Full Steam Ahead!
Web Log Entry - Friday 23rd June
by Adrian Martin (NOCS)
After the inevitable few delays, we sailed from Falmouth at
18.00 today. As soon as we left port,
AUTOSUB was deployed for the first time on this cruise to
test all systems. AUTOSUB is essentially
a mini unmanned submarine that can be programmed to perform
complicated surveys collecting biological and physical
information as it travels. One of the aims of this cruise is
to use AUTOSUB to investigate how the physical movement of the waters
influences where phytoplankton - the microscopic plants of the ocean - grow.
In particular we are interested in a phenomenon called the Deep Chlorophyll Maximum which is a concentration of phytoplankton below the surface waters. Typically at around 100m depth, phytoplankton
find a good balance between their need for sunlight (rapidly
absorbed by seawater) and nutrients (whose concentrations is higher at depth), and seem to aggregate.
After a successful AUTOSUB test we moved on at full steam, running
parallel to the Cornish coast. The sun set behind the Lizard
peninsula as we passed just before 22.00 GMT (Greenich Mean Time - the time used while working at sea). From now on it is
the open sea until our scheduled return on 9th July in Cork, southern Ireland.
Adrian Martin, Physical Oceanographer, NOCS
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Equipment Ready
Web Log Entry - Saturday 24th June
by Adrian Martin (NOCS)
The scientists and technicians on board have been busy for the last three
days installing and testing their equipment and people are now
looking forward to getting their teeth into some real data.
My personal interest is in the various physical processes that can
influence how phytoplankton grow by drawing up nutrients from
depth to feed them. We have a wide range of facilities on
board to investigate the relationship between mixing in the ocean and the microscopic phytoplankton. Two specialists from
Germany are on board, who are adept at measuring the turbulence in the ocean and how it brings nutrients up from depth in the same way
that digging over a garden can improve the soil.
We also have
Autosub and a device called the Moving Vehicle Profiler (MVP)
which is towed behind the ship oscillating up and down through
the water, providing cross-sections of physical properties such
as salinity and temperture. An instrument fitted to the hull of
the ship called the Acoustic Doppler Current Profiler (ADCP)
also measures the speed of ocean
currents. Pooling all these data will enable us to construct a sophisticated three-dimensional picture of how the water is moving and therefore
quantify what effect the circulation is having on delivering nutrients to
the hungry
phytoplankton. But with all those instruments there will be an enormous
amount
of data to process so it is going to be a very busy cruise.
Adrian Martin, Physical Oceanographer, NOCS
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First time at sea
Web Log Entry
by Roz Pidcock (NOCS)
This being my first time at sea, I was inevitably excited and apprehensive
about what
the first full day of sailing would bring. And shortly after breakfast I
found out
when my stomach turned out not to be as excited about the trip to
the PAP site as the
rest of me and i was sea sick for pretty much the whole day!
As a new
member of the
ocean physics team, there is a lot for me to learn in these first few days about the
instruments, processing methods and the software we'll be using. As it's all new to
me, i
am also curious what everyone else is doing.
Unfortunately, however, the discomfort of seasickness forced me to retire to the comfort of my cabin bed or spend my time on deck seeking fresh air. That did have its bonuses, however.
Sandy managed to spot a group of pilot whales travelling in the
opposite direction about 70-80 meters away which was fantastic! For my first
day's sailing
that is not bad and almost makes up for the seasickness!
Everyone onboard has been
very sympathetic and assures me this is
normal for
a first time at sea.
I hope so,
because there's so much going on on this cruise and i dont want to miss
the best bits!
We'll just have to see how it goes....
Roz Pidcock, Research Student
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Sunday 25th June
Time -
20.00 Greenich Mean Time
Position - 49 N, 16 30W
Weather - light wind (force 3 or 4) gentle swell and rising
temperature.
by Adrian Martin (NOCS)
Sunday was the last day before arriving at the focus of our studies – the Porcupine Abyssal Plain site, also called among us PAP. It is little more than an imaginary cross painted on the ocean at 49 degrees North, 16.5 degrees West in the middle of the ocean.
