UM Rosenstiel School scientist Lisa Beal and her research team are experiencing some less than comfortable work conditions this month. I asked Dr. Beal a few questions about her current research expedition to the Agulhas Current.
Q: Why are scientists interested in the Agulhas Current?
A: The Agulhas Current is a Western Boundary Current, like the Gulf Stream, but flows along the east coast of South Africa in the Indian Ocean. It is an interesting phenomenon for many reasons! The most obvious is its unique geography: below the tip of the African continent the current loops around on itself to form the Agulhas Retroflection, where most waters feed back into the Indian Ocean, but some leak into the Atlantic in large eddies or rings. Probably the most important, far-reaching reason that the Agulhas is of interest to scientists is that it appears to play a role in global climate change.
Paleoceanographic data and model simulations suggest that changes in the leakage of warm, salty water from the Indian Ocean into the Atlantic via Agulhas rings can cause significant changes in the northward heat transport of the Atlantic and hence in the amount of deep water formed in the North Atlantic, causing climatic changes. For instance, paleo data collected from marine sediment cores show that peaks in Agulhas leakage preceded each of the transitions from glacial to interglacial climate over the past 550,000 years. In other words, increases in Agulhas leakage are followed by warming of the global climate by up to 6 or 7 degrees centigrade, although we cannot be certain that the leakage causes these changes.
Furthermore, a 20th century simulation suggests that we can expect Agulhas leakage to be currently increasing due to anthropogenic climate change. If this is the case, it could cause a positive feedback on climate change, as indicated in the past by the paleo data, thus enhancing or speeding up global warming through its affect on the Atlantic heat transport.
Q: How long have you been studying the Agulhas Current? What new scientific knowledge has emerged on the current since you’ve been studying it?
A: I have been studying the Agulhas Current since I was a PhD student in 1995 and have authored or co-authored 14 scientific articles about the Agulhas system. Over the last fifteen years many new discoveries have been made about the system and here I highlight a few.
One of the first discoveries of this period was that there is a current underneath the Agulhas, below a depth of about 1000 m and flowing in the opposite direction, which carries North Atlantic Deep Water into the Indian Ocean. We now call this the Agulhas Undercurrent. We also established the mean transport of the Agulhas Current from a year-long mooring experiment at 32 degrees latitude south. The Agulhas rivals the Gulf Stream in strength, with a mean transport of 70 Sverdrups (million cubic meters per second). We also learned that eddies drifting from the Mozambique Channel and from the tip of Madagascar can change the path and transport of the Agulhas Current and its leakage of waters into the Atlantic, by destabilizing the flow and forming Agulhas Rings at the retroflection. Finally, through model experiments and theory we found the link between the Agulhas and Atlantic heat transport and how they are both correlated with the large-scale wind system.
Q: Describe a typical day at work on a research vessel?
A: Work on a research vessel is round-the-clock. On this cruise during a typical day we will recover or deploy a current meter mooring during daylight hours and collect CTD data at night. A mooring consists of instrumentation to measure flow speed and direction, plus flotation, placed up and down a wire and anchored to the sea bed. A CTD is a cluster of instrumentation and sample bottles lowered through the water column from the ship to measure water properties like temperature, salinity, pressure, and oxygen.
Q: What is the biggest challenge for a scientist studying global climate change?
A: My biggest challenge when going to sea to study the ocean is motion sickness! But not everyone suffers with this. More seriously, I would say that the biggest challenge in understanding the climate system and climate change is lack of data. Model simulations are only beneficial if we can validate them with data from the real world, and yet limited funding for the geosciences, oceanography in particular, severely restricts the amount of data we can collect. To understand how climate is changing over time and to be able to predict how climate change over the next century will impact humans, we need to take measurements in the atmosphere, the ocean, and on land repeatedly across the globe. This will take a consistent dedication of public resources over many decades. Can we rise to this challenge?
Follow the research team’s daily journal as they brave the Agulhas Current.
– Annie Reisewitz
Follow Annie on Twitter @annelore