Publications Vita | Publications | Conferences | Other interests

P.M. Poussart, and J. Tierney. On the use of benchtop scanning um-XRF for elemental studies of tropical trees. (In prep.)

P.M. Poussart, and D.P. Schrag and J. Tierney. Tracking El Nino from roots to shoots: Seasonally resolved d18O and Ca records from a Laguncularia racemosa Galapagos mangrove (In prep.)

P.M. Poussart, J. Tierney, J.Q, Chambers. A dendrochemical survey of ringless tree species from Manaus, Brazil. (In prep).

P.M. Poussart, N.J. Drenzek, A.L. Lima, T.I. Eglinton, C.M. Reddy and K.A. Hughen, 2005. The continental residence time of terrestrial biomarkers as determined by molecular level radiocarbon analysis. A case study from the Pettaquamscutt river basin (USA). (In prep).

P.M. Poussart, A. Lara and D.P. Schrag. Paleo-isotope dendroclimatology: 200 year delta 18O records of Fitzroya cupressoides from central Chile (In prep).

P.M. Poussart, S.C.B. Myneni, and A. Lanzirotti. Tropical dendrochemistry: A novel approach to estimate age and growth from ringless trees. Geophysical Research Letters, 33, (2006) L17711. [pdf] Article reviewed in News@nature

Abstract

Although tropical forests play an active role in the global carbon cycle and climate, their growth history remains poorly characterized compared to other ecosystems on the planet. Trees are prime candidates for the extraction of paleoclimate archives as they can be probed sub-annually, are widely distributed and can live for over 1400 years. However, dendrochronological techniques have found limited applications in the tropics because trees often lack visible growth rings. Alternative methods exist (dendrometry, radio- and stable isotopes), but the derived records are either of short-duration, lack seasonal resolution or are prohibitively labor intensive to produce. Here, we show the first X-ray microprobe synchrotron record of calcium (Ca) from a ringless Miliusa velutina tree from Thailand and use it to estimate the tree s age and growth history. The Ca age model agrees within 2 years of bomb-radiocarbon age estimates and confirms that the cycles are seasonal. The amplitude of the Ca annual cycle is correlated significantly with growth and annual Ca maxima correlate with the amount of dry season rainfall. Synchrotron measurements are fast and producing sufficient numbers of replicated multi-century tropical dendrochemical climate records now seems analytically feasible.

P.F. Poussart and D.P. Schrag. Seasonally-resolved stable isotope chronologies from northern Thailand deciduous trees. Earth and Planetary Science Letters, 235, (2005) 752-765. [pdf]

Abstract

Despite the existence of a number of climate proxies, the terrestrial expression of tropical climate variability over the past few centuries remains poorly resolved. We explore the applicability of stable isotope dendroclimatology as a tool for chronology and paleo-hydrology reconstruction on deciduous trees from monsoonal northern Thailand. Analysis of 11 trees coming from 4 different regions of northern Thailand yielded 7 records with varying degrees of delta 18O and delta 13C seasonality. We develop age models for trees lacking visible rings based on the seasonality of the delta 18O and find agreement to within less than 3 years with radiocarbon age estimates. We use the isotopic age models to reconstruct estimates of growth rates and find a significant positive correlation between growth and amplitude of the oxygen and carbon seasonal isotopic signals. A comparison of a reconstructed dendro-isotopic index from Pangmapa with regional rainfall records indicates significant correlations consistent with the locally-derived patterns but with decreased representation of the variance. Individual isotopic chronologies stemming from different tree species share common trends, which are also consistent with patterns of rainfall variability. We see an increase in the amplitude of the seasonal delta 18O cycle along with an increase in delta 18O_max over the past few decades suggesting a tracking of the recent drying trend of Thailand's monsoon.

P.F. Poussart, M.N. Evans, D.P. Schrag. Resolving seasonality in tropical trees: Multi-decade, high-resolution oxygen and carbon isotope records from Indonesia and Thailand. Earth and Planetary Science Letters, 218, (2004) 301-316. [pdf]

Abstract

Dendrochronological techniques have found limited applications in the tropics because of invisible or indistinct banding in wood. The seasonal cycles of rainfall and relative humidity in these regions, while not sufficient to produce distinct visible rings, may still generate seasonal signals in the oxygen isotopic composition of tree cellulose which can be used for climate reconstruction and chronology. We explore this approach using trees from Indonesia and Thailand, from three different families. Multi-decade delta 18O records from Javanese cross-dated teak rings and bomb radiocarbon-dated Suar wood lacking visible rings demonstrate the reproducibility of the signal between trees grown at the same locality as well as from wider geographical regions. These results confirm predictions that the trees oxygen isotopic signatures reflect an external climatic forcing. High-resolution delta 18O records reveal large seasonal cycles: up to 4 permil for Javanese Suar samples and up to 18 permil for a Thai Podocarpus sample. We show that the six delta 18O and delta 13C cycles measured on a Podocarpus match the number of growth years for the period spanning the time of wounding and cutting of the wedge section. This result demonstrates that the isotopic cycles found in this tree with indistinct annual rings are indeed seasonal and could be used for chronology. We present evidence that stable isotope chronologies of tropical trees also contain insights in tropical tree physiology and growth dynamics.

P.F. Poussart, D.P. Schrag and B.M. Buckley, 2003. Applications of tropical isotope dendroclimatology in Thailand (talk). AGU Fall Meet.

P.F. Poussart, D.P. Schrag, M.N. Evans and R.D. D'Arrigo, 2002. High resolution cellulose oxygen isotope records from Indonesian trees. In: EOS, Transactions, AGU. Vol. 83(47) Fall Meet. Suppl. p. F888

M.N. Evans, P.F. Poussart, S.R. Saleska and D.P. Schrag, 2002. Tracking ENSO with tropical trees: Progress in stable isotope dendroclimatology. In: EOS, Transactions, AGU. Vol. 83(47) Fall Meet. Suppl. p. F879

P.F. Poussart, 2000. El Nino: Signal du rechauffement planetaire?, Vertigo, Lettre de l'etranger, 1(2).

P.F. Poussart, A.J. Weaver and C.R. Barnes, 1999: Late Ordovician glaciation under high atmospheric CO2: A coupled model analysis. Paleoceanography, 14(4), 542-558 [pdf]

SB&F reviews:

Descent: The heroic discovery of the abyss, Brad Matsen, 2005.

Devil in the Mountain: A search for the origin of the Andes by Simon Lamb, 2004.

A celebration of the world's barrier islands by Orrin H. Pilkey and Mary Edna Fraser, 2003.

Prehistoric America: A journey through the ice age and beyond by Miles Barton, Nigel Bean, Stephen Dunleavy, Ian Gray and Adam White, 2003.

The weather by John Lynch, 2002.

Other:

Design of the Web Homepage of the Oak Bay Coast Guard Auxiliary Unit 33, (Spring 1998).

Design of an ethnographic map of Greater Vancouver. For inclusion in a paper published by Prof. Brian Ray, Urban Geography, McGill University, (Fall 1995).

Collective (Advanced Computerized Cartography course, Prof. Brian Ray), Ethnicity in the Metropolitan Region of Montreal, Department of Geography, McGill University, 1994.