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Friday 7 May 2004, 11.30 am (Tas time)
CSIRO Auditorium, Hobart
and via videoconference to Floreat and Cleveland
Richard Matear
CSIRO Marine Research, Hobart
Response of Ocean Ecosystems to Climate Warming
We examine six different coupled climate model simulations
to determine the ocean biological response to climate warming between
the beginning of the industrial revolution and 2050. We use vertical
velocity, maximum winter mixed layer depth, and sea ice cover to define
6 biomes. Climate warming leads to a contraction of the highly productive
marginal sea ice biome by 42% in the northern hemisphere and 17% in
the southern hemisphere; and an expansion of the low productivity permanently
stratified subtropical gyre biome by 4.0% in the northern hemisphere
and 9.4% in the southern hemisphere. In between these, the subpolar
gyre biome expands by 16% in the northern hemisphere and 7% in the southern
hemisphere, and the seasonally stratified subtropical gyre contracts
by 11% in both hemispheres. The low latitude (mostly coastal) upwelling
biome area changes only modestly. Vertical stratification increases,
which would be expected to decrease nutrient supply everywhere, but
increase the growing season length in high latitudes.
We use satellite ocean colour and climatological observations to develop
an empirical model for predicting chlorophyll from the physical properties
of the global warming simulations. Four features stand out in the response
to global warming: (1) a drop in chlorophyll in the North Pacific due
primarily to retreat of the marginal sea ice biome, (2) a tendency towards
an increase in chlorophyll in the North Atlantic due to a complex combination
of factors, (3) an increase in chlorophyll in the Southern Ocean due
primarily to the retreat of and changes at the northern boundary of
the marginal sea ice zone, and (4) a tendency towards a decrease in
chlorophyll adjacent to the Antarctic continent due primarily to freshening
within the marginal sea ice zone.
We use three different primary production algorithms to estimate the
response of primary production to climate warming based on our estimated
chlorophyll concentrations. The three algorithms give a global increase
in primary production of 0.7% at the low end to 8.1% at the high end,
with very large regional differences. The main cause of both the response
to warming and the variation between algorithms is the temperature sensitivity
of the primary production algorithms. We also show results for the period
between the industrial revolution and 2050 and 2090.
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