We are roughly 40 degrees south and 45 degrees west and heading for the Falkland Islands where we are due to arrive on Saturday. We have two more days of sampling left and I am very much looking forward to (for the first time in two weeks) not having to get up at 4:30am on Thursday!

We are now in very productive waters. The picture below shows two 25mm GFF filters which have had 1 litre of surface water (~5m depth) filtered through them. The colour in the filter is primarily caused by the concentration of phytoplankton in the water. A few days back, when we were in the very blue waters (see last post), it would probably have taken 6-8 litres of surface water (maybe more) to get anywhere near this colouration.  The yellow colour of the filter is indicative of a phytoplankton community dominated by diatoms and in the right filter you can even spot a red copepod (zooplankton) antenna. 

Phytoplankton filters

Phytoplankton filters

In a space of a day the Secchi depth (the depth at which a 30cm white disk disappears from view) changed from 35m to 19m. The Secchi disk is a white disk that is lowered into the water until the point at which it disappears. The depth of disappearance is known as the Secchi depth. The Secchi disk is one of the oldest bio-optical instruments and has been in use since the late 19th century.  In additional to the high-tech bio-optical instrumentation we have on our optics rig (see below) we also attached a Secchi disk, that way we can continue this decadal long time-series of observations. The Secchi depth can be related to the concentration of phytoplankton in the water (see figure below).  We have compared our Secchi depth measurements taken on this cruise with the average chlorophyll concentration estimated from satellite at the same location in an October climatology (we will use the concurrent chlorophyll concentrations once they are processed after the cruise). Demonstrated in the figure below, as the chlorophyll concentration decreases (a pigment indicative of phytoplankton biomass) the Secchi depth typically increases. The black line shows the typical relationship between chlorophyll and Secchi depth observed elsewhere in the global ocean. These Secchi depth measurements can also be used to validate algorithms designed to estimate the Secchi depth using satellite ocean-colour data, as demonstrated using the October monthly satellite climatology (bottom right figure below).

Optics rig, Secci disk, Secci depth against satellite chlorophyll observations

Optics rig, Secci disk, Secci depth against satellite chlorophyll observations

As we approached 40 degrees south, we have entered the region of the ocean known as the “Roaring forties” and have been blasted by 51 knot (Beaufort 10) winds and the ship has been rocking from side-to-side (see image below). Hopefully the wind is dying down tomorrow, though I am not sure the swell is?

Rough going onboard the JCR with wind speeds approaching 60mph

Rough going onboard the JCR with wind speeds approaching 60mph

Chlorophyll in the South

30th Oct, 2013

Since passing the equator and surviving the “crossing the line ceremony” we have been sampling constantly for over week. Since the start of the cruise I have now filtered nearly 1500 litres of water through 25mm 0.7 micron filter-pads.

We have now crossed the South Atlantic Gyre one of the least productive regions of the ocean (often referred to as an “oceanic desert”). In the South Atlantic Gyre, the water is as blue as it can get (see photo below).

Clear blue of the South Atlantic Gyre

Clear blue of the South Atlantic Gyre

The plot shows the AMT23 transect overlaid onto a satellite chlorophyll climatology of October. The pink dot (roughly -20 latitude and -25 longitude) highlights where this photo was taken. It is in a region of the Atlantic Ocean with the lowest total surface chlorophyll concentration (chlorophyll being a photosynthetic pigment in phytoplankton, indicative of its biomass). Alongside the map shows a remote-sensing reflectance spectra (after an initial processing) captured using our hypersepctral radiometer (Satlantic  HyperSAS) at the same location the photo was taken. The remote-sensing reflectance is essentially a ratio of upwelling radiance to downwelling irradiance (in simple terms the ratio of light coming out of the ocean to that of light going into the ocean), and it is plotted on a linear and a logarithmic scale (y-axis) as a function of wavelength (x-axis) in the UV to visible portion of the electromagnetic spectrum. As can be observed in the plot, at UV and blue wavelengths (300-500nm) the reflectance is very high, whereas as green and red wavelengths (500-700nm) the reflectance is much lower.

South Atlantic Gyre satellite chlorophyll climatology of October alongside the remotely sensed reflectance spectra

South Atlantic Gyre satellite chlorophyll climatology of October alongside the remotely sensed reflectance spectra

Part of the reason these waters are so blue is that the phytoplankton concentrations at the surface are very low (the chlorophyll pigment in phytoplankton absorbs blue light), such that the optical properties of pure sea-water dominate the reflectance signal (pure sea-water absorbs light at red and green wavelengths with a higher intensity than at blue wavelengths, and also scatters blue wavelengths with a higher intensity than red and green wavelengths).

