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Reef-builders with a sense of harmony

Cold-water corals of the species Lophelia pertusa are able to fuse skeletons of genetically distinct individuals. Scientists have made the first-ever discovery of branches of different colors that had flawlessly merged. The ability to fuse supports the reef stability and thus contributes to the success of corals as reef-builders of the deep sea.
 
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Posted by on October 30, 2014 in Blog

 

Influence of late Pleistocene glaciations on the hydrogeology of the continental shelf offshore Massachusetts, USA

Abstract

Multiple late Pleistocene glaciations that extended onto the continental shelf offshore Massachusetts, USA may have emplaced as much as 100 km3 of freshwater (salinity less than 5 ppt) in continental shelf sediments. To estimate the volume and extent of offshore freshwater, we developed a three-dimensional, variable-density model that couples fluid flow and heat and solute transport for the continental shelf offshore Massachusetts. The stratigraphy for our model is based on high-resolution, multi-channel seismic data. The model incorporates the last 3 Ma of climate history by prescribing boundary conditions of sea-level change and ice sheet extent and thickness. We incorporate new estimates of the maximum extent of a late Pleistocene ice sheet to near the shelf-slope break. Model results indicate that this late Pleistocene ice sheet was responsible for much of the emplaced freshwater. We predict that the current freshwater distribution may reach depths of up to 500 m below sea level and up to 30 km beyond Martha's Vineyard. The freshwater distribution is strongly dependent on the three-dimensional stratigraphy and ice-sheet history. Our predictions improve our understanding of the distribution of offshore freshwater, a potential non-renewable resource for coastal communities along recently glaciated margins.

 
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Posted by on October 30, 2014 in Blog

 

Imaging of CO2 bubble plumes above an erupting submarine volcano, NW Rota-1, Mariana Arc

Abstract

NW Rota-1 is a submarine volcano in the Mariana volcanic arc located ~100 km north of Guam. Underwater explosive eruptions driven by magmatic gases were first witnessed there in 2004 and continued until at least 2010. During a March 2010 expedition, visual observations documented continuous but variable eruptive activity at multiple vents at ~560 m depth. Some vents released CO2 bubbles passively and continuously, while others released CO2 during stronger but intermittent explosive bursts. Plumes of CO2 bubbles in the water column over the volcano were imaged by an EM122 (12 kHz) multibeam sonar system. Throughout the 2010 expedition numerous passes were made over the eruptive vents with the ship to document the temporal variability of the bubble plumes and relate them to the eruptive activity on the seafloor, as recorded by an in situ hydrophone and visual observations. Analysis of the EM122 mid-water dataset shows: (1) bubble plumes were present on every pass over the summit and they rose 200-400 m above the vents but dissolved before they reached the ocean surface, (2) bubble plume deflection direction and distance correlate well with ocean current direction and velocity determined from the ship's acoustic doppler current profiler, (3) bubble plume heights and volumes were variable over time and correlate with eruptive intensity as measured by the in situ hydrophone. This study shows that mid-water multibeam-sonar data can be used to characterize the level of eruptive activity and its temporal variability at a shallow submarine volcano with robust CO2 output.

 
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Posted by on October 30, 2014 in Blog

 

Understanding which parameters control shallow ascent of silicic effusive magma

Abstract

The estimation of the magma ascent rate is key to predicting volcanic activity and relies on the understanding of how strongly the ascent rate is controlled by different magmatic parameters. Linking potential changes of such parameters to monitoring data is an essential step to be able to use these data as a predictive tool. We present the results of a suite of conduit flow models Soufrière that assess the influence of individual model parameters such as the magmatic water content, temperature or bulk magma composition on the magma flow in the conduit during an extrusive dome eruption. By systematically varying these parameters we assess their relative importance to changes in ascent rate. We show that variability in the rate of low frequency seismicity, assumed to correlate directly with the rate of magma movement, can be used as an indicator for changes in ascent rate and, therefore, eruptive activity. The results indicate that conduit diameter and excess pressure in the magma chamber are amongst the dominant controlling variables, but the single most important parameter is the volatile content (assumed as only water). Modelling this parameter in the range of reported values causes changes in the calculated ascent velocities of up to 800%.

 
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Posted by on October 30, 2014 in Blog

 

The flow structure of jets from transient sources and implications for modeling short-duration explosive volcanic eruptions

Abstract

We used laboratory experiments to examine the rise process in neutrally-buoyant jets that resulted from an unsteady supply of momentum, a condition that defines plumes from discrete Vulcanian- and Strombolian-style eruptions. We simultaneously measured the analog-jet discharge rate (the supply rate of momentum) and the analog-jet internal velocity distribution (a consequence of momentum transport and dilution). Then, we examined the changes in the analog-jet velocity distribution over time to assess the impact of the supply-rate variations on the momentum-driven rise dynamics. We found that the analogue jet velocity distribution changes significantly and quickly as the supply rate varied, such that the whole-field distribution at any instant differed considerably from the time-average. We also found that entrainment varied in space and over time with instantaneous entrainment coefficient values ranging from 0 to 0.93 in an individual unsteady jet. Consequently, we conclude that supply rate variations exert first-order control over jet dynamics, and therefore cannot be neglected in models without compromising their capability to predict large-scale eruption behavior. These findings emphasize the fundamental differences between unsteady and steady jet dynamics, and show clearly that: (i) variations in source momentum flux directly control the dynamics of the resulting flow; and (ii) impulsive flows driven by sources of varying flux cannot reasonably be approximated by quasi-steady flow models. New modeling approaches capable of describing the time-dependent properties of transient volcanic eruption plumes are needed before their trajectory, dilution and stability can be reliably computed for hazards management.

