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(a) The aligned RPI slope record from RS15-LC42 and the PISO-1500 10 kyr moving average, both standardised to a mean of 0 and SD of 1. The Geomagnetic Polarity Time Series is appended below, with normal polarity chrons displayed in black, and reverse polarity chrons displayed in white. (b) Downcore plot of the RPI slope from RS15-LC42. Black points indicate the data which was used for the Match protocol, with red crosses showing data that was excluded according to acceptable thresholds in R-Value, maximum angular deviation (MAD), and demagnetization behavior. (c) RPI slope R-value, displaying the correlation coefficient between NRM and ARM at AF strengths between 0 and 40 mT. A threshold of 0.9 was defined, with the corresponding RPI slope data of all points below this threshold being excluded from the RPI-PISO match procedure. (d) The MAD of principal component analysis (PCA). Red crosses indicate data above an acceptable data threshold of 15 • (red dashed line), with all data above this value excluded from the RPI-PISO match procedure. (e) The Characteristic Remnant Magnetisation (ChRM) inclination of PCA, which aligns with the expected inclination of 80.7 • reversed polarity, and 80.7 • normal polarity. (f) The newly revised age model (solid black line) compared to the existing age model of Ohneiser et al., 2019 (dashed black line). The black triangle displays the FO of Thalassiosira antarctica between 5.40 and 5.64 mbsf at 0.65 Ma. The undulating line at 9.34 mbsf marks the interpreted hiatus spanning the C1r.1n Jamarillo subchron, with the light grey dashed lines linking the fundamental initial age control of 0.781 Ma at 8.26 mbsf, defined by the Bruhnes-Maruyama magnetic reversal. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
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Understanding how ocean circulation has varied around Antarctica in the past is vital because significant volumes of ice are grounded below sea level, and therefore ice sheet variations are strongly coupled with oceanographic variability at the continental shelf margin. This study investigates the 11.75 m sediment core RS15-LC42, retrieved from the...
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... was normalised by ARM to generate the RPI estimate. Fig. 4a displays a low WTC between the normaliser (ARM) and the RPI estimate of RS15-LC42. The newly revised age model is presented in Fig. 5, with the standardised output of the Match protocol displayed in Fig. 5a. A strong WTC between the aligned RPI estimate and PISO-1500 is observed in >20 kyr periods (Fig. 4b). Between the core-top and the B-M magnetic reversal at 8.26 m, all major peaks and troughs correspond between the RPI estimate of RS15-LC42 and the PISO-1500 ...
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... was normalised by ARM to generate the RPI estimate. Fig. 4a displays a low WTC between the normaliser (ARM) and the RPI estimate of RS15-LC42. The newly revised age model is presented in Fig. 5, with the standardised output of the Match protocol displayed in Fig. 5a. A strong WTC between the aligned RPI estimate and PISO-1500 is observed in >20 kyr periods (Fig. 4b). Between the core-top and the B-M magnetic reversal at 8.26 m, all major peaks and troughs correspond between the RPI estimate of RS15-LC42 and the PISO-1500 global stack. Below the B-M magnetic reversal (0.781 Ma) at 8.26 m, all ...
Citations
International Ocean Discovery Program (IODP) Expedition 379 to the Amundsen Sea margin of West Antarctica recovered drill cores at two sites spanning the Latest Miocene–Holocene interval with the aim of reconstructing past West Antarctic Ice Sheet dynamics. The recovered Plio-/Pleistocene sediment sequences offer an opportunity to apply and test different dating approaches in an Antarctic deep-sea drift setting, where the records are nearly continuous and unaffected by scouring of icebergs or grounded ice. Here, through palaeomagnetic analysis of continuous u-channel samples and application of X-ray fluorescence (XRF) scanning, we revise the IODP Exp. 379 Site U1533 age model for the uppermost Pliocene and Pleistocene composite interval (0.0–2.9 Ma). We first refine the magnetostratigraphic age model with high-resolution u-channel analysis and interpreted directional data. Consistent with shipboard results, all major geomagnetic polarity chrons and subchrons are identified in the Pleistocene section. The new high-resolution u-channel dataset also allows us to identify a geomagnetic polarity excursion at ∼884 ka (interpreted as the Kamikatsura excursion) and another excursion at ∼2734 ka with confidence (potentially the Porcupine excursion). Based on the improved polarity stratigraphy, we then develop two new highly resolved age models for Site U1533 using: (i) barium enrichment cycles identified in XRF scanning data, and (ii) geomagnetic relative palaeointensity (RPI). In our first age model, we correlate cyclic variations in sedimentary barium enrichment, inferred to represent changes in export productivity, to glacial‒interglacial cycles of the Lisiecki and Raymo (2005) benthic foraminiferal oxygen isotope (δ18O) stack (LR04). Nearly all Pleistocene Marine Isotope Stages (MIS) are interpreted to