Why this location? For a start there are permanent moorings here - a collection of cables extending up from the sea floor 4800 meters below my feet, nearly to the surface of the ocean. A series of inch-thick glass spheres act as floats in order to keep the cables vertical into the water so that our equipment can sample at different depths. The moorings measure a variety of properties, from how salty the water is to how much material is sinking down from the sunlit surface. These moorings constitute the European ANIMATE site and provide a vital means of monitoring the ocean's life and physics throughout the year regardless of weather or whether we are here or not.
Part of our job is to recover, service and replace these moorings for yet another year of continuous measurements. Work today concentrated on other matters, however, with last tests being made to instruments to ensure all are performing well before being used to survey the waters around the PAP site.
AUTOSUB was deployed again on a small test mission, and bar some nerves prior to recovery, all is well for sending it off alone on a three day mission tomorrow. Sediment traps were also prepared to be deployed tomorrow to sample the sinking particles in the ocean also called marine snow. These are essentially large yellow funnels with small buckets underneath to catch sinking material or what we also call marine snow. Marine snow is a collection of waste, dead organisms and molts which slowly sink to the seafloor. As they, like us, contain significant amounts of carbon extracted from carbon dioxide in the atmosphere, this process, called the biological pump, plays a crucial role in the carbon cycle of our planet. Sediment traps such as those at PAP are therefore crucial in monitoring the biological pump and how it may change in response to the carbon dioxide pumped into the atmosphere by man's activites.
The Moving Vessel Profiler (MVP) was also put overboard for the first time today. This is effectively a yo-yo towed behind the ship, bobbing up and down through the upper 300m of the ocean surface. The tool allows us to take cross-sections or cuts through the ocean showing us how organisms such as phytoplankton are distributed both horizontally and vertically. Despite first appearances, the ocean is far from being a monotonous uniformity throughout. Abundances of organisms and physical properties can vary very significantly on scales as short as a few kilometers horizontally or a few meters vertically. Furthermore, shifts in the density of seawater over short distances can produce strong currents which have a major impact on the local microscopic organisms possibly accelerating the rate at which they grow. Such boosted growth can in turn attract larger organisms such as fish and seabirds feed. There are already signs that there is a lot of life in the waters we are due to study - more on that tomorrow hopefully, when we get our first detailed observations.
At the surface, however, distraction has already been provided by a big Sunfish, a small shark (a mere two meters) and the ever attendant seabirds who are convinced we are a fishing vessel. The fulmars are the bravest constantly gliding around the vessel just above the surface though tiny stormpetrels can sometimes be seen just a little way off.
Adrian Martin, Physical Oceanographer, NOCS
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Monday 26th June
Time - 20.00 Greenich Mean Time
Position - 49 N, 16 30W
Weather - Light winds (force 2) and a fabulous sunny day
by Peter Burkill (Cruise Principal Scientist)
Pollution 1000 miles from shore!
Goose Barnacles hitchhiking a ride on floating polystyrene.
Photo P. Burkill, NOCS
enlarge |
Just the type of day that makes working at sea fantastic. On a less cheerful note, we have witnessed numerous floating polystyrene pieces even out here more than a thousand miles offshore. This is a worrying sight. What is happening to our pristine oceans!
Our serious work began today at the PAP site at 02:30 Greenich Mean Time, with the deployment of zooplankton nets. After that we collected water samples from 200 meters depth to measure the production of phytoplankton too. One of the advantages of starting pre-dawn, is that the ship's lights attract animals from the depths. This morning we saw a Sunfish (Mola mola) which is rarely seen. It is a strange animal about 1.5 metres in length, with a huge head and peculiarly shortened tail. The Sunfish is one of the few organisms that eats jellyfish. Unsurprisingly our plankton nets were full of jellyfish.
