Monday, January 28, 2013

Something on glass sponges...

Here I am building a mooring
For my masters work I looked at flow over a local glass sponge reef. It turns out that how the tides interact with a sub-surface ridge may influence the conditions the sponge reef lives in. I wrote a little about it for the UVic Ocean Student Society here.

Wednesday, January 16, 2013

Getting a sample of water

one alternative to taking water samples...

As an oceanographer, I often think about how to sample the water I’m interested in. Generally, I prefer using instruments that measure a property in place returning just an electronic data file, but sometimes, water must be taken for analysis which raises the question: how do you get water from the ocean and into a lab? The simplest solution is a bucket at the end of a rope - a technique I’ve found myself using in the past. This equipment is easy to find and easy to use. The downside is you can only get surface water this way. Getting waters from intermediate depths takes fancier gear, and it took a long time of trial and error to develop the instruments needed to collect water from these depths.

A theoretical idea…

Water sampling equipment started from an idea presented at the British Royal Society early in its history from someone who never went to sea. Robert Hook designed a box of wood to be lowered on a line. Water flow held the end valves open on the way down. When the instrument reached the desired depth, it would be hauled up, and the change in direction would close the end valves. This design ultimately evolved into our modern water sampler, however, the original wasn’t practical. The wood would swell in the water and no seal was maintained - if you hauled back the sampler and it actually contained water, there was no way to know it came from the targeted depth.

A reality check…

To reliably work, water sampling instruments made the leap from theoretical designs to functional equipment via multiple design iterations (I often wondered how much of this occurred on a deck of a ship where some poor technician was trying to make this theoretical, lab-built equipment work).

By the time of the Challenger Expedition (1872-76) a working instrument existed - a stop-cock water bottle. This sampler had spring-loaded stoppers for both ends. When it was being lowered into the ocean the stoppers would be open, allowing water to flow freely through the bottle. At the desired depth, the bottle being lowered, was pulled up slightly, allowed to fall back and then jerked to a stop - action that would close the stoppers and trap the water inside.

Several design iterations later, and still in common use, is the Niskin bottle (designed in the 1960’s). Niskin bottles are made of plastic to reduce sample contamination and the end caps have rubber washers to improve their seal. These bottles are lowered down a wire in the open position. When the bottle reaches the desired depth a metal messenger, basically a metal bead that clips onto the wire, is sent down the wire to trip the bottle closed. An added advantage is these bottles can be used in series, allowing for multiple samples to be taken at one time. They can even be arranged in a rosette for more detailed water collection schemes.

Do we need to take the water…

“To replace the laborious analysis of recovered water samples the marine scientist may employ a single sensing unit which will telemeter back to him, or record on tape, data on the temperature, salinity, conductivity, oxygen content and sound velocity of the water in which it is placed.”
                   - Historical Instruments in Oceanography by Anita McConnell, 1981

Water sampling is still necessary for many things, however, electronic sensors can be deployed for long periods of time, reporting back parameters which can provide an ongoing record at that location. Ocean networks like Venus and Neptune provide ongoing reporting that could never be obtained from water sampling alone.

As a tangent - the photo is a simple mooring I built with electronic recording instruments (salinity and temperature) that was deployed for a year, part of that under ice. Yes, it looks like a pile of rope.

Thursday, January 10, 2013

Flat earth and open polar seas

A view of the Arctic Ocean from 1849
Why do we hold onto ideas about the world around us when all the evidence points to another reality? Like that we live on a flat earth. On the flip side, some ideas may eventually prove to be true. Like an open polar ocean.

Once people thought we live on a flat earth - which makes sense if all you see of the world is what is out the window. It must have taken a lot of guts along with a dose of extreme self confidence to be among the first who went against this belief. One example is Christopher Columbus, who made the assumption the earth was round when he sailed westward to find China - fortunately for him and his crew, he was right (about the roundness of the planet, but not the distance to China).

From the window of a commercial flight anyone can see earth’s curvature by looking at the horizon. With pictures from space, we can conclusively show the earth is round. Contrary to this evidence, flat earth societies have not disbanded. Why do they hold onto the idea of a flat earth?

Another idea that persisted despite contrary evidence was an ice-free polar ocean, that the only ice was around the edges and once you broke through this ice it was clear sailing. This idea dated back to the 16th century, and perhaps earlier. Joseph Moxon, a royal hydrographer working in the 1660s, continued promotion of this ice-free idea attributing it to the 24hr a day solar heat melting the ice in the summer. He also theorized that ice only formed near landmasses where the water was fresher - an idea that morphed over the next 100 years into seawater being unable to freeze by its nature (which is easy to disprove in a lab experiment).

Since an open polar sea presented a potentially lucrative short-cut, expeditions were commissioned to break through the ice and find the open sea beyond. The all failed, some more spectacularly than others. Franklin tried to break through on one of his early missions, failed and went home, while the R/V Jeannette tried, got frozen into the ice and ultimately crushed. Still more ships were sent until Nansen tried walking to the pole and found ice all the way.

The idea of an open Arctic Ocean hasn’t gone away even after it was proven to be covered in multi-year ice instead the idea has morphed into one based on science. In the 1970s the idea reared its head again when an irrigation proposal was made to divert several major Siberian rivers that normally flow into the Arctic to central Asia instead. Beneath the layer of cold Arctic waters is a layer of warmer Atlantic water. This deep warmer water is insulated from the surface because the cold water above is fresher, meaning it remains less dense even though it is colder than the water below. If less freshwater goes into the Arctic Ocean, the cold top layer could become saltier and sink below the warmer water. The warm water then could influence the surface and melt the ice.

Another way the Arctic Ocean may loose its ice is through global warming. The polar ice cap is likely to melt completely in the summer in my life time - making a shipping shortcut across the pole a seasonal possibility.

Flat earth and open polar seas were both incorrect ideas that were held onto even when contrary evidence was found. This planet has been conclusively shown to be a sphere (or, more precisely an oblate spheroid), however, an open polar sea may become a reality.

Image is from here