Organic and inorganic carbon stocks in marine sediments around Aotearoa New Zealand [Dataset 1.0]

Background In December 2022 the Parliamentary Commissioner for the Environment (PCE) commissioned NIWA to undertake a study of the organic carbon (OC) stocks in marine sediments around Aotearoa New Zealand and their potential vulnerability to anthropogenic disturbance. This report was published in 2023 (Nodder et al., 2023) (https://pce.parliament.nz/publications/organic-carbon-stocks-and-potential-vulnerability-in-marine-sediments-around-aotearoa-new-zealand/). As a key component of the project, a novel seafloor sediment dataset that encompassed the Territorial Seas (12 nautical miles, NM) and the Exclusive Economic Zone (EEZ, 200 NM) around Aotearoa New Zealand was compiled (Figure 1). These data will form the basis of a subsequent publication in a peer-reviewed journal (Nodder et al., in preparation, “Organic and inorganic carbon stocks and potential vulnerability in marine sediments around Aotearoa New Zealand”). Datasets All seabed descriptions, geochemical data and grain-size information represent a significant compilation of available offshore data across the Aotearoa New Zealand EEZ, reflecting more than 60 years of offshore data collection (i.e., from late 1950s to present-day) (see Bostock et al., 2019a, b). Various datasets were also compiled from published and unpublished literature and reports as in the following: · Deep-water environments (continental slope to abyssal plains and trenches, >200 m water depth) (e.g., Gibbs et al., 2020; Law et al., 2010; Leduc et al., 2024; Leduc et al., 2020; Leduc et al., 2016a; Leduc et al., 2016b; Maier et al., 2025; Murray et al., 2024; Nodder et al., 2007; Nodder et al., 2025; Nodder et al., 2003; Pilditch et al., 2015; Rosli et al., 2018; Xu et al., 2021); · Continental shelf (0-200 m) (e.g., Brackley et al., 2010; Giles et al., 2007; Kniskern et al., 2014; Sikes et al., 2009; Uhle et al., 2007); · Fjords (e.g., Cui et al., 2016; Hinojosa et al., 2014; Ramirez et al., 2016); and · Coastal and estuarine habitats, including data provided in regional council reports and research papers (e.g., Berthelsen et al., 2020; Bulmer et al., 2017; Bulmer et al., 2020; Clark et al., 2018; Douglas et al., 2022; Douglas et al., 2019; Drylie et al., 2018; Gladstone-Gallagher et al., 2016; Lohrer et al., 2015; Mangan et al., 2020; Needham et al., 2011; Petersen et al., 2022; Pratt et al., 2014; Swales et al., 2021; Thrush et al., 2021; Zeldis et al., 2020). Additional datasets from shallow scallop surveys were provided by Fisheries New Zealand (Williams et al., 2024), from historic aquaculture surveys in the Te Tau Ihu Marlborough Sounds (Handley et al., 2020) and from environmental baseline surveys in two offshore petroleum licences: (OMV - Great South Basin; Beaumont et al., 2019) and (StatOil - Reinga Basin; Mitchell et al., 2016a; Mitchell et al., 2016b). To maximise the input data for our first-order assessment, all OC and sediment data were compiled, regardless of collection date. Primary datasets considered for this study include: · Organic Carbon data (Percentage OC) · Percentage Total Organic Matter (Percentage TOM) · Carbonate (Percentage CaCO3) (converted to Inorganic Carbon (IC) using the formula in Smeaton et al. (2021) based on stoichiometry where CaCO3 = 100.059 g mol-1 and C = 12.011 g mol-1, so that Fraction IC = 12.011/100.059 = 0.12. Therefore the percentage of IC in sediments is %CaCO3 multiplied by 0.12. · Grain-size fraction (Percentage Gravel, Sand, Silt, Clay, and Mud [Silt + Clay]) Since no central data repository for samples collected across the EEZ presently exists, it remains uncertain how much data may be missing from this compilation dataset. Due to the variability of source datasets, the compilation of all data into a singular input database was undertaken through the initial development of two separate compilation datasets. These datasets can be summarised by: · nzSEABED Database (Bostock et al., 2019a, b) 9970 entries · New sediment OC Database (this study; all data) 7647 entries · New sediment OC Database (this study; data with positioning) 7292 entries These databases were first compiled separately since the nzSEABED database presents an overview of NIWA’s legacy grain-size, TOM, CaCO3 and accessory mineralogy data only. Data QA/QC Although the new OC database represents data from a variety of sources, including published databases, these data were integrated into a bespoke data structure to ensure consistency between datasets for subsequent analysis. Unique sampling identifications were based on the Survey or Source data, the Site or Station number or identifier, and the Sample Depth Interval. Where an analytical detection limit was identified, the maximum credible value was used (e.g., <0.1% was altered to 0.1 in the database). Although likely resulting in an overestimation, the additional error this introduces was viewed as minimal with respect to the wider dataset. Due to the project-specific approach to sediment sampling in many offshore surveys across the Aotearoa New Zealand EEZ, many of the input datasets are inconsistent with regards to captured data types (e.g., OC vs TOM) and sediment sampling intervals. Originally, an additional 355 entries were included in the database but were either missing or had incorrect positioning, resulting in a final total of 7292 dataset entries, all of which include associated location information. Of all the entries incorporated into the new OC database, almost 50% of all data contained OC values (3651 entries in total, reducing to 3620 excluding data with no positioning information), with 3414 samples with associated CaCO3 analyses and hence IC estimates. Acknowledgements We would like to thank Simon Upton (Parliamentary Commissioner for the Environment) for his encouragement and support of the initial study. The National Estuary Dataset was compiled by the Cawthron Institute under the Oranga Taiao Oranga Tangata (OTOT) research programme, which was funded by the New Zealand Ministry of Business, Innovation and Employment (MBIE) contract MAUX1502, led by Murray Patterson (Massey University). Data from the Tauranga Subtidal Ecological Survey were provided by Cawthron Institute, led by Dana Clark. Similarly, the provision of unpublished data from the MBIE Smart Idea Blue Carbon project, led by Richard Bulmer (Tidal Research) with many collaborators is also gratefully acknowledged. Several New Zealand regional authorities provided data and permission to use it: Northland Regional Council, Auckland Regional Council, Waikato Regional Council, Bay of Plenty Regional Council, Hawkes Bay Regional Council, Horizons Regional Council, Greater Wellington Regional Council, Marlborough District Council, Nelson City Council, Tasman District Council, West Coast Regional Council, Environment Canterbury, Christchurch City Council, Otago Regional Council and Environment Southland. Data from the petroleum prospecting areas PEP55781 Reinga Basin and PEP 50119 Great South Basin are held by NIWA on behalf of StatOil/Equinor and OMV, respectively, and released with permission. 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