Number crunching in palynology

Simulated pollen counts
Simulated pollen counts

HOW DO WE UNDERSTANT PAST VEGETATION CHANGE?
Our understating of vegetation in the past, and how it has changed through time, comes mainly from the examination of macrofossils (e.g. wood and leaves) and microfossils (e.g. pollen and spores) found in the sedimentary record. The potential for microscopic fossils to provide an insight into past vegetation change on a landscape scale was pioneered by von Post (Von Post, 1916, reprinted 1967) and has been subsequently used to understand changes in regional floras (Godwin, 1956), and address conservation issues (Willis et al., 2007). Analysis of fossil pollen and spores (palynology) is now widely used on late Quaternary timescales to answer ecological questions linking vegetation and wider environmental/climatic change; these include:

  • Has there been a change in major vegetation type (biome)? For example a change between woodlands and grassland vegetation.
  • How have the ecosystem dynamics altered? For example the presence or absence of fire.
  • How has the diversity within the ecosystem changed? For example increase or decrease in sample richness.

Palynological analysis relies on obtaining a sub-sample of the pollen contained within the sediment at a specific depth (time) which allows the vegetation at that time to be reconstructed. This sub-sample is known as a pollen count. To build up a picture of vegetation change through time it is necessary to generate a sequence of pollen counts. The size of the sub-sample (pollen count) required from any particular depth (time period) is dependent on the nature of the vegetation association being investigated and the ecological question being addressed . For example, the amount of pollen analysed to determine if the vegetation was predominantly wooded or grassland is different to that required to provide information on the biological diversity within the vegetation assemblage.

Discussed below are some of the conventions related to choosing an appropriate pollen count size within palynology, with particular reference to the challenges of dealing with diverse tropical floras.

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PCRG March

In March the Palaeoenvironmental Change Research Group (PCRG) have been involved with data collection in the labs, training, fieldwork planning (and un-planning) and outreach.

Two notable pieces of pollen data collection have made significant progress this month: 1) Hayley has been working at collecting data to establish what is a suitable pollen count size to assess vegetation change within her highly diverse Amazonina samples, and 2) Lottieis on to about the last dozen samples to complete the overview of 500,000 years of pollen from Lake Bosumtwi (Ghana); an amazing pollen record and an excellent research effort which will be the cornerstone of her PhD thesis! More soon on both these pollen stories as they unfold… In addition, I am pleased to report that the list of taxa within our pollen reference collection has finally been fully digitized – Thank you Jason; details of the >3000 taxa collection will soon be available on the lab web pages.

Gigantic Prasinophytes (>100 microns)

Also in the lab: Alice Kennedy, working on ‘deep time’ palaeoecology, has identified a bloom in the foraminifera Reinholdella macfadyeni and gigantic Prasinophytes associate with marine annoxia in sediments from Yorkshire. Will be interesting to find out what these all mean at the next lab meeting!

At the beginning of March four of us (Frazer, Hayley, Lottie and myself) attended a First Aid for field work training course run by Mediact. The course was excellent with plenty of useful information and the opportunity to practice techniques such as cardiopulmonary resuscitation (on dummies) and bandaging (on each other). Unfortunately we will have to wait to practice any of the techniques in the field as our planned trip to Ecuador looks likely to be postponed due to injury to one of our members! Get well soon Frazer 🙂 On the up side this should allow me to catch up with the piles of papers I should be writing.

The month finished with an exciting outreach event. I was asked to present our research to the Oxford Geology Group. The event was hosted at the Oxford University Museum of Natural History. It was an excellent day of talks and it was fun to discuss our research with interested people.

PCRG February

Laboratory activity has continued through February with progress on pollen counts (Lottie and Hayley) and chironomid (non-biting midges) picking (Frazer). Hayley also managed to escape the microscope lab for a short period: 1) to commence work on selecting samples from tephras for Ar-Ar dating, and 2) to counduct loss-on-ignition analysis of organic samples to identify the constituents of her sediment. I did not make it on to the microscope 😦

I was however very pleased to welcome Macarena Cardenas back into the lab as a visiting Research Fellow. Maca will be working on the pollen reference collection, assisting with PhD student analysis and continuing to write papers during her renewed association.

