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32nd Annual Arctic Workshop
Abstracts |
EVIDENCE FOR EARLY HOLOCENE ATLANTIC WATER ON THE NORTH AMERICAN ARCTIC SLOPE AND AN EARLIEST HOLOCENE MELTWATER EVENTAUTHORS
Core P189AR-P45 (henceforth P45) was collected in 405 m of water at 70° 33.03?N and 141° 52.08?W on the slope of the Beaufort Sea and west of the Mackenzie River delta. The 511 cm core has a basal (uncorrected) radiocarbon date of 11,240 ± 140 BP and the date on the core top is 7920 ± 110. Four other dates define a linear rate of sediment accumulation of around 135 cm/ky. An ocean reservoir correction of ~800 yrs is applied to the dates, based on the measurements of molluscs collected prior to the ?bomb effect?. The coring site is located at a depth dominated by modified Atlantic Water. This relatively warm water mass lies below the cold and fresher coastal and shelf waters which maintain a heavy cover of sea-ice throughout much of the year. An synthesis of hydrographic data from the Arctic Ocean (Steele et al.) indicated that at the core site the water temperature is about 0.4°C with a salinity of 34.8?. We have measured a variety of sediment properties including grain-size, TOC and Carbonate weight %. We have undertaken stable isotopic measurements (d18O and d13C) on both planktonic foraminifera (N. pachyderma s) and the benthic species Cassidulina neoteretis and determined species composition at a coarser sampling resolution. A key observation is that in the early part of the record, in the earliest part of the Holocene, that the fauna is dominated by Cassidulina neoteretis, a benthic species which is used as an indicator of modified Atlantic Water. This species becomes less important after about xx ka and is replaced by elements more common in Arctic assemblages, such as Cassidulina reniforme. Despite the presence of large tidewater ice sheet margins in the Canadian Arctic Channels > 10 ka (cf. Dyke and Savelle, 2000) there is little specific evidence for pervasive iceberg rafted detritus (IRD) and indeed the sediment is finer at the base of the core. The d18O records for both benthic and planktonic foraminifera exhibit significant variability but both records also posses a statistically significant trend toward higher d18O values back in time. The highest d18O values in both data sets occurs around 9.5 ka. A notable feature of both records is a light d18O peak which occurs around 10 ka; in the benthic data the ?d18O between that peak and troughs on either side is > 1?. We believe that this ?meltwater spike? might be evidence for the large outburst flood down the Mackenzie River drainage noted by Fisher et al (2002). The ?d18O between benthic - planktonic d18O indicates that this difference has increased toward 6.8 ka
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