Variations in axial processes on the Mid-Atlantic Ridge: The median valley of the MARK area

Submersible observations and photogeology document dramatic variations in the distribution of young volcanic rocks, faulting, fissuring, and hydrothermal activity along an 80 km-long segment of the Mid-Atlantic Ridge south of the Kane Transform (MARK Area). These variations define two spreading cells separated by a cell boundary zone or a small-offset transform zone. The northern spreading cell is characterized by a median ‘neovolcanic’ ridge which runs down the axis of the median valley floor for 40 km. This edifice is as much as 4 km wide and 600 m high and is composed of very lightly sedimented basalts inferred to be < 5000 years old. It is the largest single volcanic constructional feature discovered to date on the Mid-Atlantic Ridge. The active Snake Pit hydrothermal vent field is on the crest of this ridge and implies the presence of a magma chamber in the northern spreading cell. In contrast, the southern cell is characterized by small, individual volcanos similar in size to the central volcanos in the FAMOUS area. Two of the volcanos that were sampled appear to be composed of dominantly glassy basaltic rocks with very light sediment cover; whereas, other volcanos in this region appear to be older features. The boundary zone between the two spreading cells is intensely faulted and lacks young volcanic rocks. This area may also contain a small-offset ( < 8 km) transform zone. Magmatism in the northern cell has been episodic and tens of thousands of years have lapsed since the last major magmatic event there. In the southern cell, a more continuous style of volcanic accretion appears to be operative. The style of spreading in the southern cell may be much more typical for the Mid-Atlantic Ridge than that of the northern cell because the latter is adjacent to the 150 km-offset Kane Transform that may act as a thermal sink along the MAR. Such large transforms are not common on the MAR, therefore, lithosphere produced in a spreading cell influenced by a large transform may also be somewhat atypical.     

Investigating the response of Cladocera to a major saltwater intrusion event in an Arctic lake from the outer Mackenzie Delta (NT, Canada)

An increase in the frequency and intensity of marine storm surges is a predicted consequence of climate warming, and therefore it is important to better understand the biological responses to such events in coastal regions. In late September 1999, a major storm surge resulted in a saltwater intrusion event over a large area of the Mackenzie Delta (NT, Canada) front, causing rapid salinization of lakes on the alluvial plain. Due to a lack of long-term ecological monitoring data in the region, the impacts that the saltwater intrusion event had on the biota of affected lakes were unknown. We used high-resolution paleolimnological approaches to reconstruct past assemblage changes in Cladocera from impacted Lake DZO-29 (unofficial name) in order to determine how different cladoceran species responded to a major increase in lake salinity following the 1999 storm surge. Camptocercus were extirpated from the lake following the saltwater intrusion and have not recovered. We also observed an initial decrease in Alona relative abundance following the marine flooding, likely reflecting a loss of A. quadrangularis, A. barbulata, and A. costata from the lake. A. circumfimbriata, Chydorus biovatus, C. brevilabris, and Bosmina spp. were abundant both before and after the saltwater intrusion, and Paralona pigra was present following the storm surge, but not prior to it. The most notable shift in Cladocera in the recent sedimentary record, however, occurred much earlier, with an increase in pelagic Bosmina taxa and a subsequent decrease in the benthic/littoral taxa Chydorus and Camptocercus, an assemblage shift that is consistent with a response to climate warming in this region, and strongly correlated to other changes in the lake inferred to be as a result of regional warming.     

Application of functional data analysis to investigate seasonal progression with interannual variability in plankton abundance in the Bay of Fundy,Canada

The statistical technique of functional data analysis (FDA) is applied to a time series analysis of plankton monitoring data. The analysis is focused on revealing patterns in the seasonal cycle to assess interannual variability of several different taxonomic groups of plankton. Cell concentrations of diatom, dinoflagellate and zooplankton abundances from the Bay of Fundy, Canada provide the observations for analysis. FDA was performed on the log-transformed abundance data as a new approach for treating such types of sparse and noisy data. Differences in the seasonal progression were seen, with peak numbers, timings and abundance levels varying for the three groups as determined by curve registration and higher order derivatives using the objectively fit FDA curves. Nonmetric multidimensional scaling was used to capture seasonal variation among years. These results were further assessed in terms of dominant species and the relationships between groups for different seasons and years. It is anticipated that the easy to use, general and flexible technique of FDA could be applied to a wide variety of marine ecological data that are characterized by missing values and non-Gaussian distributions.     

Correction to: The contributions of fronts,lows and thunderstorms to southern Australian rainfall

Climate Dynamics - In the original published version of the paper, the figures reported in Sect.&nbsp;4 relating the proportion of rainfall in southern Australia that is due to each of the...     

