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A collaboration between geoscience professors and pedagogic and technical support experts at Universidad de los Andes led to a teaching innovation, as part of a project entitled GEOC-SENSE. GEOC-SENSE was based on the use of active pedagogy techniques aided by information and communication technologies (ICT) to improve motivation and acquisition of transferable skills using active learning techniques and a flipped classroom structure. Lessons were divided into preclass, in-class, and postclass activities for students to acquire key concepts, to apply those concepts to solve in-class activities, and to reinforce acquired knowledge. The GEOC-SENSE project resolved major challenges previously identified in the geosciences course and, based on student surveys, improved student learning while allowing participants to develop transferable skills. This generated increased motivation in a diverse student population by making classes more dynamic and encouraging independent work. GEOC-SENSE allowed students to acquire knowledge using problem-solving skills, practical activities, and in general increased interaction in the classroom. The activities were perceived by students as directly applicable to a professional setting, making the course more relevant for students' subsequent careers. The project increased student motivation and skill development; however, it also posed challenges: mainly difficulties when working in groups and accessing the ICT tools by some of the students.

Paramos, unique and biodiverse ecosystems found solely in the high mountain regions of the tropics, are under threat. Despite their crucial role as primary water sources and significant carbon repositories in Colombia, they are deteriorating rapidly and garner less attention than other vulnerable ecosystems like the Amazon rainforest. Their fertile soil and unique climate make them prime locations for agriculture and cattle grazing, often coinciding with economically critical deposits such as coal which has led to a steady decline in paramo area. Anthropic impact was evaluated using multispectral images from Landsat and Sentinel over 37 years, on the Guerrero and Rabanal paramos in central Colombia which have experienced rapid expansion of mining and agriculture. Our analysis revealed that since 1984, the Rabanal and Guerrero paramos have lost 47.96% and 59.96% of their native vegetation respectively, replaced primarily by crops, pastures, and planted forests. We detected alterations in the spectral signatures of native vegetation near coal coking ovens, indicating a deterioration of paramo health and potential impact on ecosystem services. Consequently, human activity is reducing the extent of paramos and their efficiency as water sources and carbon sinks, potentially leading to severe regional and even global consequences. [ABSTRACT FROM AUTHOR]

Radon (222 Rn) is a naturally occurring gas that represents a health threat due to its causal relationship with lung cancer. Despite its potential health impacts, several regions have not conducted studies, mainly due to data scarcity and/or economic constraints. This study aims to bridge the baseline information gap by building an interactive dashboard (http://ircmodelingdashboard.eu.pythonanywhere.com/ , last access: 17 April 2024) that uses inferential statistical methods to estimate the spatial distribution of indoor radon concentration (IRC) for a target area. We demonstrate the functionality of the dashboard by modeling IRC in the city of Bogotá, Colombia, using 30 in situ measurements. IRC measured was the highest reported in the country, with a geometric mean of 91±14 Bq m -3 and a maximum concentration of 407 Bq m -3. In 57 % of the residences, RC exceeded the WHO's recommendation of 100 Bq m -3. A prediction map for houses registered in Bogotá's cadaster was built in the dashboard by using a log-linear regression model fitted with the in situ measurements, together with meteorological, geologic and building-specific variables. The model showed a cross-validation root mean squared error of 57 Bq m -3. Furthermore, the model showed that the age of the house presented a statistically significant positive association with RC. According to the model, IRC measured in houses built before 1980 presents a statistically significant increase of 72 % compared to IRC of those built after 1980 (p value = 0.045). The prediction map exhibited higher IRC in older buildings most likely related to cracks in the structure that could enhance gas migration in older houses. This study highlights the importance of expanding 222 Rn studies in countries with a lack of baseline values and provides a cost-effective alternative that could help deal with the scarcity of IRC data and get a better understanding of place-specific variables that affect IRC spatial distribution. [ABSTRACT FROM AUTHOR]

