TROPICAL ATLANTIC COCCOLITH SR/CA PRODUCTIVITY RECORDS FROM THE PALEOCENE-EOCENE THERMAL MAXIMUM

One hypothesis explaining the rapid recovery of temperature and atmospheric carbon following the PETM involves increased primary marine productivity and subsequent carbon burial in deep ocean sediments. The tropics, which contain the majority of the world’s oceanic surface area, are of particular importance in evaluating the geographic extent of this proposed feedback. Previous research is limited to sites in the Antarctic (ODP site 690) and the mid-latitude Pacific (ODP site 1209). Here we present Sr/Ca of coccoliths as a proxy for productivity changes at ODP site 1258 Demerara Rise in the tropical Atlantic. Sr/Ca incorporation in coccoliths has been shown to be positively correlated with productivity. We measured Sr/Ca in bulk samples of two different size sediment fractions (5-8 µm and 8-12 µm) via Atomic Absorption Spectroscopy, and in individually picked coccoliths of several genera using Secondary Ion Mass Spectrometry ion probe. This allows us to isolate the productivity responses of specific genera. Sample depths ranged from 176.0 mbsf to 171.75 mbsf, providing data points encompassing the PETM and the surrounding time period. Toweius showed a large decrease in productivity during the PETM, eventually recovering to near pre-PETM levels. In contrast, Coccolithus pelagicus showed an increase in productivity during the event. Bulk data for the 5-8 µm and 8-12 µm sediment fractions showed similar trends to Toweius and C. pelagicus, respectively. The presence of additional genera in the bulk samples accounts for minor deviations from the genus specific data. The difference in the productivity response of these two genera is likely due to varied modification of their respective ecological niches produced by the conditions of the PETM. Combined with previous research from OPD sites 690 and 1209, the data indicate that there was no unified coccolithophorid response to the PETM. In the tropics and mid-latitudes, there are examples of both productivity increases and decreases among different genera, whereas in the high latitudes all studied genera appear have increased or constant productivity.