Abstract
AbstractUpwelling within the Eastern Equatorial Pacific (EEP) Ocean is a key factor for the Earth's climate because it supports >10% of the present‐day biological production. The dynamics of upwelling in the EEP across the Plio‐Pleistocene transition—an interval particularly relevant for understanding near‐future warming due to Anthropocene‐like atmospheric carbon‐dioxide levels—have been intensively studied for the region east of the East Pacific Rise. In contrast, changes of the equatorial upwelling regime in the open Pacific Ocean west of this oceanographic barrier have received markedly less attention. We therefore provide new proxy records from Ocean Drilling Program Site 849 located within the EEP open‐ocean upwelling regime. Our target interval (∼3.35–2.0 Ma) covers the Plio‐Pleistocene transition characterized by the intensification of Northern Hemisphere Glaciation (iNHG). We use benthic δ18O values to generate a new, high‐resolution age model for Site 849, and sand‐accumulation rates together with benthic δ13C values to evaluate net export production. Although showing temporary substantial glacial‐interglacial variations, our records indicate stability in net export production on secular timescales across the iNHG. We suggest the following processes to have controlled the long‐term evolution of primary productivity at Site 849. First, nutrient export from the high latitudes to the EEP; second, a successive shoaling of the Pacific nutricline during the studied interval; and third, a simultaneous reduction in dust‐borne iron input.
Highlights
Oceanic upwelling systems are important for the Earth's atmospheric and marine carbon budget (Toggweiler & Sarmiento, 1985; Watson & Naveira Garabato, 2006)
Because the deep ocean is relatively uniform with regard to salinity, benthic foraminiferal δ18O values are typically used as a measure for relative global ice-volume and deep-ocean temperature variability (e.g., Emiliani, 1955; Lisiecki & Raymo, 2005; Shackleton, 1967; Urey, 1947; Zachos et al, 2001)
Proxy records from the equatorial upwelling region east of the East Pacific Rise (Sites 846 and 847) appear to not support this coupling during the past ∼5 Myr for secular timescales (Dekens et al, 2007; Lawrence et al, 2006). To identify whether this pattern emerges at Site 849, we provide a comparison between our new productivity proxy record and long-term upper-ocean temperature evolution at the studied site
Summary
Oceanic upwelling systems are important for the Earth's atmospheric and marine carbon budget (Toggweiler & Sarmiento, 1985; Watson & Naveira Garabato, 2006). Relatively cold, nutrient-rich and carbon-dioxide-(CO2) bearing waters from below the thermocline typically characterize the surface-water hydrography. Such conditions allow for enhanced marine primary productivity and, removal of the upwelled CO2 from the surface-ocean through organic-matter export into the deep sea. The efficiency of this so-called biological pump is of particular importance in the Eastern Equatorial Pacific (EEP) where coastal and equatorial upwelling support >10% of the biological production in the present-day oceans (Pennington et al, 2006). Modes and drivers of these changes within the EEP upwelling regime are not entirely clear
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