THE QUANTITATIVE MINERALOGY OF SURFACE AND HOLOCENE MARINE SEDIMENTS (< 2 MM SIZE FRACTION) ON THE ICELAND MARGIN: SPATIAL AND TEMPORAL VARIATIONS IN SEDIMENT TRANSPORT BY DRIFT ICE

The continental shelf off Iceland receives clastic sediments from the adjacent landmass, plus exotic mineral species transported 100's-1000's km in drift ice, i.e. various forms of sea ice or icebergs. Rather than relying only the sand fraction for estimating ice rafted debris (IRD) variations we recognize that drift ice carries sediments in all size classes with sea ice largely transporting silt-sized sediments (results from sediment traps). We use XRD scans of the < 2 mm sediment fraction, after spiking with ZnO, and milling to obtain weight % (w%) estimates of both the clay and non-clay minerals. The non-clay fraction constitutes around 50-70 w% with the largest components being various feldspars---Labradorite being the most common with between 15-22 w%. The clay minerals are dominated by saponite (25-30 w%), one of the smectite group. Analysis of the mineralogy of Icelandic glacial diamictons (tills) from the Iceland shelf shows quartz <0.5 w%, commensurate with the largely basaltic composition of the island. An analysis of ~50 seafloor surface samples show a distinctive spatial distribution of quartz, with a band of high values (2-6 w%) extending along the NW-N central shelf of Iceland and mimicking the recent and historic distribution of drift ice. We have derived downcore mineral variations in cores B997-321, -327, -330,and –338 from NW Iceland at better than 100yr/sample resolution---these cores span that last 6, 5, 10, and 11-14 14C ka BP respectively. Quartz w% data have also been obtained from MD99-2269 at a 30yr sample resolution for the last 12 cal ka. The data from these cores indicate substantial temporal variations in the delivery of quartz to NW-N Iceland at century to millennial time-scales with a notable increase in quartz w% during the Neoglacial—the last 5-6 cal ka. A detailed comparison with the records of drift ice off the coasts of Iceland over the last 1200-yr shows substantial agreement between the occurrence of ice and our proxy, quartz w%.