Paleoshoreline

{{Short description|Shoreline which existed in the geologic past}}

A '''paleoshoreline''' (ancient shoreline) is a shoreline that existed in the geologic past. (''Paleo'' is from an ancient Greek word meaning "old" or "ancient".)<ref name="dictionary.com">{{Cite web |title=paleo- |url=https://www.dictionary.com/browse/paleo |access-date=2020-12-31 |website=dictionary.com}}</ref> Paleoshorelines are driven by changes in sea level over geological time. "Sea level" refers to the average level of a marine water body over a relatively long period of time (years).<ref name="Oceanbites">{{Cite web |last=Barrett |first=Katherine |date=June 7, 2017 |title=Paleoshorelines: Time capsules of the ocean's ancient shorelines |url=https://oceanbites.org/paleoshorelines-time-capsules-of-the-oceans-ancient-shorelines/ |website=Oceanbites}}</ref> Fluctuations in sea level is largely due to the melting and freezing of ice sheets.<ref>{{Cite web |last=Poore |first=Richard |date=2011 |title=Sea Level and Climate |url=https://pubs.usgs.gov/fs/fs2-00/pdf/fs002-00_williams_508.pdf |access-date=April 30, 2024 |website=United States Geological Survey}}</ref> The position of paleoshorelines differed greatly from modern shorelines and can be used to reconstruct past sea levels, environments and ecological communities. Paleoshorelines exist due to unique preservation processes and give insight into the formation and understanding of prominent marine structures.<ref name="Oceanbites" /> Lakes may also have paleoshorelines.<ref>{{Cite book |last1=Atwood |first1=G |last2=Wambeam |first2=T.J. |last3=Anderson |first3=N.J. |title=Lake Bonneville - A Scientific Update |chapter=The Present as a Key to the Past |series=Developments in Earth Surface Processes |date=2016 |volume=20 |pages=1–27 |doi=10.1016/B978-0-444-63590-7.00001-9|isbn=978-0-444-63590-7 }}</ref> The reconstruction of paleoshorelines also aid in the understanding of species migration, modern ecological assemblages, and paleoclimates. thumb|358x358px|Paleoshoreline Average sea level can advance and recede over much longer periods (thousands or millions of years), causing paleoshorelines which may be difficult to identify, but are often found in long lasting coastal structures such as beaches, sand dunes, and coral reefs.<ref name="Oceanbites" /> Tides cause the ocean to advance and recede in a very short time scale, in most places about twice per day. Weather conditions can also cause short-term variations. Coastlines can also move by coastal erosion without a change in sea level. A perched coastline is an ancient (fossil) shoreline positioned above the present shoreline.

Just off the coast of parts of North America, in the last 21,000 years, sea level has varied from over 130 meters (430 ft) below present level to over 130 meters (430 ft) above present level.<ref name="NOAA Paleoshoreline Research">{{Cite web |title=Paleoshoreline Research |url=https://oceanexplorer.noaa.gov/explorations/02quest/background/paleo/paleo.html}}</ref><ref>{{Cite journal |last=Joy |first=Shawn |date=2019 |title=The trouble with the curve: Reevaluating the Gulf of Mexico sea-level curve |url=https://linkinghub.elsevier.com/retrieve/pii/S1040618218308462 |journal=Quaternary International |language=en |volume=525 |pages=103–113 |doi=10.1016/j.quaint.2019.07.023|bibcode=2019QuInt.525..103J |url-access=subscription }}</ref> Within those 21,000 years, humans have lived in North America the entire time.<ref>{{Cite journal |last1=Pigati |first1=Jeffrey S. |last2=Springer |first2=Kathleen B. |last3=Honke |first3=Jeffrey S. |last4=Wahl |first4=David |last5=Champagne |first5=Marie R. |last6=Zimmerman |first6=Susan R. H. |last7=Gray |first7=Harrison J. |last8=Santucci |first8=Vincent L. |last9=Odess |first9=Daniel |last10=Bustos |first10=David |last11=Bennett |first11=Matthew R. |date=2023-10-06 |title=Independent age estimates resolve the controversy of ancient human footprints at White Sands |url=https://www.science.org/doi/10.1126/science.adh5007 |journal=Science |language=en |volume=382 |issue=6666 |pages=73–75 |doi=10.1126/science.adh5007 |pmid=37797035 |bibcode=2023Sci...382...73P |issn=0036-8075|url-access=subscription }}</ref> In regions where the continental shelf has a low relief, the paleoshoreline could be over 100 miles from the modern coastline.<ref>{{Cite journal |last=Joy |first=Shawn |date=2019 |title=The trouble with the curve: Reevaluating the Gulf of Mexico sea-level curve |url=https://linkinghub.elsevier.com/retrieve/pii/S1040618218308462 |journal=Quaternary International |language=en |volume=525 |pages=103–113 |doi=10.1016/j.quaint.2019.07.023|bibcode=2019QuInt.525..103J |url-access=subscription }}</ref>

