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S. E. Ishman

Publications and source records attributed to S. E. Ishman.

At least 19 recordsLinked to original sources
USGS2003

Ecosystem history of southern and central Biscayne Bay: Summary report on sediment core analyses

During the last century, the environs of Biscayne Bay have been greatly affected by anthropogenic alteration through urbanization of the Miami/Dade County area. The sources, timing, delivery, and quality of freshwater flow into the Bay have been changed by construction of a complex canal system that controls movement of water throughout south Florida. Changes in shoreline and sub-aquatic vegetation and marine organisms have been observed and changes in water delivery are believed to be the cause. Current restoration goals are attempting to restore natural flow of fresh water into Biscayne and Florida Bays and to restore the natural fauna and flora, but first we need to determine pre-alteration baseline conditions in order to establish targets and performance measures for restoration. This research is part of an ongoing study designed to address the needs of the Biscayne Bay Coastal Wetlands Project (BBCW) of the Comprehensive Everglades Restoration Plan (CERP). By establishing the natural patterns of temporal change in salinity, water quality, vegetation, and benthic fauna in Biscayne Bay and the nearby wetlands over the last 100- 500 years the USGS, in collaboration with our partners, will provide the data necessary to set realistic targets to achieve the BBCW Project goals. Six cores from three sites in Biscayne Bay were collected in April 2002 for multidisciplinary multi-proxy analyses. This report details the results of these analyses and compares the 2002 cores to cores collected in 1997. The following are our significant findings to date: The salinity of central Biscayne Bay has become increasingly marine and increasingly stable over the last 100 years. At No Name Bank, prior to approximately 1915, the inter-decadal and decadal salinity fluctuations appear to have been greater than after 1915 when salinities stabilized at that site. Continental shelf/open marine influence on the sites has increased during the 20th century. There is no indication of inter-decadal salinity extremes or periods of hypersalinity. Freshwater and mesohaline salinities have had a minor influence on No Name bank throughout the time of deposition. At Featherbed Bank, the influence is reduced to mesohaline salinities. Card Bank has experienced relatively large swings in salinity over multi-decadal and centennial timescales, compared to central Biscayne Bay, but marine influence at the site has increased over the last century. Indications of regional scale patterns have been found, especially in the shell chemistry data and the pollen assemblages. These regional patterns indicate that the changes are not site specific and may not be limited to Biscayne Bay. Sub-aquatic vegetation has undergone bay-wide patterns of change over the last 200-500 years, which includes expansion prior to 1900 and declines during the last century in central Biscayne Bay. Thalassia appears to have increased at all three core sites sometime between 1550 and 1750 AD. A decline in Thalassia appears to have occurred after 1950 at No Name Bank and slightly earlier in the 20th century at Featherbed Bank. Card Bank does not appear to have experienced any declines in vegetation on an inter-decadal scale during the 20th century. Molluscan faunal abundance and diversity have undergone significant changes in central Biscayne Bay. Indicators of increased organic-rich sediments at No Name occur between 1869 to 1888 and between the 1930’s to 1975. These changes may correlate to human activities (settlement, population growth). These findings represent a first step towards the project’s goal to reconstruct the history of Biscayne Bay and they provide us with a working model to be tested at other sites. It is clear from our findings that Biscayne Bay has been a dynamic environment over the last 500 years, with natural changes occurring in salinity and benthic habitats. However, several significant changes have occurred in the 20th century: 1) increased stabilization of marine salinities; 2) declines in seagrass in central Biscayne Bay; 3) dramatic changes in molluscan abundance and diversity in central Biscayne Bay. The question remains - how do we better differentiate natural cycles of change from anthropogenic change within these observed trends? The preliminary implications from our research are that changes in salinity and benthic habitats have occurred naturally in Biscayne Bay on inter-decadal to centennial scales, perhaps due to climatic changes, changes in sea level, bank migrations, or a combination of factors. However, further work needs to be done to determine which components of change in the 20th century are human-induced and which are natural. By examining the historical records preserved in the sediments of Biscayne Bay, we can provide restoration trust agencies with the information necessary to set realistic targets and performance measures for Biscayne Bay.

