Palaeoecological constraints on late Glacial and Holocene ice retreat in the Southern Andes (53°S)

Late Glacial to Holocene ice retreat was investigated along a 120 km long fjord system, reaching from Gran Campo Nevado (GCN) to Seno Skyring in the southernmost Andes (53°S). The aim was to improve the knowledge on regional and global control on glacier recession with special emphasis on latitudinal shifting of the westerlies. The timing of ice retreat was derived from peat and sediment cores, using mineralogical and chemical characteristics, and pollen as proxies. Stratigraphy was based on ¹⁴C-AMS ages and tephrochronology. The ice retreat of the Seno Skyring Glacier lobe is marked by an ice rafted debris layer which was formed around 18,300 to 17,500 cal. yr B.P. Subsequently, fast glacier retreat occurred until around 15,000 to 14,000 cal. yr B.P. during which around 84% of Skyring Glacier were lost. This fast recession was probably also triggered by an increase of the Equilibrium Line Altitude (ELA) from 200 to 300 m. Subsequently, the ice surface was lowered below the ELA in an area that previously made up more than 50% of the accumulation area. Much slower retreat and glacier fluctuations of limited extent in the fjord channel system northeast of GCN occurred between around 14,000 to 11,000 cal. yr B.P. during both the Antarctic Cold Reversal and the Younger Dryas. This slow down of retreat indicates a decline in the general warming trend and/or increased precipitation, due to a southward migration of the westerlies. After around 11,000 cal. yr B.P. pollen distribution shows evolved Magellanic Rainforest and similar climate as at present, which lasted throughout most of the Holocene. Only Late Neoglacial moraine systems were formed in the period 1220–1460 AD, and subsequently in the 1620s AD, and between 1870 and 1910 AD. The results indicate that the Gran Campo Nevado ice cap has reacted more sensitive and partly distinct to climate change, compared to the Patagonian Ice Field.     

Energy balance in the ablation zone during the summer season at the Gran Campo Nevado Ice Cap in the Southern Andes

The energy balance and ablation of Glaciar Lengua were investigated during the austral summer of 1999/2000. Glaciar Lengua is located in Patagonia, in the southernmost Andes of Chile (53°S), within an extremely maritime climate. The aim of this study was to gain insight into current energy fluxes at this location and to evaluate how the energy fluxes depend on meteorological variables. From February to April 2000 an automated weather station was operated on Glaciar Lengua. Ablation was measured repeatedly at stakes during the same period. The point energy balance was calculated using the bulk approach formulation. The effective roughness length was adjusted in order to calibrate the model to the measured ablation. It was revealed that sensible heat transfer is the major contribution to the energy balance adding 54% of the energy available for melt. Net radiation contributes only 35% to the overall energy balance. Minor contributors are the latent heat flux (7%) and the heat flux by precipitation (4%). The net radiation shows little variance from day to day. Cross-correlations of the daily mean values of the energy fluxes derived from the energy balance model and meteorological variables reveal that air temperature and wind speed are the key factors controlling the summer energy balance in the ablation area. Melt derived from a multiple regression model based on these two variables correlates with computed melt with a correlation coefficient of 0.92. From the measured ablation, a summer-time degree-day factor of 7.6 mm·°C^− 1 was derived for the ablation area.     

To Move or not to Move: Community Members’ Reaction to Surface Mining Activities in the Upper West Region of Ghana

Abstract

Despite the impact of mining-induced environmental change on community livability, we know little about how disparities in knowledge of health risks associated with mining influence residents’ response, especially in an already environmentally stressed context. Guided by theoretical insights from solastalgia, we examined residents’ decision to relocate due to increasing gold mining activities in the fragile Northern Savannah Ecological Zone of Ghana. Fitting complementary log-log regression models to cross-sectional data from the Upper West Region (UWR) of Ghana, we found that residents with limited knowledge of potential health impacts of mining and those who believe mining activities were not meeting environmental standards were more likely to consider relocating. Given the centrality of land in community health and wellbeing in the UWR, Ghana’s mining guidelines should promote local participation in the regulation of mining activities and guarantee the rights of indigenes to livable native lands.     

