SUMMARY We present a glacial isostatic adjustment (GIA) model for Antarctica. This is driven by a new deglaciation history that has been developed using a numerical ice‐sheet model, and is constrained to fit observations of past ice extent. We test the sensitivity of the GIA model to uncertainties in the deglaciation history, and seek earth model parameters that minimize the misfit of model predictions to relative sea‐level observations from Antarctica. We find that the relative sea‐level predictions are fairly insensitive to changes in lithospheric thickness and lower mantle viscosity, but show high sensitivity to changes in upper mantle viscosity and constrain this value (95 per cent confidence) to lie in the range 0.8–2.0 × 1021 Pa s. Significant misfits at several sites may be due to errors in the deglaciation history, or unmodelled effects of lateral variations in Earth structure. When we compare our GIA model predictions with elastic‐corrected GPS uplift rates we find that the predicted rates are biased high (weighted mean bias = 1.8 mm yr–1) and there is a weighted root‐mean‐square (WRMS) error of 2.9 mm yr–1. In particular, our model systematically over‐predicts uplift rates in the Antarctica Peninsula, and we attempt to address this by adjusting the Late Holocene loading history in this region, within the bounds of uncertainty of the deglaciation model. Using this adjusted model the weighted mean bias improves from 1.8 to 1.2 mm yr–1, and the WRMS error is reduced to 2.3 mm yr–1, compared with 4.9 mm yr–1 for ICE‐5G v1.2 and 5.0 mm yr–1 for IJ05. Finally, we place spatially variable error bars on our GIA uplift rate predictions, taking into account uncertainties in both the deglaciation history and modelled Earth viscosity structure. This work provides a new GIA correction for the GRACE data in Antarctica, thus permitting more accurate constraints to be placed on current ice‐mass change.

Bedrock uplift in Antarctica is dominated by a combination of glacial isostatic adjustment (GIA) and elastic response to contemporary mass change. Here, we present spatially extensive GPS observations of Antarctic bedrock uplift, using 52% more stations than previous studies, giving enhanced coverage, and with improved precision. We observe rapid elastic uplift in the northern Antarctic Peninsula. After considering elastic rebound, the GPS data suggests that modeled or empirical GIA uplift signals are often over‐estimated, particularly the magnitudes of the signal maxima. Our observation that GIA uplift is misrepresented by modeling (weighted root‐mean‐squares of observation‐model differences: 4.9–5.0 mm/yr) suggests that, apart from a few regions where large ice mass loss is occurring, the spatial pattern of secular ice mass change derived from Gravity Recovery and Climate Experiment (GRACE) data and GIA models may be unreliable, and that several recent secular Antarctic ice mass loss estimates are systematically biased, mainly too high.

Aim This paper documents reconstructions of the vegetation patterns in Australia, Southeast Asia and the Pacific (SEAPAC region) in the midHolocene and at the last glacial maximum (LGM).

Sk?t, L., Humphreys, M. O., Armstead, I. P., Heywood, S., Sk?t, K. P., Sanderson, R., Thomas, I. D., Chorlton, K. H., & Sackville Hamilton, N. R. (2005). An association mapping approach to identify flowering time genes in natural populations of Lolium perenne (L.). Molecular Breeding, 15(3), 233-245. Sponsorship: BBSRC RAE2008We describe an association mapping approach using natural populations of perennial ryegrass (Lolium perenne L.) to identify molecular markers associated with heading date, an important trait affecting seasonal production, tillering, digestibility and grassland management regimes. Twenty-three natural populations originating from throughout Europe, with heading date phenotypes ranging from very early to very late, as well as three synthetic populations (varieties) were used for molecular marker genotyping using AFLP. In total, 589 polymorphic markers were identified. Hierarchical clustering, principal coordinate and other statistical analyses identified four outlying populations forming a clearly distinct sub-group. Removal of those four populations from the subsequent analysis reduced population sub-structure twofold. However, this made relatively little difference to the result of the association analysis. Linear regression identified three markers whose frequency of occurrence correlated with the heading date phenotype. Moreover, these markers were shown to be closely linked to each other within a major QTL on Chromosome 7, explaining 70% of the total variation in heading date. Pairwise linkage disequilibrium among them was also significant. These results suggest that association mapping approaches may be feasible in L. perenne, and that the use of natural populations could provide a useful source of genetic variation in traits of importance in crop improvement.Peer reviewe

Aim  To reconstruct the Late Glacial and Holocene vegetation history of western Tasmania and to test the long‐held notion of a replacement of forest by moorland during the mid to late Holocene in western Tasmania, Australia. Location  Western Tasmania, Australia. Methods  Fossil pollen data were screened with a modern pollen dataset using detrended correspondence analysis and charcoal data were analysed using significance tests. Results  At the landscape scale, the distribution of vegetation types in western Tasmania has remained remarkably stable through the post‐glacial period. Open moorland has dominated the landscape since the Late Glacial, while rain forest expanded at that time in to areas which it occupies today. Vegetation development in the Holocene is markedly different and charcoal values are significantly higher when compared with those in previous interglacial periods. Main conclusions  The dominant paradigm of a replacement of rain forest by moorland across western Tasmania during the mid to late Holocene is not supported by this regional analysis. The arrival of humans in Tasmania during the Last Glacial Stage provided an ignition source that was independent of climate, and burning by humans through the Late Glacial period deflected vegetation development and facilitated the establishment of open moorland in regions occupied by rain forest during previous interglacial periods. It is concluded that the present dominance of the landscape of western Tasmania by open moorland is the direct result of human activity during the Late Glacial and that this region represents an ancient cultural landscape.