Revision of the early Holocene lake sediment based chronology and event stratigraphy on Hochstetter Forland, NE Greenland

The previously established and often debated lake sediment based chronology and event stratigraphy from Hochstetter Forland, NE Greenland, has been re-examined. These new studies show that the last deglaciation of the coastal area is several thousand years younger than previously described. The main reason behind the difference is the fact that the older chronology was based on ¹⁴C datings of bulk sediment samples, which are now shown to contain enough coal fragments to produce erroneous ages. The re-examination was performed on sediments from two lakes located within the Nanok moraine system: one is situated at or slightly above the marine limit around 65 m. the other at 21–22 m a.s.l. The combined stratigraphy from the two lakes shows that the area was deglaciated before 9000 BP, after which followed deposition of glaciomarine sediments, fining upwards. The first vegetation seems to have been dominated by grasses, Lycopodium and Polypodiaceae. At c . 8000 BP the limnic production increased significantly and a pioneer vegetation characterized the area. At this time the 'Artemisia' grains appear. A short but distinct climatic cooling occurs at c . 7500 BP causing a significant drop in lake productivity and possibly also producing coarser sediments in the (glacio)marine environment. About 200 years later the lake productivity again increased, very rapidly, and the marine sediments became finer and more rich in molluscs, as a response to the beginning of the climatic optimum. Because of the time-lag between climate and vegetation response it took another 300 years before Betulci nana immigrated, at the same time as the 'Artemisia' grains disappeared, and another several hundred years before a real dwarf-shrub vegetation developed in these parts of Hochstetter Forland. Before the lower lake was isolated from the sea at c . 6000 BP, coarse wave-washed sediments, followed by a typical isolation sequence, were deposited in it.