Author Archives: Sarah

by Stuart Cunningham, July 2014. R/V Knorr, mid-Atlantic.

“I’m truly sorry man’s dominion
Has broken Nature’s social union,
An’ justifies that ill opinion
Which makes thee startle
At me, thy poor, earth born companion
An’ fellow mortal!” – Robert Burns, 1785.

Burns writes of our interfering with the balance of nature – inadvertent or otherwise – and our short-lived sharing of the earth’s environment: in this Poem writing about the panic of a mouse and her brood with the turning of her nest by the plough’s harrow. Settled opinion is that anthropogenic forcing is the dominant mechanism driving long-term climate change: controversies now are more about our reaction to this. Long-term in this context means that over a few decades we can see the slower man-forced changes hidden amongst larger, naturally occurring climate variation. We need now to focus on the regional impacts of global warming: measuring shorter term changes so that the long term trends can be quantified. Will my home region be warmer or drier or submerged by sea-level rise? Global average change hides the nature of much larger regional changes. Observing the ocean gives us a Plimsoll line for future change, and the stimulus for better theories of oceans and the climate.

So why are we at sea?
The atmosphere and ocean transport heat from the equatorial regions to higher latitudes: this energy transfer is our climate. The atmosphere reacts quickly, while the ocean controls slower and long-term energy transports relating to our long-term climate variations. Warming and increased precipitation at high latitudes caused by global warming means that the heat transported by the Atlantic is likely to reduce over the coming century: this has long-term implications for climate patterns (particularly in the North Atlantic where the ocean acts as a “fan assisted storage heater for Europe”(1). Beginning in 2004 a purposefully designed transatlantic monitoring array began measuring the Atlantic circulation between Morocco and Miami (2). Observing the ocean is a very buy propecia online hard and expensive technical problem. Controversial in its infancy, RAPID-MOCHA blazed a trail for oceanographers: showing how by thinking big, and with cooperation between teams of brilliant scientists and with the long-term commitment of funding agencies, oceanography and climate science can tackle one of the leading climate problems in the 21st century: what controls Atlantic ocean heat transport? how is changing now: how is it likely to change in the future?; and with the ambition to forecast climate out to decadal timescales.

RAPID-MOCHA nailed the problem in the subtropical Atlantic, and so was born the ambition to install a similar purposefully designed observing system in the subpolar North Atlantic. In the subtropics we measure the maximum heat transport by the ocean. This diminishes greatly by the subpolar region: the heat lost to the atmosphere being central to climate variability for countries around the Atlantic (affecting hurricane variability, Sahel drought, Amazonian rainfall, extreme European winters, fish stock distributions). Thus OSNAP (a child of RAPID), with moorings from Newfoundland to Greenland to Scotland, aims to measure the heat transport in the subpolar region. Combining with RAPID we measure the critical Atlantic heat transport throughout the North Atlantic and the exchanges with the atmosphere. OSNAP is another milestone in our goal of building an integrated Atlantic observing network.

Man’s dominion over Nature, we now understand, is illusory. King Knut the Great 1200 years ago understood (and quite possibly demonstrated?) the futility of believing otherwise. But we can observe, theorise and understand our climate: more, better, better planned and long-term observations are the way we will make progress in understanding. Otherwise we will be unprepared for change now and for future generations. Observing the oceans is difficult but it must be done; and it will be done. This research expedition is our contribution.

1 Ellett, D. J. The north-east Atlantic: A fan-assisted storage heater? Weather 48, 118-126, doi:papers2://publication/doi/10.1002/j.1477-8696.1993.tb05861.x (1993).

2 http://www.rapid.ac.uk/rapidmoc/
https://www.rsmas.miami.edu/users/mocha/

By Amy Bower and Stuart Cunningham

Almost within earshot of the bagpipes of Scotland, we deployed the last of the 20 moorings slated for this leg of R/V Knorr Voyage 221. It was an exciting finish to this phase of the cruise. Instead of the “normal” mooring deployment strategy where we pay out the top of the mooring first and finish with the drop of the anchor, we lowered a single instrument to within one meter of the sea floor on a heavy wire, and then sent an acoustic signal to release the instrument and let it drop to the bottom. It is an upward-facing Acoustic Doppler Current Profiler (ADCP), which will constantly emit sound signals up to the sea surface and use the Doppler shift of the return signals to measure the currents from top to bottom. As described in a previous post by technician Karen Wilson, the ADCP is encased in a trawl-resistant frame (which our Scottish colleagues call “the Spaceship” for obvious reasons) so that fishing gear pulled along the sea floor will roll over the cage and not snag it.