At 05:00 GMT we deploymed a free fall turbulence profiler that measures how much deep water containing nutrients mixes into the surface nutrient depleted layer. This process fuels the microscopic plankton that require sunlight and nutrients. Just like the plants in my vegetable garden (I wonder how my beans are growing?).
Sunfish Molo Mola - the only known animal that feeds on jellyfish.
Image: www.blueoceansociety.org
enlarge |
By 07:30 GMT, breakfast was very needed! We continued deep water sampling using a rosette of 24 automatically-closing bottles called the CTD. Attached to it are also temperature, salinity and oxygen sensors and it allows us to measure the physics, chemistry and biology of the twilight zone (Photo 1). This zone forms an interface between the sunlight warm surface water and the cold dark deep ocean.
Then a special Apstein net to catch phytoplankton was towed to determine what plants we have in the water. We hope to be able to culture them on the ship and in the laboratory to determine their growth patterns and their sinking out of the surface waters. Around midday, another CTD Rosette deployment is made with optical probes to measure light penetration and to see how the plankton relate to the daylight cycle.
After lunch it is AUTOSUB’s turn, our 7 metre long autonomous underwater vehicle. Off on its first mission to support our work, it will steam a course around the ship to assess the variability of the physical, chemical and biological content of water around the ship. We should rendez-vous with it in 3 days time.
Much of our work on this cruise concerns the deep-water moorings that were put in here a year ago. These have been collecting information over the past year and we are eager to recover them to find out how much of the biological production into the oceans sediments into the ocean's interior. We are building up a year-by-year picture of this and so will be able to compare 2005/6 with previous years. But our deck is so full of gear that first we have to create some space, so today we prepared to deploy a mooring to clear some space. Tomorrow we will begin recovering the moorings laid last year.
Our work for the day ended at 21:00 GMT with the deployment of some new free floating sediment traps called PELAGRA. These new traps are designed to work close to the ocean surface where it is notoriously difficult to get good measurements. Retiring to bed, I know the 02:00 GMT alarm call is not far off! Good night.
Peter Burkill (Cruise Principal Scientist)
Biological Oceanographer, NOCS
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Tuesday 27th June 2006
Time: 20.00 GMT
Position: 49 degrees North, 16.5 degrees West
Weather: Light wind (force 3 or 4), gentle swell, overcast and persistent fine rain.
Adrian Martin
Days begin jarringly early at 02.00 am with trawls for zooplankton followed by several sessions of turbulence profiling and "dips" with our CTD Rosette. Technically CTD stands for Conductivity Temperature Depth because the device records these properties as it is lowered through the water (conductivity can be used to infer the salinity of water). However, the sensors that measure these parameters actually sit on a much larger frame which can accomodate many more sensors. Consequently we have also been measuring such diverse properties as the amount of nutrients in the water, the "health" of the local phytoplankton and the amount of light permeating down into the water with our CTD Rosette deployments.
Additionally, the frame is surrounded with a "rosette" of 24 20-litre bottles which allow us to collect water from particular depths that interest us. In this way more intensive laboratory studies can be made of the biology and chemistry at depths and regions where we cannot currently send sensors. For most of our deployments so far the CTD has been sent down to between 200-1000m, though at the start we sent it down to a depth of 4 km. Our closest land is almost 5 km in the same direction.
Today's excitement was provided by the Great
PELAGRA Hunt. PELAGRA traps are sediment traps designed to float on their own, unattached to the ship, at a fixed depth (typically a few hundred metres) collecting sinking material, or marine snow, for a chosen period before rising back to the surface for collection. Spotting them when they do return to the surface is rather tricky though. Looking for a small orange flag in even a gently heaving ocean is what people who've mastered the needle-in-a-haystack trick move onto for a greater challenge.
