Thursday, September 22, 2011

Sunny paradoxes – part 2

A hazy sun
Since the solar system's beginning, the sun has increased its energy output by about 25 percent. What has that meant for earth? From ancient rocks, we can tell that a younger earth had surface liquid which can be taken to mean that earth has remained roughly the same temperature as we still have liquid water. If the sun was cooler back then, why wasn't the earth cooler? This is known as the 'faint young sun paradox'. A number of mechanisms may have been responsible for keeping a relatively constant surface temperature. Probably a combination of things are involved, but no one knows for sure. Here are some possibilities:

The Earth was warmer despite less incoming solar energy because of a larger greenhouse effect. For this to work, the greenhouse effect responsible would have tapered off as the sun grew brighter. The greenhouse effect is caused by an atmosphere rich in 'stuff' that prevents radiation from escaping. Two of the better culprits are water vapour and carbon dioxide (methane is a good at this too, as is nitrous oxide i.e., laughing gas). Assuming carbon dioxide played a big role, where would extra carbon dioxide come from? Way back, a more geologically active earth spewed more carbon dioxide from volcanoes. This excess carbon dioxide eventually was sunk into places like our oceans thereby reducing this greenhouse gas over time (only in the last 200 years have people begun spewing out our own contribution of this gas). So, when the sun was cooler the extra carbon dioxide created a greenhouse effect that has decreased at a similar rate as the sun heating up. Other processes probably put more of the other greenhouse gases into our atmosphere long ago and removed them slowly over time as well.

A recent thought based on big assumptions is that the early atmosphere also had more nitrogen. Nitrogen all on its own isn't a greenhouse gas on Earth (on Saturn's moon Titan, some funky stuff happens to the nitrogen, so there it acts a greenhouse gas), however extra nitrogen bounces around and hits the greenhouse gases which gives the greenhouse gases extra energy and makes them unstable or wobbly. This molecular wobble spreads out absorption lines (the range where a particular molecule absorbs energy) resulting in a wider band to absorb the radiation – thus more radiation is absorbed. On the flip side, extra nitrogen could also increase Rayleigh scattering, thus reflecting more of the incoming radiation away. So knowing which process dominated would be important.

As for why early earth wasn't colder with a cooler sun, we have good some ideas, but we really don't know for sure.

Walker, C.G., P.B. Hays and J.F. Kasting, 1981: A negative feedback mechanism for the long-term stabilization of Earth's surface temperature. Journal of Geophysical Research, 86, 9776-9782

Goldblatt, C., M.W. Claire, T.M. Lenton, A.J. Matthews, A.J. Watson and K.J. Zahnle, 2009: Nitrogen-enhanced greenhouse warming on early Earth. Nature Geoscience, 2, 891-896.

Monday, September 19, 2011

Sunny paradoxes – part 1

A sunset over Cumberland Sound
The sun continuously shines on Earth, but how much sunlight reaches us varies through the year. Since the Earth's orbit is elliptical, we are closest to the sun around 3 January and farthest around 4 July. Every illustration of the elliptical orbit of Earth that I've seen shows a hugely skewed orbit, which could lead one to think Earth would have its hottest global temperature in January.

However, the elipticalness of our orbit doesn't have much of an impact. From Wikipedia: Earth's farthest point is 152,098,232 km and the closest 147,098,290 km – a difference of 4,999,942 km, which is a small fraction of the orbit's radius (yeah, it's still a huge number, but everything in space is huge). Another way to look at this is to consider the eccentricity of Earth's orbit. Eccentricity is a measure of how circular an orbit is, zero is a perfect circle and one isn't a closed orbit (like a slingshot). Earth's eccentricity is about 0.02 – really close to a circle.

For those of us in the northern hemisphere, we are closest to the sun in the middle of winter – not the hottest time of year. Instead, it's the Earth's tilt that creates the seasons – we are tipped 23.5 degrees from the plane of Earth's orbit. When the pole closest to us is tipped away from the sun, we get winter. At the pole itself there is complete darkness (good for vampires).

The tilt of the Earth's rotation plays a greater role in our temperatures than the elipticalness of Earth's orbit. Either way, we still get a free trip of 150 million kilometres each year.

Friday, September 9, 2011

This ill-fated Arctic expedition had my name on it, but it had nothing to do with me

Recently, I read Fridtjof Nansen's Farthest North, a book about his sea voyage/scramble over the ice towards the North Pole that lasted from 1893 to 1896. Everyone got home safely in the end; an anomaly for Arctic trips at the time. Nansen designed his ship specifically to freeze into the ice. Based on a theory that the ice would drift taking the ship with it. The evidence he used to come up with this idea came from the disastrous, 1879-1881, Jeannette Arctic Expedition.

The Jeannette was a privately owned wooden steamship, originally the HMS Pandora (isn't re-naming a ship an invitation for bad luck?), that set sail from San Fransisco in 1879 and was commanded by Lieutenant DeLong of the US Navy. Sailing through Bering Strait and into the Arctic, the ship was frozen into the ice. Its ultimate destination was the North Pole – the belief at that time was that open water existed past the ice. In the summer of 1881, the ship was crushed by ice and the crew was forced to abandon it in three small boats. One boat was lost long before they reached the Siberian coast. The other two boats made it the coast, but were separated.

