Geology, Mineralogy and Geochemistry of the Late Cenozoic McMurdo Volcanic Group, Victoria Land, Antarctica

<p>Rocks of the McMurdo Volcanic Group occur as stratovolcanoes, shield volcanoes, scoria cones, plugs, flows and volcanic piles up to 4000 m high along the Ross Sea margin of the Transantarctic Mountains and make up the Balleny Islands 300 km north of the Antarctic continental margin. The rocks are predominantly undersaturated and range from alkali basalt and basanite to trachyte and phonolite. Four volcanic provinces are recognised; Balleny, Hallett, Melbourne and Erebus. The Balleny volcanic province is situated along a transform fault in the South Pacific Ocean. The rocks are predominantly basanite. Hallett volcanic province occurs along the coast of northern Victoria Land as four elongate piles formed extensive of hyaloclastites, tuffs, breccias and capped by subaerial eruptive products. The lavas are a basanite/alkali basalt-trachyte-quartz trachyte association, and were extruded over the last 7 m.y. Melbourne volcanic province stretches across the Transantarctic Mountains in northern Victoria Land and ranges in age from 0 to 7 m.y. A Central Suite of intermediate and trachytic lavas form stratovolcanoes, cones and plugs, while many small basanite outcrops constitute a Local Suite. Three lava lineages, resulting from differentiation, are recognised. 1) Lavas at The Pleiades and Mt Overlord consist of a mildly potassic trachyandesite-tristanite-K-trachyte-peralkaline K-trachyte lineage. Major, trace and rare earth element (REE) data suggest evolution by fractional crystallization of olivine, clinopyroxene, magnetite, apatite and feldspar. 2) A basanite-nepheline hawaiite-nepheline mugearite-nepheline benmoreite lineage, found at The Pleiades is believed to result from fractional crystallization of olivine, clinopyroxene, kaersutite, magnetite, apatite and feldspar. 3) An oversaturated (Q = 0 to 18%) strongly potassic quartz trachyandesite-quartz tristanite-quartz trachyte lineage occurs at only Mt Melbourne. The Erebus volcanic province covers all McMurdo Volcanic Group rocks in south Victoria Land. Mt Erebus itself is still active, but the province includes rocks as old as 15 m.y. Two lava lineages very similar chemically are recognised: 1) The Erebus lineage consists of strongly porphyritic nepheline hawaiite-nepheline benmoreite-anorthoclase phonolite. Phenocrysts of feldspar, clinopyroxene, olivine, magnetite and apatite are characteristic. The chemistry of the lineage is compatible with fractional crystallization of the phenocryst phases. 2) A kaersutite lineage consists of basanite-nepheline hawaiite-nepheline mugearite-nepheline benmoreite-kaersutite phonolite-pyroxene phonolite. Clinopyroxene (Wo44-48 En40-48 Fs7-14) is ubiquitous, kaersutite is common in all intermediate lavas and primary olivine (Fa12 to Fa26) is confined to the basanites. Major element mass balance models for lavas from Hut Point Peninsula suggest formation by fractional crystallization of olivine, clinopyroxene, spinel (includes magnetite and ilmenite), kaersutite, feldspar and apatite. Middle REE show a marked depletion consistent with kaersutite fractionation. REE abundances were evaluated using the mass balance models and published partition coefficients. Calculated REE abundances show excellent agreement with the measured values. Abundances of "incompatible" elements Pb, Rb, Cs, Th and U are not consistent with the models and "volatile enrichment" processes are invoked to explain their abundances. Intermediate lavas of the kaersutite lineage are rare in the Erebus volcanic province, occurring only at Hut Point Peninsula and Brown Peninsula. At other areas basanite and phonolite lavas predominate. However these are considered to form by fractional crystallization processes similar to Hut Point Peninsula lavas. Erebus lineage lavas differentiated at higher temperatures and, lower PH2O than those of the kaersutite lineage, which characterize the periphery of Ross Island. REE abundances and comparison with experimental melting studies indicate DVDP basanite originated by a low degree of partial melting (1-5%) of a hydrous garnet peridotite mantle at pressures of 25-30 kbars. These data suggest that Ross Island is the site of a mantle plume with a diameter of, about 100 km and centred on Mt Erebus.</p>

