A 1500-year record of temperature and glacial response inferred from varved Iceberg Lake, southcentral Alaska

We present a varve thickness chronology from glacier-dammed Iceberg Lake in the southern Alaska icefields. Radiogenic evidence confirms that laminations are annual and record continuous sediment deposition from A.D. 442 to A.D. 1998. Varve thickness is positively correlated with Northern Hemisphere temperature trends, and more strongly with a local, ∼600 yr long tree ring width chronology. Varve thickness increases in warm summers because of higher melt, runoff, and sediment transport (as expected), but also because shrinkage of the glacier dam allows shoreline regression that concentrates sediment in the smaller lake. Varve thickness provides a sensitive record of relative changes in warm season temperatures. Relative to the entire record, temperatures implied by this chronology were lowest around A.D. 600, warm between A.D. 1000 and A.D. 1300, cooler between A.D. 1500 and A.D. 1850, and have increased dramatically since then. Combined with stratigraphic evidence that contemporary jökulhlaups (which began in 1999) are unprecedented since at least A.D. 442, this record suggests that 20th century warming is more intense, and accompanied by more extensive glacier retreat, than the Medieval Warm Period or any other time in the last 1500 yr.     

冰川变化与气候变化关系的若干探讨

冰川变化是气候变化的产物,但它与气候参数的关系表现出不稳定。本文通过理论分析发现：对以上的冰川进退基本上决定于温度变化,与降水的关系不大。对１０＾１年以内的冰川波动,其大范围的总体特征亦基本上决定于温度变化。个别冰川则比较复杂,但在冰川上部无消融区的物质平衡基本上决定于降水。     

Sea-level changes, geoid and gravity anomalies due to Pleistocene deglaciation by means of multilayered, analytical Earth models

A new class of analytical, multilayered, viscoelastic Earth models based on PREM, with an incompressible, linear, viscoelastic Maxwell rheology, is applied to the modeling of global sea-level changes due to Pleistocene deglaciation. Until now, analytical schemes based on normal mode theory, have dealt with at most five layers, an elastic lithosphere, a three layered mantle including a transition zone, and a core (Spada et al., 1992. Geophys. J. Int. 109, 683–700). The novelty of our approach, used for the first time in sea-level studies, stands on an analytical scheme that can reproduce continuous elastic and rheological stratification when a sufficient number of layers is taken into account. We specifically assess the importance of our results for the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) satellite mission. GOCE will resolve the gravity field with a spatial resolution (half-wavelength) of 75 km and amplitude of 1.5 mgal, with a uniform coverage over the Earth, including presently unsurveyed, remote areas. Our models lead to post-glacial rebound induced free air gravity anomalies of a few mgals peak-to-peak in the harmonic degree range l=80–200, which will be discernible by GOCE. This finding demonstrates that post-glacial rebound has a high frequency component in the gravity field that can in principle be resolved by high resolution gravity satellite missions. We show that post-glacial rebound can contribute a substantial fraction to present-day sea-level variations and point out that for the Mediterranean Sea they are of the same order of magnitude as those induced by tectonic processes.     

海南岛南渡江三角洲海岸演变的波浪作用分析

本文应用白沙门1984年波浪统计资料,通过对南渡江三角洲北部近岸海底泥沙活动特性与东部废弃海岸泥沙沿岸输移方式及其岸外沙坝、堡岛响应波浪动力而具有的形状进行分析,揭示了波浪在南渡江三角洲北部沿岸演变中的重要作用。     

Reconstruction of palaeoceanographic conditions in the South Atlantic Ocean at the last two Terminations based on calcareous dinoflagellate cysts

