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At least 775 records · Page 43Linked to original sources
USGS1970

Comparison of chemical hydrogeology of the carbonate peninsulas of Florida and Yucatan

Aquifers of the peninsulas of Florida and northern Yucatan are Tertiary marine carbonate formations showing many lithologic and faunal similarities. In addition, the tropical to subtropical climates of the two areas are similar, each having annual rainfall of about 1000 to 1500 mm. Despite similarities in these fundamental controls, contrasts in the hydrologic and geochemical systems are numerous and striking. For example, Florida has many rivers; Yucatan has none. Maximum thickness of fresh ground water in Florida is about 700 meters; in the Yucatan it is less than 70 meters. In Florida the gradient of the potentiometric surface averages about 1 meter per kilometer; in the Yucatan it is exceedingly low, averaging about 0.02 meter per kilometer. In Florida the chemical character of water changes systematically downgradient, owing to solution of minerals of the aquifer and corresponding increases in total dissolved solids, sulfate, calcium, and Mg-Ca ratio; in the Yucatan no downgradient change exists, and dominant processes controlling the chemical character of the water are solution of minerals and simple mixing of the fresh water and the body of salt water that underlies the peninsula at shallow depth. Hydrologic and chemical differences are caused in part by the lower altitude of the Yucatan plain. More important, however, these differences are due to the lack of an upper confining bed in Yucatan that is hydrologically equivalent to the Hawthorn Formation of Florida. The Hawthorn cover prevents recharge and confines the artesian water except where it is punctured by sinkholes, but sands and other unconsolidated sediments fill sinkholes and cavities and impede circulation. In the Yucatan the permeability of the entire section is so enormous that rainfall immediately infiltrates to the water table and then moves laterally to discharge areas along the coasts.

Florida Peninsula, Yucatan Peninsula↗
USGS1990

Cold-front driven storm erosion and overwash in the central part of the Isles Dernieres, a Louisiana barrier-island arc

Tropical and extratropical storms produce significant erosion on the barrier islands of Louisiana. Over the past 100 years, such storms have produced at least 2 km of northward beach-face retreat and the loss of 63% of the surface area of the Isles Dernieres, a low-lying barrier-island arc along the central Louisiana coast. Elevations on the islands within the arc are typically less than 2 m above mean sea level. The islands typically have a washover-flat topography with occasional, poorly developed, dune-terrace topography consisting of low-lying and broken dunes. The central part of the arc consists of salt-marsh deposits overlain by washover sands along the Gulf of Mexico shoreline. Sand thicknesses range from zero behind the beach, to less than 2 m under the berm crest, and back to zero in the first nearshore trough. The sand veneer is sufficiently thin that storms can strip all the sand from the beach face, exposing the underlying marsh deposits. The geomorphic changes produced by cold fronts, a type of extratropical storm that commonly affect the Isles Dernieres between late fall and early spring are described. Between August 1986 and September 1987, repeated surveys along eleven shore-normal transects that covered 400 m of shoreline revealed the timing and extent of cold-front-produced beach change along a typical section of the central Isles Dernieres. During the study period, the beach face retreated approximately 20 m during the cold-front season but did not rebuild during the subsequent summer. Because the volume of sand deposited on the backshore (5600 m 3 ) was less than the volume of material lost from the beach face (19,200 m 3 ), approximately 13,600 m 3 of material disappeared. Assuming that underlying marsh deposits decrease in volume in direct proportion to the amount of beach-face retreat, an estimate of the mud loss during the study period is 14,000 m 3 . Thus, the decrease in volume along the profiles can be accounted for without removing any sand from the area, suggesting that a major effect of cold fronts is first to strip the sand from the beach face and then to erode the underlying marsh deposits. After being eroded, the mud is lost from the islands because currents transport it away from the islands.

