中文摘要：

冰岛北部陆架MD99-2271孔沉积硅藻组合呈现暖水硅藻数量增加、冷水硅藻数量减少和这两类硅藻数量周期性此消彼长的特点,反映了气候在趋暖的背景下,冷暖交替的过程。通过该区温度指数Rw/wc值（暖水硅藻种含量与海冰种及暖水种含量总和的比值）的变化,重建了冰岛北部陆架古海洋环境：Blling-Allerd暖期时,暖水硅藻T.nitzschioides含量较高,表明印明格暖流对研究区的影响较强;随着暖水硅藻含量减少,海冰硅藻F.cylindrus和T.bulbosa的显著增加,此时暖流强度减弱,东格陵兰寒流明显增强,冰岛北部海域进入末次冰消期以来最冷的时期——Younger Dryas冷期。11cal.kaBP左右暖水硅藻T.nitzschioides和T.oestrupii数量急剧升高,表明该海域海洋环境发生了明显变化,并逐步向全新世大暖期过渡,此时冰岛北部陆架海域现代海洋格局基本形成。全新世大暖期时,硅藻群落表现为暖水种的显著增多,海冰、极地及冷水硅藻较之前明显减少,说明冰岛北部海域主要受北大西洋暖流的分支——印明格暖流的影响,海洋环境较温暖;6cal.kaBP之后东格陵兰寒流逐渐增强,冰岛北部海洋环境转冷,全新世大暖期结束。

英文摘要：

The sustaining increase in warm diatoms and the continuing reduction in cold diatoms found from the core MD99-2271 on the North Iceland shelf reveal a warming trend of climate in this area during the time of 14.6~3cal.kaBP.The periodic counter-balance of these two types of diatoms in the diatom assemblages may indicate the temperature variation on the background of climate warming.The reconstructed paleoenvironment of the North Iceland shelf by the Rw/wc,which may indicate the temperature changes of seawater,can roughly be divided into five stages since the last deglaciation.During the warm BllingAllerd period,relatively high abundance of warm-water species T.nitzschioides suggested that the Atlantic water,presumably related to the strength of the Irminger Current,had an even stronger influence on the North Icelandic shelf.Increased abundance of sea-ice diatom species（F.cylindrus and T.bulbosa）indicate a significant increase in the influence of East Greenland Current during 12.8~11.5cal.kaBP.This coincides with the coldest period since the last deglaciation（Younger Dryas event）.The present-day oceanographic current system in this area was established at the transition to Holocene.Between 10.2~6cal.kaBP,there was a significant increase in warm-water species（T.nitzschioides and T.oestrupii）,and a marked decline of sea-ice species and cold water species.This suggests a period of enhanced influence of the Irminger current on the North Icelandic shelf,corresponding in time to the Holocene climatic optimum.Finally,the influence of the East Greenland Current became stronger at the end of the Holocene Climate Optimum,which led to the sea water temperature dropping.