Analytical transmission electron microscopy of oscillatory zoned grandite garnets

Oscillatory zoned grandite garnets from skarns of the Oslo rift region (southern Norway) have been studied using analytical transmission electron microscopy (ATEM). Our results show lamellae with a width varying from about 10 nm to more than 500 nm in both periodic and non-periodic sequences, which represent oscillatory zoning at a very fine scale. The compositions of adjacent lamellae alternate bimodally from X_and=0.55-0.75 to X_and=0.95-1.0. High resolution (HRTEM) images show that the compositional interfaces are sharp and coherent. Oscillatory zoning at the nm-scale puts constrains on the origin of oscillatory zoning in grandites and underlines the dynamic nature of the crystal growth process. The influence of growth rate is discussed against the background of local growth dynamics and external forcing at different length scales. This study emphasises the importance of adequate spatial resolution in analysing chemical variations in grandite garnets and shows that commonly applied methods (e.g. optical microscopy, backscattered electron imaging and electron or ion microprobe) are not sufficient to detect 'real' zonation patterns. Finally, proposed hypotheses on the origin of birefringence of grandite garnets with intermediate compositions are reviewed and discussed on the basis of the observed microstructure.     

Emission of Type II Radio Bursts – Single-Beam Versus Two-Beam Scenario

The foreshock region of a CME shock front, where shock accelerated electrons form a beam population in the otherwise quiescent plasma is generally assumed to be the source region of type II radio bursts. Nonlinear wave interaction of electrostatic waves excited by the beamed electrons are the prime candidates for the radio waves’ emission. To address the question whether a single, or two counterpropagating beam populations are a requirement for this process, we have conducted 2.5D particle-in-cell simulations using the fully relativistic ACRONYM code. Results show indications of three-wave interaction leading to electromagnetic emission at the fundamental and harmonic frequency for the two-beam case. For the single-beam case, no such signatures were detectable.     

Holocene sea-surface temperature variability in the Chilean fjord region

Here we provide three new Holocene (11–0 cal ka BP) alkenone-derived sea surface temperature (SST) records from the southernmost Chilean fjord region (50–53°S). SST estimates may be biased towards summer temperature in this region, as revealed by a large set of surface sediments. The Holocene records show consistently warmer than present-day SSTs except for the past ~ 0.6 cal ka BP. However, they do not exhibit an early Holocene temperature optimum as registered further north off Chile and in Antarctica. This may have resulted from a combination of factors including decreased inflow of warmer open marine waters due to lower sea-level stands, enhanced advection of colder and fresher inner fjord waters, and stronger westerly winds. During the mid-Holocene, pronounced short-term variations of up to 2.5°C and a cooling centered at ~ 5 cal ka BP, which coincides with the first Neoglacial glacier advance in the Southern Andes, are recorded. The latest Holocene is characterized by two pronounced cold events centered at ~ 0.6 and 0.25 cal ka BP, i.e., during the Little Ice Age. These cold events have lower amplitudes in the offshore records, suggesting an amplification of the SST signal in the inner fjords.     

Metasomatism of sub-arc mantle peridotites below southernmost South America: reduction of<Emphasis Type="Italic"> f</Emphasis>O<Subscript>2</Subscript> by slab-melt

