News sharing on social networks reveals how information disseminates among users. This process, constrained by user preferences and social ties, plays a key role in the formation of public opinion. In this work we analyze news sharing behavior on Twitter as bipartite news-user networks for two consecutive years of Argentinian major media outlets. Analysis of news networks revealed modular structure driven by semantic similarity of news content and homophilic media interactions, producing a fragmented media agenda. In particular, the two largest communities present a persistently polarized political leaning, reflected in the consumption of ideologically homogeneous groups of media outlets. On the other hand, the user networks show modules driven by similar profiles of news consumption, where core individuals have less diversified profiles, suggesting that the observed polarization could arise from lack of diversity to media exposure.