Geoscience Reference
In-Depth Information
10.5.3.1 Impacts of sea-level change
there is the potential for significantly changed
sediment supply. Reservoir construction is prob-
ably the most important influence on sediment
supply, but in many datasets it is difficult to dis-
tinguish the influence of climate change from
that of other changes in catchment conditions
(Walling & Fang 2003). Where shelf sediment
distribution depends upon waves and/or wind-
driven currents (e.g. the GBR shelf ), changed
seasonal wind patterns have the potential to
change the distribution of shelf sediments. For
storm-dominated shelves, changed frequency,
magnitude and preferred storm tracks might
influence the distribution of shelf sediments.
Overall, such oceanographic shifts and associated
ecological changes are increasingly acknowledged,
but the consequences on the sedimentology are
not understood.
Over the next few decades, changes in mean
sea-level (of up to a few decimetres) may affect
some parts of the world's continental shelves.
For example, the vertical extent of many coral
reefs is presently limited by sea-level, the reefs
having caught up with sea-level during the
late Holocene (Larcombe & Woolfe 1999). As
a result, a rise in relative sea-level may increase
coral cover on reef flats and thus increase rates
of carbonate production. In deeper shelf areas,
changed sea-level will have little impact over
such time-scales, because here marine processes
dominate sedimentation, and changed oceanic
circulation patterns, with consequent changes
in temperature and storminess, may be more
important.
10.5.3.2 Impacts of ocean current change
10.5.4 Research needs and gaps
Changes in shelf sedimentation directly related
to varying ocean currents have been noted
above (section 10.2.3.5 and Case Study 10.2).
Ocean currents may influence shelf sedimenta-
tion in other ways, through their introduction
of water of varying temperature and salinity,
and the consequent potential for altered shelf
sediment production. That changes in biogenic
sediment production can occur as a result of
oceanographic changes is established on time-
scales of centuries and millennia (e.g. Scourse
et al. 2002), but equivalent data are lacking on
shorter time-scales in shelf environments. On
some shelves, there are recognized changes in
shelf ecology related to variations in inputs of
oceanic waters (e.g. Beaugrand 2004), which
might be expected to change primary produc-
tion and the supply of organic matter to the
sea bed.
For continental shelves in general, and per-
haps especially for temperate shelves, there is
a lack of detailed information on past shelf
'weather and climates', i.e. the short-, medium-
and long-term variation in shelf processes.
Knowledge is lacking on the dynamics of coarse
sediments, and the role of such sediments in
shelf processes (e.g. C and N cycling). Signific-
ant limitations in understanding exist regard-
ing the rates of various processes (see Becker
et al. 2001), including sediment transport itself
and related biogeochemical processes. It is still
difficult to make real-time observations of the
nature of suspended particulates (Sternberg
& Newell 1999). Regarding contamination,
research is needed on so-called 'combined
effects', whereby the detrimental effects of a
contaminant are altered if other chemicals or
environmental conditions occur. This is a very
difficult issue because of the rapid increase in
the number of new chemicals.
Although geophysical survey devices (e.g.
swath-mapping) are improving our knowledge
of the spatial distribution of various sediment-
ary facies and biotopes, there remains a lack of
basic understanding of the links between shelf
sedimentary processes and benthic organisms,
10.5.3.3 Impacts of weather changes (floods, winds,
storms)
Shelf sedimentation is likely to be changed if
the relative magnitudes between parameters of
supply, translation and removal are altered.
Thus, if major changes in flood frequency occur,
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