Scotian Shelf inflow at Cape Sable

Transport of the Nova Scotia Current across a line off Cape Sable, where cold fresh Scotian Shelf Water rounds the cape and enters the Gulf of Maine. Positive values are into the Gulf. Informally this is the "Scotian Shelf crossover": the partition of shelf water between entering the Gulf and continuing past it.

Usage

scotian_shelf_inflow(
  env_dat,
  u = "UO",
  v = "VO",
  spacing = NULL,
  min_coverage = 0.5,
  name = "scotian_inflow"
)

Arguments

env_dat: an sf POINT object with one row per location and time step, as datamatch's access functions return, on a regular lon/lat grid, with eastward and northward velocity columns
u: name of the eastward velocity column, in m/s
v: name of the northward velocity column, in m/s
spacing: sample spacing along the section, in km. NULL uses half a grid cell.
min_coverage: fraction of sample points that must carry a velocity for the step to return a value
name: name for the new column

Value

env_dat with a scotian_inflow column, in m^2/s, positive into the Gulf of Maine

Details

Scotian Shelf Water supplies more than half of the Gulf of Maine's freshwater budget, and its inflow drives Gulf salinity at seasonal and interannual scales (Feng et al. 2016; Wang et al. 2022). The inflow is also the fresh, cold, nutrient-poor counterpart to the slope water entering through the Northeast Channel, and the two alternate episodically (Townsend et al. 2015), which is why northeast_channel_inflow() is a separate index rather than a variant of this one.

Why the section is fixed

An index named for a place is defined by that place. A "crossover" computed somewhere else is a different quantity that happens to share a function, so the endpoints are not an argument. Use section_transport() for any other line, and scotian_shelf_inflow_section() to see or plot the geometry used here.

The endpoints run from Cape Sable southwest across the shelf toward the head of the Northeast Channel. They are approximate, chosen to cut the current where it rounds the cape rather than to reproduce a particular published section, and no published index is being replicated here.

References

Feng H, Vandemark D, Wilkin J (2016). Gulf of Maine salinity variation and its correlation with upstream Scotian Shelf currents at seasonal and interannual time scales. Journal of Geophysical Research: Oceans 121. doi:10.1002/2016JC012337

Wang et al. (2022). Freshwater transport in the Scotian Shelf and its impacts on the Gulf of Maine salinity. Journal of Geophysical Research: Oceans 127. doi:10.1029/2021JC017663

Examples

if (FALSE) { # \dontrun{
env <- scotian_shelf_inflow(env)
} # }