adding contour lines to pcolor plot

Hi everyone,

I'm trying to add contour lines at 13 degrees to my pcolor plot, but I get the following error:

Error using contour

Input arguments must be numeric or objects which can be converted to double.

Data in the contour code are attached and they are:

combine averages: 153x33 double

depth: 33x1 single

dateVector: 1x153 datetime

Here's my code:

t1 = datetime(2021, 5, 1)
t2 = datetime(2021, 9, 30)
dateVector = t1:t2
combinedaverages = [dailyaverages; dailyaverages06; dailyaverages07; dailyaverages08; dailyaverages09];
figure
pcolor(dateVector, depth, combinedaverages')
set(gca, 'YDir','reverse')
shading flat
ylim([0 70])
colorbar
hold on
contour(dateVector,depth,combinedaverages',[13 13],'k');