Marine Geology↗
USGS1970

Latitudinal gradients in tertiary molluscan faunas of the Pacific coast

Tertiary molluscan faunas of the middle latitudes of the marginal eastern North Pacific are characterized by warm-water taxa whose descendants now live in more southerly latitudes. A series of profiles in which cumulative percentages of warm-water faunal elements are plotted against latitude show progressive northward decreases in the percentage of these elements in the faunas of Pacific coast Tertiary stages. Systematic changes in the relative position of these latitudinal gradients during the Middle and Late Tertiary are related to climatic change in the Pacific Basin. Widespread tropical marine climate in the middle latitudes of the eastern North Pacific during the Eocene is indicated by widespread faunal units characterized by high levels of taxonomic diversity. Succeeding Early Oligocene faunas are less diverse, suggesting cooler climatic conditions. Unusually low representations of warm-water genera characterize the molluscan faunas of the Acila shumardi Zone in central California (latitude 34°–37°N). The anomalously cool-water aspect of these faunas may record the occurrence of upwelling along a bold linear segment of the Pacific coast. During the Late Oligocene or the Early Miocene, they are replaced by faunas of unusually warm-water aspect resulting in positive anomalies in Miocene latitudinal faunal gradients in central California. The Miocene anomalies seem to result from the development of an irregular Neogene coastline with extensive, newly established shallow-water embayments.

Palaeogeography, Palaeoclimatology, Palaeoecology↗
USGS1971

Tertiary climatic fluctuations and methods of analysis of tertiary floras

On theoretical grounds, an analysis of the physiognomy of a Tertiary leaf assemblage is more direct and reliable than a circuitous floristic analysis in assigning thermal regimes to fossil assemblages. Using primarily foliar physiognomy and secondarily floristic composition, it can be shown that: ( 1 ) some middle latitude Tertiary assemblages probably lived under meteoroligically tropical climates; ( 2 ) a major and rapid climatic deterioration occurred in the Oligocene; and ( 3 ) a major climatic fluctuation probably occurred in the Late Eocene. These analyses thus substantiate the conclusions of several other paleobotanists regarding climatic fluctuations. Recent criticisms of these analyses are shown to be invalid and to be based largely on misinterpretations.

Palaeogeography, Palaeoclimatology, Palaeoecology↗
USGS1982

Ichnofossils and rhizoliths of the nearshore fluvial Jebel Qatrani Formation (Oligocene), Fayum Province, Egypt

The ichnofossils and rhizoliths of the Oligocene Jebel Qatrani Formation of Egypt are among the best preserved, most diverse in form, and most abundant of such structures yet recognized in fluvial rocks. Twenty-one forms are described. The ichnofauna contains traces (domichnia, fodinichnia, cubichnia) of probable annelid, insect, crustacean, and vertebrate origin. These include the first described fossil nest structures and gallery systems of subterranean termites (Isoptera), the first examples of Ophiomorpha from wholly fluvial rocks, and the first fossil vertebrate burrows from the African Tertiary. Rhizoliths associated with the ichnofauna and those occurring elsewhere document a variety of small, wetland plants, coastal mangroves, and much larger trees. The environment suggested by these traces is consistent with the coastal, tropical to subtropical, monsoonal rain forest, with adjacent more open areas, that is indicated by independent evidence of sedimentology, paleontology, and paleopedology.

Fayum Province↗
USGS1994

Comparison of drier- to wetter-interval estuarine roof facies in the Eastern and Western Interior coal basins, USA

Many of the Carboniferous coals in the eastern interior of the US are associated with siliciclastic roof facies that were deposited within a fluvio-estuarine transition. These facies include a variety of rhythmites, some of which exhibit tidal cycles. Drier-interval coals (Westphalian B-C, Stephanian) tend to be more laterally restricted and more commonly are associated with paleovalleys. Conversely, wetter-interval coals (Westphalian D) are very widespread and are not restricted to paleovalleys. Throughout the Lake Carboniferous, wet paleoclimates associated with these coals lead to valley incision during sea-level lowstand when large tropical rivers downcut older sediments deposited during previous sea-level highstands. During subsequent rise of sea level, these fluvial valleys were flooded and converted to estuaries where tidal ranges and sedimentation rates were significantly amplified. Based on modern analogs and interpretation of many examples of Carboniferous tidal rhythmites, the localized depositional rates in these settings are exceptionally high. The estuaries became sediment sinks, trapping sediment that is pumped in from both fluvial and marine sources. As a result, sedimentation readily keeps pace with rising baselevel. Extensive intertidal flats and shallow subtidal flats are created and prograde over the valley-confined mires. Thick tidal cycles and upright trees (some with attached foliage) record rapid burial of mires. This model is supported with examples of roof facies from the Westphalian B-C of the Eastern Interior Basin, and the Stephanian of the Western Interior Basin. In these areas facies within each cycle range from well-developed, extensive paleosols and coals, to widespread marine shales or limestones. Variations in both sea level and climate resulted in a complex history of valley fill during which coals could be developed at any time (except during widespread flooding). Minable, low-sulfur and low-ash coals occur, but the coals are relatively thin and discontinuous. Conversely, the Westphalian D coals are very widespread and significant peat accumulations were not confined to paleovalleys. Nonetheless, the lowest sulfur coals are related to rapid deposition of roof facies that occurred within the paleovalley whereas high-sulfur coals were formed in areas of lower sedimentation rate of roof facies that occurred beyond the confines of the paleovalley.

