varies with the zonal wind component and drives spatial variability in sea ice concentration.
]]>This study aimed to synthesise the recent experimental studies and develop a new, near-explicit, DMS mechanism, through a thorough literature review. A simple box model was then used with the mechanism to simulate a series of chamber experiments and evaluated through comparison with four published mechanisms. Our modelling shows that the mechanism developed in this work outperformed the other mechanisms on average when compared to the experimental chamber data, having the lowest fractional gross error for 8 out of the 14 DMS oxidation products studied. A box model of a marine boundary layer was also run, demonstrating that the deviations in the mechanisms seen when comparing them against chamber data are also prominent under more atmospherically relevant conditions.
Although this work demonstrates the need for further experimental work, the mechanism developed in this work has been evaluated against a range of experiments, which validate the mechanism and reduce the bias from individual experiments. Our mechanism provides a good basis for a near-explicit DMS oxidation mechanism that would include other initiation reactions (e.g. halogens) and can be used to compare the performance of reduced mechanisms used in global models.
]]>Our current initiative defines benchmarking scenarios for groundwater model inversion. These are targeted for community-wide use as test cases in intercomparison scenarios. Here, we develop five synthetic, open-source benchmarking scenarios for the inversion of hydraulic conductivity from pressure data. We also provide highly accurate reference solutions produced with massive high-performance computing and with a high-fidelity MCMC-type solution algorithm. Our high-end reference solutions are publicly available, as well as the benchmarking scenarios, the reference algorithm, and suggested benchmarking metrics. Thus, in comparison studies, one can test against high-fidelity reference solutions rather than discussing different approximations.
To demonstrate how to use these benchmarking scenarios, reference solutions, and suggested metrics, we provide a blueprint comparison of a specific ensemble Kalman filter version. We invite the community to use our benchmarking scenarios and reference solutions now and into the far future in a community-wide effort towards clean and conclusive benchmarking. For now, we aim at an article collection in an appropriate journal, where such clean comparison studies can be submitted together with an editorial summary that provides an overview.]]>
Here, we investigate the robustness of waterbelt states with respect to the thermodynamical representation of sea ice. We compare two thermodynamical sea-ice models, an idealized zero-layer Semtner model, in which sea ice is always in equilibrium with the atmosphere and ocean, and a three-layer Winton model that is more sophisticated and takes into account the heat capacity of ice. We deploy the global icosahedral non-hydrostatic atmospheric (ICON-A) model in an idealized aquaplanet setup and calculate a comprehensive set of simulations to determine the extent of the waterbelt hysteresis. We find that the thermodynamic representation of sea ice strongly influences snow cover on sea ice over the range of all simulated climate states. Including heat capacity by using the three-layer Winton model increases snow cover and enhances the ice–albedo feedback. The waterbelt hysteresis found for the zero-layer model disappears in the three-layer model, and no stable waterbelt states are found. This questions the relevance of a subtropical bare sea-ice region for waterbelt states and might help explain drastically varying model results on waterbelt states in the literature.
]]>Our analysis reveals a large increase in the retrieved mass flux as we transition from the ice to the rain phase in the official DPR product. This observation is in disagreement with our expectation that mass flux should remain relatively stable across the bright band in cold-rain conditions. To address these discrepancies, we propose an alternative retrieval algorithm that ensures a gradual transition of Dm (mean mass-weighted particle melted-equivalent diameter) and the precipitation rate across the melting zone. This approach also helps in estimating bulk ice density above the melting level. These findings demonstrate that DPR observations can not only quantify ice particle content and their size above stratiform rain regions but also estimate bulk density, provided uniform conditions that minimize uncertainties related to partial beam filling.
]]>The melt preserved in inclusions can thus be regarded as an example of a metasomatizing agent present at depth and responsible for the interaction between the crust and the mantle. Chemical similarities between this melt and other metasomatizing melts measured in other eclogites from the Granulitgebirge and Erzgebirge, in addition to the overall similar enrichment in trace elements observed in other metasomatized mantle rocks from central Europe, suggest an extended crustal contamination of the mantle beneath the Bohemian Massif during the Variscan orogeny.
]]>Results reveal challenges in distinguishing snow and ice melt isotopic values in summer, rendering a reliable separation between the two sources difficult. The modelling of catchment-wide snow melt isotopic composition proves challenging due to uncertainties in precipitation lapse rate, mass exchanges during rain-on-snow events, and snow fractionation. The study delves into these processes, their impact on model results, and suggests guidelines for future models. It concludes that water stable isotopes alone cannot reliably separate snow and ice melt shares for temperate alpine glaciers. However, combining isotopes with glacio-hydrological modeling enhances hydrologic parameter identifiability, in particular those related to runoff transfer to the stream, and improves mass balance estimations.]]>
Despite the potential of this technique, its effects on the marine ecosystem are still far to be understood, and there is currently no information on the potential impacts on the concentration and quality of Dissolved Organic Matter (DOM), that is the largest, the most complex and yet the least understood mixture of organic molecules on Earth. The aim of this study is to provide the first experimental evidence about the potential effects of pH peaks, that might be generated by the Ca(OH)2 dissolution in seawater, on DOM dynamics by assessing changes in its concentration and optical properties (absorption and fluorescence).
