北大西洋北部中全新世以来古海洋环境记录

利用主成分分析法对冰岛北部陆架MD99-2275孔中全新世以来沉积物硅藻数据进行研究发现,5000—3000aB.P.,冰岛北部陆架表层古海水温度逐渐上升,来自印明格暖流的北大西洋暖水对该区域的影响有所增强。自3000aB.P.以来,表层海水温度开始稳步下降,北大西洋暖水水团的影响逐步减弱,而来自东格陵兰寒流和东冰岛海流的极地冷水水团的影响显著加强。在晚全新世气候逐渐变冷的过程中,发生了几次短期而显著的气候变冷事件,分别出现在3000—2600aB.P.,1300—1000aB.P.及600—200aB.P.。该中晚全新世古海洋环境记录与格陵兰冰芯(GSIP2)氧同位素气候记录存在良好的对应关系,也与冰岛北部陆架其他海水温度记录有较好的一致性。而冰岛北部陆架区域海底地形的复杂性和海流分布的差异性,以及所采用研究方法的不同则导致该区域各古海水温度记录之间也存在一定的差异性。

Biogenic silica concentration as a marine primary productivity proxy in the Holsteinsborg Dyb, West Greenland, during the last millennium

We analyzed the biogenic silica(BSi)content and produced a diatom-based summer sea-surface temperature(SST)reconstruction for sediment core GC4 from the Holsteinsborg Dyb,West Greenland.Our aim was to reconstruct marine productivity and climatic fluctuations during the last millennium.Increased BSi content and diatom abundance suggest relatively high marine productively during the interval of AD 1000–1400,corresponding in time to the Medieval Warm Period(MWP).The summer SST reconstruction indicates relatively warm conditions during AD 900–1100,followed by cooling after AD 1100.An extended cooling period during AD 1400–1900 is characterized by prolonged low in reconstructed SST and high sea-ice concentration.The BSi values fluctuated during this period,suggesting varying marine productivity during the Little Ice Age(LIA).There is no significant correlation between the BSi content and SST during the last millennium,suggesting that the summer SST has little influence on marine productively in the Holsteinsborg Dyb.A good correspondence between the BSi content and the element Ti counts in core GC4 suggests that silicate-rich meltwater from the Greenland ice sheet was likely responsible for changes in marine productively in the Holsteinsborg Dyb.

冰岛北部陆架3000年以来夏季表层海水温度及古气候事件

冰岛北部陆架MD992271孔沉积硅藻中喜暖硅藻数量持续减少以及喜冷藻类数量不断增加，反映了该区近3000年来气候变冷的趋势，而硅藻组合中这两类硅藻数量呈周期性的此消彼长，指示在趋冷的背景下，气候的冷暖交替过程．转换函数计算结果表明，该孔夏季表层海水温度变化大致可分3个阶段，在1400cal．aBP以前，温度基本高于平均值；在1400～700cal．aBP之间，温度在平均值上下起伏，而在700cal．aBP后，温度均处于平均值之下．在这3000多年间，还存在着4次明显的降温事件，降温事件的中心分别位于约2600，1900，1300和600cal．aBP．上述夏季表层海水温度变化和冰岛北部陆架HM107—03和MD992275孔资料相对比，明显具有一致性，同时也可与GISP2冰芯氧同位素及北大西洋深海沉积记录对比，说明冰岛北部陆架晚全新世夏季表层海水温度变化，受区域性气候变化的控制．直接导致上述海水温度变化，是影响该区暖流和寒流作用此消彼长的结果，而冰岛周边海域3000年来海流分布的基本格局未有明显改变．

Summer sea-surface temperatures and climate events on the North Icelandic shelf through the last 3000 years

Diatom data from core MD992271 on the North Icelandic shelf record a cooling trend through the last 3000 years. This is indicated by a general decrease in warm water species and an increase in cold water taxa. The relative abundance of these two diatom groups changed periodically, suggesting that the climate also fluctuated within this time period. The results of diatom-based transfer function calculation show that the summer sea-surface temperatures (SSTs) before 1400 cal. a BP were generally higher than the mean value for the last 3000 years and the summer SSTs fluctuated around the mean between 1400 and 700 cal. a BP, and dropped to the values below the mean after 700 cal. a BP. Four cooling events were distinguished, centered at around 2600, 1900, 1300 and 600 cal. a BP respectively. The results are not only consistent with the data from neighbouring cores HM107-03 and MD992275, but also comparable with those from the GISP2 ice core and from other marine sediment records in the North Atlantic. This suggests that changes in the summer SSTs reflect regional climate variations in the North Atlantic. On the North Icelandic shelf, the summer SST variation is a result of changes in the in-teraction between the cold and the warm currents in the area.