Using coralline algae to understand historic marine cloud cover

Free-living coralline algae lay down growth bands formed by areas of more and less calcified cells which, in certain species, are associated with winter and summer growth respectively. Band width and cell calcification of Lithothamnion glaciale from Scotland were compared to annual and seasonal cloud cover and sea surface temperature (SST). There was a negative relationship between summer calcification (the degree of cellular carbonate infilling) and winter cloud cover. Annual and summer SST were also negatively related to summer calcification. This indicates that summer calcification may be affected by the previous winterʹs cloud cover and that summerʹs/yearʹs SST. No relationships between band width and cloud cover were observed. A cloud cover hindcast using summer calcification and SST indicated a modest rise in cloud cover trends from 1910 to 2006 and a 12 (mean) year cyclicity in cloud cover, however, the latter may be associated with other site-specific factors. This study demonstrates the utility of densitometric algochronology in understanding marine temperature and cloud cover histories.