Carbonate sand deposit model in Nordland

• Model run in UTM zone 33N • The model was run in 2014 by NIVA • Data collected 2011-2013 by NGU, NIVA included absences from kelp surveys • The data were collected in Nordland county, but the models covers also a small part of Troms in the North and Trøndelag in the south. • 1078 datapoints, but only data down to 100 m depth and with more than 50 % carbonate content were included, resulting in 473 presences. • Modelled using Maxent on presence data, validated with 139 presences and 740 absences (the validation points are spatially biased towards areas shallower than 40 m depth) • Modelled the probability of finding carbonate sand with more that 50 % carbonate content (carbonate contact below 50 % is absence together with rocky seabed and other non-carbonate sand areas) • Input variables: depth, slope, curvature (with both 250, 500 and 1000 m calculation window), wave exposure, maximum current speed and mean current speed • Depth, slope, curvature and wave exposure had spatial resolution of 25 m, models developed by NIVA. The current speed had 200 m spatial resolution (developed from NorKyst800). • Cut-off value for identifying polygon presences: 0.31 • spatial (horizontal) distribution is……. • AUC=0.88 using independent validation presences and absences