Fineresolution studies

The temporal resolution in the majority of Holocene paleoclimatic studies is about one sample per every 50-100 years with each sample representing 10-20 years. Such studies can detect broad-scale millennial changes only. Ice-core research has indicated that very abrupt, short-lived climatic changes have occurred in the Holocene. The detection of such changes and the reconstruction of centennial and decadal climate changes require fine-resolution studies. Such studies with one sample every 1-20 years and each sample representing 1-2 years are only possible from ice-cores, laminated lake or marine sediments, or speleothems, corals, tree-rings, and well-dated peat deposits. Baillie and Brown (2003), Zolitschka (2003), Cole (2003), Lauritzen (2003), and Fisher and Koerner (2003) review fine-resolution approaches based on tree-rings, laminated sediments, corals, speleo-thems, and ice-cores, respectively.

Many, but not all (e.g. Baldini et al. 2002; Snowball et al. 2002), fine-resolution studies have focused on climate variability in the past millennium (Bradley et al. 2003). The number of continuous high-resolution millennial-scale records is very low, with some ice-cores and laminated lake sediments and a few long tree-ring records mainly from high latitudes (Bradley et al. 2003). The most promising fine-resolution archive for the entire Holocene is probably speleothems (e.g. Linge et al. 2001; Dykoski et al. 2005; Tan et al. 2006). Henderson (2006) has recently proposed that "for paleoclimate, the past two decades has been the age of the ice core. The next two may be the age of the speleothem".

The Holocene 818O record from stalagmite calcite in the Dongge Cave in southern China (Dykoski et al. 2005) provides amazingly detailed information on fine-scale shifts in monsoon precipitation. Dramatic decreases in 818O occurred at the start of the Holocene and 818O remained low for 6000 years, suggesting high monsoon intensity until about 3500 years ago. Four positive 818O events in the early Holocene correlate, within their dating errors, with changes in the Greenland ice-cores and three of the events correlate with glacial meltwater pulses from the Agassiz and Ojibway glacial lakes. In addition, the Holocene is punctuated by numerous centennial- and multi-decadal-scale events with amplitudes up to half of the interstadial events seen in the record for the last glacial period. The Dongge Cave record shows that Holocene centennial- and multi-decadal-scale monsoon variability is significant but not as large as glacial millennial-scale variability. The 818O record shows significant periodicities suggesting its variation may have been influenced by solar forcing. There are several other significant peaks at El NiƱo frequencies, suggesting that changes in oceanic and atmospheric circulation patterns in addition to solar forcing have been important in controlling Holocene monsoon climate in this part of China. There is even evidence for a distinctive biennial oscillation of the Asian monsoon. The Dongge Cave record illustrates the level of detail about Holocene climate variability that can be obtained from detailed fine-resolution studies.

Such fine-resolution studies of Holocene climate indicate variability at all scales and different aspects of Holocene climate appear to have been changing in some way at all temporal and spatial scales that have been investigated. It is this variability at a range of scales that is the paradigm that is emerging from fine-resolution studies. Much remains to be discovered about this variability, its spatial and temporal patterns, and its underlying causes.

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