We live off of investments in the stock market, and give Maaser Ksafim from each year’s profits. This year we will not have any profits, and although -- hopefully -- we will not be completely wiped out, we will have significant losses. Are we still obligated to give Maaser, and if so, how do we calculate the amount to give?

You are not required to give maaser this year. The ribono shel olam shall replenish your losses.