Geoscience Reference
In-Depth Information
adding CO
2
from contact heating and decarbona-
tion (and sulphur dioxide, a second source of acid-
ity; e.g. Knoll
et al.
2007 ; Ganino and Arndt 2009 ;
Iacono-Marziano
et al
. 2009). Today, as much as 10%
of all CO
2
released from mid-ocean ridges, volca-
noes, and convergent plate margins can be attrib-
uted to Mount Etna, a volcano developed on
extensive platform carbonates (Marty and Tolstikhin
1998). Moreover, Siberian Trap magmas and lavas
intruded into and extruded onto extensive late
Palaeozoic peat and brown coal deposits, generat-
ing large additional l uxes of CO
2
and thermogenic
methane (CH
4
) to the atmosphere (Retallack and
Jahren 2008). Thus, both massive volcanism and the
geological context of the volcanism contributed to
rapid CO
2
(and SO
2
) increase, driving global warm-
ing and ocean acidii cation.
End-Permian extinctions in the oceans were
extensive but not random. Knoll
et al
. ( 1996 ) docu-
mented a strong pattern of selectivity with respect
to fundamental physiological and ecological fea-
tures of the biota. Hypercalcii ers and other animal
and algal groups with limited capacity to pump
ions across membranes show nearly complete
extinction, but groups better able to modulate the
composition of l uids from which carbonate skele-
tons were precipitated survived differentially well.
Further, taxa characterized by high rates of exercise
metabolism and well developed respiratory and cir-
culatory systems survived better than anatomically
simple hypometabolic taxa, and infauna survived
better than epifauna. In 1996, the term 'ocean acidi-
i cation' was not a part of palaeontology's vocabu-
lary, but an extensive physiological literature
suggested that observed patterns of extinction and
survival matched predictions made on the basis of
organismic tolerance to and compensation for
hypercapnia (elevated CO
2
in internal l uids).
Stimulated by environmental concerns, a large
body of research on marine organisms has accumu-
lated during that past 14 or so years, prompting a
number of general statements about vulnerability
to hypercapnia and increasing seawater acidity.
For example, Widdicombe and Spicer (2008, p. 194)
wrote:
acidii cation to impact on individuals at a physi-
ological level particularly through disruption of
extracellular acid-base balance. There is some
weak evidence that the severity of this impact
could be related to an organism's phylogeny
suggesting that both species and taxonomic
measures of biodiversity could be reduced.
However, there is also evidence that potential
species extinctions will be more strongly gov-
erned by factors related to an organism's lifestyle
and activity (e.g. infaunal v epifaunal, deep v
shallow, deposit feeder v suspension feeder, large
v small) than by its phylogeny. There is also huge
uncertainty as to what extent organism adapta-
tion or acclimation will mitigate the long term
effects of ocean acidii cation.
And, in a comparison of marine animals more and
less tolerant of hypercapnia, Melzner
et al
. ( 2009 )
proposed that 'All more tolerant taxa are character-
ized by high (specii c) metabolic rates and high lev-
els of mobility/activity'. These conclusions about
the present recall observed patterns of end-Permian
extinction.
In the light of new experimental results, especially
those on ocean acidii cation and calcii cation, Knoll
et al
. (2007) returned to the Permian-Triassic data,
focusing largely on inferred differences in the physi-
ology of skeleton formation. This exercise requires
physiological inference from fossil remains. From fos-
sils, we can establish the lifestyles of ancient organ-
isms and, to the extent that phylogeny is a good
predictor of anatomy and physiology, those can be
inferred, as well. Widdicombe and Spicer (2008) rea-
sonably stress that strict phylogenetic focus in ocean
acidii cation research may be limiting. Nonetheless,
in terms of broad physiological attributes important
for assessing hypercapnia and ocean acidii cation,
many species within marine classes and phyla share
fundamental features of metabolism and (key to
interpreting fossils) skeletal biosynthesis. Thus, while
individual species may respond variably to increased
CO
2
load, groups like corals will have a statistical ten-
dency to respond coherently—and differently from,
say, molluscs. And what the fossil record provides is
a statistical digest of extinction and survival.
Knoll
et al
.'s (2007) focus on skeletal physiology
once again showed evidence of dramatic variations
We conclude that there is clear potential for
the chemical changes associated with ocean
