No extreme bipolar glaciation during the main Eocene calcite compensation shift

Area of Science:

• Paleoclimatology
• Marine Geology

Background:

• The Eocene/Oligocene boundary (approx. 34 million years ago) marked permanent Antarctic ice sheet establishment and ocean calcite compensation depth (CCD) deepening.
• Previous views suggested Northern Hemisphere glaciation began much later (11-5 million years ago).
• Recent evidence, including Eocene ice rafting and global ice volume estimates, challenged this timeline, suggesting earlier Northern Hemisphere glaciation.

Observation:

• Marine sediment records from the equatorial Atlantic, including oxygen and carbon isotopes and calcium carbonate content, were analyzed.
• These records were used to test the hypothesis of simultaneous large ice sheets in both hemispheres around 41.6 million years ago.
• The analysis focused on reconstructing global ice volume and its distribution.

Findings:

• The analyzed sediment records indicate that global ice volume around 41.6 million years ago could be accommodated solely by Antarctic ice sheets.
• This suggests that large-scale ice sheets were not present in the Northern Hemisphere at that time.
• A brief interval preceding a temporary CCD deepening showed a shoaling CCD, increased ocean temperatures, and decreased carbon isotope values in the equatorial Atlantic.

Implications:

• The findings resolve discrepancies between geological records and climate models regarding the timing of Northern Hemisphere glaciation.
• The observed environmental changes around 41.6 million years ago suggest links to carbon cycling events, including the Eocene/Oligocene boundary and Early Eocene 'hyperthermals'.
• This research refines our understanding of early Cenozoic climate dynamics and ice sheet behavior.