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Serendipitous measurements of deep internal wave signatures are evident in oscillatory variations around the background descent rates reported by one model of Deep Argo float. For the 10,045 profiles analyzed here, the average root‐mean‐square of vertical velocity variances, 〈w′2〉 $\sqrt{\langle {w}^{\prime 2}\rangle }$, from 1,000 m to the seafloor, is 0.0045 m s−1, with a 5%–95% range of 0.0028–0.0067 m s−1. Dominant vertical wavelengths, λz, estimated from the integrals of lagged autocorrelation sequences have an average value of 757 m, with a 5%–95% range of 493–1,108 m. Both 〈w′2〉 $\sqrt{\langle {w}^{\prime 2}\rangle }$ and λz exhibit regional variations among and within some deep ocean basins, with generally larger 〈w′2〉 $\sqrt{\langle {w}^{\prime 2}\rangle }$ and shorter λz in regions of rougher bathymetry or stronger deep currents. These correlations are both expected, since larger 〈w′2〉 $\sqrt{\langle {w}^{\prime 2}\rangle }$ and shorter λz should be found near internal wave generation regions. Plain Language Summary: Ocean density increases with increasing depth, supporting internal waves below the ocean surface. These internal waves are generated near the surface by varying wind forcing such as passing storms and near the bottom by interactions of currents (including tidal) with rough bathymetry (such as seamounts and ridges). They can travel for long distances in both the vertical and the horizontal. When they break, they play important roles in mixing temperature, salinity, and other water properties. Deep Argo is an observing system designed to measure temperature and salinity profiles from the surface to the bottom of the ocean. One model of Deep Argo float serendipitously observes internal wave signals as variations in descent rate data, which it collects primarily for navigation purposes, from the surface to the seafloor. These observations reveal patterns in the magnitudes of these internal wave signals, with stronger internal wave activity near continental rises and mid‐ocean ridges and lower levels over smoother abyssal plains. Also, regions with strong deep flows, such as the Samoan Passage through which bottom water is funneled into the North Pacific, or the region south of the Campbell Plateau through which the Antarctic Circumpolar Current flows, exhibit stronger deep internal wave signatures. Key Points: Descent rate data used for navigation by one deep float model serendipitously reveal vertical velocity signatures of internal wavesDeep internal wave vertical velocities average root mean square variances are ∼0.0045 m s−1 and dominant vertical wavelengths are ∼757 mVertical velocity variances and dominant vertical wavelengths exhibit geographical patterns, varying among and within deep ocean basins [ABSTRACT FROM AUTHOR]

As the abyssal oceans warm, stratification is also expected to change in response. This change may impact mixing and vertical transport by altering the buoyancy flux, internal wave generation, and turbulent dissipation. In this study, repeated surveys of three hydrographic sections in the Southwest Pacific Basin between the 1990s and 2010s are used to estimate the change in buoyancy frequency N2. We find that below the θ=0.8°C isotherm, N2 is on average reduced by a scaling factor of s=0.88±0.06, a 12% reduction, per decade that intensifies with depth. At Θ=0.63°C, we observe the biggest change: s=0.71±0.07, or a 29% reduction per decade. Within the same period, the magnitude of vertical diffusive heat flux is also reduced by about 0.01Wm−2, although this estimate is sensitive to the choice of estimated diffusivity. Finally, implications of these results for the heat budget and global ocean circulation are qualitatively discussed. Plain Language Summary: The large‐scale circulation of the ocean is primarily driven by density differences. As dense, heavy water sinks, it fills the deep ocean basins and aids in pushing water around the globe, cycling around the world over many centuries. A key location where this happens is around Antarctica. The ice and cold winds cool the water, making it denser. This cooled water sinks, displacing the deep water and pushing it northwards. As Antarctica warms, this water carries the extra heat into the rest of the world, causing the deep ocean to rapidly warm. In the Southwest Pacific Basin, we find that this bottom intensified warming has caused a significant reduction in the stratification of the deepest layer over the past three decades. This change can disrupt the global ocean conveyor belt, impacting the transport of heat, carbon dioxide, nutrients, and other dissolved matter around the world. Key Points: A decadal stratification decrease is estimated from 25 years of repeat hydrography in the abyssal Southwest Pacific BasinThis change is significant below Θ = 0.75°C and intensifies with depth, reaching a 22%–36% decrease by Θ = 0.65°CVertical diffusive heat flux is also reduced during the same time period by ∼0.01 Wm−2/decade [ABSTRACT FROM AUTHOR]