Paleoceanographic change during the Middle Miocene climate revolution: An Antarctic stable isotope perspective

Abstract

Ocean circulation and atmospheric pCO 2 variations have been cited as potential mechanisms driving middle Miocene cooling and Antarctic cryosphere expansion. Well-dated high latitude (∼55°S) benthic foraminifer stable isotope records from the South Tasman Rise (STR; ODP Sites 1170 and 1171) exhibit familiar patterns of long and short term middle Miocene climate change and inferred carbon cycle dynamics. STR records illustrate the major middle Miocene δ 18 O increase (1.2‰) between 14.01 and 13.77 Ma. STR δ 18 O and δ 13 C records covary between 16.5 and 13.5 Ma. Integrated STR and southwest Pacific (0-55°S) stable isotope time series and time slice data indicate regional ocean circulation changes (>1500 m) commensurate with the middle Miocene global climate transition (16.8-12 Ma). STR stable isotopes and southwest Pacific meridional δ 13 C gradients suggest that Warm Saline Deep Water from the Tethys Sea dominated regional bottom waters (>1500 m) between 16.8 and 16.2 Ma, during the peak of the Miocene Climatic Optimum (MCO), and exerted intermittent influence on the STR (∼55°S) until the end of the MCO (∼13.8 Ma). A shift from low to high latitude sourced intermediate and deep waters occurred at ∼16.2 Ma. Southern Ocean derived Southern Component Water influenced the STR (>1500 m) beginning at 16.2 Ma and dominated the southwest Pacific (1500-2100 m; 0-55°S) from 14.9 to 14.2 Ma and 13.8 to 12 Ma. Although δ 18 O and δ 13 C coherence suggests some role for pCO 2 , these findings support hypotheses relating middle Miocene cooling and Antarctic cryosphere development to reorganization of oceanic circulation and meridional heat flux.