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Using seismic oceanography to image water masses within the ocean

Solving the mystery of sustained ocean fertility at the Subantarctic Front. Seismic oceanography gives us the means.

The 2009 Marsden Funding round has awarded a three-year grant for this project starting in 2010.

Marsden Project Summary:

Australasia's first seismic oceanography project is providing detailed new images of the fine-scale (<10 m) mixing processes that occur between water masses at the Subantarctic Front east of the South Island. We aim to shed light on the physical and chemical processes that lead to surprisingly sustained fertility levels in subantarctic waters which are likely linked to the transport of considerable oceanic iron across this globally significant ocean boundary. Current maps and cross-sections of physical and chemical properties of the ocean are inadequate because they are made by interpolating measurements collected by tools moored to stationary points on the surface or seafloor. Our proposal makes use of the exciting new field of seismic oceanography to produce high-resolution X-ray-like images of water masses using a technique similar to how ultrasound images a foetus. This work will combine new data collected by us, with 30-year’s-worth of existing seismic data, in order to illustrate the global significance of seismic oceanography as a sound method for assessing a range of chemical and physical oceanographic problems.

Our Team:

Principal Investigator:

Assoc Prof Andrew Gorman, Department of Geology

Assistant Investigator:

Dr. Ross Vennell, Department of Marine Science
Assoc. Prof. Russell Frew, Department of Chemistry
Prof. Steve Holbrook, University of Wyoming

Students:

Joanna Cooper, Department of Geology
Matthew Smillie, Department of Geology

Read on for more information on seismic oceanography.

Stacked 60-fold seismic line CB82-94 acquired in 1982 as part of a Canterbury Basin survey by a consortium of BP, Shell and Todd
Stacked 60-fold seismic line CB82-94 acquired in 1982 as part of a Canterbury Basin survey by a consortium of BP, Shell and Todd. With conventional processing, the part of this figure within the water column would be ‘transparent’ and not show any reflections. However, by optimising processing for the water, reflections within the water column can be identified in the prestack data for this profile, and the stacking velocity model has been adjusted to accentuate them in this stack (possible interpretations are labelled.) The data have been plotted with a narrow automatic gain control window that accentuates the reflections further. (Processing of these data made use of an academic licence for GLOBE Claritas.)

Our ocean is not transparent! Imaging ocean currents and water masses on New Zealand’s continental margins using controlled-source seismology

Maps of water masses – such as warm or cold currents and eddies – within the ocean provide critical information for assessments of fishery environments, weather forecasts, climate models, and evaluations of the economics and safety of resource extraction. Oceanographers routinely measure the properties of such water masses using tools that are dropped from stationary boats down to the bottom of the sea or attached to floating or seabed moorings, and then interpolate those measurements to produce cross-sectional interpretations.

Our group is now starting to make use of the new field of seismic oceanography – one of the most exciting recent developments in marine science to produce high-resolution ocean images. We will use 30-year’s-worth of existing seismic reflection data, plus new data collected by us on board RV Polaris II, to produce detailed X-ray-like images of water masses using a technique similar to how an ultrasound images a foetus. Our research is centred on the southeast coast of the South Island, where we aim to show the global significance of this method for

  1. assessing interactions between coastal waters and strong offshore currents and
  2. investigating the effects of layering within ocean waters caused by variations in temperature, density and salinity.

Please see Postgraduate Opportunities for information on research in this field.