be present in the barium enrichment record of Site U1533, assuming simultaneous changes in Antarctic sea-ice extent/local export productivity and global oxygen isotope stratigraphy. We then construct the second, independent age model using the Plio-/Pleistocene RPI record developed for Site U1533, which represents the longest (nearly) continuous RPI record currently available for the Antarctic margin. Comparison of the two, independently derived age models shows a variable offset, on average ± 12 kyr, with the RPI-based ages consistently older than the barium-based ages in the interval from 1.9 to 2.9 Ma and then consistently younger from 0.0 to 1.9 Ma. We interpret these offsets to result from a combination of lock-in depth effects in the younger interval (due to the relatively low sedimentation rates at this site, ∼2 cm/kyr), temporal offsets between global δ18O changes in the deep ocean and productivity response on the Antarctic margin, and/or systematic miscorrelation in the construction of the two age models. Finally, we construct a hybrid age model for the Pleistocene section of Site U1533 by combining a mixture of RPI- and barium-based age tie points that are deemed to be robust. The Site U1533 RPI record is then used, together with other Southern Ocean RPI records, to construct an Antarctic RPI stack (designated as ‘ANT-1600’) for the interval 0.0–1.6 Ma. Although sedimentation rates at two-thirds of the sites selected for the stack are lower than 10 cm/kyr, the new ANT-1600 stack is strongly coherent with the SINT-2000 RPI stack (Valet et al., 2005) on time scales of ∼20–200 kyr, allowing for its use as a regional RPI reference curve in future studies. Overall, we demonstrate that RPI at Antarctic margin/Southern Ocean sites provides a viable and valuable independent dating method for application to Plio-/Pleistocene Antarctic sediments.
The analysis of sedimentary deposits influenced by bottom currents in glaciated continental margins provides crucial insights into paleo-depositional and oceanographic conditions. These reconstructions enable the assessment of interactions between advance and retreat of grounded ice sheets and past ocean circulation patterns. However, questions regarding these interactions and their specific mechanisms remain largely unanswered due to a lack of data in this remote area. In this study, we conducted a comprehensive analysis by integrating marine geophysical data, surficial sediment cores, oceanographic measurements, and ocean circulation models. Our aim was to understand spatial and temporal variations in sedimentary and oceanographic conditions during the past glacial and interglacial periods in combination with the long-term stratigraphic evolution. By integrating and cross-referencing diverse datasets, we were able to infer how bottom-current-controlled deposits (i.e., contourites) developed along the western bathymetric high of the Central Basin in the northwestern Ross Sea margin, Antarctica. Contouritic deposits lying over and along the flanks of bathymetric highs were identified through their mound-shaped external geometry and acoustically stratified facies, characterized by reflectors pinching toward the moat. Acoustic facies and multi-beam backscatter results, in conjunction with sedimentary core data, revealed contrasting patterns. Bathymetric highs exhibited thin (<10 m thick) coarser-grained sedimentary layers with higher backscatter, while the lower slope and rise displayed thick (>10 m thick), finer-grained stratified sediments with lower backscatter. These findings indicate that seabed winnowing occurred by strong bottom current during past glacial periods as supported by sedimentological analysis. The pathways of the westward-deflected dense shelf water outflow and the westward-flowing along-slope current, as simulated by oceanographic models, explain the distinctive development of contourites influenced by bottom-current processes. Moreover, the large accumulations of sediment in the contourites, resulting from bathymetric barriers in the north of the Central Basin, may contribute to submarine slope failures.
Antarctica's continental margins pose an unknown submarine landslide-generated tsunami risk to Southern Hemisphere populations and infrastructure. Understanding the factors driving slope failure is essential to assessing future geohazards. Here, we present a multidisciplinary study of a major submarine landslide complex along the eastern Ross Sea continental slope (Antarctica) that identifies preconditioning factors and failure mechanisms. Weak layers, identified beneath three submarine landslides, consist of distinct packages of interbedded Miocene- to Pliocene-age diatom oozes and glaciomarine diamicts. The observed lithological differences, which arise from glacial to interglacial variations in biological productivity, ice proximity, and ocean circulation, caused changes in sediment deposition that inherently preconditioned slope failure. These recurrent Antarctic submarine landslides were likely triggered by seismicity associated with glacioisostatic readjustment, leading to failure within the preconditioned weak layers. Ongoing climate warming and ice retreat may increase regional glacioisostatic seismicity, triggering Antarctic submarine landslides.
