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Geochemical tracers Tracers – talking more about theory than application. Geochemical tracers trace: – Circulation – Climate Environmental conditions (e.g. nutrient levels and productivity) Geochemical tracers are proxies for past environmental conditions... and trace changes in these conditions
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Geochemical tracers - Rutgers University lect...Geochemical tracers • Tracers – talking more about theory than application. • Geochemical tracers trace: – Circulation – Climate

Feb 24, 2020

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Page 1: Geochemical tracers - Rutgers University lect...Geochemical tracers • Tracers – talking more about theory than application. • Geochemical tracers trace: – Circulation – Climate

Geochemical tracers• Tracers – talking more about theory than application.• Geochemical tracers trace:

– Circulation – Climate – Environmental conditions (e.g. nutrient levels and productivity)

• Geochemical tracers are proxies for past environmental conditions...

• and trace changes in these conditionsꜛ

Page 2: Geochemical tracers - Rutgers University lect...Geochemical tracers • Tracers – talking more about theory than application. • Geochemical tracers trace: – Circulation – Climate

The record of climate events and ocean change recorded chemically

• Tools: the substrate– What do we measure the tracers in?

• The Tools: Tracers – Geochemical tracers…..

• the application – How we really do it– what are the issues

Trace metals Organic compoundsOxygen isotopesCarbon isotopes

Page 3: Geochemical tracers - Rutgers University lect...Geochemical tracers • Tracers – talking more about theory than application. • Geochemical tracers trace: – Circulation – Climate

Measure the microfossils…Foraminifera

Coccolithophores Coccoliths

diatoms

Page 4: Geochemical tracers - Rutgers University lect...Geochemical tracers • Tracers – talking more about theory than application. • Geochemical tracers trace: – Circulation – Climate

Sediment

… it’s not just mud

Page 5: Geochemical tracers - Rutgers University lect...Geochemical tracers • Tracers – talking more about theory than application. • Geochemical tracers trace: – Circulation – Climate

The sediment record: what’s in your mud?

Benthic and planktonic

Surface and bottom

Page 6: Geochemical tracers - Rutgers University lect...Geochemical tracers • Tracers – talking more about theory than application. • Geochemical tracers trace: – Circulation – Climate

Mud to microfossils

Page 7: Geochemical tracers - Rutgers University lect...Geochemical tracers • Tracers – talking more about theory than application. • Geochemical tracers trace: – Circulation – Climate

corals

Page 8: Geochemical tracers - Rutgers University lect...Geochemical tracers • Tracers – talking more about theory than application. • Geochemical tracers trace: – Circulation – Climate

The record of climate events and ocean change recorded chemically

• Tools: the substrate– What do we measure the tracers in?

• The Tools: Tracers – Geochemical tracers…..

• the application – How we really do it– what are the issues

Page 9: Geochemical tracers - Rutgers University lect...Geochemical tracers • Tracers – talking more about theory than application. • Geochemical tracers trace: – Circulation – Climate

The Tracer tools Geochemical tracers!

Isotopes: δ13C – circulation δ18O – temperature

Organic matter:TOC – productivityBiomarkers – temperature (relative productivity)Anthropogenic compounds - pollution tracers

Trace metals- Trace metal ratios in calcite (CaCO3)

Cd/Ca (phosphate), Ba/Ca (nutrients),

Mg/Ca and Sr/Ca –temperature

Page 10: Geochemical tracers - Rutgers University lect...Geochemical tracers • Tracers – talking more about theory than application. • Geochemical tracers trace: – Circulation – Climate

Trace metal inclusions in CaCO3

Trace metals that are of similar size and charge as Ca substitute into the matrix….. or as impurities

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 (“productivity”)

Mg/Ca and Sr/Ca –temperature

Page 11: Geochemical tracers - Rutgers University lect...Geochemical tracers • Tracers – talking more about theory than application. • Geochemical tracers trace: – Circulation – Climate

CaCO3 Calcium carbonate … can have substitutions

Page 12: Geochemical tracers - Rutgers University lect...Geochemical tracers • Tracers – talking more about theory than application. • Geochemical tracers trace: – Circulation – Climate

CaCO3 substitutions are controlled by:

Temperature– inclusions are more common when temperatures are higher.

