Nutrient Mass Flux between Florida Bay and the Florida Keys National Marine Sanctuary

There is a net discharge of water and nutrients through Long Key Channel from Florida Bay to the Florida Keys National Marine Sanctuary (FKNMS). There has been speculation that this water and its constituents may be contributing to the loss of coral cover on the Florida Keys Reef tract over the past few decades, as well as speculation that changes in freshwater flow in the upstream Everglades ecosystem associated with the Comprehensive Everglades Restoration Plan may exacerbate this phenomenon. The results of this study indicate that although there is a net export of approximately 3,850 (±404) ton N year^?1 and 63 (±7) ton P year^?1, the concentrations of these nutrients flowing out of Florida Bay are the same as those flowing in. This implies that no significant nutrient enrichment is occurring in the waters of the FKNMS in the vicinity of Long Key Channel. Because of the effect of restricted southwestward water flow through Florida Bay by shallow banks and small islands, the volume of relatively high-nutrient water from central and eastern portions of the bay exiting through the channel is small compared to the average tidal exchange. Nutrient loading of relatively enriched bay waters is mediated by tidal exchange and mixing with more ambient concentrations of the western Florida Bay and Hawk Channel. System-wide budgets indicate that the contribution of Florida Bay waters to the inorganic nitrogen pool of the Keys coral reef is small relative to offshore inputs.     

Spectropolarimetry of the methane and ammonia bands of Jupiter between 6800 and 8200 Å

Spectropolarimetry of Jupiter at resolutions between 22 and 35 Å reveals a strong increase of linear polarization in the 7250-$\text{A}\text{?}$ CH₄ band. This is very probably due to the decreasing contribution toward the band center of the higher orders of scattering, which have a smaller net polarization than the first few orders. The linear polarization is also enhanced in the band at 7900 $\text{A}\text{?}$ comprising the 7920-$\text{A}\text{?}$ NH₃ and 7600- to 8200-$\text{A}\text{?}$ CH₄ bands. The normalized circular polarization shows a feature at 7250 $\text{A}\text{?}$ with a dispersion shape. This is most probably produced in a double-scattering process involving either a solid or liquid aerosol with an absorption at 7250 $\text{A}\text{?}$. Methane aerosols, the obvious candidates from a spectroscopic point of view, are, however, forbidden if current estimates of the Jovian atmospheric temperature are correct.     

Galilean satellite eclipse studies: III. Jovian methane abundance

The methane abundance in the lower Jovian stratosphere is measured using Galilean satellite eclipse light curves. Spectrally selective observations in and between absorption bands are compared. An average mixing ratio at the locations measured is [CH₄]/[H₂] ～ 1.3 × 10^?3, larger than the value 0.9 × 10^?3 expected for a solar abundance of carbon. Some zenographic variation of the mixing ratio may occur. Observationally compatible values are 1.3–2.0 × 10^?3 in the STZ, 1.3– 2.6 × 10^?3 on the GRS/STrZ edge, and 0.7–1.3 × 10^?3 in the GRS.     

