  Let $\mathbf{T} \equiv (T_1,\cdots,T_n)$ be a commuting $n$-tuple of
operators on a Hilbert space $\mathcal{H}$, and let $T_i \equiv V_i P \; (1 \le
i \le n)$ be its canonical joint polar decomposition (i.e.,
$P:=\sqrt{T_1^*T_1+\cdots+T_n^*T_n}$, $(V_1,\cdots,V_n)$ a joint partial
isometry, and $\bigcap_{i=1}^n \ker T_i = \bigcap_{i=1}^n \ker V_i = \ker P)$.
\ The spherical Aluthge transform of $\mathbf{T}$ is the (necessarily
commuting) $n$-tuple
$\hat{\mathbf{T}}:=(\sqrt{P}V_1\sqrt{P},\cdots,\sqrt{P}V_n\sqrt{P})$. \ We
prove that $\sigma_T(\hat{\mathbf{T}})=\sigma_T(\mathbf{T})$, where $\sigma_T$
denotes Taylor spectrum. \ We do this in two stages: away from the origin we
use tools and techniques from criss-cross commutativity; at the origin we show
that the left invertibility of $\mathbf{T}$ or $\hat{\mathbf{T}}$ implies the
invertibility of $P$. \ As a consequence, we can readily extend our main result
to other spectral systems that rely on the Koszul complex for their
definitions.
