#03 2023

Scientists join forces to investigate the Cape Cauldron hotspot

By Sikelelwa Mtyenene, SAASTA/NRF volunteer at SAEON

On 4 March, scientists from the USA (University of Miami), Sweden (University of Gothenburg), United Kingdom (University of Bangor) and South Africa (University of Cape Town) set out to research the Cape Basin using the Roger Revelle research vessel. The cruise formed part of the Quantifying Interoceanic Fluxes in the Cape Cauldron Hotspot of Eddy Kinetic Energy (QUICCHE) project. 

The aim of this cruise was to measure the Agulhas leakage by targeting several dynamical regimes to observe the relative submesoscale and estimate diffusivities.

The project proposed that from the measurements the scientists would be able to quantify eddy heat and salt fluxes in the same way the poleward flux has been estimated in the Southern Ocean. The Cape Basin in the southeastern part of the Atlantic Ocean is a global hotspot of eddy kinetic energy. It is fed by warm and salty waters from the subtropical Indian Ocean via the Agulhas Current. The Agulhas waters are strongly stirred and mixed with cooler and fresher water from the Atlantic Ocean by co-interacting rings and eddies.

In preparation for boarding the R/V Roger Revelle, we began conducting Covid-19 antigen tests and following protocol for 10 days before the cruise. On 1 March the science team met on the Table Mountain hike and got to know each other on our way up. The hike was easy for a few people and hard for many, but in the end most scientists got to the top. From the next day onwards, the lead scientists and their teams started loading their instruments on the ship during the mobilisation.

The remaining members of the science team boarded on 4 March and the ship set sail that afternoon. We sailed for about 23 hours to get to the area on the Cape Cauldron where the expedition would commence. We were all masked up for the first seven days, tested daily and did routine temperature checks. Finally, on day 7, Covid restrictions were lifted on the ship. During the first few days, many people suffered from seasickness, but started to recover as the first week went by.

During the cruise there was a 24-hours shift – each group had eight hours to help with deployments, hourly monitor the multibeam, partial pressure of carbon dioxide (PCO2), ship the acoustic Doppler current profiler (ADCP) and anything that needed to be done during that shifting time. Sundays were drill and barbeque days. Every Sunday resident technicians would take us through safety measures in different emergency situations when onboard, after which the captain and second mate would do BBQ outside on the braai stand for supper.

During the cruise both Eulerian and Lagrangian instrumentation were used, including moorings, a CTD system (to measure the electrical conductivity, temperature and pressure of seawater), gliders, drifters, profiling floats and microstructure turbulence profilers, capturing time and space scales from hours to seasons and from 1 to 100 km. During their deployments some small challenges surfaced – some instruments could not respond to communication after deployment and others could not be deployed in some areas due to bad weather.

All these instruments provided data that would explain the air-sea fluxes, eddy stirring and the Agulhas retrofraction in the Cape Cauldron. Nitrates, microplastics and dissolved oxygen were sampled from the water collected by the CTD.

Also on board was a filming team that captured the priceless moments of instrument deployment and, together with the card game team, conducted interviews about the instruments, the science and the roles scientists play. The interviews helped the team to create an educational card game for school children about the instruments, the science and careers at sea.

Having been exposed to the field of Marine Sciences through my studies at Cape Peninsula University of Technology, participating in the QUICCHE cruise and collaborating on an international project was an amazing opportunity. During the survey of the Cape Basin I learnt a great deal about all the ocean observers mentioned in the article and the science being conducted.

“The experience motivated me to study towards an advanced diploma in Marine Science in the hope of becoming an established marine scientist in the future.”~ Sikelelwa Mtyenene

Celebrating International Women’s Day on board

Cruise track from the ship acoustic Doppler current profiler (ADCP) data

Team gliders before deployment

Deployment of a CTD rosette

Deployment of the wire flyer

The Cape Cauldron card game tuckbox and draft cards