Date: Wed, 27 Feb 2002 19:36:00 +0000 From: "Sirovic, Ana" Subject: Message 13 Content-Type: text/plain; charset="us-ascii"; format=flowed February 27 2002, 16:00 64 degrees 25.37 S latitude 62 degrees 45.36 W longitude (Gerlache Strait) Air surface temperature: 4.0 degrees C Sea Surface Temperature (SST): 1.3 degrees C Wind speed: 2 knots, 350 degrees Air pressure: 984.7 mBar Hello! We have left Palmer Station this morning and our on our way back to Punta Arenas. Our passenger number has increased slightly, as we are taking 8 people from the station back home. On the way to Palmer we have deployed one ARP under somewhat rough conditions. But it wasn't bad enough for us to have to find an alternative spot, which is good news because this way we ge t2 year record at the same location. The day at Palmer was spent in various activities: hiking up the glacier, going out on a zodiac ride, some humpback biopsying, and 3 of us (Ryan, Jim, and I) even decided to go for a swim in the Southern Ocean (only wearing our swimsuits). I must say that the ocean was a bit cold, but it was good fun! At the end of the day there was pizza for everyone in the bar, and entertainment in the bar went on for quite a while into the night. It was a good port call! As the science is slowly wrapping up, the only things left are one ARP deployment and marine mammal observations while underway, I feel like there is one instrument I have neglected to mention so far: the CTD. Being how this is the most important oceanographic instrument, a grandmother of oceanography in a way, and how I have only glossed over (and thus possibly misrepresented) how some of the most important measurements in the ocean are made, today is the day when I get to tell you all about them! Today's feature photo, of course, is CTD begin cast over the side of the Gould, courtesy of Bob Beardsley. The biggest part of the CTD is the rosette with 24 bottles. These are used for collecting water samples at different depths (which can be analyzed for chlorophyll, nutrients, etc). But the 'heart' of a CTD is the set of instruments you can see at the bottom, just above the dark ring. These contain pressure, temperature and conductivity sensors. Temperature is the only directly measured value that is used in characterization of the water masses. Depth and salinity are determined from the measured pressure and conductivity, respectively. Other values that can be obtained from these measurements are density (determined from temperature and salinity) and sound speed (mostly determined from temperature and pressure). Additional sensors can be added to a CTD but are not always used. Other parameters that can be measured in this way are transmissivity of the water (i.e. how much light can pass through the water, a way of determining how much 'stuff' there is, flourescence (as a proxy for chlorophyll), oxygen content... During this cruise we did a total of 9 CTDs (at all the locations of the oceanographic moorings). We should be getting into the Drake passage during the morning tomorrow. Then it is just 3 more days to Punta Arenas. I'm still hoping for that glassy crossing! Ana