Late Pleistocene-Holocene Marine Geology of Nares Strait Region: Palaeoceanography from Foraminifera and Dinoflagellate Cysts, Sedimentology and Stable Isotopes

摘要

Während der Nares-Expedition 2001 wurden die Sedimente im Gebiet der Nares Strait beprobt, um Kerne für hochauflösende paläozeanographische Untersuchungen des pleistozänen bis holozänen Klimawandels zu gewinnen. Kerne mit einer Länge von über 4 m wurden aus Sedimenten des Jones Sound bei Coburg Island (Kern 6: 75°35'N, 78°41'W), im John Richardson Fjord am Kane Basin (Kern 39: 80°09,6'N, 70°50,3'W) und im nordöstlichen Hall Basin (Kern 79: 81°18,3'N, 62?16,4'W) gewonnen. Kurze Kerne und Dredgen wurden auf den Schelfrändern östlich und westlich des Smith Sound und im Kennedy Channel genommen. An den langen Kernen vom Jones Sound und Hall Basin wurden Sediment-Textur, stabile Isotope, Mikrofossilien und Palynomorphe detailliert untersucht.%A sediment-sampling program was carried out in the Nares Strait region during the Nares 2001 Expedition to obtain cores for high-resolution palaeoceanographic studies of late Pleistocene-Holocene climate change. Long cores (> 4 m) were obtained from basins near Coburg Island, Jones Sound (Core 6, 75°35'N, 78°41'W), John Richardson Fiord off Kane Basin (Core 39, 80°09.6'N, 70°50.3'W), and in northeastern Hall Basin (Core 79, 81°28.3'N, 62°16.4'W). Short cores and grab samples were taken on shelves east and west of northern Smith Sound and in Kennedy Channel. Detailed studies of sediment texture, stable isotopes, microfossils and palynomorphs were made on the longest cores from Jones Sound and Hall Basin at the southern and northern ends of the Nares Strait region. Core 6 is from a water depth of 561 m off Devon Island where the sea-ice cover (SIC) is presently > 5/10 for nine months per year. Sediment is a biotur-bated organic-rich clayey mud, with an age of 6315 ± 60 years BP near the base. The mud has a mean grain size ranging ～3-4.5 μm. Peaks of sand and granules appear at about 3.4 ka BP and increase upward, suggesting greater influx of ice-rafted detritus over the past 2000 years. Sedimentation rates of 16-19 cm/century allow for decadal-scale palaeoceanographic studies. Abundant foraminifers and common small bivalve shells are present. Benthic faunas are diverse, with common calcareous and agglutinated species, predominantly Reophax arctica and Textularia torquata. In contrast, planktonic foraminifera are sparse and have heavy δ~(18)O isotopic values (～3-5 per thousand), indicating that this fauna lives in the very cold (-1.5℃), saline (33.5) water below the pycnocline at ～125 m. Large-scale (～2 per thousand) oscillations in δ~(18)O values occur at intervals of about 2000 years. Palynomorphs include abundant dinoflagellate cysts, prasinophytes and foraminiferal linings; pollen and spores are also common. Palaeoceanographic reconstructions from dinocyst assemblages show that from ～6.5 to 3.3 ka BP, there were large oscillations in summer sea surface temperature (SST) from 3℃ cooler than now to 6℃ warmer, and that variations in SIC ranged from two months more to four months less of heavy ice compared to now. In Hall Basin, Core 79 is from a water depth of 550 m near the Petermann Glacier where SST is -1.4℃ but the thermocline is shallow and the bottom water below 200 m is warmer (-0.4 to 0℃) than in Jones Sound.