{"id":758,"date":"2021-07-07T10:25:37","date_gmt":"2021-07-07T14:25:37","guid":{"rendered":"https:\/\/wpstaging.whoi.edu\/site\/coastalgroup\/?page_id=758"},"modified":"2022-01-13T14:13:15","modified_gmt":"2022-01-13T18:13:15","slug":"ctd-conductivity-temperature-depth","status":"publish","type":"page","link":"https:\/\/www2.whoi.edu\/site\/coastalgroup\/about\/how-we-work\/field-methods\/ctd-conductivity-temperature-depth\/","title":{"rendered":"CTD (Conductivity, Temperature, Depth)"},"content":{"rendered":"\n\n\t

CTD (Conductivity, Temperature, Depth)<\/h1>\n\t

The water column is not merely an obstacle \u00a0to overcome when collecting sub-aqueous sediment cores. \u00a0There is a great deal we can learn about from the water that is of vital importance to understanding both the depositional environment and the relationship of that environment to the larger Earth systems. \u00a0The CTD (Conductivity, Temperature, and Depth) is one such device in our toolkit that allows us to quantify certain physical properties of the water ultimately aiding in our interpretation of the site.<\/p>\n

Conductivity refers to how condutive the water is to electrical current. \u00a0This serves as a proxy* for salinity. \u00a0More than simply knowing how fresh or salty a body of water of is, we’re interested in identifying the halocline. \u00a0The halocline is a distinct transition in the salinity of the water column (from lower above and higher below). \u00a0This informs us as to how mixed the bottom water is with the top water, how dynamic the site is at depth.<\/p>\n

Similar to the Halocline is the Thermocline. \u00a0Barring any geothermic influences water should decrease in temperature as depth increases. \u00a0The thermocline is an abrubt transition from less dense warm water, to denser (and saltier in a marine setting) colder water. \u00a0If there is no clear thermocline then again, the site is likely experiencing a high degree of mixing and flow.<\/p>\n

The CTD gives us the temperature and salinity values as profiles; measurements plotted by depth. \u00a0In order to do this the probe must have a way of calculating its depth through the water column. \u00a0Unlike the Chirp and Echo sounders that use sound pulses and time\/distance conversions to calculate depth the CTD has an internal pressure sensor that gives a precise depth measurements as it falls through the water column.<\/p>\n

In addition to the Conductivity and Temperature measurements the CTD also computer sound velocity.<\/p>\n

The speed of sound varies depending on the medium through which is passes. \u00a0The speed of sound at sea level is different than at the top of Mount Everest or inside an airplane or city bus owing to the various densities (and the associated acousitc impedence) of the atmosphere in those scenarios. \u00a0Water is denser than air, and colder saltier water is denser than warm fresh water.<\/p>\n

Sonar systems (like the Chirp, Hydrolite, and even our depth guns and fish finders) all use a fixed speed of sound to calculate depth. \u00a0Often that value is 1500m\/s as this is an acceptable value for most marine environments. \u00a0Yet in order to develop the precise bathymetric models that we use we need a more accurate sound velocity value specific to the location we’re working in at the time that we’re working. \u00a0The CTD gives us this value. \u00a0If the sound is faster or slower than 1500m\/s then the depths derived from the Two-Way Travel Time calculations are inaccurate, unless the correct sound velocity is used.<\/p>\n

Dissolved Oxygen (DO) is another physical property of the water that CTDs often measure. DO refers to the amount of oxygen in the water and speaks to how hypoxic (low Oxygen) or anoxic (no oxygen) the site may be. \u00a0Low oxygen levels are a sign of little to no mixing in the water column and suggests minimal bioturbation and a high degree of organic preservation.<\/p>\n\t\t\t\t\n\t\t\t\t\"CTD\"\n\t\t\t\t<\/a>\n\n","protected":false},"excerpt":{"rendered":"

CTD (Conductivity, Temperature, Depth) The water column is not merely an obstacle \u00a0to overcome when collecting sub-aqueous sediment cores. \u00a0There is a great deal we can learn about from the water that is of vital importance to understanding both the depositional environment and the relationship of that environment to the larger Earth systems. \u00a0The CTD…<\/p>\n","protected":false},"author":26,"featured_media":0,"parent":737,"menu_order":2,"comment_status":"closed","ping_status":"closed","template":"","meta":[],"_links":{"self":[{"href":"https:\/\/www2.whoi.edu\/site\/coastalgroup\/wp-json\/wp\/v2\/pages\/758"}],"collection":[{"href":"https:\/\/www2.whoi.edu\/site\/coastalgroup\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/www2.whoi.edu\/site\/coastalgroup\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/www2.whoi.edu\/site\/coastalgroup\/wp-json\/wp\/v2\/users\/26"}],"replies":[{"embeddable":true,"href":"https:\/\/www2.whoi.edu\/site\/coastalgroup\/wp-json\/wp\/v2\/comments?post=758"}],"version-history":[{"count":3,"href":"https:\/\/www2.whoi.edu\/site\/coastalgroup\/wp-json\/wp\/v2\/pages\/758\/revisions"}],"predecessor-version":[{"id":1422,"href":"https:\/\/www2.whoi.edu\/site\/coastalgroup\/wp-json\/wp\/v2\/pages\/758\/revisions\/1422"}],"up":[{"embeddable":true,"href":"https:\/\/www2.whoi.edu\/site\/coastalgroup\/wp-json\/wp\/v2\/pages\/737"}],"wp:attachment":[{"href":"https:\/\/www2.whoi.edu\/site\/coastalgroup\/wp-json\/wp\/v2\/media?parent=758"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}