Posts Tagged NIWA

New Auckland Museum Three Kings Islands Expedition Guest Work Apr 11

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From Alison Ballance, blogger for the Three Kings Islands Marine Expedition.

Many people know the Three Kings islands as the site of the Elingamite wreck, and for over a hundred years treasure hunters have flocked here in search of gold and silver. But for the scientists of the Three Kings Islands Marine Expedition these islands hold treasures of another kind – a rich diversity of marine life which they have come to observe and record. The fish life is moderately well documented, but there are many kinds of invertebrates and seaweeds found only here, many of which are unnamed and unrecorded, and the goal of the expedition is to add a few vital pieces to our understanding of the complex jigsaw puzzle of life here at New Zealand’s northern-most frontier.

Severine Hannam from Auckland Museum investigates some seaweed collected during the first dive of the Three Kings Islands  Marine Expedition.

Severine Hannam from Auckland Museum investigates some seaweed collected during the first dive of the Three Kings Islands
Marine Expedition.

The expedition arrived at the Three Kings Islands, about 55 kilometres northwest of Cape Reinga, at dawn on Wednesday, and by 7.30 am the first dive teams were already in the water. The big high sitting over New Zealand made for perfect sea conditions – calm with little wind – and expedition leader Tom Trnski from Auckland Museum said everyone was keen to make the most of the good conditions and begin collecting. There was an air of excitement on the back deck of the expedition vessel Braveheart before the dive as scientists and photographers donned wetsuits, sorted their dive gear and collecting equipment, and then headed out in the inflatable tenders to the first dive site. An hour or so later there was euphoric chatter as everyone struggled out of wet dive gear, swapping first impressions about the clarity of the water, the abundance of fish life, the richness of the seaweed cover and the overwhelming abundance of bright sponges and small jewel-like organisms covering the rock underneath.

A riot of multi-coloured sponges encrust steep underwater cliffs at the Three Kings islands.

A riot of multi-coloured sponges encrust steep underwater cliffs at the Three Kings islands.

The two-week expedition is led by Auckland  Museum and brings together 11 marine biologists from NIWA, Te Papa Tongarewa and the University of Queensland.  Also along to document the trip are two photographers and Radio New Zealand producer Alison Ballance.  The expertise on board includes fish biologists, invertebrate scientists and seaweed experts, and the specimens they collect will help build a comprehensive picture of the coastal marine life on these remote volcanic islands. The biota has many similarities to northern New Zealand, but there are many interesting omissions (no spotties or mussels which are common on the mainland), and as well there is a range of interesting endemics, such as Johnson’s sargassum which is a dominant feature.

By early Wednesday afternoon the team had completed two dives and assembled on the back deck to begin meticulously documenting all the samples. Weather permitting, the same procedure will repeat for the next nine days, and who knows what precious treasures will be found and what secrets revealed.

You can follow the Three Kings Islands Marine Expedition blog here.

Antarctic Voyage: The South Pole Guest Work Feb 18

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Written by Helen Bostock (marine geologist, NIWA)

Date: 15/02/2013
Location: 64.807561°S, 139.86694°E
Weather: Snowing and breezy – 20 knots
Sea state: 2 m swell

Today we passed over the South Pole.

Well, not quite, but very, very close by. How is this possible when we are on board a ship and haven’t set foot on Antarctica itself?

We have been close to the Magnetic South Pole. The Magnetic South Pole is the wandering point in the Earth’s Southern Hemisphere where the geomagnetic field lines are directed vertically upwards – the ‘magnetic inclination’.

The Magnetic South Pole currently sits at 64°24’S, 137°00’E, so the RV Tangaroa passed just west of this, within 100 km of the Pole. It is constantly shifting, however, due to changes in the Earth’s magnetic field, moving northwest at a rate of 10-15 km per year. Unfortunately it being the middle of the night meant that there wasn’t much to see, except that the compass kept changing.

The first calculation of the magnetic inclination to locate the Magnetic South Pole was made on January 23rd 1838, by French hydrographer Clément Adrien Vincendon-Dumoulin on the Dumont d’Urville expedition to Antarctica and Oceania in 1837-1840, on the ships L’Astrolabe and Zélée.

There were several early attempts to reach the Magnetic South Pole in the early 20th Century: during the Ernest Shackleton’s 1908-1909 Nimrod expedition when it was approximately 72°20’S, 155°12’E, on mainland Antarctica (Victoria Land) just west of the Ross Sea, and then during Douglas Mawson’s 1911-1913 Australasian Antarctic expedition (more on that in a later blog post).

So theWikiMiniAtlasSoSSo magnetic poles are different from the geographic poles. This is critical to know if you are using a compass for navigation as the compass needle points to magnetic north, not true north (or grid north). The difference between magnetic north and true north is called the ‘magnetic declination’.

Most map coordinate systems are based on true north, and magnetic declination is usually shown on the map legend so that the direction of true north can be calculated. In some areas the declination is only 5°, so you wouldn’t get too lost if you are only going short distances. In New Zealand, though, we need to correct for this difference, as the declination is greater than 20°.

Closer to the magnetic poles, the declination gets very large and compasses are not very useful. As a result, the officers on the RV Tangaroa will have to rely on their Global Positioning System (GPS), which uses multiple satellites to work out our exact position, rather than relying on the compass and earth’s magnetism.

Spotlight on bow of ship

Spotlight on the bow of the ship. [Jill Scott]


Antarctic Voyage: Multibeam mapping of the seafloor Guest Work Feb 07

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Written by Dr Helen Bostock and Peter Gerring at NIWA

Date: 5/2/2013
Position: 48.888683˚S, 167.759479˚E
Weather: cloudy
Sea state: 3-4 m swell – rough!

