Elaine Spencer and Philip Woodworth
Permanent Service for Mean Sea Level
Bidston Observatory, Birkenhead, Merseyside L43 7RA, U.K.

The new Implementation Plan for GLOSS published in 1997 describes how the GLOSS Core Network (GCN) is intended to provide a worldwide baseline network for global sea level monitoring. The GCN consists of 287 stations around the world as shown in Figure 1.  The symbols in the figure indicate which 'status category' each station falls into, using the year of the latest data entered into the Permanent Service for Mean Sea Level (PSMSL) databank as a guide:

Category 1: 'Operational' stations for which the latest data is 1994 or later;
Category 2: 'Probably operational' stations for which the latest data is within the period 1984-1993;
Category 3: 'Historical' stations for which the latest data is earlier than 1984;
Category 4: For which no PSMSL data exist.

A major difficulty with regard to Africa and South America is immediately apparent. In brief, many stations in these continents are not contributing data to the PSMSL as regularly as those from other parts of the world.  However, the situation is far from uniform.   For example, the Pacific coast of South America provides data regularly, unlike large parts of Northeast South America. South and East Africa provide more data than West Africa.
Figure 2 leads to similar conclusions but based on a larger number of gauges than in the GCN. This figure shows all the stations from which the PSMSL received data in 1998 from national sea level authorities, irrespective of whether the stations are in the GCN or not. (These data will clearly have been acquired by the authorities in years prior to 1998 but the data values arrived at the PSMSL in that year).  The large gaps in data receipts from Africa and South America are similar to those of Figure 1.
The reasons for the gaps can be different in each country. For example, in West Africa and parts of East Africa, the first issue is simply the provision by some means of the tide gauges themselves. On the other hand, we understand that in Brazil, for example, the gauges exist at many locations but that the data are not being conducted routinely through processing streams such that they are delivered finally to the PSMSL. In Venezuela, Madagascar and some other counties, a major problem is associated with the lack of good local GLOSS Contacts or communication links.
The remaining gaps in the GCN are unacceptable from an international standpoint. However, they should also be unacceptable from a national point of view as well, as local agencies will not have available the information  they  need  for  studies   of a range of coastal processes. If help is required from other organisations (perhaps by means of bi-lateral assistance arranged through the Intergovernmental Oceanographic Commission), countries should not be hesitating to make the necessary links. If training is an issue, then countries should apply to have one of their candidates attend one of the annual GLOSS training courses.
It is to be hoped that GLOSS and associated programmes (such as the Coastal Module of the Global Ocean Observing System) will lead to more intensive sea level recording and research throughout Africa and South America. The Afro-America GLOSS News is to be congratulated for publicising progress and identifying problems in these regions.

Web Pages on GLOSS

Readers might like to keep in touch with GLOSS and other sea level information via the PSMSL web pages at:
and read the GLOSS Bulletin at: