Abstract: During systematic repeat hydrography cruises to the Endeavour segment of the Juan de Fuca Ridge in the summers of 2004, 2005, and 2006, we encountered a transient increase in the water column heat content above the Salty Dawg hydrothermal field. First observed in July 2005 and mapped in greater detail in August 2005, this feature was not a typical event or megaplume since potential temperature anomalies were continuously elevated from the plume top to the seafloor. During the summer of 2005, the heat content in the waters above Salty Dawg was elevated similar to 30 TJ, and the plume top was over 150 m higher in the water column than the other years measured. Based on scaling analyses, an order of magnitude increase in the volume flux from Salty Dawg would be required to generate a neutrally buoyant plume of this size. This observation was unexpected because no substantial earthquakes were detected in the time frame of this increased heat flux. The duration of the transient suggests possible forcing mechanisms: advancement of a cracking front, a small-scale dike intrusion, aseismic crustal movement, fracture of a flow constriction to a previously unaccessible reservoir, an increase of heat in an underlying magma chamber, or movement of melt within the axial magma chamber. The transient disappeared before returning in August 2006, likely due to thermal expansion of shallow host rock, decreasing the permeability. Should such increases in seafloor heat flux prove to be common, the rate of hydrothermal cooling could be faster than previously thought.

Abstract: Temporal and spatial patterns of variability in Puget Sound's oceanographic properties are determined using continuous vertical profile data from two long-term monitoring programs; monthly observations at 16 stations from 1993 to 2002, and biannual observations at 40 stations from 1998 to 2003. Climatological monthly means of temperature, salinity, and density reveal strong seasonal patterns. Water temperatures are generally warmest (coolest) in September (February), with stations in shallow finger inlets away from mixing zones displaying the largest temperature ranges. Salinities and densities are strongly influenced by freshwater inflows from major rivers during winter and spring from precipitation and snowmelt, respectively, and variations are greatest in the surface waters and at stations closest to river mouths. Vertical density gradients are primarily determined by salinity variations in the surface layer, with stations closest to river mouths most frequently displaying the largest buoyancy frequencies at depths of approximately 4-6 m. Strong tidal stirring and reflux over sills at the entrance to Puget Sound generally removes vertical stratification. Mean summer and winter values of oceanographic properties reveal patterns of spatial connectivity in Puget Sound's three main basins; Whidbey Basin, Hood Canal, and Main Basin. Surface waters that are warmed in the summer are vertically mixed over the sill at Admiralty Inlet and advected at depth into Whidbey Basin and Hood Canal. Cooler and fresher Surface waters cap these warmer waters during winter, producing temperature inversions. (C) 2008 Elsevier Ltd. All rights reserved.