The Antarctic ice sheet has been losing mass over the past decades through the accelerated flow of its glaciers conditioned by ocean temperature and bed topography. Glaciers retreating along retrograde slopes (i.e., bed elevation drops in the inland direction) are potentially unstable, whereas subglacial ridges slow down the glacial retreat. Despite major advances in mapping subglacial bed topography, significant sectors of Antarctica remain poorly resolved and critical spatial details are missing. Here we present a novel, high-resolution, and physically-based description of Antarctic bed topography using mass conservation. Our results reveal previously unknown basal features with major implications for glacier response

Antarctica is the largest reservoir of ice on Earth. Understanding its ice sheet dynamics is crucial to unraveling past global climate change and making robust climatic and sea level predictions. Of the basic parameters that shape and control ice flow, the most poorly known is geothermal heat flux. Direct observations of heat flux are difficult to obtain in Antarctica, and until now continent‐wide heat flux maps have only been derived from low‐resolution satellite magnetic and seismological data. We present a high‐resolution heat flux map and associated uncertainty derived from spectral analysis of the most advanced continental compilation of airborne magnetic data. Small‐scale spatial variability and features consistent with known geology are better reproduced than in previous models, between 36% and 50%. Our high‐resolution heat flux map and its uncertainty distribution provide an important new boundary condition to be used in studies on future subglacial hydrology, ice sheet dynamics, and sea level change.

The timing of events leading to the earliest connection between the Pacific and Atlantic oceans at Drake Passage is controversial but important, because gateway opening probably had a profound effect on global circulation and climate. A rigorous new analysis of marine geophysical data demonstrates a major change in the motion of the South American and Antarctic plates at about 50 Ma, from N-S to WNW-ESE, accompanied by an eightfold increase in separation rate. This would have led to crustal extension and thinning, and perhaps the opening of small oceanic basins, with the probable formation of a shallow (b 1000 m) gateway during the Middle Eocene. No change in South American-Antarctic motion is observed near the Eocene-Oligocene boundary, but a deep-water connection developed between 34 and 30 Ma, when continued extension led to the initiation of seafloor spreading at the West Scotia Ridge. These timings correlate with events seen in the oxygen isotope record from benthic foraminera, and support the view that Drake Passage opening was the trigger for abrupt Eocene-Oligocene climate deterioration and the growth of extensive Antarctic ice sheets. D

[1] Drake Passage opening has often been viewed as a single, discrete event, possibly associated with abrupt changes in global circulation and climate at or near the Eocene-Oligocene boundary. A new plate tectonic model, based on recent reinterpretations of the opening history of basins in the Scotia Sea, suggests that an effective ocean gateway may have developed even earlier, during the middle Eocene. This is consistent with a growing body of evidence from sediment core proxy data for Eocene changes in Southern Ocean circulation and biological productivity. The period between earliest opening after 50 Ma and the latest Eocene was characterized by the evolution of various current pathways across the subsiding continental shelves and intervening deep basins. This shallow opening may have caused important changes in Southern Ocean circulation, contributing to Eocene cooling and the growth of Antarctic ice sheets.

An animated reconstruction shows South Pacific plate kinematics between 90 and 45 Ma, using the satellite‐derived gravity anomaly field, interpolated isochrons and plate rotation parameters from both published and new work on marine geophysical data. The Great South Basin and Bounty Trough, New Zealand, are shown as the earliest Pacific–Antarctic plate boundary that opened before 83 Ma. The earliest true Pacific–Antarctic seafloor formed within the eastern parts of this boundary, but later and farther west, seafloor formed within its Antarctic flank. After 80 Ma, the Bellingshausen plate converged with an oceanic part of the Antarctic plate to its east, while its motion simultaneously caused rifting in continental Antarctica to the south. The Pacific–Bellingshausen spreading center developed a set of long offset transform faults that the Pacific–Antarctic plate boundary inherited around chron C27 when the Bellingshausen plate ceased to move independently as part of a Pacific‐wide plate tectonic reorganization event. Southwest of these transforms the Pacific–Antarctic Ridge saw an increase in transform‐fault segmentation by ∼58 Ma. One of the long offset Pacific–Bellingshausen transforms, referred to as “V,” was modified during the C27 reorganization event when a Pacific–Antarctic–Phoenix triple junction initiated on its southern edge. Eastern parts of “V” started to operate in the Pacific–Phoenix spreading system, lengthening it even more, while its western parts operated in the Pacific–Antarctic system. This complicated feature was by‐passed and deactivated by ridge axis propagation to its northwest at ∼47 Ma. We interpret our animation to highlight possible connections between these events.

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SUMMARY An accurate model of relative plate motions in Gondwana breakup is based on visual fitting of seafloor isochrons and fracture zones (FZ) from the Riiser‐Larsen Sea and Mozambique Basin. Used predictively, the model precisely locates kinematic markers in the West Somali Basin, which allows the conclusion that the spreading centres in the West Somali and Mozambique basins and the Riiser‐Larsen Sea formed parts of the boundary between the same two plates. The locations of FZ and less well‐defined isochrons from neighbouring regions are also consistent with their formation on other lengths of this same boundary and with its relocation from the West Somali Basin and northern Natal Valley to the West Enderby Basin and Lazarev Sea during chron M10n. Small independently moving plates thus played no role in the breakup of this core part of Gondwana. In an inversion procedure, the data from these areas yield more precise finite rotations that describe the history of the two plates' separation. Breakup is most simply interpreted to have occurred in coincidence with Karoo volcanism, and a reconstruction based on the rotations shows the Lebombo and Mateke‐Sabi monoclines and the Mozambique and Astrid ridges as two sets of conjugate volcanic margins. Madagascar's pre‐drift position can be used as a constraint to reassess the positions of India and Sri Lanka in the supercontinent.

[1] Joint inversion of isochron and flow line data from the flanks of the extinct West Scotia Ridge spreading center yields five reconstruction rotations for times between the inception of spreading prior to chron C8 (26.5 Ma), and extinction around chron C3A (6.6-5.9 Ma). When they are placed in a regional plate circuit, the rotations predict plate motions consistent with known tectonic events at the margins of the Scotia Sea: Oligocene extension in Powell Basin; Miocene convergence in Tierra del Fuego and at the North Scotia Ridge; and Miocene transpression at the Shackleton Fracture Zone. The inversion results are consistent with a spreading history involving only two plates, at rates similar to those between the enclosing South America and Antarctica plates after chron C5C (16.7 Ma), but that were faster beforehand. The spreading rate drop accompanies inception of the East Scotia Ridge back-arc spreading center, which may therefore have assumed the role of the West Scotia Ridge in accommodating eastward motion of the trench at the eastern boundary of the Scotia Sea. This interpretation is most easily incorporated into a model in which the basins in the central parts of the Scotia Sea had already formed by chron C8, contrary to some widely accepted interpretations, and which has significant implications for paleoceanography and paleobiogeography.