Fanning Island: Corals and Climate Research

Kim M. CobbGeorgia Inst. of Technology

Christopher D. CharlesScripps Inst. of Oceanography, UCSD

Norwegian WindMay 30, 2005

Research Goal:To reconstruct tropical Pacific climate change of the recent past, so that we might better predict future climate change, and its regional signatures.

Fanning2005-?

Palmyra1997-?

Christmas1998-?

Research Funded by:NOAANSF

Fieldwork funded by:NCLThe Nature ConservancyPrince Khaled Bin Sultan

Bin Abdulaziz

El Niño-Southern OscillationAn ocean-atmospherephenomenon that originates in the tropical Pacific but affectsglobal climate patterns

December 1997 SST Anomalies

Why study tropical Pacific climate?

-ENSO extremes carry serious economic and social costs

- improved ENSO forecasts minimize the costs

- the impacts are not confined to the tropical Pacific

+6°

+3°

0°

-3°

Sea

Sur

face

Tem

pera

ture

A

nom

aly

(ºC

)

El Niño impacts

Palmyra, Fanning, Christmas Islands

Year

1860 1880 1900 1920 1940 1960 1980 2000

Tem

pera

ture

Dev

iatio

n (°

C)

-3

-2

-1

0

1

2

3Eastern tropical Pacific Temperature

El Niño

La Niña

1997 El Niño1982 El Niño

The instrumental record of El Niño’s

Are severe El Niño events becoming more frequentas global temperatures increase?

The uncertain climate future“Most of the observed warming over the last 50 yearsis likely to have been due to the increase ingreenhouse gas concentrations.” – Intergovernmental Panel on Climate Change 2001

Modeled global temperaturerise

Modeled sea levelrise

Research Question:How will tropical Pacific climate change as global temperatures rise?

The instrumental record of El Niño’s is too short to answersome key questions:

1. Are late 20th century El Niño events more frequent and more severethan those of the recent past?

2. Is there a correlation between average global temperature and El Niño activity?

3. How much and how fast has ENSO changed in the past?

A well-placed rope swing in the Palmyra lagoon

Corals: The geologic record of El Niño

CORALS from the tropical Pacific record El Niño’s in the geochemistry of their skeletons

Living Porites corals provide recordsfor the last 200 years

Fossil Porites corals enable us to extend the record back many centuries

Fanning Island Expedition:

Carlos

MeJordan

Joanna Jessica Planning phase:1 year

Duration: 2 weeks

Accomodations:NCL ‘compound’

Results published:2007, 2008

Expedition goals:1. Drill as many long fossil corals as possible.2. Find large living corals for future underwater drilling.3. Sample rainwater and seawater for chemical analysis.4. Install temperature loggers on coral reef.

NCL compound

Aontela Village“Big Rock”,Primary drill site

The “Death March”5km trek in searchof fossil corals

SecondaryDrill site

Snorkeling sitessurveying modernreef health

Roland pretending thathe caught a large wahoo

Dolphins surfing the bow wave

Piglets overseeing drilling

Drillholes are fun!

THANKS to Roland and Bob

Expedition Results:

~20m fossil coral drilled

Temperature loggersinstalled, good for 3yrs

~40 seawater samples

~10 rainwater samples

Palmyra Island Resultsresearch 1997 to presentpublished 2003

Research Objective: To generate >100-yr-long, high-resolution, high-fidelity climate proxy records from the tropical Pacific Ocean;to extend the record of El Niño back in time

Materials: Modern and Fossil Corals

Methods: Dating: U-Th radioactive decay seriesClimate proxy: Coral skeletal oxygen isotopes

December 1997 SSTAnd Rainfall Anomalies

Site

A baby booby at Palmyra

Generating climate reconstructions from the Palmyra corals:

1) Recover the corals, both modern (~10) and fossil (~100).

2) Prove that the coral geochemistry tracks large-scale climate.ie. Calibrate the modern coral record against the instrumental record of climate.

3) Apply geochemistry to fossil corals and date them (U/Th dating).

Aerial view of Palmyra

900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000

Date (A.D.)

Modern

The Palmyra Island Coral Collection

Little Ice Age (LIA)canals frozen in Europe

Medieval Warm Period (MWP)Greenland green

Palmyra Coral O (‰)-4.7 -5.1 -5.5 -5.9

SST (°C)

Palmyra Coral δ18O (‰)

1995

1990

1985

26 27 28 29 301980

( )( ) 1000

/)/(/

1618

1618161818 x

OOOOOO

Ostd

stdspl

−=δ

Coral δ18O is primarily a function of sea-surface

temperature

Climate Proxy: Coral oxygen isotopes (δ18O)

Drilled inMay 1998

Sam

plin

g tr

anse

ct

SS

T A

nom

oly

(°C

)

3

2

1

0

-1

-2

δ18O

(‰)

-0.6

-0.4

-0.2

0.0

0.2

NIÑO3.4 SSTPalmyra coral

Year (A.D.)