To help us the trap sends out occasional pings which we can detect at the ship to give a rough idea of distance and direction. The trap can still be very near to the ship before it is spotted by eye though. So this evening I found a line of people up on the bridge scouring the ocean surface with binoculars. Three traps were out there and pinging. Some skillful ping-tracking by the ship's officers and Richard Lampitt (the scientist who brought the Pelagra traps on the cruise) got us close to the first one, but dusk was drawing in. Around 21.00, Darcy White, the third officer, spotted the flag in the distance ahead of the boat and it was quickly hauled in and chase joined for the second PELAGRA. Night fell and the last two traps pinged frustratingly nearby in the darkness. The spotlight on top of the bridge was used to sweep the sea surface in the hope that reflective tape lining the flag would betray the traps positions but only resulted in finding lots more pieces of polystyrene which frustratingly glitter at night. All seemed lost. Then, just before midnight, Darcy caught a glimpse of something on the surface and in the searchlight beam. Roz Pidcock latched onto the second trap, only just breaking the surface and perilously close to sinking again. Could it be recovered without sinking it? Could the third be found? Could Darcy get his hat-trick?
To be continued...
Adrian Martin, Physical Oceanographer, NOCS
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Wednesday 28 June 2006
Time:
19:30 GMT
Position: 49.59.59 North, 16.49.53 West
Weather: Overcast, slight breeze, moderate swell.
by Tom Bibby
If you think finding a needle in a haystack is a tough challenge, try locating a PELAGRA trap somewhere in the North Atlantic.
PELAGRA Gold!
Samples of the free floating PELAGRA traps are worth their weight in gold concidering the effort it takes to recover them.
Photo R.Lampitt, NOCS |
Day 5 on the RSS Discovery has been an
anxious time for all onboard. Everyone is needed to help locate and recover three run-away PELAGRA traps.
PELAGRA traps are a direct method of measuring and characterising particle flux from the surface waters of the ocean into its interior. The traps are simply a floating funnel, at the base of which is a collection vessel or ‘trap’. Once deployed in the water, it collects marine snow - the sinking particles of organic matter, consisting of plankton that have died in the upper ocean. By loading with different weights, traps can be sunk to pre-determined depths where they are neutrally buoyant. There, they collect particles for a set amount of time, before returning to the surface by jettisoning weight – think of a hot air balloon under water.
By deploying a series of traps at different depths, a profile of particle flux can be measured. Upon recovery, the material in the traps is analysed for carbon content and species composition of the phytoplankton. This information is used to determine the path of carbon into the ocean interior and is critical for modelling climate change in the near future.
The advantage of the PELAGRA traps is that they move freely with the ocean currents, in a similar way to which a hot air balloon is at the mercy of winds. But, this means that once deployed, you have no idea where or if they will pop up to the surface.
We have attached satellite transmitters to the traps that send a signal once the traps are at the surface (location using satellites does not work under water, for the same reason submarines have to surface to communicate with command centers on land). Once we pinpoint the exact location, it’s a case of getting as many pairs of eyes as possible on the bridge, and arming them with binoculars and buckets of patience so they can scour the ocean.
The three deployed traps surfaced at 15.30hrs on Tuesday 26th, they had drifted 16 miles in a 24-hr period. The Discovery steamed toward their approximate location, but scientists were forced to wait until dawn the following day to visually locate the traps and attempt recovery. The crew congregated on the bridge to join in the hunt - a difficult task on a grey day in grey seas with moderate swell. Often a trap would be spotted then lost again in the vast expanse of the rolling ocean. At times like this the reality of a search and rescue hits home, you wouldn’t want to fall overboard!
Thankfully, all traps a recovered and prepared for yet another anxious PELAGRA hunt – a tiring routine.
Tom Bibby
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Friday 30th June 2006
Time: 1600GMT
Position: 49 degrees North, 16 27 degrees West
Weather: Calm and fine; progressively windier.
by Juliette Topping
A 6.30am alarm drags me out of bed to check on the progress of the CTD Rosette – the source of our precious deep ocean water with which we can decipher ocean processes. Of course, others had been up at 1.30am and 3.30am for previous sampling events, so a few bleary eyed people were wondering about by the time I arrived on deck.
Laboratory with a view. Through the window of Juliette Topping's mobile laboratory on deck of the Discovery.
