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Tracking progress towards the Paris Agreement climate goal requires understanding the 2030 emission levels implied by countries’ National Determined Contributions (NDCs). However, key uncertainties and assumptions impact greenhouse gas (GHG) emission projections implied by the NDCs. This study analyses this impact, both globally and for major emitting countries. We find that the assessed uncertainties markedly affect global GHG emission projections. Full achievement of NDC targets is estimated to result in a range of 46–60 GtCO2eq by 2030 (median estimate: 53 GtCO2eq). The uncertainty in measuring historical emissions, including land-use, as reflected by different datasets is the most important contributing factor. This is followed by two equally important factors globally: socio-economic baseline uncertainty and uncertainty about the emissions implied by current policies in case NDCs are less ambitious than these. Overall, the impact of policy uncertainty (i.e. uncertainty resulting from conditionality of or ranges in NDC targets and uncertainty in emissions resulting from current policies) is about equally important as model/technical uncertainty (i.e. uncertainty in historical emissions and socio-economic baseline variations). This new insight is important for decision makers and researchers because a larger share of the total uncertainty is now attributable to aspects that can be influenced by policy decisions compared to previous analyses of NDC uncertainty.

This global spatially explicit (0.5 by 0.5 degree) analysis presents the nitrogen (N) and phosphorus (P) inputs, processing and biogeochemical retention and delivery to surface waters and river export to coastal seas according to the five shared socioeconomic pathways (SSP). Four systems are considered: (i) human system; (ii) agriculture; (iii) aquaculture; (iv) nature. Exploring the changes during 1980–2015 and 2015–2050 according to the SSPs shows that the natural nutrient sources have been declining in the past decades and will continue to decline in all SSPs in future decades due to massive land transformations, while agriculture, human sewage and aquaculture are becoming increasingly dominant (globally up to 80% of nutrient delivery). More efforts than those employed in any of the SSPs are needed to slow down the global nutrient cycles. One of the drivers of the proliferation of harmful algal blooms is the tendency towards increasing N:P ratios in global freshwaters and export to the global coastal seas; this is the result of increasing N:P in inputs in food production, more efficient biogeochemical retention of P than of N in river basins, and groundwater N legacies, which seems to be most pronounced in a united world that strives after sustainability. The diverging strategies to achieve UN Sustainable Development Goals 14 (life below water), 2 (zero hunger) and 6 (clean water and sanitation) therefore require a balanced management system for both N and P in all systems, that accounts for future nutrient legacies.

During the last 20 years some very hot and dry summers affected Europe, resulting in regionally record‐breaking high temperature or low precipitation values. Long‐term changes of such extremely hot and dry summers are of great relevance for our society, as they are connected with manifold negative impacts on human society, natural ecosystems, and diverse economic sectors. Long‐term variations in drought and five record drought summer half years are studied based on 63 stations across Europe with high‐quality precipitation and temperature time series spanning the period 1901–2018. Eight drought indices are deployed to analyse drought intensity, frequency, and duration; four of them purely precipitation‐based and four integrating potential evapotranspiration in the computation. Additionally, three heavy precipitation indices and simultaneous increases in drought and heavy precipitation are studied. The five driest summer half years over Europe are identified (1947, 2018, 2003, 1921, and 1911). They are analysed by aggregating eight drought indices into the aggregated drought evaluation index (ADE) for five subregions. The ADE shows increasing summer drought conditions over most of Europe, except for some stations in northern Europe. The increase in drought conditions during the warm part of the year is particularly pronounced for indices integrating evapotranspiration in their definition. At the same time, the intensity of heavy precipitation events shows a positive trend, as well as an increased contribution to total precipitation. Several stations in central Europe show simultaneously increasing drought conditions and increasing heavy precipitation events. This increases the risks connected with precipitation extremes., Drought and heavy precipitation trends are studied for selected stations with long time series. Both extreme events are related to specific impacts on different economic sectors and thus society. Stations that simultaneously show increasing trends in drought and heavy precipitation mainly occur in central Europe. This indicates a probably higher exposure to these risks in central Europe as well as a demand for broader adaptation options in this region.

