Scientific understanding, prediction, and communication to stakeholders are common objectives of ocean simulations and observing campaigns. Achieving these objectives can be greatly facilitated by advanced tools for exploring dynamic three-dimensional ocean data. Many scientific visualizations of spatiotemporal simulations rely on static two-dimensional representations that omit one or more spatial dimensions, potentially obscuring important features and relationships. A toolkit capable of creating coherent three-dimensional visualizations of ocean processes should move beyond isolated two-dimensional views and support the exploration of increasingly high-resolution simulations and large multidisciplinary observational data sets. In this work, we present 3DSeaVizKit, a visualization toolkit that processes multidisciplinary oceanographic data in a modular and computationally efficient manner to create portable, web-based, interactive 3D visualizations. Built upon the Plotly JavaScript library, the toolkit enables exploratory analysis of complex ocean fields directly within a web browser. We provide a software pipeline tailored to the computational demands of multivariate 3D ocean visualization and demonstrate its utility for revealing transport pathways, coherent structures, circulation features, biogeochemical acidification interactions, subduction dynamics, and forecast uncertainties in high-resolution ocean simulations. The toolkit supports scalar fields such as temperature, salinity, and biogeochemical tracers; vector fields such as velocity and vorticity; and Lagrangian products including trajectories, flow maps, and coherent structures. Applications include the visualization of the Loop Current system and eddy interactions in the Gulf of Mexico, subduction processes and forecast uncertainties in the Alboran Sea, coupled biogeochemical and ocean acidification dynamics in Massachusetts Bay, and transport pathways and coherent structures around Nantucket and Martha’s Vineyard.