Photo Ludwig Jardillier |
A quick dash to my lab – a converted container on the portside of the ship - mounted somewhat precipitously (but I am assured safely!) near the edge of the deck, and with a wonderful view of miles of ocean stretching out before us. There I set up for what will be a 6-hour experiment.
The daily routine begins. We are investigating the feeding patterns and relationships of different microscopic organisms – mainly bacteria and tiny plant-like cells that are only slightly larger in size than bacteria. These organisms form the basis of the oceanic food webs and without their recycling of tiny particles of food and nutrients, the larger organisms like fish wouldn’t be able to flourish.
During this cruise we are conducting a series of ‘tracer’ experiments – we add a radioactively ‘labelled’ food source into big bottles of seawater, and take samples at different times over a 6-hour periods. We will count the numbers of cells, using a technique called flow cytometry, which can visualise the tiny cells for us and count them. We will also be able to look for our radioactive ‘label’ within the cells themselves, and by looking at all of the data, we will be able to work out which particular organisms are contributing to food recycling, and in what way.
For the experiments we will be using surface waters, since that is where these organisms flourish – plenty of light for the plant-like cells, and plenty of organic matter for bacteria to feed on. Once I have set up all of the equipment, it’s hard hat and safety boots on and a dash down to see if the CTD Rosette has arrived on deck. And it has! The frenzied scurry begins for that precious water the instrument has collected at different depths for us. Once we have our many litres of water, we add our radiactively-labelled food and we’re off!
It takes about an hour to process the first samples. This is a bit of a frantic process, and I feel like a juggler with my different beakers and bottles and tubes. Once it is over, I can relax for a cup of tea on deck gazing at the great view. We are always on the look out for wildlife – plenty of birds around, and floating on the water surface are many creatures – including so many of those ‘polystyrene’ barnacles. There are some beautiful jellyfish and pipefish. Amazing! The ocean is vast and clear, and so different to the coastal scene I am used to. It is quite refreshing. There’s a gentle swell and the ship surfs on the rolling waves.
I wonder around to see what others are doing. You really get a feel for complete ocean science on a cruise. In the computer room the physicists are tip tapping away on their computers, analysing all the data they’ve collected. The Autosub team are gathered around a computer, looking intensely at the screen – planning their next mission! On deck, the crew are working hard to make sure all the instruments that can be deployed during the rest of the day. In the main lab, the nutrient guys are hard at work analysing that mornings’ water samples. The wet lab is awash with massive bottles of water and complex filtering devices, to analyse the pigments within plant-like cells in the water. Down in the microscope room, the tiny creatures living in the water are being isolated and recorded.
After 2 hours it’s back to the lab for some more sampling. Then – phew – lunch time! Everything is very regulated on a ship, and you find yourself settling into a rather reassuring routine, unlike that back home where there are so many distractions. After lunch, I do a bit of work on my computer, planning the next days experiment. Then it is time to process the final samples from our experiment. Tidying up takes a while, and finally we can finish. Tomorrow will be an overnight experiment. These are quite tiring, and often we end up going to bed as everyone else is getting up, and then a few hours later it’s time to do it all over again! But it is great to be working on a ship in the middle of the ocean, and it feels like science should feel – exciting and dynamic!
Juliette Topping, Biological Oceanographer
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Saturday 1st July 2006
Position:
48 50 North, 16 30 West
Weather: Light winds (force 3-4) generally overcast
by Mark Stinchcombe
Saturday 1st July started just as usual - early!
With a wake up call set for 3.00am, sleep has also been difficult. Today was no different. I am heavily involved in
taking samples from the CTD Rosette and analysing them for nutrients in the water, primarily nitrate, silicate and phosphate, and oxygen. The more nutrients
there are in the water, the healthier the phytoplankton and so the more
quickly they can grow (just like fertilising your plants at home). If
there are enough nutrients in the water, and the conditions are right,
then phytoplankton population explosion called an algal bloom occurs.
Mark Stinchcombe at work in the ship lab.
