https://orcid.org/0000-0002-6369-3938
ABSTRACT
Rising sea and groundwater levels in coastal Florida have infringed on and wetted archaeological sites with some sites already submerged by rising sea levels. While studies of moisture-induced artifact diagenesis and destruction have been documented elsewhere, very little documentation exists for Florida and the faunal artifacts typical of Florida. This study sought to fill that gap by documenting the effects of wetting experiments on Floridian bone faunal artifacts. Our findings show that moisture-induced diagenesis and destruction is occurring at Florida sites and is more severe in older artifacts. Also, bone artifacts can retain moisture after the surrounding sediment matrix has dried. Furthermore, vertebrae across taxa are especially vulnerable to moisture-induced diagenesis while fish spines and scales are especially resistant. Although our data are limited, mammal bone seems especially vulnerable to diagenetic destruction, mammal bone being completely absent in the older assemblage, which is consistent with other artifact diagenesis studies. The implications of this study are that artifact assemblages excavated in Florida are biased by the postdeposition and pre-excavation loss of artifacts, specifically biased against diagenetic-prone bone (e.g., mammal and vertebrae) and toward diagenetic resilient bone (e.g., boney fish). This has implications both in terms of site interpretation and preservation priorities.
Introduction
Diagenesis is a term that comes from geology to describe the physical and chemical processes entailed in the creation of sedimentary rock. However, more recently diagenesis has also been used to describe post-depositional physical, chemical, and biologically mediated change in artifacts (Wilson and Pollard Citation2002). While diagenesis can preserve faunal artifacts through fossilization, it can also degrade and weather artifacts to the point of destruction and can cause increased porosity, decreased density, and elemental replacement in the faunal matrix. Furthermore, diagenesis in artifacts is often mediated and accelerated through water contact, typically groundwater, soil water, or rain infiltration (Kendall et al. Citation2018; Wilson and Pollard Citation2002). An abundance of documented cases of artifact diagenesis in the field have focused on European artifacts (e.g., Kendall et al. Citation2018) and human-made artifacts such as metal and ceramic objects (e.g., Matthiesen et al. Citation2003; Neff et al. Citation2005). In the case of faunal remains like bone, while laboratory experiments on bone have provided a theoretical framework (Kendall et al. Citation2018) systematic documentation of diagenetic effects of artifacts from the field is much more limited (Lyman Citation1994; Wilson and Pollard Citation2002) and none that we know of exists for faunal artifacts typical of Florida. Given the importance of artifact survival for interpretation of local pre-Columbian cultures in Florida, and that sea level rise is causing either direct wetting of artifacts (e.g., Cook Hale et al. Citation2018) or indirect wetting through rising groundwater tables (e.g., Lecher and Watson Citation2021), documenting the degradation and diagenesis of Floridian artifacts can inform future policy and practice. This is especially true for faunal bone artifacts, which are rather vulnerable to degradation and diagenesis, and the focus of this study. For the purpose of this study, we define a faunal artifact as nonhuman animal bone, both modified or unmodified, with unmodified to include discarded bones from meals and other harvesting practices.
The most common type of faunal artifact found in Florida is unmodified bone. Bone anatomy consists of five basic layers: periosteum, subchondral, cortical, cancellous, and marrow. It should be of note that cortical bone can commonly be known as hard bone while cancellous is more commonly referred to as spongy bone. The periosteum acts as a soft covering for the bone. This allows for a more facilitated blood flow, which helps the bone heal, grow, and even battle infections or disease. The subchondral tissue is smooth and can be found at the ends of bones. This is a more flexible layer that allows for easier attachment to cartilage or other bone-to-bone connections. The cortical bone layer, or the hard bone layer, is relatively thick. Regardless of thickness, this bone layer protects, stabilizes, and works as a foundation through which muscles can adhere to grow around it. Cancellous tissue, also known as spongy bone, is less thick than the cortical bone and has a less dense or softer nature. Like a sponge, this layer is porous and allows for fluid movement. The porosity of the bone depends both on the species and the placement in the body and can vary between organisms (see ). Bones that have more of this cancellous layer will heal faster than those with less of this layer. Bone marrow is at the core of these layers and is a soft layer, which can be classified as either red or yellow marrow. This layer contains collagen and stem cells, and it generates blood cells, fat, bone cells, or cartilage depending on type and location (Turley et al. Citation2022). Bones consist mainly of three substances: mineral, generally >60% of mass and made up mostly of carbonated hydroxyapatite, organic matter, ∼20–30% of mass and made up mostly of collagen, and water (Kendall et al. Citation2018).
