Searching for the conduit waters of old glacial carbon: deglacial intermediate to deep water records from the western sub-equatorial Pacific

Abstract:

Glacial pCO₂ levels were lower than interglacial ones and the Deep Ocean is a strong candidate for storing the excess interglacial CO₂. There are two main hypotheses about the glacial storage of atmospheric CO₂ in the Deep Ocean and subsequent deglacial outgas/release of CO₂ to the atmosphere: i) CO₂ was stored in the Southern Ocean and was ventilated through the Antarctic Intermediate (AAIW) and Equatorial Intermediate Waters (EqIW); ii) CO₂ was stored in the Deep Pacific and was ventilated through other intermediate waters. A mélange of all these intermediate waters is found in the western equatorial Pacific above the Pacific Deep Water (PDW) converting the region in an ideal setting to investigate these hypotheses.

During RV Sonne Expedition SO228, sea water samples and sediment cores were retrieved off Mindanao and Papua New Guinea at various water depths. Here we present hydrographic and sedimentary data from key locations. CTD temperature, salinity and oxygen as well as seawater δ¹³C, δ¹⁸O and δD from various stations enable to study the modern oceanography in the region. The data allows the identification of various types of intermediate and deep waters and a characterization of water properties that can be used to study these water masses back in time using the sediment cores. The paleoceanographic study will focus on the last 25 kyrs and use benthic stable isotopes and paired planktonic-benthic foraminiferal radiocarbon measurements on two sediment cores off Mindanao at 404 and 848 m water depth and four cores off Papua New Guinea at 845, 1365, 1887 and 2210 m water depth. Preliminary radiocarbon-based age models indicate varying sedimentation rates from 2 to 30 cm/ka for the cores, higher off Mindanao than off Papua New Guinea. The benthic foraminiferal assemblage of the intermediate core at 845 m water depth provides initial indications of shifting water properties at intermediate levels, potentially connected to the inflow of well versus poor ventilated waters, thus encouraging the contention that poorly ventilated deep waters may have been upwelled to these depths.