Photo
Alan Kemp, NOCS |
We are also measuring oxygen in the laboratory to calibrate an oxygen sensor which is attached to the CTD Rosette. The amount of oxygen can be used to identify different water masses in the ocean, as well
as giving an idea on the level of production of the phytoplankton.
The CTD Rosette deployments also give us a good opportunity to look out for wildlife in the
water as animals are curious about the ship. During one of the CTD casts
today, two Sunfish swam lazily past.
Mark Stinchcombe, Research Student
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VIDEO VIDEO SlideShow
Tuesday 4th July 2006
Position:
48 50 North, 16 30 West
by Richard Lampitt (NOCS)
 Long line fishing destroys
Northeast Atlantic observatory
As the cousin of the RRS Discovery, the Space Shuttle Discovery, was taking off on Independence Day for their own mission in orbit, the reality of ocean research hits us hard.
From my vantage point on the bridge I knew immediately that there was something seriously wrong. The middle part of the mooring was floating on the surface and there was no sign of the business end carrying a wealth of sensors we had deployed a year ago. This was a devastating realisation but worse was to come.
This is part of an international effort to record the time varying properties of the oceans from a variety of perspectives; biological, chemical and physical. The reasons for doing this are to understand how and why they change over short time intervals and to monitor the oceans long term including the impact of man’s activity.
Five years ago a European consortium selected this site, the Porcupine Abyssal Plain, as representative of the Northeast Atlantic building on work that had been started by a number of us back in the 1980’s. There has been an increasing range of studies at the site both in the upper ocean and on the seabed nearly 5km down. Attached to moorings extending from the seabed to the surface, we have sensors to record the amount of phytoplankton, the concentration of small particles, the concentration of essential nutrients and most importantly the concentration of carbon dioxide in the water as well as the physical structure and movement of the water column.
Deeper at 3000m we also measure the downward flux of particles or marine snow. These ‘deep-sea blizzards’ are directly linked to the upper sunlit part of the ocean which interacts with the atmosphere affecting our climate and taking up carbon dioxide (find out how).
Some of the data are transmitted in real time by satellite and the hope was that this year we would have almost all the data transmitted in this way. Our hopes have been severely dashed.
In spite of the fact that a year ago we spread our risks by putting sensors on three different moorings, all of them had been destroyed by long line fishing and not a single sensor remained. The destruction was heartbreaking. So many people had spent so much effort to put them out, large sums of money have been completely wasted and most importantly such a lot of data has been lost about a year which can never be repeated.
Some of the moorings still had substantial quantities of fishing line wrapped round them with hooks still tangled in the floats: a serious danger to the mooring team who were bringing on board the remains. This type of fishing is a new threat in the area but probably not too surprising as long lining has been spreading to almost all parts of the Atlantic over the past decade as fish stocks in more productive waters dwindle. As a result of this we decided not to deploy a new mooring on this cruise and will wait until one has been designed and constructed to withstand this kind of assault.
In stead of Kevlar, which is light and strong, we will in future probably have to use heavy and more expensive steel cables. The quest to make these crucial measurements must wait even longer and unless a ship can be found quickly we may not be able to deploy the moorings again till next year, resulting in another year lost and a serious blow to our heavily shaken program.
Richard Lampitt, Oceanographer, NOCS
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Wednesday 5th July 2006
Position:
48 50 North, 16 30 West
by Mike Lucas
 The finishing line in Cork, Ireland, is in sight as we enter the last few days of our hectic science programme. When we get there, tired souls will catch up on sleep and no doubt some of the excellent pubs will be sampled also! But before that, we still have scientific goals to accomplish.
At the moment we are two-thirds through a meso-scale survey of the region around the Porcupine Abyssal Plain site. Our physical oceanographers are mapping out a 90Km x 90Km patch of the ocean using a Moving Vessel Profiler (MVP) hoping to resolve the variability in physics and biology on a scale which is not possible using other methods.
A Moving Vessel Profiler (MVP) is basically a small aquaplane with temperature and salinity sensors which yo-yo's behind the ship at full speed.
