Geology topics

Research about Florida

Source-linked reports with geographic coverage including Florida.

At least 1,423 records · Page 79Linked to original sources

USGS1997

Influence of evaporation, ground water, and uncertainty in the hydrologic budget of Lake Lucerne, a seepage lake in Polk County, Florida

Evaporation losses and the interaction of ground water with Lake Lucerne were studied to determine the influence of these two processes on the hydrologic budget of a seepage lake. Lake Lucerne is representative of the numerous seepage lakes of sinkhole origin in the karst terrain of central Florida. Because of permeable surficial deposits, ground-water inflow is the only significant contribution from the surrounding watershed. The lake recharges the underlying Upper Floridan aquifer and, as a result, is susceptible to increased leakage induced by pumping from this aquifer. Ground-water fluxes determined in the study were analyzed to define the proportion of the total lake leakage induced by pumping from the Upper Floridan aquifer. A hydrologic budget is analyzed for the 1-year period from October 1985 to September 1986. Ground-water inflow and leakage are significant components of the hydrologic budget. Changes in the quantity of either of these fluxes can substantially alter lake stage. Ground-water inflow contributed from 20 to 37 percent of the total annual inflow to the lake. Leakage from the lake accounted for 18 to 23 percent of the total annual outflow. Water withdrawals from the Upper Floridan aquifer increased annual lake leakage by 22 percent over nonpumping conditions. Most of the increase (92 percent) in leakage occurred during April, May, and June 1986, when local citrus irrigation was highest. For the study year, ground-water inflow and leakage volumes were calculated by flow-net analysis to be equal to 10.5 and 12.6 inches, respectively, of water depth above (or below) the lake surface. These estimates were revised upward on the basis of an analysis of the error in the hydrologic-budget equation. Revised ground water inflow exceeded annual leakage from the lake. Ground-water inflow rates were increased by 120 percent to 23.6 inches, and leakage was increased by 40 percent to 17.5 inches. Differences between the two estimates probably reflect the uncertainty in the hydraulic conductivity estimates of the porous media around the lake and the unaccounted effect of transient ground-water inflow. The geometry of the sinkhole complex beneath Lake Lucerne and pumping in the Upper Floridan aquifer are primary controls on ground water interactions with the lake and, in particular, lake leakage. A numerical ground-water model was used to test the effects of these two factors on ground-water interactions with the lake. Results indicate that the intermediate confining unit below Lake Lucerne has been breached and replaced by materials about two orders of magnitude more conductive. Anisotropy in the surficial aquifer is approximately 100 and controls the depth of the ground-water flow intercepted by the lake. Lake sediments having low permeability may control the distribution of leakage through the lakebed but did not appreciably reduce total leakage rates in these simulations. Evaporation loss was the major outflow component of the hydrologic budget. Annual lake evaporation determined by the energy-budget method was 57.9 inches, about 8 inches greater than long-term estimates for the region. The greater rate was attributed to drier than normal conditions: rainfall totaled 40.9 inches during the study year, about 10 inches less than the long-term average. Similar annual evaporation rates were determined by the energy-budget method, the simpler mass-transfer method, and by corrected pan evaporation from an onsite pan; however, the probable errors associated with these other two methods were greater than for the energy budget. Weekly energy-budget evaporation rates ranged from 0.04 inch per day in early January 1986 to 0.26 inch per day in early May 1986. The largest monthly energy-budget evaporation rates occurred in April and May 1986, 7.16 and 7.12 inches per month, respectively. Monthly evaporation estimated from corrected pan evaporation generally was within 10 percent of the energy-budget estimate but differed by as much as 35 percent. Daily energy-budget evaporation also was computed for 321 days during the year.

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USGS1997

Simulation of the water-table altitude in the Biscayne Aquifer, southern Dade County, Florida, water years 1945-89