To investigate the effects of liming on DOM pools with different concentrations and quality, seawater was collected from two contrasting environments: the oligotrophic Mediterranean Sea (MedSea), known for its Dissolved Organic Carbon (DOC) concentration comparable to that observed in the oceans, and the eutrophic Baltic Sea (BalSea), characterized by high DOM concentration mostly of terrestrial origin. Ca(OH)2 was added in both waters, to reach a pH of 9 and 10.
Our findings reveal that the addition of hydrated lime has a noticeable effect on DOM dynamics in both the MedSea and BalSea, determining a reduction in DOC concentration and a change in the optical properties (absorption and fluorescence) of DOM. Thes effects, detectable at pH 9, become significant at pH 10 and are more pronounced in the MedSea than in the BalSea. These potential short-term effects should be considered within the context of the physico-chemical properties of seawater and the seasonal variability.]]>
During droughts, groundwater levels can significantly drop, impacting groundwater availability and potentially reducing heat pump efficiency. This, in turn, may lead to system overheating, decreasing effectiveness, and causing damage. Exceeding critical groundwater levels may result in well infrastructure damage, affecting water quality and energy extraction efficiency. Excessive well exploitation often leads to chemical and mechanical clogging, further influencing well performance.
In contrast to commonly used hydrogeological drought indicators, this method focuses on a probabilistic model, simplifying calculations as it only requires historical groundwater level data. By applying statistical tests and distribution functions, the study evaluates the risk of extreme groundwater level reduction. The proposed method categorizes risk into very high, high, moderate, and low levels, providing a practical tool for users and groundwater management.
The study area, located in the northwest Eurasian continent, encompasses diverse geological and hydrogeological settings. Utilizing data from 27 groundwater observation points, spanning from 1980 to 2020, the research identifies periods and regions at risk of groundwater depletion. The findings highlight specific points vulnerable to high or very high risks, emphasizing the importance of groundwater management strategies.
By analysing monthly, quarterly, and seasonal risk variations and comparing results between the decades 2001–2010 and 2011–2020, the study unveils critical insights into groundwater dynamics. Points such as 15 exhibit pronounced risk increases, indicating potential overexploitation or insufficient replenishment. Notably, certain points display decreasing risks, showcasing positive trends that align with effective groundwater management practices.
This comprehensive probabilistic approach provides valuable information for stakeholders, empowering them to make informed decisions in selecting a sustainable energy source.]]>
To this end, we apply the STL method (Seasonal Trend decomposition based on Loess) to separate the TWS signals into a seasonal signal, an interannual trend signal, and residuals. By clustering these interannual TWS dynamics for the African continent, we define the exact outline of the study's region.
In this area, a TWS decrease until 2006 was followed by a steady increase until around 2016, and Africa's most significant TWS increase occurred in 2019 and 2020. We found that besides precipitation and evaporation variability, surface water storage variations in the large lakes of the region explain large parts of the TWS variability. Storage dynamics of Lake Victoria regulated by the Nalubaale Dam alone contribute up to 50 % of the TWS changes. Satellite altimetry reveals the anthropogenically altered discharge downstream of the dam. It thus indicates that human intervention in the form of dam management at Lake Victoria substantially contributes to the TWS variability seen in the East African Rift region.]]>
Our findings therefore indicate that glacial landforms and relief of continental-scale can survive over tens to hundreds of million years. This preservation and modern exposure of the glacial paleolandscapes were achieved through burial under piles of Karoo sediments and lavas over ca. 120 to 170 million years and a subsequent exhumation since the middle Mesozoic owing to the uplift of Southern Africa. Owing to strong erodibility contrasts between resistant Precambrian bedrock and softer sedimentary infill, the glacial landscapes have been exhumed and rejuvenated.
We therefore emphasise the need of considering the legacy of glacial erosion processes and the resulting presence of glacial landscapes when assessing the post-Gondwana-breakup evolution of Southern African topography and its resulting modern-day aspect, as well as inferences about climate changes and tectonic processes. Finally, we explore the potential pre-LPIA origin for some of the landscapes. In the Kaoko region of northern Namibia, the escarpments into which glacial valleys are carved may correspond to a reminiscence of the Kaoko Pan-African Belt, whose crustal structures were either reactivated or where relief persisted since then. In South Africa, the escarpment bordering the paleohighland corresponds to crustal-scale faults that might have been reactivated during LPIA by subsidence processes. These inherited morphological or crustal features may have been re-exploited and enhanced by glacial erosion during the LPIA, as it is the case for some Quaternary glacial morphology.]]>