The uniqueness of Marine Isotopic Stages (MIS) 11 is well expressed by its anomalously long duration of high CO₂ reaching 280 ppmv and its low eccentricity orbital configuration similar to today (Tzedakis et al., 2022). Indeed, it has been served as an analogy to test the baseline scenario of the climate system in a human-free world. Hence, better comprehension of the internal feedback of the climatic system across MIS 11 will offer us the potential to better predict the future direction of our climate system.
Here, we present new benthic foraminifera d¹³C (Cibicidoides wuellerstorfi), U/Mn and Cd/Ca (Cibicidoides kullenbergi) records spanning MIS 12 to 10 from sedimentary core MD97-2115 (43°6'30"S, 171°29'7.8"W, 2160 m), retrieved within the modern Upper Circumpolar Deepwater (UCDW) off New Zealand. The Cd/Ca ratio is able to reconstruct the Cd concentration of seawater (Cd_sw) and is related to global nutrient concentrations; the U/Mn ratio is a proxy for past oxygen content of deep-water masses. Our results show Cibicidoides kullenbergi sensu lato can yield comparable Cd/Ca and U/Mn signals to its sensu stricto morphotypes. The U/Mn signal documents transient oxygen enrichments and depletions across the studied interval, which are synchronous with O₂ fluctuations documented from Antarctic Bottom Water (AABW; Glasscock et al., 2020; Jebasinski et al., 2025). In particular, we attribute the oxygenation of UCDW and AABW at Termination V (TV) to a reinvigorated Southern Ocean (SO) ventilation. Transient deoxygenations during MIS 11 are attributed to the dynamics of the O₂ exchange between the atmosphere and surface water at the Antarctic perimeter, and/or of the surface water supply from the Antarctic perimeter into UCDW and AABW in the SO. Deepwater nutrient concentration reconstructed from Cd/Ca ratio suggests an increase in nutrient content during TV, which contrasts with the δ¹³C_{C.wuellerstorfi} signature obtained at the same site as well as the invariant nutrient record previously obtained from RC13-229 in the Atlantic SO (Oppo & Rosenthal, 1994). We followed Rosenthal et al. (1997) to infer that our site may have been under the influence of a nutrient-depleted water during MIS 12. Such a water may have been formed locally through convection in the polynyas near the Antarctic Polar Front in the Southeast Indian Ocean, and may have contributed to the glacial lowering of nutrient while keeping the δ¹³C_{C.wuellerstorfi} in line with other SO records.
[1] Tzedakis et al. (2022), Quat. Sci. Rev. 284, 107493.
[2] Glasscock et al. (2020), Paleoceanogr. Paleoclimatol. 35, e2020PA003867.
[3] Jebasinski et al. (2025), Nat. Commun. 16, 9138.
[4] Oppo et al. (1994), Paleoceanography. 9, 661-675.
[5] Rosenthal et al. (1997), Paleoceanography 12, 787-796.

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