/zscore - Quick Z-Score Analysis Skill

Purpose

Rapidly calculate z-scores for speleothem δ18O, δ13C, and other proxy data to identify significant anomalies. This is the core analysis workflow used multiple times per session.

Usage

/zscore <cave_name_or_entity_id> [--start YEAR] [--end YEAR] [--proxy PROXY] [--threshold Z]

Examples:

/zscore YOKI                              # All Yok Balum data
/zscore CRC-3 --start 1850 --end 1950     # Crystal Cave 1850-1950
/zscore "Bàsura" --proxy d18O,d13C        # Multiple proxies
/zscore 390 --threshold 2.5               # Higher significance threshold

Workflow

Step 1: Get Cave Data

Use MCP tools to retrieve data:

# Search for cave
sisal_search_caves region="Italy" min_samples=50

# Get samples for specific entity
sisal_get_samples entity_id="123"

Step 2: Extract Proxy Measurements

From the returned data, extract:

• d18O_measurement - Oxygen isotope values (‰ VPDB)
• d13C_measurement - Carbon isotope values (‰ VPDB)
• interp_age - Interpolated age (years BP)
• year_CE - Calendar year (1950 - interp_age)

Step 3: Calculate Baseline Statistics

For the full record (or specified baseline period):

δ18O: μ = mean(d18O), σ = std(d18O)
δ13C: μ = mean(d13C), σ = std(d13C)

Step 4: Calculate Z-Scores

For each measurement:

z = (measurement - μ) / σ

Step 5: Identify Anomalies

Apply threshold (default |z| ≥ 2.0):

Z-Score Range	Classification
z ≤ -3.0	EXTREME NEGATIVE
-3.0 < z ≤ -2.0	SIGNIFICANT NEGATIVE
-2.0 < z < +2.0	Normal
+2.0 ≤ z < +3.0	SIGNIFICANT POSITIVE
z ≥ +3.0	EXTREME POSITIVE

Step 6: Generate Output Table

## Z-Score Analysis: [Cave Name]

**Entity**: [entity_id]
**Data range**: [start] - [end] CE
**Measurements**: [N] δ18O, [N] δ13C

### Baseline Statistics

| Proxy | Mean (μ) | Std Dev (σ) | N |
|-------|----------|-------------|---|
| δ18O | -X.XX‰ | X.XX‰ | N |
| δ13C | -X.XX‰ | X.XX‰ | N |

### Anomalies (|z| ≥ 2.0)

| Year CE | δ18O (‰) | δ18O z | δ13C (‰) | δ13C z | Classification |
|---------|----------|--------|----------|--------|----------------|
| ~1394 | -6.23 | -2.16σ | N/A | N/A | SIGNIFICANT NEG |
| ~1285 | -6.89 | -2.46σ | N/A | N/A | SIGNIFICANT NEG |

### Time Windows of Interest

[Group consecutive anomalies into windows]

| Window | Duration | Peak δ18O z | Peak δ13C z | Notes |
|--------|----------|-------------|-------------|-------|
| 1280-1295 CE | 15 yr | -2.46σ | N/A | Possible seismic |

Interpretation Guidelines

δ18O Anomalies

Direction	Typical Cause
Negative (z < -2)	Increased deep/old water contribution OR wetter conditions
Positive (z > +2)	Increased evaporation OR drier conditions

δ13C Anomalies

Direction	Typical Cause
Negative (z < -2)	More biogenic CO₂ (soil respiration)
Positive (z > +2)	More geogenic CO₂ (earthquake/volcanic) OR prior calcite precipitation

Coupled vs Decoupled

Pattern	δ18O	δ13C	Interpretation
COUPLED	Anomaly	Anomaly (same direction)	SEISMIC (Chiodini mechanism)
DECOUPLED	Anomaly	Normal OR opposite	CLIMATIC (drought, volcanic)

Output Format

The skill outputs:

1. Cave metadata (entity, coordinates, coverage)
2. Baseline statistics table
3. All anomalies table (sorted by |z|)
4. Time windows of interest (grouped anomalies)
5. Quick interpretation (coupled/decoupled assessment)

MCP Tools Used

Tool	Purpose
sisal_search_caves	Find cave entity ID
sisal_get_samples	Download measurements

Advanced Options

Multi-Proxy Analysis

/zscore YOKI --proxy d18O,d13C,MgCa

Specific Time Window

/zscore CRC-3 --start 1890 --end 1900  # Around 1896 earthquake

Higher Threshold

/zscore "Bàsura" --threshold 2.5  # More stringent (fewer false positives)

Baseline Period

/zscore YOKI --baseline 1800-1900  # Use specific period for μ/σ

Example Full Output

## Z-Score Analysis: Crystal Cave (CRC-3)

**Entity**: 456
**Coordinates**: 36.59°N, 118.82°W
**Data range**: 873 - 2006 CE
**Measurements**: 1,054 δ18O

### Baseline Statistics

| Proxy | Mean (μ) | Std Dev (σ) | N |
|-------|----------|-------------|---|
| δ18O | -8.23‰ | 0.42‰ | 1,054 |

### Anomalies (|z| ≥ 2.0)

| Year CE | δ18O (‰) | δ18O z | Classification |
|---------|----------|--------|----------------|
| ~1741 | -9.72 | -3.54σ | **EXTREME NEG** |
| ~1896 | -9.13 | -2.14σ | SIGNIFICANT NEG |
| ~1910 | -9.72 | -3.54σ | **EXTREME NEG** |
| ... | ... | ... | ... |

**Total anomalies**: 47 (4.5% of record)

### Top 5 Most Extreme

1. ~1741 CE: z = -3.54σ (Pre-Spanish earthquake?)
2. ~1910 CE: z = -3.54σ (Known M6.0 Bishop)
3. ~1929 CE: z = -2.61σ (Known M5.5 Independence)
4. ~1896 CE: z = -2.14σ (Known M6.3 Independence)
5. ~1984 CE: z = -2.71σ (Known M6.1 Round Valley)

### Interpretation

✓ Modern earthquakes (1896, 1910, 1929, 1984) all show z ≤ -2.0
✓ Pre-Spanish ~1741 anomaly consistent with Rose Canyon/Kern Canyon event
✓ Cave shows reliable seismic sensitivity

Important Notes

1. Z-scores are relative - Compare within same cave record
2. Resolution matters - Annual vs decadal samples affect detection
3. Missing data - Note gaps in record around anomalies
4. Multi-proxy preferred - Single proxy anomaly is weaker evidence
5. Follow up with /classify-anomaly - For full seismic vs climatic discrimination