Stratigraphy of bottom sediments in the Mendeleev Ridge area (Arctic Ocean)

A New Chronology of Late Quaternary Sequences From the Central Arctic Ocean Based on “Extinction Ages” of Their Excesses in 231Pa and 230Th

“…The present study adds credibility to the methodological approach outlined by Somayajulu et al (), further developed by Not and Hillaire‐Marcel () and recently applied by Gusev et al () for the setting of radiometric benchmark ages of ∼140 and ∼300 ka based on the extinction of excesses in 231 Pa and 230 Th, respectively, in low sedimentation rate environments. In the case of the northern Lomonosov and Mendeleev Ridge, this approach suggests average sedimentation rates of the order of 4.3 and 1.7 mm/ka, respectively, during the late Quaternary.…”

“…At this stage, a summary of the most robust features of 230 Th xs behavior in sediments from the central Arctic Ocean can be made: 230 Th xs ‐fluxes and inventories are similar in the Mendeleev and Lomonosov cores examined above (Figure ), likely in several other sites of the central Arctic Ocean (Gusev et al, ; Huh et al, ; Moran et al, ) and seem thus independent of the site within this area. 230 Th xs ‐fluxes and inventories are independent of the depth of the water column within the range documented here, i.e., from ∼1.2 km (Mendeleev MC‐12; Lomonosov‐030) to ∼2.5 km (Mendeleev MC‐11); thus 230 Th‐scavenging has to occur mostly outside the overlying water column and/or through a still undocumented process. If 230 Th xs ‐fluxes vary in accordance with sediment fluxes (cf. Figure b), 230 Th xs ‐inventories are independent of the sediment accumulation as illustrated by their similarity in cores from both Mendeleev and Lomonosov (MC‐11, Mc‐030, and K‐030) (Figure ), notwithstanding a 3‐fold difference in the sediment accumulation rate between the two ridges. …”

“…The first outcome of the present study on Lomonosov Ridge and that of Not and Hillaire‐Marcel () or Gusev et al () on the Mendeleev Ridge, concerns the chronostratigraphy of late Quaternary sediment in the central Arctic Ocean. Both data sets point to significantly lower sedimentation rates than those reported in the recent literature.…”

“…These data, as well as the available 14 C‐age control near core tops, point to mean sedimentation rates of ∼4.3 mm/ka (Lomonosov) versus 1.7 mm/ka (Mendeleev), which yields a mean accumulation rate over Lomonosov of about 3‐fold over that of the Mendeleev sites. At last, also based on the decay of 230 Th xs in sedimentary cores from the southern Mendeleev Ridge, Gusev et al () calculated sedimentation rates not unlike those of MC‐11 and MC‐12 from the northern area of the ridge.…”

A Thick Negative Polarity Anomaly in a Sediment Core From the Central Arctic Ocean: Geomagnetic Excursion Versus Reversal

“…If this is always the case, magnetostratigraphy will probably not be useful for the construction of a chronology for abyssal sediment sequences from the Arctic Ocean. Nevertheless, recent geochemical studies involving decay of Be (e.g., Sellén et al, ) and U‐series isotopes (e.g., Gusev et al, ; Hillaire‐Marcel et al, ; Not & Hillaire‐Marcel, ) indicate that sedimentation rates are close to those (one to several mm/kyr) originally estimated by the early magnetostratigraphic studies. All these facts indicate that challenges and uncertainty remain in the establishment of age models for the deep‐sea sediment cores and especially for the applicability and interpretation of magnetic stratigraphy in the Arctic Ocean.…”