Table 1. Porosities of various modern bone types.
In an archaeological context, the soft tissues degrade first through a combination of geochemical (e.g., dissolution) and microbial (e.g., tunneling) actions leaving the harder, denser bone tissue to degrade last (Kendall et al. Citation2018). Collagen degrades rapidly, with about half of collagen degrading within 500–1000 years depending on the depositional environment mostly due to microbial attack or hydrolysis (Collins et al. Citation1995; Hedges Citation2002). Collagen loss accelerates in warmer temperatures (Turner-Walker Citation2011). As a result, archaeological bone becomes more porous with an increase in porosity of up to 65% compared to an initial increase in porosity of ∼20% in modern bone. This increase in porosity is accompanied by the ability of archaeological bone to absorb water much more quickly than modern bone (Turner-Walker Citation1993). The effect of diagenesis on increasing porosity in bone (decreasing intercrystalline porosity while increasing macro-porosity) is so profound it has been argued that porosity itself can be used as a marker of diagenesis (Hedges et al. Citation1995). Both geochemical and microbial processes that degrade bone are accelerated by the presence of water, especially if the water flows or if the environment oscillates between wet and dry (Hedges et al. Citation1995; Kendall et al. Citation2018). Flowing water prevents the water around the bone from becoming saturated in bone mineral, slowing dissolution (Hedges Citation2002). Analysis of porosity of archaeological bone from sites in varying environmental conditions in Europe found that hydrology and therein wetting of bone had a strong impact on the preservation of bone, with bones at wet sites having higher porosity, lower protein content, and overall worse preservation (Nielsen-Marsh and Hedges Citation2000). Modeling studies of groundwater effects on bone have found that there is a significant difference in porosity on bone under different groundwater conditions, e.g., differences in chemical composition and flow (Pike et al. Citation2001). Repeated wetting and drying of bone in laboratory experiments has been shown to cause surface cracking and delamination (Pokines et al. Citation2018). Coupled with the fact that faunal remains degrade more rapidly in lower latitudes (Kendall et al. Citation2018) the warm, wet conditions of Florida create an environment for rapid faunal artifact destruction.
It should be noted that water exposure does not always lead to artifact destruction. Indeed, sometimes exposure to certain types of water can cause excellent preservation. Quick and long-term submersion in anoxic water slows artifact destruction by limiting the initial microbial attack (Hedges Citation2002). Also, changing groundwater levels and redox conditions has been shown to cause increased mineralization of bone at a neolithic site in the UK (Loy et al. Citation2023). However, the vast majority of the archaeological sites in Florida are not subject to either of these conditions, and therefore are more likely to experience artifact degradation as a result of wetting.
The degree of bone degradation can vary based on morphology, with smaller bones and bird bones as a whole tending to preserve better across a variety of environments (Nicholson Citation1996). Also, it has been demonstrated that bone of lower surface area to volume ratios tends to chemically weather faster (Von Endt and Ortner Citation1984); this means it would be expected that given two bones of the same shape the smaller bone will degrade faster chemically or of two bones of the same size the bone with more protrusions would degrade faster. In-depth studies into the theory of archaeological bone diagenesis exist elsewhere (e.g., Kendall et al. Citation2018; Wilson and Pollard Citation2002). However, the actual outcomes of these effects in situ on Floridian bone artifacts are lacking. This study aims to fill that gap by (1) documenting the ability of bone artifacts to absorb water, (2) documenting differences in the amount of water absorbed across bone type and taxon, (3) assessing how relative bone age affects the amount of water absorbed, (4) synthesizing implications for rising sea/groundwater levels in Florida on bone preservation.