Frazer, Hayley and I have also begun planning for field work in Ecuador for April-May. We will be working in collaboration with the Instituto Geophisico in Quito and the plan is to visit the Mera site which Hayley is working on, and to collect lake surface samples for Frazer to examine the midges. In preparation for the collection of midges samples expert, and project co-supervisor, Steve Brooks (Natural History Museum) visited for a day to brief us on how best to do this.

Away from research I have been working on writing exam questions and tutor marked assignments for the level 3 module The geological record of environmental change (S369, to those familliar with OU codes!). Hopefully, I have managed to set some interesting and challenging tasks for our students. . .

Relay team palaeo

The Open University Les Irvine Memorial Relay 2012 "Team Palaeo"The 21st The Open University Les Irvine Memorial Relay was held yesterday (29/02/2012) and four teams from the Environment, Earth & Ecosystems department were entered amoung the 40 which took part. Run over four legs and covering a 1.1 mile course at Walton Hall it was another fun event.

For the third year running a team of palaeoecologists took part. This year “Team Palaeo” comprised Hayley Keen, myself, Frazer Bird and Lottie Miller (left to right on photo) and we were the fastest finishing team from the department!

Nitrogen isotopes in lake sediments

COMMENT ON THE USE OF NITROGEN ISOTOPES IN PALAEOLIMOLOGICAL STUDIES
As a component of my doctoral research, I am examining nitrogen (N) isotopes within sediments obtained from Lake Bosumtwi (West Africa). Below I review and comment on the key uses and limitations of using N isotopes to interpret past environmental change with particular reference to lake sediments. Discussion is based on the key text by Talbot (2001).

REFERENCE
Talbot, M.R. 2001. Nitrogen isotopes in palaeolimnology. Tracking environmental change using lake sediments. Volume 2. Physical and geochemical methods (ed. by W.M. Last and J.P. Smol), pp. 401-439. Kluwer Academic Press, Dordrecht.

NOTE: This text is avaliable to Open University students as an ebook via the library

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British Ecological meetings

BES careers 2012

I am currently a member of the British Ecological Society (BES) council. The BES is a ‘learned society’ based at Charles Darwin House in London which publishes four academic journals, has thousands of members and is open to anyone with an interest in ecology. As part of my role on council I serve on two committees which run different aspects of the societies activity: 1) meetings, and 2) education, training and careers. This month we have had meetings of both these committees. Two highlights of the societies activity related to these committees were:

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Thinking about proxies

COMMENT ON DISCUSSION OF PROXIES IN HUNTLEY (2012)
All areas of research have strengths and limitations which are readily acknowledged by the scientists involved. The reconstruction of past climates (palaeoclimates) from biological indicators contained within the fossil record (proxies) presents some specific challenges; for example key limitations might be gaps in a sedimentary sequence or post-depositional degradation of samples. Understanding and interpreting data sets in the face of these challenges require the researcher to develop a wide range of skills. Huntley (2012) focuses upon the uncertainties within palaeoclimate reconstruction which he considers to be “frequently overlooked” (p. 2) by scientists making climate reconstructions from proxy records. Specifically Huntley urges researchers to consider carefully:

  • What a given proxy is actually capable of reconstructing, i.e. what climate variables controls its distribution?
  • What other variables might be influencing the proxy, i.e. could there be multiple influences, might these vary through time?
  • What is the spatial relevance of the proxy, i.e. macro versus micro scale?
  • Can multiple proxies be compared, either within or between sites?

In other words: which and how many climatic variables can be reconstructed form any one aspect of the fossil record?

Below I review and comment on some key arguments made by Huntley (2012) related to the use of proxies in reconstructing palaeoclimates.