The exciting part of the deployment was the final approach of the Spaceship to the sea floor. No one can see with their eyes what is happening 400 meters down—so we “see” with our ears, relying on sound signals from the Knorr and from the Spaceship to tell us how close to the bottom it is. The goal was to not release the frame until it was within a few meters of the seafloor. If we release it too early, it could flip upside down before it hits the bottom. If we hold on too long, the package might slam into the bottom and be damaged. And remember that the ship is rolling a bit, which lifts the frame up and down slightly with every swell. After much suspense, Principal Investigator Stuart Cunningham “pulled the trigger” and the frame dropped to the sea floor. Next year we will return to this site to recover the instrument and its precious cargo—the first long-term continuous measurements of the shelf edge current off Scotland.

Now the science crew is changing gears from mooring to CTD operations. For the rest of the cruise, we will be slowly making our way back along the same cruise track, stopping every so often to lower the CTD package to the bottom in order to measure the temperature, salinity, dissolved oxygen content and other seawater properties. A pair of ADCP’s mounted on the CTD package will also record the ocean current profile at each station. These stations will be spaced much more closely together than the moorings—this will give us the opportunity to get an initial high-resolution snap-shot of all the currents and water properties along the OSNAP line to compare with the measurements from the moored instruments.

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by Bill Johns

Today marks a week at sea on our cruise aboard the R/V Knorr, and things have been going quite well up to this point. We have settled into a routine of deploying two moorings per day as we lay out the combined Dutch/U.S. mooring array across the Reykjanes Ridge. Each day begins with a mooring deployment just after breakfast, then a steam to the next site (usually 20-30 miles away) and an afternoon deployment, and then we spend the night running ahead to the next two sites to perform bottom topography surveys so we can pick spots for the moorings to be deployed the next day.

Fortunately, the R/V Knorr has a multi-beam echo sounding system called Seabeam that measures the bottom topography along swaths perpendicular to the ship’s motion. These swaths have a width about 3 times the water depth, so this allows us to paint a picture of the bottom topography for several miles to either side of the ship. Without it, we would have to steam a grid pattern with the ship to get a two-dimensional view of the bottom, a very time consuming task. (Think of it as running order klonopin a paint roller over the bottom instead of drawing a single line with a pencil.)

Even with the Seabeam system, choosing mooring spots is not trivial. The bottom topography here is very rough, full of deep fractures, ridges and pinnacles that are characteristic of the newly-formed earth’s crust near mid-ocean spreading centers, which is what the Reykjanes ridge is; it is the northern arm of the great mid-ocean ridge system in the Atlantic Ocean. Finding a good spot for a mooring involves several factors, but one of the most important things is that it needs to have reasonably constant depth over an area that we can be sure to land the anchor in.

For the uninitiated, deploying a mooring consists of first streaming the whole mooring out behind the ship, starting from the top of the mooring that will be nearest the surface. Instruments and floats to support them are then added at various lengths along the mooring wire as the ship slowly steams toward the deployment site from some distance away. The last thing to be attached is the anchor, which is then lifted over the side and let go when the target spot for the mooring is reached. Actually the ship usually steams a bit past the target site before the anchor is released, because as the anchor sinks it drags all the mooring components laying on the surface toward it, causing the anchor to literally swing backward as it sinks rather than falling straight down. This is called “fall back”, and especially for very tall moorings it needs to be factored in. (And we are talking heavy anchors here, usually a few thousand pounds, that are made up of cast iron, or scrap railroad wheels, or leftover heavy anchor chain from large ships; each group onboard has their own favorite style of anchor.) Also, ocean currents can move the whole mooring horizontally as it falls, and since it can take up to a half an hour or so for an anchor to reach the bottom, this can also affect the landing spot. So, there is always some uncertainty in exactly where the anchor will wind up on the bottom, and even those with lots of experience can seldom place an anchor within a tenth of a mile of the target site in full ocean depths. That is why we try to find flat spots to land the anchors in. And these can be very hard to find along the Reykjanes Ridge!

