Ice Extent and Late Glacial and Deglacial History of W. Hunafloi, NW Iceland: Combining Terrestrial and Marine Evidence

冰岛西北半岛晚第四纪冰的范围和厚度以及冰川消融年代学的约束很差。首席调查员将就冰岛西北部的西哈纳弗洛伊西部海岸线和高地以及邻近的海槽--哈纳弗洛阿尔的冰川和退冰史开展合作研究项目。该提案建立在1996年、1997年和1999年的海上巡航以及2000年夏天进行的一项试点实地项目的基础上。该项目的目的是解决冰岛西北部部分地区的第四纪晚期冰川历史，并将陆地记录与海洋记录联系起来。这项研究将增加对海洋北极边缘冰川历史的新见解，以及关于生物“避难所”的非常古老的争论。至少有两种模型被建议用于冰岛在冰川盛期(LGM)和随后的消退期间重建冰川范围，但这些模型仅基于有限的放射性碳年代。在西北半岛，冰川重建从没有无冰区的大范围冰盖模式到在高原上存在无冰区并有维管植物存活的避难所模式。这些研究完全基于陆地冰川证据和解释，但这必须与冰川和海洋沉积物的近海沉积记录密切相关。来自Hunafloaall海槽的高分辨率3.5 kHz声波地层学和海洋岩心表明，LGM范围可能受到了相对限制。在Hunafloaall，一个含有有孔虫的基底硅云母被一个薄的(2米)的富含IRD的冰海和海洋沉积序列所覆盖。富含IRD的泥浆上的基本日期表明，冰川消融发生在1.3万年前(Ka)。来自迪米克顿的日期是有限的和20ka的。如此薄的冰川序列与冰岛西南部形成了鲜明的对比，那里的冰川沉积物厚度可达10-40+m。Hunafloaall实际上没有冰川沉积物，这令人困惑，并引发了邻近西北半岛冰川范围和年代学的严重问题。宇宙成因同位素暴露测年技术将被用来约束冰川范围的“最大”和“最小”模型。具体地说，3He和36Ci同位素将用于确定玄武岩高地表面、冰川末端和侧向冰川的年龄。将利用沉积物样本的年代学和物理性质将陆地和海洋记录联系起来。首席调查人员将继续进行以下方面的实地和实验室调查：1)这条海岸线上冰川的垂直和横向范围，包括收集用于宇宙成因同位素暴露测年的样本；2)冰川消融和随后的任何冰川扩张的模式和时间；3)海洋岩芯调查，以期区分TIP和冰川海洋硅藻，重点是更准确地确定冰川消融的开始时间；4)相对海平面的变化，以此作为冰负荷和历史的量度。实地工作将继续进行，并扩大2000年夏天开始的一项试点计划，科罗拉多大学、冰岛大学、哥德堡大学和爱丁堡大学参与其中。

ABSTRACTOPP-0004233AndrewsThe late Quaternary extent and thickness of ice and the deglacial chronology of the Northwest Peninsula of Iceland are poorly constrained. The Principal Investigators will conduct a collaborative research project on the glacial and deglacial history of the western coastline and uplands of western Hunafloi, NW Iceland, and the adjacent marine trough, Hunafloaall. The proposal builds on marine cruises in 1996, 1997 and 1999, and on a pilot field program conducted in the summer of 2000. The purpose of the project is to resolve the late Quaternary glacial history of part of NW Iceland and to correlate the terrestrial record with the marine record. This research will add new insight into the glacial history of marine arctic margins and a very old debate on biological "refugia."At least two models for the reconstruction of glacial extent during the Lower Glacial Maximum (LGM) and subsequent retreat have been suggested for Iceland, but these are based on only limited radiocarbon dates. In the NW Peninsula, the glacial reconstructions vary from an extensive ice cover model with no ice free areas to a refugia model in which ice free areas existed on the high plateaus with vascular plants surviving glaciation. These studies are based entirely on terrestrial glacial evidence and interpretations, but this must be intimately linked to the offshore sedimentary record of glacial and marine sediments. High-resolution 3.5 kHz acoustic stratigraphy and marine cores from the Hunafloaall trough suggest that the LGM extent may have been relatively restricted. In Hunafloaall, a basal dimicton containing foraminifera, is overlain by a thin (2 m) sequence of IRD-rich glacial-marine and marine sediments. Basal dates on the IRD-rich muds indicate deglaciation occurred by 13 thousand years ago (ka). Dates from the dimictons are finite and 20 ka. Such a thin deglacial sequence provides a major contrast with SW Iceland where the deglacial sediments reach thickness of 10-40+ m. The virtual absence of deglacial sediments in Hunafloaall is perplexing and raises serious questions of ice extent and chronology on the adjacent NW Peninsula.Cosmogenic isotope exposure dating techniques will be used to constrain "maximum" and "minimum" models of glacial extent. Specifically, 3He and 36CI isotopes will be used to date the basaltic upland surfaces, end and lateral moraines, and glacial erratics. Tephrachronology and physical properties of the sediment samples will be used to link the terrestrial and marine records. The Principal Investigators will continue their field and laboratory investigations on: 1) the vertical and lateral extent of glaciation along this coastline, including collection of samples for cosmogenic isotope exposure dating; 2) the pattern and timing of deglaciation and any subsequent glacier expansion; 3) investigation of the marine cores with the view toward discriminating between tills and glacial marine dimictons, and with a focus on more accurately dating the onset of deglaciation; and 4) changes in relative sea level as a measure of ice load and history. The field work will continue and expand a pilot program that began in summer of 2000, involving the Universities of Colorado, Iceland, Goteborg, and Edinburgh.