This project investigates potential geochemical and gas flux sources associated with newly discovered pockmarks in Seneca Lake, New York. The study is motivated by two longstanding and unresolved observations in the lake:

1. An acoustic phenomenon historically referred to as the "Seneca Drums", unexplained booming sounds occasionally reported around the lake.
2. Increasing chloride concentrations in Seneca Lake that exceed expected values based on known inputs and mass-balance calculations.

Subaqueous pockmarks—depressions in lakebed sediments often associated with gas seepage or fluid discharge—may represent previously unidentified pathways for methane or saline groundwater entering the lake.

This project explores whether pockmarks in Seneca Lake could act as active sources of methane or chloride, potentially contributing to both the acoustic phenomenon and unexplained increases in salinity.

Research Objectives

The primary objectives of this study are to:

• Determine whether pockmarks are actively releasing methane.
• Evaluate whether pockmarks may serve as localized sources of chloride to the water column.
• Compare geochemical conditions inside pockmarks vs. surrounding sediments.
• Assess whether pockmarks could represent a previously unaccounted source in Seneca Lake chloride mass balance calculations.

Field sampling was conducted in September 2025 in Seneca Lake, New York.

A subset of 14 newly identified pockmarks was sampled using a Niskin water sampler.

For each pockmark:

• 3 water samples were collected inside the pockmark
• 3 water samples were collected immediately outside the pockmark

These paired samples allow comparison of water chemistry within pockmark depressions and the surrounding lakebed environment.

In addition, two control sites located in areas without pockmarks were sampled to provide baseline lake conditions.

Chloride concentrations were specifically measured within pockmarks to determine whether localized chloride enrichment occurs.

Sampling design:

• 3 chloride samples collected inside each pockmark
• Total pockmarks sampled: 14

These measurements will help evaluate whether pockmarks could contribute to the observed increase in chloride concentrations in Seneca Lake.

Water samples collected inside and outside pockmarks will be analyzed for dissolved methane concentrations.

Comparisons will be made between:

• Inside pockmarks
• Outside pockmarks
• Control sites elsewhere in the lake

These analyses will help determine whether pockmarks represent active methane seep locations.

Hypothesis

If pockmarks represent active subsurface fluid pathways, we expect:

• Elevated methane concentrations within pockmarks relative to surrounding waters
• Elevated chloride concentrations inside pockmarks compared to nearby samples and control sites

Such findings would suggest that pockmarks may function as persistent geochemical sources to Seneca Lake.