Ancient DNA Uncovered From the Ocean Floor

What is there to do in the middle of the South Atlantic where the ocean is almost empty, no birds, few fish and very little plankton? It's the perfect place to look for ancient DNA on the ocean floor.

Over the millennia, continents have drifted in various directions but what has remained constant is the amount of water covering the earth, roughly 71%. Clues to the distribution of the water and the life forms it once contained can be found in the sediment at the bottom of the ocean. The real treasure of Davey Jones' locker is the ancient DNA hidden in the mud on the ocean floor 5 km below the surface.

Scientists investigate DNA of two different species of one-celled zooplankton that lived approximately 32,500 years ago. The tiny one-celled sea creatures under the microscope are foraminiferans and radiolarians. Some species of foraminifer are found fossilized in the sedimentary rock. However, there are also other species of foraminifera that do not fossilize. Their distributions and population size tell us a great deal about the climate, the ocean temperatures and areas of land that have only recently become covered by salt water. The White Cliffs of Dover are mainly composed of foraminifera remains, which attest that this area was once at the bottom of the ocean.

Pedro Martinez Arbizu, deep-sea biologist at the German Centre for Marine Biodiversity Research in Wilhelmshaven and author of the paper on South Atlantic DNA believes that the deep sea is the largest repository of ancient DNA providing a look back in time to previous biodiversity.

Micropaleontologist Bridget Wade of the University of Leeds says these new studies are "very exciting". Prior to being able to examine the DNA, there was no way of knowing how far back in time the goop at the bottom of the ocean could take us. These new findings are providing information that was never before found in the fossil records.

Researchers used pieces of DNA specific to radiolarians and foraminifera to sift out DNA from those particular groups. The DNA was then sequenced and compared to the known results of modern radiolarians and foraminifera. They discovered 169 different foraminifera species and 21 radiolarian species many of which were unknown because many of these foraminifera species don't fossilize.

According to Dr. Pawlowski, a foraminifera specialist from the university of Geneva, retrieving old DNA makes it possible to trace all species not just those that fossilize. Different species of foraminifera have different preferences for ocean temperature. Finding large amounts in a certain area gives us clues as to how the ocean temperatures have changed over time.

Another team retrieved DNA from the floor of the Black Sea, which used to be an inland lake, but became joined with the Mediterranean possibly some 9000 years ago. In the 980-meter deep waters ancient DNA revealed as many as 2700 different species including green algae, fungi and dinoflagellates, which are one-celled plankton. What the research shows is the decline of one kind of DNA and the rise of another, which is believed to coincide with the salinification of the Black Sea which researcher now believe to have occurred 600 years before previously thought.

Researchers believe these studies are able to shed some light on the history of the oceans, allowing them to put the pieces together like a giant jig-saw puzzle because much of the new information was not found in the fossil records.


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