Materials and methods
Study area
Faunal artifacts were picked from a previous excavation for which artifacts have been previously cataloged from South Inlet Park in Boca Raton, Florida (Lecher and Watson Citation2021; Watson and Lecher Citation2022). South Inlet Park is the southernmost barrier island park in Palm Beach County. It encompasses all areas from A1A to the ocean on the southern side of the Boca Raton Inlet, which is a navigable waterway connecting the intracoastal waterway and Atlantic Ocean. Historic maps have shown the change in position of the inlet, as longshore drift caused the inlet to open and close naturally, as well as shift in position. In the 1930s, the local community improved the inlet such that it would remain open.
The sites are situated in the back beach area of the barrier island, in a naturally occurring berm area. The beach area is underlain geologically by the Anastasia Formation. The Anastasia Formation is comprised of sands and limestones. The sediments are characterized by orangish brown, soft to moderately hardened, with a mix of coquina, whole and fragmented mollusk shells, and sand. Sands in the Anastasia Formation are often light gray to tan and orangish brown (Lovejoy Citation1992). The dominant tree cover at South Inlet Park is coastal scrub, with sea grape, stopper, saw palmetto, and sabal palms.
The artifacts used for this experiment came specifically from South Inlet Park Midden III, which is less than 100 m from both the Atlantic Ocean and the Boca Raton Inlet. Therein it is unsurprising that most of the faunal bone artifacts from this site are marine in nature, such as fish, sea turtle, etc. (Watson and Lecher Citation2022). No radiogenic dating exists for this site, but based on ceramic typology from this midden and neighboring sites it is dated to the Glades II (AD 750–1200) and Glades III (AD 1200–1750) periods of the Jeaga and Tequesta peoples (Endonino et al. Citation2009). This site has shown evidence of wetting through groundwater interaction (Lecher and Watson Citation2021).
Materials
The faunal bone artifacts used in this experiment consisted of unmodified bone, likely the discarded remains of a meal. A total of 12 artifact categories were used, with each artifact category containing four bones per test. The categories of faunal artifacts used were catfish, bowfin, gar, scales (not specific to species), fish spines (spinal processes from fish vertebrae, not specific to species), fish cranial bone, bird bone (not specific to element or species), shark vertebrae, reptile (not specific to element or species), unidentified vertebrae, and postcranial long bones (not specific to species or particular element). The artifact categories were chosen to encompass a range of organismal representations: broad in species but specific bone type at one end of the spectrum and specific species but broad in bone element at the other. The value of including the broad categories of unidentified vertebra and unidentified postcranial long bone that are not specific to any one taxonomic group is that it allows us to see if bones of the same type are affected similarly despite coming from different taxa, therein allowing for some generalization of those results. Artifacts were used from two different depths: level 6 representing 50–60 cm depth (more recent bone) and level 9 representing 80–90 cm depth (older bone). There was no evidence of disturbance or stratigraphic mixing, allowing us to assume the bones in the deeper level (9) are indeed older than the more shallow level (6). The analysis was completed in quadruplicate, i.e., four bones of each category for each depth were measured, with the results averaged.
The initial dry weight was measured in grams. After the initial dry weight was documented, the artifacts were submerged in tap water for 48 h. This was done by using plastic Petri dishes, filling them with water, placing a single artifact inside every Petri dish, and then closing the top and storing them for 48 h at room temperature. Though this method cannot be used to measure the actual porosity, using water retention to investigate archaeological bone porosity and bone-water interactions is considered a valid method (Hedges et al. Citation1995). After removing visible moisture from the outside, the wet weight of all of the bones was recorded after the first 48 h. Percent change in weight was calculated for all artifacts (dry vs. wet), and a paired t-test was used to ascertain significant differences in weight.
Results
The size of the bones used for this experiment was generally small, less than 3 cm and 1 g, as were most of the faunal artifacts recovered from the excavation. These bones were the most abundant types discovered in the collection (either by taxa or elemental type), and for some (e.g., reptile) there were just enough bones to complete this analysis (four bones). Each bone category was repeated at both levels, except for mammal bone, which only had enough identifiable pieces in level 6.
