Land to Ocean Transfer ofOrganic Carbon in the

Waipaoa Sedimentary System

Hannah Brackley

Landcare Research NZ Ltd

Erosion-related Carbon Losses

Introduction

Previous research has recognised an increase in OC burial on the Waipaoa River floodplain and Poverty Bay shelf since the arrival of Europeans.

Poverty Bay Shelf

De

pth

(cm

)

Organic Carbon (%)

Waipaoa Sedimentary SystemCores collected from:

• Waipaoa River Floodplain

• Poverty Bay Shelf/slope:

U2303:– 7.5 km from river mouth

– 27 m water depth

U2305:

– 22.5 km from river mouth

– 56 m water depth

W697:

– 40 km from river mouth

– 1200 m water depth

U2303 (27 m Water Depth)C

umul

ativ

e P

erce

nt

0

20

40

60

80

100

6–7 cm

% O

C

0.0

0.2

0.4

0.6

0.8

1.0

18–19 cm

% O

C

0

1

2

3

30–31 cm

% O

C0.0

0.2

0.4

0.6

0.8

1.0

6–7 cm 18–19 cm 30–31 cm

Bulk >25 m 4–25m <4 m

Bulk >25 m 4–25m <4 m

Particle Size Distributions

%OC in Size Fractions

Bulk >25 m 4–25m <4 m

% <4 m

% 4–25 m

% >25 m

U2303 (27 m Water Depth)

% ofTotal OCin Sample

> 25 m < 4 m4–25m

> 25 m < 4 m4–25 m

Wei

ght

Per

cent

0

20

40

60

80

100

> 25 m < 4 m4–25 m

Wei

ght

Per

cent

0

20

40

60

80

100

Wei

ght

Per

cent

0

10

20

30

40

50

60

6–7 cm

30–31 cm

18–19 cm

%OC as a Function of Particle Size2D Graph 2

%O

C

0.0

0.2

0.4

0.6

0.8

>25 m4-25 m<4 m

Floodplain Mid Shelf27 m

Mid Shelf56 m

UpperSlope

13C Trends from Floodplain to Slope

-26

-25

-24

-23

-22

<4 m

>25 m

Floodplain Mid Shelf27 m

Mid Shelf56 m

UpperSlope

13C

Questions

• How are flood events preserved on the shelf, and how do they influence the OC?

• How do changing terrestrial processes influence the amount and character of OC being transported offshore?

• Are the riverine particles losing their terrestrial OC when discharged to the ocean, and if so, are they reloading with marine OC?