(Table 1) Two-way travel times and depths of picked internal reflection horizons (IRHs) of the NGRIP ice core

During the summer of 2003, a ground-penetrating radar survey around the North Greenland Icecore Project (NorthGRIP) deep ice-core drilling site (75°06' N, 42°20' W; 2957 m a.s.l.) was carried out using a shielded 250 MHz radar system. The drill site is located on an ice divide, roughly 300 km north-northwest of the summit of the Greenland ice sheet. More than 430 km of profiles were measured, covering a 10 km by 10 km area, with a grid centered on the drilling location, and eight profiles extending beyond this grid. Seven internal horizons within the upper 120 m of the ice sheet were continuously tracked, containing the last 400 years of accumulation history. Based on the age-depth and density-depth distribution of the deep core, the internal layers have been dated and the regional and temporal distribution of accumulation rate in the vicinity of NorthGRIP has been derived. The distribution of accumulation shows a relatively smoothly increasing trend from east to west from 145 kg/m**2/a to 200 kg/m**2/a over a distance of 50 km across the ice divide. The general trend is overlain by small-scale variations on the order of 2.5 kg/m**2/a/km, i.e. around 1.5% of the accumulation mean. The temporal variations of the seven periods defined by the seven tracked isochrones are on the order of +-4% of the mean of the last 400 years, i.e. at NorthGRIP ±7 kg/m**2/a. If the regional accumulation pattern has been stable for the last several thousand years during the Holocene, and ice flow has been comparable to today, advective effects along the particle trajectory upstream of NorthGRIP do not have a significant effect on the interpretation of climatically induced changes in accumulation rates derived from the deep ice core over the last 10 kyr.

2003年夏季，研究团队采用屏蔽式250 MHz雷达系统，在北格陵兰冰芯计划（North Greenland Icecore Project, NorthGRIP）深冰芯钻探点位（北纬75°06′，西经42°20′；海拔2957米）周边开展了探地雷达（ground-penetrating radar）勘测。该钻探点位位于冰盖分水岭上，大致处于格陵兰冰盖主峰北北西方向约300公里处。本次勘测累计获取测线总长超430公里，覆盖以钻探点位为中心的10 km×10 km区域，另有8条测线延伸至该网格范围之外。研究人员对冰盖上层120米内的7处内部层位进行了连续追踪，这些层位完整涵盖了过去400年的积雪积累历史。基于深冰芯的年龄-深度与密度-深度分布数据，研究人员对上述内部层位开展定年工作，并反演得到了NorthGRIP周边区域积雪积累速率的时空分布特征。积雪积累速率的空间分布呈现出平稳的东西向递增趋势：在跨越冰盖分水岭的50公里范围内，积累速率从145 kg/m²/a升至200 kg/m²/a。这一整体趋势之上叠加了尺度约为2.5 kg/m²/a/km的小型空间波动，幅度约为区域平均积累速率的1.5%。由7处追踪等时层所界定的7个时段的时间变化幅度，约为过去400年区域平均积累速率的±4%，在NorthGRIP点位处具体表现为±7 kg/m²/a。若全新世以来的区域积雪积累格局在过去数千年间保持稳定，且冰流状态与现今相近，则NorthGRIP上游沿粒子运动轨迹的平流效应，不会对基于深冰芯重建的过去10 kyr气候驱动的积雪积累速率变化解释产生显著影响。