Kimberlite metasomatism at Murowa and Sese pipes, Zimbabwe

Metasomatism accompanying kimberlite emplacement is a worldwide phenomenon, although infrequently described or recognised. At the Cambrian-aged Murowa and Sese kimberlite clusters located within the Archean Zimbabwe Craton just north of the boundary with the Limpopo Mobile Zone in southern central Zimbabwe, the metasomatism is intense and well exposed and the processes can be readily studied. Dykes, sills and the root zones of pipes are exposed at the current erosion level. Kimberlite lithologies present are hypabyssal macrocrystic kimberlite (“HMK”), HMK breccia, and tuffisitic kimberlite breccia (“TKB”) including minor lithic tuffisitic kimberlite breccia (“LTKB”). Country rocks are 2.6 Ga Chibi and Zimbabwe granite batholiths emplaced into 2.6–2.9 Ga or earlier Archean tonalitic gneiss and greenstones. During initial metasomatism, the granites become spotted with green chlorite, needles of alkaline amphiboles (winchite, riebeckite, arfvedsonite) and pyroxenes (aegirine–augite) with minor carbonate and felts of talc. Oligoclase feldspar becomes converted to albite, extensively altered, dusted and reddened with hematite, whereas K-feldspar remains unaffected. The granites become converted to syenite through removal of quartz. More intense metasomatism at Murowa and Sese results in veins of green metasomatite which cut and disrupt the granite. Progressive disruption entrains granite blocks, breaking down the granite still further, spalling off needle-like granite slivers, and so giving rise to LTKB. This process of disruption and entrainment appears to be the manner of initial development of the pipe structure. The chemistry of the metasomatite is intermediate between granite and kimberlite. Compared to granite country rock it has markedly higher Mg, Cr, Ni, CO₂ and H₂O+, higher Ca, Mn, Nb, Sr, P, Fe³⁺/Fe²⁺ ratio, U, Co, and Cu, approximately equal TiO₂, K₂O, Na₂O, La, Ta, Rb, Zr, Zn and resultant lower SiO₂, Al₂O₃, Ga and Y. The metasomatite Na₂O/K₂O ratio is slightly higher than that of the granite. The metasomatic process is broadly analogous to fenitisation of granitic wall rock accompanying carbonatite complex emplacement. The metasomatism at Murowa and Sese was caused by fluids from the rising but confined proto-kimberlite melt penetrating into cracks and matrix of granite country rock and reacting with it. These fluids were CO₂-rich, hydrous, oxidising, enhanced in ultramafic elements and carried low levels of Na.     

An analytical and experimental study of zoning in plagioclase

A detailed electron microprobe study has been conducted on natural and experimentally grown zoned plagioclase feldspars. Discontinuous, sector, and oscillatory chemical zoning are observed superimposed on continuous normal or reverse zoning trends. The relative accuracy of 3 element (Na, Ca, K) microprobe traverses was found statistically to be 2 mole percent. Comparison of microprobe data on natural zoned plagioclase with zoned plagioclase grown in controlled experiments has shown that it may be possible to distinguish zonal development resulting from physio-chemical changes to the bulk magma from zoning related to local kinetic control on the growth of individual crystals.     

The effect of anatase, rutile and sodium titanate on the dissolution of boehmite and gibbsite at 90 °C

Industrial plants that refine bauxite to alumina using the high temperature process have always held the belief that anatase was detrimental to the extraction of boehmite while rutile was not. This study shows that this effect is real and that it is observable at temperatures as low as 90 °C. The extraction of gibbsite is shown to be unaffected which leads us to believe that the kinetics of both the Ti-bearing mineral and the Al-bearing mineral is important in this phenomenon. In addition, it is shown that not only is the presence of anatase an issue in boehmite extraction but so too is the presence of sodium titanate. Rutile was found to have the least impact of the three mineral phases.     

Geology of the Victor Kimberlite, Attawapiskat, Northern Ontario, Canada: cross-cutting and nested craters

The pipe shapes, infill and emplacement processes of the Attawapiskat kimberlites, including Victor, contrast with most of the southern African kimberlite pipes. The Attawapiskat kimberlite pipes are formed by an overall two-stage process of (1) pipe excavation without the development of a diatreme (sensu stricto) and (2) subsequent pipe infilling. The Victor kimberlite comprises two adjacent but separate pipes, Victor South and Victor North. The pipes are infilled with two contrasting textural types of kimberlite: pyroclastic and hypabyssal-like kimberlite. Victor South and much of Victor North are composed of pyroclastic spinel carbonate kimberlites, the main features of which are similar: clast-supported, discrete macrocrystal and phenocrystal olivine grains, pyroclastic juvenile lapilli, mantle-derived xenocrysts and minor country rock xenoliths are set in serpentine and carbonate matrices. These partly bedded, juvenile lapilli-bearing olivine tuffs appear to have been formed by subaerial fire-fountaining airfall processes.