Radon (222Rn) is a naturally occurring gas that represents a health threat due to its causal relationship with lung cancer. Despite its potential health impacts, several regions have not conducted studies, mainly due to data scarcity and/or economic constraints. This study aims to bridge the baseline information gap by building an interactive dashboard that uses inferential statistical methods to estimate indoor radon concentration's (IRC) spatial distribution for a target area. We demonstrate the functionality of the dashboard by modeling IRC in the city of Bogotá, Colombia, using 30 in situ measurements. IRC measured were the highest reported in the country, with a geometric mean of 91 ±14 Bq/m3 and a maximum concentration of 407 Bq/m3. In 57 % of the residences RC exceeded the WHO's recommendation of 100 Bq/m3. A prediction map for houses registered in Bogotá's cadaster was built in the dashboard by using a log-linear regression model fitted with the in situ measurements, together with meteorological, geologic and building specific variables. The model showed a cross-validation Root Mean Squared Error of 56.5 Bq/m3. Furthermore, the model showed that the age of the house presented a statistically significant positive association with RC. According to the model, IRC measured in houses built before 1980 present a statistically significant increase of 72 % compared to those built after 1980 (p-value = 0.045). The prediction map exhibited higher IRC in older buildings most likely related to cracks in the structure that could enhance gas migration in older houses. This study highlights the importance of expanding 222Rn studies in countries with a lack of baseline values and provides a cost-effective alternative that could help deal with the scarcity of IRC data and get a better understanding of place-specific variables that affect IRC spatial distribution. [ABSTRACT FROM AUTHOR]

Elevated cadmium (Cd) levels in cacao products have been detected in a major cacao-producing region of Colombia, with concentrations well above those permitted for export and posing a potential threat to human health. Geochemical and petrographic analyses of fertilizer, soil and rocks from three farms were used to determine the origin of Cd. Parent rocks were the main source of the Cd in soils, while organic fertilizer may have further contributed to elevated metal content in one farm. High Cd levels in the organic fertilizer were most likely due to bioaccumulation, since it was sourced from animals in the same area. Even though the soil pH range, elevated OM content and the presence of Mn and K diminish bioavailability, the extremely high Cd content in soils results nonetheless in significant uptake by the plants and subsequent accumulation in cocoa beans. Traditional methods to reduce Cd adsorption, such as the addition of calcium, will not be effective in this case. Instead, the selection of cacao species that are naturally low accumulators and amendment with soil microorganisms with mineralization and biotransformation capabilities, as well as testing of fertilizers before application, could all be cost-effective solutions to reduce Cd in the final product. [ABSTRACT FROM AUTHOR]

The TE[X.sub.86] is a recently proposed paleothermometer through which ancient seawater temperatures of up to 120 My ago can be reconstructed. It is based on the relative distribution of glycerol dibiphytanyl glycerol tetraethers as measured by high-performance liquid chromatography/atmospheric pressure chemical ionizationmass spectrometry (HPLC/APCI-MS). The aim of this study was to examine and improve several analytical aspects in the determination of this important proxy in environmental matrices. Comparison of TE[X.sub.86] analysis using single ion mode (SIM) and mass scanning (m/z 950 to 1450) detection, respectively, revealed that SIM is up to 2 orders of magnitude more sensitive and that the TE[X.sub.86] can be determined with a reproducibility of [+ or -] 0.004 or [+ or -] 0.3 [degrees]C using this method. Comparison of TE[X.sub.86] values obtained with two different HPLC/APCI-MS setups revealed no significant differences. In addition, analysis of TE[X.sub.86] of extracts obtained by Soxhlet, ultrasonic, and accelerated high-pressure extraction techniques also showed no significant differences between the methods. Our results suggest that TE[X.sub.86] analysis by HPLC/APCI-MS is robust and can be determined with analytical errors comparable to those of other temperature proxies.