== Formation == Paleoshorelines can be reconstructed and inferred by geological structures that were once exposed before sea levels rose. Over geological time, fluctuations in sea level has been primarily driven through the melting and freezing of ice sheets and plate tectonics.<ref>{{Cite web |last=Cronin |first=T. M. |title=Sea level change: Lessons from the Geologic Record |url=https://pubs.usgs.gov/fs/0117-95/report.pdf |access-date=2026-02-03 |website=U.S. Department of the Interior}}</ref><ref name="Oceanbites" /> Melting of ice sheets increases the volume of water within the ocean, ultimately causing ice sheets to retreat and sea levels to rise. Thermal expansion of water is an additional mechanism leading to volumetric sea level rise. Thermal expansion explains the phenomena of changing volumes of water when it is heated or cooled.<ref>{{Cite web |title=Educator Guide: What's Causing Sea-Level Rise? Land Ice Vs. Sea Ice |url=https://www.jpl.nasa.gov/edu/teach/activity/whats-causing-sea-level-rise-land-ice-vs-sea-ice/ |access-date=2024-05-02 |website=NASA/JPL Edu}}</ref> The shifting of plate tectonics also contributes to fluctuations in sea level rise by changing the shape of ocean basins.<ref>{{Cite web |title=Plate Tectonics and Sea Level Change {{!}} Coastal Processes, Hazards, and Society |url=https://www.e-education.psu.edu/earth107/node/1503#:~:text=Global%20or%20eustatic%20sea%20level,more%20expansive%20oceans%20between%20them. |access-date=2024-05-02 |website=www.e-education.psu.edu}}</ref>

Sediment type and time of formation, determine the ability of paleoshorelines to be preserved and identified in marine deposits. These factors aid in the understanding of how paleoshorelines have been able to withstand fluctuations in sea level throughout geological time. The calcium carbonate used in the shells of many marine invertebrates such as corals, mussels, and clams acts as an important building material that helps with the preservation of paleoshorelines, as they are more resistant to erosion and can maintain their structure through changing sea levels over geologic time.<ref>{{Cite web |title=NOAA Ocean Explorer: Sanctuary Quest: Background |url=https://oceanexplorer.noaa.gov/explorations/02quest/background/paleo/paleo.html |access-date=2024-05-02 |website=oceanexplorer.noaa.gov}}</ref>

A lake may also have a paleoshoreline.<ref name="Geomorphology">{{Cite journal |last=Komatsu |first=Goro |title=Paleoshoreline geomorphology of Böön Tsagaan Nuur, Tsagaan Nuur and Orog Nuur: the Valley of Lakes, Mongolia |journal=Geomorphology |year=2001 |volume=39 |issue=3–4 |pages=83–98 |doi=10.1016/S0169-555X(00)00095-7 |bibcode=2001Geomo..39...83K |url=https://www.sciencedirect.com/science/article/abs/pii/S0169555X00000957 |access-date=2021-01-01|url-access=subscription }}</ref><ref name="Harvard">{{Cite journal |last=Egger |first=A.E. |date=December 2012 |title=Paleoseismology from Paleoshorelines: Combining Lidar Data and Geochronology to Resolve Displacement of Pleistocene Pluvial Shorelines along Normal Faults in the Northwestern Basin and Range |journal=AGU Fall Meeting Abstracts |volume=2012 |bibcode=2012AGUFMPP11A2003E |url=https://ui.adsabs.harvard.edu/abs/2012AGUFMPP11A2003E/abstract |access-date=2021-01-01}}</ref>

