Interannual and decadal variability in zooplankton communities of the southeast Bering Sea shelf

The southeastern Bering Sea shelf ecosystem is an important fishing ground for fin- and shellfish, and is the summer foraging grounds for many planktivorous seabirds and marine mammals. In 1997 and 1998, Northern Hemisphere climate anomalies affected the physical and biological environment of the southeastern Bering Sea shelf. The resulting anomalous conditions provided a valuable opportunity to examine how longer-term climate change might affect this productive ecosystem. We compared historical and recent zooplankton biomass and species composition data for the southeastern Bering Sea shelf to examine whether or not there was a response to the atmosphere–ocean–ice anomalies of 1997 and 1998. Summer zooplankton biomass (1954–1994) over the southeastern shelf did not exhibit a decline as previously reported for oceanic stations. In addition, zooplankton biomass in 1997 and 1998 was not appreciably different from other years in the time series. Spring concentrations of numerically abundant copepods (Acartia spp., Calanus marshallae, and Pseudocalanus spp.), however, were significantly higher during 1994–1998 than 1980–1981; spring concentrations of Metridia pacifica and Neocalanus spp. were not consistently different between the two time periods. Neocalanus spp. was the only taxon to have consistent differences in stage composition between the two time periods—CV copepodites were much more prevalent in May of the 1990s than early 1980s. Since relatively high zooplankton concentrations were observed prior to 1997, we do not attribute the high concentrations observed in the summers of 1997 and 1998 directly to the acute climate anomalies. With the present data it is not possible to distinguish between increased production (control from below) and decreased predation (control from above) to explain the recent increase in concentrations of the species examined.     

High‐temperature gold‐copper extraction with chloride flux in lava tubes of Tolbachik volcano (Kamchatka)

Subvolcanic environments in supra‐subduction zones are renowned for hosting epithermal deposits that often contain electrum and native gold, including bonanza examples. This study examined mineral assemblages and processes occurring in shallow‐crust volcanic settings using recent eruption (2012–2013) of the basaltic Tolbachik volcano in the Kamchatka arc. The Tolbachik eruptive system is characterized by an extensive system of lava tubes. After cessation of magma input, the tubes maintained the flow of hot oxidized gases that episodically interacted with the lava surfaces and sulphate‐chloride precipitates from volcanic gases on these surfaces. The gas‐rock interaction had strong pyrometamorphic effects that resulted in the formation of molten salt, oxidized (tenorite, hematite, Cu‐rich magnesioferrite) and skarn‐like silicate mineral assemblages. By analogy with experimental studies, we propose that a combination of these processes was responsible for extraction of metals from the basaltic wall rocks and deposition of Cu‐, Fe‐ and Cu‐Fe‐oxides and native gold.     

Tectonothermal events in the Olympic IOCG Province constrained by apatite and REE-phosphate geochronology

The Olympic iron oxide–copper–gold province in South Australia contains numerous deposits and prospects, including the Olympic Dam Cu–U–Au–Ag deposit and the Acropolis prospect. The Acropolis prospect comprises massive, coarse-grained magnetite–apatite veins partly replaced by a hematite-stable assemblage. The apatite grains in the veins contain zones with abundant inclusions of other minerals (including monazite and xenotime) and low trace-element concentrations relative to the inclusion-free zones. The inclusion-rich apatite zones are interpreted to be formed from the recrystallisation of the inclusion-free apatite and remobilisation of U, Th and rare earth element (REE) from apatite into monazite and xenotime. Apatite, monazite and xenotime are all established U–Th–Pb geochronometers and offer the potential to constrain the alteration history of the Acropolis prospect. The LA-ICPMS U–Pb age of inclusion-free apatite is within error of the age of the host volcanic units (ca 1.59 Ga). Inclusion-rich apatite yields both near-concordant analyses that are within error of the inclusion-free apatite as well as highly disturbed (discordant) analyses. The most concordant analyses of monazite (Th–Pb) inclusions and xenotime (U–Pb) inclusions and rim grains indicate an alteration event occurred at ca 1.37 Ga and possibly also at ca 500 Ma. The disparity in age of the inclusion-rich apatite and the REE-phosphate inclusions (and rim grains) is suggested to be owing to the apatite being initially recrystallised at ca 1.59 Ga and modified again by a later event that also formed (or coarsened) most of the inclusions. Partial resetting of the majority of the monazite inclusions as well as the presence of significant amounts of common Pb has complicated the interpretation of the monazite results. In contrast, xenotime is a more robust geochronometer in this setting. The ages of the two post-1.59 Ga events that appear to have affected the Acropolis prospect do not correspond to any events known to have occurred in the Gawler Craton. The earlier (ca 1.37 Ga) age instead corresponds best with metamorphic–magmatic–hydrothermal activity in Laurentia, consistent with the proximity of Laurentia and the Gawler Craton inferred from palaeogeographic reconstructions. The later (ca 500 Ma) event corresponds to the Delamerian Orogeny and has been shown by prior studies to have also affected the Olympic Dam deposit.     