A digital model of the flow system in the highly permeable surficial Biscayne aquifer of southern Dade County, Florida, was constructed for the purposes of better understanding processes that influence the flow system and of supporting the construction of a subregional model of the transport of brackish water from a flowing artesian well. Problems that needed resolution in this endeavor included the development of methods to represent the influence of flowing surface water in seasonally inundated wetlands and the influence of a network of controlled canals developed in stages during the simulation time period (water years 1945-89). An additional problem was the general lack of natural aquifer boundaries near the boundaries of the study area. The model construction was based on a conceptual description of the Biscayne aquifer developed from the results of previous U.S. Geological Survey investigations. Modifications were made to an existing three-dimensional finite-difference simulator of ground-water flow to enable an upper layer of the grid to represent seasonally occurring overland sheet flow in a series of transient simulations of water levels from 1945 to 1989. A rewetting procedure was developed for the simulator that permitted re-saturation of cells in this layer when the wet season recurred. An ï¿½equivalent hydraulic conductivityï¿½ coefficient was assigned to the overland flow layer that was analogous, subject to various approximations, to the use of the Manning equation. The surficial semi-confining peat and marl layers, levees, canals, and control structures were also represented as part of the model grid with the appropriate choices of hydraulic coefficient values. For most of the Biscayne aquifer grid cells, the value assigned to hydraulic conductivity for model calibration was 30,000 feet per day and the value assigned to porosity was 20 percent. Boundary conditions were specified near data sites having long-term records of surface-water stages or water-table altitudes, and modifications to the simulator permitted the specification of time-varying pressures at boundary grid cells. Rainfall data from a station in Homestead generally were used as an a really uniform rainfall specification throughout the modeled region. Maximum evapotranspiration rates ranged seasonally from a minimum of 0.08 inch per day in January to a maximum of 0.21 inch per day between June and October. Shallow-root and deep-root zone depths for the evapotranspiration calculation were 3 and 20 feet in the coastal ridge and were 0.10 and 5 feet in the glades regions where peat and marl covers occurred. Results of sensitivity analyses indicated that the simulations of stages and water levels were relatively unresponsive to 50 percent changes in aquifer hydraulic conductivity, porosity, and the equivalent hydraulic conductivity of overland flow. However, 20 percent changes in rainfall and maximum evapotranspiration rates produced significantly different water levels, as did interchange of coastal ridge and glades deep-root zone (extinction) depths. Water levels were simulated very well at most measurement sites. Sensitivity analyses illustrated the significant influence of the uncontrolled agricultural drainage canals on pre-1968 regional water levels and the further influence of Black Creek Canal in draining a region of high water after 1961. Other analyses indicated that the flood-control system of 1968-82 lowered peak water levels in the affected region by as much as 1.5 feet in the wet summers of 1968, 1969, and 1981, and that Levee 67 Extended channeled flows from the S-12 spillway structures and raised overland flow stages in Shark River Slough. Hypothetical scenarios of well-field pumping in the vicinity of Levee 31N indicated that the pumping induced a significant amount of recharge from the adjacent borrow canal, the degree of which depended on the distance between the canal and the well field. The computed ratio of evapotranspiration to rainfall recharge ranged from 88 to 94 percent during water years 1945-82. The ratio increased to about 97.9 percent during water years 1983-89, possibly because of changing water-management practices and deficient rainfall.

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USGS1997

Computation of the time-varying flow rate from an artesian well in central Dade County, Florida, by analytical and numerical simulation methods

