Purpose
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New Zealand has a large and geologically complex marine Exclusive Economic Zone (EEZ) and extended continental shelf (ECS).
Data from ~150 published, unpublished, national and international collections covering >30,000 sediment analyses and observations
were compiled and integrated to produce a database (nzSEABED) and series of maps characterising the surficial sediments
of the entire New Zealand EEZ-ECS. Sediment grainsize/texture and carbonate distributions show distinct spatial patterns,
which can be explained by past and present climate, sea level fluctuations, terrigenous (from the land) sediment flux,
tectonics and volcanism, complex bathymetry, oceanography, and diagenesis. The results are compared with previous literature,
providing a comprehensive review of the distribution of surficial marine sediments for the New Zealand EEZ-ECS.The sediment
samples and data were collected from approximately the 1950-2000s using a range of different sampling methods and analytical
methods. The most common methods for sampling surface sediments were grabs, dredges and corers. Other methods included trawls,
sleds, diver samples and underwater camera observations and some methods were not recorded. All these methods may yield
a biased sample. For example, cores struggle to admit shell, and sediments coarser than gravel. Grainsize analyses were done
using a range of methods, from descriptions, sieving and more recently using Xray attenuation and laser techniques. Carbonate
analyses were done using descriptions, acid digestion and titration.
The dbSEABED software (http://instaar.colorado.edu/~jenkinsc/dbseabed/) was used to integrate the diverse, heterogeneous
collated data. All the data are quality controlled. For analytical quantitative data the values are tested for plausibility.
For word-based data, descriptions are parsed and meanings and values are attached to the essential terms. For example,
a description of “muddy sand” will be assigned as 40% mud and 60% sand. A sample which is described as “pelagic ooze” (a sample
made up of carbonate plankton skeletons), a carbonate content of 90% is attributed. Details are described in Jenkins (1997;
2002) and Buczkowski et al. (2006). The character values are based on calibrations from datasets where both descriptions
and analyses are present on thousands of samples (Harff et al., 1997; McMullen et al., 2014).
Processed and integrated sediment data from nzSEABED were imported in to ArcGIS using a Mercator projection in order to allow
for seamless interpolations across the 180°meridian. The data was interpolated using ordinary kriging based on the 12 nearest
points with a restricted distance of 100 km, and plotted the data on a 1x1 km grid. The predicted standard error (standard
deviation for any point) for percent mud for the kriging interpolation is low in well sampled regions such as the continental
shelf and Chatham Rise (8-16%), and increases in the more sparsely sampled deep waters (20-24% at >3000 m). It should be
noted that we have not included rocks in this database, thus the interpolated sediments will superimpose over rock outcrops.
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Credit
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NIWA
See:
Bostock et al., 2018. Distribution of surficial sediments in the ocean around New Zealand/Aotearoa. Part A: continental
slope and deep ocean. New Zealand Journal of Geology and Geophysics.
Bostock et al., 2018. Distribution of surficial sediments in the ocean around New Zealand/Aotearoa. Part B: continental
shelf. New Zealand Journal of Geology and Geophysics.
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