Along-Strike Differences in the Southern Alps of New Zealand: Consequences of Inherited Variation in Rheology

Long- and short-term strain variations along the Australian-Pacific plate boundary through the South Island of New Zealand, including a 300% increase in orogen width, coexistence of oblique thrusting on orthogonal structures, and variability in the locus of orogenic gold deposits, coincide with rheologically relevant geological variation. Our model investigates the consequences of thin, strong lower crust in the north and thick, weak lower crust in the south. Solution of the full 3-D mechanical equations reproduces the larger wavelength strain patterns of the orogen. A 3-D perturbation-based analytical solution leads to the identification of the sensitivity of displacement type to minor stress changes. Transition from boundary-normal thrusting to boundary-parallel thrusting occurs at the transition from strong to weak lower crust and is related to an increase in either tau(yz) (shear stress in the yz plane) or the ratio of the coordinate normal stresses, (sigma(yy)/sigma(xx)), where x and y are in the horizontal and z is vertical. Both mechanisms are compatible with the geologically dependent rheological variation employed in our model. Citation: Upton, P., P. O. Koons, D. Craw, C. M. Henderson, and R. Enlow (2009), Along-strike differences in the Southern Alps of New Zealand: Consequences of inherited variation in rheology, Tectonics, 28, TC2007, doi:10.1029/2008TC002353.

Ice Core Evidence for a Second Volcanic Eruption Around 1809 in the Northern Hemisphere

A volcanic signal observed in ice cores from both polar regions six years prior to Tambora is attributed to an unknown tropical eruption in 1809. Recovery of dacitic tephra from the 1809 horizon in a Yukon ice core ( Eclipse) that is chemically distinct from andesitic 1809 tephra found in Antarctic ice cores indicates a second eruption in the Northern Hemisphere at this time. Together with the similar magnitude and timing of the 1809 volcanic signal in the Arctic and Antarctic, this could suggest a large tropical eruption produced the sulfate and Antarctic tephra and a minor Northern Hemisphere eruption produced the Eclipse tephra. Nonetheless, the possibility that there were coincidental eruptions of similar magnitude in both hemispheres, rather than a single tropical eruption, should not be discounted. Correctly attributing the source of the 1809 volcanic signal has important implications for modeling the magnitude and latitudinal distribution of volcanic radiative forcing.

Prismatine: Revalidation for Boron-Rich Compositions in the Kornerupine Group

Kornerupine and prismatine were introduced independently by Lorenzen in 1884 (but published in 1886 and 1893) and by Sauer in 1886, respectively. Ussing (1889) showed that the two minerals were sufficiently close crystallographically and chemically to be regarded as one species. However, recent analyses of boron using the ion microprobe and crystal structure refinement, indicate that the boron content of one tetrahedral site in kornerupine ranges from 0 to 1. Kornerupine and prismatine, from their respective type localities of Fiskenaesset, Greenland and Waldheim, Germany, are distinct minerals, members of an isomorphic series differing in boron content. For this reason, we re-introduce Sauer's name prismatine for kornerupines with B > 0.5 atoms per formula unit (p.f.u.) of 22(O,OH,F), and restrict the name kornerupine sensu stricto to kornerupines with B < 0.5 p.f.u. Kornerupine sensu lato is an appropriate group name for kornerupine of unknown boron content. Kornerupine sensu stricto and prismatine from the type localities differ also in Fe2+/Mg ratio, Si - (Mg + Fe2+ + Mn) content, Al content, F content, colour, density, cell parameters, and paragenesis. Both minerals formed under granulite-facies conditions with sapphirine and phlogopite, but kornerupine sensu stricto is associated with anorthite and homblende or gedrite, whereas prismatine is found with oligoclase (An9-13), sillimanite, garnet, and/or tourmaline. Occurrences at other localities suggest that increasing boron content extends the stability range of prismatine relative to that of kornerupine sensu stricto.

What Limits Bacterial Production in the Suboxic Region of Permanently Ice-Covered Lake Bonney, Antarctica?

