Application of Kriging Interpolation for Glacier Mass Balance Computations

In order to compute the specific mass balance of a glacier, point measurements of mass balance need to be integrated and thus interpolated over the entire glacier. In this study kriging was applied as interpolation technique to mass balance data of Storglaciren, a 3 km² valley glacier, focusing on the sensitivity of results to the choice of some kriging parameters. Although the spatial means varied only little in most cases, the spatial distribution of the mass balance quantities was sensitive to the assumption on kriging parameters, suggesting that the kriging parameters need to be carefully optimized for each case if the spatial distribution is of interest.     

Mercury isotope fractionation during photoreduction in natural water is controlled by its Hg/DOC ratio

Photoreduction of Hg in natural water plays a crucial role in the production of elemental Hg and its biogeochemical cycle. Solar irradiation and dissolved organic carbon (DOC) in water are considered to be the major factors inducing Hg photoreduction. We investigated Hg isotope fractionation during photoreduction and its relationship with Hg/DOC ratios. Both mass dependent (MDF) and mass independent fractionation (MIF) was observed. MIF enriched ¹⁹⁹Hg and ²⁰¹Hg in the reactant Hg(II) and thus, significantly enhanced the fractionation between odd and even isotopes. This direction of MIF is consistent with magnetic isotope effect as the underlying cause for the odd isotope enrichment in reactants. MIF also occurred in dark controls. But in the absence of light, ¹⁹⁹Hg and ²⁰¹Hg were enriched in the product Hg(0), which is not explained by magnetic isotope effects. We propose that nuclear volume effect dominated Hg isotope fractionation under these conditions. The reduction kinetics and isotope fractionation during photoreduction strongly correlated to Hg/DOC concentration ratios. Although different reduction kinetics and fractionation factors were measured at different Hg/DOC ratios, the same Hg/DOC ratios led to almost identical results. The degree of MIF for the two odd isotopes was also affected by Hg/DOC ratios. For this reason, it is critical to study Hg photoreduction at a near-natural Hg/DOC ratio in order to better simulate natural conditions. We suggest that differences in Hg-DOC binding, which varies with Hg/DOC ratios, may be responsible for the relationship between Hg/DOC ratios and Hg photoreduction.     

“Wet” low angle subduction: a possible mechanism below the Tanzania craton 2 Ga ago

The hypothesis that much of the lithosphere of the Archaean Tanzania Craton was hydrated, by the dehydration of a buoyant subduction 2 Ga ago is presented in this study. Buoyant subduction is a potential mechanism for thermal erosion and metasomatism of extensive regions of the cold overlying continental lithosphere. This hypothesis could explain why the Tanzania Craton forms an undeformed island within the intensely deformed mobile belts. Furthermore, it would explain the formation of the eclogite and lherzolite bearing kimberlites within the Tanzania Craton far away from the trench. A buoyant, slow subduction is required because this would provide sufficient cooling from the overlying cratonic lithosphere and therefore the dipping slab could retain hydrous minerals such as antigorite in hydrated aureoles in peridotites. To test this hypothesis, the release of water during prograde metamorphism of a flat-subducting plate was modeled. It is shown that water can be transported ～800 km laterally, inboard of the trench, which is close to the north-south extension of the Archaean Tanzania Craton.     

On the diffusion of rhodamine B on both sides of a river plume front

Conclusions In spite of poor weather conditions, for which vertical mixing down to the bottom is expected in general, the rhodamine is still trapped between vertical and horizontal gradients 3 days after release. The turbulent flux through the front is so small that a significant transport through the front can probably only be effected by vortices occasionally occurring — as observed in the experiment of October '82.The front-parallel and cross-frontal spreading velocities have the same order of magnitude as in October '82. However, the decrease of rhodamine peak concentration runs much slower: in the first experiment, the spreading was hindered by only two boundaries, the front and the bottom. Now, the rhodamine is embedded in a field of gradients, allowing spreading in one dimension only, i.e. parallel to the isopycnicals. In this stage only processes reducing the gradients can intensify the exchange.To understand the dynamic of oceanic features such as fronts and vortices, it is essential to observe the movement of a marked water mass within the whole system. Again, the reconstructed distributions show clearly the ability of rhodamine to trace processes in the order of magnitude of several miles right down to very small scale processes, as the diffusion of the tracer through the front.     