 Despite the increasing interest in the South Atlantic Ocean as a key area of the heat exchange between the southern and the northern hemisphere, information about its palaeoceanographic conditions during transitions from glacial to interglacial stages, the so-called Terminations, are not well understood. Herein we attempt to increase this information by studying the calcareous dinoflagellate cysts and the shells of Thoracosphaera heimii (calcareous cysts) of five Late Quaternary South Atlantic Ocean cores. Extremely high accumulation rates of calcareous cysts at the Terminations might be due to a combined effect of increased cyst production and better preservation as result of calm, oligotrophic conditions in the upper water layers. Low relative abundance of Sphaerodinella albatrosiana compared with Sphaerodinella tuberosa in the Cape Basin may be the result of the relatively colder environmental conditions in this region compared with the equatorial Atlantic Ocean with high relative abundance of S. albatrosiana. Furthermore, the predominance of S. tuberosa during glacials and interglacials at the observed site of the western Atlantic Ocean reflects decreased salinity in the upper water layer. Received: 9 November 1998 / Accepted: 26 October 1999     

Floating pontoon breakwaters

The hydrodynamic properties of a pair of long floating pontoon breakwaters of rectangular section are investigated theoretically. The structures are partially restrained by linear symmetric moorings fore and aft. The fluid motion is idealized as linearized, two-dimensional potential flow. The breakwater motions are assumed to be two-dimensional, in surge, heave and pitch. The solution for the fluid motion is obtained by the boundary integral equation method using an appropriate Green's function. Numerical results are presented that illustrate the effects of the various wave and structural parameters on the efficiency of the breakwaters as barriers to wave action. It is found that the wave reflection properties of the structures depend strongly on their width, draft and spacing and the mooring line stiffnesses, while their excess buoyancy is of lesser importance.     

产业活动对城市生态环境的影响与政策调控——以海口市为例

产业聚集负效应所引起的生态环境恶化是城市可持续发展面临的重大课题.海口市应加大宏观管理的力度,减轻乃至消除第三、第二产业活动对城市生态环境的负面影响,努力形成与生态环境相协调的生产方式,走产业经济生态化的道路.产业政策调控的重点是:积极发展生态产业,调整优化产业结构;建立科技创新体系,推进生态产业发展;建立产业标准化体系,为企业发展提供良好的外部环境.     

New evidence on the sequence of deglacial warming in the tropical Indian Ocean

The transition from the Last Glacial Maximum to the Holocene was an internal of climate variability that was characterised by large spatial and temporal variations. Here we show that deglaciation warming in the northern Indian Ocean was initiated ca. 19 ka, which is contemporary with deglaciation warming in the Antarctica and Southern Ocean. A gradual warming occurred during the glacial/Holocene transition in the northern Indian Ocean, unlike the two‐step warming seen in Greenland and the North Atlantic. Synchronous deglacial warming ca. 19 ka in Antarctica and the northern Indian Ocean suggests a strong connection in the propagation of climate signals between Antarctica and the Indian Ocean, probably through the Indonesian Throughflow and/or Subantarctic Mode Water. Copyright © 2010 John Wiley & Sons, Ltd.     

Macrofossil evidence of alder (Alnus sp.) in Britain early in the Late Glacial Interstadial: implications for the northern cryptic refugia debate

Wood macrofossil remains of alder and willow/poplar have been recovered from a sediment sequence in the valley of the Turker Beck in the Vale of Mowbray, North Yorkshire. These remains have yielded radiocarbon dates early in the Devensian Late Glacial (14.7–14k cal a bp ), equivalent to the early part of the Greenland Interstadial (GI-1e) of the GRIP ice-core record. These are the earliest dates recorded for the presence of alder in the Late Glacial in the British Isles. Associated biological remains have provided a palaeoenvironmental record for this early part of the Greenland Interstadial, generally indicative of open environments dominated by herbaceous taxa on both the wetland and dryland surfaces. However, stands of alder, birch and willow woodland were also present, and indicate the possibility that such tree species survived in cryptic refugia in Britain as elsewhere in northern Europe during the Last Glacial Maximum. The absence of alder pollen at Turker Beck, in a sequence in which its macrofossil remains are relatively abundant, lends support to the view that pollen can be a poor indicator of the presence of tree species in Late Glacial sequences in northern and western Europe.