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Salinity and potential density in the 1/30-th-of-a-deg OFES snapshot

Salinity at 150 m across the North Pacific in the 1/30-th-of-a-deg OFES snapshot is shown in Fig. 1. The section of salinity at 19°N shown previously in this note and reproduced in Fig. 2, crosses eddies that bring large negative salinity anomalies from the eastern Pacific into the interior. This results in high horizontal variation in salinity (Fig. 2). The corresponding potential density σ is shown in Fig. 3. Notice that the vertical displacements (from the zonal mean depth) of the bottom of the layer of high salinity anomaly (between 200 and 250 m depth) seem to correspond well with those of the potential density, consistent with the observations of Johnson et al. (2010). It would be interesting, however, to know if the frequency of these vertical displacements are also consistent with the observations. To do that, we will need first to assess if these displacements are present in the 1/10-th-of-a-deg OFES model for which the temporal variations can be analyzed.

Salinity and potential density are also shown across a section at 22°N that spans approximatively the mostly-zonal trajectory of the Johnson et al.’s ARGO float (Figs. 4 and 5). For that particular time and region, the salinity appears more homogeneous horizontally (Fig. 1) than in the section at 19°N so that the zonal variations are smaller. The eddy variability seems also weaker as the vertical displacement of isopycnal surfaces are weaker (Fig. 5). Notice that, again, the bottom of the layer of high salinity and the local isopycnal surfaces stay mostly parallel.

Finally, notice that these vertical displacements seem to be rather meso than submesoscale, suggesting that, if these vertical displacements are the one seen in the observations. then eddy pumping, rather than submesoscale processes are important for the nitrate injections, at the condition that the stratification in the model is not shallower than in the observations –this needs to be checked though.

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Figure 1: Salinity at 150 m on Jan. 1, 2001 in the 1/30th-of-a-deg OFES model. The black lines show the zonal sections where salinity and potential density are shown in Figs. 2 to 5.

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Figure 2: Salinity along 19°N on Jan. 1, 2001 in the 1/30th-of-a-deg OFES model.

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Figure 3: Potential density σ along 19°N on Jan. 1, 2001 in the 1/30th-of-a-deg OFES model.

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Figure 4: Salinity along 22°N on Jan. 1, 2001 in the 1/30th-of-a-deg OFES model.

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Figure 5: Potential density σ along 22°N on Jan. 1, 2001 in the 1/30th-of-a-deg OFES model.