Development of an Arcellacean (testate lobose amoebae) based transfer function for sedimentary phosphorous in lakes.

Arcellacea (testate lobose amoebae) communities were assessed from 73 sediment-water interface samples collected from 33 lakes in urban and rural settings within the Greater Toronto Area (GTA), Ontario, Canada, as well as from forested control areas in the Lake Simcoe area, Algonquin Park and eastern Ontario. The results were used to: (1) develop a statistically rigorous arcellacean-based training set for sedimentary phosphorus (Olsen P (OP)) loading; and (2) derive a transfer function to reconstruct OP levels during the post-European settlement era (AD1870s onward) using a chronologically well-constrained core from Haynes Lake on the environmentally sensitive Oak Ridges Moraine, within the GTA. Ordination analysis indicated that OP most influenced arcellacean assemblages, explaining 6.5% (p < 0.005) of total variance. An improved training set where the influence of other important environmental variables (e.g. total organic carbon, total nitrogen, Mg) was reduced, comprised 40 samples from 31 lakes, and was used to construct a transfer function for lacustrine arcellaceans for sedimentary phosphorus (Olsen P) using tolerance downweighted weighted averaging (WA-Tol) with inverse deshrinking (RMSEPjack-77pp; r2jack = 0.68). The inferred reconstruction indicates that OP levels remained near pre-settlement background levels from settlement in the late AD 1970s through to the early AD 1970s. Since OP runoff from both forests and pasture is minimal, early agricultural land use within the lake catchment was as most likely pasture and/or was used to grow perennial crops such as Timothy-grass for hay. A significant increase in inferred OP concentration beginning ~ AD 1972 may have been related to a change in crops (e.g. corn production) in the catchment resulting in more runoff, and the introduction of chemical fertilizers. A dramatic decline in OP after ~ AD 1985 probably corresponds to a reduction in chemical fertilizer use related to advances in agronomy, which permitted a more precise control over required fertilizer application. Another significant increase in OP levels after ~ AD 1995 may have been related to the construction of a large golf course upslope and immediately to the north of Haynes Lake in AD 1993, where significant fertilizer use is required to maintain the fairways. These results demonstrate that arcellaceans have great potential for reconstructing lake water geochemistry and will complement other proxies (e.g. diatoms) in paleolimnological research.

Iron Age Pastoral Nomadism and Agriculture in the Eastern Eurasian Steppe: Implications from Dental Palaeopathology and Stable Carbon and Nitrogen Isotopes

Iron Age societies of the eastern Eurasian steppe are traditionally viewed as nomadic pastoralists. However, recent archaeological and anthropological research in Kazakhstan has reminded us that pastoralist economies can be highly complex and involve agriculture. This paper explores the nature of the pastoralist economies in two Early Iron Age populations from the burial grounds of Ai-Dai and Aymyrlyg in Southern Siberia. These populations represent two cultural groups of the Scythian World - the Tagar Culture of the Minusinsk Basin and the Uyuk Culture of Tuva. Analysis of dental palaeopathology and carbon and nitrogen stable isotopes suggests that domesticated cereals, particularly millet, and fish formed a major component of the diet of both groups. The findings contribute to the emerging picture of the nuances of Early Iron Age subsistence strategies on the eastern steppe.

Decomposing the mid-holocene Tsuga decline in eastern North America

The mid-Holocene decline of Tsuga canadensis (hereafter Tsuga) populations across eastern North America is widely perceived as a synchronous event, driven by pests/pathogens, rapid climate change, or both. Pattern identification and causal attribution are hampered by low stratigraphic density of pollen-sampling and radiometric dates at most sites, and by absence of highly resolved, paired pollen and paleoclimate records from single sediment cores, where chronological order of climatic and vegetational changes can be assessed. We present an intensely sampled (contiguous 1-cm intervals) record of pollen and water table depth (inferred from testate amoebae) from a single core spanning the Tsuga decline at Irwin Smith Bog in Lower Michigan, with high-precision chronology. We also present an intensively sampled pollen record from Tower Lake in Upper Michigan. Both sites show high-magnitude fluctuations in Tsuga pollen percentages during the pre-decline maximum. The terminal decline is dated at both sites ca. 5000 cal yr BP, some 400 years later than estimates from other sites and data compilations. The terminal Tsuga decline was evidently heterochronous across its range. A transient decline ca. 5350 cal yr BP at both sites may correspond to the terminal decline at other sites in eastern North America. At Irwin Smith Bog, the terminal Tsuga decline preceded an abrupt and persistent decline in water table depths by;200 years, suggesting the decline was not directly driven by abrupt climate change. The Tsuga decline may best be viewed as comprising at least three phases: a long-duration predecline maximum with high-magnitude and high-frequency fluctuations, followed by a terminal decline at individual sites, followed in turn by two millennia of persistently low Tsuga populations. These phases may not be causally linked, and may represent dynamics taking place at multiple temporal and spatial scales. Further progress toward understanding the phenomenon requires an expanded network of high-resolution pollen and paleoclimate chronologies.

Pristine Early Eocene Wood Buried Deeply in Kimberlite from Northern Canada

We report exceptional preservation of fossil wood buried deeply in a kimberlite pipe that intruded northwestern Canada's Slave Province 53.3±0.6 million years ago (Ma), revealed during excavation of diamond source rock. The wood originated from forest surrounding the eruption zone and collapsed into the diatreme before resettling in volcaniclastic kimberlite to depths >300 m, where it was mummified in a sterile environment. Anatomy of the unpermineralized wood permits conclusive identification to the genus Metasequoia (Cupressaceae). The wood yields genuine cellulose and occluded amber, both of which have been characterized spectroscopically and isotopically. From cellulose d O and d H measurements, we infer that Early Eocene paleoclimates in the western Canadian subarctic were 12-17°C warmer and four times wetter than present. Canadian kimberlites offer Lagerstätte-quality preservation of wood from a region with limited alternate sources of paleobotanical information. © 2012 Wolfe et al.

Identification of last interglacial deposits in eastern Beringia: a cautionary note from the Palisades, interior Alaska

Last interglacial sediments in unglaciated Alaska and Yukon (eastern Beringia) are commonly identified by palaeoecological indicators and stratigraphic position ~2-5m above the regionally prominent Old Crow tephra (124±10ka). We demonstrate that this approach can yield erroneous age assignments using data from a new exposure at the Palisades, a site in interior Alaska with numerous exposures of last interglacial sediments. Tephrochronology, stratigraphy, plant macrofossils, pollen and fossil insects from a prominent wood-rich organic silt unit are all consistent with a last interglacial age assignment. However, six 14C dates on plant and insect macrofossils from the organic silt range from non-finite to 4.0 14C ka BP, indicating that the organic silt instead represents a Holocene deposit with a mixed-age assemblage of organic material. In contrast, wood samples from presumed last interglacial organic-rich sediments elsewhere at the Palisades, in a similar stratigraphic position with respect to Old Crow tephra, yield non-finite 14C ages. Given that local permafrost thaw since the last interglaciation may facilitate reworking of older sediments into new stratigraphic positions, minimum constraining ages based on 14C dating or other methods should supplement age assignments for last interglacial sediments in eastern Beringia that are based on palaeoecology and stratigraphic association with Old Crow tephra.