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Here we present organic export production and nitrogenisotope results spanning the last 30 000 years from a core recovered offCosta Rica (Ocean Drilling Program (ODP) Site 1242) on the leading edge ofthe oxygen minimum zone of the Eastern Tropical North Pacific. Marine exportproduction reveals glacial-interglacial variations with low organic matter(total organic carbon and total nitrogen) contents during warm intervals,twice more during cold episodes and double peaked maximum during thedeglaciation, between ~15.5–18.5 and 11–13 ka B.P. When this newexport production record is compared with four nearby cores from within theEastern Pacific along the Equatorial divergence, good agreement between allthe cores is observed. The major feature is a maximum of export during theearly deglaciation. As for export production, water-column denitrification,represented by sedimentary δ<sup>15</sup>N records, along the Easterntropical North and South Pacific between 15° N and 36° S is alsocoherent over the last deglaciation. Each of the nitrogen isotope profilesindicate that denitrification increased abruptly at 19 ka B.P to a maximumduring the early deglaciation, confirming a typical Antarctic timing. It isproposed that the increase in export production and then in subsurfaceoxygen demand lead to an intensification of water-column denitrificationwithin the oxygen minimum zones in the easternmost Pacific at the time ofthe last deglaciation. The triggering mechanism would have been primarilylinked to an increase in preformed nutrients contents feeding the EquatorialUndercurrent driven by the resumption of overturning in the Southern Oceanand the return of nutrients from the deep ocean to the sea-surface. Anincrease in equatorial wind-driven upwelling of sub-surface nutrient-richwaters could have played the role of an amplifier

Increase in water column denitrification during the last deglaciation: the influence of oxygen demand in the eastern equatorial Pacific