Late-Holocene paleoenvironments of northwest Iceland from lake sediments

Frozen sediment cores from two lakes in northwest Iceland, Vatnsdalsvatn and Thiðriksvallavatn, provide a nearly 1000-year, decadal-scale record of past environmental changes, based on environmental magnetism, inductively coupled plasma optical emission spectroscopy geochemistry, carbon content, and C/N analyses. Accelerator mass spectrometry 14C and 210Pb results provide chronologies for both sites, covering the late 20th century to 960 BP at Vatnsdalsvatn and to 480 BP at Thiðriksvallavatn. These analyses reveal higher levels of sedimentary carbon during the Little Ice Age, between 600 and 50 BP, at Vatnsdalsvatn. C/N analyses suggest that some of this carbon enrichment came from terrestrial plants. Higher erosion rates during the Little Ice Age may also have increased the influx of limiting nutrients, enhancing algal productivity. Erosion is the dominant mechanism for sedimentary changes at both sites and seems to occur at predictable intervals. Geochemical indicators of erosion oscillate with a distinct 80–100 yr periodicity for nine centuries at Vatnsdalsvatn and for four centuries at Thiðriksvallavatn. These erosion cycles are consistent with long-term stability in the positive mode of the North Atlantic Oscillation but may also be attributed to local climatic effects associated with Great Salinity Anomalies.