Discovery Friday

We are currently crossing the Atlantic on the RRS Discovery. This is, in fact, the fourth ship to bear the name RRS Discovery. The original Discovery was the used by Captain Scott when he sailed to the Antarctic, attempting to conquer the south pole (although his ship didn’t bear the royal—RRS—moniker when he sailed her). The second was Discovery II—the first purpose built research vessel in the world. The third returned to the original name alone—Discovery—and served UK marine science for 50 years before retiring at the end of 2012. And now we cross the Atlantic for the first time on the newest incarnation of this prestigious lineage.

Over the next four Fridays, I will post a piece about each of these ships. The historical legacy of the previous Discoveries is nicely emphasized around this new ship with lots of old photos and paintings. I’ll post photos of a few of these with the posts. This week: RRS Discovery (2013) i.e. this ship. In some sense, this ship has the least photographs of all—vanity not being high on the agenda of this ship. One exception is the marvelous shot of Discovery being launched from Freire shipyard in Vigo.

Discovery is 100 m long and has over 6000 tonne displacement. The new Discovery has its propellers contained in two steerable pods at the aft end of the ship, unlike previous iterations that had traditional rigid screw propellers. This combined with two further thrusters toward the front of the ship (one tunnel, one steerable) allows lots of maneuverability for the scientific work, which often requires the ship to be nearly still (‘on station’) or maneuvering delicately. So unlike most ships, Discovery is designed for staying in one place well rather than just going from A to B quickly.

The crew on board consist of four departments: bridge, deck, engineering and catering. In command of the vessel is our captain, Jo Cox. Scientists and technicians make up the rest of the people on board. Us scientists work mainly in the laboratories on the upper deck, and are accommodated on the lower deck in single cabins. Three meals per day are cooked in the galley. Recreation on board is available in the forms of a DVD and book library, a gym and a communal bar/lounge; cards and darts are popular in the bar. Meals and recreation time provides a welcome rest from the intensive mooring work.

A scientist's cabin

Much of the heavy work on our moored instruments takes place from the aft deck—the deck at the back of the ship. This deck is jam packed with long wires (our longest mooring is 5100 m—over 3 miles long), buoyancy (glass and plastic spheres of different shapes that keep our moorings upright in the water). Over the cruise this will clear out and be replaced by the moorings that we recover. The moorings are deployed by technicians and deck crew. The scientists then check, calibrate and ultimately use the data. When mooring work is taking place the aft deck is a busy place: cranes dance around moving the heaviest pieces of kit, wires crisscross the deck as they come onboard, the railings at the back of the ship are down, meaning that the two men working there have only their balance and a safety harness keeping them on board.

The aft deck being readied for a  mooring deployment

Work days can be long and irregular on board so it’s nice to get a chance to relax. The forecastle deck—known to us scientists as the beach—offers some peace and quiet. This is the deck at the front of the ship, one deck down from the bridge. It’s a nice spot to read a book or sunbathe. Ships are noisy places and the foredeck is one of the few quiet spots away from engines, air conditioning units and Darren’s choice of music. The weather at the moment is calm and warm so the sea just laps and the clouds sit on a glass ceiling as far as the eye can see. With the view from up here—it’s not that bad a life, I guess.

 

"The Beach"

 

Written by Gerard (published by Darren)

Eastern boundary completed

I'll start this post by apologising for the lack of updates for the last week but we have been very busy. Our moorings running down the continental slope from Africa have now been recovered and the replacements redeployed. So the first third of the cruise can be considered complete.

The scientific party and technicians have been working hard to organise all the instruments and mooring hardware required for the replacement moorings. They have also been downloading and completing initial processing on the data from the recovered instruments. These data will feed into our overall calculations of what the AMOC has been doing for the last 18 months since we last serviced the array.

The start of a mooring deployment - cranes and winches in operation with glass buoyancy (in orange plastic hard hats)  readied on deck


There are a number of new instruments being added to the array this year as part of a new project, but we shall cover these in more detail in another post.

We now have a 3 day transit to our next mooring location on the mid-Atlantic ridge where the bathymetry is much more complex and flat areas for landing moorings much harder to come by. Luckily for us these sites have been well surveyed on previous cruises so we know where the flat spots are.

From now on we will aim to update the blog at least whenever we have transit days.

First week at sea and a short stop in Tenerife

Mooring equipment on the aft deck of RRS Discovery as she leaves Southampton.

The CTD frame being manoeuvred on deck
 before being deployed for the first profile.

Since leaving Southampton the RRS Discovery has made its way south to the Canaries.  We have not yet arrived at the first of the RAPID moorings but all on board have nonetheless been busy getting ready for the work ahead.  Each time the RRS Discovery starts a new expedition the participants need to install and setup the equipment needed for their work.  The moorings technicians have prepared dozens of instruments and many miles of wires for the moorings.   Scientists have set up the systems for gathering data underway, installed equipment for the analysis of samples, and prepared their computers for processing the mooring data that will soon be acquired.     We have also completed our first three CTD stations required to calibrate instruments prior to deployment.

A short port call in Santa Cruz provides an opportunity for additional scientists, technicians and crew to join the ship.  Some personnel will be leaving us too.  Steve has completed his work setting up the Myrtle Lander and Mike has finished work in the meteorology lab initiating the underway measurement of methane and carbon dioxide.

A number of other unofficial participants have left the ship since we arrived in port.    During our passage Discovery had become home to a surprising variety of birds.    A robin made himself at home in the main scientific lab and was often seen perching on a keyboard or monitor.    Also spotted on the ship were a falcon, two owls, and a number of finches.

