The ongoing climate change represents a very pressing problem on societies’ sustainability. According to research on impacts of climate change in recent decades and past (paleoclimatic) records used and summarized by the IPCC reports, one of the many important questions that still remains to be answered is how primary productivity in the ocean (the basis of the food chain) will respond to ocean warming and expected changes in atmosphere and ocean circulation. At present, marine phytoplankton is responsible for roughly 50% of primary production on Earth and 80 to 90% of that oceanic primary productivity occurs in about 10% of the coastal ocean that is characterized by coastal upwelling. As such, these regions play an important role in modulating the CO2 content of the atmosphere and, given that C export from the atmosphere to the ocean floor is mainly due to diatoms, these microscopic algae have an outsized importance in the control of Earth climate

1. Furthermore, paleoatmospheric CO2 content shows a one-third decrease during glacial ages (even isotopic stages)

2. decreases in atmospheric pCO2 that have been suggested to be, at least in part, due in oceanic productivity

3. In addition, coastal upwelling areas are the most important fisheries’ regions given that they feed today’s world population.

The need to understand past oceanic productivity variations and their linkage with past climate change is then of key importance for climate prediction and inform modeling, as well as for sustainability policies definition.

The best-accepted and credible proxy for past productivity reconstruction from oceanic sediments, is, up to date, diatom abundance and assemblage composition. However, this is a time consuming method, as all the microfossil related methods, which are important and needed. But, in the case of the diatoms, that build their valves of opal (hydrated Si), given the fact that the ocean is undersaturated in Si from top to bottom, in most locations of the ocean sediments are barren of diatoms. Research on other phytoplankton groups has shown that they contain specific organic markers that remain preserved in the sediments even when their fossilizable parts disappear, such as in the case of coccolithophores that produce alkenones and dinoflagelates that produce dinosterol. So far, no specific organic marker has yet been reported for diatoms as a group. Therefore, given that upwelling areas share a common dominant group and assemblages, in this project we plan to investigate the organic mark/imprint of those

upwelling related species in order to be able to reconstruct primary productivity of the past. IODP Exp339 recovered cores U1385 (APL 763 by Hodell & Abrantes) and U1391 at ± 37º 34’ N latitude, close to MD95-2042 the “reference section” used to correlate millennial-scale variability from the marine environment with ice cores from Greenland and Antarctica and with European terrestrial sequences over the last glacial cycles4. These IODP sites form a transect in a region influenced by upwelling filaments (Capes Sines and S. Vicent), give us the unique possibility of investigating inter-hemispheric climate connections in a single location back to 1.5 Ma, productivity reactions to those climate variations, as well as the possibility to check the modulation of atmospheric pCO2 by marine primary productivity. In this project we plan to do so for the time interval known as the Mid-Pleistocene Transition (600 – 1100 ka), the period during which external orbital forcing over climate changed from 40 ka to 100 ka, and encompasses warm (interglacials) and cold (glacials) periods as well as glacial/interglacial transitions very variable either in orbital, extent, intensity or amplitude, composing the perfect set for this research.