Polymetallic Nodule Mining, Waste Disposal, and Species Extinction at the Abyssal Seafloor

The size of individual mining blocks for polymetallic nodule extraction seems to be rather small, not more than 100 km² in the French mining claim. Even when adding an additional resedimentation zone to the directly impacted area, the size of the affected seabed would remain below 200 km². We assume that even rare species in the abyss inhabit larger areas and propose discussions of the International Seabed Authority and other stakeholders for the different subregions on mining strategies from the perspective of exploitation versus species extinction and conservation. Although impacts of waste disposal at the abyssal seafloor are different from those of nodule mining, the 200 km² concept may also be applied.     

Increasing water losses from snow captured in the canopy of boreal forests: A case study using a 30 year data set

Water losses from snow intercepted by forest canopy can significantly influence the hydrological cycle in seasonally snow‐covered regions, yet how snow interception losses (SIL) are influenced by a changing climate are poorly understood. In this study, we used a unique 30 year record (1986–2015) of snow accumulation and snow water equivalent measurements in a mature mixed coniferous (Picea abies and Pinus sylvestris ) forest stand and an adjacent open area to assess how changes in weather conditions influence SIL. Given little change in canopy cover during this study, the 20% increase in SIL was likely the result of changes in winter weather conditions. However, there was no significant change in average wintertime precipitation and temperature during the study period. Instead, mean monthly temperature values increased during the early winter months (i.e., November and December), whereas there was a significant decrease in precipitation in March. We also assessed how daily variation in meteorological variables influenced SIL and found that about 50% of the variation in SIL was correlated to the amount of precipitation that occurred when temperatures were lower than ?3 °C and to the proportion of days with mean daily temperatures higher than +0.4 °C. Taken together, this study highlights the importance of understanding the appropriate time scale and thresholds in which weather conditions influence SIL in order to better predict how projected climate change will influence snow accumulation and hydrology in boreal forests in the future.     

A detailed post‐IR IRSL dating study of the Niuyangzigou loess site in northeastern China

In this study, we report standard quartz SAR OSL and post‐IR infrared (IR) stimulated luminescence (post‐IR IRSL; pIRIR₂₉₀) measurements made on sand‐sized quartz and K‐feldspar extracts from the loess‐palaeosol sequence at Niuyangzigou in northeastern China. The quartz OSL characteristics are satisfactory. Extensive pIRIR_50,290 dose recovery tests were performed by adding doses on top of the natural dose. We found that dose recovery ratios improve significantly when the test dose ranges between ~15 and ~80% of the total dose, and good dose recovery (within ±5% of unity) can be obtained up to ～800 Gy. Otherwise, the dose recovery ratio deviates from unity. The D_e values also depend on the test dose size and so we conclude that the effect of test dose size should be routinely considered in pIRIR dating. First IR stimulation plateau pIRIR₂₉₀ results are compared with multiple elevated temperature ‐pIRIR (MET‐pIRIR) data. It appears that the low temperature MET‐pIRIR data are strongly affected by poor dose recovery, but this is not the case for the pIRIR₂₉₀ results. Natural signal measurements at the highest (first IR) stimulation temperature on a sample expected to be in field saturation suggest that ~10% signal loss occurs in pIRIR signals. Long‐term laboratory bleaching experiments (>80 days) show that a constant (or very difficult to bleach) residual pIRIR₂₉₀ signal is reached after ~300 h, corresponding to a dose of 6.2±0.7 Gy. Quartz OSL and feldspar pIRIR_50,290 ages are in good agreement at least back to c. 70 ka. Beyond this the quartz ages begin to underestimate but the feldspar ages are in agreement with the expected Last Interglacial age palaeosol.     

