The Evolving Paleobathymetry of the Circum‐Antarctic Southern Ocean Since 34 Ma: A Key to Understanding Past Cryosphere‐Ocean Developments

Abstract

The Southern Ocean is a key player in the climate, ocean, and atmospheric system. As the only direct connection between all three major oceans since the opening of the Southern Ocean gateways, the development of the Southern Ocean and its relationship with the Antarctic cryosphere has influenced the climate of the entire planet. Although the depths of the ocean floor have been recognized as an important factor in climate and paleoclimate models, appropriate paleobathymetric models including a detailed analysis of the sediment cover are not available. Here we utilize more than 40 years of seismic reflection data acquisition along the margins of Antarctica and its conjugate margins, along with multiple drilling campaigns by the International Ocean Discovery Program (IODP) and its predecessor programs. We combine and update the seismic stratigraphy across the regions of the Southern Ocean and calculate ocean‐wide paleobathymetry grids via a backstripping method. We present a suite of high‐resolution paleobathymetric grids from the Eocene‐Oligocene Boundary to modern times. The grids reveal the development of the Southern Ocean from isolated basins to an interconnected ocean affected by the onset and vigor of an Antarctic Circumpolar Current, as well as the glacial sedimentation and erosion of the Antarctic continent. The ocean‐wide comparison through time exposes patterns of ice sheet development such as switching of glacial outlets and the change from wet‐based to dry‐based ice sheets. Ocean currents and bottom‐water production interact with the sedimentation along the continental shelf and slope and profit from the opening of the ocean gateways.

Late Eocene Record of Hydrology and Temperature From Prydz Bay, East Antarctica

“…Paleotopographic reconstructions indicate coastline transgressions and regressions around the Lambert Graben varies with isostatic and eustatic changes (Hochmuth, Gohl, et al., 2020; Paxman et al., 2019) (Figure 1b; see also 3D map Figure ). The latter aligns with fluvial/deltaic sandstones in the oldest sediments within Hole 1166A (O’Brien et al., 2001).…”

Evolution of Sea Surface Temperature in the Southern Mid‐latitudes From Late Oligocene Through Early Miocene

“…The lowermost sediments analyzed here are characterized by a greater diversity and complexity of biomarkers and coincide with the high TOC % (>1%wt) and low CaCO 3 (<10%) characteristic of the marginal and deltaic marine settings in the Early Oligocene at the location (Exon et al (2001); Figure S1). The diversity of organic compounds might be affected by changes in diagenetic reactions as the site gradually subsides into deeper, more oxygenated waters, potentially moving out of the oxygen minimum zone by 29 Ma (Exon et al, 2001;Hill & Exon, 2004;Hochmuth et al, 2020). The good LCAs signal afterward appear to be related to the simultaneous gradual opening of the restricted basin leading to an increase in ventilation and oxygenation of the regional water column following the invigoration of currents through the opening gateway.…”

PALEOSTRIPv1.0 – a user-friendly 3D backtracking software to reconstruct paleo-bathymetries

“…New reconstructed Ross Sea bathymetry using revised data will be the object of a specific contribution. ANTOSTRAT data have been recently used in pan-Antarctic reconstructions of past topographies and bathymetries (Paxman et al, 2019;Hochmuth et al, 2020).…”

“…Figure 10. Backtracked Mid-Miocene bathymetries at about 14 Ma: a. corrected only for Airy isostasy; b. same as a. but including thermal subsidence correction with a spatially uniform β = 2.1 and the end of rifting sets at 76 Ma; c. same as b. but including eustatic sea level correction based on Miller et al (2020) δ 18 O-derived reconstruction; d. same as c. but including dynamic topography correction based on Müller et al (2018a) geodynamical model M1 (followingHochmuth et al, 2020). Colorscale is the same as in Fig.9.…”