Underwater video reveals decreased activity of rocky intertidal snails during high tides and cooler days

Nearly all of our understanding of rocky inter‐tidal ecology comes from studies conducted at low tide. To study inter‐tidal organisms at high tide, we anchored waterproof digital GoPro^® video cameras in wave‐exposed tidepools and recorded the daytime movements of the black turban snail, Tegula funebralis, over the tidal cycle between May and August 2012 near Bodega Bay, California. Overall, snails moved more quickly and presumably foraged more during low tides and on days with warmer air and perhaps water temperatures. This is similar to other ectotherms that exhibit increased metabolic rates, movement and foraging in warmer conditions. Snails also moved less during flood and high tides, may have moved downward in tidepools at flood tides, and showed evidence of reduced activity on days with larger waves. This inactivity and refuge seeking may have been a strategy to avoid dislodgment by waves. Analysis of snail trajectories showed foraging bouts indicated by alternating zig‐zagging and straight movement. There was no effect of temperature, wave height, or tidal phase on distribution of snail turning angles, suggesting that they may have foraged consistently but moved faster during warm conditions and low tides, thereby grazing a larger area. This is one of few direct recordings of inter‐tidal organisms on wave‐exposed rocky shores during high tide. The methods used here are easily transferable to other studies, which are needed to increase our understanding of behaviors that structure rocky shore communities during high tide.     

Extra-tropical atmospheric response to ENSO in the CMIP5 models

The seasonal mean extra-tropical atmospheric response to El Niño/Southern Oscillation (ENSO) is assessed in the historical and pre-industrial control CMIP5 simulations. This analysis considers two types of El Niño events, characterized by positive sea surface temperature (SST) anomalies in either the central equatorial Pacific (CP) or eastern equatorial Pacific (EP), as well as EP and CP La Niña events, characterized by negative SST anomalies in the same two regions. Seasonal mean geopotential height anomalies in key regions typify the magnitude and structure of the disruption of the Walker circulation cell in the tropical Pacific, upper tropospheric ENSO teleconnections and the polar stratospheric response. In the CMIP5 ensembles, the magnitude of the Walker cell disruption is correlated with the strength of the mid-latitude responses in the upper troposphere i.e., the North Pacific and South Pacific lows strengthen during El Niño events. The simulated responses to El Niño and La Niña have opposite sign. The seasonal mean extra-tropical, upper tropospheric responses to EP and CP events are indistinguishable. The ENSO responses in the MERRA reanalysis lie within the model scatter of the historical simulations. Similar responses are simulated in the pre-industrial and historical CMIP5 simulations. Overall, there is a weak correlation between the strength of the tropical response to ENSO and the strength of the polar stratospheric response. ENSO-related polar stratospheric variability is best simulated in the “high-top” subset of models with a well-resolved stratosphere.     

Changes in lead and zinc lability during weathering-induced acidification of desert mine tailings: Coupling chemical and micro-scale analyses

Desert mine tailings may accumulate toxic metals in the near surface centimeters because of low water through-flux rates. Along with other constraints, metal toxicity precludes natural plant colonization even over decadal time scales. Since unconsolidated particles can be subjected to transport by wind and water erosion, potentially resulting in direct human and ecosystem exposure, there is a need to know how the lability and form of metals change in the tailings weathering environment. A combination of chemical extractions, X-ray diffraction, micro-X-ray fluorescence spectroscopy, and micro-Raman spectroscopy were employed to study Pb and Zn contamination in surficial arid mine tailings from the Arizona Klondyke State Superfund Site. Initial site characterization indicated a wide range in pH (2.5–8.0) in the surficial tailings pile. Ligand-promoted (DTPA) extractions, used to assess plant-available metal pools, showed decreasing available Zn and Mn with progressive tailings acidification. Aluminum shows the inverse trend, and Pb and Fe show more complex pH dependence. Since the tailings derive from a common source and parent mineralogy, it is presumed that variations in pH and “bio-available” metal concentrations result from associated variation in particle–scale geochemistry. Four sub-samples, ranging in pH from 2.6 to 5.4, were subjected to further characterization to elucidate micro-scale controls on metal mobility. With acidification, total Pb (ranging from 5 to 13 g kg⁻¹) was increasingly associated with Fe and S in plumbojarosite aggregates. For Zn, both total (0.4–6 g kg⁻¹) and labile fractions decreased with decreasing pH. Zinc was found to be primarily associated with the secondary Mn phases manjiroite and chalcophanite. The results suggest that progressive tailings acidification diminishes the overall lability of the total Pb and Zn pools.     

