| Summary: | The remarkable synchrony between changes in temperature recorded in Greenland ice cores and variations in N isotope records from sedimentary cores recovered from the Arabian Sea and the Eastern Tropical North Pacific (ETNP) has provided evidence for teleconnections between changes in marine denitrification in the tropics and climate variations in the northern high latitudes. Changes in tropical denitrification have been attributed to changes in productivity, changes in the source of intermediate waters and the flux of dissolved oxygen to suboxic zones. Variations in marine denitrification and anammox occurring at intermediate depths in proximity to productive continental margins have had profound effects on the N:P ratio of upwelled waters between stadials and interstadials, and may have indirectly affected carbon sequestration in the ocean by changing the balance of nutrients available to primary productivity. Competitive equilibrium, the changing stoichiometric balance of elements available as nutrients and the shorter residence time of N compared to P are factors that are believed to favour diazotrophs (N2-fixing organisms) during interstadials and shift the competitive advantage to non-N2-fixing ecosystems during stadials. This study presents a very high-resolution analysis of sedimentary nitrogen isotope records, phosphorus concentrations and bulk detrital element concentrations from two cores collected along the Pacific Mexican Margin. The results show that the oxygen minimum zone (OMZ) bathing intermediate waters in ETNP is modulated by the interaction of a Northern Hemisphere climate component with the “leakage” of heavy nitrate believed to derive from the Eastern South Pacific (ESP). This southerly component has a more “Antarctic” timing and is similar to records from the Peru-Chile margin. The sedimentary core recovered from the Mazatlan margin shows a “Greenland” timing of millennial-scale events, with reduced upwelling and reduced primary productivity, a less intense OMZ leading to reduced ...
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