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Contains fulltext : 217488.pdf (publisher's version ) (Open Access), Perfect information about an environment allows a robot to plan its actions optimally, but often requires significant investments into sensors and possibly infrastructure. In applications relevant to human-robot interaction, the environment is by definition dynamic and events close to the robot may be more relevant than distal ones. This suggests a non-trivial relationship between sensory sophistication on one hand, and task performance on the other. In this paper, we investigate this relationship in a simulated crowd navigation task. We use three different environments with unique characteristics that a crowd navigating robot might encounter and explore how the robot's sensor range correlates with performance in the navigation task. We find diminishing returns of increased range in our particular case, suggesting that task performance and sensory sophistication might follow non-trivial relationships and that increased sophistication on the sensor side does not necessarily equal a corresponding increase in performance. Although this result is a simple proof of concept, it illustrates the benefit of exploring the consequences of different hardware designs - rather than merely algorithmic choices - in simulation first. We also find surprisingly good performance in the navigation task, including a low number of collisions with simulated human agents, using a relatively simple A*/NavMesh-based navigation strategy, which suggests that navigation strategies for robots in crowds need not always be sophisticated.

Phosphorus (P) concentrations in sediments are frequently used to reconstruct past environmental conditions in freshwater and marine systems, with high values thought to be indicative of a high biological productivity. Recent studies suggest that the post-depositional formation of vivianite, an iron(II)-phosphate mineral, might significantly alter trends in P with sediment depth. To assess its importance, we investigate a sediment record from the Bornholm Basin that was retrieved during the Integrated Ocean Drilling Program (IODP) Baltic Sea Paleoenvironment Expedition 347 in 2013, consisting of lake sediments overlain by brackish–marine deposits. Combining bulk sediment geochemistry with microanalysis using scanning electron microscope energy dispersive spectroscopy (SEM-EDS) and synchrotron-based X-ray absorption spectroscopy (XAS), we demonstrate that vivianite-type minerals rich in manganese and magnesium are present in the lake deposits just below the transition to the brackish–marine sediments (at 11.5 to 12 m sediment depth). In this depth interval, phosphate that diffuses down from the organic-rich, brackish–marine sediments meets porewaters rich in dissolved iron in the lake sediments, resulting in the precipitation of iron(II) phosphate. Results from a reactive transport model suggest that the peak in iron(II) phosphate originally occurred at the lake–marine transition (9 to 10 m) and moved downwards due to changes in the depth of a sulfidization front. However, its current position relative to the lake–marine transition is stable as the vivianite-type minerals and active sulfidization fronts have been spatially separated over time. Experiments in which vivianite was subjected to sulfidic conditions demonstrate that incorporation of manganese or magnesium in vivianite does not affect its susceptibility to sulfide-induced dissolution.

Recycling of phosphorus (P) from sediments contributes to the development of bottom-water hypoxia in many coastal systems. Here, we present results of a year-long assessment of P dynamics in sediments of a seasonally hypoxic coastal marine basin (Lake Grevelingen, the Netherlands) in 2012. Sequential phosphorus extractions (SEDEX) and X-ray absorption spectroscopy (XAS) indicate that P was adsorbed to Fe-(III)-(oxyhydr)oxides when cable bacteria were active in the surface sediments in spring. With the onset of summer hypoxia, sulphide-induced dissolution of the Fe-(III)-(oxyhydr)oxides led to P release to the pore water and overlying water. The similarity in authigenic Ca-P concentrations in the sediment and suspended matter suggest that Ca-P is not formed in situ. The P burial efficiency was ≤ 32%. Hypoxia-driven sedimentary P recycling had a major impact on the water-column chemistry in the basin in 2012. Water-column monitoring data indicate up to ninefold higher surface water concentrations of phosphate in the basin in the late 1970s and a stronger hypoxia-driven seasonal P release from the sediment. The amplified release of P from the sediment in the past is attributed to the presence of a larger pool of Fe-bound P in the basin prior to the first onset of hypoxia. Given that P is not limiting, primary production in the basin has not been affected by the decadal changes in P availability and recycling over the past 40 years. The changes in P dynamics on decadal time scales were