Oxygen is essential for life in the sea. Marine waters are supplied with oxygen via air-sea gas exchange with the atmosphere, and photosynthesis by phytoplankton in the photic zone. When oxygen supply is outpaced by the demand of oxygen, this may ultimately result in hypoxia (oxygen

Phytoplankton in the oceans are responsible for about half of the photosynthetic fixation of carbon on Earth. Oceanic primary production can be limited by the availability of nutrients in the photic zone. In many areas, especially in coastal zones, phosphorus (P) or nitrogen (N) is the limiting nutrient. However, there are large areas further off-shore that are characterized by high concentrations of P and N and low primary productivity. In these so called "high nutrient low chlorophyll zones", primary production is often limited by the availability of micro-nutrients. Iron (Fe) and manganese (Mn) are examples of such micro-nutrients. Especially Fe limits primary production in large parts of the ocean and, in these areas, an increased supply of Fe could lead to enhanced CO2 uptake and, ultimately, an impact on climate. Iron and manganese are delivered to the ocean through different pathways. While dust was long thought to be the major source of both Fe and Mn, recently a more complex picture of the various sources of Fe and Mn has emerged. Besides dust, hydrothermal vents, subglacial runoff and continental shelves were discovered to be important sources of Fe and Mn to the open ocean. In particular, benthic release of Fe and Mn and subsequent lateral transport, which is termed "shuttling", was found to be a major source of dissolved Fe and Mn to the ocean. The shuttling of Fe and Mn over continental shelves depends on the external supply of Fe and Mn, usually from rivers, release of Fe and Mn from the sediment and on transport processes in the water column. Mobilization of Fe(II) and Mn(II) in marine sediments is typically high in sediments with a high input of both Fe and Mn (oxyhydr)oxides (henceforth termed Fe and Mn oxides) and organic matter. In marine sediments, this organic matter is remineralized by microorganisms that use a range of electron acceptors. Oxygen is energetically the most favorable electron acceptor for microbial respiration of organic matter. Therefore, oxygen is typically depleted within the first cm of organic-rich sediments. In the absence of oxygen, organic matter is subsequently remineralized by denitrification, Mn and Fe oxide reduction, sulfate reduction and methanogenesis. Remineralization leads to the release of nutrients (e.g. ammonium, nitrate and phosphate) and, reduced species (e.g. Mn(II), Fe(II) and sulfide (H2S)) to the porewater in distinct zones of the sediment. Subsequently, Fe(II) and Mn(II) can diffuse towards the sediment-water interface. Both Fe(II) and Mn(II) are highly reactive towards oxygen and thus will typically become oxidized and precipitate in the oxic layer of the sediment. As a consequence, release of Fe(II) and Mn(II) from sediments underlying oxic bottom waters is expected to be limited. However, biological activity by macrofauna may contribute to release of Fe(II) and Mn(II) from such sediments.

The mid-Pliocene Warm Period (mPWP, 3.3-3.0 million years ago) is considered to be an analogue for the climate of the mid-21st century. Atmospheric CO2 concentrations, continental configurations, land elevations, and ocean bathymetry during the mPWP were similar to present. However, global temperatures were warmer by 2-4 °C indicating that current climate may not have achieved equilibrium. Continental temperature records are a big missing puzzle piece in our understanding of mPWP climate and in past climates in general, because there are very few climate proxies that reconstruct this parameter. In this PhD thesis, continental temperatures are reconstructed using so-called branched glycerol dialkyl glycerol tetraethers (brGDGTs) that are produced by bacteria in soils, where their molecular structure is correlated to mean air temperature (MAT). Hence, upon mobilization, transport, and deposition in coastal marine sediments, brGDGTs can be used to reconstruct MAT of the adjacent river catchment. However, their applicability as paleothermometer may be hampered by in situ production of brGDGTs in marine settings. Here, a method is presented to correct for marine-derived brGDGTs in coastal zones and applied to a sediment core from the Southern North Sea Basin. The obtained record shows that the temperature of the proto-Rhine Meuse catchment at that time (i.e. North Western Europe) was approximately 1-3 °C higher than present, which is comparable to mPWP temperatures reconstructed by climate modelling studies. Subsequent reconstruction of other climate parameters using the same sediments reveals that the evolution of marine and terrestrial climate of the Southern North Sea area was de-coupled during the mPWP.

