Spatial variation in pollen 13 C correlates with temperature and seasonal development timing

Stable carbon isotope analyses were performed on the sporopollenin of modern Pinus sylvestris pollen (delta C-13(pollen)) from a network of sites across Europe. A strong linear relationship (r(2) = 0.68 P < 0.001) is observed between C-13(pollen) and mean temperature during the month prior to efflorescence. Although the duration of pollen development almost certainly varies between sites, these results support observations that the majority of pollen mass is accumulated during the last month of its formation and that the photosynthate used to form pollen has a delta C-13 composition reflecting climatic conditions during this development period. When the delta C-13(pollen) values are compared with mean annual temperature (MAT) or degrees latitude the data cluster around two regression lines. Both groups are positively correlated with temperature and decreasing latitude, one comprising pollen from sites north of similar to 50 degreesN while the other is composed of sites south of this. The slope of the regression line is steeper for the northern group, indicating stronger temperature sensitivity. The transition in between the northern and southern groups coincides with a shift in the timing of the development period from May/June to April/May. The associated changes in development period temperature and across this transition are from 15 degreesC and -25 parts per thousand for the most southern in the northern group to 9 degreesC and -30 parts per thousand for the most northern in the southern group. If these initial results are representative of Pinus sylvestris throughout its distribution, of palaeorecords may be used to reconstruct past development period temperature and provide an indication of mean annual temperature.