This project studies past high sea levels on coastlines that preserve fossil coral reefs or marine terraces. We ascertain the magnitudes of sea-level high stands by field mapping, stratigraphic measurements, and precise elevation measurements. Geochronology is accomplished by radiocarbon dating of mollusks (for Holocene-to-last-glacial deposits), uranium-series dating of corals (for high-sea stands back to about 500,000 years old) and strontium-isotope measurements of mollusks (for high-sea stands older than about 300,000 years). It is possible to determine the past water temperatures of the oceans during these high sea stands by detailed paleozoogeographic interpretations of fossil mollusk assemblages, a time-tested traditional method of paleoclimatic studies in marine settings. We also study the effects of sea level changes on coastal river systems and dunes.
The geomorphic record of sea level change on an uplifting coastline
On a tectonically active coast, such as California, changes in sea level are recorded as marine terraces, wave-cut benches that formed in the surf zone during interglacial periods, but are now above sea level due to uplift. Wave-cut benches also form during glacial periods, but these are offshore and underwater during interglacial periods. If uplift is continuous over time, a “stair step” type of landscape develops, as shown here, with each successively higher terrace corresponding to a successively older interglacial period.
[Reference: Imbrie, J., Hays, J.D., Martinson, D.G., McIntyre, A., Mix, A.C., Morley, J.J., Pisias, N.G., Prell, W.L., Shackleton, N.J., 1984, The orbital theory of Pleistocene climate: Support from a revised chronology of the marine δ18O record, in Berger, A., Imbrie, J., Hays, J., Kukla, G., and Saltzman, B., eds., Milankovitch and climate: Understanding the response to astronomical forcing: Dordrecht, D. Reidel Publishing Company, p. 269-305.]
The geomorphic record of sea level change on a stable or subsiding coastline
Why is this research important?
One of the most pressing issues in studies of climate change is the possible rise of sea level due to loss of major ice sheets, which would impact population, infrastructure, and habitats along the world's coastlines. It is not known which polar ice sheets (Greenland, West Antarctic, East Antarctic) are most at risk for mass loss that could contribute to sea level rise. Furthermore, it is not known what the possible magnitude of sea level rise is under interglacial climate conditions, how rapidly sea level may rise, or how long high sea levels may be retained. The goals of this project are to shed light on these questions by studying warm climate analogs of the geologic past.
How high was sea level during the last interglacial period?
Key unanswered questions about past interglacial sea levels
The research conducted by this project attempts to answer these questions raised in the Intergovernmental Panel on Climate Change (IPCC) 2014 report:
- The timing of past interglacial sea-level high stands
- Marine paleotemperatures during past high-sea stands
- Magnitudes of past interglacial high-sea stands
- Rates of sea level rise
Results
What have we learned from the last interglacial?
What fossil corals can tell us
Corals are the only organisms that take up uranium from the ocean. Thus, they are the only fossils that we can use for high-precision uranium-series dating, one of our major tools to determine ages of marine deposits.
How long did the last interglacial period last?
These maps show the places where we have found either fossil coral reefs (tropical locations) or coral-bearing marine terraces (California) that have been dated by uranium-series methods to the last interglacial period. On each map, you can see the range of ages we have gotten from dating these corals that tell us how long this high-sea stand lasted.
How high was sea level in the last interglacial period?


How warm was the ocean during the last interglacial period?
It is possible to determine the past water temperatures of the oceans during these high sea stands by detailed paleozoogeographic interpretations of fossil mollusk assemblages, a time-tested traditional method of paleoclimatic studies in marine settings. These maps show how marine invertebrates, now found only in warm waters farther south at present, expanded northward beyond their present ranges, during a warm last interglacial period.

Below are publications associated with this project.
