Author: Allyson Ropp, Historic Preservation Archaeology Specialist
Water is everywhere. It covers approximately 70% of the Earth’s surface and is necessary for creating and sustaining all life. It is even the focus of many national and international days this month – including World Water Day (March 22) and National Groundwater Awareness Week (March 5 – 11).
Water is important in regulating Earth’s climate. The ocean absorbs most of the sun’s radiation which heats its waters. Both precipitation and the ocean’s currents move this warm water around the globe, leveling regional temperatures. Water is also an integral part of regulating the amount of carbon dioxide (a gas that absorbs and radiates heat) in the atmosphere. Carbon is dissolvable in water and when it is released into the ocean, the water can absorb and store the carbon preventing it from radiating heat. When the ocean is no longer able to absorb carbon, global temperatures begin to rise, and the pH level decreases which is known as acidification. This can be harmful to marine life.
Water is also impacted by Earth’s climate, when global temperatures begin to rise, the properties of water change. When air temperature increases, so does the water temperature. This causes thermal expansion, meaning water is taking up more space and contributes to rising sea levels. Warmer temperatures melt bodies of ice, which adds freshwater to marine systems and dilutes salt levels, affecting marine life. At the same time, rising sea levels push salt water into freshwater systems, contaminating water supplies. The combination of warmer air and water drives more frequent and intense weather events and brings stronger and far-reaching storm surges on coastlines.
When the properties of water change it also impacts archaeological sites and cultural heritage. Acidification, salinity shifts, and warmer waters speed up the degradation of shipwrecks and other submerged structures. Increased tropical storm intensity and frequency create more violent wave action. This exposes submerged sites to turbulent activity, which shifts sediment around sites, moves or flips sites on the seafloor, and can break off sections of shipwrecks.
Shoreline sites also face threats from sea level rise and increased wave activity. Encroaching water and increased movement erode shoreline sites eventually leading to complete submersion of these sites. During this process, portions of sites and individual artifacts can be dislodged and washed downstream, affecting our ability to interpret the site. Following submersion, these sites undergo a series of immediate changes that result in the breakdown of structural integrity.
You might think sites further inland are safe, but as the ocean water rises in coastal areas the height of the water table inland also increases. This introduces buried sites to water contaminated with salt. Saltwater is detrimental and can chemically alter artifacts and structures. Increased storm activity also brings heavy rains to inland areas, flooding sites, and destabilizing standing structures that can lead to collapse.
Overall, the current and impending changes to water and its systems will alter our future and our past. Changes to climate will alter the environment and damage or destroy archaeological sites putting our shared cultural heritage at risk. Therefore, it is important to create plans to monitor our state’s at-risk heritage and find ways to protect it for the future.
This material was produced with assistance from the Emergency Supplemental Historic Preservation Fund, administered by the National Park Service, Department of the Interior. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the Department of the Interior.
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-Main image: Flooding in the River Arts Distric of Asheville. Image by NC Historic Preservation Office
-Timelapse of projected sea level rise. Images from National Oceanic and Atmospheric Administration
-2012 and 2016 surveys of shipwreck Ella. Images by NC Office of State Archaeology