Particulate aluminium in boreal streams: Towards a better understanding of its sources and influence on dissolved aluminium speciation

The adverse impacts of the inorganic labile monomeric Al (Al_i) fraction on aquatic organisms have meant that Al (Al_tot) determination and even speciation has become a routine part of environmental monitoring and assessment. However, if samples are not filtered prior to analysis then particulate Al (Al_tot(p)) could influence the determination of Al_tot, and therefore the determination of the more toxicologically important (Al_i), both when it is measured analytically or modelled from Al_tot. This paper shows that the Al/DOC ratio in unfiltered samples can identify the Al_tot(p) fraction, and thus improve the speciation of Al_i. These findings are based on data from a study in a 67 km² catchment in northern Sweden during the snowmelt-driven spring flood of two consecutive years. Filtered and unfiltered samples were studied to determine the spatial and temporal patterns in Al_tot(p). The concentrations of Al_tot(p) were greatest in larger downstream sites where significant silt deposits are located. The sites with no silt in their drainage area showed a mean difference between filtered (Al_tot(f)) and unfiltered (Al_tot(uf)) samples of 6%, while sites with silt deposits had a mean difference of 65%. The difference between filtered and unfiltered samples was greatest at peak flow. Spikes in Al_tot(p) did not behave consistently during fractionation with a cation exchange column, resulting in increases in either measured Al_i(f) or non-labile monomeric Al (Al_o(f)). Al_tot(p) spikes were associated with sharp increases in the Al:DOC ratio. The baseflow Al:DOC ratio could be used to model filtered Al_tot from DOC with a Spearman rho of 0.75.     

The Požarevac loess–paleosol sequence: a record of increased aridity in the south-eastern margin of the Carpathian Basin during the last 350 ka

The loess sequence preserved in the Požarevac brickyard in north-eastern Serbia comprises eight loess units separated by seven paleosols. Geochronological investigation using amino acid racemization and luminescence dating support stratigraphic correlations of loess units L3, S2LL1 and L1 at the Požarevac section with loess of glacial cycles E [Marine Isotope Stage (MIS) 10], D (MIS 9–8), C (MIS 7–6) and B (MIS 5–2) across central Europe. Correlation with the marine oxygen-isotope stratigraphy and associated paleoclimatic inferences are further supported by magnetic susceptibility, particle size and carbonate content measured in Požarevac sediments. Malacological investigations at the Požarevac section reveal the continuous presence of the Chondrula tridens and Helicopsis striata faunal assemblages throughout the last 350 ka. The loess malacological fauna, which is characterized by the complete absence of cold-resistant and cold-preferring species, suggests a stable, dry and relatively warm glacial and interglacial climate, compared with other central European loess localities. Together these data suggest that the south-eastern part of the Carpathian (Pannonian, Middle Danube) Basin was a refugium for warm-preferring and xerophilous land-snails during the generally unfavorable glacial climates of the late Middle and Late Pleistocene.     

Hydrogeochemistry of Fe and Mn in small boreal streams: The role of seasonality, landscape type and scale

Stream water from a stream network of 15 small boreal catchments (0.03-67 km²) in northern Sweden was analyzed for unfiltered (total) and filtered (<0.4 μm) concentrations of iron (Fe_tot and Fe_<0.4) and manganese (Mn_tot and Mn_<0.4). The purpose was to investigate the temporal and spatial dynamics of Fe, Mn and dissolved organic carbon (DOC) as influenced by snow melt driven spring floods and landscape properties, in particular the proportion of wetland area. During spring flood, concentrations of Fe_tot, Fe_<0.4, Mn_tot, Mn_<0.4 and DOC increased in streams with forested catchments (<2% wetland area). In catchments with high coverage of wetlands (>30% wetland area) the opposite behavior was observed. The hydrogeochemistry of Fe was highly dependent on wetlands as shown by the strong positive correlation of the Fe_tot/Al_tot ratio with wetland coverage (r² = 0.89, p < 0.001). Furthermore, PCA analysis showed that at base flow Fe_tot and Fe_<0.4 were positively associated with wetlands and DOC, whereas they were not associated during peak flow at spring flood. The temporal variation of Fe was likely related to varying hydrological pathways. At peak discharge Fe_tot was associated with variables like silt coverage, which highlights the importance of particulates during high discharge events. For Mn there was no significant correlation with wetlands, instead, PCA analysis showed that during spring flood Mn was apparently more dependent on the supply of minerogenic particulates from silt deposits on the stream banks of some of the streams. The influence of minerogenic particulates on the concentration of, in particular, Mn was greatest in the larger, lower gradient streams, characterized by silt deposits in the near-stream zone. In the small forested streams underlain by till, DOC was of greater importance for the observed concentrations, as indicated by the positive correlation of both Fe_tot and Fe_<0.4 with DOC (r² = 0.77 and r² = 0.76, p < 0.001) at the smallest headwater forest site. In conclusion, wetland area and DOC were important for Fe concentrations in this boreal stream network, whereas silt deposits strongly influenced Mn concentrations. This study highlights the importance of studying stream water chemistry from a landscape perspective in order to address future environmental issues concerning mobility of Fe, Mn and associated trace metals.     