On the importance of stratigraphic control for vertebrate fossil sites in Channel Islands National Park, California, USA: Examples from new Mammuthus finds on San Miguel Island
Fluvial system response to late Pleistocene-Holocene sea-level change on Santa Rosa Island, Channel Islands National Park, California
Uranium-series ages of fossil corals from Mallorca, Spain: The "Neotyrrhenian" high stand of the Mediterranean Sea revisited
Sea level, paleogeography, and archeology on California's Northern Channel Islands
Late Quaternary sea-level history and the antiquity of mammoths (Mammuthus exilis and Mammuthus columbi), Channel Islands NationalPark, California, USA
Coastal tectonics on the eastern margin of the Pacific Rim: Late Quaternary sea-level history and uplift rates, Channel Islands National Park, California, USA
Interpreting the paleozoogeography and sea level history of thermally anomalous marine terrace faunas: A case study from the the last interglacial complex of San Clemente Island, California
Evidence of repeated wildfires prior to human occupation on San Nicolas Island, California
Ecological change on California's Channel Islands from the Pleistocene to the Anthropocene
Uranium-series ages of corals, sea level history, and palaeozoogeography, Canary Islands, Spain: an exploratory study for two Quaternary interglacial periods
Landscapes of Santa Rosa Island, Channel Islands National Park, California
Origin of the Sinai-Negev erg, Egypt and Israel: mineralogical and geochemical evidence for the importance of the Nile and sea level history
- Overview
This project studies past high sea levels on coastlines that preserve fossil coral reefs or marine terraces. We ascertain the magnitudes of sea-level high stands by field mapping, stratigraphic measurements, and precise elevation measurements. Geochronology is accomplished by radiocarbon dating of mollusks (for Holocene-to-last-glacial deposits), uranium-series dating of corals (for high-sea stands back to about 500,000 years old) and strontium-isotope measurements of mollusks (for high-sea stands older than about 300,000 years). It is possible to determine the past water temperatures of the oceans during these high sea stands by detailed paleozoogeographic interpretations of fossil mollusk assemblages, a time-tested traditional method of paleoclimatic studies in marine settings. We also study the effects of sea level changes on coastal river systems and dunes.
The geomorphic record of sea level change on an uplifting coastline
In this figure, the lower graph shows oxygen isotope variations in foraminifera in deep-sea cores (Imbrie and others, 1984), which are excellent records of glacial-interglacial cycles. Oxygen isotope periods are called "stages," with odd-numbered stages corresponding to warm interglacial periods, such as the present (oxygen isotope stage 1). Cold glacial periods are given even-numbered stage names, such as the last major ice age (oxygen isotope stage 2). Because sea level is low during glacial periods (ocean water is taken up to form ice sheets) and high during interglacial periods (ice sheets melt and return water to the ocean), the oxygen isotope curve shown here for the past ~400,000 years is to a great extent a record of sea level fluctuations as well as a record of temperature fluctuations. On a tectonically active coast, such as California, changes in sea level are recorded as marine terraces, wave-cut benches that formed in the surf zone during interglacial periods, but are now above sea level due to uplift. Wave-cut benches also form during glacial periods, but these are offshore and underwater during interglacial periods. If uplift is continuous over time, a “stair step” type of landscape develops, as shown here, with each successively higher terrace corresponding to a successively older interglacial period.
[Reference: Imbrie, J., Hays, J.D., Martinson, D.G., McIntyre, A., Mix, A.C., Morley, J.J., Pisias, N.G., Prell, W.L., Shackleton, N.J., 1984, The orbital theory of Pleistocene climate: Support from a revised chronology of the marine δ18O record, in Berger, A., Imbrie, J., Hays, J., Kukla, G., and Saltzman, B., eds., Milankovitch and climate: Understanding the response to astronomical forcing: Dordrecht, D. Reidel Publishing Company, p. 269-305.]
The geomorphic record of sea level change on a stable or subsiding coastline
Shown here is the same oxygen isotope curve as above, over the past ~400,000 years. On a tectonically stable coast, such as Florida, the land is not uplifting and because the coast is a lower-energy one, wave-cut benches are not as common as in California. However, coral reef growth can take place in favorable locations and the tops of some coral reefs are found just a bit below sea level at the time of growth. Thus, past interglacial high-stands of sea are recorded as coral reef limestones, stacked one on top of the other (see diagram). Deeper limestones are progressively older and each successive reef is marked by a buried soil (paleosol) that formed during the intervening glacial period, when sea level was low. Why is this research important?