Arkansas, Illinois, Indiana, Iowa, Kansas, Kentuck↗
USGS2017

Paleohydrologic regimes in the southwestern Great Basin, 0-3.2 my ago, compared with other long records of "gobal" climate

Nine distinct paleohydrologic regimes in the southwestern Great Basin over the last 3.2 my are recorded by the lacustrine deposits in KM-3, a 930-m core from Searles Lake, California. These are characterized as being "wet," "intermediate," or "dry" (like today). Excepting the present incomplete regime, each lasted 0.12 to 0.76 my. Major regime changes 0.01, 0.13, 0.6, and 2.5 my ago appear to coincide with recognized changes in global ice-sheet histories as represented by 18O and other records from marine sediments, but comparable changes 0.3, 1.0, 1.3, and 2.0 my ago do not appear to coincide closely with comparable perturbations in ice-sheet histories. However, all regime boundaries (during the last 1.75 my) coincide closely in time with changes in sea-surface temperatures in the tropical Atlantic, and many coincide with other deep-sea and continental paleoclimatic boundaries.The average duration of these paleohydrologic regimes was about 0.4 my (standard deviation, 0.2 my or less, depending on assumptions), and it is suggested that the regime boundaries reflect times of change in global(?) sea-surface temperatures, possibly controlled in part by the Earth's 413,000-yr orbital eccentricity cycle. During the wettest and driest regimes in the Searles Lake area, lake levels were not sufficiently affected by the 23,000-, to 42,000-, or 100,000-yr climate cycles related to high-latitude ice-sheet fluctuations to produce changes in the lacustrine sediment character. During intermediate regimes, however, when lacustrine sedimentation in this area was more sensitive to climate, the sediments, in KM-3, record lake fluctuations with average frequencies near those of the ice sheets. This seems to indicate that the high-latitude ice-sheet fluctuations caused local climatic perturbations but did not dominate the hydrologic component of climate in this area. Other lacustrine deposits in the southwestern Great Basin of California and Nevada have ages comparable in part to those of the wet to intermediate regimes indicated by KM-3, and they may all be products of finite periods when lake expansion, alluvial fan growth, increased spring discharge, and fluvial deposition were promoted in this area by widespread wet climates. Glacier expansion in the Sierra Nevada may also have been primarily an expression of, and in phase with, these wet regimes. ?? 1984.

Quaternary Research↗
USGS1994

Paleocene floral diversities and turnover events in eastern North America and their relation to diversity models

This paper uses angiosperm pollen taxon turnover (first and last appearance) and diversity events as metrics to describe the Paleocene floral history of the eastern Gulf Coast; data are from 64 samples and 67 angiosperm pollen taxa. Angiosperm pollen diversity was very low at the beginning of the Paleocene, rose slowly and then somewhat more rapidly to a maximum for the epoch in the middle of the late Paleoceneas a result of the maximum in rate of first appearances during the late early Paleocene and earliest late Paleocene. Diversity then dropped very rapidly at or near the end of the epoch as the rate of last appearances reached its maximum, resulting in the Terminal Paleocene Extinction Event. The latest Paleocene diversity decline coincided with an increase in mean annual temperature and probably in rainfall, representing the beginning of the climatic maximum for the Tertiary which characterized the early Eocene. The increase in diversity of early Paleocene floras in the eastern Gulf Coast resulted from exploitation of unfilled ecospace originating from (1) low regional diversity following the Terminal Cretaceous Extinction Event, and (2) creation of many new niches during the Paleocene, resulting, according to megafloral evidence, from a change to a new vegetation type (multistratal tropical rainforest) brought about by an increase in rainfall. The slow rate of recovery of earliest Paleocene angiosperm diversity in the eastern Gulf Coast may be explained in part by the diversity-dependence model of Carr and Kitchell (1980). However, additional factors may have contributed to the slow recovery: (1) the adverse terminal Cretaceous climates may have extended into the early Paleocene, (2) the initial Paleocene environment of the eastern Gulf Coast may have contained relatively few niches, (3) some earliest Paleocene angiosperms, particularly trees, may have had inherently poor capabilities for rapid evolution, and (4) there was a lack of significant immigration of new taxa to the region. In contrast, the earliest Eocene angiosperm flora recovered very rapidly from the Terminal Paleocene Extinction Event, and this high recovery rate resulted to a significant degree from immigration of new taxa from Europe; thus, the shape of the earliest Eocene diversity curve supports the immigration-dependence recovery model of Barry et al. (1991). ?? 1994.