The Victor South pipe has a simple bowl-like shape that flares from just below the basal sandstone of the sediments that overlie the basement. The sandstone is a known aquifer, suggesting that the crater excavation process was possibly phreatomagmatic. In contrast, the pipe shape and internal geology of Victor North are more complex. The northwestern part of the pipe is dominated by dark competent rocks, which resemble fresh hypabyssal kimberlite, but have unusual textures and are closely associated with pyroclastic juvenile lapilli tuffs and country rock breccias±volcaniclastic kimberlite. Current evidence suggests that the hypabyssal-like kimberlite is, in fact, not intrusive and that the northwestern part of Victor North represents an early-formed crater infilled with contrasting extrusive kimberlites and associated breccias. The remaining, main part of Victor North consists of two macroscopically similar, but petrographically distinct, pyroclastic kimberlites that have contrasting macrodiamond sample grades. The juvenile lapilli of each pyroclastic kimberlite can be distinguished only microscopically. The nature and relative modal proportion of primary olivine phenocrysts in the juvenile lapilli are different, indicating that they derive from different magma pulses, or phases of kimberlite, and thus represent separate eruptions. The initial excavation of a crater cross-cutting the earlier northwestern crater was followed by emplacement of phase (i), a low-grade olivine phenocryst-rich pyroclastic kimberlite, and the subsequent eruption of phase (ii), a high-grade olivine phenocryst-poor pyroclastic kimberlite, as two separate vents nested within the original phase (i) crater. The second eruption was accompanied by the formation of an intermediate mixed zone with moderate grade. Thus, the final pyroclastic pipe infill of the main part of the Victor North pipe appears to consist of at least three geological/macrodiamond grade zones.

In conclusion, the Victor kimberlite was formed by several eruptive events resulting in adjacent and cross-cutting craters that were infilled with either pyroclastic kimberlite or hypabyssal-like kimberlite, which is now interpreted to be of probable extrusive origin. Within the pyroclastic kimberlites of Victor North, there are two nested vents, a feature seldom documented in kimberlites elsewhere. This study highlights the meaningful role of kimberlite petrography in the evaluation of diamond deposits and provides further insight into kimberlite emplacement and volcanism.     

Cryptotephra from the 74 ka BP Toba super-eruption in the Billa Surgam caves,southern India

The ～74 ka BP Youngest Toba Tuff (YTT), from the largest known Quaternary volcanic eruption, has been found for the first time as a non-visible (crypto-) tephra layer within the Billa Surgam caves, southern India. The occurrence of the YTT layer in Charnel House Cave provides the first calendrical age estimate for this much debated Pleistocene faunal sequence and demonstrates the first successful application of cryptotephrochronology within a cave sequence. The YTT layer lies ～50 cm below a major sedimentological change, which is related to global cooling around the MIS 5 to MIS 4 transition. Using this isochronous event layer the Billa Surgam Cave record can be directly correlated with other archaeological sites in peninsular India and palaeoenvironmental archives across southern Asia.     

Late Holocene environmental conditions in Coronation Gulf,southwestern Canadian Arctic Archipelago: evidence from dinoflagellate cysts,other non‐pollen palynomorphs,and pollen

Boxcore 99LSSL‐001 (68.095° N, 114.186° W; 211 m water depth) from Coronation Gulf represents the first decadal‐scale marine palynology and late Holocene sediment record for the southwestern part of the Northwest Passage. The record was studied for organic‐walled microfossils (dinoflagellate cysts, non‐pollen palynomorphs), pollen, terrestrial spores, and sediment characteristics. ²¹⁰Pb, ¹³⁷Cs, and three accelerator mass spectrometry ¹⁴C dates constrain the chronology. Three prominent palaeoenvironmental zones were identified. During the interval AD 1470–1680 (Zone I), the climate was warmer and wetter than at present, and environmental conditions were more favourable to biological activity and northward boreal forest migration, with reduced sea‐ice and a longer open‐water (growing) season. The interval AD 1680–1940 (Zone II) records sea‐ice increase, and generally cool, polar conditions during the Little Ice Age. During AD 1940–2000 (Zone III), organic microfossils indicate an extended open‐water season and decreased sea‐ice, with suggested amelioration surpassing that of Zone I. Although more marine studies are needed to place this record into an appropriate context, the succession from ameliorated (Zone I) to cooler, sea‐ice influenced conditions (Zone II) and finally to 20th‐century warming (Zone III) corresponds well with several terrestrial climatic records from the neighbouring mainland and Victoria Island, and with lower‐resolution marine records to the west. Copyright © 2011 John Wiley & Sons, Ltd.