West Antarctic ice volume variability paced by obliquity until 400,000 years ago

We present results from the NBP03-01A-20PCA sedimentary record which was recovered from the outer continental margin of the central Ross Embayment. Sediments comprise mud, with sub-angular to sub-rounded fine to coarse sand, common pebbles and rare cobbles. A paleomagnetic age model indicates the succession has a basal age of c. 1.1 Ma with magnetic reversals at 4.21 m, 5.74 m, and 5.85 m depth correlated with C1n-C1r.1r-C1r.1n-C1r.2r geomagnetic reversals.

Magnetic mineral concentration and micro IBRD data were considered a proxy for the proximity of the Ross Ice Shelf grounding zone and calving line to the core site. High magnetic mineral concentration and high terrigenous content correspond to sediments deposited beneath a floating ice shelf or from icebergs calved from that source. Time series analysis of these data indicate the advance and retreat of the Ross Ice Shelf—and by extension the West Antarctic Ice Sheet— were primarily paced by 41,000-year-long obliquity cycles until at least 400,000 years ago.

Insolation was predicted to control Antarctic ice volume; however, the frequency of glacial cycles inferred from global benthic foraminiferal oxygen isotopic and ice core records were originally interpreted to indicate that Antarctic ice volume variations were paced by 100,000-year-long (eccentricity) cycles from about 800,000 years ago. This interpretation was never confirmed from sedimentological reconstructions of ice margin advance and retreat cycles around Antarctica.

On seasonal timescales, ablation at the base of the western sector of the Ross Ice Shelf is controlled by the inflow of Ross Sea surface waters warmed by the summer sun. On orbital timescales, season length is suggested to control Antarctic temperature, with long summers and short winters leading to gradual warming and vice versa. We suggest that ablation, driven by circulation of warm summer surface waters under the ice shelf, is the mechanism by which long-term insolation control of sea surface temperatures produced the orbitally paced cycles observed here.

Our study reconciles the historical mismatch between high latitude insolation variations and glacial cycles inferred from distal records. We suggest that high-latitude insolation controlled Southern Ocean heat uptake and continued to be the main pacemaker of Antarctic glaciations well into the late Pleistocene. More sedimentary records from Antarctica and the Southern Ocean are required to reconstruct the true glacial history and whether different sectors of the margin are sensitive to different forcings.

Ohneiser, C., Hulbe, C.L., Beltran, C. et al. West Antarctic ice volume variability paced by obliquity until 400,000 years ago. Nat. Geosci. 16, 44–49 (2023). https://doi.org/10.1038/s41561-022-01088-w