Quaternary basalts in the Cerro del Fraile area contain two types of mantle xenoliths; coarse-grained (2–5 mm) C-type spinel harzburgites and lherzolites, and fine-grained (0.5–2 mm) intensely metasomatized F-type spinel lherzolites. C-type xenoliths have high Mg in olivine (Fo = 90–91) and a range in Cr# [Cr/ (Cr + Al) = 0.17–0.34] in spinel. Two C-type samples contain websterite veinlets and solidified patches of melt that is now composed of minute quenched grains of plagioclase + Cr-spinel + clinopyroxene + olivine. These patches of quenched melts are formed by decompression melting of pargasitic amphibole. High Ti contents and common occurrence of relic Cr-spinel in the quenched melts indicate that the amphibole is formed from spinel by interaction with the Ti-rich parental magma of the websterite veinlets. The fO₂ values of these two C-type xenoliths range from ΔFMQ −0.2 to −0.4, which is consistent with their metasomatism by an asthenospheric mantle-derived melt. The rest of the C-type samples are free of “melt,” but show cryptic metasomatism by slab-derived aqueous fluids, which produced high concentrations of fluid-mobile elements in clinopyroxenes, and higher fO₂ ranging from ΔFMQ +0.1 to +0.3. F-type lherzolites are intensely metasomatized to form spinel with low Cr# (∼0.13) and silicate minerals with low MgO, olivine (Fo = ∼84), orthpyroxene [Mg# = Mg/(Mg + ΣFe) = ∼0.86] and clinopyroxene (Mg# = ∼0.88). Patches of “melt” are common in all F-type samples and their compositions are similar to pargasitic amphibole with low TiO₂ (<0.56 wt%), Cr₂O₃ (<0.55 wt%) and MgO (<16.3 wt%). Low Mg# values of silicate minerals, including the amphibole, suggest that the metasomatic agent is most likely a slab melt. This is supported by high ratios of Sr/Y and light rare earth elements (REE)/heavy REE in clinopyroxenes. F-type xenoliths show relatively low fO₂ (ΔFMQ −0.9 to −1.1) compared to C-type xenoliths and this is explained by the fusion of organic-rich sediments overlying the slab during the slab melt. Trench-fill sediments in the area are high in organic matter. The fusion of such wet sediments likely produced CH₄-rich fluids and reduced melts that mixed with the slab melt. High U and Th in bulk rocks and clinopyroxene in F-type xenoliths support the proposed interpretation.     

Escaped introduced sea bass (Dicentrarchus labrax) infected by Sphaerospora testicularis (Myxozoa) reach maturity in coastal habitats off Canary Islands

Aquaculture activities have introduced European sea bass (Dicentrarchus labrax) along the coasts of some of the Canary Islands. We present the first record of simultaneous male and female gonad maturation of escaped sea bass in the wild, indicating that this species is finding its essential fish habitat (EFH). Individuals with ripe gonads were only caught during January and February 2009, although the maturation and spawning season may last from November to February in the studied area (Tenerife island). Bass infected by Sphaerospora testicularis were found and the incidence of the parasite was checked. This represents the southernmost record of the parasite, probably introduced together with sea bass stock. The results are discussed from the point of view of risk assessment and the ecology of invasions being valuable for aquaculture management in Central North Atlantic and Mediterranean areas.     

A Triggered Depth‐Dependent Sampling System to Overcome the Carry‐Over Effects of the Membrane Interface Probe

The membrane interface probe (MIP) is widely used for the in situ characterization of volatile organic compounds (VOCs) in the subsurface. A main problem using the MIP system is the carry‐over effect of VOCs during the transport from the point of measurement to the detector using a conventional transfer line. This effect results in compound specific retention times, which is shown in disproportionately high measuring signals after the actual penetration of contaminated zones. In consequence, the lower extent of contamination is not clearly identifiable and may be overestimated. The presented field study presents an evaluation of different methods to overcome the carry‐over effect, especially with regard to the required measurement times that are needed to wait for a complete disappearance of the detector signals before forwarding the probe. This was accomplished by comparing data collected with a MIP system with (1) unheated transfer line and (2) a system including a heated transfer line to data collected with a system using (3) a depth‐dependent triggered sampling behind the membrane including two transfer lines. A comparison with analytical results from soil samples gave a good correlation for all three methods. Furthermore, it could be shown that the use of a heated transfer line has a time improvement of 30% compared to an unheated transfer line while the depth dependent triggered sampling using two separate transfer lines yielded a time improvement of over 90%. These results confirm the benefit of the latter method, particularly for the use in highly contaminated sediments.     

Between the devil and the deep blue sea: Functional conflicts in Cape Town''s Victoria and Alfred Waterfront

The global phenomenon of waterfront revitalization is a planning strategy commonly employed by city and port authorities eager to overcome the redundancy and associated urban decay of their docklands. The spatial transformation that generally accompanies such initiatives often results in functional conflict. Focusing on the redevelopment of the traditional dockland precinct of the South African portcity of Cape Town, this paper shows how attempts to rationalize pre-existing harbour activities resulted in conflict between the developer, the Victoria and Alfred Waterfront Company, and its largest industrial tenant, the fishing industry. The utilization of existing harbour space and, more specifically, questions of tenure and affordable rentals are identified as the principal elements of the contentious negotiations between these parties.