Developing its large-scale mining industry is an economic priority for Colombia. However, national capacity to assess and manage the water resource impacts of mining is currently limited. This includes lack of baseline data, lack of suitable hydrological models and lack of frameworks for evaluating risks. Furthermore, public opposition to large scale mining is high and is a barrier to many proposed new mining projects mainly because of concerns about impacts on water resources. There are also concerns about impacts on the uplands that are important water sources, particularly the páramo ecosystem. This paper argues the case for a new framework for Strategic Assessment of Regional Water Impacts of Mining, aiming to support land use planning decisions by government for selected mining and prospective mining regions. The proposed framework is modelled on the Australian Government's Bioregional Assessments program, converted into seven stages plus supporting activities that meet the Colombian development context. The seven stages are: (1) Contextual information; (2) Scenario definition; (3) Risk scoping; (4) Model development; (5) Risk analysis; (6) Database development; and (7) Dissemination by government to stakeholders including the general public. It is emphasised that the process and results should be transparent, the data and models publicly accessible, and dissemination aimed at all levels of expertise. [ABSTRACT FROM AUTHOR]

Archaeal tetraether membrane lipids span the whole membrane width and present two C 40 isoprenoid chains bound by two glycerol groups (or one glycerol and calditol). These lipids confer stability and maintain the membrane fluidity in mesophile to extremophile environments, making them very attractive for biotechnological applications. The isoprenoid lipid composition in archaeal membranes varies with temperature, which has placed these lipids in the focus of paleo-climatological studies for over a decade. Non-hydroxylated isoprenoid archaeal lipids are typically used as paleo-thermometry proxies, but recently identified hydroxylated (OH) derivatives have also been proposed as temperature proxies. The relative abundance of hydroxylated lipids increases at lower temperatures, but the physiological function of the OH moiety remains unknown. Here we present molecular dynamics simulations of membranes formed by the acyclic glycerol-dialkyl-glycerol-tetraether caldarchaeol (GDGT-0), the most widespread archaeal core lipid, and its mono-hydroxylated variant (OH-GDGT-0) to better understand the physico-chemical properties conferred to the membrane by this additional moiety. The molecular dynamics simulations indicate that the additional OH group forms hydrogen bonds mainly with the sugar moieties of neighbouring lipids and with water molecules, effectively increasing the size of the polar headgroups. The hydroxylation also introduces local disorder that propagates along the entire alkyl chains, resulting in a slightly more fluid membrane. These changes would help to maintain trans-membrane transport in cold environments, explaining why the relative abundance of hydroxylated Archaea lipids increases at lower temperatures. The in silico approach aids to understand the underlying physiological mechanisms behind the hydroxylated lipid based paleo-thermometer recently proposed. [ABSTRACT FROM AUTHOR]

Branched and isoprenoid glycerol dialkyl glycerol tetraethers (brGDGTs and isoGDGTs, respectively) are used to reconstruct carbon flow from terrestrial landscapes to the ocean in a proxy called the branched vs. isoprenoid tetraether index, or BIT index. The index is based on analysis of core GDGTs (C-GDGTs), that are produced from intact GDGTs (I-GDGTs) upon cell death. GDGTs are a component of the cell membranes of bacteria in soils (br) and archaea (iso) primarily in the marine environment. However, uncertainty as to the identity of the organisms that biosynthesize brGDGTs, the variation in the extent to which GDGTs represent end member carbon pools and the suspected production of brGDGTs and isoGDGTs in both marine and terrigenous environments hinders interpretation of the BIT index. Since brGDGTs remain our only tool for measuring the presence of unknown brGDGT producing organisms, it is particularly important to use the intact form of brGDGTs in living cells (rather than C-brGDGTs in relict biomass) to infer the distributions of the likely source organisms. In situ production within riverine, lacustrine and marine environments is currently thought to be possible, yet few measures of I-brGDGTs are available in these environments to support these claims. Here we assess the spatial distribution of core and intact GDGTs in the Columbia River Basin and nearby Willapa Bay (Washington and Oregon) in order to elucidate source environments and behavior of I-GDGTs vs. C-GDGTs. The presence of I-BrGDGTs throughout the studied soils, rivers and estuaries suggests in situ production across the continuum from soil to marine environments. Likewise, intact crenarchaeol, the marine end member isoGDGT used in the BIT index, was present in all samples. Widespread production of each GDGT class along terrigenous carbon transport paths likely alters the BIT index along this continuum. Core to intact ratios and the weak correlation between I-GDGT derived BIT values and carbon isotope signatures suggest a mixture of allochthonous and autochthonous sources of GDGTs in riverine and marine environments. Our findings highlight the need for further work into the provenance and behavior of GDGTs in order to improve interpretation of the BIT index and other environmental proxies that rely on them. [ABSTRACT FROM AUTHOR]

