Palynology

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thumb|A late Silurian sporangium bearing trilete spores. Such spores are the earliest evidence of life on land.">cite journal
author = Gray, J.
year = 1985
title = The Microfossil Record of Early Land Plants: Advances in Understanding of Early Terrestrialization, 1970-1984
journal = Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences (1934-1990)
volume = 309
issue = 1138
pages = 167–195
url = http://links.jstor.org/sici?sici=0080-4622(19850402)309%3A1138%3C167%3ATMROEL%3E2.0.CO%3B2-E
accessdate = 2008-04-26
doi = 10.1098/rstb.1985.0077] Green: A spore tetrad. Blue: A spore bearing a trilete mark – the $Y$-shaped scar. The spores are about 30-35 μm across.Palynology is the science that studies contemporary and fossil palynomorphs, including pollen, spores, dinoflagellate cysts, acritarchs, chitinozoans and scolecodonts, together with particulate organic matter (POM) and kerogen found in sedimentary rocks and sediments. Palynology does not include diatoms, foraminiferans or other organisms with silicaceous or calcareous exoskeletons.

Palynology is an interdisciplinary science and is a branch of earth science (geology or geological science) and biological science (biology), particularly plant science (botany). Stratigraphical palynology is a branch of micropalaeontology and paleobotany which studies fossil palynomorphs from the Precambrian to the Holocene.

A History of Palynology

Early History

The earliest reported observations of pollen under a microscope are likely to have been in the 1640s by the English botanist Nehemiah Grew [cite book
last=Bradbury
first=S
year=1967
title=The Evolution of the Microscope
publisher=Pergamon Press
place=New York
pages=375 p] who described pollen, the stamen and successfully predicted that pollen was required for successful reproduction in plants. As microscopes began to improve further studies included work by Robert Kidston and P. Reinsch examined the presence of spores in coal and compared them to modern spores [cite journal
last= Jansonius
first=J
coauthors=D.C. McGregor
year=1996
title=Introduction, Palynology: Principles and Applications
journal=AASP Foundation
volume=1
pages=1–10
url=http://www.palynology.org/history/jansonmcgrgrhist.html] . The early pioneers also included Christian Gottfried Ehrenberg (radiolarians and diatoms), Gideon Mantell (desmids) and Henry Hopley White (dinoflagellates).

Modern Palynology

The earliest quantitative analysis of pollen was published by Lennart von Post who laid out the foundations of modern pollen analysis in his Kristiania lecture of 1916cite book
last=Faegri
first=Knut
coauthors= Johs. Iversen
title=Textbook of Pollen Analysis
publisher=Blackwell Scientific Publications
year=1964
place=Oxford] Pollen analysis was initially confined to Nordic countries because many early publications were in Nordic languages.cite journal
last=Faegri
first= Knut
title=In memoriam O. Gunnar E. Erdtman
journal=Pollen et Spores
year=1973
volume=15
pages=5–12
url=http://www.palynology.org/history/erdtman.html] This isolation ended with the publication of Gunnar Erdtman's thesis of 1921 when pollen analysis became widespread throughout Europe and North America for use in studies of Quaternary vegetation and climate change. The term "palynology" was introduced by Hyde and Williams in 1944, following correspondence with the Swedish geologist Antevs, in the pages of the Pollen Analysis Circular (one of the first journals devoted to pollen analysis, produced by Paul Sears in North America). Hyde and Williams chose "palynology" on the basis of the Greek words "paluno" meaning 'to sprinkle' and "pale" meaning 'dust' (and thus similar to the Latin word "pollen"). [cite journal
last=Hyde
first=H.A.
coauthors=D.A. Williams
title=The Right Word.
journal=Pollen Analysis Circular
volume=8
pages = 6
date=1944
url=http://www.geo.arizona.edu/palynology/riteword.html]

Methods of study

Palynomorphs are broadly defined as organic-walled microfossils between 5 and 500 micrometres in size. They are extracted from rocks and sediment cores both physically, by wet sieving, often after ultrasonic treatment, and chemically, by using chemical digestion to remove the non-organic fraction.

