Characterization of Water Quality in Xiao Xingkai Lake: Implications for Trophic Status and Management

Increasing cases of lake eutrophication globally have raised concerns among stakeholders, and particularly in China. Evaluating the causes of eutrophication in waterways is essential for effective pollution prevention and control. Xiao Xingkai Lake is part of and connected to Xingkai(Khanka) Lake, a boundary lake between China and Russia. In this study, we investigated the spatio-temporal variabilities in water quality(i.e., dissolved oxygen(DO), total nitrogen(TN), total phosphorus(TP), chemica...     

Characterization of the lithological contact in the shergottite EETA79001—A record of igneous differentiation processes on Mars

Abstract— Elephant Moraine (EET) A79001 is the only Martian meteorite that consists of both an olivine‐phyric shergottite (lithology A) and a basaltic shergottite (lithology B). The presence of these lithologies in one rock has previously been ascribed to mixing processes (either magmatic or impact‐induced). Here we present data regarding phase changes across the contact between the lithologies. These data show that the contact is gradational and suggest that it is a primary igneous feature consistent with crystallization of a single cooling magma. We present a model to establish a petrogenetic connection between an olivine‐phyric and a basaltic shergottite through differentiation. The model involves the shallow or surface emplacement of a magma that contained pre‐eruptive solids (phenocrysts and minor xenocrysts). Subsequent differentiation via crystal settling and in situ crystallization (Langmuir 1989) resulted in a layered sequence of lithology A overlain by lithology B, with gradations in modal abundance of maskelynite (increasing from A to B) and pigeonite/maskelynite (decreasing from A to B), and a gradational change in pattern of pyroxene zonation (zones of magnesian augite separating magnesian and ferroan pigeonite appear and thicken into B) across the contact. A pigeonite phenocryst‐bearing zone near the contact in lithology B appears to be intermediate between lithology A and the bulk of lithology B (which resembles basaltic shergottite Queen Alexandra Range [QUE] 94201). Re‐examination of Sr isotopic compositions in lithology A and across the contact is required to test and constrain the model.     

Northwest Africa 1500: Plagioclase‐bearing monomict ureilite or ungrouped achondrite?

Abstract— Northwest Africa (NWA) 1500 is an ultramafic meteorite dominated by coarse (?100–500 μm) olivine (95–96%), augite (2–3%), and chromite (0.6–1.6%) in an equilibrated texture. Plagioclase (0.7–1.8%) occurs as poikilitic grains (up to ?3 mm) in vein‐like areas that have concentrations of augite and minor orthopyroxene. Other phases are Cl‐apatite, metal, sulfide, and graphite. Olivine ranges from Fo 65–73, with a strong peak at Fo 68–69. Most grains are reversezoned, and also have ?10–30 μm reduction rims. In terms of its dominant mineralogy and texture, NWA 1500 resembles the majority of monomict ureilites. However, it is more ferroan than known ureilites (Fo ≥75) and other mineral compositional parameters are out of the ureilite range as well. Furthermore, neither apatite nor plagioclase have ever been observed, and chromite is rare in monomict ureilites. Nevertheless, this meteorite may be petrologically related to the rare augite‐bearing ureilites and represent a previously unsampled part of the ureilite parent body (UPB). The Mn/Mg ratio of its olivine and textural features of its pyroxenes are consistent with this interpretation. However, its petrogenesis differs from that of known augite‐bearing ureilites in that: 1) it formed under more oxidized conditions; 2) plagioclase appeared before orthopyroxene in its crystallization sequence; and 3) it equilibrated to significantly lower temperatures (800–1000 °C, from two‐pyroxene and olivine‐chromite thermometry). Formation under more oxidized conditions and the appearance of plagioclase before orthopyroxene could be explained if it formed at a greater depth on the UPB than previously sampled. However, its significantly different thermal history (compared to ureilites) may more plausibly be explained if it formed on a different parent body. This conclusion is consistent with its oxygen isotopic composition, which suggests that it is an ungrouped achondrite. Nevertheless, the parent body of NWA 1500 may have been compositionally and petrologically similar to the UPB, and may have had a similar differentiation history.     

