A team of researchers from Rice University, the University of Nebraska-Lincoln, and Ohio State University recently published a paper in the May 2015 issue of Arctic, Antarctic and Alpine Research about algae discovered in frozen ice cores (long tubes drilled into frozen ice or soil). The researchers were traveling in the Andes mountaintops of Peru, collecting cores and ice samples to examine carbon content. Many Arctic and other cold-climate scientists use ice cores and frozen soil to see what the environment was like thousands of years ago. This is where much of what we know about ice age and prehistoric climates comes from. This particular team, although looking for carbon, instead found an abundance of preserved microscopic algae in their samples. These algae are a specific type of protist known as diatoms.
Diatoms are single-celled photosynthetic algae that are usually transparent because most of their composition consists of the element silicon, the main component in glass. So diatoms are effectively “glass organisms.” Silicon is also virtually non-degradable; diatom bodies are easily preserved and do not readily decompose. Being such small and simple organisms, diatoms often form the basis of many ecosystems and food chains. They are commonly found in soil and aquatic ecosystems and are one of the most abundant kinds of organisms found on the planet. By obtaining their nutrients and energy from water and sunlight, they have managed to live in almost any climate containing water. Although their discovery in the Peruvian Andies was previously unknown, it was not altogether surprising.
These extraordinary protists were discovered on a Peruvian mountain peak called the Quelccaya Ice Cap. Although Peru is currently tropical, the peak of this mountain is frozen and glaciated. Frozen diatoms have also been found in the glaciers of Greenland and Antarctica, but their presence doesn’t always mean that the organisms once lived in that particular location. Antarctica is known to have been almost entirely tropical in times when the continents formed Pangea, so its diatoms probably originated in place when Antarctica’s water was liquid. Greenland’s diatoms however, came from far away, transported by global air circulation that picked up dust from North America. A good example of a similar circulation pattern occurring today is the dust from the Sahara Desert traveling across the Atlantic and over the Americas. The question then becomes how the newly discovered Peruvian diatoms came to rest at this ice cap.
Further investigation showed that although global dust was also present in the core, it made up such a small percentage that dust was ruled out as a mode of transport. Also, many of the diatoms are so well preserved that it was judged that they could not have traveled a long distance before freezing at the mountain summit. The ice cores date from about 2,000 years ago and the species composition correlates well with living diatom communities in nearby lakes and ponds at the base of the mountain. This suggests that the top of this mountain was once tropical, and included liquid water with diatoms similar to those found today at the base. It’s truly amazing to think that such small and seemingly insignificant organisms can tell us so much about the Earth’s past only solely through their presence.