Late Pleistocene-Holocene marine geology of Nares Strait Region: Palaeoceanography from foraminifera and dinoflagellete cysts, sedimentology and staple isotypes

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 bioturbated 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 isotopic values (~3-5 ‰), indicating that this fauna lives in the very cold (-1.5 °C), saline (33.5) water below the pycnocline at ~125 m. Large-scale (~2 ‰) oscillations in δ 18 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 °C cooler than now to 6 °C 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 °C but the thermocline is shallow and the bottom water below 200 m is warmer (-0.4 to 0 °C) than in Jones Sound. SIC is presently about 8/10 for eleven months per year. Core 79 consists of dominantly clayey calcareous mud, with an upper unit of brown silty mud and scattered sand and has an age of more than 8.4 ka BP at the base. This overlies ~4 m of brown and gray coarsely banded mud with some finely laminated intervals and an age of 14.07 ka BP at the top. Shear strength is low (<8-12 KN m-2) and shows no compaction by grounded ice. Planktonic and benthic foraminafera occur throughout and their δ 18 records are consistently lighter (3-4 ‰) than in Core 6, reflecting the warmer water below 50 m. The δ 18 signals are also less variable, suggesting smaller climatic oscillations on the polar margin than in Jones Sound. The diverse benthic assemblages are dominated by the calcareous species Buliminella hensonii, Elphidium clavatum and Islandiella teretis. The banded sediment has low numbers of benthic foraminifera dominated by Cassidulina reniforme and Elphidium clavatum, with relatively high percentages of Buliminella hensoni, Islandiella teretis and some Stetsonia arctica indicating Arctic Ocean slope to deep-water conditions. The banded sediment represents deposition under pack ice or a floating ice shelf and there is no evidence of grounded ice in eastern Hall Basin during at least the past 14 ka BP.