The Greenland ice sheet and greenhouse warming

Increased melting on glaciers and ice sheets and rising sea level are often mentioned as important aspects of the anticipated greenhouse warming of the earth's atmosphere. This paper deals with the sensitivity of Greenland's ice mass budget and presents a tentative projection of the Greenland component of future sea level rise for the next few hundred years. To do this, the ‘Villach II temperature scenario’ is prescribed,output from a comprehensive mass balance model is used to drive a high-resolution 3-D thermomechanic model of the ice sheet.The mass balance model consists of two parts: the accumulation part is based on presently observed values and is forced by changes in mean anr tempeerature. The ablation model is based on the degree-day method and accounts for daily and annual temperature cycle, a different degree-day factor for ice and snow melting and superimposed ice formation. Under present-day climatic conditions, the following total mass balance results (in ice equivalent per years): 599.3 × 10⁹ m³ of accumulation, 281.7 × 10⁹m³ of runoff assuming a balanced budget, 317.6 × 10⁹m³ of iceberg calving. A 1K uniform warming is then calculated to increase the runoff by 119.5 × 10⁹ m³. Since accumulation also increases by 32 × 10⁹ m³, this leads to reduction of the total mass balance by 887.5 × 10⁹ m³ of ice, corresponding to a sea level rise of 0.22 mm/yr. For temperature increase larger than 2.7 K, runoff, exceeds accumulation, and if ice sheet dynamics were to remain unchanged, this would add an extra amount of 0.8 mmyr to the worl's oceans.Imposing the Villach II scenario (warming up to 4.23 K) and accumulating mass balance changes forward in time (static response) would then result in a global sea level rise of 7.1 cm by 2100 AD, but this figure may go up to as much as 40 cm per century in case the warming is doubled. In a subsequent dynamic model involving the ice flow, the ice sheet is found to produce a counteracting effect by dynamically producing steeper slopes at the margin, thereby reducing the area over which runoff can take place. This effect is particularly apparent in the northeastern part of the ice sheet, and is also more pronounced for the smaller temperature perturbations. Nevertheless, all these experiments certainly highlight the vulnerability of the Greenland ice sheet with respect to a climatic warming.     

Enstatite meteorite clasts in Almahata Sitta and other polymict ureilites: Implications for the formation of asteroid 2008 TC3 and the history of enstatite meteorite parent asteroids

The anomalous polymict ureilite Almahata Sitta (AhS) fell in 2008 when asteroid 2008 TC₃ disintegrated over Sudan and formed a strewn field of disaggregated clasts of various ureilitic and chondritic types. We studied the petrology and oxygen isotope compositions of enstatite meteorite samples from the University of Khartoum (UoK) collection of AhS. In addition, we describe the first bona fide (3.5 mm-sized) clast of an enstatite chondrite (EC) in a typical polymict ureilite, Northwest Africa (NWA) 10657. We evaluate whether 2008 TC₃ and typical polymict ureilites have a common origin, and examine implications for the history of enstatite meteorite asteroids in the solar system. Based on mineralogy, mineral compositions, and textures, the seven AhS EC clasts studied comprise one EH_a3 (S151), one EL_b3 (AhS 1002), two EH_b4-5 (AhS 2012, AhS 26), two EH_b5-6 or possibly impact melt rocks (AhS 609, AhS 41), and one EL_b6-7 (AhS 17), while the EC clast in NWA 10657 is EH_a3. Oxygen isotope compositions analyzed for five of these are similar to those of EC from non-UoK collections of AhS, and within the range of individual EC meteorites. There are no correlations of oxygen isotope composition with chemical group or subgroup. The EC clasts from the UoK collection show the same large range of types as those from non-UoK collections of AhS. The enstatite achondrite, AhS 60, is a unique type (not known as an individual meteorite) that has also been found among non-UoK AhS samples. EC are the most abundant non-ureilitic clasts in AhS but previously were thought to be absent in typical polymict ureilites, necessitating a distinct origin for AhS. The discovery of an EC in NWA 10657 changes this. We argue that the types of materials in AhS and typical polymict ureilites are essentially similar, indicating a common origin. We elaborate on a model in which AhS and typical polymict ureilites formed in the same regolith on a ureilitic daughter body. Most non-ureilitic clasts are remnants of impactors implanted at ~50–60 Myr after CAI. Differences in abundances can be explained by the stochastic nature of impactor addition. There is no significant difference between the chemical/petrologic types of EC in polymict ureilites and individual EC meteorites. This implies that fragments of the same populations of EC parent bodies were available as impactors at ~50–60 Myr after CAI and recently. This can be explained if materials excavated from various depths on EC bodies at ~50–60 Myr after CAI were reassembled into mixed layers, leaving relatively large bodies intact to survive 4 billion years. Polymict ureilites record a critical timestep in the collisional and dynamical evolution of the solar system, showing that asteroids that may have accreted at distant locations had migrated to within proximity of one another by 50–60 Myr after CAI, and providing constraints on the dynamical processes that could have caused such migrations.     