Why is hitting the target depth so important? Mainly it is because the moorings are designed to measure currents or water properties at specific depths, and the instruments will miss those depths if the mooring winds up where it is deeper or shallower than the mooring was designed for. Also, some of our moorings have instruments very near the surface, up to 50 m from the surface. If we land the anchor at a depth that is 50 m shallower than planned, then those instruments will be laying at the surface and can be damaged by surface waves or be run over by ships. If we miss too deep, then the instruments are not measuring the near-surface properties we want to observe. (Note that all the moorings we are deploying are “subsurface” moorings, meaning that they have no surface buoy and lie completely below the surface. We retrieve them by sending coded sonar commands to a device called an “acoustic release”that releases the rest of the mooring just above the anchor, and it is then recovered when it floats to the surface.)

So far we have been hitting our target spots pretty well, and this is something that requires excellent coordination between the scientists, the deck crew, and the bridge officers driving the ship. How do we know if we hit our targets? By transmitting sonar signals to the acoustic releases on the bottom, we can triangulate on them and determine precisely where they landed.

By now we have deployed 10 moorings, exactly half of the total number of moorings we will deploy in this cruise. On these moorings are countless instruments measuring currents, temperature, and salinity at depths from near the surface to the bottom.

While we are out on deck adding components to the moorings as they are streamed out (which can take several hours for each one), there is sometimes an opportunity to look around at the sea and take in the ocean vista. This is especially true for me, since I am usually just standing back and taking notes as others do all the hard work on deck. For the last few days I have been noticing especially the birds. First of all, there are an amazing number of sea birds out here. Ever since we have left Reykjavik, one can see birds from horizon to horizon, darting about just above the waves. I am used to seeing sea birds, but in the tropics and subtropics, where I have done most of my field work, they seem to be much more scattered and are seen only occasionally. Here they are everywhere, and it boggles the mind to think of the vast number of birds that must be out here. They are mostly Northern (or Arctic) Fulmars, which look like a very stout seagull with a trimmer tail.

Whenever we stop the ship to work, they flock to us in the hundreds and set down on the water behind the ship, waiting expectantly. Of course, they think we are a fishing vessel, and they are hoping for some morsels of by-catch. I can almost hear what they are saying to each other: “What poor fisherman these people are!” “I have been following this ship for 4 days now and haven’t yet gotten a single scrap to eat!”. It is amazing to think how we have impacted their existence, and how they have learned to follow ships for an easy meal in the years since we humans began setting out to sea (or is it even in their genes now?). Perhaps in their next stage of evolution they will learn to recognize a research vessel from a fishing boat!

Tonight is the World Cup final, and all of us who are not on watch will be huddled around the radio listening to it. Unfortunately the Dutch team did not make the final, but they had a brilliant cup, culminating in a third place victory over Brazil, and our Dutch colleagues onboard certainly have much to be proud of.

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By Amy Bower

As described in earlier posts, the purpose of OSNAP is to quantify the ocean’s role in redistributing heat and fresh water between low and high latitudes in the North Atlantic. The “overturning circulation” refers to the generally northward flow of warm and salty water in the upper ocean, and the southward return of colder, fresher water deeper down. The system of ocean currents that makes up the overturning circulation has been efficiently depicted in various schematic diagrams and is often referred to as the Great Ocean Conveyor. It is important however not to interpret this schematic as exactly representative of the deep and shallow currents in the North Atlantic. A more realistic view is shown by the second diagram below, but even this suggests overly smooth and well-behaved current pathways.

As a complement to measurements of temperature, salinity and currents at fixed locations along the OSNAP line, OSNAP co-PI Susan Lozier and I will be releasing a total of 120 freely drifting floats into the deepest currents in the subpolar North Atlantic to document the real pathways of these slow but relentless “rivers” of near-freezing water flowing along the bottom of the ocean.

So how do we track the pathways of currents two miles deep? We take advantage of the fact that sound travels exceptionally long distances in the ocean. The first step we are taking is to moor 10 sound beacons throughout the subpolar region where we plan to release the floats. A map of the beacon locations is shown below. Each beacon is anchored to the sea floor in such a way that it is suspended in the water about 1200 meters down from the surface. At a precise time each day, the beacons emit an 80-second tone at about 260 Hz. Then we release floats from the research vessel at various locations where we know the currents are located. The floats have just the right weight (measured within 1 gram) to sink and drift 200 meters above the sea floor. Attached to each float is an underwater microphone, called a hydrophone. The floats will listen for the beacons and record the time that they hear the sound signals. They will do this for two years, then drop some weight so they can rise to the sea surface and transmit the recorded information to us via satellite. Knowing the time the signal was sent, and each time it reached the float and the speed of sound in seawater, we can figure out the distance between the float and each sound beacon. As long as the float hears signals from at least two beacons, we can figure out where the float was every day. By connecting the dots from day to day, we end up with the float’s trajectory and the path of the water it was drifting with. With many floats, we can generate a description of where the currents go most frequently. We can also observe meanders and eddies in the currents.

