Monday, 27 March 2017

First recovery of the RAPID array’s novel biogeochemical component

A post by Pete Brown

As well as playing a fundamental role in the northwards transport of heat, the North Atlantic is also a key part of the global carbon cycle. Of all the extra carbon dioxide (CO2) that has been added to the atmosphere by human activities (fossil fuel burning, land-use change, concrete production etc) over the last 300 years or so, about a quarter has been and continues to be absorbed by the oceans, greatly reducing the speed at which atmospheric CO2 concentrations increase, and the rate at which their associated climate-related impacts develop.

Within this, the North Atlantic is the most effective global ocean location for CO2 absorption. Both the cooling of poleward-moving surface waters and intense biological activity act in concert to greatly reduce carbon dioxide concentrations in the shallowest water depths. To make up this deficit, CO2 is then absorbed from the atmosphere, with human-derived carbon being absorbed at the same time.

Strong biological activity (also ‘Net Primary Production’) in the North Atlantic leads to a large reduction in surface carbon levels, and a strong of uptake of CO2 from the atmosphere occurs to counter this.

Our current understanding of the magnitude of the air-sea CO2 flux in the North Atlantic (for instance, that it absorbs as much carbon each year as the total emissions of Japan and Germany combined) is derived mainly from sensors on board volunteer observing ships (such as ferries or container ships). While these do a good job at estimating the integrated annual signal, the sporadic nature of the observations they make (both in time and location) mean that much less is known about the processes that cause the flux to vary from week-to-week, month-to-month and year-to-year.


It is thought that a large part of this variability is driven by the ocean, with its transport of carbon affecting the surface ocean-atmosphere concentration gradient and storage of anthropogenic carbon, and its transport of nutrients fuelling biology activity. But transport estimates are currently restricted to only every 5 to 6 years, when transatlantic research cruises undertake full surveys of deep-ocean physics and chemistry across 24.5°N.


In order to better predict how the North Atlantic carbon sink will respond in the future to a changing climate (and thus its ability to and continue mitigate further atmospheric CO2 increases), we need to improve our understanding of the processes and drivers of the air-sea flux of CO2. In particular, the transport and carbon and nutrients into the region, and the effects they have on export production and the accumulation of anthropogenic carbon. For this we need new observations at a much higher frequency. About 16 months ago, biogeochemical sensors and autonomous water samplers were deployed across the RAPID mooring array for the first time to help meet this need. And on this trip, we’re collecting our first data from them.


In sunnier times: temperature, salinity, pressure and oxygen sensors being attached to the mooring wire

Autonomous sampler and suite of sensors in the frame below being recovered from the Eastern Subtropical North Atlantic in March 2017.
 
As part of the Atlantic BiogeoChemical Fluxes program (www.rapid.ac.uk/abc), oxygen, pH and pCO2 sensors were installed alongside autonomous samplers collecting water to be analysed for dissolved inorganic carbon, total alkalinity, inorganic nutrients (phosphate, nitrate and silicate) and organic nitrate. We’ve now collected samplers and sensors from two of the four locations where they were deployed, and installed replacements to make additional observations until Autumn 2018. Over the coming weeks and months, this fantastic new data set for the region will be analysed and investigated, numbers crunched and calculations made.


Combined pH, oxygen, temperature, salinity and pressure sensor recovered from 50m depth in March 2017.
 
Increasing the temporal resolution of observations across the subtropical gyre from once every 5-6 years to once every 4 to 24 hours (for the sensors) or 11 days (for the samplers) will allow us to massively increase our understanding of the variability of processes involved in ocean-atmosphere interaction in these locations. We’ll then combine this novel biogeochemical data with the estimates of water transport and the AMOC from the RAPID array, to investigate the transport of carbon and nutrients by the ocean at equally high frequency (approximately every 10 days). From here we’ll be able to look much more closely at the role of the North Atlantic in mitigating future atmospheric CO2 increases. Onwards and upwards!

Locations of the RAPID moorings, and those with novel biogeochemical samplers / sensors being recovered for the first time this year.



Friday, 24 March 2017

Recovering 007 and the temperature and salinity of the deep ocean

Two days ago the RRS James Cook recovered a novel profiling float.  As its serial number, 007, suggests very few of these have so far been deployed.  This one had not been working as it should and our colleagues were keen to get it back so that the problem could be diagnosed to improve the reliability of future versions.

Since 2000 oceanographers have been continuously monitoring the temperature and salinity of the upper 2000m of the worlds oceans using an array of free drifting Argo floats. Every 10 days these floats sink to a depth 1000m and drift at that depth for 9 days. On the 10th day they sink to 2000m and then return to the surface to transmit their data to a satellite. These floats can operate for up to 5 years and their data are made publicly available within hours of collection ( available here ).

