Effects of phenology and meteorological disturbance on litter rainfall interception for a Pinus elliottii stand in the Southeastern United States

Litter layers develop across a diverse array of vegetated ecosystems and undergo significant temporal compositional changes due to canopy phenological phases and disturbances. Past research on temporal dynamics of litter interception has focused primarily on litter thickness and leaf fall, yet forest phenophases can change many more litter attributes (e.g., woody debris, bark shedding, and release of reproductive materials). In this study, weekly changes in litter composition over 1 year were used to estimate litter water storage dynamics and model event‐based litter interception. Litter interception substantially reduced throughfall (6–43%), and litter water storage capacity ranged from 1 to 3 mm, peaking when megastrobili release and liana leaf senescence occurred simultaneously during fall 2015. Tropical storm disturbances occurred during the sampling period, allowing evaluation of how meteorological disturbances altered litter interception. High wind speeds and intense rainfall from 2 tropical storms increased litter interception by introducing new woody debris, which, in this study, stored more water than the pre‐existing woody debris. After 2 extreme weather events, a third (Hurricane Hermine) did not increase woody debris (or litter interception), suggesting that the canopy pool of branches susceptible to breakage had been largely depleted. Needle and bark shedding had minor effects on litter interception. Results suggest that the release of reproductive materials and meteorological disturbances appear to be the major compositional drivers of litter interception beyond their obvious contribution to litter thickness.     

Improving SST reconstructions from coral Sr/Ca records: multiple corals from Tahiti (French Polynesia)

We reconstruct SST from coral Sr/Ca ratios measured at three coral cores taken from the lagoon of Tahiti (French Polynesia). Two coral cores were drilled from the same coral colony (one horizontally and one vertically), and a third core was drilled vertically from another coral growing at a different site. We evaluate several Sr/Ca records as proxies for regional SST variations: (1) the three single-core records from Tahiti, (2) an average Sr/Ca record computed from the two cores drilled from the same coral colony, (3) an average Sr/Ca record computed from all three Tahiti cores, and (4) an average Sr/Ca record computed from the three Tahiti cores and a fourth core taken from a different island (Rarotonga). On a monthly scale, the average Sr/Ca record including the four coral cores from Tahiti and Rarotonga shows the best correlation with regional SST. The variance of the SST reconstruction is very realistic and the residual SST is low. This suggests that reconstructing SST from average proxy records gives a better representation of regional SST variations. Of the three Tahiti cores, the one that was drilled horizontally shows the best correlation with grid-SST on an annual mean scale. All three Tahiti corals show much larger interannual SST variations than that indicated by grid-SST.     

Patterns of Pacific decadal variability recorded by Indian Ocean corals

We investigate Pacific Decadal Oscillation (PDO) signals recorded by two bimonthly resolved coral δ¹⁸O series from La Réunion and Ifaty (West Madagascar), Indian Ocean from 1882 to 1993. To isolate the main PDO frequencies, we apply a band pass filter to the time series passing only periodicities from 16 to 28 years. We investigate the covariance patterns of the coral time series with sea surface temperature (SST) and sea level pressure (SLP) of the Indian and Pacific Oceans. In addition, the empirical orthogonal functions of the filtered SST and SLP fields (single and coupled) are related to the filtered coral times series. The covariance maps show the typical PDO pattern for SST and SLP, confirming the coupling between the Indian and Pacific Oceans. Both corals show the strongest signal in boreal summer. The La Réunion (Ifaty) coral better records SST (SLP) than SLP (SST) pattern variability. We suggest that the filtered La Réunion coral δ¹⁸O represents δ¹⁸O of seawater that varies with the South Equatorial Current, which, in turn, is linked with the SST PDO. The filtered Ifaty coral δ¹⁸O represents SST and is remotely linked with the SLP PDO variability. A combined coral record of the Ifaty and La Réunion boreal summer δ¹⁸O series explains about 64% of the variance of the coupled SST/SLP PDO time series. AGU OS06 special issue “Ocean’s role in climate change—a paleo perspective”.     

