The answer is certainly not. Mathematics is your friend.
The deepest point to which the ocean floor extends is over 3000 meters, but for the sake of simplicity, let's say on average, the ocean floor is 1000 meters deep.
So imagine the Earth as a giant sphere. The radius of the earth is roughly 6,380,000 meters. So imagine the outer 1000-meters of this giant sphere is water. To calculate the volume of this water we need:
Formula, volume of a sphere: 4/3 * pi * r^2
What we can do is calculate the total volume of earth, and subtract from it the volume of the non-water part, leaving us with a rough approximation of the volume of the oceans. But because the Earth is in actuality only ~70% water, we need to multiply this figure by .7.
In numbers:
([4/3 * pi * (6,380,000)^2] - [4/3 * pi * (6,380,000 - 1000)^2]) * .7
Throwing this into the calculator, we get: 5.1188 x 10^13 cubic meters of water. To get an idea of how big this is, 1 cubic meter = 1000 liters. To get a better idea of how big this is, let me type it out for you instead of using scientific notation:
Volume, Earth's ocean: 51,188,068,945,470,000 liters.
Yeah folks, over fifty quadrillion. Assuming every human urinates one liter into the ocean (and one liter is generous...you'd need a big bladder to do that), we'd have 6,500,000,000 liters of urine.
Ratio, ocean water to urine: 51,188,068,945,470,000 / 6,500,000,000 = 7,875,087.5
That is, for every one liter of urine excreted, there's over seven million liters of ocean water to match it. In essence, your little experiment will have no effect whatsoever on the temperature of the ocean.
On a similar note, the displacement caused by humans dipping into the water simultaneously will also be near-negligible. Assuming the average human displaces 20 liters of water (this is again being very generous), the amount of water displaced would be 20 * 6,500,000,000 = 13 billion liters.
Compared to the 50 quadrillion liters of water in the ocean to begin with, this displacement will have virtually no effect at all.
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