Sensitivity of Antarctic Bottom Water to Changes in Surface Buoyancy Fluxes

Abstract

The influence of freshwater and heat flux changes on Antarctic Bottom Water (AABW) properties are investigated within a realistic bathymetry coupled ocean-ice sector model of the Atlantic Ocean. The model simulations are conducted at eddy-permitting resolution where dense shelf water production dominates over open ocean convection in forming AABW. Freshwater and heat flux perturbations are applied independently and have contradictory surface responses, with increased upper-ocean temperature and reduced ice formation under heating and the opposite under increased freshwater fluxes. AABW transport into the abyssal ocean reduces under both flux changes, with the reduction in transport being proportional to the net buoyancy flux anomaly south of 608S.Through inclusion of shelf-sourced AABW, a process absent from most current generation climate models, cooling and freshening of dense source water is facilitated via reduced on-shelf/off-shelf exchange flow. Such cooling is propagated to the abyssal ocean, while compensating warming in the deep ocean under heating introduces a decadal-scale variability of the abyssal water masses. This study emphasizes the fundamental role buoyancy plays in controlling AABW, as well as the importance of the inclusion of shelf-sourced AABW within climate models in order to attain the complete spectrum of possible climate change responses.

Does Southern Ocean Surface Forcing Shape the Global Ocean Overturning Circulation?

“…NADW = North Atlantic Deep Water; AABW = Antarctic Bottom Water. simulation of AABW production (e.g., Newsom et al, 2016;Snow et al, 2016). Nonetheless, the present study highlights the importance of diapycnal mixing in the Southern Ocean, which has typically been neglected in previous conceptual model studies of the deep ocean stratification (e.g., Nikurashin & Vallis, 2011;Stewart et al, 2014;Sun et al, 2016).…”

“…There are some caveats associated with the model used in this study. The nominal 1° ocean resolution in CESM does not resolve eddies, which have been shown to be important in the response of the Southern Ocean circulation to perturbations in the surface forcing (e.g., Abernathey et al, ; Munday et al, ), nor does it resolve the near coastal processes in the Antarctic regions, which have been suggested to be important for the simulation of AABW production (e.g., Newsom et al, ; Snow et al, ). Nonetheless, the present study highlights the importance of diapycnal mixing in the Southern Ocean, which has typically been neglected in previous conceptual model studies of the deep ocean stratification (e.g., Nikurashin & Vallis, ; Stewart et al, ; Sun et al, ).…”

The Energetics of Southern Ocean Upwelling

“…and outcrops at the surface in the Southern Ocean. This cell is the primary focus of the ); less than half that observed by Lumpkin and Speer (2007)] due to the poor representation of near-coastal processes in the Antarctic region where the dense water that drives the abyssal overturning cell is formed (Snow et al 2016). …”

“…Furthermore, the lower, or abyssal, overturning cell is also a strong function of surface buoyancy fluxes that control the rate of dense water formation around Antarctica (Snow et al 2016). This dense water sinks to fill the abyssal depths of the ocean with Antarctic Bottom Water.…”

Controls on circulation, cross‐shelf exchange, and dense water formation in an Antarctic polynya

“…The Adélie region, East Antarctica, and the Mertz polynya (located above the Adélie Depression; Figure ) is a significant source of AABW [ Rintoul , ; Kusahara et al , ; Williams et al , ; Lacarra et al , ]. Polynya activity and seasonality of buoyancy fluxes potentially influence the seasonal cross‐shelf exchange [ Snow et al , ], circulation, and in turn, AABW formation. By assessing the seasonality of the Adélie Land shelf circulation and the role of buoyancy fluxes within the Mertz polynya (recorded as the third largest sea ice producer of all Antarctic polynyas [ Tamura et al , ]), we provide insight into the role of surface forcing in driving the formation of DSW and exchange of water masses across the Antarctic continental shelf break.…”