Radio source calibration for the Very Small Array and other cosmic microwave background instruments at around 30 GHz

Accurate calibration of data is essential for the current generation of cosmic microwave background (CMB) experiments. Using data from the Very Small Array (VSA), we describe procedures which will lead to an accuracy of 1 per cent or better for experiments such as the VSA and CBI. Particular attention is paid to the stability of the receiver systems, the quality of the site and frequent observations of reference sources. At 30 GHz the careful correction for atmospheric emission and absorption is shown to be essential for achieving 1 per cent precision.
The sources for which a 1 per cent relative flux density calibration was achieved included Cas A, Cyg A, Tau A and NGC 7027 and the planets Venus, Jupiter and Saturn. A flux density, or brightness temperature in the case of the planets, was derived at 33 GHz relative to Jupiter which was adopted as the fundamental calibrator. A spectral index at ∼30 GHz is given for each.
Cas A, Tau A, NGC 7027 and Venus were examined for variability. Cas A was found to be decreasing at 0.394 ± 0.019 per cent yr⁻¹ over the period 2001 March to 2004 August. In the same period Tau A was decreasing at 0.22 ± 0.07 per cent yr⁻¹. A survey of the published data showed that the planetary nebula NGC 7027 decreased at 0.16 ± 0.04 per cent yr⁻¹ over the period 1967–2003. Venus showed an insignificant (1.5 ± 1.3 per cent) variation with Venusian illumination. The integrated polarization of Tau A at 33 GHz was found to be 7.8 ± 0.6 per cent at position angle =148°± 3°.     

Instantaneous triple-probe method for the direct display of plasma parameters in a spacecraft condition

It is proposed that the instantaneous triple-probe method can be applied to the direct display of parameters; particularly in the case of probe application during measurements carried out from spacecraft. The theory of the triple-probe method has been extended for the very high speed flowing collisionless plasma condition, i.e. in which the spacecraft speed U ≈ the most probable electron thermal velocity v_e > the most probable ion thermal velocity v_i. This condition is particularly important both in the case of re-entry of spacecraft and in the solar wind plasma. Experiments have been conducted in a free molecular beam plasma chamber for S_i = U/v_i > 10. The experimental results and their relationship to the appropriate theory are presented.     

Statistical detection of the mid-Pleistocene transition

Using statistical methods we have shown quantitatively that the transition in mean and variance observed in ¹⁸O records during the middle of the Pleistocene was abrupt. By applying these methods to all of the available records spanning the entire Pleistocene it appears that this jump was global and primarily represents an increase in ice mass. At roughly the same time an abrupt decrease in sea surface temperature also occurred, indicative of sudden global cooling. This kind of evidence suggests a possible bifurcation of the climate system that must be accounted for in a complete explanation of the ice ages. Theoretical models including internal dynamics are capable of exhibiting this kind of rapid transition.     

The spatio-temporal distribution and population structure of green turtles (Chelonia mydas) in New Zealand

Despite being endangered internationally and protected nationally, little consideration has been given to the occurrence of green turtles (Chelonia mydas) in New Zealand. New Zealand lies on the southern boundary of the distributional range of green turtles in the southwestern Pacific, with individuals found within these waters historically considered to be occasional visitors or stragglers incidentally carried by ocean currents. However, the present work shows that green turtles are present year round in New Zealand’s northern waters (c. 34°–38° S). A review of sighting, stranding and incidental capture data collected between 1895 and 2013 illustrate New Zealand’s green turtle population comprises post-pelagic immature juveniles to large subadults. The female:male sex ratio of 1.7:1 is similar to those reported from warm temperate foraging grounds in eastern Australia. A subsample of new recruits indicates green turtles recruit to neritic habitats at approximately 40.8?cm curved carapace length. This study suggests that New Zealand’s neritic habitats constitute a transitional developmental ground for post-pelagic immature green turtles. We observed an exponential increase in the number of documented records over time, though whether this is due to increased numbers of turtles or increased reporting rates, or both, is unclear and warrants further investigation. More broadly, this work provides a baseline understanding of the ecology of green turtles at the edge of their range, providing opportunities to investigate regional niche modelling and connectivity of this highly mobile species, while also monitoring broad-scale effects of climate-induced environmental change.     

