you're reading...

Climate Change

New insights into old events using marine sediment

Article: could gradual changes in Holocene Saharan landscape have caused the observed abrupt shift in North Atlantic dust deposition? Sabine Egerer, Martin Clausen, Christian Reick, Tanja Stanelle. EPSL, 2017.



Whether on a cruise ship or using satellites, we scientists spend a lot of time looking at what the ocean looks like today. Just as importantly, though, we can use the ocean to study what happened in the past, and use that to predict what might happen in the future. There are many ways to do this, but one widely used source of information is sediment core records. For a brief history of how and why we get sediment cores from all over the seafloor, check out this article. In short, we can look at changes in things like mud type and chemistry to determine when and how the sediment got buried, and sometimes even where it came from. There are whole fields of science dedicated to studying what happens to sediment during and after it hits the seafloor. Today, let’s look at an example of how sediment records can tell us what happened far above the seafloor.


Back up to around 6,000 years ago. The climate is a bit different than it is today. Today, the Sahara in North Africa is a desert – hot, dry, and inhabited by only the toughest of life. Around 16,000 to 6,000 years ago, though, during the African Humid Period, North Africa was lush and rainy, with sprawling grasslands. Lakes, animals, and people dotted what is called the “Green Sahara”. However, around 6,000 years ago, this all changed. Over the next thousand years or so, the landscape changed to the desert we recognize today. This change was recorded in sediments.


Figure 1. A map of climate zones in Africa during the African Warm Period

Saharan dust gets blown into the Atlantic Ocean, where it is deposited as sediment that is recognizably Saharan. Typically, the fewer plants to cover the ground, the more dust gets blown into the ocean. When the African Humid Period ended, the amount of sediment that got buried dramatically increased, making an abrupt transition if you are looking down a sediment section like you would a timeline.

So, based on sediment records, it looks like the African Humid Period ended and the Saharan desert established very quickly. To go from observations in sediments and other type of climate records, scientists will use reconstructive models. In the past 20 years, various models have been made that either support a very fast transition from a lush, green Saharan grassland to a Saharan desert, or a more gradual transition.

Figure 2. Example of lake levels in Africa during the African Humid Period, around 9,000 years ago. From Tierney et al., 2011.

Recently, scientists from Germany and Switzerland asked if a gradual transition from green to desert could cause a dramatic shift in the amount of dust blown from the Sahara to the ocean. To do this, they used models that include both dust transport and the climate.

The experiment: The scientists used a model called ECHAM-HAM, and compared modern day results to other models to make sure the model was working well for their region. They then looked at two different scenarios, and estimated the amount of dust that would be deposited at specific ocean locations in each case. These locations were where sediment cores had been taken, and gave the researchers something to compare their estimates to. If the scientists’ estimates were close to the actual amount of dust in the sediment, then the scenario they were exploring is more likely.

The scientists were exploring two scenarios that had to do with the idea that even a gradual process can cross a threshold, which could result in an abrupt change in another process, such as dust deposition. The scenarios here were:

  1. The Vegetation Fraction Threshold, in which you must lose a certain amount of vegetation (plants) covering the ground before you get large amounts of dust blown to the ocean.
  2. Latitudinal Threshold: Plants and lakes must shift a certain amount southward before large amounts of dust deposition happen.

Results: In scenario number 1, the amount of plants and lake covering the Sahara were decreased slowly. This did not cause an abrupt change in the amount of dust deposited in sediment. In scenario number 2, the location of the plants and lakes were modeled to move southwards over time. Like scenario 1, this did not cause an abrupt increase in dust deposited. Both gradual scenarios appeared to have gradual increases in dust deposition to the ocean.

By NASA - Cropped from Image:Africa satellite plane.jpg., Public Domain, https://commons.wikimedia.org/w/index.php?curid=1654153

Figure 3. A satellite image of current day Saharan desert.


The scientists who did this study concluded that there must have been an abrupt change from a Sahara with green grasslands and lakes to the desert we see today. The scientists do make the distinction, however, that this is not the same throughout the region. The sediment from locations further south show a more gradual increase in the amount of dust deposited during the transition from a lush and desert Sahara.

This is just one of many examples of how things in the ocean, like sediments, can be used to tell us about the past! Things environment can be cleverly used as ‘proxies’ for finding out past climate events, determining what life in the past was like, and more!


No comments yet.

Post a Comment


  • by oceanbites 2 months ago
    Happy Earth Day! Take some time today to do something for the planet and appreciate the ocean, which covers 71% of the Earth’s surface.  #EarthDay   #OceanAppreciation   #Oceanbites   #CoastalVibes   #CoastalRI 
  • by oceanbites 3 months ago
    Not all outdoor science is fieldwork. Some of the best days in the lab can be setting up experiments, especially when you get to do it outdoors. It’s an exciting mix of problem solving, precision, preparation, and teamwork. Here is
  • by oceanbites 4 months 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 5 months 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 5 months 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 5 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 6 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 6 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 7 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 7 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 7 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 7 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 8 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 8 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 9 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 9 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 10 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 10 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 11 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 11 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 
WP2Social Auto Publish Powered By : XYZScripts.com