冰岛—法罗海脊东南深海底形及底流特征

DEEP SEA BEDFORMS AND THEIR BERING ON BOTTOM CURRENTS,IN SOUTHEASTERN ICELAND-FAROE RIDGE

冰岛—法罗海脊位于东北大西洋和挪威海之间,其东南侧水深600～1 200m,构成法罗—设德兰水道(FSC)和法罗浅滩水道(FBC),两者相连合为挪威海深水通道(NS-DW)。持续而强劲的底层冷水流可搬运并沉积砂和砾级碎屑。利用侧扫声纳图、地震剖面和海底摄像识别出的大小沙波、新月形大沙丘、沙流、沙带、沙影和慧星痕等各种底形分布于顺水道5个区片中。一些大沙丘和沙带等大型底形形成于全新世大西洋期,如今基本稳定,偶尔活动,其他底形均处于运动之中。深海沉积底形结合水文实测资料揭示NS-DW水道自(61°N,5°W)向南再向西流,至第3出水口(冰岛盆地),全长约850km,宽约10～30km或更宽,冷水底层厚100～200m,流速0.3～1.0m/s或更高。在更向南的区域,逐渐混合于东北大西洋。

The Iceland-Faroe Ridge is located between the Norwegian Sea and the Northeast Atlantic Ocean,with a water depth of 600～1 200 m at its southeastern flank,where the Norwegian Sea Deep Water（NSDW） flows through the Faroe-Shetland and Faroe Bank Channels（FSC,FBC）.Persistent strong bottom currents acting on the seafloor in these areas can transport coarse sediments as big as sands and gravels.A large variety of sedimentary bedforms including sand waves,barchan dunes,sand ribbons and streamers,comet marks,sand shadows and sand sheets,are identified using sidescan sonar images,seismic profiles,seabed photographs.Five areas with different bedforms are recognized along the channels.Some large scale bedforms such as sand dunes and sand ribbons formed during the Atlantic Stage of the Holocene in the northeast Atlantic Ocean are stable at present except for some reactivated old bedforms.Most of the bedforms,however,are active at present in this region. The velocity（0.3～1.0 m/s）,direction and pathway of the cold bottom current can be deduced based on both hydrographic observations and sedimentary bedforms.The cold NSDW bottom water with a thickness of 100～200 m flows from（61° N,50° W） towards south,and then turns to west,passes through the third gateway（Iceland Basin）,and then gradually mixes with the Northeast Atlantic Water.The total distance is about 850 km,and the width is about 10～30 km or more.