Review of Palaeobotany and Palynology↗
USGS1990

Sedimentary paleoenvironments of fossil platyrrhine localities, Miocene Pinturas Formation, Santa Cruz Province, Argentina

The Pinturas Formation is a pyroclastic and epiclastic aeolian deposit of Miocene age lying discordantly upon Jurassic rocks in the elevated Andean precordillera of northwest Santa Cruz Province, Argentina. The history of development of the Pinturas Formation was significantly affected by the gradual, though sporadic, draping of this aeolian sediment across a profound, slowly filling paleotopography. The Pinturas depositional cycle consisted of: (1) minor aeolian deposition followed by soil formation, and (2) major aeolian deposition followed by intervals of regional erosion. Fluvial action seems to have been almost wholly confined to intraformational erosion, and two significant intraformational erosional unconformities divide the Pinturas Formation into three sequences. The lower sequence is dominated by pyroclastic mudrocks upon which were formed very mature, probably mollic, paleosols; the middle sequence is composed largely of epiclastic sand occurring as barchanoid paleodunes; and the upper sequence consists of massive, poorly bedded pyroclastic mudrocks. Many Pinturas lacunae were reconstructed on the basis of locally preserved strata, and a novel method of holostrome reconstruction using relative paleosol maturities places Pinturas sedimentation in a more accurate temporal light. It also indicates: (1) that the Pinturas sediment accumulation rate increased with time; (2) that regional erosive intervals are correlated directly with major influxes of pyroclastic material; and (3) that the introduction of the Pinturas platyrrhine primates occurred in the sequence:Carlocebus carmenensis, C. intermedius andSoriacebus ameghinorum. Soriacebus adrianae. Pinturas paleosols appear to have formed under moist conditions, and both mature and immature varieties yield a host of ichnofossils. These include the burrows and nests of bees, scarabeid beetles, termites, and at least two different kinds of colonial rodents, in addition to rhizoliths and the calcified boles and root systems of trees. A fossil nest of a nasutitermitine termite in the lower sequence of the formation indicates the presence of tropical forest. Climatic conditions may have been drier during deposition of the barchanoid paleodunes in early late Pinturas time, or the dunes might reflect drier source areas or have simply encroached on areas of highland forest. Fossil mammals are abundant in Pinturas sediments, and attritional concentrations of them were recognized in the upper parts of paleosols and on the floors of erosional scours. Radiometric dates indicate that the fossil mammals (including platyrrhine primates) occurring in the lower and middle parts of the formation may range in age from about 16-6 to younger than 13-3 Ma (million years ago) (Santacrucian and, almost certainly, Friasian land-mammal ages). This age range is somewhat younger than previous estimates, and suggests that the Pinturas faunas correlate broadly with those from the type Santa Cruz Formation, with the presumed position of the type Friasian, and with the base of the marine Gaiman Formation in the lower valley of the Rio Chubut.

