The Agulhas leakage is thought to have major implications for heat transport and global circulation patterns of the ocean and the QUICCHE campaign seeks to measure its magnitude using a large suite of instruments on a variety of oceanographic scales.
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My name is Ali Johnson, I’m a PhD student in Physical Oceanography at the University of Rhode Island Graduate School of Oceanography (GSO). If you’ve been keeping up with our last few posts to the QUICCHE blog, you’ve heard a bit about all the different instruments we are deploying in the Cape Basin region of the South Atlantic. Today, I wanted to take a step back and give you a quick overview of why we are out here in the first place!
The Cape Basin is a particularly interesting region of the ocean because warm, salty waters of the subtropical Indian Ocean meet cooler, fresher waters of the South Atlantic. This interaction is mediated by the Agulhas Current, a southwestward flowing jet that transports Indian Ocean waters along the eastern coast of Mozambique and South Africa. When the Agulhas reaches the southernmost tip of South Africa, a majority of this water retroflects (turns back on itself) and continues east to eventually return to the Indian Ocean. A small portion of this warm and salty water however, escapes retroflection and propagates into the South Atlantic – this is called the Agulhas leakage.
The magnitude of the Agulhas leakage is thought to have major implications for heat transport and global circulation patterns of the ocean however, quantifying these fluxes is difficult and characterizing the various scales of mixing has yet to be done.
The goal of the QUICCHE project is to use a large suite of instruments to make observations of the Agulhas leakage on a variety of oceanographic scales – from the very large (100+ km) to tiny measurements of turbulence (<1km).
On this cruise, we are deploying all the instruments that will make these observations possible. I’m sure there will be lots more discussion on this blog about all the instrumentation so stay tuned to learn more about all this cool stuff we are putting in the ocean!
Speaking of, I feel like I can’t leave you without a quick plug for the instruments I am here to help deploy. Members of the Ocean Dynamics Lab at GSO design, build and deploy instruments called Current and Pressure recording Inverted Echo Sounders (CPIES). These instruments sit at the bottom of the ocean measuring bottom pressure, near bottom currents and acoustic travel time – a fancy way of saying sound speed through the water column. The concept is pretty simple, once the instrument reaches the seabed it emits an audible ‘ping’ at a pre-determined frequency. This sound travels all the way through the water column, bouncing off the surface of the ocean and returning to the CPIES a fraction of a second later. The CPIES simply measures the amount of time it takes for that ‘ping’ to return back to the seafloor.
Sound speed through water is primarily dependent on the temperature of the water so these instruments give us a fairly accurate estimate of the temperature profile in the surrounding region.
Quick shout-out to Mr. Rock’s 7th grade AcLab class at Thompson Middle School in Newport, Rhode Island – the coolest group of junior ocean scientists I know! Before I left for Cape Town, they decorated these styrofoam cups and we sent them all the way down to the bottom of the ocean (4,000 meters!) where the immense pressure squished them into teeny-tiny little cups!