Chemical Preparation

Chemical digestion follows a number of steps. Initially the only chemical treatment used by researchers was treatment with KOH to remove humic substances; defloculation was accomplished through surface treatment or ultra-sonic treatment, although sonification may cause the pollen exine to rupture. The use of hydrofluoric acid (HF) to digest silicate minerals was introduced by Assarson and Granlund in 1924, greatly reducing the amount of time required to scan slides for palynomorphs. [cite journal
last=Assarson
first=G. och E.
coauthors=Granlund, E.
title=En metod for pollenanalys av minerogena jordarter
journal=Geol. foren. Stockh. forh.
volume=46
pages=76–82] Palynological studies using peats presented a particular challenge because of the presence of well preserved organic material including fine rootlets, moss leaflets and organic litter. This was the last major challenge in the chemical preparation of materials for palynological study. Acetolysis was developed by Gunnar Erdtman and his brother to remove these fine cellulose materials by dissolving them. [cite journal
last=Erdtman
first= O.G.E.
title=Uber die Verwendung von Essigsaureanhydrid bei Pollenuntersuchungen
journal= Sven. bot. tidskr.
volume=28
pages=354–358] . In acetolysis the material is treated with acetic anhydride and sulfuric acid, dissolving cellulistic materials and providing better visibility for palynomorphs.

Some steps of the chemical treatments require special care for safety reason, in particular the use of HF which diffuses very fast through the skin and could cause severe chemical burns.

Other treatment include kerosene flotation for chitinous materials.

Analysis

Once samples have been prepared chemically, samples are mounted on microscope slides using silicon oil, glycerol or glycerol-jelly and examined using light microscopy or scanning electron microscopy.

Researchers will often study either modern samples from a number of unique sites within a given area, or samples from a single site with a record through time, such as samples obtained from peat or lake sediments. More recent studies have used the modern analog technique in which paleo-samples are compared to modern samples for which the parent vegetation is known [cite journal
last=Overpeck
first=J.T.
coauthors=T. Webb, I.C. Prentice
year=1985
title=Quantitative interpretation of fossil pollen spectra: Dissimilarity coefficients and the method of modern analogs
journal=Quaternary Research
volume=23
pages=87–108
doi=10.1016/0033-5894(85)90074-2]

When the slides are observed under a microscope the researcher will count the number of grains from each pollen taxon. This record is then used to produce a pollen diagram. This data can be used to detect anthropogenic effects such as logging [cite journal
last=Niklasson
first=Mats
coauthors=Matts Lindbladh, Leif Björkman
title=A long-term record of "Quercus" decline, logging and fires in a southern Swedish "Fagus-Picea" forest
journal=Journal of Vegetation Science
year=2002
volume=13
pages=765–774
url=http://www.bioone.org/perlserv/?request=get-abstract&doi=10.1658%2F1100-9233(2002)013%5B0765%3AALROQD%5D2.0.CO%3B2
doi=10.1658/1100-9233(2002)013 [0765:ALROQD] 2.0.CO;2] , traditional patterns of land use [cite journal
last=Hebda
first=R.J.
coauthors= R.W. Mathewes
title=Holocene history of cedar and native cultures on the North American Pacific Coast
journal=Science
volume=225
pages=711–713
year=1984
doi=10.1126/science.225.4663.711
pmid=17810290] or long term changes in regional climate [cite journal
last=Heusser
first= Calvin J.
coauthors=L.E. Heusser, D.M. Peteet
title=Late-Quaternary climatic change on the American North Pacific coast
journal=Nature
volume=315
pages=485–487
year=1985
doi=10.1038/315485a0]

Palynology can be applied to problems in many fields including geology, botany, paleontology, archaeology, pedology (soil study), and geography.

