Current state and trends in Canadian Arctic marine ecosystems: I. Primary production

During the International Polar Year (IPY), large international research programs provided a unique opportunity for assessing the current state and trends in major components of arctic marine ecosystems at an exceptionally wide spatio-temporal scale: sampling covered most regions of the Canadian Arctic (IPY-Canada??s Three Oceans project), and the coastal and offshore areas of the southeastern Beaufort Sea were monitored over almost a full year (IPY-Circumpolar Flaw Lead project). The general goal of these projects was to improve our understanding of how the response of arctic marine ecosystems to climate warming will alter the productivity and structure of the food web and the ecosystem services it provides to Northerners. The present paper summarizes and discusses six key findings related to primary production (PP), which determines the amount of food available to consumers. (1) Offshore, the warming and freshening of the surface layer is leading to the displacement of large nanophytoplankton species by small picophytoplankton cells, with potentially profound bottom-up effects within the marine food web. (2) In coastal areas, PP increases as favourable winds and the deeper seaward retreat of ice promote upwelling. (3) Multiple upwelling events repeatedly provide food to herbivores throughout the growth season. (4) A substantial amount of pelagic PP occurs under thinning ice and cannot be detected by orbiting sensors. (5) Early PP in the spring does not imply a trophic mismatch with key herbivores. (6) The epipelagic ecosystem is very efficient at retaining carbon in surface waters and preventing its sedimentation to the benthos. While enhanced PP could result in increased fish and marine mammal harvests for Northerners, it will most likely be insufficient for sustainable large-scale commercial fisheries in the Canadian Arctic.     

REE and Sr isotope characteristics of carbonate within the Cu–Co mineralized sedimentary sequence of the Nchanga Mine,Zambian Copperbelt

Carbonate, largely in the form of dolomite, is found throughout the host rocks and ores of the Nchanga mine of the Zambian Copperbelt. Dolomite samples from the hanging wall of the mineralization show low concentrations of rare-earth elements (REE) and roof-shaped, upward convex, shale-normalized REE patterns, with positive Eu*_SN anomalies (1.54 and 1.39) and marginally negative Ce anomalies (Ce*_SN 0.98,0.93). In contrast, dolomite samples associated with copper and cobalt mineralization show a significant rotation of the REE profile, with HREE enrichment, and La/Lu_SN ratios <1 (0.06–0.42). These samples also tend to show variable but predominantly negative Eu*_SN and positive cerium anomalies and an upwardly concave MREE distribution (Gd-Er). Malachite samples from the Lower Orebody show roof-tile-normalized REE patterns with negative europium anomalies (Eu*_SN 0.65–0.80) and negative cerium anomalies (Ce*_SN 0.86–0.9). The carbonate ⁸⁷Sr/⁸⁶Sr signature correlates with the associated REE values. The uppermost dolomite samples show Neoproterozoic seawater-like ⁸⁷Sr/⁸⁶Sr ratios ranging from 0.7111 to 0.7116, whereas carbonate from Cu–Co mineralized samples show relatively low concentrations of strontium and more radiogenic ⁸⁷Sr/⁸⁶Sr, ranging between 0.7136–0.7469. The malachite samples show low concentrations of strontium, but give a highly radiogenic ⁸⁷Sr/⁸⁶Sr of 0.7735, the most radiogenic ⁸⁷Sr/⁸⁶Sr ratio. These new data suggest that the origin and timing of carbonate precipitation at Nchanga is reflected in the REE and Sr isotope chemistry. The upper dolomite samples show a modified, but essentially seawater-like signature, whereas the rotation of the REE profile, the MREE enrichment, the development of a negative Eu*_SN anomaly and more radiogenic ⁸⁷Sr/⁸⁶Sr suggests the dolomite in the Cu–Co mineralized samples precipitated from basinal brines which had undergone significant fluid–rock interaction. Petrographic, REE, and ⁸⁷Sr/⁸⁶Sr data for malachite are consistent with the original sulfide Lower Orebody being subject to a later oxidizing event.     

