Via, Rachael Kathleen (2005-08). Evolution of Atlantic deep-water circulation: from the greenhouse to the icehouse. Master's Thesis. Thesis uri icon

abstract

  • To better understand how the evolution of Cenozoic deep-water circulation related to changes in global climate and ocean basin configuration, we generated Nd isotope records from Ocean Drilling Program sites in the southeastern Atlantic to track deep water mass composition through time. We used fossil fish debris from ODP Sites 1262-1264 (Leg 208), spanning present-day water depths of 2500-4750 m, to reconstruct the isotopic signature of deep waters over the past ~53 Ma. The data indicate an initial transition from relatively non-radiogenic values (??Nd=~-10) at 53 Ma to more radiogenic values (~-8.5) at ~32 Ma. From ~32 Ma to 3.85 Ma, the Nd signal becomes more nonradiogenic, ~-12.3 at the top of the record. Comparison of our data with Nd isotopic records derived from a North Atlantic Fe-Mn crust show similar non-radiogenic values (~-10.5) in the 53??32 Ma interval and a trend toward more non-radiogenic values beginning at ~20 Ma. The data likely reflect an overall shift from a Southern Ocean deep water source to the ultimate incursion of deep waters from the North Atlantic. The non-radiogenic values at the base of the record reflect a Southern Ocean source of deep water. The shift toward more radiogenic values indicates an increased contribution of Pacific waters to the Southern Ocean source as the tectonic gateways changed after ~35-33 Ma. The subsequent trend toward more non-radiogenic Nd isotope values is approximately concurrent with the increase of benthic foraminiferal ??18O values, based on comparison with a compilation of global data. Thus, changes in oceanic gateway configuration in addition to overall cooling and the build-up of continental ice on Antarctica may have altered the Nd isotope character of Southern Ocean deep waters during the early Oligocene.
  • To better understand how the evolution of Cenozoic deep-water circulation
    related to changes in global climate and ocean basin configuration, we generated Nd
    isotope records from Ocean Drilling Program sites in the southeastern Atlantic to track
    deep water mass composition through time. We used fossil fish debris from ODP Sites
    1262-1264 (Leg 208), spanning present-day water depths of 2500-4750 m, to reconstruct
    the isotopic signature of deep waters over the past ~53 Ma. The data indicate an initial
    transition from relatively non-radiogenic values (??Nd=~-10) at 53 Ma to more radiogenic
    values (~-8.5) at ~32 Ma. From ~32 Ma to 3.85 Ma, the Nd signal becomes more nonradiogenic,
    ~-12.3 at the top of the record. Comparison of our data with Nd isotopic
    records derived from a North Atlantic Fe-Mn crust show similar non-radiogenic values
    (~-10.5) in the 53??32 Ma interval and a trend toward more non-radiogenic values
    beginning at ~20 Ma.
    The data likely reflect an overall shift from a Southern Ocean deep water source
    to the ultimate incursion of deep waters from the North Atlantic. The non-radiogenic
    values at the base of the record reflect a Southern Ocean source of deep water. The shift
    toward more radiogenic values indicates an increased contribution of Pacific waters to
    the Southern Ocean source as the tectonic gateways changed after ~35-33 Ma. The
    subsequent trend toward more non-radiogenic Nd isotope values is approximately
    concurrent with the increase of benthic foraminiferal ??18O values, based on comparison
    with a compilation of global data. Thus, changes in oceanic gateway configuration in addition to overall cooling and the build-up of continental ice on Antarctica may have
    altered the Nd isotope character of Southern Ocean deep waters during the early
    Oligocene.

publication date

  • August 2005