- 1Department of Earth Science, University of Bergen and Bjerknes Center for Climate Research, Norway (pushpak.nadar@uib.no)
- 2Department of Earth Science, University of Bergen and Bjerknes Center for Climate Research, Norway (kikki@uib.no)
- 3Department of Earth Science, University of Bergen and Bjerknes Center for Climate Research, Norway (ulysses.ninnemann@uib.no)
- 4Department of Earth Science, University of Bergen and Bjerknes Center for Climate Research, Norway (nil.irvali@uib.no)
Antarctic Intermediate Water (AAIW) and Subantarctic Mode Water (SAMW) form the two main intermediate depth water masses from the Southeast Pacific Ocean. They sequester and store copious quantities of atmospheric gases, such as CO2 and O2, and are the most important global oxygen source to the thermocline and equatorial region. These intermediate ocean water masses thus regulate and modulate the benthic ecosystem and nutrient cycling. They are also sensitive recorders of changes in ocean circulation and play a critical role in contributing or triggering interhemispheric overturning changes by changing its depth, distribution, and properties. It is therefore important to understand the environmental feedback to the variations in intermediate ocean to define the tipping points in the ocean-climate system.
The variability of the AAIW specifically during abrupt climatic transitions such as the Antarctic Isotope Maxima event (AIM 8) is not yet constrained due to scarcity of well-dated high-resolution records. Antarctic Isotope Maxima (AIM) events are millennial-scale abrupt warming events during Marine Isotope Stage 3 (MIS-3; 57-29 kya) identified in the Antarctic ice core records. They are characterized by 1 to 3°C warming and cooling phase and are potentially triggered by AMOC instability due to freshwater discharge, internal sea-ice-ocean-atmospheric variability and Southern Ocean dynamics. Here, we use a high-resolution sediment core, Ocean Drilling Program (ODP) Site 1233 (41º00′S; 74º27′W at 838m water depth), recovered from intermediate water depths in the SE Pacific to study the physical and biogeochemical characteristics of the AAIW during AIM 8 using stable isotope measurements from epifaunal and infaunal benthic foraminifera.
The reconstructed [O2] shows a rapid rise in values to about 350 μmol/kg during the abrupt AIM 8 event, providing key insights on ocean ventilation and water mass structure. A stark contrast in the rate of change in [O2] signal in comparison to the rate of change in δ¹³C and δ¹⁸O signals in the interval 37–39.4 ka explains sensitivity of interior ocean ventilation as response to changing water mass structure or rates of warming. Our high-resolution study thus resolves the rates of changes in the water masses influencing oxygenation of the interior ocean at its source location in the SE Pacific. Our results highlight the drivers of oxygenation changes such as changes in ventilation, thermocline dynamics, and ocean circulation operating independently or in combination during the abrupt AIM 8 event. The magnitude and rate of ocean ventilation changes can potentially be used as an analogue for Last Glacial Maximum to define a tipping point within the ocean-climate system.
How to cite: Nadar, P. M. J., Kleiven, K., Ninnemann, U., and Irvali, N.: Oxygenation and Ventilation in the Intermediate Southeast Pacific Ocean during abrupt Antarctic warming event AIM8 , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17056, https://doi.org/10.5194/egusphere-egu25-17056, 2025.