Geographers analyzed 175 satellite images of ocean colour, which is an indicator of phytoplankton productivity at the ocean’s surface, and found that giant icebergs are responsible for storing up to 20 percent of carbon in the Southern Ocean. The researchers discovered that melting water from giant icebergs which contains iron and other nutrients, supports hitherto unexpectedly high levels of phytoplankton growth.

Correct Option (1)

Assumption 1 is valid. The passage explicitly states that melting water from giant icebergs releases iron and other nutrients, which supports "unexpectedly high levels of phytoplankton growth." Phytoplankton are primary producers, forming the base of the marine food web. Therefore, an increase in phytoplankton productivity directly impacts the primary productivity and subsequent food chains within the Southern Ocean ecosystem.

Incorrect Options:

Assumption 2 is invalid. The passage discusses the role of giant icebergs in phytoplankton productivity and carbon storage within the Southern Ocean. It does not provide any information or imply a connection between the melting of giant icebergs and global climate change effects or a broader impact on world fisheries. The scope of the information presented is confined to the local ecological effects in the Southern Ocean.

Option (2) is incorrect because Assumption 2 is not supported by the passage.

Option (3) is incorrect because Assumption 2 is invalid.

Option (4) is incorrect because Assumption 1 is valid and directly supported by the passage.