Bright line

The dark horizon
that surrounds
this diminishing ground
this shrinking island
rises with the tide.
I can, if I think
remember when
I couldn't see it
couldn't imagine it
now
the telling tang
in the air
changes,
I'm aware always
of that inexorable
bright black line,
shimmering at
glancing edges
of my vision
even in sleep,
and graying sun
reflects from tops
of breakers rolling in
toward the centre,
and I know that soon
this last outcrop
of solid rock
will be awash
then engulfed
and I must swim
back.