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This study focuses on the description and interpretation of the origin of dolocretes and their siliciclastic host rocks in the upper part of the Amata Formation (Fm) in four exposures in Latvia. The dolocretes occur in at least four intervals. The composition and structure, as well as stable oxygen and carbon isotope data of the two upper dolocrete intervals, suggest that they developed in soils. The dolocretes correspond to an episode of climate change from warm, moist to drier and hotter conditions, which started in the Late Givetian and continued to the Early–Middle Frasnian. They formed during a short-lived sea-level fall, which took place after a longer sea-level rise trend. The diversity of vertebrate fossils decreases from the lower to the upper part of the Amata Fm, which is consistent with the sea-level fall and gradual climate change marked by the studied dolocretes in the upper part of the Amata Fm.

Gas hydrates stored on continental shelves are susceptible to dissociation triggered by environmental changes. Knowledge of the timescales of gas hydrate dissociation and subsequent methane release are critical in understanding the impact of marine gas hydrates on the ocean–atmosphere system. Here we report a methane efflux chronology from five sites, at depths of 220–400 m, in the southwest Barents and Norwegian seas where grounded ice sheets led to thickening of the gas hydrate stability zone during the last glaciation. The onset of methane release was coincident with deglaciation-induced pressure release and thinning of the hydrate stability zone. Methane efflux continued for 7–10 kyr, tracking hydrate stability changes controlled by relative sea-level rise, bottom water warming and fluid pathway evolution in response to changing stress fields. The protracted nature of seafloor methane emissions probably attenuated the impact of hydrate dissociation on the climate system.

The effect of freshwater sources on wintertime sea-ice CO2 processes was studied from the glacier front to the outer Tempelfjorden, Svalbard, in sea ice, glacier ice, brine and snow. March–April 2012 was mild, and the fjord was mainly covered with drift ice, in contrast to the observed thicker fast ice in the colder April 2013. This resulted in different physical and chemical properties of the sea ice and under-ice water. Data from stable oxygen isotopic ratios and salinity showed that the sea ice at the glacier front in April 2012 contained on average 54% of frozen-in glacial meltwater. This was five times higher than in April 2013, where the ice was frozen seawater. In April 2012, the largest excess of sea-ice total alkalinity (AT), carbonate ion ([CO32−]) and bicarbonate ion concentrations ([HCO3−]) relative to salinity was mainly related to dissolved dolomite and calcite incorporated during freezing of mineral-enriched glacial water. In April 2013, the excess of these variables was mainly due to ikaite dissolution as a result of sea-ice processes. Dolomite dissolution increased sea-ice AT twice as much as ikaite and calcite dissolution, implying different buffering capacity and potential for ocean CO2 uptake in a changing climate.

We traced the origin of dissolved organic matter (DOM) in the large, shallow, eutrophic Lake Võrtsjärv in Estonia. Allochthonous DOM (Al-DOM) had higher δ13C values than autochthonous DOM (Au-DOM). The δ13C of inflow DOM varied from −28.2‰ to −25.4‰ (mean −26.7‰) and in-lake DOM varied from −28.4‰ to −26.1‰ (mean −27.2‰). Low stable isotope (SI) signatures of Au-DOM were caused by relatively 13C-depleted values of its precursors (mainly phytoplankton) with mean δ13C of −28.9‰. SI signatures of dissolved inorganic carbon (DIC) in the inflows and in the lake were also relatively low (from −15.1‰ to −3.28‰). SI values of DOM were lower during the active growing season from May to September and higher from October to April, with the corresponding estimated average proportions of Al-DOM 68% and 81%. The proportion of Al-DOM decreased with increasing water temperature, chlorophyll a, and pH and increased with increasing water level and concentration of yellow substances and DIC. The high proportion of Al-DOM in Võrtsjärv shows that, even in this highly productive ecosystem, the labile Au-DOM produced is rapidly utilized and degraded by microorganisms and thus makes a relatively small contribution to the instantaneous in-lake DOM pool.

