Let
$X$
be a normal and geometrically integral projective variety over a global field
$K$
and let
$\bar {D}$
be an adelic
${\mathbb {R}}$
-Cartier divisor on
$X$
. We prove a conjecture of Chen, showing that the essential minimum
$\zeta _{\mathrm {ess}}(\bar {D})$
of
$\bar {D}$
equals its asymptotic maximal slope under mild positivity assumptions. As an application, we see that
$\zeta _{\mathrm {ess}}(\bar {D})$
can be read on the Okounkov body of the underlying divisor
$D$
via the Boucksom–Chen concave transform. This gives a new interpretation of Zhang's inequalities on successive minima and a criterion for equality generalizing to arbitrary projective varieties a result of Burgos Gil, Philippon and Sombra concerning toric metrized divisors on toric varieties. When applied to a projective space
$X = {\mathbb {P}}_K^{d}$
, our main result has several applications to the study of successive minima of hermitian vector spaces. We obtain an absolute transference theorem with a linear upper bound, answering a question raised by Gaudron. We also give new comparisons between successive slopes and absolute minima, extending results of Gaudron and Rémond.