This thesis emphasizes the importance of extensive studies of the modern-day lake system prior to interpretation of climate-proxy records based on the occurrence and distribution of lipid biomarkers in its sediments. The biomarkers in the modern lake system show a much more complicated picture than usually is expected, and this thesis highlights in various ways the importance of studying modern systems for paleoclimate research. Firstly, certain biomarkers are shown to have a different origin than generally presumed (such as the C28 fatty acid, and des-A-arborenes). Secondly, this thesis describes significant steps in tying established and new biomarkers (such as the C19:1 n-alkene, and long-chain n-alk-1-enes) to their possible microbial sources. Thirdly, the 13C-depleted aquatic biomarkers found in Lake Chala and its sediments can be explained by physical fractionation processes associated with high pH, a common condition in East African lakes. These findings are not only important for the quality and impact of paleoenvironmental reconstructions based on biomarker δ13C values in the sediment record of Lake Chala, but for all (East African) lakes. Finally, this thesis highlights that monitoring programs need to run for many more years (>5) to fully characterize the relation between environmental conditions and the temporal patterns of the studied biomarkers, as well as to reveal the drivers and underlying patterns forcing the lake’s microbial community. Although this is practically challenging and costly to implement, it is crucial in order to improve our understanding of paleoenvironmental reconstructions based on lake sediments.

Print on Demand version available via http://www.linguaterraebooks.nl - Modern palaeontology is the earth-scientific specialism that investigates the nature and significance of fossils, that is, the study of the remains of once living organisms which have been preserved in earth’s crust. Palaeontology thus investigates the history of life on earth. It does so by applying biological and geological scientific concepts and knowledge. Before its establishment and rise to a fully-fledged scientific state, this special branch of geology passed through a long period of pre-modern development. This book deals with those generally slow and intermittently stagnant developments in the study of those strange ‘medals of Creation’, that is, the period of gestation of palaeontology as the prime study of ancient life.

Over the last decade, our understanding of cli- mate sensitivity has improved considerably. The climate system shows variability on many timescales, is subject to non-stationary forcing and it is most likely out of equi- librium with the changes in the radiative forcing. Slow and fast feedbacks complicate the interpretation of geolog- ical records as feedback strengths vary over time. In the geological past, the forcing timescales were different than at present, suggesting that the response may have behaved differently. Do these insights constrain the climate sensitiv- ity relevant for the present day? In this paper, we review the progress made in theoretical understanding of climate sensitivity and on the estimation of climate sensitivity from proxy records. Particular focus lies on the background state dependence of feedback processes and on the impact of tipping points on the climate system. We suggest how to further use palaeo data to advance our understanding of the currently ongoing climate change.