On the first leg of the R/V Knorr’s OSNAP voyage, three of the beacons (8-10 in the map above) and 10 of the floats were deployed. Some test floats released at the same time have already surfaced and let us know that those three beacons are working properly. Our first success! Yesterday, we anchored sound beacon #5 in the Irminger Basin, west of the Reykjanes Ridge (see photos below). Next week we will moor #6 and #7, and release 10 floats east of the Reykjanes Ridge. Altogether it will take four research cruises on two different vessels to get all 10 beacons and 40 floats in the water this summer. We plan to rlease 40 more floats each in the summers of 2015 and 2016. It’s “Bon Voyage” to each one as it goes off for a tour of the deep currents of the North Atlantic.

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by Bill Johns

After much anticipation and seemingly endless planning, we finally set off from Reykjavik, Iceland at 0900 last Sunday morning (July 6th) on Leg 2 of the R/V Knorr’s summer 2014 OSNAP field campaign. Luckily the sea conditions were much improved from what they had been for the last few days offshore of Reykjavik. During the cruise mobilization and loading days a low pressure system had planted itself over Iceland, and the strong winds on its back side brought unseasonably cool temperatures to Iceland and a big swell outside the harbor. This had all of us (and especially the rookies) dreading what might lie ahead. Fantastically the sun came out before departure and the winds laid down a bit, and we found ourselves running SSW toward our work area with a nice following sea on the starboard quarter and the wind at our back, out of the north at about 20 kts.

Onboard are an international group of scientists from the U.S. (University of Miami, Woods Hole Oceanographic, and Duke University), Holland (Royal Netherlands Institute for Sea Research), and the U.K. (Scottish Association for Marine Science). Our main goal for this trip is to lay out a large string of deep-sea moorings that carry arrays of instruments measuring currents, temperature and salinity, across a swath of ocean extending from Scotland to the eastern Irminger Sea. We will also be deploying some floats that drift below the surface and track themselves by listening to sound-emitting sources we are placing on some of the moorings.

Each of the groups onboard has brought with them lots of equipment, probably enough to legitimately have their own cruise, but we have thrown ourselves together to maximize efficiency. That means the ship is very heavily loaded, and although I have used the R/V Knorr myself on a number of large previous expeditions, I have never seen her so packed to the gills buy aciphex online with equipment. There is something in every nook and cranny of the deck and laboratory spaces. We will be deploying twenty (20!) deep-sea moorings on this cruise, which may well be a record number of moorings on one cruise (somebody should go look that up). The Knorr is an incredibly capable vessel. She is due to be retired later this year, and I will miss sailing on her.

Of course, on this cruise we are focused on two things: (1) carrying out our deployment and sampling operations as efficiently as possible, and (2) the World Cup! On the night before departure we watched the game between Holland and Costa Rica at a venerable establishment in Reykjavik called the “Dubliner”, and helped our Dutch colleagues root their team to victory, in a nail biting shootout. The Dutch group is the only one onboard with a dog still in the fight, so to speak, so we’ve all decided to join their camp. Unfortunately we won’t be able to watch any more games on the ship, but the enthusiasm remains high.

The scientific work will commence shortly, and we will be deploying 2-3 moorings per day, as we move east across the Irminger and Iceland basins toward the west coast of Scotland. After all is said and done, together with coordinated deployments to be done in the next month – or already accomplished – by other international partners, we will have begun our 4-year program of continuously measuring the meridional overturning circulation and associated heat and freshwater fluxes by the ocean across a complete trans-basin section from Labrador to Scotland. This program will ultimately help to determine what causes changes in the heat carried by the oceans to the Arctic and sub-Arctic regions, and how this may impact future warming and climate change in the north Atlantic region and globally.

Now… when is the next World Cup game??

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