Heritage stone in South Australia

South Australia has the greatest utilisation of heritage or building stone in Australia because of its lack of timber resources. Consequently, natural stone was intensively used from the beginning of European colonisation. Building stones in South Australia, notable for their variety given the State’s diverse geology, can be challenging to designate as to their international importance. However, dimension stone in South Australia can also be designated as having national, regional, local or prospective importance. Commonly, stone in South Australia is restricted in use to a specific town, or even a single construction, and has only local significance except where use involves special stone characteristics, unusual stone masonry or use in a building with significant heritage. For instance, the town of Second Valley has a localised use of marble, likely the earliest use (1849) of this rock type in the State. Another example, ‘Adelaide Black Granite’, quarried since 1958, should probably be recognised internationally as a ‘Global Heritage Stone Resource’, as it has had intensive monumental use around Australia, utilisation as cladding in modern buildings, as well as paving and walling in Australia’s National Parliament in Canberra. It has also been exported, notably used for the Australian Embassy in Japan and for a major War Memorial at Le Hamel, France. South Australian slate quarries also provide significant heritage stone. For example, the Willunga Slate quarry south of Adelaide has been sourced for roofing slate and walling since 1840 and is arguably the longest continuous mining operation in Australia; this resource has obvious national significance given a period of quarrying extending to the present, coupled with national distribution of its products. Probably the most widespread stone sourced in South Australia is the surface limestone or calcrete, quarried in the Adelaide area until the 1850s and used for general construction. The stone continues to be used in rural areas. While arguably only of local significance, it could be considered to have national importance because of its extensive use in churches, public building, hotels, houses and simple walling across a vast area of South Australia. Additional research is needed to clarify the heritage status of many building stones used in South Australia.     

Carbonate alteration of ophiolitic rocks in the Arabian–Nubian Shield of Egypt: sources and compositions of the carbonating fluid and implications for the formation of Au deposits

Ultramafic portions of ophiolitic fragments in the Arabian–Nubian Shield (ANS) show pervasive carbonate alteration forming various degrees of carbonated serpentinites and listvenitic rocks. Notwithstanding the extent of the alteration, little is known about the processes that caused it, the source of the CO₂ or the conditions of alteration. This study investigates the mineralogy, stable (O, C) and radiogenic (Sr) isotope composition, and geochemistry of suites of variably carbonate altered ultramafics from the Meatiq area of the Central Eastern Desert (CED) of Egypt. The samples investigated include least-altered lizardite (Lz) serpentinites, antigorite (Atg) serpentinites and listvenitic rocks with associated carbonate and quartz veins. The C, O and Sr isotopes of the vein samples cluster between ?8.1‰ and ?6.8‰ for δ¹³C, +6.4‰ and +10.5‰ for δ¹⁸O, and ⁸⁷Sr/⁸⁶Sr of 0.7028–0.70344, and plot within the depleted mantle compositional field. The serpentinites isotopic compositions plot on a mixing trend between the depleted-mantle and sedimentary carbonate fields. The carbonate veins contain abundant carbonic (CO₂±CH₄±N₂) and aqueous-carbonic (H₂O-NaCl-CO₂±CH₄±N₂) low salinity fluid, with trapping conditions of 270–300°C and 0.7–1.1 kbar. The serpentinites are enriched in Au, As, S and other fluid-mobile elements relative to primitive and depleted mantle. The extensively carbonated Atg-serpentinites contain significantly lower concentrations of these elements than the Lz-serpentinites suggesting that they were depleted during carbonate alteration. Fluid inclusion and stable isotope compositions of Au deposits in the CED are similar to those from the carbonate veins investigated in the study and we suggest that carbonation of ANS ophiolitic rocks due to influx of mantle-derived CO₂-bearing fluids caused break down of Au-bearing minerals such as pentlandite, releasing Au and S to the hydrothermal fluids that later formed the Au-deposits. This is the first time that gold has been observed to be remobilized from rocks during the lizardite–antigorite transition.     

Soil metal pollution from former Zn–Pb mining assessed by geochemical and magnetic investigations: case study of the Bou Caid area (Tissemsilt,Algeria)

Former zinc and lead mines that have been operating for half a century are located in the massif of Bou Caid (Tissemsilt, Algeria). Hazardous heavy metals emitted from the mines are abundant in the surrounding soil and cause strong metal pollution in the region. This paper investigates the extent of lead and zinc mine activity derived pollution by characterizing both magnetic and geochemical properties of samples collected in the vicinity of the mines. The results of the magnetic study show the coexistence of magnetic minerals such as magnetite, hematite and goethite. Analyses on surface soils and weathered rocks suggest that hematite and goethite have ore-related lithogenic origins. Magnetic susceptibility shows a positive correlation with lead content when present in low-to-medium concentrations (< ~500 mg/kg). At higher lead concentrations, there is no correlation with magnetic susceptibility. The relationship between magnetic susceptibility and zinc content is not straightforward. These observations are explained by the higher affinity of Pb to iron oxides at lower pollution levels and their preferential bonding to carbonates when Pb and Zn contents are extremely high, as demonstrated by Iavazzo et al. (J Geochem Explor 113:56–67, 2012) in a study of former Zn–Pb mine in Morocco. Based on the general features of the spatial maps of field-measured magnetic susceptibility, mass-specific magnetic susceptibility, Pb and Zn contents, it is concluded that field magnetic measurements provide a good qualitative proxy of pollution spread out of the mining galleries, while laboratory measurements afford a more detailed investigation of the links between iron oxides and the main heavy metals in the ore.     