Nutrients – many trace metal concentrations mimic nutrient distributions

Many environmental parameters (thermodynamics, kinetics, biology)

Page 13: Geochemical tracers - Rutgers University lect...Geochemical tracers • Tracers – talking more about theory than application. • Geochemical tracers trace: – Circulation – Climate

Organic markers or “molecular markers”

• Total organic carbon (TOC)– productivity

• Biomarkers (individual compounds) – Trace organisms– Different environments and conditions– temperature (relative productivity)

Page 14: Geochemical tracers - Rutgers University lect...Geochemical tracers • Tracers – talking more about theory than application. • Geochemical tracers trace: – Circulation – Climate

Biomarkers persist in the sediments and contain information about the presence of past organisms

mananimals

fungi flagellates

diplomonads

microsporidiaplants

ciliatesslime molds

green sulfurbacteria

grampositives

protcobacteriacyanobacteria

avobacteria

SulfolobusDesulfurococcus

Pyrodictium

ThermofilumThermoproteus

PyrobaculumPyrococcus

MethanobacteriumMethano-thermus

Methanoplanus

ArchaeoglobusHalococcus

Halobacterium

MethanosarcinaMethanospirillum

Methanopyrus

1 23 4

Methanococcus1 jannaschii

4 vanniellii

2 igneus3 thermolithotrophicus

BACTERIA

EUCARYA

ARCHAEA

Thermocrinis

Aquifex

Thermotoga

OH

OH

OH

OH

OO

OH

HO

>2.7 Ga

>2.7 Ga

HO

HO

HO

R

CH2OCHOR

CH2OR

COOH

Page 15: Geochemical tracers - Rutgers University lect...Geochemical tracers • Tracers – talking more about theory than application. • Geochemical tracers trace: – Circulation – Climate

Algal Steroids•Encode a variety of age-diagnostic signatures –

C-isotopes + steroids from algae & plants

chlorophyceans

diatoms

chrysophytes

dinoflagellates H

H

HO

HO

HHO

HHO

C29

C28

C30

C30

‘bio’ ‘geo’

Page 16: Geochemical tracers - Rutgers University lect...Geochemical tracers • Tracers – talking more about theory than application. • Geochemical tracers trace: – Circulation – Climate

Alkenones as a tracer for sea surface temperature

Alkenones record SST….

in their saturation levels

Alkenones are made only by Prymnesiophytes…

Page 17: Geochemical tracers - Rutgers University lect...Geochemical tracers • Tracers – talking more about theory than application. • Geochemical tracers trace: – Circulation – Climate

Sea Surface temperature change: New Zealand case study

Climate warming since the last glaciation

Page 18: Geochemical tracers - Rutgers University lect...Geochemical tracers • Tracers – talking more about theory than application. • Geochemical tracers trace: – Circulation – Climate

Alkenones record information about climate

The ratio of alkenones in a sample records past temperature similar to foraminifera

Southwest Pacific ~25,000 yr record

Warmer location from north proxies disagree

Cooler location from further south proxies agree better...

Last ice age

Page 19: Geochemical tracers - Rutgers University lect...Geochemical tracers • Tracers – talking more about theory than application. • Geochemical tracers trace: – Circulation – Climate

All proxies are responding to more than phenomenon you want to assess

• Many proxies are based on biological substrates with different– biochemistry– seasonality

• There are competing geochemical... – signals– controls

Page 20: Geochemical tracers - Rutgers University lect...Geochemical tracers • Tracers – talking more about theory than application. • Geochemical tracers trace: – Circulation – Climate

Geochemical tracers

Two isotopes of interest:

Oxygen isotopes:

δ18O

Carbon isotopes

δ13C

Page 21: Geochemical tracers - Rutgers University lect...Geochemical tracers • Tracers – talking more about theory than application. • Geochemical tracers trace: – Circulation – Climate

Geochemical tracers

Oxygen is:16O=99.759%17O=0.037%18O=0.204%

δ notation is simply the ratio of 16:18 in the sample relative to a standard …..