One of several birds who hitched a ride on RRS Discovery 

Where is RRS Discovery now?

At the time of this post, the RRS Discovery is rapidly approaching the Canary Islands. The current location of the ship can be seen below.

RRS Discovery leaves Southampton

Last weekend the RRS Discovery left Southampton for her 6-week expedition to service the RAPID array of moorings across the Atlantic at 26°N.   

The Royal Research Ship Discovery before leaving for the RAPID expedition

The RAPID array monitors the Atlantic Meridional Overturning Circulation (AMOC) -  a system of surface and deep currents which together act like a conveyor belt transporting salt,  fresh-water, carbon and much else around the ocean.  Measurements of the AMOC are important for better long-term weather predictions, and for understanding the role of the global ocean in Earth’s climate system.

In addition to collecting data from existing sensors on the RAPID moorings, and redeploying these, the expedition will be adding biogeochemical sensors to some of the moorings as part of the ABC Fluxes project.  This aims to calculate time series of inorganic carbon and nutrient fluxes in the Atlantic at 26°N.

The team onboard will also be deploying a recently developed telemetry system for transmitting data to shore at regular intervals throughout the 18-month deployment period. 

Updates from the expedition will be posted on this blog, and the team will be tweeting using #rapidAMOC.

The Met Office ocean analysis

Predicting what the RAPID team will find using an ocean analysis

by Laura Jackson, Chris Roberts and Drew Peterson, Met Office

At the Met Office we've been examining how well our different products (ocean analysis, decadal prediction and various density and temperature metrics) compare with the observed AMOC variability. In particular we've found that an ocean analysis developed from our Forecast Ocean Assimilation Model (FOAM) and  used in our seasonal forecasting model (GloSea) is exceptionally good at reproducing the recent AMOC changes.

The figure  shows the period from April 2004, when the RAPID data starts. Each panel shows the existing observed data from RAPID (red) alongside values from the GloSea analysis (blue). As well as the actual AMOC strength we have also calculated the AMOC in the same way as RAPID by calculating the components from the Florida Straits flow (the northwards flow between mainland USA and the Bahamas), Ekman flow (driven by the wind) and Upper Mid Ocean (flow throughout the remainder of the Atlantic  from geostrophic interior flow and velocities in the western boundary region).

The Ekman flow (not shown) is identical since observational winds are used to drive the analysis. The Florida Straits (FS) and Upper mid ocean (UMO) components don't match individually as well as their sum, suggesting that although the FS and UMO components are not perfect, the analysis as a whole is doing a good job of constraining the combined sum of transports through the FS and Antilles currents. It is possible that a higher resolution might improve the representation of flows in the shelf region.

Since our model compares so well with the observations, we wanted to use it to predict what the observations being collected at the moment might show, and to enter the survey for the MOC strength from October 2014-September 2015. Unfortunately our analysis finishes in May 2015, so we have tried to estimate the last few months of data (see below for method).

The result of this analysis suggests an increase of the AMOC from Oct 2014-Sept 2015 from the 2009-2014 average by 0.7 Sv, which is made up of an Ekman increase of 0.6 Sv and an increase of 0.1Sv from the UMO + FS. It will be interesting to see how the new RAPID data compares!

Method for last few months 

For the Ekman component, we do not have wind stress for the full period, however we found that the Ekman component had a good correlation with the NCEP zonal wind strength at the same latitude. Hence we used a simple linear regression model with the NCEP wind strength which we have for the missing months. For other components we used the seasonal climatology plus the mean anomaly from the previous 12 months (ie assuming persistence of the anomaly from seasonal climatology). These last 4 months are shown in each panel in green.

Can you predict the AMOC?

Join the experts and respond to the RAPID Challenge 2015 

On 15th October scientists and engineers from the National Oceanography Centre (NOC) leave Southampton for a 6-week expedition on RRS Discovery (IV) to gather the most recent data from the RAPID array of moorings across the Atlantic from Florida to Morocco. The moorings, with sensors that measure temperature, salinity and currents from the sea floor to near the surface, monitor the Atlantic Meridional Overturning Circulation (AMOC) at 26°N.  

The AMOC with the moorings of the RAPID array at 26 North

The AMOC transports heat northwards in the Atlantic, and is important for the climate of Northwest Europe.  Recent studies indicate that it is decreasing in strength, and the decline in heat transport has been implicated in the formation of a 'cold blob' in the North Atlantic.   

Understanding of the AMOC has advanced greatly since the start of RAPID in 2004.  We now know much more about its variability, and the new knowledge allows ocean and climate scientists to make improved predictions about how the AMOC will change. 

Data is collected from the RAPID array of moorings once every 18 months, and ten years of data is now available to ocean and climate scientists from the RAPID website.  Earlier this year the  team that looks after the RAPID array challenged other ocean and climate experts to ‘predict’ what the new data will show once it has been gathered and analysed.  The response from a team at Oxford University is the first post on this blog.  If other experts join in the challenge, we will report on their thinking as well.

Now the RAPID Challenge has been opened to the wider community.  If you read this, and want to have a go at your own ocean prediction, you are very welcome to download the data, carry out your own analysis, and let us have your own estimate.

The RAPID Challenge web pages at www.rapid.ac.uk/challenge/ provide some of the scientific background information.  It also gives access to the time-series of AMOC data so far, and allows you to submit your own estimate of what the new data for the 18 months from April 2014 to September 2015 will show.

The deadline for submission is 31st December 2015.  In early 2016 a preliminary analysis of the new data will be available.  The estimates that come closest will be published on the RAPID website and awarded a Discovery mug.