In , the bar graph indicates the differences in percentage increase in weight from initial dry to wet weight for levels 6 and 9. An increase in weight indicates absorption of water into the bone and a more significant increase indicating a more drastic amount of absorption. As for level 6 the faunal artifact categories that had no significant change were fish spines and bowfin. Borderline significant increases in weight (p < 0.1) were observed in the postcranial long bones and shark vertebrae. The remaining artifact categories either displayed a significant (p < 0.05, mammal, bird, fish cranial bone, scales, gar, and catfish) or highly significant (p < 0.01, reptile and unidentified vertebrae) increase in weight. In level 9 the only artifact category with no significant change in weight was bird bones. A borderline significant increase in weight was only observed in bowfin. The categories with significant increases were unidentified vertebrae, reptile, shark vertebrae, fish cranial bone, fish spine, and gar, and highly significant increases were observed in postcranial long bones, scales, and catfish.
Figure 1. Percent increases in weight from initial dry weight to wet weight for levels 6 (A) and 9 (B). Stars indicate significant differences * p < 0.1, ** p < 0.05, *** p < 0.01. Error bars represent standard error. Taxonomy represents the most specific level of classification that the faunal artifacts could be identified to, more specific taxonomy being toward the left on the x-axis moving toward more general taxonomic groupings toward the right. Note the y-axis scales are different for each plot.
shows the percentage differences in levels between both level 6 and 9. A 50% increase indicates the same bone type in level 9 absorbed 50% more water (by weight) than the same bone type in level 6. Mammal was excluded as there were not enough mammal pieces found in level 9. Fish spine and bird had no measurable increase in weight between the two levels. Moderate increases in weight (12–14%) were observed in the gar, scales, and postcranial long bones categories. Large increases in weight (>45%) were observed in the categories unidentified vertebrae, reptiles, shark vertebrae, fish cranial bone, bowfin, and catfish. However, error was large for catfish, bowfin, and postcranial long bone categories, indicating these increased water retention effects may not be as large as they seem.
Figure 2. Percent increases in weight increase in level 9 bones compared to level 6 bones. E.g., catfish in level 9 increased in weight when wet ∼60% more than in level 6. Error bars represent standard error.
Discussion
Differential water absorption by faunal element
All of the bones increased in weight after soaking for 48 h even after surface moisture was removed, indicating the archaeological bones were able to absorb water into their pore spaces. So many significant increases in weight within such a short time frame of exposure corresponds with previous studies that have shown archaeological bones absorb water relatively quickly (Turner-Walker Citation1993). Clearly, Floridian archaeological bones are at risk for weathering due to water exposure. However, the implications of those findings are more nuanced as bone age and morphology played a role in how much water was absorbed.
We expected significance to increase with depth as deeper bones are older as per the law of superposition, therein having more time to degrade and increase in porosity. This process has already been observed at European sites (Hedges et al. Citation1995). An increase in porosity would then lead to more water being absorbed, which then further weathers the bone increasing porosity and absorption potential again in a feedback cycle. Some of this feedback cycle can be observed in Lecher and Watson (Citation2021) as level 6, which had considerably more artifacts than level 9, was also much wetter than level 9. This indicates that the bones might be holding onto moisture after it is absorbed. Our expectations were met since most bone types absorbed significantly more water from dry to wet states in level 9 than level 6 () and most bones displayed a 20–60% increase in the amount of water they absorbed between the levels. More specifically, for most bone types the level of significance in the amount of water absorbed either stayed the same (gar, fish cranial bone) or increased (bowfin, catfish, shark vertebrae, fish spine, fish scales, and postcranial long bones).
Only for a few bones did the significance of the difference decrease (reptile, bird, and unidentified vertebrae). It is possible that the lack of an increase in significance for reptile, bird, and unidentified vertebrae is caused by confounding factors. For reptile at least the pre-depositional porosity of bone can vary widely between the parts of the body, between 3.1% and 55.7% as shown in . It’s possible that originally more porous bone dominated the level 6 artifacts and originally less porous bone dominated the level 9 artifacts, which could cause the decrease in significance observed. It could also be a sample size effect if the heterogeneity (shown by the larger error) of bone mass was larger in level 9 than level 6. This would explain why reptiles showed an increase in the percentage of water absorbed in level 9 compared to level 6 (), but not the significance ().