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The formation of Eastern Mediterranean organic matter rich deposits known as sapropels is the results of two mechanisms: (enhanced) marine productivity and preservation of organic material at depth. However, their relative contribution and their leads and lags with respect to each other remain elusive. Here, we address these questions by studying sediments deposited prior to, during, and after the most recent sapropel (S1, ∼10–6 calibrated ka before present, BP) with an integrated marine and terrestrial palynological approach, combined with existing and newly generated geochemical data. The studied core was retrieved from an area under strong influence of the Nile outflow and has high average sediment accumulation rates allowing a high temporal resolution (of several decades to centuries). Marine productivity, as reconstructed with total dinocyst accumulation rates (ARs) and biogenic CaCO3 content, starts to increase ∼1 ka prior to sapropel formation. A shift in the dinocyst taxa contributing to the productivity signal at sapropel onset indicates the rapid development of (seasonal) water column stratification. Pollen and spore ARs also increase prior to sapropel onset, but a few centuries after the increase in marine productivity. Hence, the first shift to a high marine productivity system before sapropel deposition may have been mostly favoured by the injection of nutrients via shoaling of the nutricline with a minor contribution of nutrients from land via river input and flooding of the shelves. Pollen assemblages indicate a gradual change across the sapropel onset from a savanna-like, through coastal marsh expansion, toward an open woodland assemblage, which is consistent with enhanced Nile influence and delta development. At sapropel onset a marked shift in pollen ARs could suggest increased preservation under anoxia. However, major shifts in pollen assemblages and signs of selective- or partial decomposition of terrestrial palynomorphs are absent. We therefore suggest that the high pollen ARs largely result from an increased influx of pollen by enhanced Nile discharge and extension of the freshwater plume. Three centuries after the sapropel onset, dinocyst ARs and CaCO3 content indicate that marine productivity starts to decrease, while sapropel deposition continued. Organic carbon content decreased only later and less dramatically. This may be explained by a shift in the dominance of the organisms contributing to marine productivity, to an enhanced preservation of organic matter, or a combination of both.

International audience; In human risk assessment, ingestion of soil is considered a major route of toxic Pb exposure. A large body of research has focussed on the measurement of the ‘total’ Pb contents in sediment, soil and dust as a measure for the exposure to lead. We report that Pb bioaccessibility (i.e. the maximum bioavailability), determined with an in vitro test, does not necessarily depend on the total Pb content. In contrast, the Pb bioaccessibility is initially controlled by the chemical form and particle size of the Pb source, which in turn determine its solubility. Furthermore, when anthropogenic Pb resides within the soil, it may form new, more stable, minerals and/or binds to organic matter, clay, reactive iron or other reactive phases, changing its bioaccessibility.The bioaccessible Pb fraction of 28 soils, polluted with various Pb sources (including residues of Pb bullets and pellets, car battery Pb, city waste and diffuse Pb), was determined with an in vitro-test and varied from 0.5% to 79.0% of total Pb. The highest Pb bioaccessibility (60.7% to 79.0%) was measured in soils polluted with residues of Pb bullets and pellets (shooting range), while the lowest Pb bioaccessibility (0.5%–8.3%) was measured in soils polluted with city waste (including remnants of Pb glazed potsherds and rooftiles, Pb based paint flakes, and Pb sheets). Bioaccessibility of Pb was correlated with pH, organic matter and reactive Fe. These results indicate that soil characteristics play an important role in the oral bioaccessibility of lead in polluted soils. Instead of basing human risk assessment solely on total Pb contents we propose to incorporate in vitro bioaccessibility tests, taking factors such as soil pH, organic matter content and reactive iron content into account. This approach will result in a better insight into the actual risks of Pb polluted soils to children.

The end-Triassic mass extinction is associated with a large negative carbon isotope excursion, which has been interpreted as reflecting the rapid injection of 13 C depleted CO 2 or methane associated with the emplacement of the Central Atlantic Magmatic Province. However, in a number of sections in central Europe, the negative excursion is associated with a carbonate-poor lithology, and the most isotopically depleted values are associated with the lowest percent carbonate, raising the possibility of a lithologic control on δ 13 C carb . Here we test the uniqueness of the relationship between the carbonate-poor lithology and the δ 13 C signal by comparing the geochemistry of the extinction marl with two Upper Triassic carbonate-poor beds from lower positions within the same stratigraphic sections. We find that the extinction and non-extinction marls overlap nearly completely in terms of their carbonate content, but differ substantially in their isotopic trends. The extinction marl sections show strong depletions in the δ 13 C and δ 18 O of carbonate, and enrichment in δ 13 C of bulk organic carbon, while the non-extinction marls show almost no change in these metrics. Accordingly, the difference in isotopic content must lie in differences inherent to the beds themselves and the circumstances of their deposition and early diagenesis. Although a range of primary drivers for the isotopic trends is possible, an acidification origin for the marl, and oceanic origin for the carbon isotope excursion in carbonate are compatible with our data and supported by the broader context of the extinction.