Simulation of the development of a plume of brackish water in a surficial aquifer caused by discharge from a flowing artesian well required an accurate estimate of the rate of flow during a 40-year period. The rate of flow from the well, constructed with 12-inch casing in 1944, was measured to be 2,350 gallons per minute 2 months after completion and 1,170 gallons per minute in 1964, 1965, and 1969. The rates measured 20 years apart appeared to be mutually inconsistent unless the difference could be explained by the: (1) drawdown of the aquifer over time, (2) raising of the altitude at which the water was discharged, (3) installation of 80 feet of 8-inch liner, or (4) deterioration of the condition of the well over time. The latter possibility implies losses of flows through holes in the casing and increased friction losses. Application of an analytical solution relating the time-varying rate of flow to a constant opposing head (a rewriting of the "constant drawdown" formula) failed to reconcile the measured rates, though estimates provided by use of the formula differed by only about 15 percent. Numerical simulation techniques were also used to estimate the rate of artesian flow from the source aquifer, a permeable zone at about 1,200 feet below land surface, near the top of the Upper Floridan aquifer in southeastern Florida. The selected simulation code contained a well-riser model that was used to account for friction losses in the well. Construction of a highly generalized model of the Floridan aquifer system for the flow-rate analysis, and the determination of a set of predevelopment head values for use as an initial condition, permitted simulation of the effects of recharge through leaky confining layers or from aquifer boundaries at a finite distance from the well. The conceptual model supported by the calibration of the model of the Floridan aquifer system is that a hydraulically uniform Lower Floridan aquifer ("Boulder Zone") provides recharge to the Upper Floridan aquifer through a leaky middle confining unit, and head variations in the Upper Floridan aquifer are related to variations in the thickness of the zone of fresh and brackish water extending downward into the confining unit. Results of the flow-rate analysis indicated that the flow rate should reach equilibrium after about 1 week because the Upper Floridan aquifer received recharge from the Boulder Zone through the intervening middle confining unit. The well modifications probably only decreased the rate of flow by 18 to 19 percent. A sensitivity analysis indicated that variation in the roughness coefficient of a degree that could represent severe deterioration of the well casing decreased the estimated flow rate by about 17.5 percent. Another sensitivity analysis indicated that installation of 80 feet of 8-inch liner had only a slight effect on the flow rate. The flow-rate inconsistency was not fully resolved by the analysis, but could be explained as a combination of the result of well modification, deterioration of the condition of the well, and other factors not amenable to analysis (inaccuracy in one or more of the flow-rate measurements or greater than estimated losses through the casing). The transmissivity of the source aquifer was estimated to be 11,125 feet squared per day at the well site. Besides the construction of a generalized model of the Floridan aquifer system, the most significant result of the analysis was the demonstration of a simulation approach for accurately showing the relation between aquifer characteristics and the rate of flow from artesian wells. However, this approach requires considerably more analytical effort and data describing aquifer properties than does application of the constant drawdown formula.

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USGS1997

Hematologic and serum biochemical reference intervals for Florida panthers

Ninety-four blood samples were collected from 48 (29 males and 19 females) free-ranging Florida panthers ( Felis concolor coryi ) captured in southern Florida (USA) from 1983 to 1994 for routine hematological and serum biochemical analysis. Florida panthers in the northern portion of their range had significantly higher red blood cell (mean ± SD = 7.923 × 10 6 ± 0.854 × 10 6 /μl), hemoglobin (12.53 ± 1.66 g/dl), and packed cell volume (36.97 ± 4.27%) values compared to those of panthers localized in more southern parts of Florida (7.148 × 10 6 ± 1.045 × 10 6 /μl, 11.60 ± 1.62 g/dl, and 34.82 ± 5.99%, respectively). Adults had significantly higher mean serum total protein (7.50 ± 0.59 g/dl) and packed cell volume (36.90 ± 4.97%) values than juveniles (6.88 ± 0.49 g/dl and 34.54 ± 5.30%). However, mean serum albumin concentrations were significantly higher in juveniles (3.80 ± 0.26 g/dl) when compared to adult values (3.58 ± 0.26 g/dl). Mean serum calcium concentrations were significantly higher in juveniles (10.33 ± 0.39 mg/dl) than in adults (9.66 ± 0.45 mg/dl). Additionally, mean serum iron concentrations were significantly higher in those panthers of intergrade genetic stock compared to values in those of authentic genetic stock (105.6 ± 72.1 μg/dl versus 59.3 ± 19.7 μg/dl, respectively).

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USGS1997

Winter mortality of common loons in Florida coastal waters

Diagnostic findings are presented for 434 common loons (Gavia imrner) found sick or dead on Florida beaches from 1970 through 1994, primarily during the months of December to April. The most commonly recognized problem was an emaciation syndrome (66%), followed by oiling (18%), aspergillosis (7%), trauma (5%) and miscellaneous disease entities (1%). The cause-of-death for 3% of the birds was not determined. Many of the carcasses examined (n = 173) were obtained during an epizootic which occurred from January to March of 1983 in which more than 13,000 loons were estimated to have died. An emaciation syndrome, characterized by severe atrophy of pectoral muscles, loss of body fat and hemorrhagic enteritis, was the primary finding in this epizootic. It was postulated to have a complex etiologic basis involving synergistic effects and energy costs of migration, molting and replacement of flight feathers, food resource changes, salt-loading, intestinal parasitism, environmental contaminants, and inclement weather.

