Tag Archives: Instrumentation

Rubber Duckies and Other Oceanographic Equipment

Rubber ducks in the 2009 Ken-Ducky Derby, floating along an inland stream.  Image credit: Tony Crescibene (CC-BY)
Rubber ducks in the 2009 Ken-Ducky Derby, floating along an inland stream. Image credit: Tony Crescibene (CC-BY)

On January 10, 1992, on a voyage from Hong Kong to Tacoma, Washington, the cargo vessel Ever Laurel encountered rough seas and a container was washed off the ship. The container broke open and released its contents: 28,800 yellow rubber duckies and other floating bath toys. Since then, the duckies have been floating around, moved by wind and wave, and washed up on coasts around the world. By tracking the date and location of washed-up duckies, oceanographers can get a sense for the speed and direction of surface circulation at an oceanic scale. It’s like having 28,800 messages in bottles dumped from the same known location at the same known time.

Oceanographers sometimes want to be more precise in their measurements. The duckies probably floated very high in the water (at least at first), so that the wind could easily affect their direction and speed. Additionally, the rubber duckies are hard to track while they are at sea because they are small, few, and far between.

When more precise measurements are required, oceanographers turn to specially-designed drift buoys. These maintain a lower profile above water, and have a large “holey sock” sea anchor tethered to them in order to more accurately measure the ocean surface currents and not the wind. The buoys also have a thermometer—and sometimes additional sensors for salinity or barometric pressure—and a radio transmitter to establish the buoy’s position (by Doppler shift from 401.65 MHz, not GPS) and relay data via satellite back to the operations center.

Surface Velocity Program buoys around the world.  All instruments have sea surface temperature (SST), blue instruments have sea-level pressure (SLP).  Several red points near Heard Island and between Heard Island and Perth, Australia are from the recent R/V Investigator voyage the Heard Island area.  Image credit: NOAA (public domain).
Surface Velocity Program buoys around the world. All instruments have sea surface temperature (SST), blue instruments have sea-level pressure (SLP). Several red points near Heard Island and between Heard Island and Perth, Australia are from the recent R/V Investigator voyage the Heard Island area. Image credit: NOAA (public domain).

Different floats can be used to measure temperature and salinity profiles, rather than surface currents. Argo floats are autonomous diving instruments, which can maintain neutral buoyancy and perform controlled ascent/descent to 2000 m. These floats make their temperature, pressure, and salinity measurements during a 6–12 hour ascent. Upon reaching the surface, they transmit their GPS location and the recorded data back to the operations center via satellite. Argo floats are not cheap, with each carrying a price tag of around $15k.

On the Heard Island Expedition, our team will be deploying both of these types of instruments. These measurements will improve understanding of ocean circulation, heat content, and salinity, as well as providing ground-truth sea surface temperature measurements for use in weather forecasting models. No rubber duckies will be deployed, but we’ll document any we find washed up on the beaches.

Still want more marine science? Check out DeepSeaNews!

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Geoscientist’s Toolkit: Mass Spectrometer

Mass spectrometer schematic. Image credit: Wikimedia Commons, based on an image by USGS.

Mass spectrometers are incredibly important pieces of analytical equipment. They have been used on Mars, around Saturn, around Mercury (the planet), and many places in between. They are even found at airport security checkpoints.

Every mass spectrometer has three primary components: an ion source, an analyzer, and a detector.

In the ion source, atoms or molecules are charged—usually by having an electron knocked off—and are focused into a beam within a vacuum chamber. Most ion sources ionize samples when they are already in high vacuum, but some ionize at ambient pressure and then pump the ions into the vacuum.

Next, the ions move into the analyzer. This region separates the different ions in time or space based on the ion’s mass/charge ratio (in many cases, especially in geochemistry, the charge is +1). Although there are several different analyzer designs, the one used in isotope geochemistry is generally the magnetic sector. Here, the ions are passed through a strong magnetic field. When a charged particle moves through a magnetic field, the field exerts a force on the ion, causing its path to be deflected. Less massive ions will be deflected more sharply than more massive ions (equal force gives greater acceleration to smaller masses). This is shown in the picture above.
By changing the strength of the magnetic field, the mass(es) that reach the detector can be selected.

Finally, the ions enter the detection region. Here the current from the ion beam is amplified, and that signal is then recorded. More abundant ions will lead to higher current. Some mass spectrometers, such as the one in the schematic above, are equipped with multiple detectors to measure relative isotopic abundances of several ion masses simultaneously.

For isotope geochemistry, there are two general classes of isotope measurement: stable isotopes, and radio-isotopes.

Stable isotopes are often 1H, 2H (D), 12,13C, 14,15N, and 16,17,18O, though of course many other systems are used. These measurements can provide isotopic “fingerprints”, which can track where things are moving around, and how much mass is flowing.

Radio-isotope systems include 238U/206Pb, 235U/207Pb, 14C, 40K/40Ar, 87Rb/87Sr, and 147Sm/143Nd. These systems are generally used for geochronology, or tracking mixing between distinct sources with different chemistries and histories.

Mass spectrometry as a field is diverse in aims and equipment, but the general principles are the same: an ion source, an analyzer, and a detector. These instruments are a versatile part of the geoscientist’s toolkit.