Land to Ocean Transfer of Organic 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 Depth (cm) Organic Carbon (%)

Waipaoa Sedimentary System Cores 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) Cumulative Percent –7 cm % OC –19 cm % OC –31 cm % OC –7 cm 18–19 cm30–31 cm Bulk >25  m 4–25  m <4  m Bulk >25  m 4–25  m <4  m Particle Size Distributions %OC in Size Fractions Bulk >25  m 4–25  m <4  m % <4  m % 4–25  m % >25  m

U2303 (27 m Water Depth) % of Total OC in Sample > 25  m< 4  m 4–25  m > 25  m< 4  m 4–25  m Weight Percent > 25  m < 4  m 4–25  m Weight Percent Weight Percent –7 cm 30–31 cm 18–19 cm

%OC as a Function of Particle Size FloodplainMid Shelf 27 m Mid Shelf 56 m Upper Slope

 13C Trends from Floodplain to Slope FloodplainMid Shelf 27 m Mid Shelf 56 m Upper Slope  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?