Abstract. Strong similarities in Holocene climate reconstructions derived from multiple
proxies (BSi, TOC – total organic carbon, δ13C, C∕N, MS – magnetic susceptibility, δ15N)
preserved in sediments from both glacial and non-glacial lakes across Iceland
indicate a relatively warm early to mid Holocene from 10 to 6 ka,
overprinted with cold excursions presumably related to meltwater impact on
North Atlantic circulation until 7.9 ka. Sediment in lakes from glacial
catchments indicates their catchments were ice-free during this interval.
Statistical treatment of the high-resolution multi-proxy paleoclimate lake
records shows that despite great variability in catchment characteristics,
the sediment records document more or less synchronous abrupt, cold
departures as opposed to the smoothly decreasing trend in Northern Hemisphere
summer insolation. Although all lake records document a decline in summer
temperature through the Holocene consistent with the regular decline in
summer insolation, the onset of significant summer cooling occurs ∼5 ka at high-elevation interior sites but is variably later at sites
closer to the coast, suggesting that proximity to the sea may modulate the impact
from decreasing summer insolation. The timing of glacier inception during the
mid Holocene is determined by the descent of the equilibrium line altitude
(ELA), which is dominated by the evolution of summer temperature as summer
insolation declined as well as changes in sea surface temperature for coastal
glacial systems. The glacial response to the ELA decline is also highly
dependent on the local topography. The initial ∼5 ka nucleation of
Langjökull in the highlands of Iceland defines the onset of neoglaciation
in Iceland. Subsequently, a stepwise expansion of both Langjökull and
northeast Vatnajökull occurred between 4.5 and 4.0 ka, with a second
abrupt expansion ∼3 ka. Due to its coastal setting and lower
topographic threshold, the initial appearance of Drangajökull in the NW
of Iceland was delayed until ∼2.3 ka. All lake records reflect abrupt
summer temperature and catchment disturbance at ∼4.5 ka, statistically
indistinguishable from the global 4.2 ka event, and a second widespread
abrupt disturbance at 3.0 ka, similar to the stepwise expansion of
Langjökull and northeast Vatnajökull. Both are intervals
characterized by large explosive volcanism and tephra distribution in Iceland
resulting in intensified local soil erosion. The most widespread increase in glacier advance, landscape
instability, and soil erosion occurred shortly after 2 ka, likely due to a
complex combination of increased impact from volcanic tephra deposition,
cooling climate, and increased sea ice off the coast of Iceland. All lake
records indicate a strong decline in temperature ∼1.5 ka, which
culminated during the Little Ice Age (1250–1850 CE) when the glaciers
reached their maximum Holocene dimensions.
Small glaciers disappearing in the tropical Andes: a case-study in Bolivia: Glaciar Chacaltaya (16o S)