For years, the Ohesaare core section and its rich fossil assemblages have enticed researchers to suggest various ideas about Silurian stratigraphy in the East Baltic despite several sedimentary gaps occurring through the Ludlow interval in particular. One of the gaps has removed from the Ohesaare record the most important event in the Palaeozoic history of carbon isotopes – the Mid-Ludfordian Carbon Isotope Excursion (MLCIE), which is partly accompanied by the Lau biotic and oceanic events. In our research, we have performed a detailed distribution analysis of chitinozoans, conodonts, ostracodes and vertebrate microremains with the aim of documenting the evidence regarding the levels of certain environmental events largely preceding the MLCIE. For this purpose, the Torgu Formation was subdivided into five working units. The first results indicate a gap within the uppermost part of the Torgu Formation as a possible level for the missing MLCIE. In order to verify this, we compared the fossil distribution pattern in Ohesaare with that on Gotland (Sweden) and in Kurzeme (Latvia), including δ13C data from the Uddvide (Gotland) and Ventspils (Latvia) core sections. Both Baltic and Bohemian data show rather unanimously that the MLCIE is located below the Ozarkodinacrispa conodont Biozone. However, some reports from Gotland show peak values also in higher strata; occasional records of Oz. crispa from other places may cast some doubt on these findings and raise some ecostratigraphical concerns when discussing upper Ludfordian correlation.

Siliciclastic deposits and dolostones of the Å Ä·ervelis Formation in southwestern Latvia were studied in outcrops, polished slabs, thin sections, and by geochemical methods, including stable isotope analyses. Siliciclastic fluvial deposits alternate with soils and carbonates. As the soil processes became dominant, up to 6 m thick dolocretes formed, but they still preserve remnant sedimentary structures and textures. The strong role of soil processes is indicated by the presence of ooids and pisoids together with fine laminar layers, chert and phosphatic inclusions, rhizoids, and stable isotope values. Peculiar vertical clay-dolomite structures, up to 1.7 m long, are root structures or their combination with Vertisol-like soil development. The extensive development of soil processes and formation of the vertical structures was stimulated by seasonally wet monsoon climate. The scarcity of fossils in the studied deposits does not allow their age to be determined precisely, but probably the thick dolocrete unit in the upper part of the studied succession formed during the end-Devonian glaciation and the period of related sea regression.

Light-absorbing carbonaceous aerosols emitted by biomass or fossil fuel combustion can contribute to amplifying Arctic climate warming by lowering the albedo of snow. The Svalbard archipelago, being near to Europe and Russia, is particularly affected by these pollutants, and improved knowledge of their distribution in snow is needed to assess their impact. Here we present and synthesize new data obtained on Svalbard between 2007 and 2018, comprising measurements of elemental (EC) and water-insoluble organic carbon (WIOC) in snow from 37 separate sites. We used these data, combined with meteorological data and snowpack modeling, to investigate the variability of EC and WIOC deposition in Svalbard snow across latitude, longitude, elevation and time. Overall, EC concentrations (CsnowEC) ranged from <1.0 to 266.6 ng g−1, while WIOC concentrations (CsnowWIOC) ranged from <1 to 9426 ng g−1, with the highest values observed near Ny-Ålesund. Calculated snowpack loadings (LsnowEC, LsnowWIOC) on glaciers surveyed in spring 2016 were 0.1 to 2.6 mg m−2 and 2 to 173 mg m−2, respectively. The median CsnowEC and the LsnowEC on those glaciers were close to or lower than those found in earlier (2007–2009), comparable surveys. Both LsnowEC and LsnowWIOC increased with elevation and snow accumulation, with dry deposition likely playing a minor role. Estimated area-averaged snowpack loads across Svalbard were 1.1 mg EC m−2 and 38.3 mg WIOC m−2 for the 2015–2016 winter. An ∼11-year long dataset of spring surface snow measurements from the central Brøgger Peninsula was used to quantify the interannual variability of EC and WIOC deposition in snow. In most years, CsnowEC and CsnowWIOC at Ny-Ålesund (50 m a.s.l.) were 2–5 times higher than on the nearby Austre Brøggerbreen glacier (456 m a.s.l.), and the median EC/WIOC in Ny-Ålesund was 6 times higher, suggesting a possible influence of local EC emission from Ny-Ålesund. While no long-term trends between 2011 and 2018 were found, CsnowEC and CsnowWIOC showed synchronous variations at Ny-Ålesund and Austre Brøggerbreen. When compared with data from other circum-Arctic sites obtained by comparable methods, the median CsnowEC on Svalbard falls between that found in central Greenland (lowest) and those in continental sectors of European Arctic (northern Scandinavia, Russia and Siberia; highest), which is consistent with large-scale patterns of BC in snow reported by surveys based on other methods.