Experimental study of the carbonation of partially serpentinized and weathered peridotites

Carbonation of partially serpentinized and weathered peridotites was studied experimentally under hydrothermal conditions (T: 200 °C, P_CO2: 130-180 bars). Experiments were performed in a closed system using whole rock drill core samples (height: 1 cm, diameter: 1 cm) as starting material. The initial samples were composed mainly of meshwork serpentine, relicts of primary olivine and an olivine weathering product (deweylite assemblage). Two types of solutions, each with a total salt content corresponding to that of average seawater (35 g/L dissolved salts), were used: (1) a Na-Ca-Cl solution (12.5 g/L CaCl₂ + 22.5 g/L NaCl) and (2) a NaCl solution (35 g/L NaCl). After 15-25 days of experimental treatment, the samples were partly covered with carbonates. In addition, noticeable carbonation reactions had occurred below the sample surfaces within zones with thicknesses up to 250 μm. In the Na-Ca-Cl solution, both the olivine relicts and the deweylite assemblage were partly replaced by calcite along the surrounding serpentine veins. However, the extent of calcitization was found to be considerably larger for the deweylite assemblage than for the olivine. Bulk fluid analyses show an increase in the Mg and Si concentrations with reaction time. In the NaCl solution, the deweylite assemblage was partly dissolved resulting in large voids within the reaction zone. In contrast, the olivine was replaced by magnesite. Under the conditions of our experiments, the meshwork serpentine was not reactive, but aided fluid infiltration into the rock samples. The experimentally produced microtextures closely resemble those found in natural examples. Our study elucidates the mechanisms by which carbonates form in ultramafic rocks under relatively high P_CO2-T conditions and particularly in the presence of Ca-bearing aqueous solutions. The existence of a serpentine meshtexture and the presence of weathering products formed from primary Mg-silicates may have significant beneficial effects on in situ CO₂ mineral sequestration in ultramafic rocks.     

Generation mechanisms for mesoscale eddies in the Gulf of Lions: radar observation and modeling

Coastal mesoscale eddies were evidenced during a high-frequency radar campaign in the Gulf of Lions (GoL), northwestern Mediterranean Sea, from June 2005 to January 2007. These anticyclonic eddies are characterized by repeated and intermittent occurrences as well as variable lifetime. This paper aims at studying the link between these new surface observations with similar structures suggested at depth by traditional acoustic Doppler current profiler measurements and investigates the eddy generation and driving mechanisms by means of an academic numerical study. The influence of the wind forcing on the GoL circulation and the eddy generation is analyzed, using a number of idealized configurations in order to investigate the interaction with river discharge, buoyancy, and bathymetric effects. The wind forcing is shown to be crucial for two different generation mechanisms: A strong northerly offshore wind (Mistral) generates a vortex column due to the bathymetric constraint of a geostrophic barotropic current, which can surface after the wind relaxes; a southerly onshore wind generates a freshwater bulge from the Rhône river discharge, which detaches from the coast and forms a well-defined surface anticyclonic eddy based on buoyancy gradients. These structures are expected to have important consequences in terms of dispersion or retention of biogeochemical material at local scales.     

