Previous studies have shown decreasing oxygen concentration (O2) in subsurface waters of the continental slope from California to Canada since about 1980. With longer time series we show that from southern California to northern Canada increasing O2 preceded these decreases from 1950 to about 1980. Because there has been no clear trend since 1950, we cannot yet conclude that anthropogenic climate change is the cause of these decreasing trends after 1980. These findings are based mainly on O2 on the 26.7 potential density (σθ) surface in the region north of 30°N and east of 170°W, covering both the continental margin and deep-sea regions. On the continental slope, O2 increased at most locations by 10 to 20 µmol kg−1 to about 1980, followed by declines of similar magnitude in recent years. Changes in O2 were associated with changes in temperature of the opposite sign south of 37°N, but correlation of temperature and O2 is irregular in more northerly locations. At all locations, temperature-related solubility change was a minor cause of these O2 trends. In deep-sea waters, O2 decreased with time with a more rapid decrease from about 1995 to about 2003. At Ocean Station P (OSP; 50°N, 145°W), which has the longest uninterrupted record of observations, significant linear trends of −0.4 to −0.5 µmol kg−1 y−1 were found on the 26.5, 26.7, and 26.9 σθ surfaces. In addition, a significant sinusoidal oscillation of period 18.61 years and amplitude of 18 µmol kg−1 was found on the 26.9 σθ surface at OSP and a station 400 km to the east, which fits reasonably well with the lunar nodal cycle. The phase of this oscillation was identical at both locations. Clear evidence of similar variability did not emerge at other open-ocean locations or along the continental slope.
A combination of careful harmonic analysis and high-resolution numerical modelling of tides in altimeter data from TOPEX/Poseidon and ERS-2 satellites allows detailed calculation of seasonal and interannual variability of sea level in coastal areas of the north-east Pacific Ocean. These calculations show large changes in sea level in marginal seas during the 1997–8 El Niño and La Niña events, as well as providing information on the origin and life cycle of large anticyclonic eddies, observed to be generated off the west coast of Canada.
A three-dimensional (3D) seismic reflection survey was carried out during the SISMOMAR 2005 experiment covering an area of 18x3.8 km, which includes the Lucky Strike volcano and associated hydrothermal vent sites, part of the graben on top of the volcano, and extends out to the median valley bounding faults. The survey consisted of 39 lines shot at 100 m spacing using a 4.5 km-long streamer resulting in a sixty-fold coverage and 6.25 m CDP spacing. We present here the resulting 3D time migrated volume that shows a bright reflector at about 3 km depth beneath the volcano, which is interpreted as the roof of a magma chamber, along with the base of layer 2A. We were also able to image faults on the volcano and bounding the median valley, some of which penetrate down to the vicinity of the magma chamber. We also provide the 3D geometry of the magma chamber roof and base of layer 2A, converted to depth using the velocities from the 3D refraction survey (Seher et al., same session), and a highresolution seafloor bathymetric map derived from the picks of the seafloor arrival.
Using multiple lines of evidence, we demonstrate that volcanic ash deposition in August 2008 initiated one of the largest phytoplankton blooms observed in the subarctic North Pacific. Unusually widespread transport from a volcanic eruption in the Aleutian Islands, Alaska deposited ash over much of the subarctic NE Pacific, followed by large increases in satellite chlorophyll. Surface ocean pCO 2 , pH, and fluorescence reveal that the bloom started a few days after ashfall. Ship‐based measurements showed increased dominance by diatoms. This evidence points toward fertilization of this normally iron‐limited region by ash, a relatively new mechanism proposed for iron supply to the ocean. The observations do not support other possible mechanisms. Extrapolation of the pCO 2 data to the area of the bloom suggests a modest ∼0.01 Pg carbon export from this event, implying that even large‐scale iron fertilization at an optimum time of year is not very efficient at sequestering atmospheric CO 2 .
Abstract An extensive set of measurements of currents, winds, subsurface pressures and water properties was undertaken in the summer of 1982 in Queen Charlotte Sound on the west coast of Canada. At most observation sites the summer‐averaged currents are found to be about 10 cm s−1, smaller than the tidal currents but comparable to the standard deviation of the non‐tidal currents. The strongest average flow was the outflow of surface water past Cape St James at the northwestern corner of the Sound. During strong winds from the north or northwest a strong outflow of near‐surface fresher water was also observed over Cook Bank in the south. Eddies dominate the motion in the interior of the Sound, as shown by the behaviour of a near‐surface drifter that remained in mid‐Sound for 40 days before a storm pushed it into Hecate Strait. The disorganized, weak currents in the central Sound will likely allow surface waters or floating material to remain there for periods of several weeks in summer. Empirical orthogonal function analyses of fluctuating currents, subsurface pressures and winds reveal that a single mode explains most of the wind and pressure variance but not the current variance. The first two pressure modes represent two distinct physical processes. The first mode is a nearly uniform, up‐and‐down pumping of the surface, while the second mode tilts across the basin from east to west, likely due to geostrophic adjustment of wind‐driven currents. This mode also tilts from south to north, owing to along‐strait wind stress. Most contributions to the first mode currents come from meters near shore or the edge of a trough. Coherence is high between these second mode pressures and first mode currents and winds, and lower but still significant between first mode pressures and first mode currents and winds. It is therefore difficult to predict the behaviour of currents in Queen Charlotte Sound in summer from pressure measurements at a single site, but the difference in sea‐level across Hecate Strait is a more reliable indicator.
Complex endovascular aortic interventions in patients with excessive tortuosity or difficult gantry angles can be challenging. Although fusion imaging can help navigate these issues, it is based on preoperative imaging studies, which becomes skewed after introduction of stiff wires and large devices into the aorta. The subtraction spin protocol performs two cone-beam computed tomography scans to create a subtracted image of the contrast-filled vessels after wire and device placement to accommodate vessel distortion. We have reported a complex fenestrated endovascular aneurysm repair case with a highly angulated neck to highlight the advantages of the subtraction spin protocol in anatomically hostile endovascular repairs.