Doing so we are
generating a sinusoidal record of physical parameters in the surface. This is complemented with normal CTD Rosette deplyments to collect water samples for our suite of biological measurements. At the start of the survey, we deployed the AUTOSUB that is sampling a smaller patch of ocean, hence doubling our efforts and maximizing on our time in the open ocean.
Clearly, our navigation has to be spot-on to avoid a collision with the unmanned vehicle! In addition, the free floating PELAGRA traps have once again been deployed to capture sinking particles of “marine snow” from the euphotic zone that fuels the biodiversity and productivity of benthic organisms 4000m beneath our keel.
For my part, I am responsible for making measurements of phytoplankton biomass using C-14 radioactive label. I am running incubations of the phytoplankton on-deck using this radioactive label and simulating the in situ light at 6 different depths by using varying amounts of light filters to cover ;y incubating bottles. These incubations target the productivity of particular phytoplankton sizes.
Concurrent with these measurements, my colleague Tom Bibby is using an instrument called Fast-Repetition-Rate-Fluorometer to determining the physiological status of the phytoplankton community in response to diminishing nutrient concentrations. Indeed, within the last few days, we have witnessed a change in community structure from diatoms to smaller non-diatom cells in response to nitrate and silicate limitation. In an effort to maintain their nutrient requirements, we have seen the chlorophyll-a biomass begin to sink down toward the thermocline at around 70 meters, where small cells are able to scavenge nutrients diffusing across the nutricline, but in a low light environment. In other words, a deep chlorophyll maximum is being established as the water column begins to more strongly stratify in response to reduced wind speeds and solar warming. This brings me to the other part of my work.
By measuring nitrate uptake using N-15-labelled nitrate (NO3), I am able to calculate new production or the f-ratio, which provides a measure of nitrogen or carbon “export”. This will complement other measurements of carbon export based on fixed trap moorings, on PELAGRA and from Thorium-234 estimate of particle flux.
Back at NOC, our challenge will be to integrate all of our measurements of physics, phytoplankton productivity and export into a coherent story that provides a contemporary understanding of bio-geochemical controls on primary and secondary (zooplankton & benthos) productivity at the Porcupine Abyssal Plain time-series site. This will serve as one bench-mark for future investigations and potential ecosystem responses to climate change.
Mike Lucas, Biological Oceanographer, NOCS
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Thursday 6th July 2006
Position: 48 28 degrees North, 17 07 degrees West
Weather: Moderate seas and sunny periods, not unpleasant at all
by Peter Keen, Technician
Today is the final day of our meso-scale survey, which should come to a successful conclusion at about midnight. For the last four days technicians, such as my self, have been working around the clock to ensure that the deployed instrument systems function without a hitch. Surveys such as these can be as much a test of concentration as a test of skill since the monotonous regularity of events can lead them to blur one into the other. Extra care needs to be taken to remain methodical and ensure nothing is missed or crucial data could be lost – particularly if you are towards the end of a 12 hour shift and beginning to tire. We have managed to avoid any such calamity and John Allen seems very pleased with the results we are obtaining and the completeness of the survey so far.
The CTD Rosette - the working horse of each oceanographic expedition
CLICK TO ENLARGE |
The items of equipment we are using to conduct the survey are the Moving Vessel Profiler (the MVP) and the CTD Rosette – the centerpiece of most oceanographic expeditions, which measures Conductivity, Temperature, and Depth.
The CTD Rosette actually does a great deal more. It carries sensors to measure the oxygen content of the water, profile the water currents, look at the clarity of the water, measure the amount of sunlight that is penetrating the water column, see how much chlorophyll from phytoplankton plant activity is in the water and it can also take up to 24x20 liter water samples from any depth we choose. If technicians are the foot soldiers of oceanographic science then the CTD Rosette is the workhorse and instruments such as this have been taking basic hydrographic measurements ever since scientists set to sea with the purpose of characterizing the physical properties of the oceans.