There is great interest in the membrane lipids of archaea (glycerol dialkyl glycerol tetraethers [GDGTs]) as tracers of archaeal biomass because of their utility as paleoproxies and because of the biogeochemical importance of archaea. While core GDGTs (formed by hydrolysis of polar head groups of intact GDGTs after cell death) are appropriate for paleostudies, they have also been used to trace archaeal populations. Also, despite the small size (0.2 by 0.7 μm) of cultivated marine archaea, 0.7- μm glassfiber filters (GFFs) are typically used to collect GDGTs from natural waters. We quantified both core and intact GDGTs in freeliving (0.2to 0.7- μm), suspended (0.7to 60- μm), and aggregate (>60-μm) particle size fractions in Puget Sound (Washington State). On average, the free-living fraction contained 36% of total GDGTs, 90% of which were intact. The intermediate-size fraction contained 62% of GDGTs, and 29% of these were intact. The aggregate fraction contained 2% of the total GDGT pool, and 29% of these were intact. Our results demonstrate that intact GDGTs are largely in the free-living fraction. Because only intact GDGTs are present in living cells, protocols that target this size fraction and analyze the intact GDGT pool are necessary to track living populations in marine waters. Core GDGT enrichment in larger-size fractions indicates that archaeal biomass may quickly become attached or entrained in particles once the archaea are dead or dying. While the concentrations of the two pools were generally not correlated, the similar sizes of the core and intact GDGT pools suggest that core GDGTs are removed from the water column on timescales similar to those of cell replication, on timescales of days to weeks. [ABSTRACT FROM AUTHOR]

Abstract: Archaea build their cellular membrane with glycerol dialkyl glycerol tetraether (GDGT) core lipids, bound to polar head groups to form intact GDGTs. These lipids are commonly used as indicators of archaeal biomass in the environment. Here, we measured both intact and core GDGTs and archaeal 16S rRNA gene copies (a proxy for cell abundance) in order to determine cellular GDGT content in a coastal fjord at different locations, seasons and depths. We found that the abundance of both intact and core GDGTs relative to 16S rRNA gene copy numbers varied by two orders of magnitude, were generally higher in surface than deeper water and were elevated during periods associated with seasonal phytoplankton blooms. Core and intact GDGTs followed similar trends, but the ratio of core GDGT/16S rRNA gene copy number reached a maximum in October, following a peak in the ratio of intact GDGT/16S rRNA gene copy number that occurred in August. Our data suggest that spatial and temporal variability in these ratios must be considered when attempting to quantify cell numbers in the environment using either GDGTs or 16S rRNA genes. We used optimized extraction methods for both GDGTs and DNA. However, there is still potential for bias in qPCR methodology that could influence the GDGT/16S rRNA gene copy ratio. The apparent variability in cellular membrane lipid concentration could serve to evaluate the status of archaeal populations as it relates to: (i) varying cell size resulting from changes in either community structure or nutritional status, (ii) population turnover times and (iii) changing environmental factors that affect the lifetime of intact GDGTs after cell death. [Copyright &y& Elsevier]

