The 'conservative' behavior of an ion in seawater (constant concentration/ratio regardless of location) reflects a long oceanic residence time relative to ocean mixing time, typically because the ion is not significantly consumed or released by biological processes; non-conservative ions like Ca2+ are actively cycled through biological calcification (shell/skeleton formation) and dissolution, causing their concentrations to vary spatially and with depth.
Sodium (Na+) behaves conservatively in seawater because it is essentially not taken up or released by biological processes (negligible biological uptake), so its concentration is...
Full option-by-option analysis available to enrolled students.