Local effective slope at a paleo-reconstruction site

Returns a per-draw vector of the local \(\beta_{\delta^2 H_p}\) calibration slope at a single site, combining the global precipitation-isotope slope with the spatial slope GP prediction at that site. The fitted coefficient is converted from standard deviations of wax per standard deviation of precipitation to per mil wax per per mil precipitation. Every posterior draw is preserved; only its units change.

Usage

local_effective_slope(
  longitude,
  latitude,
  model_name,
  override = NULL,
  n_draws = NULL,
  verbose = FALSE
)

Arguments

longitude

Numeric, single longitude in decimal degrees.

latitude

Numeric, single latitude in decimal degrees.

model_name

Character, calibration model name (see available_models()). Must be a spatial model (*_sp) for the site-specific slope to differ from the global mean; non-spatial models return the global posterior unchanged.

override

Optional numeric in per mil wax per per mil precipitation. NULL (default) uses the model slope. A single value broadcasts across all draws. A vector of length n_draws is used per draw.

n_draws

Integer, optional number of posterior draws to use (NULL uses all). Forwarded to load_posteriors().

verbose

Logical, whether to print progress messages.

Value

Numeric vector of length n_draws, the per-draw effective slope at the site in per mil wax per per mil precipitation (after override, if any).

Details

Two modes:

• Default: returns the model's per-draw slope at the site.

• Override (single value or per-draw vector) replaces the model slope with a defended local value (e.g., from independent evidence about source-water seasonality, leaf-water enrichment, or vegetation).

The Bayesian inversion propagates its paired local-slope draws internally. Pass this vector as slope = ... only when deliberately overriding that internal calculation with a separately defended slope posterior.

Mechanistic reference values (e.g. the simple two-pool stationarity bound alpha = 1 + epsilon_app/1000 ~ 0.88 under epsilon_app ~= -120 permil; Sessions 2005) are documented for interpretation but are never applied to the returned draws. The frequency of draws above any chosen reference is computable directly from the returned vector (mean(slope > 0.88)) and carries scientific information about how often the calibration implicates non-stationarity at the site.

Examples

if (FALSE) { # \dontrun{
local({
  old <- options(leafwax.suppress_preview_warning = TRUE)
  on.exit(options(old))

  # St. Louis with the baseline_sp model
  s <- local_effective_slope(
    longitude = -90, latitude = 38,
    model_name = "baseline_sp",
    n_draws = 200
  )
  slope_summary <- summary(s)

  # How often does the calibration imply a slope above the simple-model
  # stationarity bound at this site?
  fraction_above_bound <- mean(s > 0.88)

  # Override with a defended local slope
  s_fixed <- local_effective_slope(
    longitude = -90, latitude = 38,
    model_name = "baseline_sp",
    override = 0.55
  )

  # Pass through to the inversion. The slope vector and the
  # inversion's posterior must use the same n_draws: pair
  # local_effective_slope(..., n_draws = N) with
  # invert_d2H(..., n_posterior_draws = N, slope = s), or pass a
  # single point estimate (e.g., median(s)).
  result <- invert_d2H(d2H_wax = -180, d2H_wax_sd = 3,
                       longitude = -90, latitude = 38,
                       model_name = "baseline_sp",
                       n_posterior_draws = 200,
                       slope = s,
                       prior = d2h_prior_normal(-70, 30),
                       verbose = FALSE)
})
} # }