Abrupt intensification of North Atlantic Deep Water formation at the Nordic Seas during the late Pliocene climate transition

Abstract

Knowledge of the evolution of North Atlantic Deep Water (NADW) is key to understanding the past evolution of the climatic system. Here we developed a new rock‐magnetic method to determine the constituent magnetic minerals of sediments and report on the evolution of NADW during 2.2–2.9 Ma. We measured isothermal remanence acquisition curves of North Atlantic deep‐sea sediments drilled at the Gardar Drift and decomposed the first derivatives of these curves into high‐coercivity and low‐coercivity components. Residuals of the decomposition were sufficiently small throughout the study interval, confirming that the Gardar Drift sediments represent a mixing of the two end‐members. Fractional changes of the high‐coercivity component represent variation of the Iceland‐Scotland Overflow Water, a branch of NADW formed at the Nordic Seas. The high‐coercivity component increased significantly during an interglacial period just after ~2.68 Ma, which suggests that NADW formation in the Nordic Seas abruptly intensified at this time.

Sea-Surface Dynamics Changes in the Subpolar North Atlantic Ocean (IODP Site U1314) during Late Pliocene Climate Transition Based on Calcareous Nannofossil Observation

“…In this study, the LO of D. tamalis dates to an age 2.76 Ma. The estimated age is derived from age model developed by Hayashi et al [13] afterward modified by Sato et al [11] by astronomically tuning in physical and magnetic properties (magnetic susceptibility and natural gamma radiation) to the LR04 δ 18 O records [17]. Based on the nannofossil event found at Site U1314, the studied interval is belonging to Zone NN16 [19].…”

“…Hayashi et al [13] constructed an orbital resolution age model for the period of 2.1 -2.75 Ma by tuning a hybrid environmental proxy record to the global-standard oxygen isotope curve [17]. Afterward, Sato et al [11] modified the age model partly and extended the age model up to 2.9 Ma. They used magnetic susceptibility (MS) and natural gamma radiation (NGR) as tuning materials where the short-term variations (associated with iced-rafted debris) are eliminated.…”

“…The splice section was obtained down to 281 mcd (meter composite depth) from the cores of three holes (Holes A, B, and C) drilled with an advanced piston corer using non-magnetic core barrels [16]. The two deepest cores of Hole B were appended to the splice down to 299 mcd [11]. Hayashi et al [13] constructed an orbital resolution age model for the period of 2.1 -2.75 Ma by tuning a hybrid environmental proxy record to the global-standard oxygen isotope curve [17].…”

“…Thus, changes in abundance of some species of calcareous nannoplankton can be used to reconstruct palaeoceanographic changes on the sea-surface [6] [7] [8]. Various researchers have been investigated the dynamics of the past ocean condition in the subpolar North Atlantic and its relation to the timing of the closure CAS based on microfossils, deep-sea sediments, chemical components, and their association [9] [10] [11]. However, calcareous nannofossil studies during late Pliocene in this area have not been done yet.…”

Millennial-Scale Interaction between Ice Sheets and Ocean Circulation during Marine Isotope Stage 100

“…The north-south contrast in magnetic property was obviously demonstrated by the ratio of anhysteretic remanent magnetization to initial susceptibility for the last glacial sediments (Kissel, 2005). In our previous study of the IODP Site U1314, Sato et al (2015) associated magnetic properties of sediments with the NADW production that appeared orbitalscale variability during 2.2-2.9 Ma and abrupt intensification after ∼2.68 Ma.…”