Abstract: One of the primary prerequisites for the application of organic proxies is that they should not be substantially affected by diagenesis. However, studies have shown that oxic degradation of biomarker lipids can affect their relative distribution. We tested the diagenetic stability of the and TEX86 palaeothermometers upon long term oxygen exposure. For this purpose, we studied the distributions of alkenones and glycerol dialkyl glycerol tetraethers (GDGTs) in different sections of turbidites at the Madeira Abyssal Plain (MAP) that experienced different degrees of oxygen exposure. Sediments were deposited anoxically on the shelf and then transported by turbidity currents to the MAP, which has oxic bottom water. This resulted in partial degradation of the turbidite organic matter as a result of long term exposure to oxic bottom water. Concentrations of GDGTs and alkenones were reduced by one to two orders of magnitude in the oxidized parts of the turbidites compared to the unoxidized parts, indicating substantial degradation. High-resolution analysis of the Pleistocene F-turbidite showed that the index of long chain alkenones increased only slightly (0.01, corresponding to <0.5°C) in the oxidized part of the turbidite, suggesting minor preferential degradation of the C37:3 alkenone, in agreement with previous studies. TEX86 values showed a small increase (0.02, corresponding to ∼2°C) in the F-turbidite, like , while for other Pliocene/Miocene turbidites it either remained unchanged or decreased substantially (up to 0.06, corresponding to ∼6°C). Previous observations showed that the BIT index, a proxy for the contribution of soil organic matter to total organic carbon, was always substantially higher in the oxidized part in all the turbidites, as a result of preferential degradation of marine-derived GDGTs. This relative increase in soil-derived GDGTs affects TEX86, as the isoprenoid GDGT distribution on the continent can be quite different from that in the marine environment. Our results indicate that the organic proxies are affected by long term oxic degradation to different extents; this should be taken into account when applying these proxies in palaeoceanographic studies of sediments which have been exposed to prolonged oxic degradation. [Copyright &y& Elsevier]

Abstract: The Drammensfjord, in southern Norway, is an enclosed anoxic basin with a laminated sedimentary record. The fjord is a transition area between the marine and terrestrial environments and thus its sedimentary archive contains information on both environments. In order to reconstruct recent environmental changes in southern Norway, two sediment cores covering the last 90years were analyzed. We used the Branched versus Isoprenoid Tetraether (BIT) index as an indicator of terrestrial organic mater input and compared it to the stable carbon isotopic composition of total organic carbon (δ 13CTOC). The δ 13CTOC and BIT index show opposing trends, with δ 13CTOC indicating an increase in terrestrial input while the BIT index suggests a decrease towards the present. This contradiction is probably due to the different sources reflected by δ 13CTOC (vegetation, soil and anthropogenic input) and the BIT index (only soil organic matter input). In addition, an increase in the recycling of respired CO2 within the fjord’s water column could have depleted the δ 13CTOC of the marine component towards more negative values, thus seemingly indicating an increase in terrestrial input, whilst the BIT index could have been affected by a reduction of riverine input and/or an increase in archaeal biomass production. The TetraEther indeX of lipids with 86 carbons (TEX86) was determined as a proxy for past water surface temperatures. While some of the signal could be coming from the chemocline, our results suggest that TEX86 indicates surface (upper 25m) temperatures. Moreover, TEX86 temperature patterns seem to follow variations in the historical record of averaged spring to fall Oslo air temperature relatively closely, suggesting the signal is produced during this period. Therefore, TEX86 temperature records of fjord sediment cores can potentially be a useful tool in reconstructing past variations of coastal climates. [Copyright &y& Elsevier]

