# `oxygen_boundary()`

**Category:** Oxygen-profile diagnostics

**Status:** experimental development API; DEC-036 certified C7 subset

## Purpose

Resolve the connected low-oxygen component containing a certified profile
minimum and report its observed upper/lower boundary evidence for an explicit
user threshold. The package supplies no default OMZ/ODZ threshold.

## Real signature

```r
oxygen_boundary(
  x,
  threshold,
  threshold_unit = NULL,
  variable = NULL,
  support = c("local", "all")
)
```

`threshold_unit = NULL` means the exact source unit. Only exact multiplicative
conversion inside the source quantity family is allowed. Point crossings may
be exact or locally interpolated across contiguous support. Cell means and
gapped brackets remain bracket-only evidence; open edges are not extrapolated,
and exact thickness requires two exact/interpolated point boundaries.

Oxygen identity is established exclusively from supported preserved CF
`standard_name` plus units. Variable names, `long_name`, saturation, AOU,
density conversions, mL/L, smoothing, and universal classifications are not
part of C7.

Related functions: `transition_layer()`, `depth_gradient()`, `depth_feature()`.