Journal of Human Evolution↗
USGS1984

Accumulation of organic matter in Cretaceous oxygen-deficient depositional environments in the central Pacific Ocean

Complete records of organic-carbon-rich Cretaceous strata were continuouslycored on the flanks of the Mid-Pacific Mountains and southern Hess Rise in the central North Pacific Ocean during DSDP Leg 62. Organic-carbon-rich laminated silicified limestones were deposited in the western Mid-Pacific Mountains during the early Aptian, a time when that region was south of the equator and considerably shallower than at present. Organic-carbon-rich, laminated limestone on southern Hess Rise overlies volcanic basement and includes 136 m of stratigraphic section of late Albian to early Cenomanian age. This limestone unit was deposited rapidly as Hess Rise was passing under the equatorial high-productivity zone and was subsiding from shallow to intermediate depths. The association of volcanogenic components with organic-carbon-rich strata on Hess Rise in the Mid-Pacific Mountains is striking and suggests that there was a coincidence of mid-plate volcanic activity and the production and accumulation of organic matter at intermediate water depths in the tropical Pacific Ocean during the middle Cretaceous. Pyrolysis assays and analyses of extractable hydrocarbons indicate that the organic matter in the limestone on Hess Rise is composed mainly of lipid-rich kerogen derived from aquatic marine organisms and bacteria. Limestones from the Mid-Pacific Mountains generally contain low ratios of pyrolytic hydrocarbons to organic carbon and low hydrogen indices, suggesting that the organic matter may contain a significant proportion of land-derived material, possibly derived from numerous volcanic islands that must have existed before the area subsided. The organic carbon in all samples analyzed is isotopically light ( δ 13 C − 24 to − 29 per mil) relative to most modern rine organic carbon, and the lightest carbon is also the most lipid-rich. There is a positive linear correlation between sulfur and organic carbon in samples from Hess Rise and from the Mid-Pacific Mountains. The slopes and intercepts of C-S regression lines however, are different for each site and all are different from regression lines for samples from modern anoxic marine sediments and from Black Sea cores. The organic-carbon-rich limestones on Hess Rise, the Mid-Pacific Mountains, and other plateaus and seamounts in the Pacific Ocean are not synchronous but do occur within the same general middle Cretaceous time period as organic-carbon-rich lithofacies elsewhere in the world ocean, particularly in the Atlantic Ocean. Strata of equivalent age in the deep basins of the Pacific Ocean are not rich in organic carbon, and were deposited in oxygenated environments. This observation, together with the evidence that the plateau sites were considerably shallower and closse to the equator during the middle Creataceous suggests that local tectonic and hydrographic conditions may have resulted in high surface-water productivity and the preservation of organic matter in an oxygen-deficient environment where an expanded mid-water oxygen minimum developed and impinged on elevated platforms and seamounts.

Organic Geochemistry↗
USGS1984

Changing patterns of Pennsylvanian coal-swamp vegetation and implications of climatic control on coal occurrence

Improved regional and interregional stratigraphic correlations of Pennsylvanian strata permit comparisons of vegetational changes in Euramerican coal swamps. The coal-swamp vegetation is known directly from in situ coal-ball peat deposits from more than 65 coals in the United States and Europe. Interpretations of coal-swamp floras on the basis of coal-ball peat studies are extended to broader regional and stratigraphic patterns by use of coal palynology. Objectives of the quantitative analyses of the vegetation in relation to coal are to determine the botanical constituents at the peat stage and their environmental implications for plant growth and peat accumulation. Morphological and paleoecological analyses provide a basis for deducing freshwater regimes of coal swamps. Changes in composition of Pennsylvanian coal-swamp vegetation are quire similar from one paralic coal region to another and show synchrony that is attributable to climate. Paleobotany and paleogeography of the Euramerican province indicate a moist tropical paleoclimate. Rainfall, runoff and evapotranspiration were the variable climatic controls in the distribution of coal-swamp vegetation, peat accumulation and coal resources. In relative terms of climatic wetness the Pennsylvanian Period is divisible into five intervals, which include two relatively drier intervals that developed during the Lower-Middle and Middle-Upper Pennsylvanian transitions. The climate during Early Pennsylvanian time was moderately wet and the median in moisture availability. Early Middle Pennsylvanian was drier, probably seasonally dry-wet; late Middle Pennsylvanian was the wettest in the Midcontinent; early Late Pennsylvanian was the driest; and late Late Pennsylvanian was probably the wettest in the Dunkard Basin. The five climatic intervals represent a general means of dividing coal resources within each region into groups with similar botanical constituents and environments of peat accumulation. Regional differences in basinal geology and climate were significant variables, but the synchronous control of paleoclimate was of primary importance.