Florida↗
USGS2000

A paleoecologic reconstruction of the history of Featherbed Bank, Biscayne National Park, Biscayne Bay, Florida

Using multiple-proxy biological indicators, a paleoecological history of the past 550 years of Featherbed Bank, Biscayne Bay, has been reconstructed from a short (2.26 m) sediment core. Paleoecological changes in ostracode, mollusc, and foraminifer assemblages show that core SEI297-FB-1 can be divided into three distinctly different zones, which together provide evidence for distinct changes in historical environmental conditions at Featherbed Bank. Assemblages from fossil biotic communities within zone 1, representing approximately 1440 to 1550 AD, are characterized by open-marine biota with relatively limited numbers of epiphytic biota. Molluscan faunal indicators suggest the sediment was capable of supporting infaunal organisms and that faunal richness was relatively limited during this time period. A change in the biotic community occurred around 1550 AD and continued until the late 1800's distinguishing zone 2. Fossil biotic indicators from zone 2 show a strong dominance of epiphytic organisms within all of the biotic communities examined. Foraminifers, molluscs, and ostracodes capable of subsisting in salinities slightly lower than normal marine begin to flourish in this time period, and there is a marked decline in infaunal molluscs. Zone 2 assemblages are replaced around 1900 AD by increased numbers of organisms that typify open-marine conditions and a return to decreased epiphytic assemblages, similar to zone 1. Zone 3 assemblages, however, show some strong dissimilarities from zone 1, including limited infaunal molluscs, increased abundances of the ostracode Malzella floridana, and a significant increase in molluscan faunal richness.

Florida↗
USGS1999

Historical trends in salinity and substrate in central and northern Florida Bay: A Paleoecological Reconstruction using modern analogue data

Understanding the natural spatial and temporal variability that exists within an ecosystem is a critical component of efforts to restore systems to their natural state. Analysis of benthic foraminifers and molluscs from modern monitoring sites within Florida Bay allows us to determine what environmental parameters control spatial and temporal variability of their assemblages. Faunal assemblages associated with specific environmental parameters, including salinity and substrate, serve as proxies for an interpretation of paleoecologic data. The faunal record preserved in two shallow (<2 m) cores in central Florida Bay (Russell Bank and Bob Allen Bank) provides a record of historical trends in environmental parameters for those sites. Analysis of these two cores has revealed two distinct patterns of salinity change at these sites: 1) a long-term trend of slightly increasing average salinity; and 2) a relatively rapid change to salinity fluctuations of greater frequency and amplitude, beginning around the turn of the century and becoming most pronounced after 1940. The degree of variability in substrate types at each locality limits interpretations of substrate trends to specific sites. A common sequence of change is present in the Russell Bank and Bob Allen Bank cores: from mixed grass and bare-sediment indicators at the bottom of the cores, to bare-sediment dwellers in the center, to a dominance of vegetative-cover indicators at the top of the cores. Changes in interpreted salinity patterns around the turn of the century are consistent with the timing of the construction of the Flagler Railroad from 1905 to 1912, and the Tamiami Trail and the canal and levee systems between 1915 and 1928. Beginning around 1940, the changes in the frequency and amplitude of salinity fluctuations may be related to changes in water management practices, meteorologic events (frequent hurricanes coupled with severe droughts in 1943 and 1944), or a combination of factors. The correspondence of these changes in Florida Bay with changes in the terrestrial Everglades suggests factors affecting the entire ecosystem are responsible for the salinity and substrate patterns seen in Florida Bay.