Uranium depositional controls at the Prairie Flats surficial uranium deposit, Summerland, British Columbia

A hydrological and geochemical investigation of the Prairie Flats surficial uranium deposit in Summerland, BC was undertaken to identify the principal controls on uranium deposition. A network of piezometers was installed and used to measure the hydraulic conductivities of the host sediments as well as the general flow direction and aqueous geochemistry of the resident groundwaters. Two hydrostratigraphic units were identified: a peat and clay unit overlying a sand and gravel unit. Measured hydraulic conductivities were on the order of 10^-7 and 10^-5 m/s, respectively, and the vertical hydraulic gradients indicate significant groundwater discharge upward into the peat and clay unit. Prairie Flats groundwaters are neutral to alkaline in pH, enriched in Ca²⁺ and HCO₃^-, and have dissolved uranium concentrations ranging from 10 to nearly 1,000 µg/l. Groundwater flow and geochemistry data were used to estimate the flux of uranium in groundwater at the site. A major fraction of the uranium is taken up by adsorption to organics. There is also evidence for subsequent desorption by the formation of soluble complexes with bicarbonate. Uranium that is not held by adsorption is most likely precipitated as uraninite, UO_2(c). Reducing conditions in the peat and clay unit (Eh<0.1 V) relative to the underlying sand and gravel unit (Eh>0.2 V) may explain the high concentrations of uranium nearer ground surface. The current flux of uranium into the flats is significantly smaller than that calculated from the size and age of the deposit, which may be an indication of changing rates of deposition in response to varying climatic and hydrogeologic conditions over time.     

Geology of the Acropolis prospect,South Australia,constrained by high-precision CA-TIMS ages

Abstract

Acropolis is an Fe-oxide–copper–gold prospect ～20?km from Olympic Dam, South Australia, and marked by near-coincident gravity and magnetic anomalies. Prospective Fe-oxide–apatite?±?sulfide veins occur in Mesoproterozoic and Paleoproterozoic volcanic and granitoid host units beneath unmineralised sedimentary formations. We have produced a geological map and history of the prospect using data from 16 diamond drill holes, including LA-ICPMS and high-precision CA-TIMS ages. The oldest unit is megacrystic granite of the Donington Suite (ca 1850?Ma). A non-conformity spanning ca 250 My separates the Donington Suite and felsic lavas and ignimbrites of the Gawler Range Volcanics (GRV; 1594.03?±?0.68?Ma). The GRV were intruded by granite of the Hiltaba Suite (1594.88?±?0.50?Ma) and felsic dykes (1593.88?±?0.56?Ma; same age as the Roxby Downs Granite at Olympic Dam). The felsic dykes are weakly altered and lack Fe-oxide–apatite–sulfide veins, suggesting that they post-date the main hydrothermal event. If correct, this relationship implies that the main hydrothermal event at Acropolis was ca 1594?Ma and pre-dated the main hydrothermal event at Olympic Dam. The GRV at Acropolis are the same age as the GRV at Olympic Dam and ca 3–7 My older than the GRV exposed in the Gawler Ranges. The gravity and magnetic anomalies coincide with sections through the GRV, Hiltaba Suite and Donington Suite that contain abundant, wide, Fe-oxide veins. The GRV, Hiltaba Suite and Donington Suite are unconformably overlain by the Mesoproterozoic Pandurra Formation or Neoproterozoic Stuart Shelf sedimentary formations. The Pandurra Formation shows marked lateral variations in thickness related to paleotopography on the underlying units and post-Pandurra Formation pre-Neoproterozoic faults. The Stuart Shelf sedimentary formations have uniform thicknesses.

1. KEY POINTS

2. Fe-oxide–apatite?±?sulfide veins are hosted by the Gawler Range Volcanics (1594.03?±?0.68?Ma), the Hiltaba Suite granite (1594.88?±?0.50?Ma) and Donington Suite granite (ca 1850?Ma).

3. The age of felsic dykes (1593.88?±?0.56?Ma) interpreted to be post-mineralisation implies that the main hydrothermal event at Acropolis was ca 1594?Ma.

4. The Gawler Range Volcanics at Acropolis are the same age as the Gawler Range Volcanics at Olympic Dam and ca 3 to 7 My older than the Gawler Range Volcanics exposed in the Gawler Ranges.

     

Fine‐scale diet of the Australian sea lion (Neophoca cinerea) using DNA‐based analysis of faeces

We applied DNA‐based faecal analysis to determine the diet of female Australian sea lions (n = 12) from two breeding colonies in South Australia. DNA dietary components of fish and cephalopods were amplified using the polymerase chain reaction and mitochondrial DNA primers targeting the short (~100 base pair) section of the 16S gene region. Prey diversity was determined by sequencing ~50 amplicons generated from clone libraries developed for each individual. Faecal DNA was also combined and cloned from multiple individuals at each colony and fish diversity determined. Diets varied between individuals and sites. Overall, DNA analysis identified a broad diversity of prey comprising 23 fish and five cephalopod taxa, including many species not previously described as prey of the Australian sea lion. Labridae (wrasse), Monacanthidae (leatherjackets) and Mullidae (goat fish) were important fish prey taxa. Commonly identified cephalopods were Octopodidae (octopus), Loliginidae (calamary squid) and Sepiidae (cuttlefish). Comparisons of fish prey diversity determined by pooling faecal DNA from several samples provided a reasonable but incomplete resemblance (55–71%) to the total fish diversity identified across individual diets at each site. Interpretation of diet based on the recovery of prey hard‐parts identified one cephalopod beak (Octopus sp.) and one fish otolith (Parapriacanthus elongatus). The present study highlights the value of DNA‐based analyses and their capabilities to enhance information of trophic interactions.     

Apparent and actual galaxy cluster temperatures

The redshift evolution of the galaxy cluster temperature function is a powerful probe of cosmology. However, its determination requires the measurement of redshifts for all clusters in a catalogue, which is likely to prove challenging for large catalogues expected from XMM-Newton , which may contain of the order of 2000 clusters with measurable temperatures, distributed around the sky. In this paper we study the apparent cluster temperature, which can be obtained without cluster redshifts. We show that the apparent temperature function itself is of limited use in constraining cosmology, and so concentrate our focus on studying how apparent temperatures can be combined with other X-ray information to constrain the cluster redshift. We also briefly study the circumstances under which the non-thermal spectral features can provide redshift information.     

Mineralium Deposita Referees 1992

Mineralium Deposita Referees 1992