Criscimagna_Ellie_Lab4

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University of Miami *

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112

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Apr 3, 2024

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MSC 112 Lab 4, Temperature, Salinity, and Density Lab September 21, 2023 Ellie Criscimagna Purpose : Density is one of the most important properties in relation to motion of the ocean. Even small changes can create strong currents. While density is very important, salinity is another critical specification. Along with temperature, salinity controls density, therefore, controlling the differentiation or stratification of the ocean and its circulation. Salinity is measured as a concentration of 35 grams of salt per kg of water or in other words 35 parts per thousand. The most common units of salinity are PSU or practical salinity units. Salinity is often measured through electrical conductivity, however, conductivity is also affected by temperature, and therefore temperature must be known. With an instrument known as the CTD (conductivity-temperature-depth), the conductivity and temperature are used to measure salinity at different depths. Density is measured as g/cm 3 . Solutes have greater mass than water, so density increases with salinity. Density also varies with changes in temperature, as well as pressure and depth. Density of fresh water is 1 g/cm 3 and the density of seawater is typically just above 1 g/cm 3 , so to simplify the measurement. Sigma-t is calculated as (seawater density - 1.0)*1000. Therefore, a σt of 20.00 is equivalent to 1.020 g/cm 3 . To simplify all of the above, density of the ocean is a crucial property in terms of ocean movement. However, density is affected by salinity, temperature, and pressure/depth, so it is important to measure these three properties to get an accurate representation of the density.
Methods : Part I. First, a container with a removable divider was used. One half was filled with fresh water and the other half was filled with seawater. A conductivity meter was then used to measure the salinity and temperature of the two solutions. These measurements were then placed on a T-S (temperature-salinity) diagram which calculates density using isopycnals. After connecting the two dots, the average density was predicted. Different dyes were placed in the two solutions to differentiate them before the divider was removed. The behavior of the two different water solutions was observed. Then, the solution was mixed thoroughly and the conductivity meter was used to measure the exact temperature and salinity. A density calculator was used to measure the exact density at a pressure of zero. Part II. A table was provided with pressure (dbar), temperature (˚C), and salinity (‰). Then a density calculator was used to fill in the column labeled ( σt).
Results : Part I. Figure 1. As seen in Figure 1., the freshwater measured 0.16‰ and 20.2˚C, the saltwater measured 30.8‰ and 8.9˚C, the mixed solution was estimated to be ~16.0‰ and ~15˚C, and the mixed solution was measured to be 17.03‰ and 18.1˚C. In terms of density relative to the isopycnals, the freshwater measured just under 1.000 g/cm 3 , the saltwater measured ~1.025 g/cm 3 , and the mixed solution was ~1.013 g/cm 3 . However with the use of a density calculator, the density of the mixture was measured to be 1.012585 g/cm 3 , or a σt of 12.585.
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