One of the most pressing issues in studies of climate change is the possible rise of sea level due to loss of major ice sheets, which would impact population, infrastructure, and habitats along the world's coastlines. It is not known which polar ice sheets (Greenland, West Antarctic, East Antarctic) are most at risk for mass loss that could contribute to sea level rise. Furthermore, it is not known what the possible magnitude of sea level rise is under interglacial climate conditions, how rapidly sea level may rise, or how long high sea levels may be retained. The goals of this project are to shed light on these questions by studying warm climate analogs of the geologic past.
When past sea levels were higher, where did the water come from? Here are the possibilities, with the amount of sea level rise they could provide now. How high was sea level during the last interglacial period?
Paleo-sea level = 5.5 meters + 3.0 meters = 8.5 meters above presentOn a tectonically stable coast such as the Florida Keys, we can estimate how high sea level was in the past, because fossil coral reefs give us a “high water mark” for a past interglacial period. Here at Windley Key, the top of a coral reef is 5.5 meters above modern sea level and has been dated to ~120,000 years ago (oxygen isotope stage 5), the last interglacial period. The types of corals in this reef require water depths of at least 3 meters. Thus, sea level ~120,000 years ago must have been 5.5 meters above present, plus at least 3 meters more (for habitat depth), indicating at least 8.5 meters above present. Paleo-sea level = 7.5 meters (top of shoal) + 1.0 meter (depth for ooids) = 8.5 meters above presentAnother type of sea level record in Florida is from limestones composed of ooids, tiny, egg-shaped grains of sand that precipitate from sea water inorganically. Shallow areas where ooids form at present in the Bahamas are typically in water about 1 meter deep. Thus, here in downtown Miami, Florida, the Miami Limestone (composed of ooids) is found at an elevation of about 7.5 meters above sea level. It has also been dated to the last interglacial period, ~120,000 years ago (isotope stage 5). When this elevation is added to the typical depth of formation of ooids (1 meter of water), we infer a past sea level of about 8.5 meters above present, very similar to the Florida Keys coral reef record. Key unanswered questions about past interglacial sea levels
The research conducted by this project attempts to answer these questions raised in the Intergovernmental Panel on Climate Change (IPCC) 2014 report:
- The timing of past interglacial sea-level high stands
- Marine paleotemperatures during past high-sea stands
- Magnitudes of past interglacial high-sea stands
- Rates of sea level rise
Results
What have we learned from the last interglacial?
What fossil corals can tell us
Corals are the only organisms that take up uranium from the ocean. Thus, they are the only fossils that we can use for high-precision uranium-series dating, one of our major tools to determine ages of marine deposits.
Florida Keys fossil reef corals, fossil corals from Puerto Rico, California fossil solitary corals, and fossil coral from Isla Guadalupe, Baja California
We can date corals with two uranium-series clocks: The ratio of 230Th/234U as well as the ratio of 234U/238U in a sample can tell us the age in years of the sample. How long did the last interglacial period last?
These maps show the places where we have found either fossil coral reefs (tropical locations) or coral-bearing marine terraces (California) that have been dated by uranium-series methods to the last interglacial period. On each map, you can see the range of ages we have gotten from dating these corals that tell us how long this high-sea stand lasted.
Uranium-series ages of reefs we have dated in the western Atlantic Ocean. Best estimates: A high sea level that lasted 8,000 to 14,000 years.
Length of the last interglacial—Pacific. Uranium series ages on the west coast give us the best estimate as 123,000 to 114,000 years. A high sea level that lasted at least 9,000 years.
Uranium-series ages of the last-interglacial Waimanalo reef on O'ahu, Hawai'i. A high sea level that lasted at least 12,000 years, and possibly 21,000 years. How high was sea level in the last interglacial period?
Elevations of corals we have dated from last-interglacial marine deposits on tectonically stable coastlines indicate a paleo-sea level of +5 meters to +10 meters.
Sources/Usage: Public Domain. Visit Media to see details.National Parks and Seashores on coasts that could be affected by future sea level rise.
Sources/Usage: Public Domain. Visit Media to see details.What would Florida have looked like during the last interglacial period when sea level was several meters higher than present?: The blue line show the present coastline, but much of southern Florida would have been underwater, as well as sites where many of Florida's coastal cities are situated.
How warm was the ocean during the last interglacial period?
