Volcanic activity in the Azores. Report for 1959–1964

During the period 1959 to 1964 recorded volcanic activity in the Azores islands (Atlantic Ocean) was manifested by fumarolic fields in S. Miguel, Terceira, Graciosa, Pico and Faial and by two submarine eruptions off Pico and S. Jorge. Fumarolic activity increased in the Faial Capelinhos vent (in eruption 1957–58) after December 1963; it is concluded that the phenomenon is related to the 1963 and 1964 eruptions in the S. Jorge Channel. During February 1964 an important seismic swarm of more than 500 earthquakes, with volcanic tremor, occurred in S. Jorge.

     

Benthic metabolism and the fate of dissolved inorganic nitrogen in intertidal sediments

We determined patterns of benthic metabolism and examined the relative importance of denitrification (DNF) and dissimilatory nitrate reduction to ammonium (DNRA) as sinks for nitrate (NO₃⁻) in intertidal sediments in the presence and absence of benthic microalgal (BMA) activity. By influencing the activity of BMA, light regulated the metabolic status of the sediments, and, in turn, exerted strong control on sediment nitrogen dynamics and the fate of inorganic nitrogen. A pulsed addition of ¹⁵N-labeled NO₃⁻ tracked the effect and fate of dissolved inorganic nitrogen (DIN) in the system. Under illuminated conditions, BMA communities influenced benthic fluxes directly, via DIN uptake, and indirectly, by altering the oxygen penetration depth. Under dark hypoxic and anoxic conditions, the fate of water column NO₃⁻ was determined largely by three competing dissimilatory reductive processes; DNF, DNRA, and, on one occasion, anaerobic ammonium oxidation (anammox). Mass balance of the added ¹⁵N tracer illustrated that DNF accounted for a maximum of 48.2% of the ¹⁵NO₃⁻ reduced while DNRA (a minimum of 11.4%) and anammox (a minimum of 2.2%) accounted for much less. A slurry experiment was employed to further examine the partitioning between DNF and DNRA. High sulfide concentrations negatively impacted rates of both processes, while high DOC:NO₃⁻ ratios favored DNRA over DNF.     

Cadmium and phosphate in coastal Antarctic seawater: Implications for Southern Ocean nutrient cycling

Cadmium is a biologically important trace metal that co-varies with phosphate (PO₄³⁻ or Dissolved Inorganic Phosphate, DIP) in seawater. However, the exact nature of Cd uptake mechanisms and the relationship with phosphate and other nutrients in global oceans remain elusive. Here, we present a time series study of Cd and PO₄³⁻ from coastal Antarctic seawater, showing that Cd co-varies with macronutrients during times of high biological activity even under nutrient and trace metal replete conditions. Our data imply that Cd/PO₄³⁻ in coastal surface Antarctic seawater is higher than open ocean areas. Furthermore, the sinking of some proportion of this high Cd/PO₄³⁻ water into Antarctic Bottom Water, followed by mixing into Circumpolar Deep Water, impacts Southern Ocean preformed nutrient and trace metal composition. A simple model of endmember water mass mixing with a particle fractionation of Cd/P (α_Cd–P) determined by the local environment can be used to account for the Cd/PO₄³⁻ relationship in different parts of the ocean. The high Cd/PO₄³⁻ of the coastal water is a consequence of two factors: the high input from terrestrial and continental shelf sediments and changes in biological fractionation with respect to P during uptake of Cd in regions of high Fe and Zn. This implies that the Cd/PO₄³⁻ ratio of the Southern Ocean will vary on glacial–interglacial timescales as the proportion of deep water originating on the continental shelves of the Weddell Sea is reduced during glaciations because the ice shelf is pinned at the edge of the continental shelf. There could also be variations in biological fractionation of Cd/P in the surface waters of the Southern Ocean on these timescales as a result of changes in atmospheric inputs of trace metals. Further variations in the relationship between Cd and PO₄³⁻ in seawater arise from changes in population structure and community requirements for macro- and micronutrients.     