The TEX86 is a recently proposed paleothermometer through which ancient seawater temperatures of up to 120 My ago can be reconstructed. It is based on the relative distribution of glycerol dibiphytanyl glycerol tetraethers as measured by high-performance liquid chromatography/atmospheric pressure chemical ionization-mass spectrometry (HPLC/APCI-MS). The aim of this study was to examine and improve several analytical aspects in the determination of this important proxy in environmental matrices. Comparison of TEX86 analysis using single ion mode (SIM) and mass scanning (m/z 950 to 1450) detection, respectively, revealed that SIM is up to 2 orders of magnitude more sensitive and that the TEX86 can be determined with a reproducibility of ±0.004 or ±0.3 °C using this method. Comparison of TEX86 values obtained with two different HPLC/APCI-MS setups revealed no significant differences. In addition, analysis of TEX86 of extracts obtained by Soxhlet, ultrasonic, and accelerated high-pressure extraction techniques also showed no significant differences between the methods. Our results suggest that TEX86 analysis by HPLC/APCI-MS is robust and can be determined with analytical errors comparable to those of other temperature proxies. [ABSTRACT FROM AUTHOR]

Colombia's water supply catchments are under increasing pressure from urban development, industry, mining and agriculture and associated emissions. In particular, the impacts of coal mining on water quality are commonly questioned; however, the answers are complicated in regions with multiple types of land use and discharge. Investigation of the degree and reasons for water quality degradation in such regions has been limited. Furthermore, the impacts on soils and the Paramo ecosystems, and their relationship to water quality, are commonly disregarded. Here we present a review of the environmental impacts in the Lenguazaque catchment in the department of Cundinamarca. Surface water, sediments and soil measurements taken on a transect from Paramo to the valley were analyzed along with coal mine outlet, urban discharge and agricultural data. Observed alterations of baseline water quality include a significant decrease in dissolved oxygen concentration and an increase of electrical conductivity, turbidity, color and total solids concentration. High heavy metals were also measured, in both water and soil samples. The metal accumulation capacity of soils is effective and reduces concentrations measured in water. Nonpoint sources include runoff and airborne particles released from coke production, both difficult to quantify and characterize. Point sources such as agricultural, mining and urban wastewater discharges are commonly found in the area and their composition has been previously documented. This study indicates that in order to reduce contamination, illegal and small-scale mining in the area should be controlled and that further treatment of mine and urban discharges is needed. It also demonstrated the key role that soils play in the mitigation of metal pollution in rivers emphasizing that those should be included in Colombian environmental quality legislation. • We observed significant alterations of baseline water quality. • High heavy metals were also measured, in both water and soil samples. • The metal accumulation capacity of soils is effective and reduces concentrations in water. • Point sources such as agricultural, mining and urban wastewater discharges. • Nonpoint sources include runoff and airborne particles released from coke production. [ABSTRACT FROM AUTHOR]

This study reconstructs the climatic conditions at both sides of the Isthmus of Panama during its closing time (10-4 Ma). We use molecular proxy records from the Pliocene down to the late Miocene to better understand the early effects of the closing on regional and global climate and ocean circulation1.We measured lipid biomarkers for terrestrial riverine and eolian transport as well as marine production and temperature. Abundance of biomarkers is in general lower in the Pacific than in the Caribbean in agreement with other studies in the area. An increase in terrestrial riverine input is observed from 7.2 Ma at both sides but it then decreases in the Pacific while it remains high in the Caribbean probably related to increased precipitation and runoff2. Additionally, eolian n-alkane transport seems to be influenced by changes in trade wind intensity. In the Pacific, we see a clear shift between more humid conditions before 6 Ma and drier after while the Caribbean displays only little variation and our data indicate an overall drier regime. This could be related to shifts in the source region of the material and/or the drift of the Pacific core away from the equator3.The two cores show an overall temperature decrease consistent with global climatic patterns between 8 and 4 million years. Both UK'37 and TEX86H show similar temperature ranges with an average 28°C which is in agreement with other temperature reconstructions. However, our SST data suggest a slightly warmer Caribbean. Unlike other studies in the tropical pacific3, we do not observe a marked difference between surface and subsurface temperature. This may be because either temperatures were very similar in the first 0-200m of the water column, the difference has been diluted by the error associated to both proxies and/or analytical differences between measuring laboratories. We see three main contrasting periods one from 4-4.5 Ma after a major closing event and coinciding with the establishment of the ocean current system in both sides. The second between 4.8-5.5 Ma which is concurrent to the Messinian salinity crisis. Finally, the third is between 7 and 8 Ma overlapping with one of the uplift pulses of Los Andes and the period when the Isthmus is supposed to have reopened1.1. Lear, C. H., et al. (2003). Earth and Planetary Science Letters, 210(3-4), 425-436.2. Bickert et al. (2004). Paleoceanography, 19(1), 1-11.3. Seki, O. et al. (2012). Paleoceanography and Paleoclimatology, 27(3), 1-14. [ABSTRACT FROM AUTHOR]