The lack of identifiable mammal bones in level 9 made it impossible to compare weight increases for that taxonomic group. However, the lack of mammal bone may be an indicator in and of itself. Mammal bone is made up of a large portion of cancellous (spongy) bone, which makes it more vulnerable to chemical and microbial weathering exposure. Furthermore, mammal bones have been observed to show more extensive weathering than other taxonomic groups in long-term burial experiments (Nicholson Citation1996).
Looking at how taxonomy or bone type played a role in the amount of water absorbed, almost all bone types saw a significant increase in the amount of water absorbed. The only bones that did not were bowfin and fish spine in Level 6 and bird in Level 9. Scales and fish spines both saw the lowest amount of water absorbed relative to their starting weights. Many of the fish tested in this paper have scales covered in an enamel-like coating called ganoine (Wheeler and Jones Citation1989) that can act as an aquitard limiting water absorption until the enamel is degraded.
In fish, the processes that extend off the vertebrae (spines) act as struts or support for the relatively light bones of the fish (Wheeler and Jones Citation1989). The general composition of fish spines is either dentine or bone, sealed with enamel/enameloid (Jerve Citation2016). Dentine and enamel both represent some of the strongest material found in the bodies of animals. As already noted with scales, enamel, as well as dentine, may act as an aquitard, which in turn limits how much water can be absorbed by the bone.
For boney fish in general, the amount of absorption is also related to the bone structure. Unfortunately, it is most common for the spinal process to break away from the vertebra centra, which makes identification challenging. However, since teleosts (the largest infraclass of ray finned-boney fishes) comprise roughly about 30,000 fish species, it is likely that many of the spines that were used for the experiment were part of this classification. Therefore, it is likely that many of the bones were acellular bone (mineral bone without cells). Since acellular bones have an absence of osteocytes (whose function is to modify bone microenvironment, bone function, and resorption, and respond to strain, among others) it is possible that the acellular bone is considered denser for this reason (Ottewell Citation2016). Regardless, the absence of cells within the bone would limit initial porosity and vascularity (how well the pores are connected and allow for fluid movement). These characteristics of the bones would make them more resistant to diagenesis than other bone types that are more vascular or are cellular.
Vertebrae (both shark vertebrae and unidentified vertebrae) consistently absorbed the largest relative amount of water. Vertebrae are very porous compared to many other bones (e.g., ) because they contain a large portion of bone marrow, osteoblasts and osteocytes, cells responsible for bone creation and restructuring (Ottewell Citation2016). The rest of the bone types had similar increases in the relative amount of water absorbed, 20–40% for level 6 and 50–80% for level 9. There is a relationship between bone density and porosity, and animals of similar morphology tend to have similar densities (Kendall et al. Citation2018; Lam et al. Citation1999). Therefore, it seems reasonable that the majority of boney fish taxa (bowfin, gar, and catfish) and parts (crania) have similar relative increases in weight.
In terms of artifact preservation these findings indicate that fish scales and fish spines are relatively better preserved compared to other faunal artifacts and may prove an especially important indicator of the presence of original habitation. Long-term field experiments have shown that smaller fish bones tend to be better preserved across a range of environments than larger fish bones and other animals, which concurs with our observations in this experiment (Nicholson Citation1996). However, fish scales and spines are also some of the most likely faunal artifacts to be under-sampled if a quarter-inch or larger screen size is utilized for collection (Mendes Cruz et al. Citation2022). In contrast, vertebrae appear to be the most at-risk faunal artifacts in terms of water-mediated degradation as different types of vertebrae had the largest percent increases in weight due to water absorption. Vertebrae have some protection from degradation as their squat and round shape is more difficult to break than longer bones, which is probably one of the reasons they are some of the most common faunal remains found in the excavation these bone artifacts were taken from (Watson and Lecher Citation2022). Nonetheless, vertebrae are often fragmentary, sometimes without enough anatomical markers to determine the species or more general taxonomic group they came from, a problem enhanced by water-mediated degradation and weathering. All other faunal artifacts seem to have the same moderate level of vulnerability in terms of water-mediated degradation.
