Abstract
The Antarctic Peninsula’s Pacific margin is one of the best studied sectors of the Antarctic continental margin. Since the 1990s, several research cruises have targeted the continental rise with geophysical surveys, conventional coring and deep-sea drilling. The previous studies highlighted the potential of large sediment drifts on the rise as high-resolution palaeoenvironmental archives. However, these studies also suffered from chronological difficulties arising from the lack of calcareous microfossils, with initial results from geomagnetic relative palaeointensity (RPI) dating promising a possible solution.This paper presents data from new sediment cores recovered on cruise JR298 from seven continental rise sites west of the Antarctic Peninsula and in the Bellingshausen Sea with the objectives to (i) seek calcareous foraminifera, especially at shallow drift sites, to constrain RPI-based age models, and (ii) investigate the depositional history at these locations. We present the results of chronological and multi-proxy analyses on these cores and two cores previously collected from the study area. We establish new age models for the JR298 records and compare them with published RPI-based age models. In addition, we evaluate the reliability of different palaeoproductivity proxies and infer depositional processes.Planktic foraminifera are present in various core intervals. Although their stable oxygen isotope (δ18O) ratios, tephrochronological constraints and glacial-interglacial changes in sediment composition provide age models largely consistent with the RPI chronologies, we also observe distinct differences, predominantly in the Bellingshausen Sea cores. Enrichments of solid-phase manganese together with evidence for “burn-down” of organic carbon in late glacial and peak interglacial sediments document non-steady-state diagenesis that may have altered magnetic mineralogy and, thus, RPI proxies. This process may explain discrepancies between RPI-based age models and those derived from δ18O data combined with tephrochronology. The data also indicate that organic carbon is a much less reliable productivity proxy than biogenic barium or organically-associated bromine in the investigated sediments.In agreement with previous studies, sediment facies indicate a strong control of deposition on the rise by bottom currents that interacted with detritus supplied by meltwater plumes, gravitational down-slope transport processes and pelagic settling of iceberg-rafted debris (IRD) and planktic microfossils. Bottom-current velocities underwent only minor changes over glacial-interglacial cycles at the drift crests, with down-slope deposition only rarely affecting these shallow locations. Maximum concentrations of coarse IRD at the seafloor surfaces of the shallow sites result predominantly from upward pumping caused by extensive bioturbation. This process has to be taken into account when past changes in IRD deposition are inferred from quantifying clasts >1 mm in size.
Highlights
The western continental rise of the Antarctic Peninsula is characterized by eight large and four smaller mounds rising between several hundred and 2000 m above the surrounding seafloor (Fig. 1; Rebesco et al, 2002; Hillenbrand et al, 2008b; Hernandez-Molina et al, 2017)
The splicing of the piston cores (PC) with the giant box core (GBC) was conducted by visual correlation of (i) distinct lithological and structural features, and (ii) characteristic down-core changes and/ or prominent peaks in physical properties, X-ray fluorescence (XRF) scanner data, water content, total organic carbon (TOC) and CaCO3 contents, and grain-size composition
We distinguish four major Facies A to D and three subordinate and rarely occurring Facies E to G (Table 4; Fig. 16; Supplementary Text). These facies strongly resemble sediment types previously reported from the western Antarctic Peninsula rise by Pudsey and Camerlenghi (1998), Pudsey (2000), Lucchi et al (2002) and Lucchi and Rebesco (2007) but have to be considered as “endmembers” because especially the laminated to stratified facies vary and transition down-core over a few decimetres or even several centimetres
Summary
The western continental rise of the Antarctic Peninsula is characterized by eight large and four smaller mounds rising between several hundred and 2000 m above the surrounding seafloor (Fig. 1; Rebesco et al, 2002; Hillenbrand et al, 2008b; Hernandez-Molina et al, 2017). The mounds are separated by deepsea channels originating at the base of the continental slope, and usually have a gentle NE side and a steep SW flank. They are interpreted as contourite mounded drifts formed by fine-grained detritus, which initially had been supplied by turbidity currents travelling through the channels before the fine-grained particles were entrained into a generally SW-ward flowing bottom current (Rebesco et al, 1997) [NB: here we use the term “contourite” sensu lato, i.e., as describing any sediment deposited or reworked by a bottom current (e.g., Rebesco et al, 2014; Stow and Smillie 2020)]. Drifts 7 and 4 were drilled at Sites 1095, 1096 and 1101 by Ocean Drilling Program (ODP) Leg 178 (Barker et al 1999, 2002)
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