The Geochemistry of Supraglacial Streams of Canada Glacier,Taylor Valley (Antarctica), and their Evolution into Proglacial Waters

We have investigated the geochemistry of supraglacial streams on the Canada Glacier, Taylor Valley, Antarctica during the 2001–2002 austral summer. Canada Glacier supraglacial streams represent the link between primary precipitation (i.e. glacier snow) and proglacial Lake Hoare. Canada Glacier supraglacial stream geochemistry is intermediate between glacier snow and proglacial stream geochemistry with average concentrations of 49.1 μeq L⁻¹ Ca2+, 19.9 μeq L⁻¹ SO₄²⁻, and 34.3 μeq L⁻¹ HCO₃⁻. Predominant west to east winds lead to a redistribution of readily soluble salts onto the glacier surface, which is reflected in the geochemistry of the supraglacial streams. Western Canada Glacier supraglacial streams have average SO₄²⁻:HCO₃⁻ equivalent ratios of 1.0, while eastern supraglacial streams average 0.5, suggesting more sulfate salts reach and dissolve in the western supraglacial streams. A graph of HCO₃⁻ versus Ca2+ for western and eastern supraglacial streams had slopes of 0.87 and 0.72, respectively with R2 values of 0.84 and 0.83. Low concentrations of reactive silicate (> 10 μmol L⁻¹) in the supraglacial streams suggested that little to no silicate weathering occurred on the glacier surface with the exception of cryoconite holes (1000 μmol L⁻¹). Therefore, the major geochemical weathering process occurring in the supraglacial streams is believed to be calcite dissolution. Proglacial stream, Anderson Creek, contains higher concentrations of major ions than supraglacial streams containing 5 times the Ca²⁺ and 10 times the SO₄²⁻. Canada Glacier proglacial streams also contain higher concentrations (16.6–30.6 μeq L⁻¹) of reactive silicate than supraglacial streams. This suggests that the controls on glacier meltwater geochemistry switch from calcite and gypsum dissolution to both salt dissolution and silicate mineral weathering as the glacier meltwater evolves. Our chemical mass balance calculations indicate that of the total discharge into Lake Hoare, the final recipient of Canada Glacier meltwater, 81.9% is from direct glacier runoff and 19.1% is from proglacial Andersen Creek. Although during a typical, low melt ablation season Andersen Creek contributes over 40% of the water added to Lake Hoare, its overall chemical importance is diluted by the direct inputs from Canada Glacier during high flow years. Decadal warming events, such as the 2001–2002 austral summer produce supraglacial streams that are a major source of water to Lake Hoare.     

Do S-type granites commonly sample infracrustal sources? New results from an integrated O, U–Pb and Hf isotope study of zircon

In contrast to I-type granites, which commonly comprise infracrustal and supracrustal sources, S-type granites typically incorporate predominantly supracrustal sources. The initial aim of this study was to identify the sources of three Scottish Caledonian (~460 Ma) S-type granites (Kemnay, Cove and Nigg Bay) by conducting oxygen, U–Pb and Hf isotope analyses in zircon in order to characterise one potential end-member magma involved in the genesis of the voluminous late Caledonian (~430–400 Ma) I-type granites. Field, whole-rock geochemical and isotopic data are consistent with the generation of the S-type granites by melting their Dalradian Supergroup country rocks. While Hf isotope compositions of magmatic zircon, U–Pb data of inherited zircons, and high mean zircon δ¹⁸O values of 9.0 ± 2.7‰ (2SD) and 9.8 ± 2.0‰ for the Kemnay and Cove granites support this model, the Nigg Bay Granite contains zircons with much lower δ¹⁸O values (6.8 ± 2.1‰), similar to those found in Scottish I-type granites. This suggests that the Nigg Bay Granite contains low-δ¹⁸O material representing either altered supracrustal material, or more likely, an infracrustal source component with mantle-like δ¹⁸O. Mixing trends in plots of δ¹⁸O vs. εHf for S-type granite zircons indicate involvement of at least two sources in all three granites. This pilot study of Scottish Caledonian S-type granites demonstrates that, while field and whole-rock geochemical data are consistent with local melting of only supracrustal sources, the oxygen isotopic record stored in zircon reveals a much more complex petrogenetic evolution involving two or more magma sources.     