REFERENCE
Huntley, B. (2012) Reconstructing palaeoclimates from biological proxies: Some often overlooked sources of uncertainty. Quaternary Science Reviews 31: 1-16.

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PCRG January

January 2012 has been a busy one for the Palaeoenvironmental Change Research Group members we have been getting out and about (attending three research meetings), there has been activity in the labs (pollen, chironomids and geochemical analysis all being undertaken) and developments with the publication of our research (book chapter published and two papers moved along in the publication process).

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Environmental change in the humid tropics and monsoonal regions

JUST PUBLISHED
Bush, M.B. & Gosling, W.D. (2012) Environmental change in the humid tropics and monsoonal regions. The SAGE handbook of environmental change: Volume 2. Human Impacts and Response (ed. by J.A. Matthews, P.J. Bartlein, K.R. Briffa, A.G. Dawson, A. De Vernal, T. Denham, S.C. Fritz and F. Oldfield), pp. 113-140. SAGE, London. ISBN: 978-0-857-02360-5

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Open University Geological Society

Last Saturday (21st January) the West Midlands Open University Geological Society held a day of lectures at the Department of Earth Sciences, University of Birmingham. I was one of five invited speakers who covered a wide range of topics related to geology: Snowball Earth (McMillan, Birmingham), earthquakes in Chile (Ryder, Liverpool), salt mines of Cheshire (Carlon), Icelandic eruptions (Watson, Bristol) and myself on glacial-interglacial cycles in the tropics. The Dome lecture theater was full and it was exciting to be able to engage OUGS members directly with reaserch being conducted in the Palaeoenvironmental Change Research Group at The OU. Therefore, many thanks to Ron Whitfield for inviting me and organising the event. I will certainly be recommending attending and speaking at these events to my departmental collegues.

Visit the OUGS website to find out about other activities and events like this.

Hutton Club

On Friday I had the privilege of presenting research from the Palaeoenvironmental Change Research Group to the Hutton Club at the University of Edinburgh (Institute of Geography). My talk, entitled “Assessing the impact of Quaternary glacial-interglacial cycles in the tropics”, drew on: 1) empirical data on past vegetation change from sedimentary records spanning multiple glacial-interglacial cycles; Lake Titicaca (370,000 years), Erazo (middle Pleistocene) and Lake Bosumtwi (500,000 years), and 2) model climate-vegetation data from the GENIE-1 model. The combination of these new long tropical records with model data strongly suggests that the long-term pattern of vegetation response to global glacial-interglacial cycles is differently structured at low-latitudes when compared with mid-latitudes. The different pattern of change suggested in response to past global climate variation might suggest that the response of tropical vegetation change to predicted future climate change could be different to that anticipated for mid- and high-latitudes.

To find out more check out the references below.

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Biodiversity & Ecosystem Services

PAGES (Past Global Changes)
Focus 4: (Past) Human-Climate-Ecosystem Interaction (PHAROS)
Biodiversity Theme Workshop at the Department of Zoology, University of Oxford (9-11 Jan)

Using fossil records to map potential threats, opportunities and likely future developments for biodiversity and ecosystem services
Organised by: Dr. Elizabeth Jeffers, Dr. Shonil Bhagwat and Prof. Kathy Willis

This small (about 30 attendees) workshop brought together academic researchers mainly working in the field of past environmental change to discuss the use, and potential use, of data sets in understanding the key environmental challenges facing society. The bulk of the discussion took place with reference to ‘ecosystem services’. Three types of ecosystem service were mentioned early on for which it was thought that the fossil record can provide a unique long term perspective (beyond historical records): 1) provisioning services (e.g. food, timber, biofuels), 2) regulating services (e.g. carbon), and 3) cultural services (e.g. national parks, tourism).

Below I will summarize some of the issues discussed. Please note that this does not cover the full range of discussion or all of the many high quality contributions. For further information click here to visit the workshop web page.

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