 
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Posted by on October 30, 2014 in Blog

 

Understanding a submarine eruption through time series hydrothermal plume sampling of dissolved and particulate constituents: West Mata, 2008–2012

Abstract

Four cruises between 2008 and 2012 monitored the continuing eruption of West Mata volcano in the NE Lau Basin as it produced plumes of chemically altered water above its summit. Although large enrichments in 3He, CO2, Fe, and Mn were observed in the plumes, the most notable enrichment was that of H2, which reached concentrations as high as 14843 nM. Strongly enriched H2 concentrations in the water column result from reactions between seawater or magmatic water and extremely hot rocks. In 2008, the observation of elevated H2 concentrations in the water column above West Mata pointed to vigorous ongoing eruptions at the volcano's summit. The eruption was confirmed by visual observations made by the ROV Jason 2 in 2009 and demonstrated that H2 measurements are a vital instrument to detect ongoing volcanic eruptions at the seafloor. Elevated H2 in 2010 showed that the eruption was ongoing, although at a reduced level given a maximum H2 concentration of 4410 nM. In 2012, H2 levels in the water column declined significantly, to a maximum of only 7 nM, consistent with visual observations from the Quest-4000 ROV that found no evidence of an ongoing volcanic eruption. Methane behaved independently of other measured gases and its concentrations in the hydrothermal plume were very low. We attribute its minimal enrichments to a mixture of mantle carbon reduced to CH4 and biological CH4 from diffuse flow sites. This study demonstrates that ongoing submarine volcanic eruptions are characterized by high dissolved H2 concentrations present in the overlying water column.

 
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Posted by on October 30, 2014 in Blog

 

Anthropophile elements in river sediments: Overview from the Seine River, France

Abstract

In contrast to larger river systems that drain relatively pristine basins, little is known about the sediment geochemistry of rivers impacted by intense human activities. In this paper, we present a systematic investigation of the anthropogenic overprints on element geochemistry in sediments of the human-impacted Seine River, France. Most elements are fractionated by grain size, as shown by the comparison between suspended particulate matter (SPM) and riverbank deposits (RBD). The RBD are particularly coarse and enriched in carbonates and heavy minerals and thus in elements such as Ba, Ca, Cr, Hf, Mg, Na, REEs, Sr, Ti, Th, and Zr. Although the enrichment/depletion pattern of some elements (e.g. K, REEs, Zr, etc.) can largely be explained by a binary mixture between two sources, other elements such as Ag, Bi, Cr, Cd, Co, Cu, Fe, Mo, Ni, Pb, Sb, Sn, W and Zn in SPM in Paris show that a third end-member having anthropogenic characteristics is needed to account for their enrichment at low water stage. These “anthropophile” elements, with high enrichment factors (EF) relative to the upper continental crust (UCC), display a progressive enrichment downstream and different geochemical behaviors with respect to the hydrodynamic conditions (e.g. grain size) compared to elements having mainly a natural origin. Our findings emphasize the need for systematic studies of these anthropophile elements in other human-impacted rivers using geochemical normalization techniques, and stress the importance of studying the chemical variability associated with hydrodynamic conditions when characterizing riverine element geochemistry and assessing their flux to the ocean.

 
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Posted by on October 30, 2014 in Blog

 

Urban seismic network detects human sounds

When listening to the Earth, what clues can seismic data reveal about the impact of urban life? Although naturally occurring vibrations have proven useful to seismologists, until now the vibrations caused by humans haven’t been explored in any real depth. Researchers have described their efforts to tap into an urban seismic network to monitor the traffic of trains, planes, automobiles and other modes of human transport.
 
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Posted by on October 30, 2014 in Blog

 

Plump turtles swim better: First models of swimming animals

Bigger is better, if you're a leatherback sea turtle. For the first time, researchers have measured the forces that act on a swimming animal and the energy the animal must expend to move through the water.
 
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Posted by on October 30, 2014 in Blog

 

Ammonium source in open ocean tracked by researchers

To understand the extent to which human activities are polluting Earth's atmosphere and oceans, it's important to distinguish human-made pollutants from compounds that occur naturally. A new study finds that deposition of ammonium, a source of nitrogen pollution, over the open ocean comes mostly from natural marine sources, and not from human activity.
 
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Posted by on October 29, 2014 in Blog