The "Little Ice Age" maximum in southeast Iceland: integrating the glacial, climatic and historical records of change

This thesis investigates the 'Little Ice Age' (LIA) glacial maximum in southeast Iceland through integration of the glaciological, climatological and historical records of change in order to enhance current understanding about the timing, expression and consequences of glacier-climate interactions.

Previous opinions have differed regarding the timing of the LIA maximum extension of Icelandic glaciers with possibilities generally ranging from the mid-/late- 18th to late 19th centuries. Moraines along the margins of Skalafellsjokull and Heinabergsjokull, two Vatnajokull outlet glaciers in southeast Iceland, were dated in order to examine whether disparities may have arisen due to differing glacier response rates, selective preservation of evidence or unreliable dating techniques. Approximately 12,000 lichens were measured on 40 moraine fragments to provide surface age proxies. The population gradient lichenometric technique yields late 18th to early 19th century moraine dates, whereas the conventional 'average of the five largest' method clusters moraine dates to the late 19th century. Subsequently, an updated tephrochronology for southeast Iceland (based on geochemistry and tephrastratigraphy) obtained from 25 reference soil profiles was used to identify tephra layers within 15 additional soil profiles dug around the LIA moraines. Tephrochronology is consistent with the LIA maximum extent for both glaciers occurred between AD 1755 and 1873. A late 18th to early 19th century LIA maximum at Skalafellsjokull and Heinabergsjokull accords with widespread glacial maxima across Iceland, indicative of a pervasive response to climatic deterioration.

A positive degree-day mass balance model was implemented for Skalafellsjokull, Heinabergsjokull and Lambatungnajokull to assess the linkages between spatial expression of LIA glacier maxima with potential climatic envelopes during the late 18th to early 19th centuries. Reconstructions suggest that LIA maximum glacier mass balance was induced by a ~1-1.5°C temperature reduction associated with severe sea-ice years during the 1780s. Equilibrium line altitudes may have lowered by -140 m during the LIA maximum. The model also indicates that glacier hypsometry significantly affects differential response of the three Vatnajokull outlet glaciers under various climatic regimes. Additional statistical tests (Watson's U2 and cluster analysis) of lichenometric data, undertaken to identify contemporaneous moraine clusters and reconstruct the detailed pattern of past ice margins, support the idea of inferences regarding differential glacier response at Skalafellsjokull and Heinabergsjokull.

Consequences of the LIA glacial maximum were also explored to illustrate the relationship between glacial maxima and environmental changes perceived by residents of southeast Iceland. An intensive ethnographic survey incorporating local narrative and perception indicates that, although climatic deterioration during the 17,h-19th centuries ultimately affected farming viability, it was the interplay of climate with concomitant cultural and socio-economic factors that ensured effective strategies were emplaced to preserve life and livelihood. Ethnographic survey and local literature investigations are strongly coherent with the glacial chronology and point to a LIA maximum during the late 18th to early 19th centuries. However, sensitive landscapes can 'store memories' through the accumulation of disturbances during periods of climatic variability, eventually reaching a critical threshold and inducing landscape instability, such as occurred during the 19th century. This may have led to previous conclusions implying widespread late 19th century LIA glacier maxima across the region.

It appears that the Icelandic LIA glacial maximum occurred only slightly later than that in Norway or Greenland and implies differential regional responses to secular changes in the NAO. A negative phase of the NAO during the late 18th century, in conjunction with extensive sea-ice, led to prolonged cold conditions across Iceland conducive to glacier advance. The Icelandic LIA glacial chronology is in-phase with that of the Pacific Northwest and out-of-phase with Alaska due to synoptic climatic associations across the Northern Hemisphere, although maximum extents were reached earlier in the latter locations. However, an apparent asynchrony between Iceland and New Zealand in both the timing of LIA glacial maxima and temperatures associated with the individual chronologies implies a complicated global signal. At present, it remains impossible to attribute the direct cause of the LIA, although extant evidence suggests that forcing factors linked to the internal dynamics of the climate system itself may have been responsible for the LIA, though external factors enhanced LIA climate variability.