The climate impact of black carbon (BC) is notably amplified in the Arctic by its deposition, which causes albedo decrease and subsequent earlier snow and ice spring melt. To comprehensively assess the climate impact of BC in the Arctic, information on both atmospheric BC concentrations and deposition is essential. Currently, Arctic BC deposition data are very scarce, while atmospheric BC concentrations have been shown to generally decrease since the 1990s. However, a 300-year Svalbard ice core showed a distinct increase in EC (elemental carbon, proxy for BC) deposition from 1970 to 2004 contradicting atmospheric measurements and modelling studies. Here, our objective was to decipher whether this increase has continued in the 21st century and to investigate the drivers of the observed EC deposition trends. For this, a shallow firn core was collected from the same Svalbard glacier, and a regional-to-meso-scale chemical transport model (SILAM) was run from 1980 to 2015. The ice and firn core data indicate peaking EC deposition values at the end of the 1990s and lower values thereafter. The modelled BC deposition results generally support the observed glacier EC variations. However, the ice and firn core results clearly deviate from both measured and modelled atmospheric BC concentration trends, and the modelled BC deposition trend shows variations seemingly independent from BC emission or atmospheric BC concentration trends. Furthermore, according to the model ca. 99 % BC mass is wet-deposited at this Svalbard glacier, indicating that meteorological processes such as precipitation and scavenging efficiency have most likely a stronger influence on the BC deposition trend than BC emission or atmospheric concentration trends. BC emission source sectors contribute differently to the modelled atmospheric BC concentrations and BC deposition, which further supports our conclusion that different processes affect atmospheric BC concentration and deposition trends. Consequently, Arctic BC deposition trends should not directly be inferred based on atmospheric BC measurements, and more observational BC deposition data are required to assess the climate impact of BC in Arctic snow.

We review our current understanding of groundwater flow history in the northern part of the Baltic Artesian Basin (BAB) from the end of the Late Pleistocene to current conditions based on the hydrogeological studies carried out in 2012–2020 by the Department of Geology, Tallinn University of Technology and its partners. Hydrogeochemical data and various numerical models are combined in order to understand the link between glaciations and groundwater flow. The results of our earlier research and published literature on groundwater flow history in the BAB are also taken into account. The reconstruction of groundwater flow history is based on the database of the isotopic, chemical and dissolved gas composition of groundwater. The database contains data on 1155 groundwater samples collected during 1974–2017. We find that groundwater in the BAB is controlled by the mixing of three distinct water masses: interglacial/modern meteoric water (δ18O ≈ –11‰), glacial meltwater (δ18O ≤ –18‰) and an older syngenetic end-member (δ18O ≥–4.5‰). The numerical modelling has suggested that the preservation of meltwater in the northern part of the BAB is controlled by confining layers and the proximity to the outcrop areas of aquifers. Aquifers containing groundwater of glacial origin are in a transient state with respect to modern topographically-driven groundwater flow conditions. The most important topics for future research that can address gaps in our current knowledge are also reviewed.

The effect of freshwater sources on wintertime sea-ice CO 2 processes was studied from the glacier front to the outer Tempelfjorden, Svalbard, in sea ice, glacier ice, brine and snow. March–April 2012 was mild, and the fjord was mainly covered with drift ice, in contrast to the observed thicker fast ice in the colder April 2013. This resulted in different physical and chemical properties of the sea ice and under-ice water. Data from stable oxygen isotopic ratios and salinity showed that the sea ice at the glacier front in April 2012 contained on average 54% of frozen-in glacial meltwater. This was five times higher than in April 2013, where the ice was frozen seawater. In April 2012, the largest excess of sea-ice total alkalinity ( A T ), carbonate ion ([CO 3 2− ]) and bicarbonate ion concentrations ([HCO 3 − ]) relative to salinity was mainly related to dissolved dolomite and calcite incorporated during freezing of mineral-enriched glacial water. In April 2013, the excess of these variables was mainly due to ikaite dissolution as a result of sea-ice processes. Dolomite dissolution increased sea-ice A T twice as much as ikaite and calcite dissolution, implying different buffering capacity and potential for ocean CO 2 uptake in a changing climate.