Thermodynamics and Variability of Antarctic Bottom Water in the Weddell Sea
Bailey, S. (2020)
Presented at: Ocean Sciences Meeting 2020
The circulation of deep and abyssal waters (waters at or below 2,000m) is an important part of the Southern Ocean global meridional overturning circulation (SOMOC). The SOMOC ventilates the deep ocean while transporting nutrients and tracers (i.e. nitrogen, phosphorous and oxygen). Bottom water is a particularly important part of the climate system, because it can store large amounts of heat and carbon. Changes in the circulation of the abyssal ocean may have significant impacts on Earth's climate. Understanding how the deep ocean reacts to a warming climate will improve predictions of sea level rise and oceanic uptake of CO2.
The densest, coldest and highest-oxygen water in the abyssal ocean is Antarctic Bottom Water (AABW), contributing ~80% to the global deep ocean volume, and most of it being produced in the Weddell Sea region. Climate variability (i.e. ENSO/SAM coupling) has the potential to modify all aspects of bottom water formation; however, the net impact on AABW is not well understood. Recent studies have put additional focus on water-mass transformation (WMT) within the upper branch; however, a robust study of bottom water WMT through a full seawaters equation of state (EOS) has yet to be produced. A key to establishing how AABW formation sources thermodynamically transform due to the nonlinearity of seawaters equation of state (i.e. thermobaric and cabbeling terms), is to consider the fundamental contradiction that Antarctic surface buoyancy fluxes seem to be dominated by freshwater fluxes, but AABW buoyancy is controlled by temperature because due to the thermobaric effect colder water is heavier with depth.
This project aims to investigate AABW circulation by employing a WMT framework through the use of existing low-resolution models, such as SOSE and NASA's ECCOv4 product. With these models, our project aims to quantify interannual variability of AABW, and to examine how the nonlinearity of the thermobaric effect impacts AABW formation. One of the goals is to determine the extent of this term's contribution to seawaters equation of state in this WMT framework. We expect temperature to play an essential role as we look at the bottom 2,000m of SOMOC's lower branch (i.e. the effect of thermobaricity becomes the dominant term in our framework). It is important to understand the thermodynamic drivers of AABW formation and to quantify its variability, as it will lead to a better understanding of how ocean circulation reacts to a changing climate.View Document (PDF, 910 KB) »