Lanthanoid behaviour in an acidic landscape

Lanthanoids were studied in a boreal landscape where an abundance of acid sulfate soils and Histosols provide a unique opportunity to increase the understanding of how these metals behave in acidic soils and waters and interact with soil and aqueous organic matter. In the acid sulfate soils lanthanoids are mobile as reflected in high to very high concentrations in soil water and runoff (typically a few mg l⁻¹ but up to 12 mg l⁻¹) and abundant release by several relatively weak extractants (ammonium acetate EDTA, sodium pyrophosphate, hydroxylamine hydrochloride) applied on bulk soil. Normalisation with the lanthanoid pool in the underlying parent materials (sulphide-bearing sediments deposited in brackish-water) and soil water showed that the extensive release/retention in the acidic soil was accompanied by large, and variable, fractionation trends across the lanthanoid series. In low-order streams draining these soils, the lanthanoid concentrations were high and, as indicated by frontal ultrafiltration and geochemical modelling, largely dissolved (<1 kDa) in the form of the species LnSO₄⁺ and Ln³⁺. In other moderately acidic stream waters (pH 4.3-4.6), organic complexation was predicted to be important in the <1 kDa fraction (especially for the heavy lanthanoids) and strongly dominating in the colloidal phase (1 kDa-0.45 μm). Along the main stem of a stream in focus (catchment area of 223 km²), lanthanoid concentrations increased downstream, in particular during high flows, caused by a downstream increase in the proportion of acid sulfate soils which are extensively flushed during wet periods. The geochemical models applied to the colloidal Ln-organic phase were not successful in predicting the measured fractionation patterns.     

Ultraviolet spectral reflectance properties of common planetary minerals

Ultraviolet spectral reflectance properties (200-400 nm) of a large number of minerals known or presumed to exist on the surfaces of Mars, the Moon, and asteroids, and in many meteorites, were investigated. Ultraviolet reflectance spectra (200-400 nm) of these minerals range from slightly blue-sloped (reflectance decreasing toward longer wavelengths) to strongly red-sloped (reflectance increasing toward longer wavelengths). Most exhibit one or two absorption features that are attributable to FeO charge transfers involving Fe³⁺ or Fe²⁺. The UV region is a very sensitive indicator of the presence of even trace amounts (<0.01 wt%) of Fe³⁺ and Fe²⁺. The major Fe³⁺O absorption band occurs at shorter wavelengths (∼210-230 nm), and is more intense than the major Fe²⁺O absorption band (∼250-270 nm). Ti-bearing minerals, such as ilmenite, rutile and anatase exhibit UV absorption bands attributable to Ti⁴⁺O charge transfers. While the positions of metal-O charge transfer bands sometimes differ for different minerals, the variation is often not diagnostic enough to permit unique mineral identification. However, iron oxides and oxyhydroxides can generally be distinguished from Fe-bearing silicates in the 200-400 nm region on the basis of absorption band positions. Within a given mineral group (e.g., low-calcium pyroxene, olivine, plagioclase feldspar), changes in Fe²⁺ or Fe³⁺ abundance do not appear to result in a measurable change in absorption band minima positions. Absorption band positions can vary as a function of grain size, however, and this variation is likely due to band saturation effects. The intensity of metal-O charge transfers means that some minerals will exhibit saturated UV absorption bands even for fine-grained (<45 μm) powders. In cases where absorption bands are not saturated (e.g., Fe²⁺O bands in some plagioclase feldspars and pyroxenes), changes in Fe²⁺ content do not appear to cause variations in band position. In other minerals (e.g., olivine), changes in band positions are correlated with compositional and/or grain size variations, but this is likely due to increasing band saturation rather than compositional variations. Overall, we find that the UV spectral region is sensitive to different mineral properties than longer wavelength regions, and thus offers the potential to provide complementary capabilities and unique opportunities for planetary remote sensing.     

Mesospheric vertical thermal structure and winds on Venus from HHSMT CO spectral-line observations

We report vertical thermal structure and wind velocities in the Venusian mesosphere retrieved from carbon monoxide (¹²CO J=2-1 and ¹³CO J=2-1) spectral line observations obtained with the Heinrich Hertz Submillimeter Telescope (HHSMT). We observed the mesosphere of Venus from two days after the second Messenger flyby of Venus (on 5 June 2007 at 23:10 UTC) during five days. Day-to-day and day-to-night temperature variations and short-term fluctuations of the mesospheric zonal flow were evident in our data. The extensive layer of warm air detected recently by SPICAV at 90-100 km altitude is also detected in the temperature profiles reported here.These data were part of a coordinated ground-based Venus observational campaign in support of the ESA Venus Express mission. Furthermore, this study attempts to cross-calibrate space- and ground-based observations, to constrain radiative transfer and retrieval algorithms for planetary atmospheres, and to contribute to a more thorough understanding of the global patterns of circulation of the Venusian atmosphere.     