1900 1920 1940 1960 1980 2000

SST

Anom

oly

(°C

) 1

0

-1

-2

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

R = -0.66

R = -0.84

δ18O

(‰)

How well do Palmyra corals record El Niños?

Red = instrumental record of El NiñosBlack = modern coral δ18O

Less

sm

ooth

edM

ore

smoo

thed

900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000

Date (A.D.)

Palmyra Island Coral Collection

Turning to the fossil corals….

Single records

1°C

Palmyra Coral δ18O Sequences

warmer

colder

Date A.D.

Modern

1°C

Cobb et al., Nature, 2003

What does this coral reconstruction of tropical Pacific climate tell us?

You tell me!

930 960

δ18O

(‰)

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

1170 1200Years

1320 1350 1380 1410 1440 1650 1680 1890 1920 1950 1980

El Niño

La Niña

1997El Niño

An extended history of El Niño activity from the Palmyra coral records

Most fr

eque

nt, in

tense

El Niño

even

ts of

recon

struc

tion

ENSO chara

cteris

tics ca

n

chan

ge in

less

than

a de

cade

Future Research in the Line Islands

1) Date the new Fanning Island fossil corals. (next 6 months)

2) Select long sequences for climate reconstruction via isotopic analysis(next 1-2 years)

3) Collect living corals from Fanning for calibration of coral isotopic signal(August 2005 cruise to Line Islands)

4) Analyze results using statistical techniques, compare to otherpaleoclimate records, publish results (ongoing).

Food for Thought

Coral reefs are disappearing at alarming rates worldwide,due to the combined influence of rising ocean temperaturesand human disturbances (sediment runoff, over-fishing, dynamite fishing, etc).

Reef ecosystems have weakened to the point that natural climate variations, such as a large El Niño event could be the “straw that breaks the camel’s back”.

Web Resources

My homepage: http://shadow.eas.gatech.edu/~kcobb

General El Niño info: http://www.pmel.noaa.gov/tao/elnino

NOVA El Niño page: http://www.pbs.org/wgbh/nova/elnino/

Gunung Buda Speleothem Project

Goal: to reconstruct annual to centennial-scale rainfall variability from an ENSO-sensitive region over the last glacial cycle

Materials: ~40 speleothems (0.1 – 1.8m long)

Dating: U-series geochemistry

Climate proxies: growth rate, δ18O, δ13C, Sr/Ca, Mg/Ca, optical properties

Approach: 1. On-site geochemical calibration2. High-precision U/Th dates 3. Reproducibility tests4. billions and billions of datapoints

ba02 (69cm)ba03 (135cm)

ba04b (89cm)baby1 (10cm)baby2 (8cm)baby3 (5cm)

gc03 (23cm)gc04 (6cm)

mj01 (23cm)mj02 (20cm)

sch01 (33cm)sch02 (86cm)

sch03 (36cm)ssc01 (75cm)

ssr01 (46cm)ssr02 (13cm)ssr03 (38cm)

0 20 40 60 80 100Age (kybp)

U/Th dating results to date

NOTE: stalagmites have infinite resolution(1 drop every 30 seconds to 10 minutes),temporal resolution of climate recordslimited only by analytical capabilities (in other words, how low can you go?)

How are precipitationchanges recorded incave dripwatergeochemistry?

Timeseries of rainwater and cave dripwater geochemistry

δ18O

(‰) a

nd δ

13C

(‰)

-12

-10

-8

-6

-4

Long Napir rainwaterMulu rainwaterMulu driwpater (fast)Mulu dripwater (slow)Buda dripwater (all)Buda rainwaterMulu dripwater δ13C (slow)Mulu dripwater δ13C (fast)

Date

10/01/03 12/01/03 02/01/04 04/01/04

Mg/

Ca

0.0039

0.0042

0.0045

0.0048

0.0051

0.0054S

r/Ca

2.2e-4

2.4e-4

2.6e-4

2.8e-4

3.0e-4

3.2e-4

[Ca]

(um

ol/L

)

800

1000

1200

1400

1600

1800

Mulu dripwater Mg/Ca (slow)Mulu dripwater Sr/Ca (slow)Mulu dripwater [Ca] (slow)Mulu dripwater Mg/Ca (fast)Mulu dripwater Sr/Ca (fast)Mulu dripwater [Ca] (fast)

core-top δ18O

core-top δ13C

Dai and Wigley, 2000

Borneo experiencessevere drought duringEl Niño events