time travelling to climates of the past

Time travelling to climates of the past Mark Hodson, Emma Versteegh

Mark Hodson and Emma Versteegh, Time-travelling to climates of the past

How do we know that the climate is changing?


How do we know what will happen in the future?


How can we trust the models?

Present Day Cretaceous


Looking into the past: calcium carbonate

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Calcium carbonate

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Calcium carbonate: stalagmites and stalactites

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Calcium carbonate: stalagmites and stalactites

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Calcium carbonate: shells

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Calcium carbonate: shells

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Earthworm calcium carbonate

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Image: Amy Stewart


Earthworm calcium carbonate


“It may be doubted whether there are many

other animals which have played so important a part in the history of the world,

as have these lowly organized creatures."

Darwin, 1881


…several small, or two or three larger, or a single very

large concretion of carbonate of lime as much as 1.5 mm in

diameter…they are often found in the gizzard, intestines and in

the castings of worms…

Darwin, 1881


What is the function of granules?

•  Elimination of excess Ca •  Neutralisation of gut pH •  Fixing metabolic CO2

•  Osmoregulation


Metal mobility


Material Science

(a) BSE image of a mixed calcite-ACC granule. (b) Corresponding EBSD orientation contrast map. Calcite generates good Kikuchi patterns (inset) and crystal orientations are colour coded. ACC lacks a Kikuchi pattern (inset), rendering it black in the EBSD map.


Production experiment

•  11 contrasting soils

•  1 earthworm per 300 g soil

•  27 days


Production experiment


Putting granules into perspective •  Granule production =

65 x 103 – 5.7 x 106 tonnes CaCO3 a-1

9 – 840 Olympic swimming pools


Putting granules into perspective

•  Granule production =

–  0.01 – 0.5 % UK C emissions

–  Up to c. 5 % of C emitted from soils

–  0.04 – 3 % of C fixed by temperate grassland

–  +100% Ca fixed by plants, released to soils from minerals,

in rainfall


Granules and climate change

I formed … years ago

and the temperature was…


Dating

You gotta check this out, Stuart. Vinnie’s over on the couch putting the moves on Zelda Schwartz – but he’s talkin’ to the wrong end


Calcite chemistry


U

Calcite chemistry


Dating

234

230

92 U

90 Th


Uranium-234 radioactive decay chain

Dating


Dating

time

amou

nt

thorium

uranium / thorium

uranium


Silbury Hill


Silbury Hill

U-series isochron plot of multiple analyses of earthworm granules form Silbury hill. The earliest date for this is circa 4400 B.P. which is consistent with the U-series age for the carbonate granules, indicating they are contemporaneous with the soil formation.

230 Th/U age = 4.67 ± 0.44 ka MSWD = 63, probability = 0.000

230Th / 232Th

238U / 232Th


Granules and climate change

I formed 1000 years ago

and the temperature was…


Atomic structure


Isotopes

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Heavy water


Forming calcite

calcium Ca2+

carbon dioxide CO2

water H2O

+ +


Forming calcite at low temps

calcium Ca2+

carbon dioxide CO2

water H2O

+ +

light heavy

low temperature calcite enriched in heavy O


Forming calcite at high temps

calcium Ca2+

carbon dioxide CO2

water H2O

+ +

light heavy

higher temperature less heavy O enrichment


Enrichment of heavy isotope decreases with temperature

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enric

hmen

t in

heav

y ox

ygen


Separating water molecules



evaporation

Subtropics

Water vapour depleted in heavy water



condensation

Mid latitudes

Further depletion of heavy water in atmosphere Heavy water enriched water



condensation

Poles

Water vapour very depleted in heavy water


Varying water composition


Establishing a thermometer

3 temperatures

x 3 waters

x 2 soils


Measuring isotopes

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granule

Oxygen isotope composition



58

enric

hmen

t in

heav

y ox

ygen

in c

alci

te

enrichment in heavy oxygen in water



temperature

enric

hmen

t in

heav

y ox

ygen

Earthworm calcite Stalagmites Mussels


Temperature equation

1000 ln α = 20.21 (103 T-1) - 38.58

α = (1000 + δ18OcVSMOW) / (1000 + δ18OwVSMOW)

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A speleothem climate record

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← warmer - colder →


A shell climate record

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Applying the thermometer

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Applying the thermometer


Time travelling Boxgrove 500,000 years ago

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