Dynamic modelling of hydrochemistry is a valuable tool to study and predict the recovery of surface waters from acidification, and to assess the effects of confounding factors (such as delayed soil response and changing climate) that cause hysteresis during reversal from acidification. The availability of soil data is often a limitation for the regional application of dynamic models. Here we present a method to upscale site-specific soil properties to a regional scale in order to circumvent that problem. The method proposed for upscaling relied on multiple regression models between soil properties and a suite of environmental variables used as predictors. Soil measurements were made during a field survey in 13 catchments in the Pyrenees (NW Spain). The environmental variables were derived from mapped or remotely sensed topographic, lithological, land-cover, and climatic information. Regression models were then used to model soil parameters, which were supplied as input for the biogeochemical model MAGIC (Model for Acidification of Groundwater In Catchments) in order to reconstruct the history of acidification in Pyrenean lakes and forecast the recovery under a scenario of reduced acid deposition. The resulting simulations were then compared with model runs using field measurements as input parameters. These comparisons showed that regional averages for the key water and soil chemistry variables were suitably reproduced when using the modelled parameters. Simulations of water chemistry at the catchment scale also showed good results, whereas simulated soil parameters reflected uncertainty in the initial modelled estimates. [Copyright &y& Elsevier]

The TEX 86 H paleothermometer based on isoprenoid glycerol dialkyl glycerol tetraethers (isoGDGTs) has widely been applied in various marine settings to reconstruct past sea surface temperatures (SSTs). However, it still remains uncertain how well this proxy reconstructs annual mean SSTs. Here, we assess environmental factors governing the TEX 86 H paleothermometer in the Mediterranean Sea, by studying the distribution of isoGDGTs in surface sediments, suspended particulate matter (SPM), and two sediment cores. A redundancy analysis using the fractional abundance of the six major isoGDGTs indicates that the sedimentary isoGDGTs are mostly influenced by three environmental factors explaining a large part (74%) of the variance in isoGDGT distribution. In order of decreasing significance, these factors are annual mean SST, continental organic matter input as indicated by the BIT index, and water depth. However, when considering only the four isoGDGTs that are used for the TEX 86 H proxy, water depth is the most significant parameter, explaining 63% of the variance. Indeed, a strong positive relationship between water depth and TEX 86 H is observed in both surface sediments and SPM from the Mediterranean Sea. This is driven by an increase in fractional abundances of GDGT-2 and crenarchaeol regio-isomer and a decrease in the fractional abundances of GDGT-1 and GDGT-3 with increasing water depth, leading to a bias to higher temperatures of TEX 86 H in deep-water surface sediments. The fact that the water-depth trend is also apparent in SPM suggests that this change might be due to a change in thaumarchaeotal community thriving below surface mixed-layer waters and that this signal is, at least partly, incorporated into sedimentary isoGDGTs. Interestingly, surface-sediment TEX 86 H values from >1000 m water depth do not show a correlation with water depth anymore and instead are correlated to annual mean SSTs. A composite deep-water TEX 86 H dataset of surface sediments from both the Mediterranean Sea and the Red Sea, interconnected regional restricted basins with relatively high bottom-water temperatures and high salinity, forms a distinctive correlation line, statistically distinct from that of the general global correlation. Application of this correlation on two sedimentary records from the western Mediterranean Sea covering the last deglaciation yields SSTs nearly identical to those obtained with the U 37 K ′ paleothermometer, whereas the global calibration substantially overestimates SSTs. Our results show that the warm bias of the TEX 86 H proxy in the Mediterranean Sea is not due to seasonality, as previously suggested. Further research is needed to elucidate the mechanism behind the strong water depth trend of TEX 86 H in the Mediterranean Sea which is not apparent in open ocean settings. [ABSTRACT FROM AUTHOR]

