Shelf Sea Biogeochemistry blog

Showing posts with label zooplankton. Show all posts
Showing posts with label zooplankton. Show all posts

Monday, 13 April 2015

The breath of the ocean

My name is Jose Lozano and I am a PhD student from the University of Vigo, Spain. In this cruise (DY029), I work with  Elena Garcia, post-doc at the University of East Anglia, taking samples and doing  measurements of oxygen (O2) respiration in the Celtic Sea (Candyfloss) by using different methods, Optodes (optical sensor devices, which is designed to measure absolute oxygen concentration and % saturation), Electron Transport System and Winkler (a test used to determine the concentration of dissolved oxygen in water samples).

Net community production (NCP) is a measure of the net amount of carbon removed from the atmosphere, which represents the difference between Gross Primary Production (carried out by phytoplankton through the photosynthesis) and Dark Community Respiration (from both phyto and zooplankton). Plankton found in the world’s oceans are crucial to much of life on Earth. They are the foundation of the bountiful marine food web, produce half the world’s oxygen and suck up harmful carbon dioxide.  It is therefore vital for scientists to closely observe the oceanographic and biological variables related with these little buoyant organisms, temperature, nutrient content, light extinction or partial pressure existing in the water column.

During the cruise we have very busy schedules, not only the scientists but also the crew and  the technicians. They all work constantly, making the practice of science much easier, by cleaning, cooking, creating tools, or fixing devices. We, the scientists, couldn't make it without their support.



Dolphins, Photo: Jose Lozano

When you spend 24 hours a day in an oceanographic vessel, even in hours of rest, you feel very tempted to go on deck to chill out and breathe the fresh air at the stern. In a good day you can feel the ocean breathing gently and musically through the waves, the cool wind blowing on your face, you can observe the wildlife, the terns and the gannets flying over your head and families of common dolphins jumping playful just few meters away from the vessel. You can even see some land animals, such as owls, garden birds or little spiders, which are travelling with us on the ship. All these organisms, from the smallest diatom to the biggest marine mammal, breathe oxygen (though in the case of archaea or bacteria, other molecules may be used) in order to obtain energy from organic matter, so to be able to keep going.
        


Sandwich tern. Photo: Jose Lozano

Tuesday, 10 March 2015

Springtime phytoplankton blooms in the Celtic Sea

Louis Byrne, British Oceanographic Data Centre, NOC

The seasonal changes in the Celtic Sea primarily revolve around the development of water column stratification in spring and when it breaks down in late summer to early autumn.  Right now in March, the Celtic Sea is fully mixed, however with the days getting longer and warmer (we hope), the surface of the Celtic Sea is also warming. As the surface warms its density decreases and the water becomes lighter compared to the colder waters below which don’t have access to the suns heat. (Fig 1.) To help watch for these changes we have a daily set of sea surface chlorophyll and temperature satellite images sent from the NEODAAS team at PML to the ship, and any developments of blooms and changes to the temperature can be seen as they occur.


Fig. 1: Temperature profiles in the mid latitudes in the ocean. Dashed (- - - -) line is for the winter and the continuous line for the summer season
.Source: http://nptel.ac.in/

This will eventually result in the creation of two distinct bodies of water, with a warm surface layer resting above a colder layer below, much like a cocktail which often have two or three coloured layers sitting on top of one another.

As well as causing the onset in stratification, the increase in temperature and sunlight also causes a truly massive increase in the number of phytoplankton in an event known as a plankton bloom [many plankton blooms are so large they can be seen from space! (see Fig.2)]. This results in a feeding frenzy as zooplankton (Fig. 3) numbers surge and they are in turn eaten by other organisms, passing the energy down the food web.


Fig. 2: Plankton Bloom in the Celtic Sea. Captured by the Envisat's Medium Resolution Imaging Spectrometer (MERIS) on 23 May 2010. Credits ESA

The phytoplankton bloom starts just before the onset of stratification, and then continues in the surface layer as the water there is warmer and receives much more sunlight. Eventually the phytoplankton will use all of the nutrients available in the surface layer and most of the plankton will die off. When this happens their cells will fall through the water column, causing a large increase in the biological material available on the seabed.


"Copepodkils". Licensed under CC BY-SA 3.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Copepodkils.jpg#/media/File:Copepodkils.jpg
 
When stratification breaks down at the end of summer, the water column in the Celtic Sea is again fully mixed. The bottom layer of water is still nutrient rich and these nutrients are also mixed into the surface of the water column, and become available for photosynthesis. This causes a smaller phytoplankton bloom at the end of summer before the days darken, and the cycle is complete.

Monday, 2 March 2015

Shelf Seas Biogeochemistry – A short introduction

By Louis Byrne, British Oceanographic Data Centre, NOC

We woke up on Monday to a sea which was perhaps even worse than Sunday. We were still a fair distance away from site A and were not scheduled to reach site A till approximately 2100 Monday evening. Due to the rough seas I spent the majority of the day hugging my toilet bowl, but not before making the rookie mistake of blocking my sink with the remains of my breakfast, which Geoff the Steward was not too happy about.  Due to a day spent in transit not much happened, and due to my sea-sickness I was not around to see what did, therefore I thought it would be a good time to introduce the reason why we’re rushing towards the Celtic Sea at a slow and steady speed of seven knots.

