Glacio-limnological interactions at lake-calving glaciers

Glaciers;Icebergs;Limnology;Mass budget (Geophysics)

Haresign, Eleanor C. ; Warren, Charles ; Warren, Charles

University:University of St Andrews

Department:Earth & Environmental Sciences and Geography & Sustainable Development (Schools of)

关键词: Glaciers;    Icebergs;    Limnology;    Mass budget (Geophysics);   

Others  :  https://research-repository.st-andrews.ac.uk/bitstream/handle/10023/2793/EleanorCHaresignPhDThesis.pdf?sequence=3&isAllowed=y

来源: DR-NTU

【 摘 要 】

Iceberg calving is an efficient ablation process which introduces mechanical instability toglacier systems and can cause non-linear climatic response. This thesis uses glaciological andlimnological data to examine the relative contributions of calving and melting to mass loss atglacier termini, and the interplay between glaciological and limnological processes. Calvingdynamics are investigated at two lake-terminating glaciers; Glaciar Leon in Chile andFjallsjokull in Iceland. Glaciar Leon, a temperate, grounded outlet of the North PatagonianIcefield, terminates at an active but stable calving margin in Lago Leones. The calving rate of880 m a-1 in a mean water depth of 65 m is high for lake-calving glaciers. Detailed survey ofthe physical limnology of Lago Leones, important for considering heat transfer to thesubaqueous ice face, revealed thermocline development towards the terminus betweenspring and summer. Melting at the waterline along the glacier terminus facilitates calving byundercutting the subaerial calving cliff, and accounts for around a quarter of mass loss at theterminus. Waterline melting is also an important rate-controlling process for calving atFjallsjokull. Precise quantification of melt rates (subaerial, waterline and subaqueous) at thetermini of calving glaciers is difficult and hazardous, but this study has demonstrated thevalue of two techniques: (1) detailed survey of melt notch growth, and (2) use of a radiocontrolledboat to record water temperatures at the ice-water interface. Continuousautomated monitoring showed that lake-level fluctuations are integral to calving behaviour,influencing calving event timing and size over diurnal and hourly timescales. Fjallsjokull issensitive to climatic forcing whereas Glaciar Leon, which exhibits larger seasonal thanannual fluctuations, is less sensitive. Additional controls on calving at both sites are (1)buoyancy, (2) longitudinal stretching, and (3) the force balance at the ice-water interface.Calving operates along a continuum defined by the relative importance of interacting calvingmechanisms, to which the climatic response of calving glaciers is sensitive.