Neil Ogle

Late-surviving megafauna in Tasmania, Australia, implicate human involvement in their extinction

Establishing the cause of past extinctions is critical if we are to understand better what might trigger future occurrences and how to prevent them. The mechanisms of continental late Pleistocene megafaunal extinction, however, are still fiercely contested. Potential factors contributing to their demise include climatic change, human impact, or some combination. On the Australian mainland, 90% of the megafauna became extinct by ≈46 thousand years (ka) ago, soon after the first archaeological evidence for human colonization of the continent. Yet, on the neighboring island of Tasmania (which was connected to the mainland when sea levels were lower), megafaunal extinction appears to have taken place before the initial human arrival between 43 and 40 ka, which would seem to exonerate people as a contributing factor in the extirpation of the island megafauna. Age estimates for the last megafauna, however, are poorly constrained. Here, we show, by direct dating of fossil remains and their associated sediments, that some Tasmanian megafauna survived until at least 41 ka (i.e., after their extinction on the Australian mainland) and thus overlapped with humans. Furthermore, a vegetation record for Tasmania spanning the last 130 ka shows that no significant regional climatic or environmental change occurred between 43 and 37 ka, when a land bridge existed between Tasmania and the mainland. Our results are consistent with a model of human-induced extinction for the Tasmanian megafauna, most probably driven by hunting, and they reaffirm the value of islands adjacent to continental landmasses as tests of competing hypotheses for late Quaternary megafaunal extinctions.

High‐resolution δ13C measurements of oak show a previously unobserved spring depletion

We have subdivided single tree rings into between 24 and 35 contiguous samples and measured the δ 13 C value for each. These high-resolution measurements show a previously unobserved spring depletion as part of a pattern of enrichment-depletion-enrichment-depletion through a single growing season as opposed to the depletion-enrichment-depletion cycle previously thought to exist. The earlywood/latewood transition does not coincide with identifiable isotopic boundaries and therefore is not a suitable demarcation point for sampling as part of palaeoclimatic study. Latewood and post spring depletion values of δ 13 C were separately correlated with geophysical parameters. Post spring depletion wood yielded better correlations and is therefore more suitable for palaeoclimatic study

Palaeovolcanic forcing of short-term dendroisotopic depletion: The effect of decreased solar intensity on Irish oak

[1] The climatic effects of historical volcanic eruptions are well documented in the literature. What are less certain however, are the effects of eruptions on more distant environments, particularly vegetation. Here we present subannual delta(13)C records from two high-resolution Irish oak ( Quercus spp.) chronologies that span the Laki (Grimsvotn) 1783-84 and Tambora 1815 eruptions. In both instances, a significant depletion in delta(13)C is recorded within the trees following the eruption (similar to 1.8%o). Historical meteorological datasets from observatories near to the trees sampled demonstrate that the shifts in carbon isotopic content cannot be accounted for by changes in local climate. We postulate atmospheric loading of ejecta from the eruptions resulted in significantly reduced irradiance, increasing discrimination within the trees.

Organic composition and multiphase stable isotope analysis of active, degrading and restored blanket bog

Here we used organic composition and stable isotopic analysis to evaluate the effects of drainage and restoration at an ombrotrophic peatland, to assess whether rewetting of blanket bogs will reverse degradation. The organic composition of the peat and the isotopic fractionation between the solid (peat), liquid (pore water) and gas (soil gas) phases on actively accumulating, degrading and restored locations are compared. Fourier Transform Infrared Spectroscopy (FTIR) analysis of the organic material has shown a high level of humification (low decomposition) in the active peat. Stable isotope analysis in the solid, liquid and gas phases has corresponded with this and indicated that the active location is enriched in 13C in the solid and gas phases, 15N in the solid phase, 18O in the liquid and gas phases and D in the liquid phase, suggesting a closed system with limited isotopic fractionation and thus limited water movement and decomposition. The degrading location has a lower level of humification, and is depleted in 13C in the solid phase due to ingression of vascular plants. The restored location has high humification and enrichment of 13C and 15N in the solid phase, and D in the liquid phase suggesting increased microbial activity. 13C and 18O in the gas phase and 18O in the liquid phase are depleted, as a result of microbial mediated gas production and rewetting. FTIR analysis has also indicated a subsurface zone of increased decomposition between the acrotelm and catotelm in both the active and degrading peat. This is due to a stable water table and is not present within the restored location, which we attribute to water table fluctuation associated with rewetting. This zone of increased decomposition adds to the complexity of blanket bog peatlands and the assumption that all systems can be generalized under one conceptual model.