What would happen if phytoplankton of an ocean is completely destroyed for some reason ? 1. The ocean as a carbon sink would be adversely affected. 2. The food chains in the ocean would be adversely affected. 3. The density of ocean water would drastically decrease. Select the correct answer using the codes given below :

Phytoplankton are the primary producers of the marine ecosystem, forming the base of the food chain [3]. Their destruction would collapse the entire marine food web, as they provide organic material for all higher trophic levels, including zooplankton and fish [1]. Furthermore, phytoplankton are critical for the biological carbon pump, responsible for transferring carbon dioxide from the atmosphere to the ocean depths [2]. They fix approximately 50 billion tons of carbon annually, and their loss would severely impair the ocean's capacity to act as a carbon sink [3]. However, the density of ocean water is primarily determined by temperature and salinity (thermohaline factors) rather than biological components like microscopic phytoplankton. While they influence biogeochemical cycling, their complete removal would not 'drastically decrease' the physical density of the water itself. Therefore, only statements 1 and 2 are correct.

Sources

1. [1] Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 3: MAJOR BIOMES > Food Chains in Marine Biomes > p. 33
2. [3] https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/phytoplankton
3. [2] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 14: Marine Organisms > The Carbon Cycle and climate change > p. 208