Rough seas of the South Atlantic

Rough seas of the South Atlantic

We are now heading for the Falkland’s where we are due to arrive in a week and a half.   The sea is already getting rough (see image below taken this evening). However, we are heading for greener waters which means two very importance things: i) we are lightly to see more marine life (e.g. whales ect…)  and ii) I will be filtering less water!

Dawn at sea

Dawn at sea

You are walking through a sunny street in a village back home, you hear the birds chirping in the morning, and the people´s funny voices and the laughters from the windows of the surrounding houses. Everything seems so quiet and peaceful. The ground is solid and still. Suddenly, a sharp alarm calls and you wake up within a dark cabin. You realise that your bed is moving slightly from one side to the other, and you hear the cracks and weird noises of the wooden walls around your bed. For a second you feel like if you are within the stomach of a huge beast. You just have discovered that it is 5 o’clock in the morning and that you are in a ship. But somehow you are not surprised, so you stand up quickly.

Minutes later, and still sleepy, you walk through a corridor that goes up and down, from one side to the other, it seems like a joke, but it is not, and you are still able to walk and keep the equilibrium by placing your hands on the walls or wherever is needed. You are going straightforward to your space in the labs where all the material is ready from the day before, the sampling from the morning CTD is coming, though you may go first to the canteen to have a light breakfast. There in the labs, little by little, more and more people, scientists, seamen and technicians, appear silently from every door around… The deep sound of the sea and the murmur of the waves is all the time present. People say good morning, walking carefully on their steel toe rubber boots while they put a helmet on their heads, carrying their dark plastic bottles, tubes, little notebooks, pencils and whatever they need for their sampling.

If you are lucky, you may see , right before the rossette with the niskin bottles is taken from the black depths, a flying fish jumping over the dark surface of the sea, a gleaming red squid trying to catch some food before the sun rises, or may be the elegant shadow of an albatros planing around the ship.

A range of wildlife to see at sea; a masked booby

A range of wildlife to see at sea; a masked booby

The heavy rosette with the CTDs and the 24 niskin bottles is rising from the surface like a wet ghost, hanging from a very solid brown cable. The technicians need to coordinate and to communicate with each other at this moment, so all the precious water from different depths is kept in the niskin bottles and no device is damaged.  Everybody expects it to land on a metal frame on the deck, and tied by thick salty ropes.

Within the scientist, it is very appreciated when somebody trys to cheer you up, and you feel well when you produce the smile of somebody. There is always someone in the same situation than you, and you may be surprised to feel it everyday, through the hours of hard and tiring work, an empathy that you may not experience on land.

This could be the begining of a normal day in a cruise on board of a oceanographic ship, an experience totally extraordinary for most of the people (at least for me). You may not live it again, so you have to enjoy it every moment.

The past week has flown by. The figure below (courtesy of Arwen Bargery) shows the ocean temperature, salinity, fluorescence (an index of phytoplankton biomass), oxygen and beam transmission, derived from the vertical profiles at each station so far sampled. As we moved south through the North Atlantic, we have observed a general increase in ocean temperature (especially at the surface) and salinity. The fluorescence data indicate that at the start of the cruise we were in high chlorophyll waters (relatively speaking), the fluorescence signal then weakened as we moved towards 30 degrees North and the maximum concentration (often referred to the deep-chlorophyll maximum, DCM) deepened, after which we have observed a shallowing of the DCM and a slight increase in the fluorescence signal as we moved toward the equator, likely related to upwelling of nutrient rich waters associated with this region.

Samples so far

Samples so far

My daily routine, described in the previous blog post, has not deviated too much. However, a few days back I helped Giorgio Dall’Olmo deploy two Bio-Argo floats. These devices are at the cutting edge of bio-optical oceanography. Argo floats essentially consist of a floating device that support a number of oceanographic instruments, including temperature, conductivity (from which we can derive salinity) and pressure (from which we can derive depth) sensors. In addition to these instruments, the Bio-Argo floats contain a suite of bio-optical instruments including light sensors, fluorometers and devices that measure optical backscattering. The floats sink to around 1000m and, once every 5 or so days, the device floats journeys to the surface while measuring these oceanographic variables. This information is then transmitted to a satellite and which relays it to the Argo network, where scientists can access the data in near-real time.

Whereas ocean-colour satellite data can only observe the surface of the ocean (40m at maximum) these Bio-Argo floats extend the synoptic capabilities of satellite remote-sensing down into and through the photic zone (the region of the surface ocean where light penetrates). The synergistic use of Bio-Argo floats and satellite ocean-colour data are lightly to revolutionise our understanding of marine biogeochemistry and I was very excited to help deploy two of these new floats with Giorgio.