Molybdenum (Mo) enrichments in marine sediments are a common indicator of the presence of sulphide near thesediment-water interface and can thereby record historic bottom-water oxygen depletion. Here, we assess theimpact of temporal changes in manganese (Mn) cycling and bottom-water oxygen on sedimentary Mo dynamicsin a seasonally-hypoxic coastal marine basin (Lake Grevelingen, the Netherlands). High resolution line scansobtained with LA-ICP-MS and discrete sample analyses reveal distinct oscillations in Mo with depth in thesediment. These oscillations and high sediment Mo concentrations (up to ~130 ppm) are attributed to depositionof Mo-bearing Mn-oxide-rich particles from the overlying water, the release of molybdate (MoO42−) tothe pore water upon reduction of these Mn-oxides, and subsequent sequestration of Mo. The latter process onlyoccurs in summer when sulphide concentrations near the sediment-water interface are elevated. Gravitationalfocussing of Mn oxides explains the observed increased input of Mo with increasing water depth. Diffusion ofMoO42− from the overlying water contributes only a small amount to the sediment Mo enrichments. Cablebacteria may indirectly impact sediment Mo dynamics by dissolving Mn-carbonates and thereby enhancing thepool of Mn-oxides in the system, and by contributing to remobilisation of sediment Mo during oxic periods. Asediment record that spans the past ~45 years indicates that sediment Mo concentrations have increased overthe past decades, despite less frequent occurrences of anoxia in the bottom waters based on oxygen measurementsfrom water column monitoring. We suggest that the elevated Mo in recent sediments reflects both enhancedrates of sulphate reduction and sulphide production in the surface sediment as a result of increased inputof organic matter into the basin from the adjacent North Sea since 1999, and an associated enhanced “Mnrefluxing” in the marine lake in summer.

A multi-tracer approach is applied to assess the impact of boundary fluxes (e.g. benthic input from sediments or lateral inputs from the coastline) on the acid-base buffering capacity, and overall biogeochemistry, of the North Sea. Analyses of both basin-wide observations in the North Sea and transects through tidal basins at the North-Frisian coastline, reveal that surface distributions of the d13C signature of dissolved inorganic carbon (DIC) are predominantly controlled by a balance between biological production and respiration. In particular, variability in metabolic DIC throughout stations in the well-mixed southern North Sea indicates the presence of an external carbon source, which is traced to the European continental coastline using naturally-occurring radium isotopes (224Ra and 228Ra). 228Ra is also shown to be a highly effective tracer of North Sea total alkalinity (AT) compared to the more conventional use of salinity. Coastal inputs of metabolic DIC and AT are calculated on a basin-wide scale, and ratios of these inputs suggest denitrification as a primary metabolic pathway for their formation. The AT input paralleling the metabolic DIC release prevents a significant decline in pH as compared to aerobic (i.e. unbuffered) release of metabolic DIC. Finally, long-term pH trends mimic those of riverine nitrate loading, highlighting the importance of coastal AT production via denitrification in regulating pH in the southern North Sea.

During the past ~8000 years the Baltic Sea has experienced three distinct intervals of hypoxia, of which the last one is still ongoing. These intervals are characterized by enhanced sedimentary organic matter burial and enrichment of redox-sensitive metals, such as molybdenum and iron. The first two of these intervals occurred during the Holocene Thermal Maximum (HTM) and the Medieval Climate Anomaly (MCA), two phases with high temperatures and changed precipitation patterns. Studies focussing on the Holocene sedimentary record of the Baltic Sea aim at clarifying the causes of the initiation, evolution and termination of these hypoxic intervals, as well as their consequences. This information could help to potentially aid in finding solutions for the mitigation of present-day hypoxia in the Baltic Sea. The factors contributing to hypoxia development during the HTM and MCA are still debated. Here we present data from a core retrieved during Integrated Ocean Drilling Program (IODP) Expedition 347 in the Landsort Deep basin, the deepest basin of the Baltic Sea at 463m water depth. Sediments were analysed at a high resolution using inorganic geochemical and (mainly marine) palynological proxies. Dinoflagellate cyst (dinocyst) assemblages and total elemental compositions provide clues on the role of salinity in enhancing stratification, ultimately causing hypoxia. During the onset of the HTM changes in salinity, as indicated by the palynology, closely follow changes in sedimentary organic carbon burial and trace metal concentrations. This suggests that stratification was an important cause of hypoxia during the HTM. In contrast, the palynology suggests that reduced stratification did not contribute to re-oxygenation during the termination of the HTM. We did not observe major changes in the palynology throughout the hypoxic interval of the MCA. Our results thus suggest that changes in salinity did not cause the onset and termination of hypoxia during the MCA.

