16 April 2004

Gypsum Crystals, Soot, Spores and Protozoa in New Mexico Snow

Forrest M. Mims III

In the last installment of this column, we were cruising along highways in West Texas and New Mexico in my old 1982 pickup trying to capture a few particles of soot blown across the Pacific Ocean from major fires in Southeast Asia. In addition to some sophisticated instruments, I used a super simple air simpler made by attaching a loop of clear tape to one end of a plastic tube.

Those Asian fires pumped large volumes of smoke across much of the United States during March and early April 2004. On some days the smoke reached Africa.

Soot fell from the smoke only in some regions, and I was trying to find one of them during my field trip to New Mexico. After sunset on 26 March in Las Cruces, dark layers over the horizon resembled smoke layers I have seen elsewhere on many occasions. Measurements with an Aerocet laser particle counter showed no unusually high particle counts like those measured in Texas when smoke arrives from Central American each spring. Thus, while the smoke was overhead, little or none was near the surface.

On 27 March, the smoke high in the sky caused a pronounced solar aureole, a bright glow around the Sun. The aureole had the same appearance from the Sacramento Mountains and from the basins below. The aerosol optical thickness (AOT) was very high for the usually clear New Mexico sky. At 440 nm in the blue, the AOT was 0.30. This is several times higher than the clear sky AOT. The AOT was only slightly higher when measured from the plains between the mountains and Artesia, which suggests that the smoke layer was very uniformly dispersed and well above the mountains.

I measured the AOT using two Solar Light Microtops Sun photometers (www.solar.com) and a GLOBE Sun photometer (www.globe.gov) based on the VHS-1 design given by Mims at www.concord.org/haze. Shawn Carlson described the basic design in The Amateur Scientist ("When Hazy Skies are Rising," Scientific American 276, 106-107, May 1997; see The Amateur Scientist 2.0 CD available from the SAS store at http://www.sas.org/Merchant2/merchant.mvc).

The smoke was so thick that I also measured the solar spectrum from 290 nm to 1200 nm using an Ocean Optics fiber optic spectrometer (www.oceanoptics.com). These data will be compared with similar spectroscopic measurements of sunlight made through very clear skies at the summit of Mauna Kea in Hawaii and through smoke arriving in Texas from Central America.

A microscopic view of the tape from my ultra simple air sampler exposed during 16 kilometer (10 miles) transects along highways and at various fixed sites revealed mineral grains, insect fragments, plant matter, a few pollen grains and several genuses of fungal spores, including Alternaria, Curvalaria, Cladosporium and one that resembles Stemphylium.

There was very little carbon on the tape samples until the return trip. On Highway 285 north of Fort Stockton, Texas, on the evening of 27 March, many apparent carbon particles were collected in a region where the the Naval Research Lab's smoke forecast showed Asian smoke at ground level. During this transect, a dark band lined the eastern horizon. This band was apparently smoke. While this tape sample is important, it and the others took a back seat to samples collected by nature high in the Sacramento Mountains between Cloudcroft and the National Solar Observatory.

Large patches of snow were still on the ground in many areas when I drove through on 25 March. So I stopped for a closer look and was surprised to find that the snow was covered by a layer of dust.

On February 19, a huge dust storm blew fine gypsum crystals from White Sands National Monument into and over the Sacramento Mountains. Apparently this storm deposited considerable material on the mountain snow.

I collected some of the dirty snow in fresh sandwich bags purchased at a store in Cloudcroft. I also collected some clean snow under the dirty layer. After checking in at a motel in Alamogordo, I placed a single drop of the dirty snow melt on a glass microscope slide and began examining it through a microscope placed on the hood of my pickup. The drop was filled with dust, black carbon particles and spores. Within a few minutes, the water evaporated in the dry New Mexico air, leaving behind an easily examined crust of particulate matter.

The snow was so interesting that I decided to return for more samples. I purchased some clear plastic bottles, alcohol and a plastic spreader at an Alamogordo department store. I sterilized the bottles, rinsed them with distilled water and collected both clean and dirty snow on the morning of the return trip on 27 March. Back home, I placed single drops of snow melt on microscope slides and began scanning them through a better microscope, the one our daughter Sarah used to finalize her discovery of fungal spores in smoke from Yucatan.

A single drop of the dirty snow melt contained a few thousand fungal spores and many thousands of tiny grains of gypsum! Also present were transparent orange crystals and what appeared to be a few slivers of volcanic glass, possibly from the lava fields just north of White Sands.

The snow melt also contained many tiny flecks of apparent soot. Because the Asian smoke dropped considerable soot over the Sacramento Mountains, at least according to the Naval Research Lab's NAAPS smoke and aerosol forecast model (http://www.nrlmry.navy.mil/aerosol/), it is quite possible that some of this soot had crossed the Pacific Ocean. Local sources could be generally ruled out, for the clean snow below the dirty layer was largely devoid of soot.

The presence of the many fungal spores poses interesting questions. Some may have been local while others may have arrived with the dust. Based on my daughter Sarah's discovery of viable fungal spores arriving in Texas with smoke from Central America, (http://earthobservatory.nasa.gov/Study/
SmokeSecret/smoke_secret.html), maybe some of the spores arrived with the Asian smoke.

The spores include representation from the genuses Alternaria, Nigrospora, Curvalaria, Cladosporium, Penicillium (or possibly Aspergillus) and what resembles the ascospores Splanchnonema and Leptosphaeria. The most common spore in the snow melt is not shown in E. Grant Smith's "Sampling and Identifying Allergenic Pollens and Molds" (Blewstone Press, 2000) or Bryce Kendrick's "The Fifth Kingdom" book and CD (Mycologue Publications, 2000). These spores consist of two attached, slightly flattened spheres around 5 micrometers in diameter. The most similar spore in Smith is from Fuligo septica, a Myxomycete or slime mold. If these spores are indeed from slime molds, then their source might be dead trees in the immediate vicinity of the snow where the samples were collected. I plan a return visit to see what kinds of slime molds are growing in the area where the snow was collected.

I'll close with another mystery. While observing various drops of snow melt through the microscope, often the particle being inspected would suddenly begin to move. This made photography a bit difficult. Closer examination revealed that the particles were being disturbed by the rapid movement of tiny aquatic creatures through the water. These were unicelluar protozoa

Some of the protozoa in the New Mexico snow melt resembled transparent spherical and oblong Christmas tree ornaments. Others were more like cylinders. All were only about 10 micrometers in size, and most moved very rapidly. How those protozoa ended up in that dirty alpine snow I collected raises fascinating questions about the transport of all kinds of biological materials over considerable distances.

To answer some of these questions, I contacted Dr. Ronald Hoham of Colgate University. Hoham is one of a handful of biologists who study snow ecology. He told me about rotifers, which are much larger than protozoa, that can also be found in snow. One of their principle foods is algae that live in snow.

Did the protozoa I collected arrive from a dry lake bed in the Tularosa Basin below the Sacramento Mountains? Or is it possible that some of them arrived with the Southeast Asian smoke? Next spring when dust blows up to the Sacramento Mountains, I hope to find the means to again visit. This time, I will capture some dust from the air, place it in water and look for protozoa.

Forrest M. Mims III and his science are featured online at www.forrestmims.org.

This is an expanded version of a feature originally published in Forrest Mims's weekly science column in the Seguin Gazette-Enterprise, Seguin, Texas. The column is written for a general audience.