Bob and Giorgio with an Argo float

Bob and Giorgio with an Argo float

Bob and Giorgio deploy an Argo float

Bob and Giorgio deploy an Argo float

The temperature and humidity are now soaring as we approach the equator and shortly, I will be experiencing my first “crossing the line ceremony”. Meaning that my first day off in nearly two weeks will involve trying to dodge, as best I can, the dreaded consequences of passing the equator for the first time on a ship (flights don’t count unfortunately). Wish me luck!

The sampling routine

13th Oct, 2013

Sampling started on Wednesday following confirmation of our cruise route. For the last four days my routine has been intense. I am up at 5am to set up for the pre-dawn conductivity temperature and depth profile (CTD) during which the first optics cast is deployed. 

Pre-dawn conductivity temperature and depth (CTD) profile

Pre-dawn conductivity temperature and depth (CTD) profile

 

I then filter water for three hours to extract phytoplankton pigment data at different water depths, before setting up the hyperspectral radiometer (see http://www.amtblog.org.uk/index.php/1861). The filtering datasets are then logged and I then spend the rest of the morning processing the hyperspectral data. 

After lunch, I help Giorgio Dall’Olmo with second optics cast while the second CTD is deployed. 

Giorgio setting up for the second optics cast

Giorgio setting up for the second optics cast

 

Giorgio deploying second optics cast

Giorgio deploying second optics cast

 

The afternoon and early evening is spent filtering more water for pigments, particulate organic carbon and fatty acids. After dinner I just have time to call my wife and relax before crashing to sleep with the “motion of the ocean”.

As the chaos subsides

11th Oct, 2013

Air Temp 19.3°C

Sea Surface Temp 20.8°C

Well now we are well and truly underway, our pre-dawn station (No. 05) this morning saw us about 450 miles to the west of northern Portugal and by tomorrow morning we should be somewhere between Madeira and the Azores. We have a revised cruise track to account for the reduced time available to this cruise. This will take us closer than recent transects to the west coast of Europe and North Africa in the northern hemisphere and to the eastern coast of South America in the south.

New track
New track

Science activities are gradually loosing the frantic nature always associated with the early days of every cruise. All around people have played hunt the pipette, accused each other of hiding bottles and complained loudly about the disorganisation of others, whilst leaving their own trail of chaos. But all is beginning to gel and this mornings sampling station was a quieter and more ordered affair.

A failure in the ships air conditioning has been rectified and the temperature in the main laboratory has plummeted from a balmy 32.5°C to somewhere in the mid 20s which, while bearable, has seen jumpers discarded and shorts appearing a few days earlier than expected. There was a worry that if temperatures continued to increase people would soon be working in pants and vests..

Wildlife watchers have observed several whales and dolphins, and we are joined on a regular basis by a varied group of migratory songbirds. I must be spending too much time inside the ship, so far I have seen a grey wagtail and managed to catch the backside of some whale disappearing into the distance at about 500 metres away.

Hopefully, now that we are settling into a calmer routine, the early cruise weariness has eased (though this usually happens only a few days before the end of cruise exhaustion sets in!) and people start getting some results, we will have some science updates posted.

Setting up the equipment

7th Oct, 2013
AMT23 departs from Immingham

AMT23 departs from Immingham

After a 5 day delay in departure we have got underway on the 5th October leaving Immingham, UK and headed for Portsmouth where we arrived today to re-fuel before eventually heading for the Falklands.

As part of the 23rd Atlantic Meridional Transect we will be taking oceanographic measurements over the next five weeks. These measurements will be used to help validate and parameterise a new bio-optical model being developed within an European Space Agency project.

Setting up the hyperspectral radiometers

Setting up the hyperspectral radiometers

Tilt and roll sensor

Tilt and roll sensor

Radiometric equipment is now set-up, and with the exception of a few teething issues, data is now coming in from the hyper-spectral radiometer. Setting up the radiometer was fun, it involved being hoisted up in a crane and attaching the downwelling irradiance sensor to the front mask and setting up the sky and water radiance sensors on the front of the ship with the tilt and roll sensor. Filtration rigs are also set up and we are hoping to being sampling at our first cruise station on Wednesday. The cruise track can be followed at http://www.sailwx.info/shiptrack/shipposition.phtml?call=ZDLP

And off we go…

6th Oct, 2013

James Clark Ross in Immingham

James Clark Ross in Immingham Tuesday 1st October saw 18 marine scientists from around the UK with colleagues from Spain and India converge on Immingham for the start of this years AMT cruise.

AMT23 has come back to the ship of the programs conception – the RRS James Clark Ross for the first time in 5 years. Due to some issues with one of the ships cranes and other logistical issues mobilisation of the cruise was extended by several days, but as I write we have now left Immingham and the River Humber behind and are making steady progress south through the North Sea.

