Australia: The Land Where Time Began |
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Capricorn Eddy – A Driver Prominent in the Ecology and Future of
the Southern Great Barrier Reef (GBR)
The study reported in this paper focuses on the Capricorn Eddy, a
mesoscale eddy feature, which typically forms within an indentation of a
continental shelf in the southern
Great Barrier Reef
(GBR). In this study relevant-scale sea surface dynamics were studied at
mesoscale and sub-mesoscale by the use of satellite data at moderate
resolution (1 km). In situ
measurements and model data that are available were used to validate
satellite observations as well as to specify the nature of the processes
that are occurring within the water column. The characteristic features
are identified and physical theory is employed to develop an
understanding of processes that are associated. In particular, it is
shown that the effect of the eddy is to raise cooler oceanic subsurface
water, that is nutrient enriched, and transport it to the reef zone, and
eventually into the lagoon. It is demonstrated in this study that to
determine the biological responses on the scale of reef communities,
linkages between large scale oceanography and the mesoscale and
submesoscale patterns are crucial, and may be key to understanding
climate change impacts at the relevant spatial scales.
Rapid warming and ocean acidification has occurred in tropical oceans on
a scale that has not occurred for at least 720,000 years, and possibly
as long as 20 million years (Hoegh-Guldberg at
al., 2007). It appears that
the ability of biological systems to keep up with the changes has been
exceeded as a result of the rapidity of these environmental changes that
have occurred in distribution and genetic structure. Widespread
extinction of many species and collapse of ecosystems are predicted by
many analysts if the current rates of change of atmospheric carbon
dioxide continue at their present rates (Myers & Knoll, 2001; Vernon,
2008; Wake and Vrendenberg, 2008).
The finer temporal and special scales have remained uncharted, which
represents a challenge for the research and ecosystem management
community, though broad characteristics of these changes have been
documented. For example, as waters have warmed there has been an
increased frequency and intensity of coral bleaching events, and
expectations are that sea temperatures will soon exceed the threshold at
which mass bleaching and mortality on a yearly basis (Hoegh-Guldberg at
al., 1999; Sheppard, 2003;
Hoegh-Guldberg at al., 2007).
However, it is apparent that no 2 bleaching events are identical, in
terms of their temporal and spatial scales, and their overall intensity
(Oliver et al., 2008).
Variability of timing and stress (Weeks et
al., 2008), the physical
conditions predominating in a particular location, as well as the
communities and their resilience (Berkelmans & Willis, 1999; Brown et
al., 2002; McClanahan et
al., 2007), will drive
significant differences from site to site in the ecological impacts and
the responses that are required from managers of natural resources.
According to Weeks et al. at present, the underlying reasons for this
variability have been poorly described and are much less well
understood. However, it can be assumed that variation on a small scale
may ultimately result from patterns of causative physical factors and
mechanisms. It is certain that cooling influences, such as cooler waters
being upwelled from greater depths, are important to understanding how
other factors; salinity changes, solar radiation, sedimentation,
nutrients, may influence the outcome of primary stresses such as
temperature. The resilience of reefs to rapid environmental changes that
are expected in an enhanced greenhouse world may ultimately be
determined by these coinciding factors. In this respect, an
understanding of the dynamics of ocean processes, on scales from global
to local, will become imperative within the goal of understanding and
predicting the impacts of global change. The design of investigations
that are process-oriented of key issues, as well as the projection of
local effects of climate change based on projections of climate change
on the larger scale ocean and atmospheric dynamics, would be guided by
such predictability. These local projections and understandings are
critical to any effective natural ecosystem management response.
The Capricorn Eddy
It was first noted in 1970 in a surface drifter study (Woodhead, 1970)
that there was an eddy in the region adjacent to the mouth of the
Capricorn Channel. It was postulated later that the establishment of a
stable cyclonic eddy in the lee of the shelf bathymetry was contributing
to north-westward flow in the Capricorn Channel region (Griffin et
al., 1987). It has been shown
by subsequent oceanographic deployments and studies of sea surface
temperatures by satellite that these cyclonic features trigger upwelling
along the continental shelf (Kleypas & Burrage, 1994; Middleton et
al., 1994; Burrage et
al., 1996).
Conclusion
The circulation of the East Australian Current (EAC) and consequent eddy
dynamics are primary mechanisms of forcing in the southern Great Barrier
Reef (GBR), having a direct impact on the ecology and the future of the
ecosystem. An understanding of the patterns and processes relevant at
spatial scales is key understanding the impacts of climate change. In
regard to the future and anticipated responses from managers of coral
reef ecosystems this has huge importance. In regards to this, the
regional and local impacts of recent mass coral bleaching event on the
Great Barrier Reef have been distinct, though the reasons for these
patterns have not been clear. In this paper Weeks et
al. have explored the
critical links between oceanography at the large scale and the mesoscale
and submesoscale patterns of physical and biological conditions that are
crucial to the determination of biological responses on the scale of
reef communities and sections of the reef. An understanding of which
reefs are more naturally adapted to, and are more environmentally
resilient, and more able to withstand the impacts of a warming ocean,
and will produce more accurate tools for predicting patterns of mass
coral bleaching, will be provided by incorporation of oceanographic
variability. The design of process-oriented investigations of key
issues, as well as the local effects of climate change based on
projections of climate change on the larger scale ocean and dynamics of
the atmosphere, which are critical to any effective management response,
would be guided by such predictability.
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Author: M.H.Monroe Email: admin@austhrutime.com Sources & Further reading |