Transcript Paleoclimate indicators

Indikator Paleoclimate
Apa itu ITU PALEOKLIMAT??
• The study of past
climates prior to the
instrument record.
• Scientists use indirect
evidence (data) during
past time periods to
determine the climate
at that time period.
• These climate imprints
are referred to as
proxies.
Mengapa belajar PALEOKLIMAT??
• Akan membantu kita mengetahui
bagaimana iklim itu berubah-ubah
sepanjang masa.
• Untuk memperkirakan perubahan iklim di
masa datang.
Warm
Cold
Warm
Apa yg. menyebabkan Iklim
berubah sepanjang jaman?
Penyebabnya sangat kompleks, dan
inilah beberapa sebab tsb:
1.
2.
3.
4.
Perubahan output matahari
Perubahan orbit Bumi
Perubahan dalam distribusi benua
Perubahan isi gas rumah kaca di atmosfer.
1. Perubahan penyinaran matahari
(Milancovic cycle)
2. Perubahan orbit bumi?
• Mungkin karena
asteroid yg.
Menabrak bumi
dan
memunculkan
bulan
• tetapi..
• Sangat tinggi
perubahan
musim di
daerah tropis
Orbital forcing: Milankovitch Theory
• Obliquity (miring): 41,000 yr cycle
Orbital forcing: Milankovitch Theory
Eccentricity - aneh: 100,000 years
Orbital forcing: Milankovitch Theory
Precession: 19,000-23,000 years
The major axis of each planet's elliptical orbit also precesses
within its orbital plane, in response to perturbations in the
form of the changing gravitational forces exerted by other
planets. This is called perihelion precession.
It is generally understood that the gravitational pulls of the
sun and the moon cause the precession of the equinoxes on
Earth which operate on cycles of 23,000 and 19,000 years.
Orbital scale insolation change
• Strong 23 ky
(precession) and
40 k cycles
(Obliquity)
• 100 ky cycle is not
obvious
3. Perubahan distribusi benua; jenis batuan
dapat digunakan sebagai indikator iklim
Ordovician
• The Ordovician (pron.: /ɔrdəˈvɪʃən/) is a geologic period and system,
the second of six of the Paleozoic Era, and covers the time between
485.4 ± 1.9 to 443.4 ± 1.5 million years ago (ICS, 2004[5]). It follows
the Cambrian Period and is followed by the Silurian Period.
• Sea levels were high during the Ordovician; in fact during the
Tremadocian, marine transgressions worldwide were the greatest for
which evidence is preserved in the rocks.
• During the Ordovician, the southern continents were collected into a
single continent called Gondwana. Gondwana started the period in
equatorial latitudes and, as the period progressed, drifted toward the
South Pole. Early in the Ordovician, the continents Laurentia (presentday North America), Siberia, and Baltica (present-day northern Europe)
were still independent continents (since the break-up of the
supercontinent Pannotia earlier), but Baltica began to move towards
Laurentia later in the period, causing the Iapetus Ocean to shrink
between them. The small continent Avalonia separated from Gondwana
and began to head north towards Baltica and Laurentia. The Rheic
Ocean between Gondwana and Avalonia was formed as a result.
Hot House World
(300-5 Ma) Mesozoic/Cenozoic)
• Thermal max: 55 Ma (Cenozoic)
• Clues:
– Marine T proxies
– Tropical plants fossils, alligator, & pollens up in the arctic
– Organic-rich deposit (anoxia)
– Much lighter in δ18O (-40‰ vs. 0 of ocean, and vs. -25 ‰ if
melt all ice now. Must have additional T effects.)
– No glaciomarine deposit
Causes of the hot house?
• Tectonic block circum polar current 
can’t form arctic ice sheet?
• Can’t form deep water since there is no
strong T gradient (est. 12ºC vs. ~0 now)
• CH4 Clathrate release>> positive
greenhouse feedback
– supported by lighter δ13C
Land mass distribution
• Higher tropical albedo (Land albedo > ocean)
Accumulation of significant thicknesses of limestone and
Reef-bearing limestone is restricted to ~20º + - equator
Gondwana tillite, Ontario
Rock record of glaciation, this one ~2.3 billion years ago!
The concept of climate proxies
• A climate proxy is something that
records or reflects a change in temp or
rainfall but does not DIRECTLY
measure temperature or precipitation
For example…
Tree
Rings
Sediment
Cores
Pollen
Examples
of Climate
Proxies
Stable
Isotopes
Ice Cores
Coral
Reefs
Serrations on leaf margins indicate temperature: jagged
edges indicate cooler climate
Leaf waxiness is an indicator of moisture retention
Tree rings:degree of
seasonality
In the tropics
there is no
difference in
growing
seasons
and tree rings
are not well
developed.
These are tree
rings from a
tree in a
temperate
climate
•
•
•
•
•
•
•
Tree-ring-1
Tree-ring-2
Tree-ring-3
Tree-ring-4
Tree-ring-5
Tree-ring-6
Tree-ring-7
Vegetation zones in Europe parallel latitude now and 9,000
yr before present
Middle Cretaceous climate indicators
W = warmwater animal
occurrences;
E = evaporite
minerals;
C = coal
deposits. Coal
is not particularly
temp sensitive
but animals and
evaporation are.
