Seasonal Turbulence Observations from Robotics and Modelling in the Southern Ocean

The Southern Ocean is one of the stormiest places on earth; here strong mid-latitude storms frequently traverse large distances of this ocean. Beneath these passing storms, this ocean is characterized high eddy kinetic energy (eddies and fronts occupying the meso to sub-mesoscale). The passage of intense storms over this underlying meso to sub-mesoscale eddy variability may strongly impact the upper-ocean environment where phytoplankton live, yet exactly how remains unclear. This project plans for the first time to address this important climate knowledge gap by showing how these intense storms impact upper ocean physics and biogeochemistry with unique observations and modelling. Novel twinned autonomous ocean robots (Wave Glider coupled to a Slocum with a turbulence package) experiments have been designed to directly observe scale sensitivities and links between storm driven wind forcing, upper-ocean mixing and phytoplankton growth. Several numerical models (idealised and regional) have been setup to (a) understand further the associated storm-driven mechanisms and (b) explore how changes in storm characteristics could impact annual primary production in the SO. Given that the SO is arguably the main source of medium-term uncertainty in global CO2 fluxes, understanding such climate sensitivities is of critical importance.

Research objectives:

The overarching hypothesis of this proposal is that storms are important drivers of global air-sea CO2 flux through associated impacts on seasonal and mean physical structuring (stratification and mixing) and primary production in the Southern Ocean. Thus, the aim of this research is to understand the role of storms on upper-ocean mixing, stratification and biological consequences from local to seasonal and annual mean states. This will be undertaken by pursuing the following key aims each with a set of research objectives:

Aim 1: Local-scale: How does the passage of a storm reconfigure upper-ocean physics and biology during summer in the SubAntarctic?

Aim 2: Seasonal and regional-scale: How do storm-driven upper-ocean responses and the associated mechanisms differ through the season and in different regions of the Southern Ocean?

Aim 3: System-mean scale: How do storms shape the seasonal and annual-mean states of upper-ocean physics and primary production in the Southern Ocean?

Project Team:

Sarah Nicholson (PI), Pedro Monteiro (co-PI), Sebastiaan Swart (co-PI), Daniel B. Whitt, Ilker Fer, Anthony Bosse, Marcel du Plessis, Nicolette Chang, Isabelle Giddy, Ayanda Mpalweni , Tumelo Moalusi