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USGS1997

Assessment of acreage and vegetation change in Florida's Big Bend tidal wetlands using satellite imagery

Fluctuations in sea level and impending development on the west coast of Florida have aroused concern for the relatively pristine tidal marshes of the Big Bend. Landsat Thematic Mapper (TM) images for 1986 and 1995 are processed and evaluated for signs of change. The images cover 250 km of Florida's Big Bend Gulf Coast, encompassing 160,000 acres of tidal marshes. Change is detected using the normalized difference vegetation index (NDVI) and land cover classification. The imagery shows negligible net loss or gain in the marsh over the 9-year period. However, regional changes in biomass are apparent and are due to natural disturbances such as low winter temperatures, fire, storm surge, and the conversion of forest to march. Within the marsh, the most prominent changes in NDVI and in land cover result from the recovery of mangroves from freezes, a decline of transitional upland vegetation, and susceptibility of the marsh edge and interior to variations in tidal flooding.

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USGS1997

Dynamic flood monitoring in coastal environments

No abstract available.

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USGS1996

Ground-Water Discharge to Biscayne Bay

Introduction The South Florida Ecosystem Restoration Program is an intergovernmental effort, involving a number of agencies, to reestablish and maintain the ecosystem of south Florida. One element of the restoration effort is the development of a firm scientific basis for resource decision making. The U.S. Geological Survey (USGS), one of the agencies, provides scientific information as part of the South Florida Ecosystem Restoration Program. The USGS began their own program, called the South Florida Ecosystem Program, in fiscal year 1995 for the purpose of gathering hydrologic, cartographic, and geologic data that relate to the mainland of south Florida, Florida Bay, and the Florida Keys and Reef ecosystems. Over the years, the construction of canals and levees has altered the natural hydrologic conditions of the Everglades. The canals and levees were constructed to convey water, prevent flooding, and store water in conservation areas for future use. The U.S. Army Corps of Engineers (COE) in Jacksonville, Fla., is planning to construct gated spillways and culverts to allow for the restoration of natural sheetflow conditions to Everglades National Park (ENP). These proposed changes may further affect the hydrologic conditions of ENP and other parts of the ecosystem, thus leading to the following questions: Is ground water flowing to Biscayne Bay a significant component of the water budget in south Florida? Would the quantity of ground water flowing to Biscayne Bay be greatly affected by changes in the operation of gates and control structures in canals? How much change in ground-water discharges to Biscayne Bay has occurred due to modifications to the hydrologic system? Federal, State, and local agencies need to know the effect that changes in the operation of gates and control structures in canals will have on the water-budget components of the natural water systems in south Florida, including ground-water flow to Biscayne Bay.

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USGS1996

South Florida Ecosystem Program; seepage beneath Levee 30 in northern Dade County

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USGS1996

South Florida Ecosystem Program web site

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USGS1996

Hydrogeology of the surficial aquifer system in Southwest Florida

Restoration and management of the south Florida ecosystem will be guided by hydrologic models that simulate water flowing through the wetlands and shallow subsurface aquifers beneath them. The restoration of the ecosystem is, essentially, the restoration of the natural hydrologic system. As surface water is re-diverted from manmade canals to its more natural state as overland flow, several changes are predicted to occur. First, because water flowing over land moves more slowly than in canals, overland flow should remain in the wetland ecosystem for a longer period each year. Second, as the flowing water spreads out over the wetlands, recharge to the shallow aquifers should increase as more of that water infiltrates into the ground. The U.S. Corps of Engineers and the South Florida Water Management District (SFWMD) will use hydrologic models to anticipate the consequences of these proposed restoration plans. This research program is designed to provide essential subsurface data to improve hydrologic models for land and water managers in southwest Florida where subsurface information is lacking. Obtaining hydrogeological data requires core drilling, corehole testing, and rock and sediment analysis.

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USGS1996

South Florida High-accuracy elevation data collection project

Background The major issues facing ecosystem restoration and management in south Florida are centered on the availability and distribution of clean, fresh water. Surface water flow modeling studies are an important aspect of the scientific information needs of the ecosystem restoration initiative. Hydrologic models provide much needed predictive capabilities for evaluating options for management of parks, refuges, and lands planned for acquisition, as well as for understanding the impacts of land management practices in surrounding areas. Models must account for the expansive and extremely low relief terrain of south Florida, where surface waters of the natural system are transported by sheet flow from Lake Okeechobee through the Everglades to Florida Bay and the Gulf of Mexico. To model sheet flows, highly accurate elevation data that define the surface topography are required as the most critical input parameter to the Natural Systems Model and other hydrologic models. These data are necessary for calculating water surface slope, depth, velocity, and direction of flow. Hydrologists have stated vertical accuracy requirements of between 3 and 15 centimeters. These accuracy requirements are so stringent, because of the extremely flat terrain, that any standard or other currently available data products would not suffice for this modeling application.