Mammal remains at Rantis Cave,Israel, and Middle–Late Pleistocene human subsistence and ecology in the Southern Levant

Rantis Cave is a recently discovered filled cave in central Israel, displaying a rich faunal accumulation of micromammals, ungulates and carnivores. U–Th dating assigns the beginning of accumulation to ca. 140 ka. The accumulation is culturally assigned to the late half of the Middle Paleolithic (MP) period. Single‐grain optically stimulated luminescence measurements attest to a complex sedimentological history. We present the cross‐disciplinary results of taphonomic and geomorphological analyses, which point to the cave serving as a natural pitfall trap for the large fauna, with little human or carnivore activity. The fauna is dominated by Dama among the ungulates and by Microtus among the micromammals. These data in conjunction with ungulate tooth mesowear analysis suggest a xeric Mediterranean environment on the eastern margin of the southern Levantine foothills. The relative taxonomic abundance of ungulate taxa shows some differences from anthropogenic MP sites, possibly reflecting the prey choice patterns of MP hunters. Overall, the natural accumulation scenario for Rantis Cave provides a rare paleoenvironmental and paleoeconomic reference to the rich anthropogenic MP faunas of the Southern Levant, enabling the reconstruction of a rich and diverse environmental setting for this important human dispersal route. Copyright © 2011 John Wiley & Sons, Ltd.     

Expansion rate and geometry of floating vegetation mats on the margins of thermokarst lakes,northern Seward Peninsula,Alaska, USA

Investigations on the northern Seward Peninsula in Alaska identified zones of recent (<50 years) permafrost collapse that led to the formation of floating vegetation mats along thermokarst lake margins. The occurrence of floating vegetation mat features indicates rapid degradation of near‐surface permafrost and lake expansion. This paper reports on the recent expansion of these collapse features and their geometry is determined using geophysical and remote sensing measurements. The vegetation mats were observed to have an average thickness of 0.57 m and petrophysical modeling indicated that gas content of 1.5–5% enabled floatation above the lake surface. Furthermore, geophysical investigation provides evidence that the mats form by thaw and subsidence of the underlying permafrost rather than terrestrialization. The temperature of the water below a vegetation mat was observed to remain above freezing late in the winter. Analysis of satellite and aerial imagery indicates that these features have expanded at maximum rates of 1–2 m yr^‐1 over a 56 year period. Including the spatial coverage of floating ‘thermokarst mats’ increases estimates of lake area by as much as 4% in some lakes. Copyright © 2011 John Wiley & Sons, Ltd.     

Organic and inorganic correlations for Northwest Africa 852 by synchrotron‐based Fourier transform infrared microspectroscopy

Relationships between organic molecules and inorganic minerals are investigated in a single 34 μm diameter grain of the CR2 chondrite Northwest Africa 852 (NWA) 852 with submicron spatial resolution using synchrotron‐based imaging micro‐FTIR spectroscopy. Correlations based on absorption strength for the various constituents are determined using statistical correlation analysis. The silicate band is found to be correlated with the hydration band, and the latter is highly correlated with stretching modes of aliphatic hydrocarbons. Spatial distribution maps show that water+organic combination, silicate, OH, and C‐H distributions overlap, suggesting a possible catalytic role of phyllosilicates in the formation of organics. In contrast, the carbonate band is anticorrelated with water+organic combination, however uncorrelated with any other spectral feature. The average ratio of asymmetric CH₂ and CH₃ band strengths (CH₂/CH₃ = 2.53) for NWA 852 is similar to the average ratio of interplanetary dust particles (~2.40) and Wild 2 cometary dust particles (2.50), but it significantly exceeds that of interstellar medium objects (~1.00) and several aqueously altered carbonaceous chondrites (~1.40). This suggests organics of similar length/branching, and perhaps similar formation regions, for NWA 852, Wild 2 dust particles, and interplanetary dust particles. The heterogeneous spatial distribution of ratio values indicates the presence of a mixture of aliphatic organic material with different length/branching, and thus a wide range of parent body processes, which occurred before the considered grain was formed.     

Estimation of trace element concentrations in the lunar magma ocean using mineral‐ and metal‐silicate melt partition coefficients

This study uses experimentally determined plagioclase‐melt D values to estimate the trace element concentrations of Sr, Hf, Ga, W, Mo, Ru, Pd, Au, Ni, and Co in a crystallizing lunar magma ocean at the point of plagioclase flotation. Similarly, experimentally determined metal‐silicate partition experiments combined with a composition model for the Moon are used to constrain the concentrations of W, Mo, Ru, Pd, Au, Ni, and Co in the lunar magma ocean at the time of core formation. The metal‐silicate derived lunar mantle estimates are generally consistent with previous estimates for the concentration of these elements in the lunar mantle. Plagioclase‐melt derived concentrations for Sr, Ga, Ru, Pd, Au, Ni, and Co are also consistent with prior estimates. Estimates for Hf, W, and Mo, however, are higher. These elements may be concentrated in the residual liquid during fractional crystallization due to their incompatibility. Alternatively, the apparent enrichment could reflect the inappropriate use of bulk anorthosite data, rather than data for plagioclase separates.