Proxies for sea-level change

savagecowcreekMechanics

Feb 22, 2014 (3 years and 5 months ago)

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Proxies for sea
-
level change


East China Normal University,
张梦莹

10061700311


Climate has a significant impact on the Earth. Especially for coastal area
,

climate change will influence sea level directly. When the
temperature

warms
, the

glacier would melt and lead to high sea
-
level, and

vice versa. For
long
-
time
scale, sea

level
is
also changed by geological tectonic
movement,

hydrological features and
features of regional sedimentation and so on. For
example, sea
-
level r
ose

on the
China’s Yangtze river delta during early to mid
-
Holocene
that was
mainly caused by
global climate warming trend.
Thus,
the sea level
is also affected by the interaction of
regional climate warming and contemporaneous lowering of the delta plain surface
by tectonic subsidence and sediment compaction.

How can we learn about the change of sea
-
level in
the
past lengthy historical
period? M
any experts have done a lot of work and proved
that
there are many
proxies
that
can be used to reflect the sea
-
level and restore the environment of
ancient
marine, including

pollen ,
foraminifera and radiocarbon
-
dated peat ,etc.
These proxie
s
usually have different accuracy due to different formation environment
of themselves
.
H
ow much we
can
comprehend the proxies
?


Generally
speaking,
it’s

difficult to get the accurate ancient sea
-
level.
However, we

can judge the trend of
sea
-
level change through curves basing on the proxies data.

As a
proxy, pollen

could reflect ancient environment and climate more precise
even thousands of years ago. Different category and amount of pollen combination
will demonstrate the very vegetation types relatively accurate.
P
hyllacladus,
dacrycarpus, myrica

and rhododendrom belong to high mountain rainforest
vegetation,
while
gesneriaceae
,

sapona
ceous
,

actinidiaceae
,

palmae
and
andeuphorbiaceae belong
s

to the tropical lowland rainforest.
Besides
,

cyperaceous

and gramineae compositae belong to the herbs. The vegetation and sea level both
stem from climate change. So it is an important method to study
the
sea level
through this positive correlation between pollen and climate

(Pollen
can only
sever
as indirect e
vidence to
indicate the sea level fluctuations, but a direct evidence to the
sea level).

In
addition, foraminifera

is another useful measure to construe the condition
of the sea
-
level.
Foraminifera
is

one kind of the
oldest ancient protozoon. They came
into being more than 500 million years ago in the
ocean, and

there are various
species nowadays. Foraminifera are
controlled

by many ecological
factors, including

water salinity, temp
erature, depth and nature of the seabed. In
addition, the

sea
water pH value, light transmittance, nutrition supply, sedimentation rate are also the
controling factors of the foraminifera distribution. According to different genera of
the Fora
minifera we can deduce what the depositional environment
is, and

then
come to the conclusion of how the sea level changing.


Furthermore, as an additional method to determine sea
-
level change
is the
peat
that

incompletely decompos
ed
as relict
deposits of plants. The peat

can be used as
sea
-
level gauges because they tend to be formed by in situ
pre
servation

of woody
plants,

grasses and flora tolerant to fresh and brackish water conditions. Its
formation is the resu
lt of various nature
factors, and

the most important of which are
hydrological and
sub
aerial

conditions.
Especially

peat of seaboard reflects the direct
influence of seawater which record
s

the real information of sea level change.

Except what have introduced
above, there

are many other proxies can direct
sea
-
level, including

sand
embankment, beach

shell,

algae,

coral reef and so on.
Because each of

the proxies will have different precision under different conditions
,

so we should select several proxies
that
are fit the local characteristics of
the
study
area
,
so as to acquire much more accurate sea
-
level change curves rather than just
rely
in
g

on
signal

prox
y

when
establishing
the sea
-
level change.


References:

[1]Yongqiang Zong,

Mid
-
Holocene sea
-
level highstand along theSoutheast Coast of
China
.

[2]
魏子昕,上海地区全新世海平面变化及环境演化,上海地质,
1997.4

[3]
潘安定,陈碧姗等,孢粉学定量重建古气候方法探讨,热带地理,
2008.28

6


[4]F.I.IsIa,
南半球的全新世海平面波动


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