Twenty-first century glacier slowdown driven by mass loss in High Mountain Asia

International audienc

Inducible expression of Pisum sativum xyloglucan fucosyltransferase in the pea root cap meristem, and effects of antisense mRNA expression on root cap cell wall structural integrity

Mitosis and cell wall synthesis in the legume root cap meristem can be induced and synchronized by the nondestructive removal of border cells from the cap periphery. Newly synthesized cells can be examined microscopically as they differentiate progressively during cap development, and ultimately detach as a new population of border cells. This system was used to demonstrate that Pisum sativum L. fucosyl transferase (PsFut1) mRNA expression is strongly expressed in root meristematic tissues, and is induced >2-fold during a 5-h period when mitosis in the root cap meristem is increased. Expression of PsFut1 antisense mRNA in pea hairy roots under the control of the CaMV35S promoter, which exhibits meristem localized expression in pea root caps, resulted in a 50–60% reduction in meristem localized endogenous PsFut1 mRNA expression measured using whole mount in situ hybridization. Changes in gross levels of cell wall fucosylated xyloglucan were not detected, but altered surface localization patterns were detected using whole mount immunolocalization with CCRC-M1, an antibody that recognizes fucosylated xyloglucan. Emerging hairy roots expressing antisense PsFut1 mRNA appeared normal macroscopically but scanning electron microscopy of tissues with altered CCRC-M1 localization patterns revealed wrinkled, collapsed cell surfaces. As individual border cells separated from the cap periphery, cell death occurred in correlation with extrusion of cellular contents through breaks in the wall

Manifestations and mechanisms of the Karakoram glacier Anomaly

Global-scale glacier shrinkage is one of the most prominent signs of ongoing climatic change. However, important differences in glacier response exist at the regional scale, and evidence has accumulated that one particular region stands out: the Karakoram. In the past two decades, the region has shown balanced to slightly positive glacier budgets, an increase in glacier ice flow speeds, stable to partially advancing glacier termini and widespread glacier surge activity. This is in stark contrast to the rest of High Mountain Asia, where glacier retreat and slowdown dominate, and glacier surging is largely absent. Termed the Karakoram Anomaly, recent observations show that the anomalous glacier behaviour partially extends to the nearby Western Kun Lun and Pamir. Several complementary explanations have now been presented for the Anomaly’s deeper causes, but our understanding is far from complete. Whether the Anomaly will continue to exist in the coming decades remains unclear, but its long-term persistence seems unlikely in light of the considerable warming anticipated by current projections of future climate

Contrasting patterns of early twenty-first-century glacier mass change in the Himalayas

Glaciers are among the best indicators of terrestrial climate variability, contribute importantly to water resources in many mountainous regions(1,2) and are a major contributor to global sea level rise(3,4). In the Hindu Kush-Karakoram-Himalaya region (HKKH), a paucity of appropriate glacier data has prevented a comprehensive assessment of current regional mass balance(5). There is, however, indirect evidence of a complex pattern of glacial responses(5-8) in reaction to heterogeneous climate change signals(9). Here we use satellite laser altimetry and a global elevation model to show widespread glacier wastage in the eastern, central and southwestern parts of the HKKH during 2003-08. Maximal regional thinning rates were 0.66 +/- 0.09 metres per year in the Jammu-Kashmir region. Conversely, in the Karakoram, glaciers thinned only slightly by a few centimetres per year. Contrary to expectations, regionally averaged thinning rates under debris-mantled ice were similar to those of clean ice despite insulation by debris covers. The 2003-08 specific mass balance for our entire HKKH study region was -0.21 +/- 0.05 m yr(-1) water equivalent, significantly less negative than the estimated global average for glaciers and ice caps(4,10). This difference is mainly an effect of the balanced glacier mass budget in the Karakoram. The HKKH sea level contribution amounts to one per cent of the present-day sea level rise(11). Our 2003-08 mass budget of -12.8 +/- 3.5 gigatonnes (Gt) per year is more negative than recent satellite-gravimetry-based estimates of -5 +/- 3 Gt yr(-1) over 2003-10 (ref. 12). For the mountain catchments of the Indus and Ganges basins(13), the glacier imbalance contributed about 3.5% and about 2.0%, respectively, to the annual average river discharge(13), and up to 10% for the Upper Indus basin(14)