Deep water nutrient and oxygen gradients in a modern coastal upwelling zone and their paleoceanographic implications

Abstract

Dissolved phosphate and oxygen data from the waters at >300 m depth beneath the Peru upwelling system imitate observed onshore/offshore surface productivity data. Positive onshore phosphate gradients and negative onshore oxygen gradients are greater in deeper water (up to 1000 m), reflecting the decreasing degree of horizontal mixing at depth. Mass balance reconstructions of surface productivity, nutrient remineralization, and onshore‐offshore chemical gradients suggest that the lack of wide continental shelves during glacial climates would lead to more pronounced dissolved nutrient and oxygen gradients in the deep water adjacent to continental margins. Horizontal δ13C gradients in sediments beneath highly productive coastal upwelling zones may have been as high as 0.5–1.0‰ per 100 km, suggesting caution in the interpretation of benthic δ13C samples adjacent to continental margins during low sea level stands.