Laboratories

Microfossil Separation Lab

The microfossil separation lab was set up, and is operated, by Dr. Reed Scherer to support his research involving diatoms and the ice sheets of Antarctica. Diatoms are single-celled plants which inhabit both fresh and salt water. They secrete a frustule of silica the shape of which is diagnostic of the species, so they can be identified in the fossil record. ( A frustule can be thought of as being like the shell secreted by larger life forms, e.g. sea shells.) Because diatom populations are very sensitive to climate and other environmental factors, they can be used to investigate conditions that may have existed in the area of interest at some time in the past. Dr. Scherer is interested in the extent of ice sheet coverage as it has changed with time. If diatoms are found in sediments beneath grounded ice sheets ( ice sheets which are sufficiently thick that they rest on the bottom of the sea ) then this suggests the ice was absent from that area, or was at least sufficiently thinner that it was floating, at some time in the past. The age of the event can be estimated from a knowledge of the species of diatoms present and of their evolutionary history, which has been previously established.

View of Jochen Baier and lab interiorDiatoms are very tiny objects, ranging in size between 6 and 200 micrometers in long dimension. Because of that they are very easily moved about with air currents or on clothing, or can be tracked about on shoes, and the lab is therefore designed as a "clean" lab. This means that a lab coat is worn over street clothing, there are special disposable blue "booties" worn over street shoes, and that special practices are observed in the lab to prevent contamination of samples. Air in the lab is continuously filtered, and a positive pressure is maintained so that all leaks are from within the lab to the outside world, never the reverse. In the first photograph, Ph.D. student Jochen Baier is in the clean lab, demonstrating equipment he uses to prepare permanent microscope slides from sediment cores for his research.

View of Jessica Olney with micro sieveAs stated above, diatoms are very tiny objects. There are therefore special problems which attend separating them not only from the sediment in which they are found, but from one another. The second photograph, taken during an open house to inaugurate the new lab, shows Ph.D. student Jessica Olney inspecting a micro sieve machine, which can help accomplish this. The device employs sieves, some of which may have openings on the order of 5 micrometers across, to separate microfossils according to size. ( Imagine a sieve with square, tapered, smoothed openings that are 5 micrometers on a side, all cut with exquisite precision!)

Another problem which can develop is that the host material, whether it be sediment or ice, can hold a great many or very few microfossils. Diatom-rich sediment may contain on the order of 500 million diatoms per gram, whereas ice or glacial sediments may have something like a few thousand per gram. How, then, does one concentrate the few diatoms in an ice core so that they can be collected and examined?

Jochen Baier with separatory conesJochen explains that the answer has to do with these long plastic cones he's showing us. A section of ice core is placed in the cone and allowed to melt. The liquid is drawn off the bottom and passed through a micropore filter to recover the fossils. The ancient water is saved and sent to another lab for chemical analysis. Diatoms in the ice show that these tiny fossils can be carried by the wind for thousands of miles across the Antarctic wasteland.

The research carried out in the microfossil separation lab, and the associated ESEM, relate directly to the very important question of climate stability, colloquially referred to as "global warming." Are the ice sheets stable over time, or have they broken up before? If they have broken up in the past, what was the extent of the breakup, the time scale of it, and what were the causes? Evidence currently suggests, for instance, that there was at least one major disintegration of the West Antarctic Ice Sheet within the last 500,000 years -- long before man would have had a significant impact on the global ecosystem. These are the sorts of questions the microfossil separation lab is equipped to investigate.