Pre-depositional effects
Human impacts on bone pre-deposition also affect how well faunal artifacts are preserved. Removal of flesh around bone increases diagenesis and deterioration (Nicholson Citation1996). As the faunal artifacts used in this experiment appear to have been the remains of meals, it’s likely the meat was removed from the bone prior to deposition. Previous studies have shown that butchering and processing of animal carcasses affect the number and type of bones to enter the burial context. The process of cutting apart an animal for consumable materials often leads to fragmentation of bone, which in turn affects what will be preserved in an archaeological site (Noe-Nygaard Citation1977). The method of butchering an animal also generally leads to disarticulation of the skeleton. It has been noted that disarticulated skeletons tend to degrade easier than an articulated skeleton (Lyman Citation1994). The cutting process as a whole would make the bone more fragile and more susceptible to weathering and breakage.
Boiling faunal artifacts can also hasten diagenesis, although it’s unclear that cooking by other means (e.g., grilling or roasting) accelerates diagenesis (Nicholson Citation1996). Boiling results in the loss of collagen from bone, as well as the increase of porosity (Roberts et al. Citation2002). As our study demonstrated, porosity increases the chance of water absorption and further damage to the bone. It might also cause accelerated diagenesis through thermal alteration, which in turn might increase the pace of mineral alteration, and microbial attack might proceed more rapidly (Roberts et al. Citation2002). Boiling of bone can also result in dissolution or fragmentation of the bone, which in turn will affect its post-depositional survival. Several of the bone artifacts from South Inlet Park had scorch marks on them, indicating they might have been cooked. It’s unclear if any of the faunal remains were boiled. Further research is needed to determine the effects of cooking (burning or boiling) on the faunal remains recovered from South Inlet Park.
Another damaging effect that could lead to quicker diagenesis over time would be that of carving. Purposely picking at and scraping away layers of bone can lead to the interior layer of that bone being exposed, which can cause damage over time and easier destruction of that artifact. Purposeful cutting on bone might be the result of butchering. Cut marks were observed on some of the animal remains recovered from South Inlet Park. One study suggested that even a short time in the postdepositional environment led to a loss of visibility of the cut marks, as well as an increase in fragmentation stemming from the cuts made in the bone (Willis and Boehm Citation2014). From an archaeological perspective, loss of bone either due to fragmentation or even the loss of visible cut marks due to degradation means the loss of potential data about the human ecological relationship at the time of deposition. Carving might also result from the construction of a bone into a tool, such as a pick or pin. The tool might be carved into the shape desired for the job (such as sharpening a bone to a point). These types of tools might also show microscopic or macroscopic cuts or nicks on the edge of the tool, a result of frequent use. It is possible that some of the faunal artifacts recovered at South Inlet were used in this manner; however, no systematic study of use wear has been done. This represents a future avenue for research.
Other purposeful cutting might be decorative in nature. In the Hutchinson site, near the northern Everglades in 2016, carved bones were discovered which depicted zoomorphic effigies (Davenport Citation2019). Other decorative pins, such as an elaborately carved deer head bone pin, were recovered within the Everglades area in the 1960s and 1970s indicating carving of faunal bone did occur in the larger south Florida range (Griffin Citation1988). No clear signs of purposeful human modification were found in the faunal artifacts used for this study.
Postdepositional effects
Bone preservation might be aided by the nature of the archaeological site post deposition. Some studies have suggested that bone buffers the surrounding substrate by leaching minerals, making a micro-chemical change and causing the surrounding matrix to become more alkaline. Stable environments with little to no chemical or hydrological changes might see less bone degradation compared to a site with a high degree of dynamic water flow. If the water table is prone to fluctuating more frequently through the archaeological layer, the buffered zone created by bone material would have to constantly be reestablished, thus causing more and more bone dissolution (High et al. Citation2015). As demonstrated in this study and a previous publication by Lecher and Watson (Citation2021), the environment at South Inlet Park may become increasingly wet as sea levels rise. This in turn might result in increased destabilization of the microchemistry within the midden sites at the park. Fluctuating water levels are not limited to coastal areas however, as Cyr (Citation2016) observed archaeological sites bordering a river in Alabama were prone to cycles of dampening and drying induced by climatic changes to river hydrology.
