Monitoring deep‐ocean temperatures using acoustic ambient noise

Abstract

Measuring temperature changes of the deep oceans, important for determining the oceanic heat content and its impact on the Earth's climate evolution, is typically done using free‐drifting profiling oceanographic floats with limited global coverage. Acoustic thermometry provides an alternative and complementary remote sensing methodology for monitoring fine temperature variations of the deep ocean over long distances between a few underwater sources and receivers. We demonstrate a simpler, totally passive (i.e., without deploying any active sources) modality for acoustic thermometry of the deep oceans (for depths of ~ 500–1500 m), using only ambient noise recorded by two existing hydroacoustic stations of the International Monitoring System. We suggest that passive acoustic thermometry could improve global monitoring of deep‐ocean temperature variations through implementation using a global network of hydrophone arrays.

Short‐ and Long‐Term Variations in the Reykjanes Geothermal Reservoir From Seismic Noise Interferometry

“…SI refers to the principle of generating virtual source responses by cross-correlating existing seismic records (Bakulin & Calvert, 2006). Many applications have arisen that exploit the technique to infer characteristics of the subsurface (e.g., Draganov et al, 2007;Sens-Schönfelder & Wegler, 2011;Shapiro et al, 2005), the Sun (Duvall et al, 1993), the oceans (Roux & Fink, 2003;Woolfe et al, 2015), buildings (Kohler et al, 2007;Snieder & Safak, 2006), and the atmosphere (Fricke et al, 2014;Haney, 2009).…”

Ecoacoustics: A Quantitative Approach to Investigate the Ecological Role of Environmental Sounds

“…When extended to an ecoacoustic approach (using appropriate metrics), PAM changes to passive ecoacoustic monitoring (PEM), which can also detect physical parameters from the environment, such as the rain regime [111], ocean weather [112], or temperature [113]. Empirical evidence of the efficiency of PEM has been accumulated on Mediterranean maqui [84], on temperate freshwater [85,114,115], and in the marine environment [116][117][118][119].…”

Long-range correlations of microseism-band pressure fluctuations in the ocean

“…Cross-correlation functions of pressure fluctuations in the ocean have been investigated in the 0.5-30 mHz band, where the correlations characterize deep-water infragravity waves and their sources (Webb 1986;Godin et al 2014b), and at acoustic frequencies above 1 Hz, where geoacoustic parameters of the seafloor (Brown et al 2014), spatial (Godin et al 2010) and temporal (Woolfe et al 2015) variations of the sound speed in water and ocean current velocity (Godin et al 2014a) have been retrieved from noise cross-correlations.…”

“…(b) Noise power spectra from 2011 January and (c) daily cross-correlation functions between stations N1 and S1 over year 2011, showing seasonal variation in amplitudes. Woolfe et al 2015). The hydrophone station at Ascension consists of two triangular arrays spaced 123 km apart along a line oriented roughly NE-SW (Fig.…”