Abstract
AbstractLate Pliocene deep Atlantic δ13C data have been interpreted as evidence for enhanced Atlantic Meridional Overturning Circulation (AMOC) compared to the present, but this hypothesis is not supported by the Pliocene Model Intercomparison Project (PlioMIP). Here, we adopt a new approach to assess variability in deep ocean circulation based on paired stable carbon (δ13C) and oxygen isotopes (δ18O) of benthic foraminifera, both (semi)conservative water mass tracers. Assuming that deep Atlantic benthic δ13C‐δ18O variability is predominantly driven by mixing, we extrapolate the δ13C‐δ18O data outside the sampled range to identify the end‐members. At least three end‐members are needed to explain the spatial δ13C‐δ18O variability in the deep North Atlantic Ocean: two Northern Component Water (NCW) and one Southern Component Water (SCW) water masses. We use a ternary mixing model to quantify the mixing proportions between SCW and NCW in the deep Atlantic Ocean. Our analysis includes new data from Ocean Drilling Program Sites 959 and 662 in the eastern equatorial Atlantic and suggests that the AMOC cell was deeper during the M2 glacial than during late Pliocene interglacials. Moreover, we identify a new cold and well‐ventilated water mass that was geographically restricted to the southeast Atlantic Ocean between 3.6 and 2.7 Ma and did not contribute significantly to the δ13C‐δ18O variability of the rest of the basin. This high‐δ13C high‐δ18O water mass has led to the misconception of a reduced latitudinal δ13C gradient. Our analyses show that the late Pliocene δ13C gradient between NCW and SCW was similar to the present‐day value of 1.1‰.
Highlights
The late Pliocene (3.6–2.6 Ma) interglacial climates may be the best past analogs for end 21st century climate (Haywood et al, 2011)
Our analyses show that the late Pliocene δ13C gradient between Northern Component Water (NCW) and Southern Component Water (SCW) was similar to the present‐day value of 1.1‰
Deep Atlantic stable carbon isotope records reflect the site‐specific relative contribution of 13C‐enriched deep water sourced from the North Atlantic and Arctic region (e.g., Northern Component Water [NCW]) to 13C‐depleted deep water sourced from the Southern Ocean and Antarctic regions (e.g., Southern Component Water [SCW]) (Kroopnick, 1980, 1985)
Summary
The late Pliocene (3.6–2.6 Ma) interglacial climates may be the best past analogs for end 21st century climate (Haywood et al, 2011) Within this time frame, a well‐studied interval is the late Pliocene Mid‐Piacenzian Warm Period (MPWP, 3.264–3.025 Ma). Within the major part of the modern Atlantic basin, δ13CDIC is not significantly impacted by organic matter remineralization, so that it generally acts as a conservative water mass tracer (Oppo & Fairbanks, 1987). This means that the δ13CDIC of a water mass will only change when it mixes with a water mass that has a different δ13CDIC signature. Possible complications with using δ13C as a water mass tracer in palaeoceanographic reconstructions may arise when it loses its conservative properties due to low extremely low deep van der WEIJST ET AL
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
