Antiphased dust deposition and productivity in the Antarctic Zone over 1.5 million years

Abstract

The Southern Ocean paleoceanography provides key insights into how iron fertilization and oceanic productivity developed through Pleistocene ice-ages and their role in influencing the carbon cycle. We report a high-resolution record of dust deposition and ocean productivity for the Antarctic Zone, close to the main dust source, Patagonia. Our deep-ocean records cover the last 1.5 Ma, thus doubling that from Antarctic ice-cores. We find a 5 to 15-fold increase in dust deposition during glacials and a 2 to 5-fold increase in biogenic silica deposition, reflecting higher ocean productivity during interglacials. This antiphasing persisted throughout the last 25 glacial cycles. Dust deposition became more pronounced across the Mid-Pleistocene Transition (MPT) in the Southern Hemisphere, with an abrupt shift suggesting more severe glaciations since ~0.9 Ma. Productivity was intermediate pre-MPT, lowest during the MPT and highest since 0.4 Ma. Generally, glacials experienced extended sea-ice cover, reduced bottom-water export and Weddell Gyre dynamics, which helped lower atmospheric CO2 levels.

One‐To‐One Coupling Between Southern Ocean Productivity and Antarctica Climate

“…Previous literature has established the age model of Site U1537 (Reilly et al, 2021;Weber, Raymo, Peck, Williams, & Expedition 382 Scientists, 2021, Weber et al, 2022, which provides a solid basis for the age model of this paper. The age model of Site U1537 over the past 170 ka has been constructed by correlating the magnetic susceptibility (MS) of Site U1537 to EPICA Dome C (EDC) dust records (Lambert et al, 2012;Weber, Raymo, Peck, Williams, & Expedition 382 Scientists, 2021, Weber et al, 2022. According to Weber et al (2012), Ca records of Site U1537 could indicate atmospheric circulation because Site U1537 is located below the carbonate compensation depth with less than 1% biogenic carbonate.…”

Episodes of Early Pleistocene West Antarctic Ice Sheet Retreat Recorded by Iceberg Alley Sediments

“…382 NGR records have a lower resolution (10 cm) than most other physical property data collected during the expedition (typically at 2 cm for spectral reflectance color data), but we used them to establish tie‐lines because they have a strong signal‐to‐noise ratio. The well‐documented linear relationship between the sediment color component b* and opal content of Scotia Sea sediments over the LGM‐Holocene (Sprenk et al., 2013) has recently been demonstrated to hold for sediments from this region over the past 1.4 Ma (Weber et al., 2022). We therefore also use shipboard color reflectance component b* records, as a first‐order proxy for opal‐rich sediments (with high b* values) and as an independent check on our NGR‐based tie‐lines.…”

“…This suggestion is further substantiated by the fact that gravel and pebble concentrations reported shipboard for Dove Basin IODP sites U1536 and U1537 sediments are also highest in their Pliocene and early Pleistocene sections (Weber, Raymo, et al., 2021). Core recovery at these more southerly Scotia Sea sites was much higher than at U1538 and large portions of their Quaternary stratigraphies have been spliced (Weber, Raymo, et al., 2021, 2022). The higher concentrations of iceberg‐rafted gravels and pebbles in the Pliocene and early Pleistocene sequences of U1536 and U1537 therefore cannot be attributed to fall‐in.…”

“…Map insert shows main surface ocean currents (blue lines; Assmann et al, 2005;Gladstone et al, 2001;Murphy et al, 2013) directing icebergs to Site U1538. Also shown are -major ice drainage divides (dashed blue lines), approximate boundaries between tectonic domains (dashed brown lines; Vaughan & Storey, 2000), bathymetric troughs (gray dashed line on the shelf breaks), the shelf break (dashed black lines), southern boundary of the Antarctic Circumpolar Current (and dotted line offshore; Orsi et al, 1995) for sediments from this region over the past 1.4 Ma (Weber et al, 2022). We therefore also use shipboard color reflectance component b* records, as a first-order proxy for opal-rich sediments (with high b* values) and as an independent check on our NGR-based tie-lines.…”

Latitudinal Variance in the Drivers and Pacing of Warmth During Mid‐Pleistocene MIS 31 in the Antarctic Zone of the Southern Ocean

“…A potentially higher precision age model for this time interval has been presented for Site U1537 using the assumption that magnetic susceptibility variations as well as x-ray fluorescence counts of Ca and Fe are synchronous with glacial-interglacial variability defined by the LR04 benthic isotope stack (Weber et al, 2022). This new age model by Weber et al (2022) falls within the larger uncertainty structure of the Reilly et al (2021) magnetostratigraphic age model. For this study we plot our data on the median age of the magnetostratigraphic age model, as the two age models are largely similar in this time interval and this decision requires fewer assumptions about the phasing of climate signals in the Early Pleistocene.…”