Although shelf seas make up only 5% of the ocean surface, they have been estimated to be the most valuable biome on earth, with high levels of primary productivity supporting diverse ecosystems. High concentrations of nutrients support the growth of phytoplankton, which are single celled marine organisms that photosynthesise like plants on land. Like plants on land, Phytoplankton are the base of the marine food web and they provide a diverse food source for many marine creatures, such as zooplankton.
 



Phytoplankton are the foundation of the oceanic food chain.

Zooplankton are tiny marine animals which are food for fish and countless other marine organisms, that are then in turn eaten by others. It is in this way that the sun’s energy fixed by phytoplankton on the surface of the water column is distributed throughout the marine ecosystem, underpinning more than 90% of global fisheries and offering many other important ecosystem services.

In addition to supporting the entire marine food web, the photosynthesis carried out by phytoplankton also removes significant amounts of carbon dioxide from our atmosphere.  Although tiny, phytoplankton have a disproportionately massive effect on our atmosphere, and are responsible for creating as much as half of the oxygen that we breathe, removing an equally large amount of carbon dioxide as they do it. Some of the carbon extracted by the phytoplankton will sink to the sea floor and be stored in the sediments (often for thousands of years!), reducing the overall concentration of carbon dioxide in our atmosphere.

In order for the shelf seas to sustain these high levels of production, the phytoplankton must be supplied with nutrients, but where do these nutrients come from? It is the need for us to better understand the role of shelf seas in the global nutrient cycle, how this supply of nutrients determines the shelf’s primary and secondary production and how this affects other processes such as carbon storage which has led to the Shelf Seas Biogeochemistry programme.

At 2100 on Monday night we reached site A and decided that the seas were too rough to sample that night. Therefore, an 0600 hours CTD cast was scheduled for the following morning, and we were hopeful that our cruise was about to get its first piece of data.

For those of you wishing to see the answer to yesterday’s question, the answer is Richard Cooke of the National Oceanography Centre, Liverpool.

Tuesday, 25 November 2014

More jellies

Ocean research cruise blog of Jonathan Sharples

 

The children at Churchtown Primary School are I gather busy working on the questions we asked them about sinking salp poo. The zooplankton group on board are getting very excited about their results, and already planning the scientific papers that they want to write. We collected more of the zooplankton yesterday so that we can make better estimates of the rate at which they eat and the rate at which they release the faecal pellets. In an attempt to get an idea of what these delicate organisms look like in the ocean we attached a few waterproof cameras to the CTD, and lowered them into the sea surface to record pictures for half an hour or so. I set the challenge to get a picture of a jellyfish or salp in the process of releasing faecal pellets into the water. There was a clear winner (Clare Ostle, from the University of East Anglia), but she was working very early this morning and is currently in bed – so I’ll get the photo for tomorrow.

an interesting bucket of jellies


Meanwhile, to help the kids at Churchtown think about this problem, the picture below has some good examples of the salps (the long, tubular jellies, connected in spirals) and the tiny jellyfish. Another rally interesting organism in this photo can also be seen, just about. The photo looks like it has a fine sprinkling of sawdust in it. These are tiny colonies of a photosynthesising bacteria called trichodesmium. It’s special in the ocean because it is a nitrogen fixer – it is able to use nitrogen gas dissolved in seawater, rather than the form of inorganic nitrogen (nitrate) that most phytoplankton need. That means they can grow in areas where nitrate is in very low concentrations, such as the large areas of open ocean in the sub-tropics. Finding them here is odd, because there is enough nitrate around and so the trichodesmium should not have any advantage compared to other phytoplankton. I’ll find out a bit more about them for another blog entry.


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salps and tiny jellyfish


Saturday, 22 November 2014

22 November, 2014 08:49

Ocean research cruise blog of Jonathan Sharples

 

We had a very successful day yesterday – managed to get through all that was planned, plus most of what I’d planned for the next day as well. Deploying the moorings began shortly after 0800. This tends to be a long, careful process as the mooring wire is gradually unwound over the stern, instruments are clamped onto it at the planned depths, buoys are slotted in at key stages to hold it all up in the water, and then finally the 500 kg clump of chain is attached and dropped into the sea. By lunchtime we had deployed the long temperature/salt logger mooring and also the bedframe with the current meters. The second current meter mooring has been delayed until today, while the techs sort out an issue with the memory cards that it uses. That allowed us to go and hunt for the wandering wirewalker mooring and also the glider that we deployed when we first got here from Falmouth, but which has refused to dive.



Both the wirewalker and the glider have been sending us regular position information via a satellite link, which meant that finding them and getting them on board was very quick. We arrived back at the mooring site just after sunset, ready to do some more zooplankton work.

It’s a lovely day today – a glorious sunrise (complete with dolphins) and an almost flat sea. However, we’ve just heard that the long-term forecast is looking a little grim. A particularly nasty-looking low pressure system is due this side of the Atlantic next weekend. Forecasts that far out tend to be a little uncertain, but it’s worrying enough for us to think carefully about when we can get back to this site to recover the wirewalker and the 2 gliders that are here.

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