The answer is the second one (b): Chemical oceanographer.
Explanation for each option:
a. Physical oceanographer: This type of scientist studies the physical properties and processes of the ocean, such as currents, waves, and tides, rather than chemical properties like salinity and dissolved oxygen.
b. Chemical oceanographer: This is the correct answer. Chemical oceanographers focus on the chemical composition of seawater, including salinity, dissolved oxygen, and nutrients, which aligns with the activities described in the question.
c. Marine biologist: Marine biologists study the organisms living in the ocean and their interactions with the environment, rather than the chemical properties of the water itself.
d. Marine geologist: Marine geologists study the structure and composition of the ocean floor and the processes that shape it, not the chemical properties of seawater.
In summary, a marine scientist studying salinity, dissolved oxygen, and nutrients would be classified as a chemical oceanographer.