Glacierclimate interactions at different timescales

In the sections below I will address what we know of these interactions on different time-scales. As we will see the actual 'glacier/ice sheet' relationships to climate, through mass balance (e.g. Figs 21.2 & 21.4), become increasingly tenuous so that in many cases the 'glacier response' is interpreted by proxies that do not delimit a specific glacier or ice sheet, such as the S18O of benthic foraminifera, which records an integrated global ice volume signal (Shackleton & Opdyke, 1973). It is necessary to re-emphasize that the mass balance is the product of a winter accumulation minus summer mass losses. Hence, although the literature on past glacial changes tends to focus on inferred temperature changes this should not hide the fact that changes in accumulation must also be taken into account.

In a similar vein, the use of ice-rafted debris (IRD) as an indicator of climatic change during the Holocene in marine sediments is increasingly being used, although there are significant caveats as to what interpretations can be placed on an increase in a particular sand-size fraction (Andrews, 2000). A first question is whether the IRD event represents the transport and deposition of sand-size particles from icebergs or from material entrained in sea-ice? If IRD increases at a site it may be that icebergs have changed their tracks or that the entrainment of sediment in outlet glaciers has changed (Warren, 1992). It is usually assumed that the only reason for changes in IRD is a change in the iceberg flux and that this is related to climate. As noted earlier, however, the response of tidewater glaciers to climate is not simple and involves glacier dynamics (Mann, 1986).

In the examples below my own biases are evident with a focus on the area from Iceland to the Canadian mainland. Iceland is an important area within the North Atlantic as it is strongly influenced by changes in marine conditions such as the Great Salinity Anomaly (GSA) (Dickson et al., 1988), including the extent of sea-ice and changes in the thermohaline circulation (Malmberg & Jonsson, 1997; Jonsson, 1992). Iceland's climate also reflects the atmospheric NAO (Hurrell, 1995; Rodwell et al., 1999), as one end member of the NAO is the strength of the Iceland Low.

Tablou Electrica
Figure 21.4 (A) Feed-back loops associated with the effect of increased runoff and freshwater export from the Arctic Ocean (from Mysak & Power, 1992). (B) Feed-backs between ice extent, climate, and glacier response in north Iceland (Stotter et al., 1999).

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