Isotopes and trace elements as natal origin markers of Helicoverpa armigera--an experimental model for biosecurity pests.

Protecting a nation's primary production sector and natural estate is heavily dependent on the ability to determine the risk presented by incursions of exotic insect species. Identifying the geographic origin of such biosecurity breaches can be crucial in determining this risk and directing the appropriate operational responses and eradication campaigns, as well as ascertaining incursion pathways. Reading natural abundance biogeochemical markers using mass spectrometry is a powerful tool for tracing ecological pathways as well as provenance determination of commercial products and items of forensic interest. However, application of these methods to trace insects has been underutilised to date and our understanding in this field is still in a phase of basic development. In addition, biogeochemical markers have never been considered in the atypical situation of a biosecurity incursion, where sample sizes are often small, and of unknown geographic origin and plant host. These constraints effectively confound the interpretation of the one or two isotope geo-location markers systems that are currently used, which are therefore unlikely to achieve the level of provenance resolution required in biosecurity interceptions. Here, a novel approach is taken to evaluate the potential for provenance resolution of insect samples through multiple biogeochemical markers. The international pest, Helicoverpa armigera, has been used as a model species to assess the validity of using naturally occurring δ2H, 87Sr/86Sr, 207Pb/206Pb and 208Pb/206Pb isotope ratios and trace element concentration signatures from single moth specimens for regional assignment to natal origin. None of the biogeochemical markers selected were individually able to separate moths from the different experimental regions (150-3000 km apart). Conversely, using multivariate analysis, the region of origin was correctly identified for approximately 75% of individual H. armigera samples. The geographic resolution demonstrated with this approach has considerable potential for biosecurity as well as other disciplines including forensics, ecology and pest management.

The atmospheric lead record preserved in lagoon sediments at a remote equatorial Pacific location: Palmyra Atoll, northern Line Islands.

Anthropogenic lead (Pb) inputs to the atmosphere increased greatly over the past century and now dominate Pb supply to the oceans. However, the Pb content of sediments across the equatorial Pacific region is relatively unknown, and data exist only for deep sea sites where Pb deposition lags surface water inputs by up to a century. Here we present ICP-MS analyses of Pb of a core from a lagoon at Palmyra Atoll, northern Line Islands, that spans approximately the past 160 years. The non-bioturbated sediments of the euxinic lagoon, coupled with rapid rates of deposition, provide a unique fine-scale record of atmospheric Pb supply at a remote Pacific location. These first observations of historic Pb sedimentation in an atoll lagoon reveal a 63-fold increase in Pb flux to sediments during the past century and correlate directly with the North American consumption of leaded gasoline that began in 1926.

Mg isotope evidence for contemporaneous formation of chondrules and refractory inclusions.

Primitive or undifferentiated meteorites (chondrites) date back to the origin of the Solar System, and thus preserve a record of the physical and chemical processes that occurred during the earliest evolution of the accretion disk surrounding the young Sun. The oldest Solar System materials present within these meteorites are millimetre- to centimetre-sized calcium-aluminium-rich inclusions (CAIs) and ferromagnesian silicate spherules (chondrules), which probably originated by thermal processing of pre-existing nebula solids. Chondrules are currently believed to have formed approximately 2-3 million years (Myr) after CAIs (refs 5-10)--a timescale inconsistent with the dynamical lifespan of small particles in the early Solar System. Here, we report the presence of excess (26)Mg resulting from in situ decay of the short-lived (26)Al nuclide in CAIs and chondrules from the Allende meteorite. Six CAIs define an isochron corresponding to an initial (26)Al/(27)Al ratio of (5.25 +/- 0.10) x 10(-5), and individual model ages with uncertainties as low as +/- 30,000 years, suggesting that these objects possibly formed over a period as short as 50,000 years. In contrast, the chondrules record a range of initial (26)Al/(27)Al ratios from (5.66 +/- 0.80) to (1.36 +/- 0.52) x 10(-5), indicating that Allende chondrule formation began contemporaneously with the formation of CAIs, and continued for at least 1.4 Myr. Chondrule formation processes recorded by Allende and other chondrites may have persisted for at least 2-3 Myr in the young Solar System.

Early history of Earth's crust-mantle system inferred from hafnium isotopes in chondrites.

The 176Lu to 176Hf decay series has been widely used to understand the nature of Earth's early crust-mantle system. The interpretation, however, of Lu-Hf isotope data requires accurate knowledge of the radioactive decay constant of 176Lu (lambda176Lu), as well as bulk-Earth reference parameters. A recent calibration of the lambda176Lu value calls for the presence of highly unradiogenic hafnium in terrestrial zircons with ages greater than 3.9 Gyr, implying widespread continental crust extraction from an isotopically enriched mantle source more than 4.3 Gyr ago, but does not provide evidence for a complementary depleted mantle reservoir. Here we report Lu-Hf isotope measurements of different Solar System objects including chondrites and basaltic eucrites. The chondrites define a Lu-Hf isochron with an initial 176Hf/177Hf ratio of 0.279628 +/- 0.000047, corresponding to lambda176Lu = 1.983 +/- 0.033 x 10-11 yr-1 using an age of 4.56 Gyr for the chondrite-forming event. This lambda176Lu value indicates that Earth's oldest minerals were derived from melts of a mantle source with a time-integrated history of depletion rather than enrichment. The depletion event must have occurred no later than 320 Myr after planetary accretion, consistent with timing inferred from extinct radionuclides.