{"id":255,"date":"2011-01-20T11:11:18","date_gmt":"2011-01-20T15:11:18","guid":{"rendered":"http:\/\/web.colby.edu\/colbyatsea\/?p=255"},"modified":"2011-01-20T12:43:36","modified_gmt":"2011-01-20T16:43:36","slug":"sampling-at-sea-everyone-must-obey-the-bottle-cop","status":"publish","type":"post","link":"https:\/\/web.colby.edu\/colbyatsea\/2011\/01\/20\/sampling-at-sea-everyone-must-obey-the-bottle-cop\/","title":{"rendered":"Sampling at Sea: Everyone Must Obey the Bottle Cop"},"content":{"rendered":"
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Rosette Sampler with 12 bottles<\/p><\/div>\n

In one of my earlier posts I described the scheduling challenge of stopping to take samples while still moving the ship eastward toward Cape Town.\u00a0\u00a0 We are now at station 22 out of a total of 120 stations.\u00a0\u00a0 This puts us about one day behind schedule and Barney has decided to eliminate six stations to put us back on track and to allow for at least one day of bad weather.\u00a0\u00a0 The crew doesn\u2019t like to deploy gear over the side when the wind is blowing over forty knots, and any wind over thirty makes sampling VERY interesting.\u00a0\u00a0\u00a0 It has been blowing between twenty to thirty knots for most of the trip and we are getting pretty good at collecting samples in rough weather.<\/p>\n

The scientists on the ship use at least five different sampling systems.\u00a0 As a bit of background, it is important to know that the ocean is not uniform top to bottom.\u00a0 The surface water is warmer than the deep water and can have very different concentrations of oxygen, nutrients, and dissolved metals.\u00a0\u00a0 On this cruise we use different sampling gear to collect samples from just a few centimeters below the surface to over 5000 meters in depth.<\/p>\n

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Lanyard hooks at top of rosette<\/p><\/div>\n

Most of our samples are taken with Niskin bottles.\u00a0\u00a0 Niskin bottles are heavy PVC tubes with top and bottom caps connected with a strong piece of surgical tubing.\u00a0 The top and bottom are held open with a lanyard that can be \u201ctriggered\u201d or released at depth.\u00a0\u00a0 When the lanyard is released the end caps snap closed capturing a water sample.\u00a0\u00a0 For most of our samples we use a large steel rosette that holds 12 Niskin bottles.\u00a0\u00a0 The center of the rosette has a lanyard release mechanism that is controlled by the scientists on the ship.\u00a0\u00a0 Using the rosette system we can collect samples from 12 different depths.\u00a0\u00a0 The rosette also has a sensor package to measure depth, temperature, salinity, dissolved oxygen, and a number of optical properties.\u00a0 The scientist in charge of the water cast records sensor data as the rosette is being lowered into the ocean.\u00a0 Using the sensor data, interesting features of the water column are identified and the sample depth for each of the 12 bottles is determined.\u00a0\u00a0 The water samples are collected as the rosette is raised to the surface.<\/p>\n

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Profile of oxygen, temperature and density as a function of depth<\/p><\/div>\n

We are using twelve, twenty liter Niskin bottles on the rosette.\u00a0\u00a0 That means that we must lift over 500 pounds of water plus 300 pounds of rosette out of the ocean and onto the deck of a rolling ship at the end of each cast.\u00a0 The short video below shows a rosette being deployed and then recovered on the Melville.\u00a0 It takes six people to collect samples using the rosette; the Captain to keep the ship stationary, the winch operator to raise and lower the rosette, and four people on the deck to hook the rosette and guide it to the deck.<\/p>\n\r\n\r\n