Middle Miocene ice sheet dynamics, deep‐sea temperatures, and carbon cycling: A Southern Ocean perspective

Relative contributions of ice volume and temperature change to the global ∼1‰ δ 18 O increase at ∼14 Ma are required for understanding feedbacks involved in this major Cenozoic climate transition. A 3‐ma benthic foraminifer Mg/Ca record of Southern Ocean temperatures across the middle Miocene climate transition reveals ∼2 ± 2°C cooling (14.2–13.8 Ma), indicating that ∼70% of the increase relates to ice growth. Seawater δ 18 O, calculated from Mg/Ca and δ 18 O, suggests that at ∼15 Ma Antarctica's cryosphere entered an interval of apparent eccentricity‐paced expansion. Glaciations increased in intensity, revealing a central role for internal climate feedbacks. Comparison of ice volume and ocean temperature records with inferred p CO 2 levels indicates that middle Miocene cryosphere expansion commenced during an interval of Southern Ocean warmth and low atmospheric p CO 2 . The Antarctic system appears sensitive to changes in heat/moisture supply when atmospheric p CO 2 was low, suggesting the importance of internal feedbacks in this climate transition.