Caloric expenditure depends on many variables when diving, but the main determinants are: 1. Caloric expenditure of baseline metabolism of the individual, 2. Metebolic requirements to maintain normothermia (influenceded by things like water temperature, body mass index, degree of insulation in gear, shivering, degree of peripheral vasodialation). 3.Metabolic requirements for physical activity (influenced by things like type and duration of physical activity, the individuals body habitus, and level of conditioning). Floating calmly in body temperature water should approximate baseline metabolic rate. Welding a cross-member on an oil rig in the North Sea, at depth, during a storm would yield a different calotric expenditure.
In the parameters of your particular question, there are too many variables that are not defined to be able to give you a good answer (your activity level, your BMI, water temp, what is your gear, physical conditioning, how efficiently you are performing your chosen diving activities, average heart rate).
One way to approximate your caloric expenditure (excluding temperature variables), would be to measure your heart rate when you are doing an activity of known calorie expenditure, and compare that to your heart rate during your particular dive. You would then have a rough idea of your physical activity level in relation to the activity level of your "calorie known" activity.
Hope this helps.