The impact of artificially impounded, residential headwater lakes on downstream water temperature

In the southeastern United States, which has very few natural lakes, developers often impound headwater streams to create esthetic lakes as focal points in the residential landscape. Given the prevalence and increasing abundance of these water features, it is important to assess and quantify the spatial and temporal impacts these lakes have on headwater stream temperatures. Any changes in the downstream thermal regime may influence not only the biological functioning of a stream, but also important physical and chemical water quality characteristics. The purpose of this study was to quantify the magnitude and extent of the downstream temperature disturbance associated with three different, artificially impounded, residential headwater lakes in Greenville, South Carolina. Water temperature loggers were installed upstream, in-lake, and downstream of three surface-release residential lakes and monitored at 5-min intervals from July 2007 to April 2008. In July/August 2007, longitudinal stream temperature profiles were measured at 50-m intervals both upstream and downstream of each lake in order to assess the spatial extent of the lake’s temperature disturbance. The lakes altered the downstream thermal regime at all three sites, increasing temperature by as much as 8.4 °C and decreasing diurnal variability by as much as 3.9 °C within the period of record. Furthermore, the longitudinal profiles of all three stream-lake systems showed no significant signs of downstream recovery to the upstream temperatures. The ecological effects of such temperature disturbances on stream biotic communities were not quantified in this study, but are likely significant. This study considered lakes only in South Carolina, but the observed changes to the downstream thermal regime are presumably similar for impounded residential headwater lakes across the US Southeast given the similar climate regime and comparable design and construction of these lakes across the region.     

Seismic characterization of the fall 2007 eruptive sequence at Bezymianny Volcano,Russia

We examine an eruptive sequence in late 2007 at Bezymianny Volcano to characterize the magmatic plumbing system and eruption-related seismicity. Earthquake locations reveal seismicity below and offset to the north of the volcano along a tectonic fault. Based on historical seismicity, the magma chamber is postulated to have a top at about 6 km depth. Minor dome explosions, large sub-plinian eruptions and dome collapses are analyzed using an automated event classification scheme. Low-frequency tremor, interpreted as gas escape, and low-frequency earthquakes are a dominant proportion of the energy released. We also examine multiplet earthquakes whose behavior during the study period changed significantly and systematically before the largest eruption, demonstrating the potential of tracking multiplets to assess changing conditions with the conduit.     

Accuracy of OPUS solutions for 1- to 4-h observing sessions

We processed 30 consecutive days of Global Positioning System (GPS) data using the On-line Positioning Users Service (OPUS) provided by the National Geodetic Survey (NGS) to determine how the accuracy of derived three-dimensional positional coordinates depends on the length of the observing session T, for T ranging from 1 h to 4 h. We selected five Continuously Operating Reference Stations (CORS), distributed widely across the USA, and processed the GPS data for each with corresponding data from three of its nearby CORS. Our results support the current OPUS policy that recommends using a minimum of 2 h of static GPS data. In particular, 2 h of data yielded a root mean square error of 0.8, 2.1, and 3.4 cm in the north, east, and up components of the derived positional coordinates, respectively. Results drastically improve for solutions containing 3 h or more of GPS data.     

The AUSTRAL VLBI observing program

The AUSTRAL observing program was started in 2011, performing geodetic and astrometric very long baseline interferometry (VLBI) sessions using the new Australian AuScope VLBI antennas at Hobart, Katherine, and Yarragadee, with contribution from the Warkworth (New Zealand) 12 m and Hartebeesthoek (South Africa) 15 m antennas to make a southern hemisphere array of telescopes with similar design and capability. Designed in the style of the next-generation VLBI system, these small and fast antennas allow for a new way of observing, comprising higher data rates and more observations than the standard observing sessions coordinated by the International VLBI Service for Geodesy and Astrometry (IVS). In this contribution, the continuous development of the AUSTRAL sessions is described, leading to an improvement of the results in terms of baseline length repeatabilities by a factor of two since the start of this program. The focus is on the scheduling strategy and increased number of observations, aspects of automated operation, and data logistics, as well as results of the 151 AUSTRAL sessions performed so far. The high number of the AUSTRAL sessions makes them an important contributor to VLBI end-products, such as the terrestrial and celestial reference frames and Earth orientation parameters. We compare AUSTRAL results with other IVS sessions and discuss their suitability for the determination of baselines, station coordinates, source coordinates, and Earth orientation parameters.