Positions of the floats that have delivered data within the last 30 days  
The upper ocean has become well sampled with nearly 4000 floats delivering data. However, we know relatively little about how the temperature of the ocean below 2000m is changing.   Some pilot programs with deep profiling floats that can reach 4000m or 6000m depth have recently started and we hope that in the coming years they will be sampling the deep ocean across the world

Our colleagues at NOC are working on one pilot program and during an expedition in this region one year ago 4 deep Argo floats where deployed.    It is one of these that we recovered this week.    During this expedition we are deploying 6 more deep Argo floats from Scripps Institution of Oceanography in the USA.



Deep Argo float recovery
The Argo program is a collaborative partnership of more than 30 nations from all continents. The data from the program has revolutionised our capability to observe climatically important variations in the heat content of the ocean.





Tuesday, 21 March 2017

Research cruises humanise us

A post from Chata Seguro

How many times have we heard that traveling opens your mind, makes you more empathetic and – why not? – more intelligent? And the reason is that we get out of our comfort zone and we are “forced” to learn from other cultures just by standing in the middle of a new environment.
What is not so obvious is that it also happens in research cruises. You may be wondering why. How is that possible if you are only travelling with the same group of people that you normally cross in the corridor or in the canteen? There is nothing new with that, right? Well, actually no.  During a research cruise, especially long ones, you are “forced” to interact with complete strangers but also with old colleagues in a different way. You are not the centre of your own agenda: you try to be there where you are useful because on a ship, the word team makes real sense, and that humanises us.
Nowadays, we have everything we need to make our life comfy and independent. That is a double-edged sword, because while, for example, technology makes our life easier it also isolates us. You may think that it is not true because you talk everyday with your colleagues or family, but how many times do you learn something new from them? How many times does somebody’s opinion surprise you and makes you really think? 
There is something magical on every cruise, does not matter how many times have you sailed, every cruise is different, and it is not only because you navigate different seas but more importantly with different people. Here, the internet is slow, you need to take turns to use the computer, calling home is more difficult than just typing a number from your phone and it is these inconveniences that annoyed us so much on the first days that have become part of the routine now. The biggest advantage is that while these technological inconveniences affect our mood less and less, jokes, games, histories and laughs grow to occupy this space more and more.
As a foreigner, I experienced the shock of the polite and friendly but sometimes rather cold urban society. Surprisingly, we all became warm friends (crew, technicians and scientists) while on the cruise. You do your best to treat others well. On land we are not patient enough: why would we waste our time on someone we don’t care about? On land, we lose many good opportunities to hear what others have to say, whilst research cruises bring us many. Research cruises humanise us. I can simply not imagine myself having great conversations while looking at the sunset or the starry sky with a complete stranger on land, but it is so easy on a research cruise, and it feels so good! Life is different floating in a nutshell in the middle of the Atlantic. You discover new things almost in every conversation, and importantly, you also re-discover yourself telling about your life to others.
Time to enjoy conversations and the setting sun
New times are coming: autonomous vehicles, satellite data, buoys and auto-samplers, modelling, all of which will generate much more science-data for the same number of cruises. This is a huge advantage in the name of science, knowledge, the environment and of course for the benefit of the society, but we should not allow technologies and staying in our comfort zone to dehumanise us – or robotics to replace us. I hope we will never loose our north star. 

Monday, 20 March 2017

Shrinking art

A post by Delphine Lobelle

We have passed the Mid-Atlantic Ridge and are half-way through the cruise (with just under 3 weeks left until April 8th!). After 3 full days of deploying and retrieving the deepest moorings and CTDs (measuring Conductivity, Temperature and Depth), we will steam towards the Bahamas. We will first see land on March 28th, stopping off for a few hours in Nassau where the IT technician must get off the ship to calibrate the gravity metre instrument for the next seismic cruise (JC146) and Yvonne will be substituted by Gerard for the western boundary leg. 

Yesterday afternoon, the CTD was deployed to the bottom of the Atlantic (over 5000 m) with not only all the Niskin bottles, MicroCATs and acoustic releases attached but also socks and t-shirts transporting our artwork! This tradition includes drawing on a polystyrene cup, waiting 5 hours for it to descend through the full depth of the water column and then resurface. The increase in pressure with depth compresses the polystyrene to a shrunken version of its former self. We did a quick check and 13 mini-cups of water fit into 1 pre-compressed cup (i.e. it holds 1/13th of its original volume!). 
The artwork is secured to the CTD before deployment

Deployment of the CTD
There are many ways to stay entertained during our free time onboard, with a range of board games (including a chess tournament we started), card games, poker night, hundreds of DVDs available, going to the gym and sauna or jumping in the aft-deck ‘pool’ (a large bucket of water 1 person can just about squeeze into), but the cup-decorating revealed some truly gifted artist-scientists and technicians on board. I’ve tried to disguise my cups among those Darren brought from his children’s classmates since my skills don’t surpass those of a 10-year old’s… I’ll leave you to try to spot them in the photo!

Shrunken art work - and one that has yet to be compressed.