International Journal of Coal Geology↗
USGS1989

The role of catastrophic geomorphic events in central Appalachian landscape evolution

Catastrophic geomorphic events are taken as those that are large, sudden, and rare on human timescales. In the nonglaciated, low-seismicity central Appalachians, these are dominantly floods and landslides. Evaluation of the role of catastrophic events in landscape evolution includes assessment of their contributions to denudation and formation of prominent landscape features, and how they vary through space and time. Tropical storm paths and topographic barriers at the Blue Ridge and Allegheny Front create significant climatic variability across the Appalachians. For moderate floods, the influence of basin geology is apparent in modifying severity of flooding, but for the most extreme events, flood discharges relate mainly to rainfall characteristics such as intensity, duration, storm size, and location. Landslide susceptibility relates more directly to geologic controls that determine what intensity and duration of rainfall will trigger slope instability. Large floods and landslides are not necessarily effective in producing prominent geomorphic features. Large historic floods in the Piedmont have been minimally effective in producing prominent and persistent geomorphic features. In contrast, smaller floods in the Valley and Ridge produced erosional and depositional features that probably will require thousands of years to efface. Scars and deposits of debris slide-avalanches triggered on sandstone ridges recover slowly and persist much longer than scars and deposits of smaller landslides triggered on finer-grained regolith, even though the smaller landslides may have eroded greater aggregate volume. The surficial stratigraphic record can be used to extend the spatial and temporal limits of our knowledge of catastrophic events. Many prominent alluvial and colluvial landforms in the central Appalachians are composed of sediments that were deposited by processes similar to those observed in historic catastrophic events. Available stratigraphic evidence shows two scales of temporal variation: one related to Quaternary climate changes and a more-recent, higher-frequency variation due to rare events during the Holocene. In much of the central Appalachians, landforms related to Quaternary climate changes persist as the most prominent features, despite the modifying effects of late-Holocene catastrophic events.

Geomorphology↗
USGS1991

Pliocene sea surface temperatures of the North Atlantic Ocean at 3.0 Ma

Sea-surface temperature (SST) estimates based on quantitative analysis of planktic foraminifer faunas in North Atlantic deep sea cores suggest that high-frequency, low-amplitude variability related to orbital forcing was superimposed on long-term changes that delineate intervals within the Pliocene that were both warmer and cooler than today. SST estimates from several DSDP and ODP sites, as well as land sections, have been combined into a synoptic view of SST during a Pliocene warm interval centered at about 3.0 Ma. The Pliocene North Atlantic warm interval SST estimates show little evidence for warming in tropical regions whereas mid- to high-latitude areas show moderate to strong warming. SST estimates for the last interglacial (Isotope Stage 5e) show a similar pattern, but warming during the last interglacial was not as pronounced as the Middle Pliocene warming. The regional distribution of SST estimates during these past warm events suggests an increase in ocean circulation.

Quaternary Science Reviews↗
USGS1996

Middle Pliocene vegetation: Reconstructions, paleoclimatic inferences, and boundary conditions for climate modeling

The general characteristics of global vegetation during the middle Pliocene warm period can be reconstructed from fossil pollen and plant megafossil data. The largest differences between Pliocene vegetation and that of today occurred at high latitudes in both hemispheres, where warming was pronounced relative to today. In the Northern Hemisphere coniferous forests lived in the modern tundra and polar desert regions, whereas in the Southern Hemisphere southern beech apparently grew in coastal areas of Antarctica. Pliocene middle latitude vegetation differed less, although moister-than-modern conditions supported forest and woodland growth in some regions now covered by steppe or grassland. Pliocene tropical vegetation reflects essentially modem conditions in some regions and slightly cooler-than-or warmer-than- modern climates in other areas. Changes in topography induced by tectonics may be responsible for many of the climatic changes since the Pliocene in both middle and lower latitudes. However, the overall latitudinal progression of climatic conditions on land parallels that seen in the reconstruction of middle Pliocene sea-surface temperatures. Pliocene paleovegetational data was employed to construct a 2 ° × 2 ° global grid of estimated mid-Pliocene vegetational cover for use as boundary conditions for numerical General Circulation Model simulations of middle Pliocene climates. Continental outlines and topography were first modified to represent the Pliocene landscape on the 2 ° × 2 ° grid. A modern 1 ° × 1 ° vegetation grid was simplified and mapped on this Pliocene grid, and then modified following general geographic trends evident in the Pliocene paleovegetation data set.

