kim cobb's water isotopes talk at agu

Precipitation and seawater isotopes from Hawaii to the equator across the 2014-2015ENSO cycle

Kim M. Cobb (Georgia Tech)@coralsncaves

Jessica L. Conroy (U. Illinois Urbana-Champaign)

Christopher Bosma, Lucas Everitt, Pamela Grothe(Georgia Inst. of Technology)

Jessica Moerman (Johns Hopkins)

Julia Baum (U. Victoria)

David Noone (Oregon State University)

Samantha Stevenson, Mark Farnsworth (NOAA)

Brian Powell, Mark Merrifield, Niklas Schneider (U. Hawaii-Manoa)

Coral d18O reconstructions of climate require anunderstanding ofseawater d18O variations

World Ocean Atlas, 2009

(E-P) oceancirculation

seawater d18O(salinity?)

climate

Coral d18O = SST + d18Osw

d18Ovapor

d18Orain

To unlock the full potential of paleo-isotope records,we need to know:

1) How does d18O of seawater vary through space and time?(and relationship to salinity?)

2) What are the relative contributions of ocean circulationversus atmospheric fluxes to d18Osw variability at a given site?

3) What are the local vs. regional drivers of rainfalld18O variability at a given site?

To unlock the full potential of paleo-isotope records,we need to know:

1) How does d18O of seawater vary through space and time?(and relationship to salinity?)

2) What are the relative contributions of ocean circulationversus atmospheric fluxes to d18Osw variability at a given site?

3) What are the local vs. regional drivers of rainfalld18O variability at a given site?

Applications: improve paleo-proxy interpretations validation/assimilation data for isotope- equipped models

Borneo

Cobb lab daily rainwater collections began in 2005 in Borneo

Map of pastand/or presentGNIP rainfallcollection sites;plotted on rainfall δ18Osource here

Oahu

ChristmasPalmyra

Galapagos

Ecuador

Palau

PNG

Borneo

Cobb/Conroy lab water isotope collection sites daily rainwaters since 2005, weekly seawaters since 2012

Map of pastand/or presentGNIP rainfallcollection sites;plotted on rainfall δ18Osource here

http://www.esrl.noaa.gov/psd/map/clim/sst.shtml

The right place at the right time . . .

http://www.esrl.noaa.gov/psd/map/clim/olr.shtml

Aspects of the water isotope budget that changeacross a major El Niño event:

Aspects of the water isotope budget that changeacross a major El Niño event:

EVERYTHING

Aspects of the water isotope budget that changeacross a major El Niño event:

EVERYTHING

Focus on rainfall, seawater d18O obs today . . .

But seePP41D-06 Identifying Oxygen Isotopic Signatures of ENSO Dynamics Through Isotope-Enabled Regional Ocean ModelingS. Stevenson et al., Thursday 9:15am MW 2010

Christmas coral d18O vs. iso-ROMS coral d18O

Stevenson et al.,Paleo. 2015

coral

Christmas coral d18O vs. iso-ROMS coral d18O

Stevenson et al.,Paleo. 2015

coral

GOAL:iso-hindcast of 2014-2016 ENSO cycle

2015: A record-breaking El Niñoin central tropical Pacific

2015: A record-breaking El Niñoin central tropical Pacific

FieldworkNov 2015Nov 1997

loggers track open-ocean temperatures

water temperatures > 31°C measured last month at Christmas Island

leeward and windward side quite similar,at least during El Niño event

d18 O

(‰)

Christmas Rainfall d18ORa

infa

ll (m

m/d

ay) Christmas Rainfall Amount

-4.2‰-2.1‰

2210

d18 O

(‰)

Christmas Rainfall d18ORa

infa

ll (m

m/d

ay) Christmas Rainfall Amount

-4.2‰2.1‰

2210

Getting more rain, and lighter rain,during El Niño event

impact on seawater isotope budget?

dD=5.8d18O+7.7dD=7.0d18O+6.5dD=8.1d18O+13.3dD=7.7d18O+13.0

2014

2015

Christmas Rainfall LMWLs

d18O (‰)

dD (‰

)

LMWL slope goes from~5 during normal conditions to ~8during El Niño event

dD=5.8d18O+7.7dD=7.0d18O+6.5dD=8.1d18O+13.3dD=7.7d18O+13.0

2014

2015

Christmas Rainfall LMWLs

d18O (‰)

dD (‰

)

LMWL slope goes from~5 during normal conditions to ~8during El Niño event

d-excess goes from10‰ to 15‰ goinginto El Niño event

d18 O

sw (‰

)Christmas Seawater d18O

Salin

ity (p

su)

Christmas Salinity

0.2‰

0.48‰

34.434.6‰

d18 O

sw (‰

)Christmas Seawater d18O

Salin

ity (p

su)

Christmas Salinity

0.2‰

0.48‰

34.434.6‰

>0.3‰ decrease in d18Osw

will have major effect on coral d18O

d18 O

(‰)

Christmas SSS vs seawater d18Osw

Salinity (psu)

d18Osw– SSSrelationshippoorly constrained,but little changeoutside El Niñoevent

d18 O

(‰)

Christmas SSS vs seawater d18Osw

Salinity (psu)

d18Osw– SSSrelationshippoorly constrained,but little changeoutside El Niñoevent

we will add 4xmore data byend of 2016,spanningstrong La Niña event

Oahu

ChristmasPalmyra

Galapagos

Ecuador

Palau

PNG

Borneo

A pan-Pacific iso-view of a strong ENSO extreme

Map of pastand/or presentGNIP rainfallcollection sites;plotted on rainfall δ18Osource here

Conclusions

The 2015/2016 El Niño event has already led to:

anomalous warming of ~4°C on Christmas reef

doubling of rainfall rates, and ~2‰ decrease in d18OR, consistent with amount effect

~0.3‰ decrease in d18OSW

expect coral d18O decrease of >1‰

Opportunities for capacity-building

TPOS2020: isotope-equipped?or at least iso-friendly by design? (urgent)

We need a new archive for water isotope data.- interest in community workshop?

Fate of long-term isotopic timeseries?

THANKS

THANKS