Surface circulation patterns and the pathways of sea surface carbon dioxide (CO₂) off northern Chile (~27.5° S) between 30 and 10 kyr BP: global and/or local forcing?

Abstract. We present a reconstruction of past changes in partial pressure of CO₂ (pCO₂) from northern Chile (~27° S), between 10 and 30 kyr BP, based on carbon isotope composition of C_37:2-alkenone. The high-pCO₂ during the entire time series indicates that northern Chile upwelling system has been a permanent source of CO₂ to the atmosphere. The multiproxy reconstruction suggests that the CO₂ outgassing and sequestration pathways were modulated by local and global mechanisms. During global glacial conditions, an enhanced coastal upwelling forcing resulted in high-availability of deep water macronutrients and a CO₂-supersaturated water column, which combined with high-inputs of iron from the continent, intensified the carbon sequestration pathway of the biological pump, through diatom biomass export. During the deglacial, a decrease in the upwelling forcing, an increment in water column stability and reduced continental inputs of iron are consistent with a larger role of calcifying organisms in the plankton assemblage in terms of carbon sequestration pathway through the carbonate system.