//
you're reading...

Book Review

Earth’s strongest current even stronger than previously thought

Source: Donohue, K. A., Tracey, K. L., Watts, D. R., Chidichimo, M. P., & Chereskin, T. K. Mean Antarctic Circumpolar Current Transport Measured in Drake Passage. Geophysical Research Letters.

The greatest current on Earth

The first time I crossed the Antarctic Circumpolar Current on board a ship, I remember watching the ship’s instruments intently as the sea surface temperature dropped suddenly, and the surface currents spiked as we crossed a front. Looking out the porthole, the surface of the water looked the same, but our measurements showed the ocean we were in was very different. For the next few days, the ship was battered by storms and howling winds until we crossed the southern boundary of the current and entered the relative calm of the Ross Sea near Antarctica, where the sun shone on icebergs drifting in the gentle waves.

antarctic-circumpolar-current-los-alamos-national-laboratory-flickr-cc-by-nc-nd-2-0-small-600x320

The surface speed of the ocean showing the strong Antarctic Circumpolar Current circling the Antarctic continent. From Los Alamos National Laboratory.

The Antarctic Circumpolar Current (ACC) is the largest ocean current on Earth. Strong winds drive its flow around the Antarctic Continent, providing a big ocean conveyer belt that where water from all of the world’s major oceans comes together and mixes in the vigorous jets and eddies of the ACC. The ACC has the power to influence Earth’s climate, by carrying heat, nutrients and carbon along its path. As our climate is changing, tracking changes in the strength of the ACC is essential to understand how the Oceans are changing.

 

Going with the flow

Despite the enormous scale and power of the ACC, or perhaps because of it, scientists have struggled for decades to measure the flow of the ACC. To measure the volume of water transported by the ACC means collecting frequent measurements that cover a wide band of ocean, withstanding strong velocities and braving extreme storms from the atmosphere.

Scientists put in a large effort in the 1970’s to measure the ACC strength with current meter and bottom pressure measurements combined with shipboard measurements. They found the mean ACC transport 134 Sverdrups (Sv), where 1 Sv is 1 million cubic meters per second. To put that in perspective, if you combine the flow from all the rivers in the world into the ocean, they add up to about 1.2 Sv. The 134 Sv estimate was a great start, but the measurements didn’t have ideal coverage in space and time, so there were large uncertainties of 27 Sv associated this number. Since then, scientists have used satellite sensing of the sea surface to estimate the ACC strength, but again there are still large uncertainties. Getting an accurate estimate of the ACC flow from observations is important for climate studies, because the strength of the ACC is frequently used to check the validity of ocean and climate models.

 

A new era of current tracking

A team of scientists from the Rhode Island, Argentina and San Diego ventured to the Southern Ocean to get a more accurate estimate of the ACC strength. The team planned their experiment in Drake Passage, the gap between the tip of South America and the tip of the Antarctic Peninsula where the ACC is squeezed through at its narrowest point. The researchers deployed 22 instruments on the seafloor from 2007 to 2011, measuring bottom pressure, bottom currents and ocean properties every hour. With this new data, the researchers were able to come up with a new estimate of the ACC strength, with narrower uncertainty. They came up with 173.3 ± 10.7 Sv, which is 30% larger than the commonly used estimate of 134 Sv. This new estimate is likely larger because more closely spaced instruments were able to capture the many narrow, strong flows at the seafloor that might have been missed in earlier measurements.

grl55191-fig-0001

Figure 1 from Donohue et al. showing the location of the instruments used to measure the Antarctic Circumpolar Current strength in Drake Passage from 2007 to 2011.

Full speed ahead

This research team was not alone at trying to improve on the early estimates of ACC strength, and they compared their result with other recent estimates from different data, and found their number agreed well with 2 out of 3 recent estimates. This means we now have a more accurate estimate of ACC strength to use as a baseline to compare the quality of climate models. However, the experiment only ran for 4 years because of the large cost of deploying and maintaining instruments, so now the challenge is to come up with a way to measure the ACC continuously, to assess how it is changing over many years, decades and centuries. It will take ingenuity from the oceanography community, and ongoing funding to continue to monitor changes in the ACC. And hopefully the next generation of oceanography PhD students will cross the ACC aboard a ship just like I did, but with much more understanding of the mysteries of the current flowing beneath them.

Discussion

No comments yet.

