Automated Analysis of Planktic Foraminifers Part I: Application to Macroevolution and Climate Change
Abstract
Size and shape data of microfossils are tedious to gather manually but are efficiently obtained electronically. Using automated microscopy (see Part II, Bollmann et al., this volume) we have collected digitized images and extracted size information of >1.6 million foraminiferal tests in globally distributed Holocene and Cenozoic samples. In the Holocene the maximum sizes and maximum abundances co-occur under similar "optimum" environmental conditions. Total assemblage test sizes show a strong correlation with surface water temperature and stratification: they increase from high to low latitudes and show deviations from this general relationship towards smaller sizes in frontal systems and upwelling areas. Cenozoic size changes in planktic foraminiferal assemblages were pronounced in low latitude and minor in high latitude areas. The global size record reveals the following major features: (a) a dramatic size decrease at the K/T-boundary, followed by (b) an interval of "dwarfs" (Paleocene - late Eocene), (c) a transition period from the late Eocene to the mid-Miocene, when low-latitude assemblages started evolving towards larger size, and (d) an interval of growth to gigantism in tropical and subtropical assemblages from mid-Miocene to Recent. Comparisons with proxy data show that low latitude planktic foraminiferal size increases are positively correlated to polar cooling. We infer that cooling of deep-waters led to enhanced stratification of surface waters and thus to increases in number and stability of ecological niches into which species could evolve. Whether these processes affected all species or only some awaits size analyses of single taxa (see Part III, Schiebel et al., this volume). The observed macroevolutionary size increase of planktic foraminifers in the Cenozoic seems largely abiotically driven.
- Publication:
-
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA....12320S