Submersion drastically alters the process of decomposition compared to a terrestrial environment; this field is known as aquatic forensic taphonomy. The unique properties of the aquatic setting—temperature, current, and chemistry—dictate the rate at which tissue changes. Understanding these submerged changes is necessary for forensic investigators attempting to determine the time a body has spent underwater.
Immediate Effects of Submersion
Upon entering the water, the body typically exhibits negative buoyancy and sinks, especially if the lungs are filled with water. Since the body’s density is slightly greater than water, it settles on the bottom sediment. Submersion immediately begins rapid body cooling, where the surrounding water accelerates the drop in core temperature. This quick loss of heat, termed algor mortis, directly affects the initial rate of internal chemical and bacterial activity.
External physical changes begin almost immediately as the skin absorbs water through osmosis. The most noticeable early sign is maceration, commonly referred to as “washerwoman hands.” The keratin layer of the palms and soles becomes waterlogged, leading to white, wrinkled, and thickened skin. This wrinkling can appear at the fingertips in as little as 20 to 30 minutes in warm water.
Over a period of days to weeks, this macerated skin may detach from the body in a glove-like or stocking-like fashion. This is a non-putrefactive change, meaning it results from water saturation rather than bacterial action. The timeline for maceration is one of the earliest physical markers forensic specialists use to estimate the post-mortem submersion interval. These external changes precede the more significant internal processes of decay.
Buoyancy, Gases, and Refloating
Once the body is submerged, internal biological decomposition, known as putrefaction, begins in earnest. This process is driven by the anaerobic bacteria that naturally reside within the gastrointestinal tract. These microorganisms, no longer controlled by the immune system, begin to consume the soft tissues of the body from the inside out. This consumption creates metabolic byproducts, primarily gases such as methane, hydrogen sulfide, and carbon dioxide.
These gases accumulate and become trapped within the body cavities, particularly the abdomen and chest. As the volume of trapped gas increases, it dramatically lowers the overall density of the body. According to Archimedes’ principle, this decrease in density leads to a significant increase in buoyancy. The body, which initially sank, eventually becomes buoyant enough to rise to the water’s surface.
The time it takes for a body to refloat is highly variable but is directly linked to water temperature and gas production. In warm water, this process can occur within a few days, but cold water severely inhibits bacterial growth, meaning refloating may take weeks or months. When the body surfaces, it often floats face-down because the chest and abdomen are the most buoyant sections. Eventually, the pressure from the internal gas can cause tissues to rupture, releasing the gas and causing the body to sink a second time.
Environmental Impacts and Long-Term Preservation
The aquatic environment is the main factor determining the rate and type of long-term post-mortem change. Water temperature is the most significant variable, as cold water below 7 degrees Celsius drastically slows bacterial metabolism and decomposition. The cold environment can preserve tissues for extended periods, far longer than decay would take on land. Conversely, warm water accelerates all biological processes, leading to rapid bloating and tissue breakdown.
The salinity and chemical composition of the water also play a role in the preservation of the remains. Saltwater, due to its higher density, is more buoyant than freshwater, which can affect the floating dynamics. Water currents and depth also influence the rate of decomposition by affecting the water temperature surrounding the body and introducing scavengers. Strong currents can cause physical trauma, accelerating disarticulation and the removal of soft tissue.
In cold, anoxic (low-oxygen) aquatic environments, a unique form of preservation called saponification can occur. This process involves the hydrolysis of body fat into a grayish-white, waxy substance known as adipocere, or “grave wax.” Anaerobic bacteria, such as Clostridium perfringens, facilitate this chemical conversion. Adipocere formation acts as a preservative layer, essentially encasing the body and halting further putrefaction.
Aquatic fauna, including fish, crustaceans, and other invertebrates, contribute to the breakdown of soft tissue through scavenging. The presence and activity of these organisms depend on the specific ecosystem and water temperature. In some cases, scavenging can lead to rapid skeletonization, especially in warmer waters with high populations of aquatic life. The distinct pattern of tissue loss caused by different fauna can provide investigators with clues about the specific environment in which the body decomposed.
Estimating Time Since Death and Recovery
Forensic specialists use the observed physical and biological changes to estimate the Post-Mortem Submersion Interval (PMSI), which is the time elapsed since the body entered the water. They utilize a scoring system, such as the Total Aquatic Decomposition Score (TADS), which quantifies the degree of decomposition, maceration, and adipocere formation. This morphological assessment is often correlated with the water’s accumulated degree days (ADD)—a measure that accounts for water temperature over time—to improve the accuracy of the estimate.
Water recovery presents unique challenges that complicate forensic analysis and identification. The constant flow of water can wash away trace evidence, such as fibers or foreign material, that might have been deposited at the time of death. Furthermore, the skin peeling and tissue loss associated with maceration and scavenging make positive identification more difficult. The condition of the remains requires specialized expertise from forensic anthropologists to determine identity and the circumstances of death.