The paleorecord of ENSO events

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The paleo-record of ENSO events

• The Tools Tracers
• Geochemical tracers..
• the application
• How we really do it
• what are the issues

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The paleo-record of ENSO events (or of anything)

• Go from the Tools (Tracers).
• to the application..
• Geochemical tracers of? Climate
• The substrates
• Microfossils
• Chemical fossils
• The controls on substrates
• Biologically mediated
• Long term recorders
• permanent records
• Controls and issues on the record
• chronology

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The tools
Geochemical tracers! Ones we know ?13C
circulation ?18O temperature TOC
productivity Biomarkers temperature (relative
productivity) Trace metals- Trace metal ratios in
calcite (CaCO3) Cd/Ca (phosphate), Ba/Ca
(nutrients), Mg/Ca and Sr/Ca temperature
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Review of carbon isotopes biologically mediated
Plants discriminate against 13C during
photosynthesis. The the ultimate ?13C amount
varies with plant type and substrate.
Libes chapt. 29
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Controls on 13C in the ocean
Water downwells DIC enriched Low nutrients High
O2
13C
13C
13C
12C
13C
13C
12C
12C
12C
13C
13C
DIC (in Water) more depleted with increasing age
13C
12C
12C
12C
12C
12C
Porewaters very sensitive to remineralization can
be very depleted in 13C
12C
12C
12C
12C
12C
12C
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The vertical profile of ?13C reflects the global
thermohaline circulation
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Trace metal inclusions in CaCO3
Trace metals that are of similar size and charge
as Ca substitute into the matrix..
interpretation is based on the simple principle
that if there is more in the water there is more
in the calcite Empirically, we have found their
chemistry is controlled by Cd/Ca (phosphate),
Ba/Ca (nutrients), Mg/Ca and Sr/Ca
temperature
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El Niño in the organic record
TOC productivity.but you get increased runoff
with rain and TOC is ambiguous Biomarkers
temperature (relative productivity) lets look
at this.
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Biomarkers persist in the sediments and contain
information about the presence of past organisms
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Algal Steroids

• Encode a variety of age-diagnostic signatures
• C-isotopes steroids from algae plants
• chlorophyceans
• diatoms
• chrysophytes
• dinoflagellates

geo
bio
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Alkenones as a tracer for sea surface temperature
Alkenones are made only by Prymnesiophytes
Alkenones record SST. in their saturation levels
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Alkenones can record information about climate
The ratio of alkenones in a sample records past
temperature similar to ?18O
Subtropical Atlantic 250,000 yr record
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Alkenones as a recorder of ENSO events
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The paleo-record of climate events Controls and
Issues

• Chronology time control
• Without time control any record is meaningless
• Sediments (good permanent long-term record)
• Plus many microfossils and other recorders
• Problem bioturbation
• Solution laminated sediments
• Problem degradation, hiatuses, erosion
• Deep sea sediments often have a complete record
• Corals (tree rings are similar)
• Excellent continuous, in-place records
• Problem corals die, they have vital effects.

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Paleo records of climate

• Choose your substrate and your record source well
  for the task
• Long vs short,
• Well constrained vs broad control
• you can get a record but you have to know how to
  read it

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How do we get a time series record from the
sediments?
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It starts with a core
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Once you have sediment you have to process it
How do you Get the mud out of the pipe?
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Extrude the core, cut the core liner.
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Processing the core onboard ship
Split the sections
Label the sections
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Measure, describe, sample
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Sample analysis
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A downcore record about climate
Equatorial Pacific 150,000 yr record
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The el niño record

• What is el niño geochemically?
• Biologically Changes in productivity.
• Should produce changes in what markers?
• Physically changes in temperature (and
  rainfall)
• Should produce changes in what markers?

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The el niño record

• What is el niño geochemically?
• Biologically Changes in productivity.
• Should produce changes in what markers?
• TOC
• Biomarkers
• Physically changes in temperature
• Should produce changes in what markers?
• ?18O
• Trace metals
• Biomarkers

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ENSO has a cross Pacific see-saw signal
(The chemists view) Rain and cold in Peru is dry
in Australia Dry and hot in Peru its wetter in
Australia (normal) But its not a fully
symmetrical signal The signal in the east is
temperature The signal in the west is
precipitation
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The El Niño temperature signal varies across the
Pacific
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Using temperature records to get a long record of
ENSO events

• Long records can only come from cores which
  means lower resolution
• Focus on SST variation across the Pacific
• Temperature change is greatest in the east
• The western warm pool has smaller changes
• Over long time frames this gradient can trace
  changes in El Niño strength

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Mg/Ca record of temperature in the equatorial
Pacific
2 Ma
Present
The gradient of temperature changes with time.
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But we can get high resolutions records that can
resolve ENSO events

• We look to an undisturbed substrate. CORALS.

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Dating is done on coral heads
Not branching corals!
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The coral is slabbed and sliced
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The slabs are sectioned along growth planes
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You can see the annual growth bands by x-ray
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?18O as a tracer of ENSO a review on isotopes
Isotope of concern Oxygen ?18O

• notation is simply the ratio of 1618 in the
  sample relative to a standard
• ( 16O/18O sample 16O/18O standard ) x 1000
• 16O/18O standard

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oxygen isotopes of the water
controlled by temperature and salinity
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?18O as a tracer of ENSO a review on isotopes
Oxygen ?18O in carbonates is controlled
both by How much ?18O is in the water this is
affected by precipitation (salinity) and By the
temperature of the water it is precipitated in
So It traces both temperature and
precipitation Lets have a look
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Study location determines the El Niño signal
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Combining records for better control on
interpretationsis Multiproxy estimation proof
the Tarawa record is precipitation

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Combining records for better control

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The Eastern Pacific ENSO signal

• Temperature is a major component of the signal
• Knowing this we can interpret records that go
  back farther than the instrument records.
• We can use tracers to tell us more..

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Galapagos Corals
A 5 point moving average of annual ?18O for
Galapagos corals
There are long term trends that extend beyond the
instrument recordthat only proxy records can
show us
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Mg/Ca record of temperature in the equatorial
Pacific
2 Ma
Present
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? 18O in the East Pacific is primarily affected
by temperature
But cool water is upwelled water that is old
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Radionuclide Geochemical tracer 14C
Guilderson et al , 1994
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Instrument records of physical properties can
only show so much
Satellite record of SST shows a step change. But
SST alone cant show us the genesis of that change
Guilderson and Schrag, 1992
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Isotopes and SST comparison
A multi-proxy record can tell us more about the
causes of phenomena we observe in one record or
another
Guilderson and Schrag, 1992