It is possible to determine the past water temperatures of the oceans during these high sea stands by detailed paleozoogeographic interpretations of fossil mollusk assemblages, a time-tested traditional method of paleoclimatic studies in marine settings. These maps show how marine invertebrates, now found only in warm waters farther south at present, expanded northward beyond their present ranges, during a warm last interglacial period.
Warmer last-interglacial waters in the eastern Pacific Ocean.
The range of Strombus mutabilis indicate that warm Indo-Pacific waters expanded during the last interglacial period.
Sources/Usage: Public Domain. Visit Media to see details.The range of Lambis chiragra chiragra indicate that warm Indo-Pacific waters expanded during the last interglacial period. - Multimedia
- Publications
Below are publications associated with this project.
Filter Total Items: 27On the importance of stratigraphic control for vertebrate fossil sites in Channel Islands National Park, California, USA: Examples from new Mammuthus finds on San Miguel Island
Quaternary vertebrate fossils, most notably mammoth remains, are relatively common on the northern Channel Islands of California. Well-preserved cranial, dental, and appendicular elements of Mammuthus exilis (pygmy mammoth) and Mammuthus columbi (Columbian mammoth) have been recovered from hundreds of localities on the islands during the past half-century or more. Despite this paleontological wealAuthorsJeffery S. Pigati, Daniel R. Muhs, John P. McGeehinFluvial system response to late Pleistocene-Holocene sea-level change on Santa Rosa Island, Channel Islands National Park, California
Santa Rosa Island (SRI) is one of four east-west aligned islands forming the northern Channel Islands chain, and one of the five islands in Channel Islands National Park, California, USA. The island setting provides an unparalleled environment in which to record the response of fluvial systems to major changes of sea level. Many of the larger streams on the island occupy broad valleys that have beAuthorsR. Randall Schumann, Jeffery S. Pigati, John P. McGeehinUranium-series ages of fossil corals from Mallorca, Spain: The "Neotyrrhenian" high stand of the Mediterranean Sea revisited
The emergent marine deposits of the Mediterranean basin have been recognized as an important record of Quaternary sea level history for more than a century. Previous workers identified what have been interpreted to be two separate high stands of sea in the late Quaternary, namely the “Eutyrrhenian” (thought to be ~ 120 ka) and the “Neotyrrhenian” (thought to be either ~ 100 ka or ~ 80 ka). On MallAuthorsDaniel R. Muhs, Kathleen R. Simmons, Naomi PoratSea level, paleogeography, and archeology on California's Northern Channel Islands
Sea-level rise during the late Pleistocene and early Holocene inundated nearshore areas in many parts of the world, producing drastic changes in local ecosystems and obscuring significant portions of the archeological record. Although global forces are at play, the effects of sea-level rise are highly localized due to variability in glacial isostatic adjustment (GIA) effects. Interpretations of coAuthorsLeslie Reeder-Myers, Jon M. Erlandson, Daniel R. Muhs, Torben C. RickLate Quaternary sea-level history and the antiquity of mammoths (Mammuthus exilis and Mammuthus columbi), Channel Islands NationalPark, California, USA
Fossils of Columbian mammoths (Mammuthus columbi) and pygmy mammoths (Mammuthus exilis) have been reported from Channel Islands National Park, California. Most date to the last glacial period (Marine Isotope Stage [MIS] 2), but a tusk of M. exilis (or immature M. columbi) was found in the lowest marine terrace of Santa Rosa Island. Uranium-series dating of corals yielded ages from 83.8 ± 0.6 ka toAuthorsDaniel R. Muhs, Kathleen R. Simmons, Lindsey T. Groves, John P. McGeehin, R. Randall Schumann, Larry D. AgenbroadCoastal tectonics on the eastern margin of the Pacific Rim: Late Quaternary sea-level history and uplift rates, Channel Islands National Park, California, USA