During the late Miocene, the Mediterranean developed into a hypersaline basin wherein ultimately gypsum and halite precipitated. Little is known about the evolution of the Paratethys Sea, which was situated northeast of the Mediterranean. The results described in this thesis provide valuable new insights in the late Miocene evolution of the Paratethys Sea. The migration patterns of dinoflagellate cysts and strontium isotope ratios confirm previous studies that the Pontian Flooding event (re-) connected the major Paratethyan basins at ~6.1 Ma. Furthermore, this thesis provides evidence that the Paratethys Sea did not desiccate during the Messinian Salinity Crisis (MSC; 5.97-5.33 Myr ago). The claim that the deep Black Sea Basin desiccated in response to the MSC is based on incorrect age constraints for a peculiar layer (the so-called “Pebbly Breccia”) in DSDP Hole 380A. During the MSC, dinocyst assemblages in the Paratethys seem unaffected by the events occurring in the adjacent Mediterranean Basin. Indications of continuous presence of fresh and brackish waters in the Paratethys suggest that the Paratethys with its enormous hinterland could have played a major role in MSC.

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Intense rainfall events significantly affect Alpine and Alaskan glaciers through enhanced melting, ice-flow acceleration and subglacial sediment erosion, yet their impact on the Greenland ice sheet has not been assessed. Here we present measurements of ice velocity, subglacial water pressure and meteorological variables from the western margin of the Greenland ice sheet during a week of warm, wet cyclonic weather in late August and early September 2011. We find that extreme surface runoff from melt and rainfall led to a widespread acceleration in ice flow that extended 140 km into the ice-sheet interior. We suggest that the late-season timing was critical in promoting rapid runoff across an extensive bare ice surface that overwhelmed a subglacial hydrological system in transition to a less-efficient winter mode. Reanalysis data reveal that similar cyclonic weather conditions prevailed across southern and western Greenland during this time, and we observe a corresponding ice-flow response at all land- and marine-terminating glaciers in these regions for which data are available. Given that the advection of warm, moist air masses and rainfall over Greenland is expected to become more frequent in the coming decades, our findings portend a previously unforeseen vulnerability of the Greenland ice sheet to climate change.

Sulfidization of iron oxyhydroxides can be accompanied by a release of adsorbed uranium, thus enhancing the mobility of uranium in systems undergoing a shift in redox conditions. We investigated the phase distribution and redox state of uranium in batch experiments, in which lepidocrocite with adsorbed U(VI) was reacted with sulfide. The amount of added sulfide was varied in the experiments performed, at pH 8 and ionic strength of 0.1 M. Sulfide, when not added in excess, was removed from solution within less than 1 h of reaction time. Consumption of dissolved sulfide was accompanied by reduction of Fe(III) and formation of iron sulfide. Each addition of sulfide led to an instantaneous release of uranium into solution. This release is most likely caused by the exchange of hydroxide groups at the lepidocrocite surface by thiol groups which have a lower tendency to bind uranium. Along with the consumption of dissolved sulfide, part of the released uranium became reassociated with the solid phase. This can be explained by a reversal of the ligand exchange process at the solid surfaces. However, steady state concentrations of dissolved uranium remained higher than before sulfide addition, indicating that the product of lepidocrocite sulfidization has a lower affinity for uranium than the starting material. Reduction of U(VI) also contributed to the transfer of dissolved uranium back to the solid phase. X-ray absorption spectroscopy revealed that reduction of U(VI) occurred in all experiments. The extent of U(VI) reduction depended on sulfide addition, however, formation of UO 2 occurred within a period of 48 h only when sulfide was added in excess. This suggests that the presence of dissolved sulfide is a prerequisite for fast reduction of U(VI) and formation of UO 2 . This would imply that the fast reaction of lepidocrocite with sulfide outcompetes reduction of U(VI) and, by this, kinetically inhibits the thermodynamically more favorable reduction of U(VI) to uraninite. Our results demonstrate that the transition from oxic to sulfidic conditions can lead to intermittent mobilization of uranium which is not expected based on equilibrium thermodynamics.