Teresa Chereskin is the lead PI of the cDrake (CPIES in the Drake) project and is currently in the middle of the Drake Passage on board the icebreaker Nathaniel B. Palmer, deploying these things:
CPIES instrumentation suite as it is moored on the ocean floor
What is your job on the cruise?
I’m Chief Scientist, so it’s my responsibility to coordinate the sampling and to keep track of our schedule. Mostly, I need to plan for contingencies like weather and instrument problems and address them as they arise. We’ve built in weather time, but it’s hard to predict the weather down here accurately. Before the cruise, I looked at the weather reports from past Drake crossings of the US Antarctic Program ships, and I also have experience from last year’s cruise to build on. We’ve been fortunate so far with weather. My Co-PIs Katy Donohue and Randy Watts from the University of Rhode Island and I work collaboratively, and we’ve done a lot of brainstorming on possible problems or situations which we might encounter. We’ve brought spare instruments based on experience from prior experiments.
On my watch I also run the lowered ADCP, an acoustic Doppler current profiler mounted on the CTD rosette that measures ocean currents from surface to bottom during a CTD cast.
Where did the idea for this project come from?
I’ve been making ocean current measurements from transits of the ‘Laurence M. Gould’ for about a decade. We now have a unique time series of upper ocean currents with more than 200 velocity sections, and we’ve learned a lot about the Antarctic Circumpolar Current (ACC) in the Drake Passage from these observations.
With this data set, we have refined the knowledge about the jets of filaments that make up the ACC. We know that the ACC is strong to the deepest level we can measure, to 1000 m, and we have statistical confidence because we have so many transects. From the ADCP observations we know that the variability is highest between the northernmost 2 fronts, the Subantarctic Front (SAF) and the Polar Front (PF).
The ACC and the Southern Ocean as a whole are very difficult environments for making measurements and also logistically difficult to get to. The polar regions are, in a way, the last frontier of ocean exploration, and we need to make measurements here to test theories and to model the ocean circulation.
For this project we want to understand the dynamical balance of the ACC. What determines the volume of water transported, how is the transport distributed between the multiple jets, how does it vary over time? How does the ACC interact with the significant topography of the Drake Passage? Addressing these questions requires measurements of the full water column, which we cannot get from the ADCP time series. But the prior knowledge from the time series was critical in designing our experiment.
How long will it take to work up the data from the CPIES?
The telemetry data from the CPIES we get from this cruise will likely be worked up sometime next spring. We’re getting a rough look at it on the ship, but there’s a lot of processing still to be done. The other datasets will be close to final form by the end of the cruise on 13 December.
Can you report anything already?
We have found very strong bottom currents. The strength of these currents has been hypothesized but never, to my knowledge, directly measured in the Drake Passage. These currents exert a torque on the bottom and provide a mechanism for putting a “brake” on the ACC via bottom friction.
Our CPIES have a very low profile and a 160 lb anchor. We thought that they would sit undisturbed on the ocean bottom – but at one site we can tell from the pressure records that it was moved deeper on 3 occasions in the past year, likely because it was sitting on a slope and being pushed by these very strong currents.
How did you get into oceanography?
I have an undergraduate degree in mathematics and took a survey course in oceanography in college. That’s when I first learned about physical oceanography, which applies physics and fluid mechanics to the study of the ocean – this sounded fascinating to me. I’ve now been a research oceanographer for about 30 years.
What would you rather be doing?
My present job is a pretty close match to my dream job, except on days when bureaucracy gets me down. I get to travel to interesting places and work on significant and challenging projects and get paid for it. Working in Antarctica has been a dream come true.
What was the biggest challenge in pulling this project together?
We had a lot of brainstorming sessions about what temporal and spatial resolution and length of time series we would need to be able to address our hypotheses – basically, what the instrument array on the seafloor needed to look like. I think the challenge was in designing an experiment for an extreme environment with only limited resources. For me, exploiting both ocean physics and measurement techniques in order to formulate an experiment that can address a scientific hypothesis is both the most challenging and most rewarding aspect of being a sea-going physical oceanographer.
Talking to Antarctica
Thanks for the link, Kurt – there are quite a lot of these ‘live’ outreach activities by projects that work on the stations now, but not so much from the research vessels.
‘CPIES’? Define abbreviations at first use. Bloody scientists.
Big blue letters on the picture above – good morning, Henry! :)
Good morning, Steffi. I did see the picture eventually. But it’s an annoying trait of NN that the pictures are initially too small to see without an atomic force microscope, only attaining the threshold of visibility on a second or third pass.
Is that on your iphone?
No, it’s all the time.
Interesting – it’s huge on my end. Something to bear in mind, thanks!
I asked Teri about the ‘break’ the bottom currents provide in the Drake passage, and what that does. Her answer:
They provide a way to slow down the current.
One of the unanswered questions about the ACC is what sets its transport, the volume of water that it carries. The canonical number, from hydrographic measurements, is about 140 million cubic meters per second. That’s more than any other major ocean current, such as the Gulf Stream. If you predict how much it ‘should’ carry based on the observed winds, that should be much more. So the question is what maintains the balance, and the hypothesis is that the current is slowed down by all the steep topography in its path.