2.3 Sediment
The sediment budget (Fig. 3) is a crucial foundation for constructing budgets of other geochemical properties. Although the Mackenzie loadings are well constrained (Macdonald et al., 1998), it is less certain what portion of this load stops in the delta leading to uncertainty in other sedimentary components for the shelf.
Because we have no direct measurements of particle export, the quantity escaping the shelf is estimated as the difference between input and sedimentation leading to an uncertainty of the same order as the estimate. On arctic shelves ice is an important way to export particles (Reimnitz et al., 1993) and yet we have no data for this process on the Mackenzie shelf.
2.4 Dissolved inorganic phosporus (DIP)
The DIP budget (Fig. 4) shows that shelf-edge exchanges dominate and that very little DIP enters in runoff. Using concentrations based on salinity-DIP relationships (Macdonald et al., 1987) to estimate shelf edge exchanges implies a loss (ΔP) to shelf sediments if the budget is to be balanced. This may partly explain high sediment P observed over the central shelf (Ruttenberg and Goni, 1996) but it is also likely that DIP is removed to sediments in the estuary by flocculation and particle settling (cf. Macdonald et al., 1987; Ruttenberg and Goni, 1990). In Mackenzie shelf sediments, there is a close relationship between solid phase Fe and P and a decrease in solid-phase P with depth (Gobeil et al., 1991). Phosphorus, therefore, is clearly linked to Fe geochemistry and a portion of the P must undergo regeneration back to the water column. It is difficult to use sediment measurements of total P to estimate the fraction of P actively cycling (Fig. 4) because the Mackenzie River supplies large amounts of solid phase P (〜870 μg/g), some of which may be available, carried by a large and variable background sediment flux (Gobeil et al., 1991, Ruttenberg and Goni, 1996).
2.5 Dissolved inorganic nitrogen (DIN)
An important component of the DIN budget is supplied by the Mackenzie River (Fig. 5). There is a significant sink (ΔN) in sediments which, compared to ΔP, exceeds the Redfield ratio (ΔN: ΔP = 26:1 - Redfield = 16:1) suggesting a preferential loss of DIN.