Applications

Palynology is used for a diverse range of applications, related to many scientific disciplines:

* Biostratigraphy and geochronology. Geologists use palynological studies in biostratigraphy to correlate strata and determine the relative age of a given bed, horizon, formation or stratigraphical sequence.
* Palaeoecology and climate change. Palynology can be used to reconstruct past vegetation (land plants) and marine and freshwater phytoplankton communities, and so infer past environmental (palaeoenvironmental) and palaeoclimatic conditions.
* Organic palynofacies studies, which examine the preservation of the particulate organic matter and palynomorphs provides information on the depositional environment of sediments and depositional palaeoenvironments of sedimentary rocks.
* Geothermal alteration studies examine the colour of palynomorphs extracted from rocks to give the thermal alteration and maturation of sedimentary sequences, which provides estimates of maximum palaeotemperatures.
* Limnology studies. Freshwater palynomorphs and animal and plant fragments, including the prasinophytes and desmids (green algae) can be used to study past lake levels and long term climate change.
* Taxonomy and evolutionary studies.
* Forensic palynology- the study of pollen and other palynomorphs for evidence at a crime scene.
* Allergy studies. Studies of the geographic distribution and seasonal production of pollen, can help sufferers of allergies such as hay fever.
* Melissopalynology - the study of pollen and spores found in honey.
* Archaeological Palynology examines human uses of plants in the past. This can help determine seasonality of site occupation, presence or absence of agricultural practices or products and plant-related activity areas within an archaeological context. Bonfire Shelter is one such example of this application.

Because the distribution of acritarchs, chitinozoans, dinoflagellate cysts, pollen and spores provides evidence of stratigraphical correlation through biostratigraphy and palaeoenvironmental reconstruction, one common and lucrative application of palynology is in oil and gas exploration.

Palynology also allows scientists to infer the climatic conditions from the vegetation present in an area thousands or millions of years ago. This is a fundamental part of research into climate change.

References

*Moore, P.D., et al. (1991), "Pollen Analysis" (Second Edition). Blackwell Scientific Publications. ISBN 0-632-02176-4
*Traverse, A. (1988), "Paleopalynology". Unwin Hyman ISBN 0-04-561001-0
*Roberts, N. (1998), "The Holocene an environmental history", Blackwell Publishing. ISBN 0-631-18638-7

External links

* [http://www.geo.arizona.edu/palynology/ifps.html International Federation of Palynological Societies]
* [http://www.palynology.org American Association of Stratigraphic Palynologists, Inc. (AASP)]
* [http://www.shef.ac.uk/uni/academic/N-Q/palysc/index.html Centre for Palynology, University of Sheffield, UK]
* [http://www.ifpindia.org/Palaeoenvironments-in-South-India.html Palynology Laboratory, French Institute of Pondicherry, India]
* [http://www.rbgkew.org.uk/scihort/palyn.html The Palynology Unit, Kew Gardens, UK]
* [http://www.paldat.org/ PalDat, palynological database hosted by the University of Vienna, Austria]
* [http://www.nhm.ac.uk/hosted_sites/tms/ The Micropalaeontological Society]
* [http://www.palynology.org/ The American Association of Stratigraphic Palynologists (AASP)]
* [http://www.shef.ac.uk/~cidmdp/ Commission Internationale de Microflore du Paléozoique (CIMP)] , international commission for Palaeozoic palynology.
* [http://www.cimp.ulg.ac.be/Acritarchs.html CIMP Subcommission on Acritarchs]
* [http://www.cimp.ulg.ac.be/Chitinozoans.html CIMP Chitinozoan Subcommission]
* [http://www.linnean.org Linnean Society Palynology Specialist Group (LSPSG)]
* [http://www.scirpus.ca/cap/cap.shtml Canadian Association of Palynologists]
* [http://www.geo.arizona.edu/palynology/polident.html Pollen and Spore Identification Literature]