calcite dissolution in sediments

[jornbr]

In sediment.F90 (p4zsed.F90 in PISCES r4.0-HEAD.r13720), calcite dissolution in sediment depends on the calcite saturation state of the overlying water (Eq 91 in paper):

fabm-pisces/src/sediment.F90

Lines 113 to 114 in 4fa3027

	zfactcal = MIN( excess, 0.2 )
	zfactcal = MIN( 1., 1.3 * ( 0.2 - zfactcal ) / ( 0.4 - zfactcal ) ) ! Jorn: Eq 91

Does zfactcal represent the preserved fraction, as hinted at by the paper and matching the fact that it increases with increasing saturation [= decreasing zfactcal]? Or does it represent the dissolved fraction, as it is treated in the original PISCES code? In the latter case, however, excess takes negative values when the water is supersaturated. This leads to zfactcal being positive and dissolution occurring. Is that intentional? It leads to further oversaturation and even faster dissolution - a positive feedback.