Spatial and temporal patterns of iceberg rafting (IRD) along the East Greenland margin,ca. 68°N,over the last 14 cal.ka

Twelve 1–2 m, 10-cm-diameter gravity cores collected in 1988 and 1991, from the continental shelf and fjords of East Greenland near Kangerlussuaq Fjord/Trough (ca. 68°N, 32°W), have distinct changes in lithofacies and in the quantity of iceberg rafted (IRD) sediments. These changes are readily observed in X-radiographs of the split cores. We quantify the IRD contribution through grain-size analyses and counting the number of clasts >2 mm from the X-radiographs. Chronological control is provided by acclerated mass spectroscopy ¹⁴C dates on foraminifera. During deglaciation, after 14 cal.ka there was one interval of IRD accumulation ca. 12–13 cal.ka, followed by a brief return to IRD conditions centred at 9 cal.ka. Thereafter, a prominent feature of most cores on the shelf is an increase in IRD accumulation that started ca. 5–6 cal.ka, and which has increased toward the present. Indicators of iceberg rafting, such as the net sand flux and numbers of clasts >2 mm ka⁻¹, follow a power law distribution when graphed against distance from the present East Greenland coast, a measure of the position of the glacier margins. The form of the relationship indicates that there is a dramatic decrease in the supply of sediment from the fjords to the shelf. These relationships are used to estimate changes in the location of the ice margin during the late Quaternary based on a site on the East Greenland slope, Denmark Strait, and to discuss factors that can negate such a simple transfer function. © 1997 by John Wiley & Sons Ltd.     

Relative sea‐level changes since 15 000 cal. yr BP in the Nanortalik area,southern Greenland

We present new results for relative sea‐level change for southern Greenland for the interval from 9000 cal. yr BP to the present. Together with earlier work from the same region this yields a nearly complete record from the time of deglaciation to the present. Isolation and/or transgression sequences in one lake and five tidal basins have been identified using lithostratigraphic analyses, sedimentary characteristics, magnetic susceptibility, saturated induced remanent magnetisation (SIRM), organic and carbonate content, and macrofossil analyses. AMS radiocarbon dating of macrofossils and bulk sediment samples provides the timescale. Relative sea level fell rapidly and reached present‐day level at ～9300 cal. yr BP and continued falling until at least 9000 cal. yr BP. Between 8000 and 6000 cal. yr BP sea level reached its lowest level of around ～10 m below highest astronomical tide. At around 5000 cal. yr BP, sea level had reached above 7.8 m below highest astronomical tide and slowly continued to rise, not reaching present‐day sea level until today. The isostatic rebound caused rapid isolation of the basins that are seen as distinct isolation contacts in the sediments. In contrast, the late Holocene transgressions are less well defined and occurred over longer time intervals. The late Holocene sea‐level rise may be a consequence of isostatic reloading by advancing glaciers and/or an effect of the delayed response to isostatic rebound of the Laurentide ice sheet. One consequence of this transgression is that settlements of Palaeo‐Eskimo cultures may be missing in southern Greenland. Copyright © 2006 John Wiley & Sons, Ltd.     

Holocene sediment properties of the East Greenland and Iceland continental shelves bordering Denmark Strait (64–68°N), North Atlantic

The oceanographic Polar Front separates the East Greenland and Iceland margins. Surface water temperatures across Denmark Strait vary by 8–12 °C and represent one of the steepest oceanographic gradients on earth. The East Greenland margin is a polar environment, with extensive sea‐ice cover and calving glacier margins; in contrast, the Iceland shelf is much more temperate, and freshwater run‐off is a key component in land–ocean sediment transfers. Average sediment properties from these two contrasting climate and oceanographic continental shelf environments are compared in the spatial domain at 13 sites; the data represent the last 10 000 radiocarbon years of `normal' marine sedimentation for the two regions. The two regions have similar average rates of sediment accumulation (around 43·5 cm kyr<sup>?1</sup>), so that this key variable is factored out in explaining any differences in sediment properties. Dry sediment density, moisture content, hygroscopic moisture, total organic carbon and carbonate contents, mass magnetic susceptibility and the percentages of sand and silt are compared focusing on: (1) median values for sediment properties; and (2) downcore variability, measured by the coefficient of variation (CV). There are significant differences in all but one (hygroscopic moisture) of the sediment properties between Iceland and East Greenland; in four cases, the sense of the differences was not as predicted. In terms of downcore variation (CV), no difference was found between the two regions, nor between the 13 sites, whereas there are some significant differences between the variables. Carbonate and mass magnetic susceptibility have the largest spreads, and moisture content and dry sediment density are the least variable. Protocols are developed to identify the `type core' in a regional series of sites. The results indicate a need to develop a regional perspective on sediment properties, both as inputs to models of sedimentary processes in different polar/arctic environments, and as an indication of which sediment properties might be best suited for palaeoenvironmental downcore time series.     

Identification of arid phases during the last 50 cal. ka BP from the Fuentillejo maar‐lacustrine record (Campo de Calatrava Volcanic Field,Spain)

Geochemical (element analysis, molecular analysis of organic compounds), physical, palynological, mineralogical and sedimentary facies analysis were performed to characterise the sedimentary record in Fuentillejo maar‐lake in the Central Spanish Volcanic Field of Campo de Calatrava, in order to reconstruct the palaeoenvironmental and palaeoclimatic processes which controlled vegetation patterns and deposition of different sedimentary facies. The upper 20 m of core FUENT‐1 show variations in clastic input, water chemistry, vegetation and organic fraction sources in the lake throughout the Late Pleistocene and Holocene. The temporal framework provided by ¹⁴C accelerator mass spectrometry dating allows assigning the sequence to the last 50 cal. ka BP. Arid phases identified in the FUENT‐1 sequence are correlated to Heinrich events (HE) and to stadials of the Dansgaard/Oeschger (D/O) cycles. Siliciclastic facies with high magnetic susceptibility values, high Juniperus pollen content, a low Paq index (aquatic macrophysics proxy index), a decrease in the relative percentage of the n‐C₂₇ and an increase in the n‐C₃₁ alkanes are indicative of arid and colder climatic events related to HE 2, HE 1 and the Younger Dryas (YD). Similar short cold and arid phases during the Holocene were identified at 9.2–8.6, 7.5–7 and 5.5–5 cal. ka BP. In dolomite–mud facies, the pollen data show an increase in the herbs component, mainly – Chenopodiaceae, Artemisia and Ephedra – steppe taxa; a low Paq index, a decrease in the relative percentage of the n‐C₂₇ alkane and an increase in the n‐C₃₁ alkane are also observed. This facies was probably the result of lower lake levels and more saline–alkaline conditions, which can be interpreted as linked to arid–warm periods. These warm and arid phases were more frequent during Marine Isotope Stage (MIS) 3 and the interstadials of MIS 2. HE 4, HE 2, HE 1 and the YD in core FUENT‐1 were immediately followed by increases of warm steppe pollen assemblages that document rapid warming similar to the D/O cycles but do not imply increasing humidity in the area. Fuentillejo hydrology is controlled by changes in the atmospheric and oceanic systems that operated on the North Atlantic region at millennial scale during the last 50 cal. ka BP. Copyright © 2009 John Wiley & Sons, Ltd.