Magnetic signature of different vegetation species in polluted environment

Detailed magnetic study on vegetation samples from several strongly polluted and clean sites in Bulgaria is carried out in order to evaluate suitability of different species as passive dust collectors in magnetometry. From each location, available species among lichens, mosses, poplar leaves, dandelion, needles have been sampled. Magnetic susceptibility calculated on mass-specific basis shows wide variability between diamagnetic signal up to 846 × 10⁻⁸ m³/kg. Lichens and mosses are found to be the species, showing magnetic signals with the strongest contrast between clean and polluted environment. The main magnetic phase is magnetite-like according to the results from thermomagnetic analysis of susceptibility on magnetic extracts. Scanning electron microscopy (SEM) microphotographs reveal the presence of abundant particulate matter on vegetation surface both with anthropogenic (spherules) and lithogenic origin. Magnetic grain size deduced by the ratio of saturation remanent magnetization (SIRM) and mass-specific magnetic susceptibility (χ) and coercivities (B_c and B_cr) suggest that different species accumulate preferentially small SD-like grains from pollution emissions. Contrasting relationship of the ratio of anhysteretic remanent magnetization (ARM) and χ for polluted vs clean sites deduced by needles and lichens may be related to transformation of the accumulated dust particles within lichens’ tissue. This finding indicates that the exact species used as biological dust collector is of importance when studying spatial grain size distribution of magnetic dust particles. Pilot study on polycyclic aromatic hydrocarbons (PAH) content and its relation to magnetic parameters shows good correspondence between high levels of PAHs and high SIRM values for locations affected by non-ferrous industrial production.     

Ocean-bottom seismometer observations of seismic activity at Loihi Seamount,Hawaii

This study reports the result of deep ocean-bottom seismometer recording of an undersea volcanic event in progress. An array of five three-component, isolated sensor ocean-bottom seismometers (ISOBS) was deployed for 28 days on the summit and flanks of Loihi Seamount, Hawaii, to monitor seismicity. The deployment was prompted by reports from the Hawaiian Volcano Observatory (HVO) of a swarm of small-magnitude events located beneath the active submarine volcano in late September, 1986. Monitoring of this earthquake swarm by the University of Hawaii commenced 1 October 1986. Although seismicity tapered off rapidly after 11 October, more than 200 events were located. Systematic changes in spatial clustering during the initial swarm activity suggest changing patterns of stress within this crustal volume, possibly due to induced stress resulting from magma movement in the underlying crust or deep portions of the edifice.Most of the very shallow (< 10 km) events were located beneath the summit and southwest flank of the elongate edifice. No shallow tremor was observed despite a search through the data, although such tremor may have ceased prior to deployment of the ocean-bottom seismometers (OBS). Constraints on the association between seismicity and observed topographic and tectonic elements of Loihi are also of primary importance. Many of the earthquakes located near the steep flanks generated rock falls that were recorded on the OBSs. This is consistent with the results of dredge and bottom photography data indicating that the flanks are covered with fragments of shattered lava pillows and flows. Dike intrusion and mass wasting are major influences on the morphology of Loihi. Intact flows have been observed near the deep portion of the south rift zone; however, few events were located in that region during this swarm.     

What is suspended sediment?

Suspended sediment is conventionally regarded as that sediment transported by a fluid that it is fine enough for turbulent eddies to outweigh settling of the particles through the fluid. Early work in the fluvial field attributed suspension to turbulence, and led to the notion of a critical threshold for maintaining sediment in suspension. However, research on both turbulence structures and the interactions between suspended sediment and bedforms in rivers has shown a more complex story and, although there appear to have been no studies of the impact of bedforms on aeolian suspended sediment concentrations, turbulent flow structures and transport rates of saltating particles have been shown to be affected. This research indicates that suspended sediment neither travels with the same velocity as the flow in which it is suspended, nor is it likely to remain in suspension in perpetuity, even under conditions of steady flow or in unsteady flow the where dimensionless critical threshold is permanently exceeded. Rather, like bedload, it travels in a series of hops, and is repeatedly deposited on the bed where it remains until it is re‐entrained. Is there, therefore, a qualitative difference between suspended and saltating sediment, or is it just a quantitative difference in the size of the jump length and the frequency of re‐entrainment? It is our contention that the distinction of suspension as a separate class of sediment transport is both arbitrary and an unhelpful anthropocentric artefact. If we recognize that sediment transport is a continuum and applies to any fluid medium rather than split into different “processes” based on arbitrary thresholds and fluids, then recognizing the continuity will enable development of an holistic approach sediment transport, and thus sediment‐transport models that are likely to be viable across a wider range of conditions than hitherto. Copyright © 2015 John Wiley & Sons, Ltd.