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USGS1996

South Florida Ecosystem Program database development

Purpose The South Florida Ecosystem Restoration Program is an intergovernmental effort to reestablish and maintain the ecosystem of south Florida. One element of the restoration effort is the development of a firm scientific basis for resource decision making. The U.S. Geological Survey (USGS) is one of the agencies that provides scientific information as part of the South Florida Ecosystem Program (SFEP). The program, which was begun in fiscal year 1995, provides multidisciplinary hydrologic, cartographic, geologic, and biologic data that relate to the mainland of south Florida, the Florida Bay, and the Florida Keys and Reef ecosystems. A database with established transfer formats, definitions, and spatial registration greatly promotes dissemination of scientific data and information in a cost-effective manner. Shared databases may help elevate the quality and quantity of available information. By acquiring data from the database, individual users can certify and evaluate data. With appropriate management oversight, this generally leads to improved consistency and increased reliability in the database.

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USGS1996

Sediment quality assessment studies of Tampa bay, Florida

A survey of the toxicity of sediments throughout the Tampa Bay estuary was performed as part of the National Oceanic and Atmospheric Administration's National Status and Trends Program. The objectives of the survey were to determine the spatial extent and severity of toxicity and to identify relationships between chemical contamination and toxicity. Three independent toxicity tests were performed: a 10-d amphipod survival test of the whole sediments with Ampelisca abdita , a sea urchin fertilization test of sediment pore water with Arbacia punctulata , and a 5-min Microtox® bioluminescence test with solvent extracts of the sediments. Seventy-three percent of the 165 undiluted sediment pore-water samples were significantly toxic relative to reference samples with the sea urchin fertilization test. In contrast, only 2% of the 165 samples were significantly toxic in the amphipod tests. The causes of toxicity were not determined. However, concentrations of numerous trace metals, pesticides, polychlorinated biphenyl (PCB) congeners, polycyclic aromatic hydrocarbons (PAHs), and ammonia were highly correlated with pore-water toxicity. Concentrations of many substances, especially total dichlorodiphenyltrichloroethanes (DDTs), endrin, total PCBs, certain PAHs, lead, and zinc, occurred at concentrations in the toxic samples that equaled or exceeded concentrations that have been previously associated with sediment toxicity.

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USGS1996

Mercury studies in the Florida Everglades

Public concern for wildlife and human health problems due to mercury (Hg) toxicity has increased substantially since the mid-1980's. These concerns are manifested primarily by the issuance of fish consumption advisories in the majority of U.S. states, Canada, and several European countries because of high levels of mercury in game fish. Although the precise causes for this contamination problem are not completely understood, it appears that there are both source and ecosystem-specific factors that can result in elevated levels of mercury in game fish. Because mercury is known to adverse affect the human brain and nervous system, health concerns arise when elevated concentrations of mercury are detected in game fish from ecosystems where there is subsistence level consumption of fish. In extreme cases such as the Everglades, where mercury concentrations in fish consistently exceed the Florida advisory level of 1.5 parts per million, even occasional fish consumption is not recommended. For most aquatic ecosystems, atmospheric deposition is the primary source of mercury. although there are numerous instances of geologic and anthropogenic point-source contamination. There are many sources of mercury to the atmosphere, both natural and human related. Natural sources include outgassing from the oceans, volcanoes, and natural mercury deposits. Coal combustion, waste incineration, chloralkai production, and metal processing are the dominant human-related sources to the atmosphere. In ecosystems for which atmospheric deposition is the dominant source, resulting concentrations of total mercury in water are very low, generally less than 10 nanograms per liter (ng/L). The challenge to scientists is to explain the series of processes that lead to toxic or near-toxic levels of mercury in organisms near the top of the food chain (bioaccumulation), when aqueous concentrations and source-delivery rates are so low. To understand this phenomenon adequately, scientists must apply an interdisciplinary approach wherein various components of an ecosystem (atmosphere, biota, surface water, ground water, and sediments) are studied-contemporaneously. The purpose of this fact sheet is to describe the mercury contamination problem in south Florida, and the interdisciplinary project that was assembled under the auspices of the U.S. Geological Survey South Florida Ecosystem Program to investigate the underlying processes that cause mercury bioaccumulation.

