Ian D. Campbell

Late Holocene ,-..; 1500 yr climatic periodicities and their implications

Fourier and nonlinear regression analysis of a 4000+ yr paleoclimate proxy record in western Canada shows strong periodicities of ∼1500 yr and several weaker century- to millenial-scale periodicities. In conjunction with the 23 708 yr Milankovitch periodicity, these produce a model of climate fluctuation through the postglacial consistent with recognized paleoclimatic fluctuations of the past 15 000 yr in the northern mid-latitudes. These results suggest that postglacial climatic anomalies such as the Little Ice Age and the Younger Dryas were at least in part periodic phenomena rather than the result of unique, aperiodic events. Projecting these periodicities into the future suggests that even in the absence of anthropogenic climate forcing, a natural warming trend will continue until ca. a.d. 2400.

Long-distance transport of pollen into the Arctic

Airborne particulates can be carried over long distances, but for significant quantities of particulates larger than a few micrometres in diameter to be transported more than a few kilometres usually requires a means of injecting the material high into the atmosphere, such as a volcanic eruption, forest fire or desert windstorm. But an unusual event occurred in the Canadian Arctic last year, in which significant amounts of pine and spruce pollen (30-55 μm long) were transported roughly 3,000 km.

Pollen preservation: Experimental wet‐dry cycles in saline and desalinated sediments

Abstract Experimental degradation of pollen by repeated wet‐dry cycles in saline and desalinated sediments show differences in preservation between taxa and between salinity environments. In desalinated sediment, from which the salts were removed artificially, pollen is rapidly degraded, with a significant net loss of pollen after ten wet‐dry cycles. Picea pollen, which remains identifiable even when heavily damaged, suffers greater breakage in desalinated sediments. Artemisia pollen is rapidly rendered unidentifiable by degradation of the sculptural elements in both saline and desalinated sediments. In comparison to desalinated sediments, saline sediments appear to contain less damaged pollen. Growing salt crystals may envelop the pollen grains and stabilize them against mechanical breakage otherwise incurred by flexing of the pollen wall during desiccation. Caution should be exercised when analyzing sediments subject to wet‐dry cycles, and laboratory procedures modified if necessary to avoid desiccation...

Modelling long-term peatland dynamics. I. Concepts, review, and proposed design

This article reviews the existing conceptual and simulation models for peatlands and develops a model framework for simulating peatland dynamics in boreal regions. Clymos peat bog growth model has been used as the conceptual foundation in published simulation models, but in these models the structural and functional layers of litter, acrotelm and catotelm are not dynamically integrated. Organic-matter decomposition processes in these layers operate at different rates over various time scales. The processes in more active litter and acrotelm layers largely pre-determine the net peat accumulation in the catotelm. On the basis of evaluating litter and peat-core data, we propose a model design that connects different layers through changing water-table depth, driven by effective moisture. The model framework includes single and double negative exponential decay functions that together produce net peat accumulation or degradation and hence carbon balance. The model is designed to be generic in structure, but can be validated using estimated parameters and observed peat accumulation data for continental western Canada. The objectives of this model exercise are (1) to understand the interactions of different biological and environmental factors in boreal peatlands, and (2) to realistically simulate peat accumulation and decay over the last several millennia using proxy paleoclimate data as drivers and peat profiles for validation.

Long-Term Perspectives on Fire-Climate-Vegetation Relationships in the North American Boreal Forest

The ecological role of fire in the modern boreal forest has been reviewed by several authors (Wright and Heinselman 1973; Wein and MacLean 1983; Johnson 1992, Payette 1992). Wildfire and climate are intimately linked (Swetnam 1993). Shorter-term weather patterns are clearly an important determinant of fire activity at daily-to-monthly time scales. At longer time scales of decades and centuries, Swetnam (1993) has shown that fire occurrence in Giant Sequoia groves was related to climate. However, other factors such as topography and fuel play a role in the fire regime. Fuel type, structure, moisture, accumulation, density, flammability, and continuity can affect the fire regime.1 An extreme example highlighting the role of fuel can be found in many deserts where fires should be frequent due to the hot and dry environment but are absent because there is no fuel. Therefore, climate controls fire directly through opportunities for ignition and spread but also through regulation of the accumulation and structure of fuel at decadal or greater time scales.

