Posts Tagged Southern ocean

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: 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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