Subgrid topography from ETOPO

This how-to shows how to obtain subgrid-scale seafloor information from the ETOPO1 1-arc-minute global relief model and bin it onto an AIBECS grid. Two diagnostics are exposed:

• fractiontopo — fraction of subgrid sediment in each wet box,

• roughnesstopo — proxy for topographic roughness.

Loading the ETOPO data requires Distances and NCDatasets so the AIBECSETOPOExt extension activates.

using AIBECS, Plots
using Distances, NCDatasets
using JLD2 # required by `OCIM2.load`

Load ETOPO and the target grid

grd, _ = OCIM2.load()
Z, lats, lons = ETOPO.load()                 # bedrock variant by default

(Union{Missing, Float64}[-56.0 -60.0 … -4229.0 -4228.0; -56.0 -60.0 … -4229.0 -4228.0; … ; -56.0 -60.0 … -4229.0 -4228.0; -56.0 -60.0 … -4229.0 -4228.0], -89.99999999999997:0.016666666666666663:90.0, -180.0:0.016666666666666666:180.0)

Fraction of sediment per box

f = ETOPO.fractiontopo(grd)
plothorizontalslice(f, grd, depth = 3000u"m", color = :viridis)

Cells with f > 0 at depth z correspond to grid boxes whose subgrid topography pokes above z.

Roughness proxy

r = ETOPO.roughnesstopo(grd)
plothorizontalslice(r, grd, depth = 3000u"m", color = :inferno)

Higher values flag boxes overlapping the seafloor with significant elevation variability — useful when parameterising boundary fluxes (e.g. sediment release) or interior mixing.

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