On splitting rank of non-compact type symmetric spaces and bounded cohomology

Let $X=G\mathrm{/}K$ be a higher rank symmetric space of non-compact type, where $G$ is the connected component of the isometry group of $X$. We define the splitting rank of $X$, denoted by $\text{srk}(X)$, to be the maximal dimension of a totally geodesic submanifold $Y\subset X$ which splits off an isometric $\mathbb{R}$-factor. We compute explicitly the splitting rank for each irreducible symmetric space. For an arbitrary (not necessarily irreducible) symmetric space, we show that the comparison map $\eta :H_{c,b}^{\ast }(G,\mathbb{R})\to H_c^{\ast }(G,\mathbb{R})$ is surjective in degrees $\ast \ge \text{srk}(X)+2$, provided $X$ has no small direct factors.