Geology, Mineralogy and Geochemistry of the Late Cenozoic McMurdo Volcanic Group, Victoria Land, Antarctica

<p>Rocks of the McMurdo Volcanic Group occur as stratovolcanoes, shield volcanoes, scoria cones, plugs, flows and volcanic piles up to 4000 m high along the Ross Sea margin of the Transantarctic Mountains and make up the Balleny Islands 300 km north of the Antarctic continental margin. The rocks are predominantly undersaturated and range from alkali basalt and basanite to trachyte and phonolite. Four volcanic provinces are recognised; Balleny, Hallett, Melbourne and Erebus. The Balleny volcanic province is situated along a transform fault in the South Pacific Ocean. The rocks are predominantly basanite. Hallett volcanic province occurs along the coast of northern Victoria Land as four elongate piles formed extensive of hyaloclastites, tuffs, breccias and capped by subaerial eruptive products. The lavas are a basanite/alkali basalt-trachyte-quartz trachyte association, and were extruded over the last 7 m.y. Melbourne volcanic province stretches across the Transantarctic Mountains in northern Victoria Land and ranges in age from 0 to 7 m.y. A Central Suite of intermediate and trachytic lavas form stratovolcanoes, cones and plugs, while many small basanite outcrops constitute a Local Suite. Three lava lineages, resulting from differentiation, are recognised. 1) Lavas at The Pleiades and Mt Overlord consist of a mildly potassic trachyandesite-tristanite-K-trachyte-peralkaline K-trachyte lineage. Major, trace and rare earth element (REE) data suggest evolution by fractional crystallization of olivine, clinopyroxene, magnetite, apatite and feldspar. 2) A basanite-nepheline hawaiite-nepheline mugearite-nepheline benmoreite lineage, found at The Pleiades is believed to result from fractional crystallization of olivine, clinopyroxene, kaersutite, magnetite, apatite and feldspar. 3) An oversaturated (Q = 0 to 18%) strongly potassic quartz trachyandesite-quartz tristanite-quartz trachyte lineage occurs at only Mt Melbourne. The Erebus volcanic province covers all McMurdo Volcanic Group rocks in south Victoria Land. Mt Erebus itself is still active, but the province includes rocks as old as 15 m.y. Two lava lineages very similar chemically are recognised: 1) The Erebus lineage consists of strongly porphyritic nepheline hawaiite-nepheline benmoreite-anorthoclase phonolite. Phenocrysts of feldspar, clinopyroxene, olivine, magnetite and apatite are characteristic. The chemistry of the lineage is compatible with fractional crystallization of the phenocryst phases. 2) A kaersutite lineage consists of basanite-nepheline hawaiite-nepheline mugearite-nepheline benmoreite-kaersutite phonolite-pyroxene phonolite. Clinopyroxene (Wo44-48 En40-48 Fs7-14) is ubiquitous, kaersutite is common in all intermediate lavas and primary olivine (Fa12 to Fa26) is confined to the basanites. Major element mass balance models for lavas from Hut Point Peninsula suggest formation by fractional crystallization of olivine, clinopyroxene, spinel (includes magnetite and ilmenite), kaersutite, feldspar and apatite. Middle REE show a marked depletion consistent with kaersutite fractionation. REE abundances were evaluated using the mass balance models and published partition coefficients. Calculated REE abundances show excellent agreement with the measured values. Abundances of "incompatible" elements Pb, Rb, Cs, Th and U are not consistent with the models and "volatile enrichment" processes are invoked to explain their abundances. Intermediate lavas of the kaersutite lineage are rare in the Erebus volcanic province, occurring only at Hut Point Peninsula and Brown Peninsula. At other areas basanite and phonolite lavas predominate. However these are considered to form by fractional crystallization processes similar to Hut Point Peninsula lavas. Erebus lineage lavas differentiated at higher temperatures and, lower PH2O than those of the kaersutite lineage, which characterize the periphery of Ross Island. REE abundances and comparison with experimental melting studies indicate DVDP basanite originated by a low degree of partial melting (1-5%) of a hydrous garnet peridotite mantle at pressures of 25-30 kbars. These data suggest that Ross Island is the site of a mantle plume with a diameter of, about 100 km and centred on Mt Erebus.</p>

