The correct statement is 2, as photosynthesis by phytoplankton in the oceans plays a critical role in the carbon cycle. These microscopic marine plants absorb carbon dioxide during photosynthesis, converting it into organic matter, which effectively reduces carbon dioxide concentrations in the atmosphere. Statement 1 is incorrect because carbon dioxide does not escape into the outer stratosphere; it primarily remains in the lower atmosphere. Statement 3 is also incorrect as polar ice caps do not actively "trap" air; they are more reflective of global climate changes rather than a significant factor in regulating atmospheric CO2 levels. Thus, the role of phytoplankton is crucial in mitigating atmospheric carbon through biological processes.