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USGS1996

Decadal-scale changes in benthic foraminiferal assemblages off Key Largo, Florida

Assemblages of foraminiferal tests in sediments sampled off Key Largo, Florida, in 1982, 1991, and 1992 were significantly different from assemblages sampled along the same traverses in 1959–1961. Larger, algal symbiont-bearing taxa, primarily Soritidae, comprised 50–80% of the specimens in samples collected in 1959–1961, whereas Miliolidae and Rotaliidae comprised 65-90% of the specimens collected in 1991 and 1992. Test abundance in 1992 samples ranged from 1.0 × 10 2 /g to 8.1 × 104/g; tests were least abundant in coarse, well-sorted sediments. The lack of test-density data for the 1959-1961 samples prevented assessment of whether densities of smaller foraminifera have increased, symbiotic foraminifera have decreased, or both. Between 1982 and 1992, densities of smaller foraminifera appear to have increased. Although the causes of these changes in foraminiferal assemblages are not known, possible factors include nutrient loading inshore, winnowing and transport of tests by storm activity, and disease. The shift in dominance from long-lived, algal symbiont-bearing taxa in 1959--1961 to small, fast-growing, heterotrophic taxa in 1992 is consistent with predictions of community response to gradually increasing nutrient flux into south Florida's coastal waters. This study indicates that published accounts of foraminiferal assemblages from sediments collected 30 or more years ago can be valuable resources in efforts to determine if biotic changes have occurred in coastal ecosystems. This study also indicates that family-level identifications may be sufficient to detect decadal-scale changes in foraminiferal assemblages in reef-tract sediments.

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USGS1996

The stable oxygen and carbon isotopic record from a coral growing in Florida Bay: a 160 year record of climatic and anthropogenic influence

A 160 year record of skeletal δ 13 C and δ 18 O was examined in a specimen of the coral Solenastrea bournoni growing in Florida Bay. Variations in the δ 18 O of the skeleton can be correlated to changes in salinity while changes in the δ 13 C reflect cycling of organic material within the Bay. Based on the correlation between salinity and skeletal δ 18 O, we have concluded that there has been no long term increase in salinity in this area of Florida Bay over the past 160 years. Using salinity correlations between the various basins obtained from instrumental data, we have been able to extend our interpretations to other parts of Florida Bay reaching similar conclusions. In contrast to current ideas which have focused on changes in Florida Bay water quality over the past 20-yr history of the Bay as causative in its decline, we have determined that changes in water quality in this basin were already set in motion between 1905 and 1912 by the construction of the Florida East Coast Railway from Miami to Key West. The construction of the railway resulted in the restriction of the exchange of water between the Florida reef tract and the Gulf of Mexico causing Florida Bay to become more eutrophic. Evidence of this process is observed in the sudden shift to relatively lower δ 13 C values coincident with railway construction. Natural events also appear to have influenced the water in the Bay. Between 1912 and 1948 frequent hurricanes had the effect of increasing exchange of water between the Bay and reef tract and removing large quantities of organic rich sediments. However, since 1948 the number of hurricanes affecting the area has decreased and the products of the oxidation of organic material have been increasingly retained within the basin promoting the initiation of eutrophic conditions.

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USGS1996

Sea-level records at ~80 ka from tectonically stable platforms: Florida and Bermuda

Studies from tectonically active coasts on New Guinea and Barbados have suggested that sea level at ∼ 80 ka was significantly lower than present, whereas data from the Atlantic and Pacific coasts of North America indicate an ∼ 80 ka sea level close to that of the present. We determined ages of corals from a shallow submerged reef off the Florida Keys and an emergent marine deposit on Bermuda. Both localities are on tectonically stable platforms distant from plate boundaries. Uranium-series ages show that corals at both localities grew during the ∼80 ka sea-level highstand, and geologic data show that sea level at that time was no lower than 7–9 m below present (Florida) and may have been 1–2 m above present (Bermuda). The ice-volume discrepancy of the 80 ka sea-level estimates is greater than the volume of the Greenland or West Antarctic ice sheets. Comparison of our ages with high-latitude insolation values indicates that the sea-level stand near the present at ∼80 ka could have been orbitally forced.

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