Florida↗
USGS1998

Preliminary paleontologic report on core 37 from Pass Key, Everglades National Park, Florida Bay

Sediments from Pass Key core 37, in eastern Florida Bay (N 25.1478, W 80.5745) record a history of rapid sedimentation during this century. The lowest portion of the core contains benthic fauna indicative of relatively low salinities and sparse seagrass coverage. This period is followed by an increase in salinity and seagrass. In the middle portion of the core, a slight decrease in salinity and an increase in seagrass occur. These shifts in the benthic fauna correspond to a period when the terrestrial flora change, and an increase in dinocyst absolute abundance occurs, indicating changes in factors affecting the entire South Florida ecosystem. These changes may represent a period of increased terrestrial flushing, due to rainfall, water management practices or a combination of both. The benthic faunas in the upper portion of the core indicate an increase in salinity and seagrass density. This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards or with the North American Stratigraphic Code. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

Florida↗
USGS1998

Lithostratigraphy, petrography, biostratigraphy, and strontium-isotope stratigraphy of the surficial aquifer system of western Collier County, Florida

In 1996, seven cores were recovered in western Collier County, southwestern Florida, to acquire subsurface geologic and hydrologic data to support ground-water modeling efforts. This report presents the lithostratigraphy, X-ray diffraction analyses, petrography, biostratigraphy, and strontium-isotope stratigraphy of these cores. The oldest unit encountered in the study cores is an unnamed formation that is late Miocene. At least four depositional sequences are present within this formation. Calculated age of the formation, based on strontium-isotope stratigraphy, ranges from 9.5 to 5.7 Ma (million years ago). An unconformity within this formation that represents a hiatus of at least 2 million years is indicated in the Old Pump Road core. In two cores, Collier-Seminole and Old Pump Road, the uppermost sediments of the unnamed formation are not dated by strontium isotopes, and, based on the fossils present, these sediments could be as young as Pliocene. In another core (Fakahatchee Strand-Ranger Station), the upper part of the unnamed formation is dated by mollusks as Pliocene. The Tamiami Formation overlies the unnamed formation throughout the study area and is represented by the Ochopee Limestone Member. The unit is Pliocene and probably includes the interval of time near the early/late Pliocene boundary. Strontium-isotope analysis indicates an early Pliocene age (calculated ages range from 5.1 to 3.5 Ma), but the margin of error includes the latest Miocene and the late Pliocene. The dinocyst assemblages in the Ochopee typically are not age-diagnostic, but, near the base of the unit in the Collier-Seminole, Jones Grade, and Fakahatchee Strand State Forest cores, they indicate an age of late Miocene or Pliocene. The molluscan assemblages indicate a Pliocene age for the Ochopee, and a distinctive assemblage of Carditimera arata and Chione cortinaria in several of the cores specifically indicates an age near the early/late Pliocene boundary. Undifferentiated sands overlie the Pliocene limestones in two cores in the southern part of the study area. Artificial fill occurs at the top of most of the cores. The hydrologic confining units penetrated by these cores are different in different parts of the study area. To the west, a hard tightly cemented dolostone forms the first major confining unit below the water table. In the eastern part of the study area, confinement is more difficult to determine. A tightly cemented sandstone, much younger than the dolostones to the west and probably not laterally connected to them, forms a slight confining unit in one core. Thick zones of poorly sorted muddy unconsolidated sands form a slight confining unit in other cores; these probably are not correlative to either the sandstone or the dolostones to the west. The age and sedimentologic observations suggest a complex compartmentalization of the surficial aquifer system in southwestern Florida. The calibrations of dinocyst and molluscan occurrences with strontium-isotope stratigraphy allows us to expand and document the reported ranges of many taxa. This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards or with the North American Stratigraphic Code. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

Florida↗
USGS1998

Environmental impacts on the southern Florida coastal waters: A history of change in Florida Bay

