Bottom Gravity Currents and Overflows in Deep Channels of the Atlantic Ocean

Abstract

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Multiple Abyssal Jets Flowing Into the Vema Deep, Romanche Fracture Zone

“…The total increase in bottom conservative temperature over the entire sill between the Vavilov and Vema deeps is 0.046°C or 0.40 mK/km (0.040°C per 100 km distance), indicating quite low rate of abyssal mixing. For comparison, the increase in bottom potential temperature between the entrance and exit of the Romanche FZ exceeds 1°C (more than 1.0 mK/km on average) (Morozov et al., 2021); the increase in the eastern part of the strait is 0.5°C/250 km (2.0 mK/km) (Ferron et al., 1998); the increase along the spillway in the western part of the fracture zone reaches 0.15°C (3.4 mK/km) (Tarakanov et al., 2018). However, even a value of 0.39 mK/km is quite high in comparison with other abyssal channels and especially abyssal basins; for instance, the horizontal gradient of potential temperature in the Vema Channel is less than 0.1 mK/km (Frey et al., 2018).…”

“…It is well known that acceleration of bottom flows occurs at such abyssal sills; the dynamics of these flows was studied theoretically (Whitehead, 1998; Whitehead et al., 1974) as well as by numerical simulations (Frey et al., 2019; Wadley & Bigg, 1995), laboratory experiments (Cossu et al., 2010; Davarpanah Jazi et al., 2020; Morozov et al., 2012), and field observations (see e.g., a review in Morozov et al. (2021)). Despite numerous works dedicated to the direct current observations of the AABW flows in the Romanche FZ, they were concentrated in the western (Tarakanov et al., 2013; van Haren et al., 2014) or eastern (Mercier & Speer, 1998) part of the fracture zone.…”

“…In the Atlantic sector of the Southern Ocean, these dense waters are produced mainly in the Weddell Sea. The main northward flow of AABW in the Atlantic is concentrated in its western part (Hogg, 2001; Morozov et al., 2021). After reaching the northern periphery of the Brazil Basin, this flow divides into two branches (Tarakanov et al., 2018).…”

“…In the Romanche FZ, isotherm 2°C of potential temperature approximately corresponds to salinity S = 34.88 psu, potential density σ 4 = 45.86 kg/m 3 or neutral density γ n = 28.106 kg/m 3 (Morozov et al., 2021). Generally, the abyssal waters in the eastern Atlantic are more homogeneous and less dense than those of the western Atlantic; the difference in the bottom potential temperature between these basins can be as high as 1.5°C (Morozov et al., 2021). This change is caused by topographic blocking and intense mixing in the Romanche FZ (Ferron et al., 1998; Morozov et al., 2012; Tarakanov et al., 2018; van Haren et al., 2014).…”

“…This limit is also determined in other publications by potential density isoline σ 4 = 45.90 kg/m 3 or neutral density isolines of 28.11 kg/m 3 (Ganachaud, 2003) or 28.141 kg/m 3 (Hernández‐Guerra et al., 2014). In the Romanche FZ, isotherm 2°C of potential temperature approximately corresponds to salinity S = 34.88 psu, potential density σ 4 = 45.86 kg/m 3 or neutral density γ n = 28.106 kg/m 3 (Morozov et al., 2021). Generally, the abyssal waters in the eastern Atlantic are more homogeneous and less dense than those of the western Atlantic; the difference in the bottom potential temperature between these basins can be as high as 1.5°C (Morozov et al., 2021).…”