The MVP on the other hand is a towed undulating vehicle that runs behind the ship and undulates like a yoyo at full speed. Vehicles like the MVP are sometimes referred to as Tow Fish – though it has to be said that oceanographers call almost anything that goes in the water a fish! The instruments on the MVP are similar in style to the CTD with the exception that the MVP does not collect water samples. What it is capable of, however, is completing a series of rapid, fairly shallow (300m) profiles on an almost continuous basis. It adds another dimension to the single point profile of the CTD effectively running a transect. The vehicle itself is a heavy cast aluminium body that drops nose first down through the water as the winch back on the ship spools cable out fast enough that the ‘fish’ is literally left behind to rapidly sink without being towed forward by the ship. That is until it reaches the desired depth and the brake goes on. It has a lot of catching up to do!
And the moment it is being towed again the fish rises through the water column and the winch begins to slowly wind it in. Data is sent back to the ship in real time. With this system we are able to do a profile to 300m every 10 to 15 minutes and greatly increase the density of our data’s spatial resolution. We have been towing the MVP at just over 11 knots so that gives us about one profile per nautical mile.
But at 12 O’clock the survey will be finished and the ship has other calls to attend to. We still have to pick up the PELAGRA floating sediment traps tomorrow and AUTOSUB went on another mission this evening so in about 24 hours time will also be looking for a lift back to Cork. Such is the nature of oceanographic voyages - there is always something to do!
Peter Keen, Technician
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Thursday 6th July 2006
Position: 48 28 degrees North, 17 07 degrees West
by Alan Kemp, Oceanographer
First thing Thursday marked the end of an intensive three day survey around the main site we are occupying. This was aimed at producing a hitherto unavailable 3-dimensional picture of what is happening in the upper ocean and should provide valuable information on the patterns of physical and biological variability within the ocean surface layer (top 500 m). My own day commenced as usual at 01.00 GMT with preparation for regular daily net-hauls from different depths designed to record the amount and variation of zooplankton activity at the site.
A particular interest that I have in the cruise is to study the role of diatom algae in the ocean. These microscopic, single celled organisms are the world’s most important primary producer – an analogy would be that they are like the grass of the sea. The are the base of the food chain and so the entire ocean ecosystem depends on them. Diatoms are the dominant agent of photosynthesis and they drive the “biological pump” that draws down carbon dioxide from the atmosphere, converts it to algal biomass and ultimately deposits and buries much on the sea floor. Their evolution has been long and complex and analysis of the diatoms genome shows that although regarded as plants these versatile organisms are capable of storing energy as fat (an animal characteristic) as well as in the form of carbohydrate – the normal “plant” energy store method.
When we arrived at the site last week, we saw the later stages of a diatom ‘bloom’ when large numbers of these algae reproduce rapidly to form a rich biomass on which organisms up the food chain i.e. zooplankton and, ultimately fish, depend. Unsurprisingly, the zooplankton were also thriving and abundant. Just a day later, however, the diatoms disappeared from the water, perhaps after having used up all the nutrients (just like land plants, these algae require phosphate and nitrate). As soon as the diatoms disappeared, so too did the zooplankton abundance decrease – their primary food source having disappeared. Within daysm, the site was transformed from a burgeoning ecosytem to a relatively barren marine “desert” with only remnants of activity.
To record the activity of the diatom algae we are taking bottle samples from the water but we are also deploying plankton nets to samlpe the zooplankton. In order to make sure we are sampling exactly the depths that intereset us, we are sending a weight (known as a “messenger”) down the rope on which the nets are suspended. This triggers a closing mechanism and the samples tell us where in the water column, the main algal growth and accompanying zooplanktoin activity is taking place and also differences in the depth habitats that different species occupy.
We are taking the nets during the day doing so to avoid much of the zooplankton which migrate down to the lower darker parts of the surface ocean to avoid larger predators. Samples of diatoms are rapidly examined using microscopes and may also be maintained in culture for future experimentation.
Now its off to my bunk so that I’m up in good time for Friday’s 01.00 net deployments! Good night!
Alan Kemp
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