Occurrence and distribution of polycyclic aromatic hydrocarbons in surface sediments of San Diego Bay marinas

Polycyclic aromatic hydrocarbons (PAHs) have garnered much attention due to their bioaccumulation, carcinogenic properties, and persistence in the environment. Investigation of the spatial distribution, composition, and sources of PAHs in sediments of three recreational marinas in San Diego Bay, California revealed significant differences among marinas, with concentrations in one site exceeding 16,000 ng g^? 1. ‘Hotspots’ of PAH concentration suggest an association with stormwater outfalls draining into the basins. High-molecular weight PAHs (4–6 rings) were dominant (> 86%); the average percentage of potentially carcinogenic PAHs was high in all sites (61.4–70%) but ecotoxicological risks varied among marinas. Highly toxic benzo(a)pyrene (BaP) was the main contributor (> 90%) to the total toxic equivalent quantity (TEQ) in marinas. PAHs in San Diego Bay marina sediments appear to be derived largely from pyrogenic sources, potentially from combustion products that reach the basins by aerial deposition and stormwater drainage from nearby streets and parking lots.     

Deriving snow‐cover depletion curves for different spatial scales from remote sensing and snow telemetry data

During the melting of a snowpack, snow water equivalent (SWE) can be correlated to snow‐covered area (SCA) once snow‐free areas appear, which is when SCA begins to decrease below 100%. This amount of SWE is called the threshold SWE. Daily SWE data from snow telemetry stations were related to SCA derived from moderate‐resolution imaging spectroradiometer images to produce snow‐cover depletion curves. The snow depletion curves were created for an 80 000 km² domain across southern Wyoming and northern Colorado encompassing 54 snow telemetry stations. Eight yearly snow depletion curves were compared, and it is shown that the slope of each is a function of the amount of snow received. Snow‐cover depletion curves were also derived for all the individual stations, for which the threshold SWE could be estimated from peak SWE and the topography around each station. A station's peak SWE was much more important than the main topographic variables that included location, elevation, slope, and modelled clear sky solar radiation. The threshold SWE mostly illustrated inter‐annual consistency. Copyright © 2015 John Wiley & Sons, Ltd.     

Shallow seismicity, triggered seismicity, and ambient noise tomography at the long-dormant Uturuncu Volcano, Bolivia

Using a network of 15 seismometers around the inflating Uturuncu Volcano from April 2009 to 2010, we find an average rate of about three local volcano-tectonic earthquakes per day, and swarms of 5–60 events a few times per month with local magnitudes ranging from −1.2 to 3.7. The earthquake depths are near sea level, more than 10 km above the geodetically inferred inflation source and the Altiplano Puna Magma Body. The Mw 8.8 Maule earthquake on 27 February 2010 triggered hundreds of earthquakes at Uturuncu with the onset of the Love and Rayleigh waves and again with the passage of the X2/X3 overtone phases of Rayleigh waves. This is one of the first incidences in which triggering has been observed from multiple surface wave trains. The earthquakes are oriented NW–SE similar to the regional faults and lineaments. The b value of the catalog is 0.49, consistent with a tectonic origin of the earthquakes. We perform ambient noise tomography using Love wave cross-correlations to image a low-velocity zone at 1.9 to 3.9 km depth below the surface centered slightly north of the summit. The low velocities are perhaps related to the hydrothermal system and the low-velocity zone is spatially correlated with earthquake locations. The earthquake rate appears to vary with time—a seismic deployment from 1996 to 1997 reveals 1–5 earthquakes per day, whereas 60 events/day were seen during 5 days using one seismometer in 2003. However, differences in analysis methods and magnitudes of completeness do not allow direct comparison of these seismicity rates. The rate of seismic activity at Uturuncu is higher than at other well-monitored inflating volcanoes during periods of repose. The frequent swarms and triggered earthquakes suggest the hydrothermal system is metastable.     

Superficial deep-water sediments of the Eastern Marmara Basin

Superficial sediments (top Im) of the Eastern Mediterranean Basin, Sea of Marmara, Turkey accumulated rapidly (0.087 ± 0.012 g/cm² · y) by hemipelagic sedimentation with only limited amounts of gravity flow or bottom current action under low oxygenated but not anoxic conditions. They have restricted faunas, relatively higher organic carbon (1–1.8%) and lower calcium carbonate (14–20%) contents than other Eastern Mediterranean Basin sediments. Sedimentation shows little change over the last millenium except for an increase in Cu, Zn, Pb, Cr, and P over the last few centuries. The increase was most likely caused by increased metallurgical activities since the eighteenth century but are not at sufficient levels for the area to be regarded as polluted.     

Infiltration von Flusswasser in Dünengebieten

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