THE AZOLLA STORY

HOW AN AMAZING PLANT CHANGED

OUR CLIMATE 50 MILLION YEARS AGO

(SECOND HALF OF THE TALK)

DR JONATHAN BUJAK

PART 5

the Arctic Coring Expedition (ACEX)

IODP Leg 302 aka the Arctic Coring Expedition (ACEX)

the drillship Vidar Viking sailed into the Arctic

supported by Norwegian and Russian icebreakers

ACEX was a great success

It cored the

Lomonosov Ridge

close to the North Pole

ACEX

Lomonosov Ridge

North Pole

ACEX

…..recovering

420m of cored section

including the crucial

50 million year old interval

when CO2 fell so abruptly

and the results

amazed everyone!

more than 90% of the

50 million year old section

was filled with the

remains of Azolla

and the Azolla fossils

occur as undisturbed

laminated layers

mudstone layer

Azolla layer

Azolla layer

layers of undisturbed Azolla remains that gently sank to the sea floor

and they also occur within

a succession of marine rocks….

…..but Azolla is a freshwater plant

how could it grow

in the middle of the Arctic Ocean?

what do we know about Azolla?

PART 6

we meet Azolla

Azolla is a floating aquatic freshwater fern

the oldest 70 million year old fossils from the Late Cretaceous have identical

morphology to modern forms indicating similar biology and habitat

they have small spongy leaves

and tendrils dangling beneath the leaves in the water

Azolla is one of the fastest growing plant on the planet

doubling its biomass in just 2 to 3 days

and it is widely used in the Far East

as a green biofertilizer to increase rice production

Azolla being grown outdoors in India for cattle fodder

as well as a livestock feed in India and the Far East

but why is it used as a biofertilizer?

and how can it grow so rapidly free-floating

on water without any nutrients from the soil?

the key is Azolla’s

leaf structure

Azolla’s leaves

contain cavities that are

filled with nitrogen

source: Carrapiço, 2002

these provide an enclosed

micro-environment

for the nitrogen-fixing

cyanobacterium Anabaena

source: Carrapiço, 2002

enabling the two organisms to have a mutually beneficial symbiosis

Azolla provides a home for the cyanobacterium Anabaena

which sequesters the nitrogen needed to fertilize Azolla

nitrogen

micro-environment

Azolla’s sporophyte

sporocarps

megasporocarp

megasporocarp’s chamber

megasporocarp’s chamber

fertilization

new sporophyte

and the two organisms remain together during Azolla’s reproductive cycle

so that Anabaena is passed to successive generations via Azolla’s spores

Azolla’s sporophyte

sporocarps

megasporocarp

megasporocarp’s chamber

megasporocarp’s chamber

fertilization

new sporophyte

with the result that they have co-evolved for more than 70 million years

making the Azolla-Anabaena symbiosis extremely efficient

for example, Azolla and Anabaena have complementary photosynthesis

and are therefore able to utilize light from most of the visible spectrum

Azolla contains chlorophyll-a,

chlorophyll-b and coratinoids

whereas Anabaena contains

chlorophyll-a, phycocyanin,

allophycocyanin and phycoerythrin

Azolla-Anabaena is the only known symbiosis in which

the two organisms remain together during the plant’s reproductive cycle

and it was designated a ‘Superorganism’

by Francisco Carrapiço in 2009 *

* Carrapiço, F. 2009. ‘Azolla as a superorganism. Its implication in the symbiotic studies’. In: “Stress Biology”. Seckbach, J. and Grube, M. (Eds). Springer.

cyanobacteria were widespread three billion years ago when the Earth’s atmosphere

was devoid of oxygen – but they had to go ‘underground’ and colonize

anaerobic enviroments when the atmosphere became oxygenated

stromatolites composed of cyanobacteria three billion years ago

Azolla and Anabaena established their symbiotic relationship 70 million years ago –

the oldest evidence is from the Cretaceous Bearpaw Formation of the

Canadian Mackenzie Delta which was characterized by subtropical swamps

dinosaurs rummaging in the soil may have

inadvertently triggered the original symbiosis –

the most successful plant-cyanobacterial

partnership that is know today

resulting in Azolla-Anabaena’s ability

to fix more than 1000 kg of

atmospheric nitrogen per acre per year *

providing a natural biofertilizer in the water

for rice production

* Barke et al. unpublished data

with the nitrogen becoming

available for rapid growth of Azolla

which can then fix up to 6000 kg

of atmospheric carbon per acre per year *

free-floating on water

* unpublshed data, various sources

recent studies also show that

• Azolla can tolerate salinities of up to 5 psu **

(practical salinity units)