PAPEL DOS PEIXES NA RECICLAGEM DE NUTRIENTES EM RIACHOS TROPICAIS

Fish can contribute directly and indirectly to nutrient recycling in aquatic environments, affecting community structure and ecosystem processes. Through the excretion of metabolic waste, fish make inorganic nutrients available in the environment that can be used by algae and bacteria. Nitrogen and phosphorus are often limiting nutrients in streams, so fish can be a relevant source of these nutrients. Many factors can influence excretion rates, including diet, body nutrient demand (for reproduction and growth), ontogeny, body size, temperature and other abiotic factors. Currently, two theories propose to explain which factors control excretion rates: 1) The Theory of Ecological Stoichiometry is based on mass balance models and uses the amount of nutrients in the diet and the fish nutrient demand as predictors of excretion rates; and 2) the Metabolic Theory of Ecology that uses body size and temperature as factors that regulate an organism metabolic rates and, thus, its excretion rates. The relative importance of fish as nutrient recyclers in streams varies depending on species intrinsic characteristics and environmental factors. This includes the magnitude of excretion rates from the entire fish community, the nutrient concentration and nutrient input into the stream, the stream nutrient demand and the period of activity and behavior of the fish. For example, species that are abundant in oligotrophic streams have the potential to represent an important source of nutrients. But other peculiarities, such as diet, specific nutrient demands, or migratory behaviors, can make them important sources or sinks of nutrients in a stream. This article reviews studies that address the role of fish as nutrient recyclers and explains the most common techniques used in this type of studies.

Surface Mass Balance Models Vs. Stake Observations: A Comparison in the Lake Vostok Region, Central East Antarctica

The surface mass balance (SMB) is very low over the vast East Antarctic Plateau, for example in the Vostok region, where the mean SMB is on the order of 20–35 kg m-2 a-1. The observation and modeling of spatio-temporal SMB variations are equally challenging in this environment. Stake measurements carried out in the Vostok region provide SMB observations over half a century (1970–2019). This unique data set is compared with SMB estimations of the regional climate models RACMO2.3p2 (RACMO) and MAR3.11 (MAR). We focus on the SMB variations over time scales from months to decades. The comparison requires a rigorous assessment of the uncertainty in the stake observations and the spatial scale dependence of the temporal SMB variations. Our results show that RACMO estimates of annual and multi-year SMB agree well with the observations. The regression slope between modelled and observed temporal variations is close to 1.0 for this model. SMB simulations by MAR are affected by a positive bias which amounts to 6 kg m-2 a-1 at Vostok station and 2 kg m-2 a-1 along two stake profiles between Lake Vostok and Ridge B. None of the models is capable to reproduce the seasonal distributions of SMB and precipitation. Model SMB estimates are used in assessing the ice-mass balance and sea-level contribution of the Antarctic Ice Sheet by the input-output method. Our results provide insights into the uncertainty contribution of the SMB models to such assessments.

