MoF: Sea Surface Temperature and Sea Surface Salinity

[timvdstap]

MeasurementType

sea_surface_temperature || sea_surface_salinity

Issue

From my understanding there is currently not a P01 term for sea surface temperature or sea surface salinity. In P01 there is temp of water body and salinity of water body, but nothing specific to the sea surface. There's P07 definitions: sea_surface_temperature and sea_surface_salinity.

Proposed definitions: sea_surface_temperature: Sea surface temperature ("SST") is the temperature of sea water near the surface (including the part under sea-ice, if any).

Mappings could include: P06:UPAA | Degrees Celsius P06:UPKA | Kelvins P02:TEMP | Temperature of the water column

sea_surface_salinity: Sea surface salinity ("SSS") is the salt content of sea water close to the sea surface. This term does not imply any particular method of calculation. The units of sea surface salinity are dimensionless and the units attribute should usually be given as parts per thousand.

Mappings could include: P06:UUUU | Dimensionless P02:PSAL | Salinity of the water column B39:salin | sea surface salinity

[JoBeja]

Dear Tim, From the emof point of view, the recommendation is to only use P01 terms and not other collections like P07. This is because if searching functionalities are to be implemented on parameters, it's easier if we have a consistent approach to how we map parameters to the corresponding codes. The temperature code you mention (TEMPR01) encompasses the whole water column, why do you need something applicable only to the sea surface? Regarding salinity, you mention a code which has units of ppt, the code that would apply, based on the information you shared, is PSALPR01, which is dimensionless. As the temperature code, it covers the water body, it's not limited to the sea surface.

If you want to check all the water temperature/salinity codes, you can check P02 https://vocab.nerc.ac.uk/collection/P02/current/TEMP/ and https://vocab.nerc.ac.uk/collection/P02/current/PSAL/ (apologies if you already knew this)

Looking forward for the BODC team's comments and their view on your request.

[timvdstap]

From my understanding (I'm not an oceanographer) temperature and salinity measurements specific to sea surface are common practice in oceanography and other standards often have specific definitions for these terms that differ from the measurements associated with the overall (sea) water column (see e.g., CF Conventions standard names). I would imagine that having controlled vocabulary specific to those terms would benefit interoperability of the data in OBIS with other databases.

As for salinity, I think that's defined as the grams of salt per 1000 grams of water (i.e., ppt), wherein approx. one gram of salt per 1000 grams of water is also defined as one practical salinity unit (PSU), which is dimensionless. This might give a more clear indication of the differences between both: Seabird PSU vs ppt definition.

[JoBeja]

Hi, The terms TEMPPR01 and PSALPR01 (and some others like these) encompass the whole water column, from surface to the deepest depth. There is no need for a specific term that is applied only to the sea surface. For salinity, unless the measurements are explicitly collected in mass units (like in the code you have identified), you can use PSALPR01 or PSALZZXX for example. We (at EurOBIS) usually receive salinity in dimensionless units, so would use PSALPR01 in most cases. As a general rule of thumb, for physical oceanography parameters, it is advisable that you use the generic term that fits the data. If none can be found but there is a more specific term that describes the measurement, that's the one to choose. Hope this helps.

[danibodc]

Hi,

We had a brief discussion about this yesterday, but Gwen is now away for the next 10 days so thought I would provide a summary of what was discussed.

We have previously defined the sea surface microlayer or skin in P01 which were specific to satellite measurements: https://vocab.nerc.ac.uk/search_nvs/P01/?searchstr=microlayer&options=identifier,preflabel,altlabel,status_accepted&rbaddfilter=inc&searchstr2=

Overall this would be quite difficult to define, as the depths involved will differ depending on the method. For shipboard underway systems this might be the top 5 or so metres, satellites the top few millimetres, etc.

In the past there has been an internal decision not to try and define this. But Gwen can see a business case for this in the future considering it has been defined elsewhere in P07 and as an Essential Ocean Variable - albeit with not very clear definitions of the depths involved. Would therefore need to add the various methodologies to make this clear.

To be continued once Gwen is back!

[JoBeja]

Thanks Dani, Indeed, going forward with this would require a good definition because the proposed definition is also not precise (in my view) as ice can have varied thickness. Would the immediate water layer beneath it be considered akin to sea surface if the ice was meters thick? Let's wait for Gwen.