CUSTARDCarbon Uptake and Seasonal Traits of

Antarctic Remineralisation Depth

CUSTARD is part of

Role of the Southern Ocean in the Earth System 

(RoSES)

Also includes• ORCHESTRA (PI Mike Meredith, NERC centres)• SONATA (PI Corinne le Quere)• PICCOLO (PI Karen Heywood)

55S60S 50S65S

500m

1000m

4000m

surface

SAMW

AAIW

AABW

CDW

SubAntarcticFront

PolarFront

Latitude

Dep

th

55S60S 50S65S

500m

1000m

4000m

surface

SAMW

AAIW

AABW

CDW

SubAntarcticFront

PolarFront

Latitude

Dep

th

55S60S 50S65S

500m

1000m

4000m

surface3

4

SAMW

AAIW

AABW

CDW

2

1

SubAntarcticFront

PolarFront

Latitude

Dep

th

0.35 Pg C /yr

S. Ocean total C uptake rate =1.2 Pg C /yrLandschützer et al. (2015) Science

Southern Oceannatural Cuptake rate

Carbon flux into the Southern Ocean

Uncertainty 1861-2005

Anthropogenic 20 Pg C a

Natural >50 Pg C b

a Frölicher et al (2015) J.Climb CUSTARD preliminary modelling

S

Depth of remineralisation

300mSi

nkin

g ra

te (m

/d)

0.8

0.6

0.4

0.2

0.0Iron

repleteIron

stressedRedrawn fromMuggli et al. (1996) MEPS

1.0

Image courtesy of M. Iversen

Actinocyclus sp.

Seasonal influences onremineralisation depth

• Iron• Silicate• Phytoplankton community• Phytoplankton physiology• Primary and export production

Hypothesis:

The seasonal interplay ofupper limb surface biogeochemistry, circulation and remineralisation

controls how long carbon entering the ocean is kept out of the 

atmosphere. 

Approach

• Focus on key water mass formation area

• Sensors, mooring & gliders: annual cycle

• Cruise: gradients, dynamic spring period

• Modelling: consequences for C

Location

Holte & Talley (2009) JAOTech

Sr1b

Location

OOITN

TS

Holte & Talley (2009) JAOTech

What are the seasonal air-sea C flux and macronutrient drawdown? (WP1)

• C data in key mode water area• Seasonal CO2 and drivers • Seasonal silicate & nitrate• Augmented by repeat transects

in spring Bouman et al. (2012)

o wintero summer

Landschützer et al. (2013)

OOITS

What is the seasonality in iron stress and its impacts? (WP2)

• Full year time series of productivity & iron stress

• Response to iron stress• Iron dynamics in key spring

period Browning et al. (2014)

Redrawn from Moore et al. (2007)

silic

ate:

nitr

ate

(mol

:mol

)4

3

2

1

0

noadded

ironadded

iron

low high

Iron stress

What is the seasonality in remineralisation depth? (WP3)

• Annual time-series of remin. depth• Cutting-edge glider method (GOCART)• Cruise Marine Snowcatcher samples:

- benchmark, composition, speed

Flux

at 4

00

mFl

ux a

t 10

0m

days

How does seasonality in S. Oceanremin. depth affect C storage? (WP4)

• Quantify fate of organic C• Multiple models for robustness• Parameterisations

?

Cruise

The CUSTARD team

WP1 WP2

WP3 WP4

CUSTARD

CARBON ironsilica

phytoplankton

mode water

remin.depth

Extra

Southern OceanNatural CUptake rate

~0.2 Pg C yr-1

Based on estimate with largest uncertainty in Marsay  et al. (2015)

From Takeda et al. (1998) Nature

From Brown,…Landschützer, Bakker et al., (2015) GBC

Seasonal variation in export

Calculated using the export algorithm of Henson et al. (2012)

Jul         Sep        Nov          Jan        Mar        May 

0.4

0.3

0.5

0.2

0.1

Expo

rt flux (gCm

‐2day‐1 )