Variability in dissolved organic matter fluorescence and reduced sulfur concentration in coastal marine and estuarine environments

Fluorescence characterization of dissolved organic matter (DOM) and measurements of Cr-reducible sulfide (CRS) are presented for 72 coastal marine and estuarine water samples obtained from the USA and Canada. Each sample is identified according to source: terrigenous, autochthonous, wastewater or mixed. Fluorescence data are resolved into contributions from humic, fulvic, tyrosine and tryptophan-like fluorophores. Humic and fulvic-like fluorophores correlate well with dissolved organic C (DOC) (r² = 0.73 and 0.71, respectively) but tyrosine and tryptophan-like fluorophores show no correlation with DOC. Quality factors are identified by normalization of fluorescence contributions to DOC. Humic and fulvic components show no statistical differences between sources but the amino acid-like fluorescence quality factors show significant variations between source, with highest values for autochthonous sources (0.07 ± 0.01 arbitrary fluorescence units per mg of C) versus low values (0.015 ± 0.005) for terrigenous source waters. CRS concentrations are highly variable from 0.07 ± 0.01 to 7703 ± 98 nM and do no correlate with DOC except when terrigenous source waters (n = 13) are separated out from the total sample set (r² = 0.55). There is an open question in the literature; does DOC source matter in terms of protective effects towards metal toxicity? Here is shown that DOC molecular-level quality does vary and that this variation is mostly in terms of the contributions of amino acids to total fluorescence.     

Origin of post‐Minoan caves and volcaniclastic cave fill,Thera (Santorini), Greece

The Aegean island of Thera (Santorini) was covered by tephra from its cataclysmic Late Bronze Age (ca. 3600 yr B.P.) eruption. Vertical exposures of the eruptive sequence show secondary, nonvolcanic, circular (in cross section) features composed of stratified sediment. Many are inaccessible from the floors of modern quarries and appear to be caves filled with younger sediment, but show no connection to the land surface. A filled cave was found in the wall of a modern gully outside the modern quarries, and a filled cave was found in a terrace scarp, well above the modern gully. Natural (and probably rapid) incision by gullies into the thick tephra deposit left many locations with lateral access to tephra. Inhabitants from post‐Minoan to recent times excavated tephra for materials and buildings, and caves were subsequently filled by sporadic (possibly seasonal) flood events that deposited sediment. These gullies may have provided access for modern tephra removal that isolated the filled caves high on the modern quarry walls. © 2003 Wiley Periodicals, Inc.     

Holocene carbon storage and testate amoeba community structure in treed peatlands of the western Hudson Bay Lowlands margin,Canada

The Hudson Bay Lowlands (HBL) stores a significant proportion of the northern peatland carbon pool, and constraints on the factors controlling local-scale variation are needed to better predict soil carbon stocks. We investigated two treed peatland sites, a fen and a bog, to understand how local ecohydrological factors impacted long-term carbon storage. Ecohydrological conditions were reconstructed using quantitative water table depth reconstructions from testate amoebae (TA) and broad peat type classifications. We also linked these factors and carbon storage to changes in TA community structure through the investigation of morphological and functional traits. Both sites have high rates of peat vertical accretion during the warmer Middle Holocene. A shift to a drier, Sphagnum-dominated habitat after 7400 cal a bp at the bog site, however, led to lower apparent carbon accumulation rates (aCARs) than at the fen site. aCARs decreased with the transition to a cooler Late Holocene climate at both sites. Both sites have higher total carbon masses (kg m⁻²) than other more open and younger HBL localities, demonstrating the potential importance of treed peatlands in regional carbon storage. Shifts in the frequency of TA traits corresponded to changing ecohydrological conditions and provided insights into the role of TA in carbon storage.     

Thin section petrography of northern Lesser Antilles ceramics

Thin sections from 44 sherds representing eight prehistoric sites on four islands (Barbuda, Montserrat, Anguilla, St. Martin) in the northern Lesser Antilles (West Indies) were examined using a petrographic microscope. Point counting distinguished three temper associations: (1) exclusively volcanic,(2) volcanic and carbonate, and (3) volcanic, carbonate, and grog. Exclusively volcanic or dominantly volcanic (with low carbonate) temper associations occur in all Saladoid and many post-Saladoid sherds, with plagioclase feld-spar and volcanic rock fragments being most abundant. Thin sections with significant carbonate content or with grog were restricted to post-Saladoid sherds from Barbuda and to a lesser extent Anguilla. the presence of volcanic grains in sherds from the limestone islands of Barbuda and Anguilla indicates that volcanic islands in the region served as sources of pottery (or volcanic temper) for these two islands.