Western Atlantic - Hello Labrador Current!

July 22, 2010
Lat/Lon: 42* 57.0595 / 048* 10.9752'
Air Temp: 18.6*C / 65.5*F
Wind Speed: 12.58 kts
Humidity: 94.1%
Water Temp: 14.86*C / 58.75*F
Depth: 3285m /~ 3.3 km / 2.05 miles

It is CHILLY!!! Visibility is low, obscured by low clouds. The water temperature dropped 6 degrees in the course of one hour! Long sleeve shirts and raincoats are in order. Hello Labrador
Current!

With the fog horn sounding, we continue steaming north.

During the 5:30 am multicore drop the science team spotted a pod of beautiful pilot whales! We've also been seeing Leach's Storm Petrels flying and landing on the boat here and there. (As an aside, the site linked for the Leach's Storm Petrel seems to be a really terrific bird ID website.)

Here is another map that gives you a better idea of where we are located. Open the map and find, "Northwest Atlantic Mid-Ocean Canyon". We are located approximately just south and west of the "O" in "Ocean", in the Newfoundland Basin. When we begin our return home along the east coast of North America it is the Labrador Current that we will be riding home.

Right now we're in a cycle of steam northwest-multicore-steam again-multicore. There are some gravity cores in there too. We've stopped the formal 2-watches and we're now going to have a posted schedule and be sure that all coring events will be adequately staffed.

Yesterday the blog covered the logistics of sampling and processing the muds from the cores. In addition to that process, the cores are run through the "Geotek Logger". I love their logo: "If it's worth coring, it's worth logging..."

The science team uses the Geotek Logger to gather two parameters: "Gamma attenuation"
and "Magnetic susceptibility". In the picture to the right I am standing next to the Geotek Logger with Ricardo, Sarah and Kathryn. You can see two white PVC sections (core segments) full of mud on the track. We're running Long Core segments here. The top of each core has a red cap and the bottom has a black cap. Both are sealed with electric tape to prevent the mud from dripping out.

Look carefully at the image. Between the two core lengths there is a yellow "radioactive" sticker on a lead container in which the chunk of radioactive Cesium-137 is housed. Gamma rays are sent through each mud core sample and detected on the other side. Because gamma radiation is extremely damaging to human tissue the direction of the beam is to the outside of the boat where there is no walkway so no one will be hit with the radiation; it is an important precaution.

The Geotek Logger is a very useful tool to have on the ship. It is a unique data gathering tool because it is "non-destructive". Once the cores are brought to the WHOI labs they will be cut in half (lengthwise) into the "working" and "archive" halves. At that point the researcher and his/her team dig into the "working" side. The archived half is sent to the archive repository and will serve as the record of findings. After months / years of investigating the core, the "working" side has been really picked over so the core has, essentially, been destroyed.

The gamma attenuation is used to measure the density of the mud in the cores. Gamma emitted from the source (Cesium-137) passes through the mud in the core and a portion of the gamma ray are scattered. The gamma rays that were not scattered pass through the core sample to the detector on the other side. Higher density materials in the core segment increase the scattering of the gamma rays, thereby decreasing the amount of gamma reaching the detector. Gamma ray scattering is lower when the density of the core materials is lower allowing more gamma rays to reach the detector.

Take another look at the picture at the top of this blog entry. Gamma attenuation is in yellow on the left. Look carefully - do you see "spikes"on the graph? They were created by the plastic covers and air between two core segments.

The other parameter measured with the Geotek Logger is "Magnetic susceptibility". This is represented by the green line on the picture at the top of this blog entry. As the core segment is pushed down the track, it first encounters the gamma rays and then a magnetic field. In the Geotek logger picture above, notice the white rectangle with a round opening for the core to pass through. It has a red support strap holding it in place. A magnetic field is generated in the ring. If the material within the core is non-magnetic the sensor will detect a weakening of the magnetic field. If the core material passing through is magnetic - even only somewhat - a strengthening of the magnetic field is detected.

So why are some of these muds magnetic and others not?

This question is remarkably complex. The basic sources of magnetic materials are from volcanic materials and land materials. Volcanoes emit varying degrees of iron-rich matter which can flow or be blown over the ocean, settling to the sea floor and adding to the sequence of sediment there.

Land materials are introduced via rivers, wind and icebergs. The icebergs are particularly relevant for this research cruise as they are particularly climate dependent. When there is a great deal of ice on the planet, icebergs, laden with mineral fragments from the land, drift with the ocean currents, melting and dropping the small rocks
into deep ocean water. Climate scientists refer to these as "IRD"s: Ice Rafted Debris, . They are distinctly different than other deep ocean sediments because they tend to be larger and angular. Once free from the ice the rock fragments settle to the sea floor atop other marine sediments and are buried by more marine sediments.

The marine sediments that the chief scientist is looking for are the remains of tiny organisms that once lived in the upper regions of the ocean. So while he's not particularly interested in the sediments from the land, they do contribute to our understanding of Earth's climate past.

The picture to the right shows a pile of cores that were generated from only one Long Core sampling event! They're strapped down to prevent them from getting too carried away with the motion of the ocean! Right now with our coring and transit schedule, much of the logging on the Geotek will be done while we are underway so we need to be extra careful that the cores are tied down!







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