08 Jun - Onwards and Upwards
RRS James Clark Ross Diary
Noon Position: 30° 17.6 N, 30° 25.43.0 W)
Distance Travelled since Grimsby: 41,425.5 Nautical Miles
Air temperature @ Noon today: 23.3°C
Sea temperature @ Noon today : 22.9°C
Weather: Good, NE, 2, 1025.0
Onwards and Upwards
The James Clark Ross has been steaming north for another week making continued good progress towards old Blighty. The ship is still stopping twice a day to allow the AMT scientists to take the myriad of water samples that they need for all their experiments. The rest of the day and night is spent heading home at a sedate 11.5 knots. We had only one change of course again this week but saw a very unusual sight on Sunday. High above the ship we spotted a vapour trail from a commercial airline flight. It may not seem unusual for those at home but it is the first one I've seen for 9 months and a sign of the impending reintroduction to civilization awaiting the JCR very soon.
It's a tough life for the lads on the bridge so Paul Clarke has taken up juggling in his spare time to keep himself amused. We've always thought he was a bit of a clown but clearly he needs plenty of practice!
To make the most of the hot weather we are still enjoying and make up for the downpour when crossing the line, Hamish organized a BBQ on the aft deck. Saturday night saw everyone outside stuffing themselves with lots of delicious food cooked on the recently made BBQ. Richie Phipps had knocked one up from an old oil drum for crossing the line and it worked a treat as Hamish and Mike served up lots of steaks, kebabs and even Montevideo style fried cheese!
AMT 12 - 'It's all about the right kind of atmosphere'
One of the main aims of the Atlantic Meridional Transect (AMT) is to 'determine the role of atmosphere-ocean exchange... in the formation and fate of organic matter'. What does that mean in simple terms?
Gases pass continuously from the ocean to the atmosphere above, by simple diffusion. This is a two way process and gases such as carbon dioxide or oxygen can move from the air to water and vice versa depending on their relative concentrations. The physical properties of the gas and water also have an effect eg temperature. Matter can also fall into the ocean mainly in the form of dust that has been blown out to sea from the land and rain. Imagine the ocean and air constantly exchanging gases and particles between them trying to achieve a balance.
This balance is never achieved because of 'organic matter' ie living things. Humans need oxygen to live, and we exhale carbon dioxide when we breathe out. So do phytoplankton in the water. They use oxygen from the surrounding water and produce carbon dioxide. Hence the oxygen levels in the water go down and carbon dioxide rises. This change then leads to more oxygen moving into the water from the air and more carbon dioxide moving from the water to the air. This is done by simple diffusion as the air and water try to achieve a balance or equilibrium.
Life is not quite that simple however but the principles are the same. When the phytoplankton trap sunlight to make food (using photosynthesis like plants) they release oxygen and use up carbon dioxide. Therefore phytoplankton are sometimes net producers of oxygen or carbon dioxide or net users. Phytoplankton are present in such huge quantities in the oceans that these simple processes have an profound effect on the atmosphere above.
OK, the story so far......
1 Gases move between the atmosphere and the sea.
2 Phytoplankton have a major effect on some of these gases.
Why is this important and why study it?
Global warming is happening. The earth is getting hotter and this is down to the change in gases in our atmosphere. Since the industrial revolution, humans have been burning lots of fuels (coal, oil, wood etc) that increase the amount of carbon dioxide in the air and make the planet warmer. The level of carbon dioxide has risen by 25% increase since the industrial revolution. Other important gases that are involved in global warming are methane, nitrous oxide and dimethylsulphide.
Carbon dioxide (CO2) is removed from the atmosphere by the oceans. There are two main ways that this happens.
Firstly, warm water moves from the caribbean to the Arctic in the Gulf Stream as this water cools then by simple physical laws it absorbs more CO2 and also sinks to the bottom of the sea around Greenland. This cold water, rich in CO2 then moves slowly south down through the Atlantic as North Atlantic Bottom Water and, after whirling round Antarctica cooling further and collecting more CO2, it eventually comes up in the Pacific Ocean, hundreds or thousands of years later. This deep cold water effectively acts as a 'sink' for CO2 and removes it from the air. This helps to keep the planet from warming up by removing some of the CO2 we pump in the air. This 'physical' process is the main sink for CO2 from the atmosphere.
