On the Consumption of Antarctic Bottom Water in the Abyssal Ocean

Abstract

Manuscript (non-LaTeX)Click here to download Manuscript (non-LaTeX) Full manuscript.docx ABSTRACT 24The abyssal ocean is primarily filled by cold, dense waters formed around Antarctica and 26 collectively referred to as Antarctic Bottom Water (AABW). At steady state, AABW must be consumed in the ocean interior at the same rate it is produced, but how and where this 28 consumption is achieved remains poorly understood. Here, we present estimates of abyssal water mass transformation by geothermal heating and parameterized internal wave-driven mixing. We 30 use maps of the energy input to internal waves by tidal and geostrophic motions interacting with topography combined with assumptions about the distribution of energy dissipation to evaluate

Turning Ocean Mixing Upside Down

“…This expression for the full diapycnal velocity, normal to the isopycnal, is derived, for example, in Marshall et al (1999) but differs from the one reported in McDougall (1984) andde Lavergne et al (2016), who only considered its vertical component. This difference is important when considering regions of weak vertical stratification like the turbulent BBLs.…”

“…Here, we will consider the simpler case of a linear equation of state, which is sufficient to study the qualitative aspects of mixing-driven flows. The reader is referred to the recent paper by de Lavergne et al (2016) for a discussion of the mass transport generated by mixing in the abyssal ocean with a nonlinear equation of state. Our goal is to illustrate how interior mixing drives both downwelling across density surfaces in the ocean interior and upwelling along the boundaries, rather than providing an accurate estimate of the observed ocean overturning circulation.…”

“…The global transport of tracers like heat and freshwater is affected by additional flows along density surfaces, like isopycnal stirring and mixing by geostrophic eddies, which will not be discussed. Our approach is similar to the one taken by Nikurashin and Ferrari (2013) and by de Lavergne et al (2016), who studied the role of mixing in driving water mass transformations in the deep ocean using available estimates of internal wave-driven mixing. But our focus is on understanding and quantifying the crucial role played by the turbulent bottom boundary layers.…”

“…The turbulent density flux map produced by Nikurashin and Ferrari (2013) considered only mixing associated with topographic waves that break locally near their generation sites. De Lavergne et al (2016) attempted to estimate the mixing associated with nonlocal waves, but their results were quite uncertain. To get a sense of the overall importance of these nonlocal waves in driving diapycnal flows in the abyss, we appeal to the observational evidence that, away from regions where strong topographic waves are generated, ocean mixing is weak and characterized by a background turbulent diffusivity of about 10 25 m 2 s 21 (Waterhouse et al 2014).…”

“…De Lavergne et al (2016) studied the effect of the geothermal heat flux in their analysis, which we ignored, and showed that it lightens waters along the ocean boundaries and drives a few additional Sverdrups to the total BBL transport. Based on the work presented in this paper, this implies that the geothermal heat flux further reinforces the diapycnal upwelling of bottom waters along the BBLs.…”