Data from the paper shows Arctic sea ice concentrations were similar [or less than] the present during the Medieval & Roman Warm Periods & the late Holocene Climate Optimum, when solar activity was relatively high. The authors find Arctic sea ice was at the highest concentrations during the Little Ice Age [LIA], corresponding to a period of very low solar activity [the LIA is coincidentally when instrumental observations of global temperatures began].
|Total Solar Irradiance shown in top graph, LIA = Little Ice Age, MCA = Medieval Climate Anomaly = Medieval Warm Period, DACP = Dark Ages Cold Period, RWP = Roman Warm Period, HTM = Holocene Thermal Maximum|
A diatom-based sea-ice reconstruction for the Vaigat Strait (Disko Bugt, West Greenland) over the last 5000 yr
- A diatom-based sea-ice transfer function has been established off West Greenland.
- The reconstructed sea ice coincides with the instrumental data for the last 75 years.
- Sea-ice condition is influenced by changes in the West Greenland Current components.
- The period of the most extensive sea-ice cover occurred during the Little Ice Age.
- Solar forcing may be an important contributor to the sea-ice changes.
A diatom-based sea-ice concentration (SIC) transfer function was developed by using 72 surface samples from west of Greenland and around Iceland, and validated against associated modern SIC. Canonical correspondence analysis on surface sediment diatoms and monthly average of SIC indicated that April SIC is the most important environmental factor controlling the distribution of diatoms in the area, justifying the development of a diatom-based SIC transfer function. The agreement between reconstructed SIC based on diatoms from West Greenland and the satellite and modelled sea-ice data during the last ~ 75 yr suggests that the diatom-based SIC reconstruction is reliable for studying the palaeoceanography off West Greenland.
Relatively warm conditions with a strong influence of the Irminger Current (IC) were indicated for the early part of the record (~ 5000–3860 cal. yr BP), corresponding in time to the latest part of the Holocene Thermal Maximum. Between 3860 and 1510 cal. yr BP, April SIC oscillated around the mean value (55%) and during the time interval 1510–1120 cal. yr BP and after 650 cal. yr BP was above the mean, indicating more extensive sea-ice cover in Disko Bugt.
Agreement between reconstructed April SIC and changes in the diatom species suggests that the sea-ice condition in Disko Bugt was strongly influenced by variations in the relative strength of two components of the West Greenland Current, i.e. the cold East Greenland Current and the relatively warm IC. Further analysis of the reconstructed SIC record suggests that solar radiation may be an important forcing mechanism behind the historic sea-ice changes.
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