//
you're reading...

Climate Change

Why the Southern Ocean is getting less salty

Source: Haumann, F. A., Gruber, N., Münnich, M., Frenger, I and S. Kern, 2016, Sea-ice transport driving Southern Ocean salinity and its recent trends, Nature 537, 89-92 doi:10.1038/nature19101

 

The Southern Ocean, the big expanse of Ocean that surrounds Antarctica, has been getting less salty over the past few decades. This is a very clear signal of climate change in the oceans, but proving what has caused the ocean to get fresher has been a challenge for scientists until now.

Sources of Salt

There are very few sources of salt going into the ocean, so for the Southern Ocean to get less salty, freshwater has to be added from somewhere else. Initially scientists thought it could be either from enhanced melting of Antarctic glaciers or increased rain over the Southern Ocean. While glacial melting is  definitely contributing to making the ocean less salty very close to Antarctica, it can’t explain the large trends further away from the coast. Rainfall has increased over the Southern Ocean in global climate models, but not enough to explain the changes in salinity. A third possibility is that the salinity trends could be caused due to changes in the transport of sea-ice.

640px-Antarktyda_i_Antarktyka

Antarctica surrounded by sea-ice from space. From NASA.

Ice factories

Sea-ice is formed along the edges of the Antarctic coast when seawater freezes, leaving the salt behind, making the surrounding water saltier. Strong winds blow the ice away from the coast, where it eventually melts, adding freshwater back to the ocean in a different location. Sea-ice transport is essentially like a conveyer belt for freshwater, picking it up near Antarctica where it freezes and dropping it off in the open ocean where it melts. If the transport of sea-ice away from Antarctica speeds up, more freshwater is moved from Antarctica to the open ocean. A group of scientists from Switzerland and Germany looked into the satellite sea-ice record to see if changes in see ice transport could explain the Southern Ocean salinity trends.

Screen Shot 2016-09-01 at 5.42.03 PM

Figure 1 from Haumann et al. 2016 showing the effect of sea ice transport on salinity in the Southern Ocean. The left picture shows the normal effect of sea ice, with blue arrows showing the direction of freshwater transport. Freshwater is taken out of the ocean at the Antarctic coast where ice freezes, blown offshore and added to the open ocean where sea ice melts. The right picture shows the effect of sea-ice transport on salinity trends, where there is more transport of freshwater away from the coast by ice, causing the open ocean to become less salty.

 

Icy trends

To calculate how much freshwater is transported by sea-ice, the researchers combined measurements of sea-ice concentration, drift and thickness from satellites and model-based reconstructions to figure out the volume of the sea ice and its movement. Combining all of this information, the scientists found a large trend in the transport of freshwater by sea-ice around Antarctica from 1982-2008. Most of this trend comes from one particular location, the Ross Sea, where sea-ice has been transporting freshwater away from Antarctica much more rapidly in recent decades.

Screen Shot 2016-09-01 at 5.42.19 PM

Figure 2 from Haumann et al. 2016. On the top is the mean sea-ice freshwater transport (left) and flux of freshwater into the ocean (right) and on the bottom is the trend in sea-ice freshwater transport (left) and flux of freshwater (right). The bright orange area in the south of panel c shows the large trend in the Ross Sea.

Scientists already know why sea-ice transport has increased in the Ross Sea. Strong winds blow cold air from Antarctica over the Ross Sea, pushing sea-ice away from the coast and in recent decades these winds have gotten much stronger, speeding up the sea-ice conveyer carrying fresh water away from Antarctica. The researchers found that the increased transport, especially in the Ross Sea, added enough fresh water to the Southern Ocean to explain the measured change in salinity, and that the biggest changes in freshwater input coincide with the locations where salinity has decreased the most.

Screen Shot 2016-09-06 at 9.10.57 AM

Figure 3 from Haumann et al. 2016. This shows the flux of freshwater into the ocean only due to sea-ice processes. On the left is the freshwater input into the ocean from melting ice, the middle panel shows the removal of freshwater by sea ice freezing and the right shows freshwater export associated with sea-ice transport.

Ice and climate

The fact that sea-ice transport can explain salinity changes in the Southern Ocean shows that Antarctic sea-ice transport is more important for changes in global climate than previously thought. Changes in salinity affect water density and ocean stratification; when the surface ocean is strongly stratified with fresher, less dense water on top, it is tough for nutrient-rich, saltier water at depth to get mixed back to the surface. This translates to less nutrients for plants and animals to grow at the surface. This nutrient limitation and reduced mixing can reduce the uptake of carbon dioxide by organisms and other processes, leading to changes in the ocean’s absorption of carbon dioxide. The role of Antarctic sea-ice in our climate system shown in this study shows that we need more accurate, long-term measurements of sea-ice and how it is changing in Antarctica.

Discussion

No comments yet.

Post a Comment

Instagram

  • by oceanbites 5 days 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 weeks 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 3 weeks 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 1 month 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 2 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 2 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 2 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 2 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 3 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 3 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 4 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 4 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 5 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 5 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 6 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 6 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 7 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 7 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
  • by oceanbites 8 months ago
    Today is the day of  #shutdownacademia  and  #shutdownstem  and many of us at the Oceanbites team are taking the day to plan solid actions for how we can make our organization and the institutions we work at a better place
  • by oceanbites 8 months ago
    Black lives matter. The recent murders of Ahmaud Arbery, Breonna Taylor, and George Floyd have once again brought to light the racism in our country. All of us at Oceanbites stand with our Black colleagues, friends, readers, and family. The
WP2Social Auto Publish Powered By : XYZScripts.com