Fram Strait Ice Export during the Nineteenth and Twentieth Centuries Reconstructed from a Multiyear Sea Ice Index from Southwestern Greenland

Abstract

Historical observations of multiyear ice, called ?storis,? in the southwest Greenland waters exist from the period 1820?2000, obtained from ship logbooks and ice charts. It is argued that this ice originates in the Arctic Ocean and has traveled via the Fram Strait, southward along the Greenland coast in the East Greenland Current, and around the southern tip of Greenland. Therefore, it is hypothesized that these observations can be used as ?proxies? for reconstructing the Fram Strait ice export on an annual basis. An index describing the storis extent is extracted from the observations and a linear statistical model formulated relating this index to the Fram Strait ice export. The model is calibrated using ice export values from a hindcast study with a coupled ocean?ice model over the period 1949?98. Subsequently, the model is used to reconstruct the Fram Strait annual ice export in the period 1820?2000. The model has significant skill, calculated on independent data. Based on this reconstruction, it is discussed how time periods with large and small ice export on multidecadal timescales coincide with time periods of cold and warm North Atlantic sea surface temperatures reported by others. This implies that trend studies based on satellite observations should be regarded with some care, since the time period of satellite observations, the last decades, where a particularly strong negative trend is observed in the ice export, is preceded by a time period with a positive trend. The occurrence of ?great salinity anomalies? (GSAs) is also connected to the multidecadal variability. The GSAs observed in Greenland waters around 1968?70 and 1980?82 both occurred when the general level of ice export was high. Prior to these there was a long period with generally low ice export and no GSAs, but during an epoch around the turn of the nineteenth century several GSAs occurred. Finally, it is found that the correlation between the Fram Strait ice export and the North Atlantic Oscillation (NAO) index has alternating intervals of significant and nonsignificant correlation throughout the period.