Age determination of sediments off western Svalbard

Late Quaternary sediment yields from the Isfjorden drainage area (7327 km**2), a high arctic region on Svalbard characterized by an alpine landscape, have been reconstructed by using seismic stratigraphy supported by sediment core analysis. The sediments that accumulated in the fjord during and since deglaciation can be divided into three stratigraphic units. The volumes of these units were determined and converted into sediment yield rates averaged over the drainage basin. During deglaciation, 13 to 10 ka, the sediment yield was ~860 tons(t)/km**2/yr. In the early Holocene it decreased to 190 t/km**2/yr, and then increased to 390t/km**2/yr during the late Holocene Little Ice Age. When normalized to the approximate glacierized area, these rates correspond to a sediment yield of ~800 t/km**2/yr . Sediment yield from non-glacierized parts of the drainage is estimated to be 35 t/km**2/yr. At times when ice advanced to the shelf edge, sediment was scoured from the fjord and deposited on the outer shelf and in a well-defined deep sea fan. Between 200 ka and 13 ka, 328 km**3 of sediment accumulated here, corresponding to a mean sediment yield rate of 335 t/km**2/yr. This is broadly consistent with calculations based on the above rates of sediment yield in glacierized and non-glacierized areas, and on estimates, based on glacial geology, of the temporal variation in degree of glacierization over the past 200 kyr. These figures indicate that much of the glacigenic sediment on the shelf and slope was eroded from the uplands of Svalbard by small glaciers during interstadials and interglacials. The sediments were temporarily stored in the fjord prior to redeposition on the shelf and slope during ice sheet advance. Taken into consideration, such redisposition of pre-eroded material will reduce estimates of primary ice sheet erosion rate.基于沉积物岩芯分析支撑的地震地层学方法，研究者重建了斯瓦尔巴群岛高北极区域伊斯峡湾流域（面积7327 km²，阿尔卑斯型地貌）的晚第四纪沉积物产率。冰消期及冰消期后峡湾内沉积的沉积物可划分为三个地层单元。研究人员测定了这些单元的体积，并将其转换为流域平均的沉积物产率。在13~10 ka的冰消期内，沉积物产率约为860 吨/(km²·年)；早全新世时期产率降至190 吨/(km²·年)，随后在晚全新世小冰期阶段回升至390 吨/(km²·年)。若以近似冰川覆盖面积进行归一化处理，上述产率对应约800 吨/(km²·年)的沉积物产率；流域非冰川区的沉积物产率估算值为35 吨/(km²·年)。当冰盖推进至陆架边缘时，峡湾内的沉积物会被冲刷，并沉积在外陆架与特征明确的深海扇中。在200 ka至13 ka期间，该区域累计沉积了328 km³的沉积物，对应平均沉积物产率为335 吨/(km²·年)，这与基于前述冰川区与非冰川区沉积物产率的计算结果，以及基于冰川地质学估算的过去20万年冰川覆盖度时间变化结果基本吻合。上述数据表明，陆架与陆坡上的多数冰成沉积物，是间冰阶与间冰期时期由小型冰川从斯瓦尔巴高地侵蚀而来的。这些沉积物会先在峡湾中暂时储存，随后在冰盖推进阶段再沉积至陆架与陆坡。此类预侵蚀物质的再沉积作用，会降低原始冰盖侵蚀速率的估算值。