DELIVERABLE D2.1 - Ifremer

sections (Figure 5) of multiple hydrographic stations where a profiling package islowered through the water column.Figure 5. Icelandic Standard Sections. Since 1970 hydrographic measurements have been made on thesestations four times a year to depths exceeding 2000m, in winter (February/March), spring (May/June),summer (August/September) and autumn (October/November).[www.hafro.is/Sjora/ downloaded19/04/10].These types of measurements have been possible since the last decades of the 19 thCentury and over the last century a number of repeat sections became standard. Forthe long trans-basin sections the repetition of the standard section maybe as rare asonce per decade, while a few have become as frequent as once every 2 years and areperformed by international research programmes. Shorter sections relatively close tothe continental shelf can have a monitoring programme that requires repetition twicea year or seasonally (e.g. the Icelandic Standard Sections – Figure 5). The strengths ofthe standard section approach are (1) high quality repeated data, (2) high verticalresolution, and (3) wide spatial extent. Weaknesses are the regional coverage,temporal resolution and effort/costs. It also remains difficult to make measurementsnear the seabed and to resolve water column features at steep slopes. Standardsections sample the properties of the deep ocean very well but observing itsmovement is more difficult, not least because the platform itself is moving.Measurements of the deep velocity field are now possible using loweredinstrumentation but the most used methodology indirectly determines volumetransports based upon variations in the ocean density as determined by temperatureand salinity. Extensions to the traditional ship-based survey are those made bypowered autonomous vehicles carrying a package of sensors.Moored monitoring systemsMonitoring programmes of this type are diverse, and the types of measurementstend to be targeted at the particular process that is being monitored. Types includebottom landers, weather ships (continuously anchored ships) and in-line moorings.Strengths to this approach are the ability to focus on a particular process of interest12