MERSEA and BOSS4GMES in-situ TAC (Coriolis)

Yearly averaged temperature and salinity anomalies vertical sections, zonal integration on global, Atlantic, Pacific and Indian ocean

Temperature and salinity  anomalies (figure 1) : 

     In the year 2007, the development of a strong La Nina event can be observed in the maps of temperature (Fig.3 temperature at 10 m depth), especially during the second half of the year. During the same time, a pattern of positive salinity anomalies occurs in the Pacific Warm Pool, extending into the central equatorial Pacific in the last season of the year (Fig.3 salinity at 10 m depth). But not only the Pacific near surface layer is marked with large scale variability patterns of the temperature and salinity anomaly field. Temperature anomalies in the northern Atlantic Ocean are distributed into a tripole pattern which is associated with the North Atlantic Oscillation atmospheric forcing. In the Indian Ocean, a basin wide meridional dipole pattern in salinity occurs in the first half of the year 2007.
     Different to the salinity field, amplitudes of temperature anomalies become strongest at 100m depth, with large signatures in the tropical Pacific and Indian Ocean (Fig.3 at 100 m depth). The pattern in the Pacific Ocean is triggered by the El Nino Southern Oscillation event, and the strong zonal temperature dipole in the Indian Ocean is connected to the so called Indian Ocean Dipole event. But also at greater depth, large regions of temperature and salinity anomalies can be observed, i.e. in the North Atlantic and in the southern oceans, especially in the Indian Ocean (Fig. 3 at 1000 m depth).

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Figure 1 : Zonal average of annual mean temperature anomalies for the global ocean and the different
ocean basins during 2003-2007. Anomalies are evaluated relative to a mean seasonal cycle of the same time period.

   

Strong interannual and long-term fluctuations occur in the temperature as well as in the salinity field in the upper 2000m depth of the global ocean (Fig.1). During the year 2003, mostly cool temperature anomalies can be observed on global average, strongly influenced by low temperature anomalies in the Atlantic Ocean. The measurements during the year 2007, however, are dominated by positive temperature anomalies on the global average suggesting a warming trend during that measurement period. This warming trend emerges in all three ocean basins.

Since only 5 years of measurements resolve global fluctuation patterns, the question cannot be answered wether this warming trend can be associated with long-term global fluctuations or global warming. But what the measurements clearly show is that changes of hydrographic anomalies occur on global scales for temperature, but not for salinity (Fig.2). The zonal averages of the salinity anomalies indicate large scale, regional patterns of interannual variability. In the Atlantic Ocean, salinity fluctuations reach down to more than 800m depth, whereas in the Pacific and Indian Ocean, salinity fluctuations are strongest in the upper 400m depth.

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 Figure 2 :  Zonal average of annual mean salinity anomalies for the global ocean and the different
ocean basins during 2003-2007. Anomalies are evaluated relative to a mean seasonal cycle of the same time period.

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depth level	10 m	100 m	1000 m
temperature
salinity

Figure 3 : maps of temperature and salinity anomalies in 2007 (3 month average) relative to 2003-2007 annual mean cycle at different depths.

Linear trends of heat and salt content :

    Strongest changes of global ocean heat content during 2003-2007 exist in the upper 500m depth of the tropical basin and in the upper 1000m at mid-latitudes (Fig.4). In the tropical
basin, 5-year changes of heat content in the Pacific Ocean mostly cause strong trends in the global average. This signatures can be associated to the development of a weak El Ni˜o in 2006, and a strong La Ni˜a in 2007. At northern and southern mid-latitudes, strong trends in the Atlantic Ocean dominate the global average. A similar distribution can be observed in the trend of global salt content (Fig.5). The most intense trends of global salt content occur in the upper 500m depth of the tropical basin, indicating a freshening tendency in the northern and a saltening in the southern hemisphere. This global signature is not only restricted to fluctuations in the Pacific Ocean, since trends of comparable strength exist also in the tropical Atlantic and Indian Ocean. In the extratropics, a global freshening tendency occurs in both hemispheres.

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            Figure 4 : linear trends (2003-2007) of heat content anomalies, vertical section, zonal integration.

Figure 5 : linear trends (2003-2007) of salt content anomalies, vertical section, zonal integration.

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