One boat's crew of eleven, including the Chief Engineer George Melville, were found by locals and saved. In the other boat was thirteen people, including Lieutenant DeLong. His last journal entry was dated 30 October 1881 and it is assumed he died shortly thereafter. Melville put together a search party for the others and by 1882, some of the bodies were discovered and sent back to the United States.

The Jeannette was crushed by ice in the area north of Siberia (77 degrees 15' north, 154 degrees 59' east). Three years later bits of paperwork and clothing from the ship were found on the southwest coast of Greenland – on the opposite side of the Arctic. This discovery led to the theory that these items had drifted right over the North Pole in the ice – the theory that inspired Nansen's voyage. There is more info on the voyage here  

The photo is a picture of a picture which I took in the museum in Iqaluit - there was no caption about what ship it is. Photos of the Jeannette can be found here.

Tuesday, September 6, 2011

Final update

one of the ship's constant arctic fulmar companions
Friday, 19 August 2011, I had the afternoon to explore one of the fjords opening into Cumberland Sound for a CTD cast. This one had the largest river in the area, so, I thought it might be interesting. It was part of the un-charted areas, so we went in slowly with the ship until there was about 7 m of water. Then, three of us loaded into the zodiac with the CTD and 400 m of line (I thought it could get much deeper further in, plus I didn't want to cut the line). The fjord hid behind a chain of islands (the largest was Kekertelung Island), so we still had a long way to go. At the fjord mouth, a sand bar blocked our way – it got so shallow the boat motor was hitting the ground. I never saw sand anywhere in the area, it was just rocks right down and into the water, even the echo sounder on the ship returned a hard signal, indicating there were rocks below the surface. I can only guess that the sand came from the river. We had to turn around so, I picked a near by bay for the cast. The water turned out to be over 80 m deep with a thick fresh water layer on top. When we got back on the ship, we headed back into Pangurtung to refuel.

Sunday, 21 August 2011 – Kevin and I were shown how to take samples of jellyfish and preserve them for future study. We dropped a zooplankton net (a fine round net slightly larger than an umbrella) down to the bottom and hauled it back up. Once back on board, everything inside was washed down into a collecting bucket which happened to be black. We caught some jelly fish – little ones about the size and shape of a thimble. Against the dark of the bucket, they flashed blue, purple and green.

Monday, 22 August 2011 – We were stuck in Pangurtung another day for reasons outside my control. I was offered the opportunity to go ashore, so I took it (I can only hang around so long on such a small ship without getting bored). The ship's captain wanted to find buckets he could use to empty the bilges and our best option was to check out the dump. Everything in Pangurtung is in walking distance, so we set out on foot (plus I needed the exercise). The dump was full of what looked like still usable stuff – a barbie doll still with a full head of hair, a pair of children's rubber boots with no sign of wear and so on. There were buckets, but no lids, so we left empty handed.

Tuesday, 23 August 2011 – We left anchor to retrieve my mooring. Unfortunately, the wind had picked up and there was significant swell in the sound. Some waves were greater than 5 m. Once near the mooring we started with a CTD cast (to check the moored instruments against), then we took some water samples. It was too rough to attempt to catch jelly fish. By this point, a scientist and a crew member had succumbed to sea sickness and I wasn't feeling so good myself. Water was now washing across the back deck on each large wave and everything lashed down was beginning to shift in scary ways. Using the ship's sonar, the mooring float 30 m below the surface was located and as soon as we got close, we let the acoustic release go. Soon, the orange float popped up and we grabbed it and started pulling the mooring on board. As soon as it was secure, we all went inside and the ship headed for a sheltered cove (Brown Harbour) to wait out the storm a anchor. That night winds reached 54 knots.

Wednesday, 24 August 2011 – In the morning I downloaded the instruments from the mooring, reset them, then built a new mooring to stay out for the winter. By the early afternoon, the wind had dropped, so we ventured back into the sound to deploy the mooring. This time, we set it up so we just needed to flake out the mooring behind us and cut a single line to release the anchor. We only needed to slow down, not stop. As soon as it was deployed, we headed back to Pangurtung for a crew change.

Friday, 26 August 2011 – I finally got a day to do CTD casts in one location (I'd been asking to do this since I arrived on board). The casts took about 12 minutes each and I did one on the hour for 12 hours. I'm hoping this will give me a good idea of how the water changes over a tidal cycle.

Saturday, 27 August 2011 – my second to last day fishing. A private yacht had ventured into the sound so its rich owners could tour around. As we were the only other ship around, the two captains started talking, which resulted in an invite for the yacht owners to come watch us fish and maybe see greenland sharks. At the most awkward point in the fishing, the yacht owners including their two young daughters showed up to watch. Not one of them was wearing a life jacket – it was kinda scary watching the little kids climb out of their zodiac and onto the ship without one (we always wore life jackets on deck). It felt kinda like we were in a zoo as the rich folks photographed us working. The kids quickly started to feel seasick as the ship was drifting. Fortunately, we caught a shark so they could take a look and then head home to their fancy yacht.

Sunday, 28 August 2011. After a final round of fishing, we returned to Pangurtung. I spent the night at the lodge and headed home the next morning.