New discoveries on Marlborough seafloor

TUESDAY, AUGUST 28, 2018

The findings of the most complex underwater coastal survey of the seafloor undertaken in New Zealand, including previously undiscovered natural features and sunken boats, are to be formally presented to the Marlborough community tomorrow.

The Queen Charlotte Sound/Tōtaranui and Tory Channel/Kura Te Au mapping project was undertaken by NIWA and Discovery Marine Ltd in partnership with Land Information New Zealand (LINZ) and the Marlborough District Council. It was completed using the latest multibeam echo sounder technology to gather more than five billion data points.

The survey was undertaken from two NIWA research vessels and included 280 days on the water mapping more than 43,000 hectares.

Multibeam echo sounders produce a fan of acoustic beams or sound waves directed downwards from the bottom of a boat. These beams reflect off the seafloor, enabling the surveyors to calculate the depth of the seafloor, and map the seafloor habitat in extraordinary detail.

The data has been used to produce an extensive new catalogue of navigational charts which were last updated in the 1940s, seabed maps and 3D images, giving the Marlborough community the most detailed picture of the physical and biological features underneath their coastal waters of any region in New Zealand.

NIWA General Manager Operations and marine geologist Dr Helen Neil said the seafloor survey revealed natural features such as complex pockmark structures, scouring, sand waves, sediment braids and freshwater seeps not previously known about, as well as an extensive survey of the kelp habitats in the sounds.

“The results of this survey deliver a quantum step in our knowledge of the Sounds’ complex coast within NZ’s extensive marine estate and provides a foundation for any further science in the region,” she said.

“From a visual viewpoint, some of the most exciting finds were sediment wave fields up to 20 m high, numerous seafloor pockmarks attributed to freshwater seeps, gravel-filled deep water current scours, complex rocky reefs with extensive kelp habitat. NIWA also believes this is a nationally significant project using cutting-edge science that will benefit the thousands of people who use the Marlborough Sounds year-round for business or recreation.”

The survey also revealed a number of manmade features and structures on the seafloor, including the marine farms of the region, a trench that remains from the 1940s, dug for a war-time communications cable between islands in the Sounds, once considered for use as a base for the Pacific Fleet.

Several shipwrecks and sunken boats were also located, some known to divers and locals, and some unknown. One of those was the wreck of the Hippolas, a barque which struck Walker Rock in 1909 and was abandoned with no loss of life.

Marlborough Mayor John Leggett said that the Marlborough Sounds are the jewel in Marlborough’s crown.

“Council now as a comprehensive data-rich appraisal of this vitally important coastal marine area. This will help Council in the sustainable management of coastal resources, and inform the community’s growing desire for more comprehensive marine protection to maintain biodiversity.”

Tomorrow’s official launch takes place from 1.30pm and will be attended by Conservation Minister Eugenie Sage.

A public information evening is being held at Port Marlborough Pavilion, 181 Waikawa Rd, Picton starting at 6.30pm.

The extensive catalogue of information from the survey is freely available for use by the Marlborough community, iwi and researchers. It provides a comprehensive data-rich undersea appraisal that will underpin decision making surrounding the region’s valuable marine ecosystems and resources.

Marlborough survey facts - :

Queen Charlotte Sound/Tōtaranui, Tory Channel/Kura Te Au seafloor mapping survey

• Undertaken by two NIWA research vessels, Ikatere and Rukuwai

• More than 43,000 hectares of seabed mapping using multibeam echo sounder technology

• 280 days spent on the water

• 30 terabytes of new data

• 312 days of data processing, habitat interpretations

• 1,179,152 file sets of multibeam, water column and navigational data

• 36,360 Geoswath sounder files

• 208 three dimensional visualisations

• 163 seafloor videos

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