Trophic structure and pathways of biogenic carbon flow in the eastern North Water Polynya

In the eastern North Water, most of the estimated annual new and net production of carbon (C) occurred during the main diatom bloom in 1998. During the bloom, at least 30% of total and new phytoplankton production occurred as dissolved organic carbon (DOC) and was unavailable for short-term assimilation into the herbivorous food web or sinking export. Based on particle interceptor traps and ²³⁴Th deficits, 27% of the particulate primary production (PP) sank out of the upper 50 m, with only 7% and 1% of PP reaching the benthos at shallow (≈200 m) and deep (≈500 m) sites, respectively. Mass balance calculations and grazing estimates agree that ≈79% of PP was ingested by pelagic consumers between April and July. During this period, the vertical flux of biogenic silica (BioSi) at 50 m was equivalent to the total BioSi produced, indicating that all of the diatom production was removed from the euphotic zone as intact cells (direct sinking) or empty frustules (grazing or lysis). The estimated flux of empty frustules was consistent with rates of herbivory by the large, dominant copepods and appendicularians during incubations. Since the carbon demand of the dominant planktivorous bird, Alle alle, amounted to ≈2% of the biomass synthesized by its main prey, the large copepod Calanus hyperboreus, most of the secondary carbon production was available to pelagic carnivores. Stable isotopes indicated that the biomass of predatory amphipods, polar cod and marine mammals was derived from these herbivores, but corresponding carbon fluxes were not quantified. Our analysis shows that a large fraction of PP in the eastern North Water was ingested by consumers in the upper 50 m, leading to substantial carbon respiration and DOC accumulation in surface waters. An increasingly early and prolonged opening of the Artic Ocean is likely to promote the productivity of the herbivorous food web, but not the short-term efficiency of the particulate, biological CO₂ pump.     

The Taurewa Eruptive Episode: evidence for climactic eruptions at Ruapehu volcano, New Zealand

 The ca. 10,500 years B.P. eruptions at Ruapehu volcano deposited 0.2–0.3 km³ of tephra on the flanks of Ruapehu and the surrounding ring plain and generated the only known pyroclastic flows from this volcano in the late Quaternary. Evidence of the eruptions is recorded in the stratigraphy of the volcanic ring plain and cone, where pyroclastic flow deposits and several lithologically similar tephra deposits are identified. These deposits are grouped into the newly defined Taurewa Formation and two members, Okupata Member (tephra-fall deposits) and Pourahu Member (pyroclastic flow deposits). These eruptions identify a brief (<ca. 2000-year) but explosive period of volcanism at Ruapehu, which we define as the Taurewa Eruptive Episode. This Episode represents the largest event within Ruapehu's ca. 22,500-year eruptive history and also marks its culmination in activity ca. 10,000 years B.P. Following this episode, Ruapehu volcano entered a ca. 8000-year period of relative quiescence. We propose that the episode began with the eruption of small-volume pyroclastic flows triggered by a magma-mingling event. Flows from this event travelled down valleys east and west of Ruapehu onto the upper volcanic ring plain, where their distal remnants are preserved. The genesis of these deposits is inferred from the remanent magnetisation of pumice and lithic clasts. We envisage contemporaneous eruption and emplacement of distal pumice-rich tephras and proximal welded tuff deposits. The potential for generation of pyroclastic flows during plinian eruptions at Ruapehu has not been previously considered in hazard assessments at this volcano. Recognition of these events in the volcanological record is thus an important new factor in future risk assessments and mitigation of volcanic risk at Tongariro Volcanic Centre. Received: 5 July 1998 / Accepted: 12 March 1999     

Development of Iron Speciation Reference Materials for Palaeoredox Analysis

The development and application of geochemical techniques to identify redox conditions in modern and ancient aquatic environments has intensified over recent years. Iron (Fe) speciation has emerged as one of the most widely used procedures to distinguish different redox regimes in both the water column and sediments, and is the main technique used to identify oxic, ferruginous (anoxic, Fe(II) containing) and euxinic (anoxic, sulfidic) water column conditions. However, an international sediment reference material has never been developed. This has led to concern over the consistency of results published by the many laboratories that now utilise the technique. Here, we report an interlaboratory comparison of four Fe speciation reference materials for palaeoredox analysis, which span a range of compositions and reflect deposition under different redox conditions. We provide an update of extraction techniques used in Fe speciation and assess the effects of both test portion mass, and the use of different analytical procedures, on the quantification of different Fe fractions in sedimentary rocks. While atomic absorption spectroscopy and inductively coupled plasma‐optical emission spectrometry produced comparable Fe measurements for all extraction stages, the use of ferrozine consistently underestimated Fe in the extraction step targeting mixed ferrous–ferric minerals such as magnetite. We therefore suggest that the use of ferrozine is discontinued for this Fe pool. Finally, we report the combined data of four independent Fe speciation laboratories to characterise the Fe speciation composition of the reference materials. These reference materials are available to the community to provide an essential validation of in‐house Fe speciation measurements.