Paleoshorelines have also been inferred on Mars;<ref name="SpringerLink">{{Cite book |last=Erkeling |first=Gino |chapter=Paleoshoreline |date=November 20, 2015 |title=Encyclopedia of Planetary Landforms |chapter-url=https://link.springer.com/referenceworkentry/10.1007%2F978-1-4614-3134-3_248 |access-date=2020-12-29 |website=SrpingerLink|pages=1501–1507 |doi=10.1007/978-1-4614-3134-3_248 |bibcode=2015epl..book.....H |isbn=9781461431343 }}</ref><ref name="Should Paleoshorelines of ancient Martian Oceans be close to present-day equipotential Surfaces?">{{Cite journal |last=Ruiz |first=Javier |date=November 20, 2003 |title=Should Paleoshorelines of ancient Martian Oceans be close to present-day equipotential Surfaces? |journal=Proceedings of the Third European Workshop on Exo-Astrobiology |volume=545 |page=281 |bibcode=2004ESASP.545..281R |url=http://adsabs.harvard.edu/full/2004ESASP.545..281R }}</ref> see Burgsvik Beds and Martian dichotomy.

thumb|right|upright=2.2|alt=Image of the Bering land bridge being inundated with rising sea level across time|Paleoshorelines illustrated: Beringia sea levels (blues) and land elevations (browns) measured in metres from 21,000 years ago to present

==Scientific importance==

Paleoshorelines capture valuable records of environmental change and can tell us about modern shelf ecosystems. These structures can indicate distributions of seabed features that are habitats of marine life; they may also reveal the location of coastal resources once used by humans, of archaeological significance.<ref name="Oceanbites" />

==Examples==

* The Bering Land Bridge once stood above water, and is the most commonly evoked migration route for the first peoples in the Americas from Asia. Throughout the Pleistocene, the land bridge has been exposed during glaciations, and has been inundated since about 11,000-13,000 YBP.<ref>{{Cite web |author1=Jennifer Nalewicki |date=2023-01-03 |title=Bering Land Bridge formed much later than originally thought, study suggests |url=https://www.livescience.com/bering-land-bridge-formation-ice-age |access-date=2024-05-01 |website=livescience.com |language=en}}</ref> The Bering Land Bridge is a paleoshoreline that acted as a migration route for humans, animals, and plants that is now submerged due to rising sea levels.<ref>{{Cite web |last1=Nome |first1=Mailing Address: P. O. Box 220 |last2=Us |first2=AK 99762 Phone: 907-443-2522 Contact |title=Beringia - Bering Land Bridge National Preserve (U.S. National Park Service) |url=https://www.nps.gov/bela/learn/beringia.htm |access-date=2024-05-01 |website=www.nps.gov |language=en}}</ref> Underwater archeology is being used to study the human migration along the Bering Land Bridge.<ref>{{Citation |last1=Dixon |first1=James E. |title=Gateway to the Americas: Underwater Archeological Survey in Beringia and the North Pacific |date=2014 |work=Prehistoric Archaeology on the Continental Shelf: A Global Review |pages=95–114 |editor-last=Evans |editor-first=Amanda M. |url=https://doi.org/10.1007/978-1-4614-9635-9_6 |access-date=2024-05-01 |place=New York, NY |publisher=Springer |language=en |doi=10.1007/978-1-4614-9635-9_6 |isbn=978-1-4614-9635-9 |last2=Monteleone |first2=Kelly |editor2-last=Flatman |editor2-first=Joseph C. |editor3-last=Flemming |editor3-first=Nicholas C.|url-access=subscription }}</ref> * Once Doggerland, an area of the North Sea, was once exposed above water, connecting Great Britain to the rest of Europe.<ref name="National Geographic">{{Cite web |title=Doggerland - The Europe That Was |url=https://education.nationalgeographic.org/resource/doggerland/ |access-date=2020-12-31}}</ref> * In a sudden event, the 1700 Cascadia earthquake caused the coastline of what are now British Columbia, Washington, Oregon and north California to "drop several feet".<ref name="oregon.gov">{{Cite web |title=Cascadia Subduction Zone |url=https://www.oregon.gov/OEM/hazardsprep/Pages/Cascadia-Subduction-Zone.aspx |access-date=2020-12-31 |website=oregon.gov}}</ref> * In Asia, the Yonaguni Monument, a submerged rock formation near the Ryukyu Islands, once stood above sea level; whether the formations are human-made is still argued.<ref name="Japan's Ancient Underwater 'Pyramid' Mystifies Scholars">{{Cite web |last=Ryall |first=Julian |title=Japan's Ancient Underwater "Pyramid" Mystifies Scholars |url=https://www.nationalgeographic.com/news/2007/9/yonaguni-jima-japan-underwater-city/ |archive-url=https://web.archive.org/web/20190807234832/https://www.nationalgeographic.com/news/2007/9/yonaguni-jima-japan-underwater-city/ |url-status=dead |archive-date=August 7, 2019 |access-date=2020-12-31 |website=nationalgeographic.com|date=19 September 2007 }}</ref>