Yesterday, just before the rough seas started and most of the science team took to their beds suffering with sea sickness, the geology team started running the multibeam seafloor mapping system.

We are collecting some opportunistic seafloor data on the voyage transits to and from Antarctica. We also hope to map the continental shelf around the Mertz Glacier to add to the data that was collected on previous voyages. These detailed maps will be used to understand the oceanographic flow, evidence of past Antarctic ice extent (using the ice berg scours on the sea floor), as well as the distribution of biology and sediments.

NIWA marine ecology technician Mark Fenwick in the multibeam lab, running the system. Credit: Helen Bostock

How do we map the seafloor with the multibeam?

Let’s start with a bit of history. Back in the good old days, the positions of features on the seabed were plotted using soundings taken by lead-line.

The position of the sounding was fixed using a quadrant, compass bearings off land features, and later on a sextant. Charting was extremely labour-intensive and not very accurate. More commonly, directions and hazards were handed down through the generations by word of mouth or learned by experience – not always good ones!

After World War II, single beam echo sounders became widely available. Echo sounding is a technique for measuring water depths by transmitting an acoustic pulse (or ping) from a transducer mounted on the hull of a vessel and listening for the reflection (or echo) from the sea floor. The time taken for that ping to travel to the seabed and back again is converted into a depth by halving the time taken between transmission and reception, and multiplying that time by the speed of sound in water (somewhere near 1500 metres per second).

Most of the charts that currently map the world’s coasts and oceans were made using these soundings, and these single beam echo sounders are commonly found on even small boats.

However, single beam sounders don’t provide 100% coverage of the seafloor. Lines of sounding are recorded and these soundings are used to generate depth contours. In between the soundings are areas which potentially contain large rocks or holes. So, in 1964, a technique for multiple narrow-beam depth sounding was patented by SeaBeam. This system allowed survey vessels to produce high-resolution coverage of wide swaths of the ocean bottom.

The multibeam system fitted to the Tangaroa is a Simrad EM302. It has 432 beams. These are sent out from the ship in a fan shape (see this video explaining how it works), and can cover an area of seafloor up to 5 km or more in width with each pass of the ship, although the coverage is much smaller for shallower depths.

Of course things are a little more complicated than this – aren’t they always? For one thing, the speed of sound through the water is not constant. This leads to the beams being bent or refracted as they travel to and from the bottom. To compensate for this, we have to know the sound velocity of the water which changes with density. We can use the data from the CTD (see the previous blog post in this series) to calculate this.

Secondly, the ship is not stationary – it is constantly in motion, which is why people get sea sick. The ship’s position must be precisely known at all times and this is achieved using GPS (Global Positioning System; the same as in your phones or satnav), which can tell us where we are within a metre or less. We also have to correct the swath data for the ship’s roll, pitch and yaw.

The end result of all this is that we can create very accurate maps of the seabed, which can be used for a whole range of science.

Undersea New Zealand, a high resolution image of the complex and diverse marine realm around New Zealand. Credit and copyright: NIWA

Antarctic voyage: the Mertz Polynya Guest Work Jan 31

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Ever wondered what it is really like to be working on a ship off Antarctica?

Dr Helen Bostock, marine geologist at NIWA, writes:

On the 2nd February I will be part of a team of 22 Australian, French and New Zealand, scientists departing Wellington on board NIWA’s R.V. Tangaroa.

The science team is made up of oceanographers and geologists, and we will be heading out on a 42-day voyage to the Mertz Polynya region of Antarctica.

Credit: Peter Marriot, NIWA from 2008 voyage to the Ross Sea as part of the International Polar Year

In these blog posts I will discuss the planning, preparation and training required for this kind of voyage; everyday life at sea; how and why we are doing the science; any wildlife that come across; the experience of a large Southern Ocean storm; the frustrations of being stuck on a 70 m boat for 6 weeks; and any other mishaps or unexpected events that we experience during the voyage….

Why study the Mertz Polynya?

Back in February 2010 the tongue of the Mertz Glacier broke off after being rammed by a huge iceberg. The Mertz Polynya is one of three areas around Antarctica where the deep waters of the ocean are formed. The so-called “Antarctic bottom waters” are created during the formation of sea ice, which leaves behind very salty, dense water. This salty water sinks to the bottom and flows over the edge of the continental shelf, like an overflowing dam, to the bottom of the Southern Ocean.

So one of the main aims of this voyage is to understand how changes in the Mertz Polynya, caused by the break off of the glacier tongue, will affect the formation of Antarctic bottom water and the flow in to the deep ocean, and the potential global implications of these changes.

The voyage will also be sampling seafloor sediments and taking underwater video to see what lived under the Mertz Glacier Tongue before it broke away. Sediment cores may also provide clues as to how often the glacier tongue has broken off in the past.

The transit to the Mertz Polynya from Wellington will take over a week. But we won’t be bored. We will be collecting lots of samples along the way as we cross the Southern Ocean.

Map of NIWA’s R. V Tangaroa path to the Mertz Polynya area, Antarctica. Credit: NIWA

We will be continuously sampling the surface waters and the air for the CO2 content. We will be towing a “continuous plankton recorder” behind the ship, which collects and preserves plankton. And we will also be collecting a couple of sediment cores and deploying some Argo floats, which measure the temperature and salinity of the ocean. (All of these will be explained in more detail in future blogs.)

These observations and samples will add to the ongoing Subantarctic and Southern Ocean research programmes in New Zealand, Australia and New Zealand. This research is funded by Australian Antarctic Climate and Ecosystem Cooperative Research Centre, L’ocean, France, and NIWA government funded core research, New Zealand.

Follow us on our expedition and experience the excitement, trials and tribulations of marine scientists working at sea!

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