Phytoplankton dynamics and cyanobacterial dominance in Murchison Bay of Lake Victoria (Uganda) in relation to environmental conditions

Murchison Bay is a shallow embayment in the north-western part of Lake Victoria, strongly influenced by urban pollution from the Ugandan capital Kampala. Two stations, representing the semi-enclosed innermost part of the bay and the wider outer part of the bay, were sampled in the period from April 2003 to March 2004, in order to assess the phytoplankton community and the nutrient status in the bay. Murchison Bay was highly eutrophic with average concentrations (n=25) of total phosphorous >90 μg L⁻¹ and total nitrogen >1100 μg L⁻¹ in the inner part of the bay. The phytoplankton community was dominated by a variety of cyanobacterial species and diatoms. Cyanobacteria were dominant in the whole bay, whereas diatoms were more abundant in the outer part of the bay. Moreover, the proportion of N-fixing species like Anabaena sp. was higher in the outer part of the bay, whereas species like Microcystis sp. were more abundant in the inner part of the bay. The phytoplankton community, especially in the outer part of the bay, may be influenced by light limitation. Low NO₃-N concentrations in the bay may also indicate a possible N-limitation, thus favouring growth of N-fixing cyanobacteria. The open bay is, however, a complex system, and additional environmental factors and loss processes most likely affect the phytoplankton community.     

Infrared spectroscopic investigation of hydroxyl in β-(Mg,Fe)2SiO4 and coexisting olivine: Implications for mantle evolution and dynamics

Wadsleyite (β-(Mg,Fe)₂SiO₄) is a major constituent of the Earth's transition zone and is known to accommodate OH. The portion of the transition zone between 400–550 km could be an important source or sink for hydroxyl in plumes and slabs intersecting this region. Micro-infrared spectroscopy has been carried out on the β-phase and coexisting metastable olivine synthesized in a multianvil apparatus at 14 GPa and 1550–1650 K under hydrous conditions. Single-crystal and polycrystal specimens of both phases were analyzed in the 1800–8500 cm^?1 frequency region to determine the speciation, abundances, and partitioning behavior of the hydrous components in coexisting β-phase and olivine. β-phase spectra consistently show three distinct OH bands at 3329, 3580, and 3615 cm^?1. OH concentrations range from 10000–65000 H/10⁶ Si. A strong positive correlation of grain size and extent of transformation with OH concentration in the β-phase indicates that grain-growth and transformation rates are enhanced in a hydrous environment. Olivine spectra are variable, but consistently show a prominent broad-band absorbance representing molecular H₂O, consistent with the infrared signature of the starting material. OH concentrations in olivine range from <300–1400 H/10⁶ Si. The highest OH concentrations measured for olivine and the β-phase may represent solubility limits, in which case the OH solubility ratio between these two phases is approximately 1∶40. Where both phases coexist and are undersaturated with OH, the partitioning ratio of OH between them is about 1∶100. The large solubility contrast between olivine and the β-phase suggests a mechanism for hydrating the transition zone via olivine carried down in subducting slabs. Plumes impinging on an OH-rich upper transition region could cause H₂ or H₂O to be released upon transformation of the β-phase to olivine, resulting in initiation of secondary upwellings. If dissolution of OH weakens the β-phase, and if OH is present in the mantle, the region between 400–550 km could be a zone of low viscosity.     

Managing by principle: A critical analysis of the European principles of Integrated Coastal Zone Management (ICZM)

A set of eight principles is contained in the European Recommendation on Integrated Coastal Zone Management. The principles have been adopted with the minimum of critical review. The six core principles form two groups, one concerned with strategic goals and one that has a local focus. The principles are presented as a menu of free-standing options, with no prioritization either within or between groups. This can produce irreconcilable differences in strategy. The principles require clarification, prioritization of the strategic principles and recognition that they are an indivisible integrated set which should not be used to select principles to advance a particular agenda.