Abstract: Although a large amount of soil carbon (C) is stored in subsurface soils, most studies on soil C dynamics focus on the upper layers. The aim of this study is to assess the factors that regulate C mineralization in mountain grassland soils under standard laboratory conditions to compare regulation mechanisms at surface and subsurface horizons. For this purpose soil samples of surface and subsurface horizons from 35 locations were incubated under laboratory conditions, CO2 efflux rates were measured and microbial biomass C (MBC) and net N mineralization were determined. We also analysed the samples for pH, extractable C after fumigation (Cfe), potentially mineralizable N (PMN), reactive and non-reactive P, sum of exchangeable bases and clay content in order to assess the influence of soil characteristics on C mineralization. The influence of climate of each site on soil C mineralization under the same laboratory conditions was also explored for surface and subsurface horizons. C mineralization in surface horizons related positively with Cfe content, suggesting that microbial activity in this horizon was mainly regulated by the availability of C. By contrast, in subsurface horizons, C mineralization related with PMN and was independent of measured C fractions, suggesting that microbial activity in subsurface horizons was limited by the availability of N and that the available forms of C were more stable in these horizons. The effects of local climate on laboratory C mineralization were significant in both soil horizons, with lower rates of C mineralization being recorded in soils from wetter and warmer sites. This fact, suggested that the C stabilisation mechanisms in mountain grassland soils may be affected by the climate in which soils develop. [Copyright &y& Elsevier]

Large tropical river dam projects are expected to accelerate over the forthcoming decades to satisfy growing demand for energy, irrigation and flood control. When tropical rivers are dammed the immediate impacts are relatively well studied, but the long-term (decades-centuries) consequences of impoundment remain poorly known. We combined historical records of water quality, river flow and climate with a multi-proxy (macrofossils, diatoms, biomarkers and trace elements) palaeoecological approach to reconstruct the limnological evolution of a shallow basin in Gatun Lake (Panama Canal, Panama) and assess the effects of multiple linked factors (river damming, forest flooding, deforestation, invasive species, pollution and hydro-climate) on the study area. Results show that a century after dam construction, species invasion, deforestation and salt intrusions have forced a gradual change in the study basin from a swamp-type environment towards a more saline lake-governed system of benthic–littoral production likely associated with the expansion of macrophyte stands. Hydrology still remains the most important long-term (decades) structural factor stimulating salinity intrusions, primary productivity, deposition of minerals, and reduction of water transparency during wet periods. During dry periods, physical-chemical conditions are in turn linked to clear water and aerobic conditions while nutrients shift to available forms for the aquatic biota in the detrital-rich reductive sediments. Our study suggests that to preserve the natural riverine system functioning of this area of the Panama Canal, management activities must address long-term ecosystem structural drivers such as river flow, runoff patterns and physical-chemical conditions. Unlabelled Image • Multi-proxy data reveal the effects of impoundment in a basin in the Panama Canal. • Records show a shift from a swamp-type environment to a lake system. • Despite human impacts, hydrology still governs the functioning of the lake basin. • Management of the basin must focus on maintaining long-term river hydrodynamics. [ABSTRACT FROM AUTHOR]