Mixed-layer depth (Δσθ 0.02)
Mixed-layer depth: where sigma-theta is 0.02 kg/m3 greater than at 10 m (CalCOFI legacy definition)
mkey mld_sigma_theta_002P06 units ULAAseries mld_sigma_theta_002
one value per cast One value per cast. This measurement is worked out once for each cast rather than read at every depth, so it has no depth profile and no anomaly against a normal; its values are rows of sample_measurement, not of obs_env.
CalCOFI holds 9,360 values of it from 9,360 sampling events in one dataset, 1993–2026, one per cast.R The mixed layer is the wind-stirred skin of the ocean above the density step that keeps deeper water from rising into it; how deep it is decides how much light the plankton in it get and whether deep nutrients can reach them, and off California warmer, more layered years have gone with fewer zooplankton.C
- 9,360
- values
- 0
- flagged
- 1993–2026
- years
- 1
- dataset
- every month
- months
Measured in
1 dataset
i
One row per series, one cell per year, darker with more values — the same strip the front
door draws per dataset and a species page draws per taxon. Each row is one dataset's own
measurement_type; the label is written once, in the title above.
i
One row per series, one cell per year, darker with more values — the same strip the front door draws per dataset and a species page draws per taxon. Each row is one dataset's own measurement_type; the label is written once, in the title above.
-
series
mld_sigma_theta_002· source columnsigma_theta_aveone value per cast no flag at this grain no P01 concept
Explorerdb-queryThis page as JSON R · Python · Parquet
Every way in 6 ways · Parquet · R · Python · JSON
Read from measurements.json of release v2026.10.21, written at release by calcofi4db::build_measurements_catalog() beside taxa.json. The catalog's index is /measurements/; the JSON-LD on this page is a schema.org/DefinedTerm in the NERC P01 term set with a PropertyValue per series.
Explorerdb-querySELECT * FROM read_json('…/v2026.10.21/catalog.json')
-- objects[] WHERE table = 'sample_measurement'
-- then filter the rows:
-- measurement_type IN ('mld_sigma_theta_002')library(calcofi4r)
con <- cc_get_db() # the promoted release
tbl(con, "sample_measurement") |> filter(measurement_type %in% c("mld_sigma_theta_002"))import calcofi4py as cc
con = cc.cc_get_db()
con.sql("SELECT * FROM sample_measurement WHERE measurement_type IN ('mld_sigma_theta_002')").df()How it is measured Computed from the CTD profile (1 m bins)
The mixed-layer depth, headline: the depth at which sigma-theta is 0.02 kg/m3 greater than at a reference depth of 10 m, the CalCOFI legacy definition (CTD team: "MLD is the depth at which sigma-theta is 0.02 kg/m3 greater [than at] a reference depth of 10 m"); taken on the 1 m bins and interpolated linearly between the bracketing bins; absent where the cast never crosses or does not reach 10 m. (the record's own derivation (measurement_type.csv); questions Q01 (Rasmus Swalethorp, 2026-09-23))
- take sigma-theta at 10 m
- find the first depth 0.02 kg/m3 denser
Why it matters 4 ways to say it
other ways to say why · 3
- This is the headline mixed-layer depth, the CalCOFI legacy definition the CTD team asked for: the depth at which sigma-theta is 0.02 kg/m3 greater than at a reference depth of 10 m (Rasmus Swalethorp, SIO, 2026-09-23). There is no single mixed-layer depth: each criterion draws the line at a different density or temperature step from a 10 m reference, so the depths published here differ by design; compare a depth only with one made by the same criterion. needs a citation before it can be the pick
- Wikipedia Pycnocline source
- Wikipedia The oceanic or limnological mixed layer is a layer in which active turbulence has homogenized some range of depths. The surface mixed layer is a layer in which this turbulence is generated by winds, surface heat fluxes, or processes such as evaporation or sea ice formation which result in an increase in salinity. Mixed layer · CC BY-SA 4.0 · rev. 1373305767
Units and range m · 0 … 6500 declared · 0 flagged
m · P06 units ULAA
details
- bounds
- The registry declares
0 … 6500 mformld_sigma_theta_002; a value outside it is dropped at the ingest (drop_out_of_bounds()). - observed
- CTD Derived Products
mld_sigma_theta_00210.02 · median 18.84 · 133.1 m (5th–95th percentile 10.29–60.73) - flags
- CTD Derived Products
mld_sigma_theta_002carries no quality code at the release grain; qual_ok keeps all 9,360. - baseline
- A monthly climatology exists for this measurement (the release's climatology table: 1993–2013, dataset × station × the cruise's month × 10 m bin), so the Explorer can draw anomalies against it rather than values.
- derivation
- calcofi4db::ctd_mld(criterion = 'sigma_theta', threshold = 0.02, ref_depth = 10) on the 1 m bins, interpolated linearly between the bracketing bins; the provider's definition (Rasmus Swalethorp 2026-09-23, questions Q01): 'the depth at which sigma-theta is 0.02 kg/m3 greater [than at] a reference depth of 10 m'; absent where the cast never crosses or does not reach 10 m
The familiar scale i
Bars are each series' 5th–95th percentile, the line its minimum to maximum, the ring its median;
the marks are metadata/measurement_scale.csv's, each hovering to its own source.
i
Bars are each series' 5th–95th percentile, the line its minimum to maximum, the ring its median;
the marks are metadata/measurement_scale.csv's, each hovering to its own source.
By month every month
By month i
Values per calendar month, one row per series: CalCOFI's quarterly cruises show as peaks in
the months the ships sail.
i
Values per calendar month, one row per series: CalCOFI's quarterly cruises show as peaks in the months the ships sail.
Cite the release, v2026.10.21
Cite the release; each dataset's own citation, licence and DOI are on its page — CTD Derived Products. The Explorer's Share → Cite writes it for the view you make.