High trait positive affect (PA) protects against depressive symptoms through cognitive responses such as rumination. However, how rumination in response to positive emotions (positive rumination) protects against depressive symptoms while rumination in response to negative emotions (brooding) predicts depressive symptoms is poorly understood. We hypothesized that (a) positive rumination and brooding represent a shared cognitive process of affect amplification on distinct affective content and (b) less brooding and greater positive rumination would distinctly mediate greater trait PA in predicting fewer depressive symptoms. Our prospective design among 321 adults first compared three confirmatory factor analysis models of the relationship between brooding and positive rumination. We then utilized structural equation modeling to examine whether brooding and positive rumination mediated the relationship between trait PA and depressive symptoms, controlling for baseline depressive symptoms, trait negative affect (NA), and the distinct effects of each mediator. Results supported a conceptualization of brooding and positive rumination as distinct but related constructs, represented as a common process of affect amplification to explain how rumination may amplify resilience or risk in predicting depressive symptoms (χ = 195.07, Δχ = 8.78, p < .001, CFI = .91, RMSEA = .07). Furthermore, positive rumination and brooding were distinctly predicted by trait PA, suggesting that trait PA exerts distinct effects on protective and risk forms of rumination. Less brooding mediated the relationship between greater trait PA and fewer depressive symptoms (β = -.04, p = .012), but positive rumination did not (β = .02, p = .517). Rumination may represent a protective and a risk factor, which may better enable individuals who brood to redirect their rumination on positive content and thereby reduce their risk of depressive symptoms.