Revised age model of DSDP Site 95-612

Alkenone-based Cenozoic records of the partial pressure of atmospheric carbon dioxide (pCO2) are founded on the carbon isotope fractionation that occurred during marine photosynthesis (epsilon [p37:2]). However, the magnitude of epsilon [p37:2] is also influenced by phytoplankton cell size - a consideration lacking in previous alkenone-based CO2 estimates. In this study, we reconstruct cell size trends in ancient alkenone-producing coccolithophores (the reticulofenestrids) to test the influence that cell size variability played in determining epsilon [p37:2] trends and pCO2 estimates during the middle Eocene to early Miocene. At the investigated deep-sea sites, the reticulofenestrids experienced high diversity and largest mean cell sizes during the late Eocene, followed by a long-term decrease in maximum cell size since the earliest Oligocene. Decreasing haptophyte cell sizes do not account for the long-term increase in the stable carbon isotopic composition of alkenones and associated decrease in epsilon [p37:2] values during the Paleogene, supporting the conclusion that the secular pattern of epsilon [p37:2] values is primarily controlled by decreasing CO2 concentration since the earliest Oligocene. Further, given the physiology of modern alkenone producers, and considering the timings of coccolithophorid cell size change, extinctions, and changes in reconstructed pCO2 and temperature, we speculate that the selection of smaller reticulofenestrid cells during the Oligocene primarily reflects an adaptive response to increased [CO2(aq)] limitation.

Global compilation of benthic data sets I

Approaches to quantify the organic carbon accumulation on a global scale generally do not consider the small-scale variability of sedimentary and oceanographic boundary conditions along continental margins. In this study, we present a new approach to regionalize the total organic carbon (TOC) content in surface sediments (<5 cm sediment depth). It is based on a compilation of more than 5500 single measurements from various sources. Global TOC distribution was determined by the application of a combined qualitative and quantitative-geostatistical method. Overall, 33 benthic TOC-based provinces were defined and used to process the global distribution pattern of the TOC content in surface sediments in a 1°x1° grid resolution. Regional dependencies of data points within each single province are expressed by modeled semi-variograms. Measured and estimated TOC values show good correlation, emphasizing the reasonable applicability of the method. The accumulation of organic carbon in marine surface sediments is a key parameter in the control of mineralization processes and the material exchange between the sediment and the ocean water. Our approach will help to improve global budgets of nutrient and carbon cycles.