PP21B-2231
Marine phytoplankton CO2 records since the Miocene - magnitudes of change inplied by cellular process models

Tuesday, 15 December 2015
Poster Hall (Moscone South)
Heather M Stoll, University of Oviedo, Oviedo, Spain
Abstract:
CO2 proxy records from the Mio-Pliocene rely heavily on data from the carbon isotopic fractionation of marine phytoplankton during photosynthesis (ep). However, fractionation is also sensitive to cell size, growth rate, and the degree of active C concentration at the site of photosynthesis. The ACTI-CO cell model provides one venue for exploring the implications of these multiple factors for the CO2 value consistent with a given ep determination. Using our recent alkenone ep record from the last 14 Ma, we explore in ACTI-CO mechanisms for using constraints of coccolith size for cell geometry, and coccolith calcification and isotopic fractionation coccoliths to constrain changes in carbon acquisition and the consequences for CO2 estimates.

In addition, we present a new ep  reconstruction for the past 13 Ma from the Equatorial Pacific based on diatom-bound organic matter . The isolation of pennate diatoms assures a similar cell geometry for the entire period, so that unlike the alkenone record, ep is not sensitive to temporal changes in cell size. The similar trends in CO2 from the size-corrected alkenone erecord and the diatom record suggest that there is a common global CO2 trend, and that size correction of the alkenone record reliably accounts for cell geometry effects. We employ the ACTI-CO model to evaluate the potential influence of changes in active carbon uptake on the magnitude of CO2 decrease since the Miocene.