River Humber

River Humber

Onboard are researchers from PML and NOC,S and the Universities of East Anglia, Warwick, York, Southampton and Vigo. Instrumentation has been installed, some is calibrated and some is being threatened with spanners and screwdrivers as the usual early cruise technical challenges are confronted.

Bob Brewin and Ian Brown from Plymouth Marine Laboratory with AMT colleagues

Bob Brewin and Ian Brown from Plymouth Marine Laboratory with AMT colleagues

The next few days will see us visiting the naval port at Portsmouth to take on aviation fuel for the British Antarctic Survey air fleet before heading south in earnest, destination Port Stanley, Falkland Islands, date of arrival – currently unknown!!

The 23rd AMT cruise will depart the UK from Immingham, Lincolnshire w/c 1st October 2013 and arrive in Port Stanley, Falkland Islands w/c 4th November 2013.

The cruise will be on board the RRS James Clark Ross.

For more information please contact:

Principal Scientist

Dr Mike Zubkov – mvz@noc.ac.uk

Logistics

Dr Andy Rees – apre@pml.ac.uk

Christine Wing – cwin@pml.ac.uk

More information will be announced soon.

Click here for logistical information and forms relating to the AMT 23 cruise.

RRS James Clark Ross. Image courtesy of P.Bucktrout (BAS)

RRS James Clark Ross. Image courtesy of P.Bucktrout (BAS)

Bio-Argo floats: Robots to monitor ocean biology and biogeochemistry

Hi there, my name is Giorgio Dall’Olmo and I am a scientist at the Plymouth Marine Laboratory.  I want to tell you about a small revolution that is taking place in the field of biological and chemical oceanography.

Figure 1: Bio-Argo float being deployed in the blue waters of the sub-tropical gyre. The white bottom contains the inflatable bladder used to regulate the buoyancy of the float (photo by Virginie van Dongen-Vogels).

By now you should have understood that scientists go on research cruises to gather information about the ocean, its organisms, its chemistry, and its physics.  Satellites orbiting around the Earth provide us with a second important means to observe the ocean.

Both these observing systems, however, have important limitations.  Research cruises can help determining the horizontal, temporal, and vertical distribution of various ocean properties, but are extremely expensive and thus limited in space and time.  In contrast, satellite sensors scan the ocean at the global scale with a relatively high temporal and spatial resolution, but can only detect a limited set of parameters near the surface and under cloud-free conditions (some sensors can “see” through clouds).

Most biological, chemical, and physical processes develop in a three-dimensional ocean that continuously changes over time.  So, what are we missing with the current observation methods?

The truth is that we do not know for sure.

Our understanding of ocean processes can be further improved by a third observational method: Argo floats (Figure 1).  These are autonomous robotic platforms that carry scientific instruments and that can regulate their buoyancy.  Once deployed, they spend most of the following 3-5 years at a “parking” depth of 1000 m in a dormant state.  Every ten days or so, they turn on, sink to 2000 m, turn on their scientific instruments and collect data as they rise to the surface.  From there, they transmit the data to land via a satellite link and then sink back to the parking depth where the cycle restarts.  About 3500 Argo floats are currently recording temperature and salinity profiles that are fundamental for understanding ocean physics (see Argo web site).  But what about biology and biogeochemistry?

Well, that is where the revolution is happening!

Argo floats have recently been equipped with sensors that can measure biological and chemical properties. We call these “Bio-Argo floats” and the data they are collecting are opening exciting new opportunities to further our understanding of ocean biology and biogeochemistry.

Figure 2: Giorgio waiting for a Bio-Argo float to be ready for deployment. (1) antenna; (2) conductivity, temperature and pressure sensors; (3) dissolved oxygen sensor; (4) chlorophyll and coloured dissolved organic matter fluorometers, and optical backscattering sensor; (5) transmissometer; (6) ballast to support the biological and biochemical sensors; (7) nitrate sensor (photo by Virginie van Dongen- Vogels).

During AMT22, besides six “traditional” Argo floats, we also deployed eight Bio-Argo floats: four in the northern and four in the southern sub-tropical gyres.  They will contribute data to a larger project lead by Dr. Herve’ Claustre at the Laboratoire d’Oceanographie de Villefrance-sur-mer (France, http://www.OAO.obs-vlfr.fr/).

Besides temperature, salinity and depth, the instruments on these floats also measure chlorophyll fluorescence (a proxy of phytoplankton pigment concentration), optical scattering (a proxy of particle concentration), dissolved oxygen (produced by photosynthesis and consumed by living organisms), nutrients (needed by all ocean organisms), as well as light (the main ocean fuel, Figure 2).

Importantly, these floats will monitor the gyres after the passage of the cruise.  We will thus be able to better understand how the ship-based “snapshot view” of these ecosystem will evolve with time.

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