Since the fossils in ocean sediments just tell us the surface ocean conditions like carbon and nutrient. But the vertical changes of the ocean is quite poorly understood. So could any scientists tell us how to evaluate the past nutrient conditions of the surface to deep ocean exchanges? Any robust proxy tools?
Hi Fangliang:
The stratification of the past oceans is normally reconstructed via carbon isotope of benthic and planktic foraminifera. There are so many papers published in this field which genrally intended to reconstruct the the past ocean circulations (e.g., Nunes and Norris, 2006). Planktic foraminifera live in different depths (surface, middle, and deep) of the photic zone which C. Emiliani was the first to point out to this phenomenon back in the 40s. Using d13C of both benthic and planktic forams, you can map the gradients of nutrients (e.g., Kennett and Stott. 1991). So to answer your question, yes! biological and geochemical proxies can reconstruct the paleo-nutrients.
Dear Fangliang
The chemical composition of the ocean is related to submarine currents, sediment supply and etc. any change in chemical composition is reflected on morphological characteristics of biota and flora. Since the bathymetric character is one the most significant factor of paleoecologic during geologic time scale, therefore any changes in chemical and physical characteristics in water stratification can affected on taxonomy and morphology of fossils directly. The changes on morphological is distinguishable on ontogeny trend (Hart, 1990). Actually paleoecological description of biota and flora are recognized on the mentioned changes (Bolz, 1977).
Regards
Massih
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