A first estimate of organic carbon storage in Holocene lake sediments in Alberta, Canada

This paper reports a first estimate of the Holocene lake sediment carbon pool in Alberta, Canada. The organic matter content of lake sediment does not appear to depend strongly on lake size or other limnological parameters, allowing a simple first estimate in which we assume all Alberta lake sediment to have the same organic matter content. Alberta lake sediments sequester about 15 g C m-2 yr-1, for a provincial total of 0.23 Tg C yr-1, or 2.3 Pg C over the Holocene. Alberta lakes may represent as much as 1/1700 of total global, annual permanent carbon sequestration.

CANPLOT: a FORTRAN-77 program for plotting stratigraphic data on a PostScript device

Abstract Many types of stratigraphic data (for example pollen, diatoms, bulk geochemistry) are presented conveniently in a depth/frequency diagram having several frequency curves on a common depth scale. CANPLOT is a FORTRAN-77 program for plotting such stratigraphic data on a PostScript output device. Several options are included, such as stratigraphically constrained cluster analysis of the data, and a variety of graphical enhancements for producing camera-ready figures.

The late Holocene paleohydrology of Pine Lake, Alberta: a multiproxy investigation

This paper reports on a high-resolution, multi-proxy, late-Holocene study from a lake in the Aspen Parkland of southern Alberta, Canada. A sediment core spanning the last 4000+ yrs from Pine Lake was analyzed for charcoal, granulometry, grain roundness, tephra content, geochemistry, mineralogy and pollen. This multi-proxy record indicates: (1) increasing anoxia causing a shift in S deposition from gypsum to pyrite due to increasing moisture availability in the late Holocene; (2) a decrease in Mg flux into the lake due to the development of the aspen forest, which reduced water flow through the Mg-rich shallow sand aquifer; the aspen forest expansion was in turn induced by the extirpation of plains bison prior to settlement; and (3) a change in the upland fire regime from frequent low-biomass grass fires to less frequent but higher biomass under-story fires, also as a result of the expansion of the aspen forest. Not only are the different proxies sensitive to different rates and magnitudes of change, they also show different sensitivities to different types of hydrological change: the mineralogy and geochemistry are sensitive to changes in water level and redox potential, and to changes in the relative strengths of the aquifers feeding the lake, while the granulometry is sensitive to total hydrological balance. Thus, apparently contradictory proxy results should be viewed as complementary.

Power function for interpolating dates in recent sediment

Many paleolimnological studies deal with short cores; the upper 20 to 30 centimeters of lake sediment are often poorly compacted and it may be perilous to interpolate dates using straight lines. A power function (AGE=a+b*DEPTHc) provides a good approach for interpolating dates where only a few dated horizons are available in a core. This may be particularly useful where multiple short cores are taken from a single site, and dated by correlation of key horizons with a master core which is 210Pb dated. This approach assumes a constant rate of dry sediment deposition.

Fire-induced decrease in forest cover on a small rock outcrop in the Abitibi region of Québec, Canada

Abstract Rocky outcrops represent about 30% of the boreal forest of Abitibi, Québec, Canada. Although these outcrops have similar edaphic and climatic conditions, their vegetation can vary. Some are composed of a closed forest of black spruce (Picea mariana) and eastern white cedar (Thuja occidentalis), while others support open Pinus-dominated stands. A long-term study using palynology and charcoal analysis was used to determine the processes involved in creating the open vegetation observed on one outcrop located at Roquemaure. Changes in the fire regime through time seem to be the explanatory factor. Vegetation on this outcrop started 3,775 calibrated years ago as a closed Picea mariana-dominated stand. Increase in fire frequency ca 1,465 calibrated years ago led to the replacement of the Picea mariana-dominated stand by the more open Pinus woodland observed today. Changes in climate from wet to dry might explain this increase in fire frequency. Dry soils and exposed bedrock created by climate change and increased fire frequency limited the regeneration of Picea mariana. For future landscape management, long-term studies should be taken into consideration to determine the natural variability of ecosystems.