Radiocarbon ages and diatom abundance in cores GA306-BC4 and GA306-GC4 obtained during Galathea 3 cruise, West Greenland

Diatom assemblages from Holsteinsborg Dyb on the West Greenland shelf were analysed with high temporal resolution for the last 1200 years. A high degree of consistency between changes in frequency of selected diatom species and instrumental data from the same area during the last 70 years confirms the reliability of diatoms (particularly sea-ice species and warm-water species) for the study of palaeoceanographic changes in this area. A general cooling trend with some fluctuations is marked by an increase in sea-ice species throughout the last 1200 years. A relatively warm period with increased influence of Atlantic water masses of the Irminger Current (IC) is found at AD 750-1330, although with some oceanographic variability after AD 1000. A pronounced oceanographic shift occurred at AD 1330, corresponding in time to the transition from the so-called 'Medieval Warm Period' (MWP) to the 'Little Ice Age' (LIA). The LIA cold episode is characterized by three intervals with particularly cold sea-surface conditions at AD 1330-1350, AD 1400-1575 and AD 1660-1710 as a result of variable influence of Polar waters in the area. During the last 70 years, two relatively warm periods and one cold period (the early 1960s to mid-1990s) are indicated by changes in the diatom components. Our study demonstrates that sedimentary records on the West Greenland shelf provide valuable palaeoenvironment data that confirm a linkage between local and large-scale North Atlantic oceanographic and atmospheric oscillations.

对西格陵兰陆架霍尔斯坦斯堡湾（Holsteinsborg Dyb）过去1200年的硅藻组合开展了高时间分辨率分析。近70年来，选定硅藻物种的丰度变化与该区域实测数据之间具有高度一致性，这证实了硅藻（尤其是海冰硅藻种与暖水硅藻种）在该区域古海洋学变化研究中的可靠性。过去1200年里，海冰硅藻种丰度的增加反映出区域整体呈波动降温趋势。公元750年至1330年期间存在一段相对温暖的时期，该时段受伊尔明格海流（Irminger Current, IC）携带的大西洋水团影响显著增强，但公元1000年后该区域海洋环境存在一定波动。公元1330年发生了一次显著的海洋环境转型，其时间节点恰好对应从所谓“中世纪暖期（Medieval Warm Period, MWP）”向“小冰期（Little Ice Age, LIA）”的过渡。小冰期冷期以三段海表温度极低的时段为特征，分别为公元1330—1350年、1400—1575年以及1660—1710年，这一特征源于该区域受极地水团影响的不稳定性。近70年来，硅藻组合的变化揭示出两段相对温暖时段与一段寒冷时段（1960年代初至1990年代中期）。本研究表明，西格陵兰陆架的沉积记录可提供极具价值的古环境数据，证实了该区域局部与北大西洋大范围海洋及大气振荡之间存在关联。