Ocean variability translates into acoustic variability, and for any given acoustic system there is a complex relationship between signal stability and randomization and the space/time scales of the ocean ( Colosi, 2016). This variability may be caused by eddies ( Cornuelle et al., 1985 Wolfson and Tappert, 2000), internal tides ( Dushaw et al., 1995, 2011), internal waves ( Colosi, 2016), and spicy thermohaline structure ( Dzieciuch et al., 2004 Colosi et al., 2013). Of fundamental importance are the features of the water masses (e.g., the sound channel) and their inherent variability due to ocean processes ( Colosi, 2016).
Changes in these water masses on time scales from interannual to buoyancy period are of fundamental interest to a broad spectrum of Arctic scientists, including acousticians.ĭeep-water sound propagation can be used for many practical applications including remote sensing, navigation, and communication. The cumulative effect of these layered water masses is a highly stratified upper ocean, with strong density gradients and high buoyancy frequencies, especially at the transitions between water masses. Below the PWW, a strong halocline and thermocline marks the transition to water of Atlantic origin, simply called Atlantic Water (AW), which is characterized as warm (T > 0☌) and salty (S > 34.5 Rudels et al., 2004). ( 1998) found that its lateral extent may be variable in time. Although this water mass seems to be fairly consistent in its properties, Steele et al. PWW is believed to be formed by ice formation on the Chukchi Shelf during winter months ( Pisareva et al., 2015). Below PSW is the PWW that is generally found below 150 m and can be identified by a temperature minimum and salinities greater than 33 ( Coachman and Barnes, 1961). ( 2014) have shown that the PSW has increased in heat content and freshwater content in recent years, with potential impacts to stratification and vertical heat fluxes. PSW is characterized as having a temperature maximum greater than –1.0☌ ( Steele et al., 2004) with salinities of 31–33 ( Shimada et al., 2001 Steele et al., 2004). Coachman and Barnes ( 1961) named these layers Pacific summer water (PSW) and Pacific winter water (PWW). These waters are of Pacific origin and fill the upper to intermediate depths of the Canada Basin. One consequence of this feature is a subsurface acoustic duct that can allow long-range acoustic propagation with little energy loss. Below the surface waters around 100-m depth, a temperature maximum has emerged that appears to be increasing in intensity and lateral extent ( Jackson et al., 2010 Toole et al., 2010 Steele et al., 2011). The observed strong variations in vertical and horizontal sound-speed structure will have significant impacts on acoustic applications, especially in the realm of communications, navigation, and remote sensing.Ĭhanges in the mean and fluctuating sound-speed structure in the upper few hundred meters of the ocean are of intense acoustical interest. Both processes have vertical decorrelation lengths less than 100 m. Spicy sound-speed fluctuations were much stronger, particularly in the upper 100 m where a maximum of 0.25 m s –1 was observed. The root mean square sound-speed fluctuations from internal waves were small with values less than 0.1 m s –1. Frequency spectra of spice show a form similar to the internal-wave spectra but with a slightly steeper spectral slope, presumably due to the horizontal advection of the spice by internal-wave currents. Internal-wave frequency spectra show a spectral slope much lower than the Garrett-Munk model, with the energy level roughly 4% of the standard Garrett-Munk value. Frequency spectra and vertical covariance functions were used to describe the space/time scales of displacements and spice. Moored and shipborne observations of temperature and salinity were made in the upper 600 m of the ocean, allowing analysis along isopycnals (surfaces of constant density) to separate sound-speed structure due to internal-wave-induced vertical displacements from those originating from density-compensated temperature and salinity variations termed spice. The Canada Basin Acoustic Propagation Experiment (CANAPE) is an effort to study Arctic acoustics this paper reports on ocean sound-speed measurements from a pilot study undertaken between 30 July and 16 August 2015. The acoustic response to this adjustment is of fundamental interest, as acoustics provide an important means for Arctic remote sensing, communication and navigation, and there are important biological implications for marine mammals and other organisms that use sound. The Arctic seas are in a period of transition as they adjust to stimuli from anthropogenic climate change.
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