The Pacific Rim is a region where tectonic processes play a significant role in coastal landscape evolution. Coastal California, on the eastern margin of the Pacific Rm, is very active tectonically and geomorphic expressions of this include uplifted marine terraces. There have been, however, conflicting estimates of the rate of late Quaternary uplift of marine terraces in coastal California, partiAuthorsDaniel R. Muhs, Kathleen R. Simmons, R. Randall Schumann, Lindsey T. Groves, Stephen B. DeVogel, Scott A. Minor, Deanna LaurelInterpreting the paleozoogeography and sea level history of thermally anomalous marine terrace faunas: A case study from the the last interglacial complex of San Clemente Island, California
Marine invertebrate faunas with mixtures of extralimital southern and extralimital northern faunal elements, called thermally anomalous faunas, have been recognized for more than a century in the Quaternary marine terrace record of the Pacific Coast of North America. Although many mechanisms have been proposed to explain this phenomenon, no single explanation seems to be applicable to all localitiAuthorsDaniel R. Muhs, Lindsey T. Groves, R. Randall SchumannEvidence of repeated wildfires prior to human occupation on San Nicolas Island, California
Understanding how early humans on the California Channel Islands might have changed local fire regimes requires a baseline knowledge of the frequency of natural wildfires on the islands prior to human occupation. A sedimentary sequence that was recently discovered in a small canyon on San Nicolas Island contains evidence of at least 24 burn events that date to between ∼37 and 25 ka (thousands of cAuthorsJeffrey S. Pigati, John P. McGeehin, Gary L. Skipp, Daniel R. MuhsEcological change on California's Channel Islands from the Pleistocene to the Anthropocene
Historical ecology is becoming an important focus in conservation biology and offers a promising tool to help guide ecosystem management. Here, we integrate data from multiple disciplines to illuminate the past, present, and future of biodiversity on California's Channel Islands, an archipelago that has undergone a wide range of land-use and ecological changes. Our analysis spans approximately 20,AuthorsTorben C. Rick, T. Scott Sillett, Cameron K. Ghalambor, Courtney A. Hofman, Katherine Ralls, R. Scott Anderson, Christina L. Boser, Todd J. Braje, Daniel R. Cayan, R. Terry Chesser, Paul W. Collins, Jon M. Erlandson, Kate R. Faulkner, Robert C. Fleischer, W. Chris Funk, Russell Galipeau, Ann Huston, Julie King, Lyndal L. Laughrin, Jesus Maldonado, Kathryn McEachern, Daniel R. Muhs, Seth D. Newsome, Leslie Reeder-Myers, Christopher Still, Scott A. MorrisonUranium-series ages of corals, sea level history, and palaeozoogeography, Canary Islands, Spain: an exploratory study for two Quaternary interglacial periods
We present the first U-series ages of corals from emergent marine deposits on the Canary Islands. Deposits at + 20 m are 481 ± 39 ka, possibly correlative to marine isotope stage (or MIS) 11, while those at + 12 and + 8 m are 120.5 ± 0.8 ka and 130.2 ± 0.8 ka, respectively, correlative to MIS 5.5. The age, elevations, and uplift rates derived from MIS 5.5 deposits on the Canary Islands allow calcuAuthorsDaniel R. Muhs, Joaquín Meco, Kathleen R. SimmonsLandscapes of Santa Rosa Island, Channel Islands National Park, California
Santa Rosa Island (SRI) is the second-largest of the California Channel Islands. It is one of 4 east–west aligned islands forming the northern Channel Islands chain, and one of the 5 islands in Channel Islands National Park. The landforms, and collections of landforms called landscapes, of Santa Rosa Island have been created by tectonic uplift and faulting, rising and falling sea level, landslidesAuthorsR. Randall Schumann, Scott A. Minor, Daniel R. Muhs, Jeffery S. PigatiOrigin of the Sinai-Negev erg, Egypt and Israel: mineralogical and geochemical evidence for the importance of the Nile and sea level history
The Sinai–Negev erg occupies an area of 13,000 km2 in the deserts of Egypt and Israel. Aeolian sand of this erg has been proposed to be derived from the Nile Delta, but empirical data supporting this view are lacking. An alternative source sediment is sand from the large Wadi El Arish drainage system in central and northern Sinai. Mineralogy of the Negev and Sinai dunes shows that they are high inAuthorsDaniel R. Muhs, Joel Roskin, Haim Tsoar, Gary Skipp, James R. Budahn, Amihai Sneh, Naomi Porat, Jean-Daniel Stanley, Itzhak Katra, Dan G. Blumberg