Storage,mixing, and fluxes of water in the critical zone across northern environments inferred by stable isotopes of soil water

Quantifying soil water storage, mixing, and release via recharge, transpiration, and evaporation is essential for a better understanding of critical zone processes. Here, we integrate stable isotope (²H and ¹⁸O of soil water, precipitation, and groundwater) and hydrometric (soil moisture) data from 5 long‐term experimental catchments along a hydroclimatic gradient across northern latitudes: Dry Creek (USA), Bruntland Burn (Scotland), Dorset (Canada), Krycklan (Sweden), and Wolf Creek (Canada). Within each catchment, 6 to 11 isotope sampling campaigns occurred at 2 to 4 sampling locations over at least 1 year. Analysis for ²H and ¹⁸O in the bulk pore water was done for >2,500 soil samples either by cryogenic extraction (Dry Creek) or by direct equilibration (other sites). The results showed a similar general pattern that soil water isotope variability reflected the seasonality of the precipitation input signal. However, pronounced differences among sampling locations occurred regarding the isotopic fractionation due to evaporation. We found that antecedent precipitation volumes mainly governed the fractionation signal, temperature and evaporation rates were of secondary importance, and soil moisture played only a minor role in the variability of soil water evaporation fractionation across the hydroclimatic gradient. We further observed that soil waters beneath conifer trees were more fractionated than beneath heather shrubs or red oak trees, indicating higher soil evaporation rates in coniferous forests. Sampling locations closer to streams were more damped and depleted in their stable isotopic composition than hillslope sites, revealing increased subsurface mixing towards the saturated zone and a preferential recharge of winter precipitation. Bulk soil waters generally comprised a high share of waters older than 14 days, which indicates that the water in soil pores are usually not fully replaced by recent infiltration events. The presented stable isotope data of soil water were, thus, a useful tool to track the spatial variability of water fluxes within and from the critical zone. Such data provide invaluable information to improve the representation of critical zone processes in spatially distributed hydrological models.     

A Wandering Population of the HexactinelIid Sponge Pheronema carpenteri on the Continental Slope off Morocco, Northwest Africa

Abstract. A photo transect along the continental slope off Morocco, Northwest Africa revealed an extensive population of the hexactinellid sponge Pheronema carpenteri ( thomson , 1869). The population forms a distinct band parallel to the depth contours between 740 and 820 m. Because of the long persistence of dead hexactinellid skeletons, living and dead individuals of P. carpenteri were recorded, together with the spicular remains of disintegrated individuals. Furthermore, the presence of small individuals and that of other epifaunal elements were recorded. The peaks of abundance of dead and living sponges, respectively. are not at the same depth, the maximum abundance of living individuals being above that of the dead ones; small, i.e ., probably young P. carpenteri individuals were observed only in the upper zone. This can be interpreted as a successional phenomenon, i.e ., the population of P. carpenteri has apparently 'moved' slowly up the slope. The fauna associated with the P. carpenteri population along the Moroccan coast seems to be much poorer than that associated with another band-shaped population in the Porcupine Seabight investigated by B ett & R ice (1992). indicating that the presence of dense hexactinellid populations does not invariably lead to conspicuous benthic faunal enrichment.