Bacterial production assays (thymidine incorporation rates) were used to evaluate the activity of heterotrophic bacteria at the chemocline region in both the East (ELB) and West (WLB) Lobes of permanently ice-covered Lake Bonney, in the Taylor Valley of Antarctica. The magnitude of activity varied dramatically within the depth interval of 1 to 2 m from moderate to very low levels below the chemocline, especially in the East Lobe, where chemical distributions indicate the absence of a normally functioning nitrogen cycle. Several parameters (e.g. addition of nutrients or chelators, dilution) were manipulated in incubation experiments in order to identify factors that would enhance activity in the suboxic deep waters of the East Lobe. Activity, in terms of thymidine incorporation, was consistently detected in the deep-water communities, implying that, although the water may be 'toxic', the cells remain viable. None of the treatments resulted in consistent enhancement of thymidine incorporation rates in samples from below the chemocline. Bacterial populations above the chemocline appear to be phosphorus-limited. The nature of the limitation, toxicity or inhibition that limits bacterial activity in the suboxic waters has not been identified.

Denitrification in the Hypolimnion of Permanently Ice-Covered Lake Bonney, Antarctica

The distribution of denitrification was investigated in the hypolimnion of the east and west lobes of permanently ice-covered Lake Bonney, Taylor Valley, Antarctica. Anomalously high concentrations of dissolved inorganic nitrogen (DIN; nitrate, nitrite, ammonium and nitrous oxide) in the oxygen-depleted hypolimnion of the east lobe of the Lake implied that denitrification is or was active in the west, but not in the east lobe. While previous investigations reported no detectable denitrification in the east lobe, we measured active denitrification in samples from both the east and west lobes. In the west lobe, measured denitrification rates exhibited a maximum at the depth of the chemocline and denitrification was not detectable in either the oxic surface waters or in the deep water where nitrate was absent. In the east lobe, denitrification was detected below the chemocline, at the depths where ammonium, nitrate, nitrite and nitrous oxide are all present at anomalously high levels, Trace metal availability was manipulated in incubation experiments in order to determine whether trace metal toxicity in the east lobe could explain the difference in nitrogen cycling between the 2 lobes. There were no consistent stimulatory effects of metal chelators or nutrient addition on the rate of denitrification in either lobe, so that the mechanisms underlying the unusual N cycle of the east lobe remain unknown. We conclude that all the ingredients necessary to allow denitrification to occur are present in the east lobe. However, even though denitrification could be detected under certain conditions in incubations, denitrification is inhibited under the in situ conditions of the lake.

Biodiversity and Ecosystem Function in the Gulf of Maine: Pattern and Role of Zooplankton and Pelagic Nekton

This paper forms part of a broader overview of biodiversity of marine life in the Gulf of Maine area (GoMA), facilitated by the GoMA Census of Marine Life program. It synthesizes current data on species diversity of zooplankton and pelagic nekton, including compilation of observed species and descriptions of seasonal, regional and cross-shelf diversity patterns. Zooplankton diversity in the GoMA is characterized by spatial differences in community composition among the neritic environment, the coastal shelf, and deep offshore waters. Copepod diversity increased with depth on the Scotian Shelf. On the coastal shelf of the western Gulf of Maine, the number of higher-level taxonomic groups declined with distance from shore, reflecting more nearshore meroplankton. Copepod diversity increased in late summer, and interdecadal diversity shifts were observed, including a period of higher diversity in the 1990s. Changes in species diversity were greatest on interannual scales, intermediate on seasonal scales, and smallest across regions, in contrast to abundance patterns, suggesting that zooplankton diversity may be a more sensitive indicator of ecosystem response to interannual climate variation than zooplankton abundance. Local factors such as bathymetry, proximity of the coast, and advection probably drive zooplankton and pelagic nekton diversity patterns in the GoMA, while ocean-basin-scale diversity patterns probably contribute to the increase in diversity at the Scotian Shelf break, a zone of mixing between the cold-temperate community of the shelf and the warm-water community offshore. Pressing research needs include establishment of a comprehensive system for observing change in zooplankton and pelagic nekton diversity, enhanced observations of "underknown'' but important functional components of the ecosystem, population and metapopulation studies, and development of analytical modeling tools to enhance understanding of diversity patterns and drivers. Ultimately, sustained observations and modeling analysis of biodiversity must be effectively communicated to managers and incorporated into ecosystem approaches for management of GoMA living marine resources.