The Arctic region is subject to a great amplitude of climate variability and is currently undergoing large-scale changes due in part to anthropogenic global warming. Accurate projections of future change depend on anticipating the response of the Arctic climate system to forcing, and understanding how the response to human forcing will interact with natural climate variations. The Svalbard Archipelago occupies an important location for studying patterns and causes of Arctic climate variability; however, available paleoclimate records from Svalbard are of restricted use due to limitations of existing climate proxies. Here we present a sub-decadal-to multidecadal-scale record of summer temperature for the past 1800 yr from lake sediments of Kongressvatnet on West Spitsbergen, Svalbard, based on the fi rst instrumental calibration of the alkenone paleothermometer. The age model for the High Arctic lake sediments is based on 210 Pb, plutonium activity, and the fi rst application of tephrochronology to lake sediments in this region. We fi nd that the summer warmth of the past 50 yr recorded in both the instrumental and alkenone records was unmatched in West Spitsbergen in the course of the past 1800 yr, including during the Medieval Climate Anomaly, and that summers during the Little Ice Age (LIA) of the 18 th and 19 th centuries on Svalbard were not particularly cold, even though glaciers occupied their maximum Holocene extent. Our results suggest that increased wintertime precipitation, rather than cold temperatures, was responsible for LIA glaciations on Svalbard and that increased heat transport into the Arctic via the West Spitsbergen Current began ca. A.D. 1600.
The 350-km-long, east-west trending Wetar back arc thrust belt in eastern Indonesia is a result of the collision of Australia with the Indonesian island arc. Along the northwest margin of Wetar Island a short (50 km) section of the thrust belt trends northeast, coincident withthe offset of the Indonesian arc by the newly discovered left-lateral Wetar-Atauro fault, which runs along the shelf region and trends northeast. The Wetar-Atauro fault may be viewed as a large-scale lateral ramp or wrench fault separating the eastern Wetar thrust belt from the western Wetar thrust belt. The interaction of strike-slip faulting and back arc thrust faulting creates several arc "blocks" whose geometry strongly affects the structure of the deformed wedge of sediment accreting in the Wetar back arc thrust belt. The varying orientations of the arc "backstop" make the Wetar back arc thrust belt a perfect laboratory for the study of oblique convergence. Along most of its length the Wetar thrust belt parallels the arc slope. However, along the northeast trending offset in the thrust belt, SeaMARC II side-scan sonar plus seismic reflection data show that the trend of the thrust belt is not parallel to the trend of the arc slope; rather, it is intermediate between the trend of the arc slope and the perpendicular to the expected convergence direction. The side-scan images allow us to map the geometry of four main thrust faults: the Wetar, Liran, Atauro, and Alor faults. The Wetar, Liran, and Atauro faults trend northeast, parallel to the thrust front, and do not have an en echelon relationship. The westernmost fault in the survey area, the Alor fault, trends almost east-west. The orientation of the Wetar-Atauro fault is consistent with a maximum principal stress within the arc oriented between 8 ø and 23 ø west of north, depending on the internal coefficient of friction. This agrees well with the P-axes of nearby earthquake focal mechanisms which trend consistently west of north, suggesting that the regional principal tectonic compression is oriented west of north. Because the thrust belt is oblique to the arc slope, we infer the structural directions are influenced by both the arc backstop and by the regional tectonic stress. The tectonic compression due to arc-continent collision in this region may be modified by the arc geometry in several ways: (1) the stress necessary to support the arc topography may be significant close to the arc, (2) the change in thickness of the elastic part of the lithosphere may cause a concentration of tectonic stress, and (3) the difference in material properties between the relatively rigid arc "bulldozer" and the weak basin sedimentary fill may be an important factor in producing a thrust belt that conforms roughly to the shape of the arc. The structure of the Wetar back arc thrust zone demonstrates that the development of small rigid blocks within a major collision zone may produce complex structural patterns and local directions of shortening that are highly oblique to the main direction of plate conv...
Open-File Report 90-0234A Discussion (paper copy) 90-0234B Geochemical data files, ASCII, (1) 51/4" 360K floppy diskette 1990 Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards nor with the North American stratigraphic codes. Although these data have been used by the U.S. Geological Survey and have been successfully imported into a number of data base and spreadsheet programs, no warranty, expressed or implied, is made by the USGS as to how successfully or accurately the data can be imported into any specific application software running on any specific hardware platform. The fact of distribution shall not constitute any such warranty, and no responsibility is assumed by the USGS in connection therewith.
Sediment yield can be a sensitive indicator of catchment dynamics and environmental change. For a glacierized catchment in the High Arctic, we compiled and analyzed diverse sediment transfer data, spanning a wide range of temporal scales, to quantify catchment yields and explore landscape response to past and ongoing hydroclimatic variability. The dataset integrates rates of lake sedimentation from correlated varve records and repeated annual and seasonal sediment traps, augmented by multi‐year lake and fluvial monitoring. Consistent spatial patterns of deposition enabled reconstruction of catchment yields from varve‐ and trap‐based fluxes. We used hydroclimatic data and multivariate modeling to examine annual controls of sediment delivery over almost a century, and to examine shorter‐term controls of sediment transfer during peak glacier melt. Particle‐size analyses, especially for annual sediment traps, were used to further infer sediment transfer mechanisms and timing. Through the Medieval Warm Period and Little Ice Age, there were no apparent multi‐century trends in lake sedimentation rates, which were over three times greater than those during the mid‐Holocene when glaciers were diminished. Twentieth‐century sedimentation rates were greater than those of previous millennia, with a mid‐century step increase in mean yield from 240 to 425 Mg km−2 yr−1. Annual yields through the twentieth century showed significant positive relations with spring/summer temperature, rainfall, and peak discharge conditions. This finding is significant for the future of sediment transfer at Linnévatnet, and perhaps more broadly in the Arctic, where continued increases in temperature and rainfall are projected. For 2004–2010, annual yields ranged from 294 to 1330 Mg km−2 yr−1. Sediment trap volumes and particle‐size variations indicate that recent annual yields were largely dominated by spring to early summer transfer of relatively coarse‐grained sediment. Fluvial monitoring showed daily to hourly sediment transfer to be related to current and prior discharge, diurnal hysteresis, air temperature, and precipitation. Copyright © 2017 John Wiley & Sons, Ltd.
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