A year‐long acoustic survey for critically endangered North Atlantic right whales was conducted at two sites on the central and western Scotian Shelf. Autonomous hydrophones recorded sound continuously from July 2004 to August 2005. Right whale contact calls (upcalls) were identified using automatic recognition software, and the resulting detections were checked manually. Substantial numbers of hours with upcalls were observed at both sites, with approximately four times as many hours with calls at the western site as the central one. Calls occurred mainly from August through October, with the earliest calls in late June and the latest at the end of December at both sites. In addition to this seasonal trend, there was a significant diel pattern in calling at the central site but not at the more westerly site. Results are analyzed in light of feeding ecology and broad‐scale movements of right whales.

We present multiple lines of evidence for years to decade-long changes in the location and character of volcanic activity at West Mata seamount in the NE Lau basin over a 16 year period, and a hiatus in summit eruptions from early 2011 to at least September 2012. Boninite lava and pyroclasts were observed erupting from its summit in 2009, and hydroacoustic data from a succession of hydrophones moored nearby show near-continuous eruptive activity from January 2009 to early 2011. Successive differencing of seven multibeam bathymetric surveys of the volcano made in the 1996-2012 period reveals a pattern of extended constructional volcanism on the summit and northwest flank punctuated by eruptions along the volcano's WSW rift zone (WSWRZ). Away from the summit, the volumetrically largest eruption during the observational period occurred between May 2010 and November 2011 at 2920 m depth near the base of the WSWRZ. The (nearly) equally long ENE rift zone did not experience any volcanic activity during the 1996-2012 period. The cessation of summit volcanism recorded on the moored hydrophone was accompanied or followed by the formation of a small summit crater and a landslide on the eastern flank. Water column sensors, analysis of gas samples in the overlying hydrothermal plume and dives with a remotely operated vehicle in September 2012 confirmed that the summit eruption had ceased. Based on the historical eruption rates calculated using the bathymetric differencing technique, the volcano could be as young as several thousand years.

Volcanoes at spreading centres on land often exhibit seismicity and ground inflation months to years before an eruption, caused by a gradual influx of magma to the source reservoir [1][2][3][4] . Deflation and seismicity can occur on time scales of hours to days, and result from the injection of magma into adjacent rift zones [5][6][7][8] . Volcanoes at submarine rift zones, such as Axial Seamount in the northeast Pacific Ocean, have exhibited similar behaviour [9][10][11][12] , but a direct link between seismicity, seafloor deformation and magma intrusion has never been demonstrated. Here we present recordings from ocean-bottom hydrophones and an established array of bottom-pressure recorders that reveal patterns of both microearthquakes and seafloor deformation at Axial Seamount on the Juan de Fuca Ridge, before it erupted in April 2011. Our observations show that the rate of seismicity increased steadily during a period of several years, leading up to an intrusion and eruption of magma that began on 6 April 2011. We also detected a sudden increase in seismo-acoustic energy about 2.6 h before the eruption began. Our data indicate that access to real-time seismic data, projected to be available in the near future, might facilitate short-term forecasting and provide sufficient leadtime to prepare in situ instrumentation before future intrusion and eruption events.

NW Rota-1 is a submarine volcano in the Mariana volcanic arc that is notable as the site where underwater explosive eruptions were fi rst witnessed in A.D. 2004. After years of continuous low-level eruptive activity, a major landslide occurred at NW Rota-1 in August 2009, triggered by an unusually large eruption that produced 10 times the acoustic energy of the background level of activity. An anomalous earthquake swarm preceded the eruption, suggesting that the sequence started with a magmatic intrusion and associated faulting beneath the volcano. We quantify the size and extent of the landslide using bathymetric resurveys and interpret the timing of events using data from an in situ hydrophone. This is the fi rst instrumental documentation of an earthquake-eruption-landslide sequence at a submarine volcano, and illustrates the close interaction between magmatic activity and mass wasting events in the growth of undersea arc volcanoes.

The creation of ocean crust by rapid injection of magma at midocean ridges can lead to eruptions of lava onto the seafl oor and release of "event plumes," which are huge volumes of anomalously warm water enriched in reduced chemicals that rise up to 1 km above the seafl oor. Here, we use seismic data to show that seafl oor eruptions and the release of hydrothermal event plumes correspond to diking episodes with high injection velocities and rapid onset of magma emplacement within the rift zone. These attributes result from high excess magma pressure at the dike source, likely due to a new infl ux of melt from the mantle. These dynamic magmatic conditions can be detected remotely and may predict the likelihood of event plume release during future seafl oor spreading events.

The recent volcanic history of Axial Seamount: Geophysical insights into past eruption dynamics with an eye toward enhanced observations of future eruptions.

[1] An array of moored hydrophones was used to monitor the spatiotemporal distribution of small-to moderate-sized earthquakes and ice-generated sounds within the Bransfield Strait, Antarctica. During a 2 year period, a total of 3900 earthquakes, 5925 icequakes and numerous ice tremor events were located throughout the region. The seismic activity included eight space-time earthquake clusters, positioned along the central neovolcanic rift zone of the young Bransfield back-arc basin. These sequences of small magnitude earthquakes, or swarms, suggest ongoing magmatic activity that becomes localized along isolated volcanic features and fissure-like ridges in the southwest portion of the basin. A total of 122 earthquakes were located along the South Shetland trench, indicating continued deformation and possibly ongoing subduction along this margin. The large number of icequakes observed show a temporal pattern related to seasonal freeze-thaw cycles and a spatial distribution consistent with channeling of sea ice along submarine canyons from glacier fronts. Several harmonic tremor episodes were sourced from a large ($30 km 2 ) iceberg that entered northeast portion of the basin. The spectral character of these signals suggests they were produced by either resonance of a small chamber of fluid within the iceberg, or more likely, due to periodicity of discrete stick-slip events caused by contact of the moving iceberg with the seafloor. These pressure waves appear to have been excited by abrasion of the iceberg along the seafloor as it passed Clarence and Elephant Islands.

International audienceAutonomous hydrophones arrays are an excellent tool for monitoring mid-ocean ridge seismic activity. The major advantage of using arrays of autonomous hydrophones for recording deep-ocean ridge earthquakes is its low magnitude detection thresholds achievable using hydroacoustic techniques. Regional analysis of the detection thresholds of the different autonomous hydrophones arrays deployed along the Mid-Atlantic Ridge reveals the strong influence of the detection threshold in the number of recorded events and it must be taken into account in any further analysis. In this study, the analysis of both autonomous hydrophones and teleseismically detected Mid-Atlantic Ridge seismicity reveals that the background seismicity from the relatively short recording periods of the autonomous hydrophones mimic the results of the much longer teleseismic recording. It also reveals that seismicity generally cluster at both the segment scale and on Mantle Bouguer Anomaly maxima. The big majority of these clusters seem to be related to dyke intrusions and propagation along the Mid-Atlantic Ridge. These dyke intrusions interact with the mainshock-aftershock sequences. The seismic sequences mainshock-aftershock analysis reveals that the strength of the faults is highly influenced by the mode, or style, of faulting. Detachment faults, which are ubiquitous along the Mid-Atlantic Ridge, can produce more prolific shorter duration seismic sequences revealing faster and reduced strain releases in comparison to higher angle normal faults. This reduced strain release is most likely to occur due to the presence of higher levels of serpentinization on detachment faults. Higher levels of serpentenisation can also promote an aseismic transient slip on the mainshock-aftershock sequences