A multitracer approach is applied to assess the impact of boundary fluxes (e.g., benthic input from sedimentsor lateral inputs from the coastline) on the acid-base buffering capacity, and overall biogeochemistry,of the North Sea. Analyses of both basin-wide observations in the North Sea and transects through tidalbasins at the North-Frisian coastline, reveal that surface distributions of the d13C signature of dissolved inorganiccarbon (DIC) are predominantly controlled by a balance between biological production and respiration.In particular, variability in metabolic DIC throughout stations in the well-mixed southern North Sea indicatesthe presence of an external carbon source, which is traced to the European continental coastline usingnaturally occurring radium isotopes (224Ra and 228Ra). 228Ra is also shown to be a highly effective tracer ofNorth Sea total alkalinity (AT) compared to the more conventional use of salinity. Coastal inputs of metabolicDIC and AT are calculated on a basin-wide scale, and ratios of these inputs suggest denitrification as aprimary metabolic pathway for their formation. The AT input paralleling the metabolic DIC release preventsa significant decline in pH as compared to aerobic (i.e., unbuffered) release of metabolic DIC. Finally, longtermpH trends mimic those of riverine nitrate loading, highlighting the importance of coastal AT productionvia denitrification in regulating pH in the southern North Sea.

Uptake of anthropogenic carbon dioxide (CO2) from the atmosphere has resulted in a range of changes in ocean chemistry, including the lowering of pH, collectively referred to as ocean acidification. Rates of coastal-zone acidification exceed those of the open ocean since coastal-ocean pH is influenced by many other processes than absorption of CO­2 alone. These processes do not only play a role in long-term acidification but also impact pH on seasonal timescales. Examples are enhanced atmospheric sulphur and nitrogen deposition, as well as eutrophication, the latter which can additionally result in the development of low-oxygen waters. The degree to which these processes induce a change in pH depends both on their rates and the extent to which the water can buffer acid production or consumption. This acid-base buffering capacity has been shown to decrease substantially in hypoxic waters, suggesting that low-oxygen conditions exacerbate ocean acidification. In this dissertation the key factors controlling the seasonal pH variability and longer-term pH changes in both the coastal and open ocean were examined, showing that buffering mechanisms play a crucial role in the impact of any biogeochemical or physical process on pH. Monthly or seasonal water-column chemistry and process-rate measurements in a transiently hypoxic coastal marine basin indicate that, despite generally higher process rates in the surface water of the basin, the amplitude of pH variability as mainly governed by the balance between primary production and respiration is greater in the seasonally-hypoxic bottom water, due to a considerable reduction of its acid-base buffering capacity in summer. A proton budget, based on these measurements and set up for each season, shows that the net change in pH is much smaller than the flux of protons induced by each of the individual processes. The interplay between absorption of atmospheric CO2 and atmospheric sulphur and nitroge

Coastal areas are impacted by multiple natural and anthropogenic processes and experience stronger pH fluctuations than the open ocean. These variations can weaken or intensify the ocean acidification signal induced by increasing atmospheric pCO2. The development of eutrophication-induced hypoxia intensifies coastal acidification, since the CO2 produced during respiration decreases the buffering capacity in any hypoxic bottom water. To assess the combined ecosystem impacts of acidification and hypoxia, we quantified the seasonal variation in pH and oxygen dynamics in the water column of a seasonally stratified coastal basin (Lake Grevelingen, the Netherlands). Monthly water-column chemistry measurements were complemented with estimates of primary production and respiration using O2 light–dark incubations, in addition to sediment–water fluxes of dissolved inorganic carbon (DIC) and total alkalinity (TA). The resulting data set was used to set up a proton budget on a seasonal scale. Temperature-induced seasonal stratification combined with a high community respiration was responsible for the depletion of oxygen in the bottom water in summer. The surface water showed strong seasonal variation in process rates (primary production, CO2 air–sea exchange), but relatively small seasonal pH fluctuations (0.46 units on the total hydrogen ion scale). In contrast, the bottom water showed less seasonality in biogeochemical rates (respiration, sediment–water exchange), but stronger pH fluctuations (0.60 units). This marked difference in pH dynamics could be attributed to a substantial reduction in the acid–base buffering capacity of the hypoxic bottom water in the summer period. Our results highlight the importance of acid–base buffering in the pH dynamics of coastal systems and illustrate the increasing vulnerability of hypoxic, CO2-rich waters to any acidifying process.

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