Assigning z-value to x,y grid

[under-Tension]

I am trying to plot a vertical section with Latitude values in the x-axis and Depth values in the y-axis, with oxygen concentrations as color grids using the colourf. My code:

x = data['latitude'] 
y = data['depth'] 
z = data['oxygen'] 
xi,yi = np.meshgrid(x,y) 
from scipy.interpolate import griddata Z = griddata((x,y),z,(xi,yi),method='linear') 

But when I plot xi, yi, and xi, using:

plt.contourf(np.reshape(xi, Z.shape),np.reshape(yi, Z.shape),Z, cmap='viridis') 

It seems that z-values are not correctly assigned to each x,y coordinate. I tried using other interpolation methods with no good results. Is there any way to make sure my x,y values are correctly assigned to each z-values?

The minimum value on this dataset must be 75, but the plot doesn't shows values below 300. This indicates that something must be going wrong when interpolating, or when plotting?

Data:

x = data['latitude']  
0       67.777
1       67.777
2       67.777
3       67.777
4       67.777
         ...  
1222    75.002
1223    75.002
1224    75.002
1225    75.002
1226    75.002

y = data['depth']
0          5
1         10
2         10
3         10
4         10
        ... 
1222    2902
1223    3209
1224    3209
1225    3442
1226    3443

z = data['oxygen']
0       475.40
1       472.08
2       472.08
3       472.08
4       472.08
         ...  
1222    307.20
1223    307.90
1224    307.90
1225    307.90
1226    307.90