Investigating Fast- and Slow-settling Phosphorus Fractions in Lakes using Steady-state Modeling

&lt;p&gt;Phosphorus (P) is the key and limiting nutrient in the eutrophication of freshwater resources. Modeling P retention in lakes using steady-state mass balance models (i.e. Vollenweider-type models) provides insights into the lake P management and a simple method for large-scale assessments of P in lakes. One of the basic problems in the mass balance modeling of P in lakes is the removal of P from the lake water column by settling. A fraction of the incoming P into the lake from the watershed is associated with fast-settling particles (e.g. sediment particles) that result in the removal of that fraction of P quickly at the lake entrance. However, existing models considering a constant fraction of fast-settling TP for all lakes are shown to result in overestimation of the retention of P in lakes with short hydraulic residence time. In this study, we combine a hypothesis of the fast- and slow-settling P fractions into the steady-state mass balance models of P retention in lakes. We use a large database of lakes to calibrate the model and evaluate the hypothesis. The results of this work can be used for the improvement of the prediction power of P retention models in lakes and help to better understand the processes of P cycling in lakes.&lt;/p&gt;

Impact of the choice of surface mass balance models and their calibration on large-scale glacier change projections

&lt;p&gt;A recent large model intercomparison study (GlacierMIP) showed that differences between the glacier models is a dominant source of uncertainty for future glacier change projections, in particular in the first half of the century.&amp;#160; Each glacier model has their own unique set of process representations and climate forcing methodology, which makes it impossible to determine the model components that contribute most to the projection uncertainty. This study aims to improve our understanding of the sources of large scale glacier model uncertainty using the Open Global Glacier Model (OGGM), focussing on the surface mass balance (SMB) in a first step. We calibrate and run a set of interchangeable SMB model parameterizations (e.g. monthly vs. daily, constant vs. variable lapse rates, albedo, snowpack evolution and refreezing) under controlled boundary conditions. Based on ensemble approaches, we explore the influence of (i) the parameter calibration strategy and (ii) SMB model complexity on regional to global glacier change. These uncertainties are then put in relation to a qualitative selection of other model design choices, such as the forcing climate dataset and ice dynamics model parameters.&amp;#160;&lt;/p&gt;

Phosphorous Supply to a Eutrophic Artificial Lake: Sedimentary versus Groundwater Sources

The eutrophic Lake Eichbaumsee, a ~1 km long and 280 m wide (maximum water depth 16 m) dredging lake southeast of Hamburg (Germany), has been treated for water quality improvements using various techniques (i.e., aeration plants, removal of dissolved phosphorous by aluminum phosphorous precipitation, and by Bentophos® (Phoslock Environmental Technologies, Sydney, Australia), adsorption) during the past ~15 years. Despite these treatments, no long-term improvement of the water quality has been observed and the lake water phosphorous content has continued to increase by e.g., ~670 kg phosphorous between autumn 2014 and autumn 2019. As no creeks or rivers drain into the lake and hydrological groundwater models do not suggest any major groundwater discharge into the lake, sources of phosphorous (and other nutrients) are unknown. We investigated the phosphorous fluxes from sediment pore water and from groundwater in the water body of the lake. Sediment pore water was extracted from sediment cores recovered by divers in August 2018 and February 2019. Diffusive phosphorous fluxes from pore water were calculated based on phosphorus gradients. Stable water isotopes (δ2H, δ18O) were measured in the lake water, in interstitial waters in the banks surrounding the lake, in the Elbe River, and in three groundwater wells close to the lake. Stable isotope (δ2H, δ18O) water mass balance models were used to compute water inflow/outflow to/from the lake. Our results revealed pore-water borne phosphorous fluxes between 0.2 mg/m2/d and 1.9 mg/m2/d. Assuming that the measured phosphorous fluxes are temporarily and spatially representative for the whole lake, about 11 kg/a to 110 kg/a of phosphorous is released from sediments. This amount is lower than the observed lake water phosphorous increase of ~344 kg between April 2018 and November 2018. Water stable isotope (δ2H, δ18O) compositions indicate a water exchange between an aquifer and the lake water. Based on stable isotope mass balances we estimated an inflow of phosphorous from the aquifer to the lake of between ~150 kg/a and ~390 kg/a. This result suggests that groundwater-borne phosphorous is a significant phosphorous source for the Eichbaumsee and highlights the importance of groundwater for lake water phosphorous balances.