Post a Comment

Instagram

  • by oceanbites 1 day ago
    Being on a research cruise is a unique experience with the open water, 12-hour working shifts, and close quarters, but there are some familiar practices too. Here Diana is filtering seawater to gather chlorophyll for analysis, the same process on
  • by oceanbites 1 month ago
    This week for  #WriterWednesday  on  #oceanbites  we are featuring Hannah Collins  @hannahh_irene  Hannah works with marine suspension feeding bivalves and microplastics, investigating whether ingesting microplastics causes changes to the gut microbial community or gut tissues. She hopes to keep working
  • by oceanbites 1 month ago
    Leveling up - did you know that crabs have a larval phase? These are both porcelain crabs, but the one on the right is the earlier stage. It’s massive spine makes it both difficult to eat and quite conspicuous in
  • by oceanbites 2 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring Cierra Braga. Cierra works ultraviolet c (UVC) to discover how this light can be used to combat biofouling, or the growth of living things, on the hulls of ships. Here, you
  • by oceanbites 2 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Elena Gadoutsis  @haysailor  These photos feature her “favorite marine research so far: From surveying tropical coral reefs, photographing dolphins and whales, and growing my own algae to expose it to different
  • by oceanbites 3 months ago
    This week for  #WriterWednesday  on Oceanbites we are featuring Eliza Oldach. According to Ellie, “I study coastal communities, and try to understand the policies and decisions and interactions and adaptations that communities use to navigate an ever-changing world. Most of
  • by oceanbites 3 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Jiwoon Park with a little photographic help from Ryan Tabata at the University of Hawaii. When asked about her research, Jiwoon wrote “Just like we need vitamins and minerals to stay
  • by oceanbites 3 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring  @riley_henning  According to Riley, ”I am interested in studying small things that make a big impact in the ocean. Right now for my master's research at the University of San Diego,
  • by oceanbites 3 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Gabby Stedman. Gabby is interested in interested in understanding how many species of small-bodied animals there are in the deep-sea and where they live so we can better protect them from
  • by oceanbites 4 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Shawn Wang! Shawn is “an oceanographer that studies ocean conditions of the past. I use everything from microfossils to complex computer models to understand how climate has changed in the past
  • by oceanbites 4 months ago
    Today we are highlighting some of our awesome new authors for  #WriterWednesday  Today we have Daniel Speer! He says, “I am driven to investigate the interface of biology, chemistry, and physics, asking questions about how organisms or biological systems respond
  • by oceanbites 5 months ago
    Here at Oceanbites we love long-term datasets. So much happens in the ocean that sometimes it can be hard to tell if a trend is a part of a natural cycle or actually an anomaly, but as we gather more
  • by oceanbites 5 months ago
    Have you ever seen a lobster molt? Because lobsters have exoskeletons, every time they grow they have to climb out of their old shell, leaving them soft and vulnerable for a few days until their new shell hardens. Young, small
  • by oceanbites 6 months ago
    A lot of zooplankton are translucent, making it much easier to hide from predators. This juvenile mantis shrimp was almost impossible to spot floating in the water, but under a dissecting scope it’s features really come into view. See the
  • by oceanbites 6 months ago
    This is a clump of Dead Man’s Fingers, scientific name Codium fragile. It’s native to the Pacific Ocean and is invasive where I found it on the east coast of the US. It’s a bit velvety, and the coolest thing
  • by oceanbites 7 months ago
    You’ve probably heard of jellyfish, but have you heard of salps? These gelatinous sea creatures band together to form long chains, but they can also fall apart and will wash up onshore like tiny gemstones that squish. Have you seen
  • by oceanbites 7 months ago
    Check out what’s happening on a cool summer research cruise! On the  #neslter  summer transect cruise, we deployed a tow sled called the In Situ Icthyoplankton Imaging System. This can take pictures of gelatinous zooplankton (like jellyfish) that would be
  • by oceanbites 8 months ago
    Did you know horseshoe crabs have more than just two eyes? In these juveniles you can see another set in the middle of the shell. Check out our website to learn about some awesome horseshoe crab research.  #oceanbites   #plankton   #horseshoecrabs 
  • by oceanbites 8 months ago
    Feeling a bit flattened by the week? So are these summer flounder larvae. Fun fact: flounder larvae start out with their eyes set like normal fish, but as they grow one of their eyes migrates to meet the other and
  • by oceanbites 8 months ago
    Have you seen a remote working setup like this? This is a photo from one of our Oceanbites team members Anne Hartwell. “A view from inside the control can of an underwater robot we used to explore the deep parts
WP2Social Auto Publish Powered By : XYZScripts.com