Numerical investigation of tunneling in saturated soil: the role of construction and operation periods

This paper numerically investigates the slurry shield tunneling in fully saturated soils with different hydraulic conductivities in short- and long-term scales. A fully coupled hydromechanical three-dimensional model that accounts for the main aspects of tunnel construction and the hydromechanical interactions due to tunneling process is developed. An elasto-plastic constitutive model obeying a double hardening rule, namely hardening soil model, is employed in the numerical simulations. The research mainly focuses on assessing the influence of soil hydraulic conductivity and the method to simulate backfill grouting in the tail void on the evolution of ground subsidence, excess pore water pressure and lining forces. Two different consolidation schemes have been taken into account to computationally address the tunnel construction in soil with low and high hydraulic conductivities. In addition, different methods are employed to simulate the tail void grouting as a hydromechanical boundary condition and to study its effects on the model responses. Finally, the influences of infiltration of the fluidized particles of grouting suspension into the surrounding soil and its corresponding time–space hydraulic conductivity evolution on the displacements and lining forces are studied.     

Natural Cycles and Transfer of Mercury Through Pacific Coastal Marsh Vegetation Dominated by Spartina foliosa and Salicornia virginica

The potential for marsh plants to be vectors in the transport of mercury species was studied in the natural, mature, tidal China Camp salt marsh on San Pablo Bay. The fluxes of organic matter, mercury (THg), and monomethylmercury (MeHg) were studied in natural stands of Spartina foliosa and Salicornia virginica. Seasonal fluxes from the sediment into aboveground biomass of live plants and subsequent transfer into the dead plant community by mortality were measured. Loss of THg and MeHg from the dead plant community through fragmentation, leaching, and excretion were calculated and were similar to net uptake. Seasonal data were added up to calculate annual mass balances. In S. foliosa, annual net production was 1,757 g DW m^?2, and the annual net uptakes in the aboveground biomass were 305 μg THg m^?2 and 5.720 μg MeHg m^?2. In S. virginica, annual net production was 2,117 g DW m^?2, and the annual net uptakes in aboveground biomass were 99.120 μg THg m^?2 and 1.990 μg MeHg m^?2. Of both plant species studied, S. foliosa had a slightly lower production rate but greater mercury species uptake and loss rates than S. virginica, and, consequently, it is to be expected that S. foliosa matter may affect the local and possibly the regional food web relatively more than S. virginica. However, the actual effects of the input of mercury-species-containing plant-derived particulate matter into the food webs would depend on trophic level, food preference, seasonal cycle of the consumer, total sediment surface area vegetated, location of the vegetation in the marsh landscape, and estuary bay landscape. Since the levels of mercury species in dead plant material greatly exceed those in live plant material (on a dry weight basis), detritivores would ingest greater mercury species concentrations than herbivores, and consumers of S. foliosa would ingest more than consumers of S. virginica. The greatest THg and MeHg losses of both plant species due to mortality and to fragmentation–leaching–excretion occurred in late spring and early autumn, which corresponds to peak MeHg levels observed in sediments of coastal systems of previous studies, suggesting enhanced THg–MeHg export from the marsh to the nearshore sediment.     

Influence of changed vegetations fields on regional climate simulations in the Barents Sea Region

In the context of the EU-Project BALANCE () the regional climate model REMO was used for extensive calculations of the Barents Sea climate to investigate the vulnerability of this region to climate change. The regional climate model REMO simulated the climate change of the Barents Sea Region between 1961 and 2100 (Control and Climate Change run, CCC-Run). REMO on ~50 km horizontal resolution was driven by the transient ECHAM4/OPYC3 IPCC SRES B2 scenario. The output of the CCC-Run was applied to drive the dynamic vegetation model LPJ-GUESS. The results of the vegetation model were used to repeat the CCC-Run with dynamic vegetation fields. The feedback effect of the modified vegetation on the climate change signal is investigated and discussed with focus on precipitation, temperature and snow cover. The effect of the offline coupled vegetation feedback run is much lower than the greenhouse gas effect.     

Predictability of the mid-latitude Atlantic meridional overturning circulation in a multi-model system

Assessing the skill of the Atlantic meridional overturning circulation (AMOC) in decadal hindcasts (i.e. retrospective predictions) is hampered by a lack of observations for verification. Models are therefore needed to reconstruct the historical AMOC variability. Here we show that ten recent oceanic syntheses provide a common signal of AMOC variability at 45°N, with an increase from the 1960s to the mid-1990s and a decrease thereafter although they disagree on the exact magnitude. This signal correlates with observed key processes such as the North Atlantic Oscillation, sub-polar gyre strength, Atlantic sea surface temperature dipole, and Labrador Sea convection that are thought to be related to the AMOC. Furthermore, we find potential predictability of the mid-latitude AMOC for the first 3–6 year means when we validate decadal hindcasts for the past 50 years against the multi-model signal. However, this predictability is not found in models driven only by external radiative changes, demonstrating the need for initialization of decadal climate predictions.