Iceberg Alley, East Antarctic Margin: Continuously laminated diatomaceous sediments from the late Holocene

A 24-meter jumbo piston core (NBP0101 JPC41) collected from an inner shelf basin in Iceberg Alley reveals an approximately 2000-year history of unusually high primary productivity. Iceberg Alley, an ~ 85 km long and 10-20 km wide cross-shelf trough on the Mac.Robertson Shelf, East Antarctica, reaches depths of 850 m and is bounded on either side by shallow banks that are lined with grounded icebergs. The sediments are laminated on a mm- to cm-scale throughout and are highly biosiliceous. Microscopic examination of smear slides, quantitative diatom slides, and sediment thin sections reveals that the sediments are visually dominated by the diatom Corethron pennatum, a large and lightly silicified species notable for its long and narrow shape; the valves, girdle bands and spines are all exceptionally well-preserved, suggesting rapid sedimentation. Other common species include sea ice-related Fragilariopsis, such as F. curta and F. cylindrus, with lesser contribution from other large diatoms, including Rhizosolenia spp. and Chaetoceros Ehrenberg subg. Chaetoceros. Chaetoceros Ehrenberg subg. Hyalochaete Gran resting spores, typically associated with large early-season blooms and common in many laminated sedimentary sections around the Antarctic margin, are surprisingly rare. Laminae with any significant terrigenous component are also very rare. Individual laminations appear to represent blooms, and in some cases sub-seasonal events are likely preserved. We suggest that this productive system is associated with the continuous presence of low-salinity meltwater derived from a combination of sea ice melt and grounded icebergs, which may be a source for a steady supply of micronutrients such as iron to the surface mixed layer.