Millennial‐scale variability of deep‐water temperature and δ18Odw indicating deep‐water source variations in the Northeast Atlantic, 0–34 cal. ka BP

Abstract

Paired measurements of Mg/Ca and δ18Occ (calcite δ18O) in benthic foraminifera from a deep‐sea core recovered on the Iberian Margin (MD99‐2334K; 37°48′N, 10°10′W; 3,146 m) have been performed in parallel with planktonic δ18Occ analyses and counts of ice‐rafted debris (IRD). The synchrony of temperature changes recorded in the Greenland ice cores and in North Atlantic planktonic δ18Occ allows the proxy records from MD99‐2334K to be placed confidently on the GISP2 time‐scale. This correlation is further corroborated by AMS 14C‐dates. Benthic Mg/Ca measurements in MD99‐2334K permit the reconstruction of past deep‐water temperature (Tdw) changes since ∼34 cal. ka BP (calendar kiloyears before present). Using these Tdw estimates and parallel benthic δ18Occ measurements, a record of deep‐water δ18O (δ18Odw) has been calculated. Results indicate greatly reduced Tdw in the deep Northeast Atlantic during the last glaciation until ∼15 cal. ka BP, when Tdw warmed abruptly to near‐modern values in parallel with the onset of the Bølling‐Allerød interstadial. Subsequently, Tdw reverted to cold glacial values between ∼13.4 and ∼11.4 cal. ka BP, in parallel with the Younger Dryas cold reversal and the H0 ice‐rafting event. Similar millennial‐scale Tdw changes also occurred during the last glaciation. Indeed, throughout the last ∼34 cal. ka, millennial δ18Odw and Tdw changes have remained well coupled and are linked with IRD pulses coincident with Heinrich events 3, 2, 1, and the Younger Dryas, when transitions to lower Tdw and δ18Odw conditions occurred. In general, millennial Tdw and δ18Odw variations recorded in MD99‐2334K describe an alternation between colder, low‐δ18Odw and warmer, high δ18Odw conditions, which suggests the changing local dominance of northern‐sourced North Atlantic Deep Water (NADW) versus southern‐sourced Antarctic Bottom Water (AABW). The observed similarity of the Tdw and GISP2 δ18Oice records would therefore suggest a common component of variability resulting from the coupling of NADW formation and Greenland climate. A link between Greenland stadials and the incursion of cold, low‐δ18Odw AABW in the deep Northeast Atlantic is thus implied, which contributes to the relationship between Greenland climate and the millennial benthic δ18Occ signal since ∼34 cal. ka BP.