Limitations of the study
One caveat of this study is that bone does not have the same density as water. Pure water has a density of 1 g/cm3, whereas the density of bone is typically higher, e.g., 1.85 g/cm3 in humans (Yang et al. Citation2014). Because of these disparate densities, the mass of water absorbed by the bone cannot be used to calculate a porosity of the bones themselves. Furthermore, it cannot be assumed that the total amount of pore space in the bone is completely filled with water. The amount of water absorbed is not just a function of the porosity of the bone itself, but also the permeability. Permeability is determined not just by how much pore space there is in a medium, but also by how well those pore spaces are connected and how much capillary forces increase or decrease absorption. Bone permeability has been documented to vary across species (Beno et al. Citation2004). In this way, the measurements here are more indicative of effective porosity, or the amount of water absorbed under gravity and not other forces. It may be the case that the bone pore spaces were not completely filled with water; in which case the wet weights could have been larger, which would have only created larger statistical differences.
A second limitation of the study is that only 12 bone artifact categories were evaluated, some of them being quite broad (e.g., postcranial long bone of several taxa). This study represents the first step in the study of bone artifact diagenesis in Florida, and indeed documentation of actual effects of water-mediated diagenesis in bone artifacts is lacking throughout the southeast US with most of the literature on the topic including European artifacts. Further study of other bone artifact categories (i.e., other species, bone element groupings, or age of the animal at death, which in some species can impact bone porosity and permeability) is warranted to fully understand how diagenesis is impacting faunal bone artifacts in the region. However, despite these limitations, the data and interpretations of the wetting experiments were able to indirectly show an increased water absorption with the older bones compared to the more recent bones most likely due to diagenesis-induced increased porosity, and that bones are able to absorb a significant amount of water to influence diagenesis.
Conclusion
Artifact wetting due to groundwater/sea level rise is already occurring throughout Florida in coastal areas. The sites these artifacts were retrieved from in Boca Raton displayed wetting as evident from sediment moisture data (Lecher and Watson Citation2021). On the Gulf Coast of Florida, excavations of Pine Island have shown “waterlogged” sites near the shoreline, where excavations were at the very least damp with water leaking from the walls of the excavation (Walker et al. Citation2019). A known issue in the community, Collier County is even integrating the rise of groundwater levels into their calculations for prioritizing sites for preservation (Kangas et al. Citation2022). It has become a question not of if artifacts entrained in sites will become wet/submerged due to rising groundwater/sea level, but when the artifacts become wet/submerged. With the knowledge of how wetting increases faunal artifact degradation, stakeholders can make more informed decisions in matters of site preservation, and researchers are armed with knowledge of how their artifact assemblages are skewed by degradation of faunal remains.
In terms of stakeholder preservation efforts, this could mean focusing excavation efforts on sites at risk of being submerged in groundwater in the near future or creating infrastructure to keep sites dry for the time being, such as installing wells around especially important sites to keep groundwater levels down. Alternatively, if sites are identified as already being submerged or substantially moistened due to sea level or groundwater level rise, acknowledging that the faunal bone artifacts within those sites may be degraded enough by diagenesis that they are essentially already lost, and should receive less priority for preservation efforts. In terms of research, archaeologists excavating moist and wet sites should be mindful that the artifact assemblages they are producing are biased by diagenesis. Some bone artifacts that are especially vulnerable to water-mediated diagenesis (such as mammal or reptile) may be underrepresented in that much of the bone material originally deposited may be lost before excavation.
Acknowledgements
We would like to thank Sara Ayers-Rigsby and Micheline Hilbert for their assistance with the laboratory analysis. We also thank Christian Davenport, Palm Beach County archeologist, for his invaluable expertise and guidance.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Data availability statement
Data from this paper can be retrieved by contacting the corresponding author.
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