Time to refine mercury mass balance models for fish

Mercury mass balance models (MMBMs) for fish are powerful tools for understanding factors affecting growth and food consumption by free-ranging fish in rivers, lakes, and oceans. Moreover, MMBMs can be used to predict the consequences of global mercury reductions, overfishing, and climate change on mercury (Hg) concentration in commercially and recreationally valuable species of fish. Such predictions are useful in decision-making by resource managers and public health policy makers, because mercury is a neurotoxin and the primary route of exposure of mercury to humans is via consumption of fish. Recent evidence has emerged to indicate that the current-day version of MMBMs overestimates the rate at which fish eliminate mercury from their bodies. Consequently, MMBMs overestimate food consumption by fish and underestimate Hg concentration in fish. In this perspective, we explore underlying reasons for this overestimation of Hg-elimination rate, as well as consequences and implications of this overestimation. We highlight emerging studies that distinguish species and sex as contributing factors, in addition to body weight and water temperature, that can play an important role in how quickly Hg is eliminated from fish. Future research directions for refining MMBMs are discussed.

An Improved Equilibrium Optimizer Algorithm for Tackling Global Optimization Problems

This paper introduces a new, metaheuristic optimization algorithm, named an Improved Metaheuristic Equilibrium Optimizer (IMEO). The algorithm Equilibrium Optimizer (EO), is inspired by its method of estimating both equilibrium and dynamics, based on mass balance models. Studying the EO closely, we find that EO does not have the potential to get closer to the optimal global solution when it solves certain problems. To improve EO efficiency, this paper suggests using an improvement, called an elite opposition learning-based, that increases the speed and accuracy of EO convergence, and helps the algorithm to get a better solution. Falling into local optima is a big problem, EO suffers from the fact that when we look deeply at the standard EO mathematical formula, we found that the algorithm is trying to get out of the local optima, but sometimes it can't, so we're introducing a new mathematical formula based on using cosine trigonometric function. To validate the proposed algorithm efficiency, The IMEO algorithm is evaluated on 23 benchmarks and compared with other common naturalistic heuristic algorithms. The statistical analysis shows that the results of IMEO achieve better performance compared to the standard EO and several well-known algorithms on several benchmark issues.

Assimilating near real-time mass balance observations into a model ensemble using a particle filter

Glaciers fulfil important short-term functions like drinking water supply and they are important indicators of climate change. This is why the interest in near real-time mass balance nowcasting is high. Here, we address this interest and provide an evaluation of seven continuous observations of point mass balance based on on-line cameras transmitting images every 20 minutes on three Swiss glaciers during summer 2019. Like this, we read 352 near real-time daily point mass balances in total from the camera images, revealing melt rates of up to 0.12 meter water equivalent per day (m w.e. d−1) and the biggest total melt on the tongue of Findelgletscher with more than 5 m w.e. in 81 days. These observations are assimilated into an ensemble of three temperature index (TI) and one simplified energy balance mass balance models using an augmented particle filter with a custom resampling method. The state augmentation allows estimating model parameters over time. The custom resampling ensures that temporarily poorly performing models are kept in the ensemble instead of being removed during the resampling step of the particle filter. We analyse model performance over the observation period, and find that the model probability within the ensemble is highest on average with 58 % for an enhanced TI model, a simple TI model reaches about 19 %, while models incorporating additional energy fluxes have probabilities between 8 % and 15 %. When compared to reference forecasts produced with both mean model parameters and parameters tuned on single mass balance observations, the mass balances produced with the particle filter performs about equally well on the daily scale, but outperforms predictions of cumulative mass balance. The particle filter improves the performance scores of the reference forecasts by 91–97 % in these cases. A leave-one-out cross-validation on the individual glaciers shows that the particle filter is able to reproduce point observations at locations on the glacier where it was not calibrated, as the filtered mass balances do not deviate more than 8 % from the cumulative observations at the test locations. A comparison with glacier-wide annual mass balance by Glacier Monitoring Switzerland (GLAMOS) involving additional measurements distributed over the entire glacier, mostly show good agreement, but also deviations of up to 0.41 m w.e. for one instance.