\(\newcommand{\p}[1]{\frac{\partial }{\partial #1}}\) \(\newcommand{\pp}[2]{\frac{\partial #1}{\partial #2}}\) \(\newcommand{\dd}[2]{\frac{d #1}{d #2}}\) \(\newcommand{\h}{\frac{1}{2}}\) \(\newcommand{\op}[1]{\operatorname{#1}}\)

8.7.3.20. Sinking and Swimming

Plankton and particulate organic matter sink with prescribed velocities. The downward flux from a grid cell to the cell below (in mmol m^–2 s^–1) is

\[F_{k,k+1} = w_{\mathrm{sink}} p_k\]

where \(w_{\mathrm{sink}}\) is one of the sinking velocities in Table 8.58 and \(p_k\) is the corresponding tracer concentration in the upper grid cell.

If DARWIN_BOTTOM_SINK is defined, plankton and particulates can also sink into the bottom (where they are lost).

Plankton can also swim upwards with a fixed velocity,

\[F_{k+1,k} = w_{\mathrm{swim}} p_{k+1}\]

Table 8.58 Velocity parameters for particulate organic matter and plankton

trait	parameter	tracer
	wPIC_sink	PIC
	wC_sink	POC
	wN_sink	PON
	wP_sink	POP
	wSi_sink	POSi
	wFe_sink	POFe
biosink	a,b_biosink	plankon (c, n, p, fe, si and Chl quotas if present)
bioswim	a,b_bioswim	plankon (c, n, p, fe, si and Chl quotas if present)