Geochemistry of carbon at DSDP Leg 60 Holes

The 11 frozen cores from the Mariana Trough area from Holes 452 through 455, 459B, 460, and 460A are characteristically low in organic carbon (less than 0.2%) and contain a predominance of n-alkanes within the saturates fraction. There is no odd-predominance of n-alkanes as is typical of immature recent sediments. However, recent sediments containing immature organic matter with normal distributions of n-alkanes {OEP1 approximately equal to 1) are characteristic of sediments derived from purely marine sources (Brooks, 1970; Powell and McKirdy, 1973; Tissot et al., 1975). This type of sediment is very rare. However, at least one case where an immature sediment contains an OEP of near 1 has been reported in samples similar to those reported herein - that is, the Cariaco Trench (Hunt, 1979).

The modulating effect of light intensity on the response of the coccolithophore Gephyrocapsa oceanica to ocean acidification

Global change leads to a multitude of simultaneous modifications in the marine realm among which shoaling of the upper mixed layer, leading to enhanced surface layer light intensities, as well as increased carbon dioxide (CO2) concentration are some of the most critical environmental alterations for phytoplankton. In this study, we investigated the responses of growth, photosynthetic carbon fixation and calcification of the coccolithophore Gephyrocapsa oceanica to elevated inline image (51 Pa, 105 Pa, and 152 Pa) (1 Pa ~ 10 µatm) at a variety of light intensities (50-800 µmol photons/m**2/s). By fitting the light response curve, our results showed that rising inline image reduced the maximum rates for growth, photosynthetic carbon fixation and calcification. Increasing light intensity enhanced the sensitivity of these rate responses to inline image, and shifted the inline image optima toward lower levels. Combining the results of this and a previous study (Sett et al. 2014) on the same strain indicates that both limiting low inline image and inhibiting high inline image levels (this study) induce similar responses, reducing growth, carbon fixation and calcification rates of G. oceanica. At limiting low light intensities the inline image optima for maximum growth, carbon fixation and calcification are shifted toward higher levels. Interacting effects of simultaneously occurring environmental changes, such as increasing light intensity and ocean acidification, need to be considered when trying to assess metabolic rates of marine phytoplankton under future ocean scenarios.