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T2
Constraining peatland environmental change: exploiting the emerging eastern
North American crypto-tephrostratigraphic record
H. Mackay 1 *, P.D.M. Hughes 1 , P.G. Langdon 1
1 Palaeoenvironmental Laboratory (PLUS), Geography and Environment, University of Southampton
The relatively recent advances in tephrochronology have led to the investigation of nonvisible
(crypto) tephra horizons in sediment distal from volcanic origins. Such studies have
been predominantly centered on western Europe; however the potential of North American
cryptotephras is rapidly emerging. This not only facilitates the construction of more robust
chronologies in areas thought to be outside the scope of this technique, but also the
provision of isochrons enhances comparisons of environmental spatial synchronicity
across sites and regions.
Four tephrostratigraphies across a transect of peatlands in Maine, Nova Scotia and southwestern
Newfoundland have been constructed. A total of 18 horizons were detected over
the last ca. 4000 years, the preliminary geochemical analysis of which suggest that
constrained eruptions originate from the Cascade Range and Alaska ca. 5000-6000 km to
the west of the sites. These results complement the one existing record from eastern
Newfoundland (Pyne-O’Donnell et al. 2012), facilitating the extension of the late Holocene
crypto-tephrostratigraphic framework for the eastern seaboard of North America.
Peatlands are considered to be ideal archives for preserving tephrostratigraphies since
cryptotephra horizons are often present in discrete layers, thought to represent primary
airfall. Such preservation in this setting is critiqued here, assisted by radiocarbon
measurements.
The tephra horizons are used as pinning-points between records to address the wider aim
of the study: to examine the terrestrial manifestations of late Holocene climatic change
across an eastern North American climatic gradient. Of particular interest are the
temporal and spatial characteristics of changes in peatland accumulation and
reconstructed water table depth during the most dominant late Holocene climatic
perturbations: the Medieval Warm Period and the Little Ice Age. This time period is
constrained by the most dominant eruption, White River Ash (AD ~843), which is present
in all sites and the subsequent Mount St Helens eruption (AD ~1482) which is restricted to
the more northerly records.
Changes in bulk density, organic matter content, carbon content, plant macrofossil and
testate amoebae records investigate the relationship between peat accumulation and
changes in the moisture balance. Results reveal differences in the sensitivity of the four
peatlands to environmental change across the transect and to different climatic forcing
throughout the last 2000 years. The identification of these differences is facilitated by the
improved temporal precision; highlighting the role that crypo-tephrochronology plays in
enhancing palaeoenvironmental reconstructions and understanding of the environmental
history of eastern North America.
Keywords: cryptotephra, North America, isochrons, peatlands, palaeoenvironmental
change.
Pyne-O’Donnell et al., 2012. High-precision ultra-distal Holocene tephrochronology in North America.
Quaternary Science Reviews 52, 6-11.