Secondly, as phytoplankton live and grow they can either produce or use CO2 by respiration or photosynthesis. In some areas phytoplankton are net producers and in others they are net users. They are important in the regulation of CO2 but to what extent is debatable. Their role is still to be fully elucidated but is thought to be relevant as they respond quicker to changes around them than the physical process exchanging CO2.
To study the effects of phytoplankton on both CO2 and O2, water samples are incubated onboard for 24 hours and the change in levels of gas are then measured in the water. The concentrations at different depths are measured and compared with those in the air.
Another gas to be studied is N2O which is 280 times more potent than CO2 as a greenhouse gas. It can be produced by bacteria in areas of up-welling water rich in nutrients. Areas such as those near the African coast are known as 'natural chimneys' as they release N2O into the atmosphere. Methane (CH4) is also being measured as this greenhouse gas can be produced by anaerobic metabolism of phytoplankton. The final gas to be measured on the cruise is dimethylsulphide. Produced by phytoplankton called coccolithophores amongst others, this sulphur-containing gas, enters the atmosphere and reacts to create particles, thus being a major source for cloud formation by acting as the nuclei that clouds condense around. The DMS levels are being measured both in sea and also in any rain that might fall (see crossing the line! - Ed).
As mentioned above, material can fall out of the air in the form of rain or particles into the ocean. This can form an important route for adding nutrients to the water and this cruise has been measuring the nitrogen, phosphorous and iron in the air. The Monkey Island has sprouted extra gizmos and now can sample the clean air flowing over the ship for both gases present and the particles in the air. A filter with brown staining caused by dust from the Sahara can be seen being opened below alongside PSO Tim, with his clean air samplers.
These filters process 1m³ of air per minute for 20 hours a day. Whilst sailing through the South Atlantic the filters often appeared grey due to soot in the air from low temperature burning of fuel in Africa and South America. These particles fall into the ocean and provide a large source of nitrogen, an important nutrient. However recently the filters have become a brown colour from the dust blow out from the Sahara desert. A large dust storm can be seen coming from the Sahara in the satellite photograph below. This dust is rich in iron and so the deserts provide the sea with a another critical nutrient. Interestingly the Southern Ocean around Antarctica has no deserts feeding iron into the water and therefore has very low levels, limiting the rate of phytoplankton growth, but that's a different story. Using reverse weather forecasting, the origin of the particles can be predicted. They will be analysed back in the UK to gauge the quantity of nutrients entering the water from the air as particles.
Iron is an important nutrient for the phytoplankton as it required for many of the enzymatic processes taking place within cells. The reason for this is that when the phytoplankton first developed, millions of years ago, the water was a reducing environment and lots of free iron was present. This iron became important in many cellular processes but as the algae were so successful in producing oxygen, the phytoplankton slowly changed the atmosphere above them. However this then turned the early seas into an oxidizing environment which results in very low levels of free iron in the water because iron is very insoluble in such conditions. In a way the phytoplankton cut themselves off from one of their essential nutrients. This process did have the added bonus of making the atmosphere of the earth 21% oxygen and this allowed oxygen breathing organisms, such as humans, to evolve! Anyway I digress. Getting back to the important measurements of iron in the water around us they are very difficult. The JCR is looking slightly rusty at the moment and so is shedding large amounts of iron into the air and water around it. Since the levels of iron in the water are 1 part per 100,000,000,000 parts of water, then a little rust goes a long way in contaminating water samples. Even the wire that lowers the CTD sampling device has rust on it and can contaminate the water! To make matters worse the measurement iron is very difficult at so low levels, several orders of magnitude less than the waters around the UK. The CTD used to collect the water samples can be seen below and is designed to not contaminate the water it collects.
AMT is using the JCR to sample both the air and water around the ship and provide important data on how gases and particles move between the two. This work has relevance for global warming and predicting future climate change.......
Phew, time for a break and watch the therapeutic blue sea....
Man of the week
Thank-yous this week: all the galley boys for the BBQ
Coming up next week: Acute channelitis!