ALBERT

Description: Most recent developments of Schmidt-hammer exposure-age dating (SHD) as a calibrated-age dating tool have been limited by the use of locations at two age control points. This has necessitated: (1) making assumptions about a linear R-value—age relationship; and (2) basing predictions of age errors only on R-value variance at the two age control points. This paper analyses 9900 R-values obtained from multiple-age control points on a sequence of glacio-isostatically raised shorelines with well constrained ages (Skuleskogen High Coast World Heritage Site and environs, Gulf of Bothnia, northern Sweden) ranging from modern to 10.5 ka in age. The sampling design involved 30 measurements on granite beach boulders from 30 sites at 11 age control points. The R-value—age relationship is best described by a linear function (ordinary least squares, OLS) with an R 2 of 0.89 ( p 〈 0.0001). Predicted-age errors are calculated using two approaches: (1) OLS regression, which takes account of the uncertainties associated with the regression line and the age control points; and (2) weighted total least squares (WTLS) regression which, in addition, takes account of possible shoreline age errors and the heteroscedasticity of R-value residuals with increasing age. With both approaches, 95% predicted-age errors are relatively modest: ±355—455 years and ±300—515 years, respectively, with larger R-value variance and hence uncertainty for older surfaces, and the possibility of further improvement from a more selective field sampling scheme that differentiates between age-related and non-age-related rock-surface variability. Our results also indicate that for certain lithologies and weathering environments, it is possible to construct reliable calibrated-age curves from relatively few age control points.

Description: Increases in the frequency of large to extreme rainfall events are widely predicted with global warming, but evidence from the humid tropics is hampered by a paucity of long-term data. This paper assesses changes in daily rainfall magnitude–frequency and their geomorphological consequences in the equatorial environment of northern Borneo using (1) rare daily rainfall data series for 1906–2012 assembled from archival and current sources and (2) geomorphological process data from the Danum Valley area of eastern Sabah. Rainstorm changes are explored using (1) analysis of frequencies of daily falls above threshold values, (2) extreme-value analysis comparing differences in locally weighted scatterplot smoothing (LOESS) best-fit curves for successive 20-year periods and (3) a novel approach constructing graphs of long-term change in daily falls of 1- to 10-year return period derived from overlapping 20-year LOESS curves. Substantial increases, some statistically significant, since 1980 (intensifying since 1999) are detected at most stations in (1) the frequency of daily falls ≥50, 100 and 200 mm and (2) the magnitudes of daily falls with return periods of 0.2–5.0 years. The scale and temporal patterns of historical change vary with (1) coastal aspect and (2) different parts of the return period spectrum. The period 1921–1940 exhibited higher rainstorm magnitude–frequency than 1952–1979 and demonstrates the dangers of simple deductions derived from post-1960 data comparisons. Geomorphological responses indicated by long-term monitoring at Danum (eastern Sabah), where there has been a marked upswing in heavy rainfalls since 1999, include a threefold increase in slopewash rates, more frequent high flows and higher sediment loads. The very high soil pipe sediment yields, rates of pipe roof collapse and stream channel extension recorded from 2002 to 2012 in pipe systems at Danum may be a consequence of this upswing. Increased landsliding is also a likely consequence, exacerbated in logged, agricultural and urban terrain.

Description: Combining nine tree growth proxies from four sites, from the west coast of Norway to the Kola Peninsula of NW Russia, provides a well replicated (〉 100 annual measurements per year) mean index of tree growth over the last 1200 years that represents the growth of much of the northern pine timberline forests of northern Fennoscandia. The simple mean of the nine series, z -scored over their common period, correlates strongly with mean June to August temperature averaged over this region ( r = 0.81), allowing reconstructions of summer temperature based on regression and variance scaling. The reconstructions correlate significantly with gridded summer temperatures across the whole of Fennoscandia, extending north across Svalbard and south into Denmark. Uncertainty in the reconstructions is estimated by combining the uncertainty in mean tree growth with the uncertainty in the regression models. Over the last seven centuries the uncertainty is 〈 4.5% higher than in the 20th century, and reaches a maximum of 12% above recent levels during the 10th century. The results suggest that the 20th century was the warmest of the last 1200 years, but that it was not significantly different from the 11th century. The coldest century was the 17th. The impact of volcanic eruptions is clear, and a delayed recovery from pairs or multiple eruptions suggests the presence of some positive feedback mechanism. There is no clear and consistent link between northern Fennoscandian summer temperatures and solar forcing.