Subsurface Oxygen Maximum (SOM)

OceanGraph detects a supported local maximum in a profile’s dissolved oxygen measurements. SOM is an exploration indicator for upper-ocean oxygen structure, not a guarantee that every physical maximum will be detected.

Use SOM

After signing in and loading profiles, choose Data layer → SOM (under Tools on narrower layouts). SOM requires dissolved oxygen data; Only profiles with BGC helps narrow the search, but does not guarantee oxygen availability.

Profiles without oxygen or a valid SOM are shown as no-data markers. Marker tooltips show SOM pressure and oxygen.

The vertical profile shows SOM as a purple dashed line when the selected observation’s curve is displayed and SOM falls within 0–Max (dbar). The line marks the same depth across displayed variables; Trajectory and a section are not required.

On an oxygen section, valid SOM values appear as purple points connected only across consecutive profile cycles. Gaps indicate a missing cycle or a profile where SOM was not detected or could not be calculated.

Detection

• With a valid MLD, candidates must be deeper than MLD and no deeper than 300 dbar. Without MLD, the range is 30–300 dbar. Profiles with MLD at 300 dbar or deeper are not assigned SOM.
• Detection uses finite source oxygen observations after quality masking and numeric-range checks. Internal gaps are interpolated only to evaluate peak shape; downloaded Profile JSON is not filled.
• A candidate must be an observed local maximum with at least 5 µmol/kg prominence and enough observed support around the peak. Endpoints, monotonic profiles, weak or unsupported narrow peaks, and peaks created only by interpolation are not reported.
• Candidates are ranked by prominence, oxygen value, then shallower pressure. When MLD exists, a supported peak within 100 dbar below MLD is preferred when available.

The result stores pressure in dbar and dissolved oxygen in µmol/kg. If no candidate satisfies the criteria, SOM is undefined.