• Azolla’s optimum growth is in 20 hours of daylight *

• and its growth is increased by elevated CO2 **

*Barke et al. in press; **Speelman et al. (2009)

so how does this relate

to Arctic events 50 million years ago?

PART 7

THE ARCTIC AZOLLA EVENT

during the Paleocene and early Eocene the Arctic Ocean had an

open marine connection to the Tethyan Ocean via the Turgay Strait

illustration from Barke & Bujak, NATURE, in press

but the connection was severed when the strait closed due to

tectonic uplift at the end of the early Eocene 50 million years ago

50 Ma

illustration from Barke & Bujak, NATURE, in press

resulting in enclosure of the Arctic Ocean,

basin stratification and bottom-water anoxia

50 Ma

illustration from Barke & Bujak, NATURE, in press

similar to today’s Black Sea

illustration from Barke & Bujak, NATURE, in press

today’s Arctic Ocean has relatively low salinity compared to the world’s oceans

due to freshwater input from its large catchment area…..

…..and 50 million years ago higher temperatures and rainfall increased river discharge

resulting in surface freshwater plumes and low salinity across the basin

illustration from Barke & Bujak, NATURE, in press

with a net runoff into the Arctic Ocean estimated

at 15 million cubic kilometres per year

Source: Speelman (2010)

this freshened surface waters across the entire Arctic Ocean

to values of 0 to 6 psu*

overlapping Azolla’s maximum salinity tolerance of 5 psu**

* Barke & Bujak (in press); ** Speelman (2010)

Azolla

so Azolla was able to rapidly spread across the surface

of the Arctic Ocean due to its symbiosis with Anabaena…..

Azolla

CO2 drawdown

…..Anabaena provided the nitrogen needed to fertilize Azolla

enabling it to sequester large volumes of CO2 into its plant biomass

and bottom-water anoxia resulted in the absence of benthic organisms

that normally recycle organic material up through the water column

anoxia

so that the Azolla plants with their sequestered CO2

were deposited on the sea floor as a succession of

undisturbed laminated sediments

local anoxia

geochemical studies indicate that the Azolla interval

is a petroleum source rock that may extend beneath the entire Arctic Ocean*

CO2 drawdown

petroleum source rock

* Ruediger Stein, Alfred Wegener Institute, 2006

local anoxiapetroleum source rock

…..so that Azolla has the potential to provide

a gas-prone source of energy beneath Arctic

and a biofuel from modern Azolla

the Azolla event lasted for almost a million years

It ended when the Turgay Strait re-opened

providing us with an model for the Azolla Event

illustration from Barke & Bujak, NATURE, in press

50 million years ago

Azolla sequestered

enormous quantities

of atmospheric carbon

triggering

the onset

of climatic

cooling

which resulted in today’s icehouse world

with glaciation at both poles

as atmospheric CO2 progressively fell…..

during the Azolla event (50 Ma)

though the Miocene (14 Ma)

into the Pliocene (2 Ma)

and the Pleistocene - including the Last Glacial Maximum (14,000 BP)

and today’s Holocene interglacial…..

…..as featured in National Geographic May 2005

“The Great Green North: Was the icy Arctic once a warm soup of life?”

Azolla

as well as NATURE

June 2006

“The Cenozoic Arctic Ocean:

from greenhouse to icehouse

in 55 million years” *

* Brinkhuis, Bujak et al., 2006

…..and the New York Times in November 2004

Need a picture of NYT page

So did a single plant called Azolla

really change the Earth’s climate from a

greenhouse to icehouse state?

the answer has implications for past

and present climate change

which is crucially important today

Contact Dr Jonathan Bujak

for more details about modern and fossil Azolla

and its potential to help us

mitigate climate change today

info@azollabiosystems.co.uk