Stable isotopes of oxygen: a proxy for
temperature but now considered an
almost direct measurement
• Stable isotopes: do not decay over time. Ex,
O16 and O18.
O18 is produced from O16 through
nucleosynthesis in supernovae
Anything that incorporates oxygen into its
chemical structure will do so with some ratio
of O18:O16. We can measure the ratios of
these isotopes in the lab
O18/O16 fractionation
H2O is evaporated from
sea water. The oxygen in
the H2O is enriched in the
lighter O16.
This H2O condenses
in clouds,falling on land
as precipitation. Thus,
H2O that is part of the
terrestrial water cycle is
enriched in the light O16
isotope and sea water is
enriched in the heavier
O18 isotope
Glacial ice is therefore
made up primarily of
water with the light O16
isotope. This leave the
oceans enriched in the
heavier O18, or “more
positive.”
During glacial periods,
more O16 is trapped in
glacial ice and the
oceans become even
more enriched in O18.
During interglacial
periods, O16 melts out
of ice and the oceans
become less O18 rich, or
“more negative” in O18
If we collect a shell made out of CaCO3, we can analyze
the O18:O16 ratio by the following formula:
delta O18= [(O18/O16 sample/O18/O16 standard) -1 ] x1000
The standard that your sample is compared to
is either one prepared from ocean water or
from a fossil standard. Positive delta O18
values mean that your sample is enriched in
the heavy O isotope; negative delta O18
values mean it’s depleted in the heavy O18.
Curve of average O18 isotope variation over
the past 2my based on analysis of deep
sea sediment
The curve illustrates changes
in global ice volume in
successive glacial (blue) and
interglacial (green) cycles of the
Quaternary Period.
Note that this graph does not
show fluctuating temperatures,
but changes in the dilution of sea
water as a result of freshwater
influx from melting glacial ice, i.e.,
this is a climate proxy
Sr87/Sr86
a proxy for salinity/rainfall (evap vs prec)
During wet climates, more
Sr is released from weathering
minerals in granite
Middle Cretaceous and early Tertiary
temperatures
A reconstruction of
changing atmospheric
CO2 levels (blue) and
resulting global temps
(pink) over the past
100 my, based on
analysis of climate
proxies such as pollen,
leaf serration, and
O18 values. Note that
the Mid-Late
Cretaceous was
significantly warmer than
the early Tertiary (or today)
Not proxies, but direct measures
Sr:Ca ratios in aragonite: a measure of
seawater temperature
Trace elements such as cadmium, barium, manganese and
strontium replace Ca in the lattice of aragonite (a CaCO3
mineral). These trace elements often substitute for Ca as a
result of climate-related variables.
The following relationship between Sr:Ca ratios and temp
was developed: Sr:Ca x 103 = 10.48 (=/- 0.01) - 0.0615
(+/- 0.0004) x temp.
Thus we can measure trends in Sr:Ca ratios in coral aragonite
skeletons as a way to determine surface sea water temps.
Ocean surface temps and climate in the
Tertiary
Surface temps
measured in shellbearing sediment from
the western Pacific Ocean.
Relatively warm surface
waters from 49-35 M.a.
are followed by a
climate change to cooling
and the buildup of glaciers.
By 2.5 M.a. the onset
of glaciation in the
Northern hemisphere
occurred, several M.a. after
it started in Antarctica.
Hypothesize about the Cambrian climate
of VT
Although zonal, the zones can be
compressed
Zonal compression can result from changes in the movement of
heat from the equator to poles
Take away points..
• What is a “climate proxy?”
• What are examples of:
geochemical proxies?
biological proxies?
lithologic proxies?
When you see how paleoclimate reconstruction
for a geologic period, can you describe the
various techniques used to create it?
•
•
•
•
Ice core proxy
Pollen
Coral skeleton
Speleothem
• Weather and
climate
observations
can be found in
ships logs,
farmers’ diaries,
newspaper
accounts, and
other written
records.
• Sediment cores can be taken from
lakes, the shallow ocean, or the
deep ocean.
• In some cases the thickness of
these layers can be used to infer
past climate.
• In other cases, these layers are
composed of organic material that
can be analyzed for other climate
proxies.
• Pollen grains are well
preserved in lake and ocean
sediment.
• The analysis of each of
these sediment layers
provides information on the
vegetation present at that
time.
• Scientists can infer past
climates (warm or cold)
based on the distribution
and changes in plant
species.
• The most common element used in
climate studies is oxygen.
• The isotopes of oxygen are:
–O18 (rare)
–O17
–O16 (common)
• The ratio of O18 to O16 is affected by
temperature and can be used as a
climate proxy.
• Corals are composed of calcium carbonate.
• This carbonate contains isotopes of oxygen
that can be used to determine the water
temperature when and where the corals
grew.
• As snow and ice accumulate in polar
glaciers a paleoclimate record
accumulates of the environmental
conditions of the time of formation.
• Ice cores can analyzed using stable
isotope approaches for water or air
bubbles within the ice as a record of past
atmospheric
• gas concentrations.
• Tree growth is influenced by climate. These
patterns can be seen in tree ring width and
isotopic composition.
• Trees generally produce one ring each year.
• Trees ring records can extend back to the last
1000 years.
Semua contoh-contoh yang digunakan
secara individu atau bersama-sama
dapat membantu mengumpulkan iklim
masa lalu jangka waktu atau wilayah
tertentu