Marine Micropaleontology↗
USGS1994

Joint investigations of the Middle Pliocene climate I: PRISM paleoenvironmental reconstructions

The Pliocene epoch represents an important transition from a climate regime with high-frequency, low-amplitude oscillations when the Northern Hemisphere lacked substantial ice sheets, to the typical high-frequency, high-amplitude Middle to Late Pleistocene regime characterized by glacial—interglacial cycles that involve waxing and waning of major Northern Hemisphere ice sheets. Analysis of middle Pliocene (∼3 Ma) marine and terrestrial records throughout the Northern Hemisphere forms the basis of an integrated synoptic Pliocene paleoclimate reconstruction of the last significantly warmer than present interval in Earth history. This reconstruction, developed primarily from paleontological data, includes middle Pliocene sea level, vegetation, land—ice distribution, sea—ice distribution, and sea-surface temperature (SST), all of which contribute to our conceptual understanding of this climate system. These data indicate middle Pliocene sea level was at least 25 m higher than present, presumably due in large part to a reduction in the size of the East Antarctic Ice Sheet. Sea surface temperatures were essentially equivalent to modern temperatures in tropical regions but were significantly warmer at higher latitudes. Due to increased heat flux to high latitudes, both the Arctic and Antarctic appear to have been seasonally ice free during the middle Pliocene with greatly reduced sea ice extent relative to today during winter. Vegetation changes, while more complex, are generally consistent with marine SST changes and show increased warmth and moisture at higher latitudes during the middle Pliocene.

Global and Planetary Change↗
USGS1994

The applicability of terrestrial visitor impact management strategies to the protection of coral reefs

A dramatic expansion in nature-based tourism to tropical coastal destinations has occurred in the past 20 years. Tourism development, combined with intense recreational pressures, has irreversibly transformed and degraded many popular scenic natural environments. This paper examines the management of recreational impacts to coral reefs using Virgin Islands National Park as a case study. A review of terrestrial recreational ecology research explores the implications and potential applicability of some principal findings to the protection of coral reefs. Visitor impact management recommendations for the protection of coral reefs are offered. Managers can minimize coral reef recreational impacts by (1) restricting high-impact uses, (2) containing rather than dispersing recreational use, (3) encouraging the use of resistant environments, (4) teaching low-impact recreational practices, and (5) enforcing park rules and regulations.

Ocean and Coastal Management↗
USGS2022

Wetlands under global change

Wetlands are among the ecosystem types most threatened by global change, including both climate change and other anthropogenic factors such as sea level rise, urban development, deforestation, agricultural land use, drainage, levees, tidal flow restrictions, pollution, eutrophication, and fires. Wetlands not only store disproportionate amounts of carbon compared to other terrestrial ecosystems, but they lie at the terrestrial-aquatic interface crucial to understanding landscape and global scale biogeochemical cycles. In this chapter, we focus on the major global change factors affecting wetlands and the responses of different wetland types to those global change factors. Special attention is given to direct responses to increasing atmospheric carbon dioxide levels. Because of their hydrological connections and placement at the terrestrial-aquatic interface, the conservation of wetlands involves accounting for uncertainties related to interacting stressors. While the past decades have seen many important experimental and observational studies of wetland responses to global change factors, large uncertainties remain, especially within tropical regions where even the basic extent of wetland ecosystems is not well documented.

Book chapter↗
USGS2023

Planktic foraminifera

Planktic foraminifera are single-celled marine organisms that secrete calcium carbonate tests. They live in the ocean's photic zone, and when they die, their tests, each about the size of a grain of sand, collect on the ocean floor. The geographic distribution of planktic foraminifera is mostly governed by the temperature and salinity of the ocean surface, and species assemblages are generally arranged in latitudinal bands from polar to tropical, with more species occupying warmer waters. Their ubiquity in the world's oceans since the Cretaceous Period makes them ideal biostratigraphic markers, and their sensitivity to environmental changes makes them excellent proxies of past ecological, oceanographic and climatic history.

Book chapter↗