Page 22: Geochemical tracers - Rutgers University lect...Geochemical tracers • Tracers – talking more about theory than application. • Geochemical tracers trace: – Circulation – Climate

“del” notation

δA= (RA -1) x1000RSt

which is the same as (18/16O)CaCO3 sample –1) x1000(18/16O)CaCO3 std

The result is we use “per mil” ‰ as our unitsand we always speak about the data in reference to: the isotope of interest

Page 23: Geochemical tracers - Rutgers University lect...Geochemical tracers • Tracers – talking more about theory than application. • Geochemical tracers trace: – Circulation – Climate

Fractionation of oxygen isotopes

Emerson and Hedges 2008

Page 24: Geochemical tracers - Rutgers University lect...Geochemical tracers • Tracers – talking more about theory than application. • Geochemical tracers trace: – Circulation – Climate

δ18O as a tracer of the short term isotope record

Oxygen δ18O in carbonates is controlled both by:

How much δ18O is in the water – this is affected by precipitation (salinity)

and

By the temperature of the water it is precipitated in

So on short time scales:

It traces both temperature and precipitation (not ice volume)

Page 25: Geochemical tracers - Rutgers University lect...Geochemical tracers • Tracers – talking more about theory than application. • Geochemical tracers trace: – Circulation – Climate

The temperature effect on δ18O

0 ‰ ____‰

____‰

at 10°C

0 ‰ ____‰

____‰

at 20°C

Page 26: Geochemical tracers - Rutgers University lect...Geochemical tracers • Tracers – talking more about theory than application. • Geochemical tracers trace: – Circulation – Climate

0 ‰

evaporation precipitation

____‰

____‰

____‰

____‰

The precipitation effect on δ18O

Page 27: Geochemical tracers - Rutgers University lect...Geochemical tracers • Tracers – talking more about theory than application. • Geochemical tracers trace: – Circulation – Climate

Galapagos Corals

A 5 point moving average of annual δ18O for Galapagos corals

←co

ld

war

m →

Page 28: Geochemical tracers - Rutgers University lect...Geochemical tracers • Tracers – talking more about theory than application. • Geochemical tracers trace: – Circulation – Climate

δ18O as a tracer of temperature: a review on Oxygen isotopes…. δ18O

δ18O in carbonates is controlled both by:

How much δ18O is in the water –

By the temperature (and salinity) of the water it is evaporated and precipitated in.

And the extent to which that distillation has gone on.

On long time scales:

It traces both temperature and ice volume

Page 29: Geochemical tracers - Rutgers University lect...Geochemical tracers • Tracers – talking more about theory than application. • Geochemical tracers trace: – Circulation – Climate

oxygen isotopes in the climate record

Ice -35‰

snow

Emerson and Hedges 2008

Page 30: Geochemical tracers - Rutgers University lect...Geochemical tracers • Tracers – talking more about theory than application. • Geochemical tracers trace: – Circulation – Climate

The record of δ 18O in the sediment record

The distillation is controlled by temperature (salinity) and ice volume.

The record is primarily a function of temperature and ice volume Emerson and Hedges 2008

Page 31: Geochemical tracers - Rutgers University lect...Geochemical tracers • Tracers – talking more about theory than application. • Geochemical tracers trace: – Circulation – Climate

The marine isotopic record

Emerson and Hedges 2008

Is a climatic “standard”

Page 32: Geochemical tracers - Rutgers University lect...Geochemical tracers • Tracers – talking more about theory than application. • Geochemical tracers trace: – Circulation – Climate

The marine isotopic record

Emerson and Hedges 2008

Is a climatic “standard”

Col

der

War

mer

Le

ss ic

e M

ore

ice