[Taxacom] Pacific biogeography

JF Mate aphodiinaemate at gmail.com
Mon Dec 17 15:01:15 CST 2012

The email feels like it was meant for someone else. Although our
improved understanding of the geological history of the Pacific has
helped to solve some problems (i.e. taxa older than the islands they
currently inhabit) it is not very clear to me how seafloor subsidence
(a well known phenomenon BTW) would significantly alter the
biogeographical status quo or how this can be invoked to support
panbiogeographical theories. Any ideas?


On 17 December 2012 09:07, Michael Heads <m.j.heads at gmail.com> wrote:
>  Dear Taxacomers,
> A few months ago we were debating Hawaiian biogeography. In a discussion of
> this topic in the book cited below, I mapped the 2000, 4000 and 5000 m
> isobaths of the central Pacific. O’Grady et al. (Taxon 61: 702. 2012) have
> now suggested that this was ‘disingenuous’, because sea-level has not
> dropped by more than 100 m or so. But the authors overlooked the *1000s* of
> meters of subsidence that the Pacific seafloor itself has undergone. This
> is well-known to geologists and I discussed it in the book.
> As the seafloor has drifted away from the East Pacific Rise - the spreading
> ridge that produced it - it has cooled (increasing its density) over tens
> of millions of years and has subsided by these large amounts. This has
> led to the submergence of most of the islands that were perched on it.
> The current high islands are new ones. Evidence for the subsidence is seen
> in the numerous atolls of the region, formed by coral reefs which have
> grown as the seafloor subsided. The many flat-topped seamounts (guyots)
> located north, south, east and west of Hawaii are former high islands that
> were eroded to sea-level before being submerged with the tectonic
> subsidence.
> Michael Heads
> --
> Wellington, New Zealand.
> My new book: *Molecular panbiogeography of the tropics. *
> University of California Press, Berkeley.
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