==References==

==Further reading== * {{cite journal |doi=10.1016/S0012-8252(01)00063-0 |bibcode=2001ESRv...55..191D |title=Paleoshoreline record of relative Holocene sea levels on Pacific islands |last1=Dickinson |first1=William R. |journal=Earth-Science Reviews |date=2001 |volume=55 |issue=3 |page=191 }} * {{cite journal | doi=10.1080/08120099.2018.1558417 | title=Paleoshorelines and lowstand sedimentation on subtropical shelves: A case study from the Fraser Shelf, Australia | date=2019 | last1=Passos | first1=T. U. | last2=Webster | first2=J. M. | last3=Braga | first3=J. C. | last4=Voelker | first4=D. | last5=Renema | first5=W. | last6=Beaman | first6=R. J. | last7=Nothdurft | first7=L. D. | last8=Hinestrosa | first8=G. | last9=Clarke | first9=S. | last10=Yokoyama | first10=Y. | last11=Barcellos | first11=R. L. | last12=Kinsela | first12=M. A. | last13=Nothdurft | first13=L. N. | last14=Hubble | first14=T. | journal=Australian Journal of Earth Sciences | volume=66 | issue=4 | pages=547–565 | bibcode=2019AuJES..66..547P }} * {{cite journal |doi=10.1038/s41598-019-57049-8 |title=Shelf sand supply determined by glacial-age sea-level modes, submerged coastlines and wave climate |date=2020 |last1=Ribó |first1=Marta |last2=Goodwin |first2=Ian D. |last3=o'Brien |first3=Philip |last4=Mortlock |first4=Thomas |journal=Scientific Reports |volume=10 |issue=1 |page=462 |pmid=31949172 |pmc=6965639 |bibcode=2020NatSR..10..462R }} * {{cite journal | jstor=4298984 | title=Holocene Paleoshoreline Record in Tonga: Geomorphic Features and Archaeological Implications | last1=Dickinson | first1=William R. | last2=Burley | first2=David V. | last3=Shutler | first3=Richard, Jr | journal=Journal of Coastal Research | date=1999 | volume=15 | issue=3 | pages=682–700 }} * {{cite journal |doi=10.1023/A:1007998519385 |date=1998 |last1=Tackman |first1=Gary E. |last2=Currey |first2=Donald R. |last3=Bills |first3=Bruce G. |last4=James |first4=Thomas S. |title=Paleoshoreline evidence for postglacial tilting in Southern Manitoba |journal=Journal of Paleolimnology |volume=19 |issue=3 |pages=443–463 |bibcode=1998JPall..19..443T }}

==External links and references== * [https://oceanexplorer.noaa.gov/explorations/02quest/background/paleo/paleo.html Paleoshoreline research] * [http://courseresources.mit.usf.edu/ms/oce4930/m4/4_2paleoshorelines/presentation_html5.html Paleoshorelines of Florida, USA] * [https://nautiluslive.org/blog/2018/11/02/submerged-shorelines-southern-california-borderland Submerged Shorelines in the Southern California Borderland] * [https://serc.carleton.edu/estempd/curricular_material/activities/235541.html Paleoshorelines of Mono Lake, California, USA]

Category:Paleogeography