Analyses of four cores located in the northern transitional, eastern, and central portions of Florida Bay reveal historical patterns of change in salinity and seagrass distribution. Salinity and the distribution of seagrass beds are two critical issues for the restoration of Florida Bay. The distribution of benthic fauna in Bob Allen 6A and Russell Bank 19B cores illustrates changes in environmental parameters prior to 1900. Natural fluctuations occur in salinity, but the amplitude of those fluctuations was limited to a 15–20% shift about the mean. Subtle changes occur in the benthic fauna around 1910, but beginning around 1940, the pattern of salinity fluctuation departs substantially from the pre-1900 pattern. Post-1940, the salinity oscillates 40–60% about the mean. This pattern is seen in all indicators measured. Around 1970, a significant but short term decline occurred in salinity. The Taylor Creek T24 core from the northern transitional zone reflects changes in freshwater flow that have occurred during this century. The upper portion of the core records a significant increase in salinity, with a slight decrease occurring in recent years. The Pass Key 37 core represents an area of very high sedimentation rates; an increase in salinity occurs in the upper portion of the core. Natural fluctuations in seagrass distribution are inferred from the shifts in relative abundance of epiphytal species preserved in the cores. All four cores show an increase in epiphytes and therefore in seagrass coverage during this century. An increase also occurs in epiphytal species that can dwell on either Thalassia or macro-algal mats associated with Thalassia beds. These data suggest an increase in algal-mats has occurred during this century. The Bob Allen 6A core records an extensive period during the 1800's of little to no vegetative cover of the substrate based on the near absence of epiphytic species in that segment of the core. Following this period, the epiphytal species increase rapidly in abundance, implying that vegetation may have the ability to disseminate rapidly.

Florida↗
USGS1997

Ecosystem history of South Florida; Biscayne Bay sediment core descriptions

The 'Ecosystem History of Biscayne Bay and the southeast Coast' project of the U.S. Geological Survey is part of a multi-disciplinary effort that includes Florida Bay and the Everglades to provide paleoecologic reconstructions for the south Florida region. Reconstructions of past salinity, nutrients, substrate, and water quality are needed to determine ecosystem variability due to both natural and human-induced causes. Our understanding of the relations between the south Florida ecosystem and introduced forces will allow managers to make informed decisions regarding the south Florida ecosystem restoration and monitoring. The record of past ecosystem conditions can be found in shallow sediment cores. This U.S. Geological Survey Open-File Report describes six shallow sediment cores collected from Biscayne Bay. The cores described herein are being processed for a variety of analytical procedures, and this provides the descriptive framework for future analyses of the included cores. This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards or with the North American Stratigraphic Code. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

Open-File Report↗
USGS1997

Preliminary paleontologic report on cores 19A and 19B, from Russell Bank, Everglades National Park, Florida Bay

The fauna and flora preserved in two cores, 19A and 19B, from the south side of Russell Bank (N 25 03.831', W 80 37.486') in north-central Florida Bay, Everglades National Park, Florida, record a history of environmental change over the last century. The benthic foraminifera and molluscs indicate fluctuating salinities with increasing average salinity upcore in core 19B. Shifts from low salinity (12-15 ppt) to higher average salinity (30 ppt) occurred at 70-66 cm and 24-18 cm in core 19B (approximately 1937-1940 and 1975-1980). The inverse, shifts from periods of higher average salinity to periods of lower salinity, occurred at 140 cm, 90 cm, and 42 cm (approximately 1880, 1921, and 1960). Significant changes in the molluscan fauna indicative of specific substrate types occur at 88 cm, 68 cm, and 22 cm. The lower portion of the core is dominated by a mixture of sediment and grass dwellers, the middle portion by sediment dwellers, and the upper portion of the core by grass and finally grass and algae dwellers. Changes occur in the floral assemblages in core 19A, but the significance of these changes is unclear. Three subtle shifts occur in the pollen assemblages indicating the onshore vegetation was responding to some environmental factor. Two peaks in dinocyst abundance occur in core 19A, but the composition of dinocyst assemblages remains relatively stable throughout the core. Correspondence between changes in salinity and onshore vegetation changes is consistent with results from previous cores. The pattern of increased salinity upcore is consistent with patterns seen in core T24 from the mouth of Taylor Creek and in core 6A from Bob Allen mudbank.

Florida↗
USGS1996

Productivity cycles of 200-300 years in the Antarctic Peninsula region: Understanding linkages among the sun, atmosphere, oceans, sea ice, and biota

Compared to the rest of the world's oceans, high-resolution late Holocene paleoclimatic data from the Southern Ocean are still rare. We present a multiproxy record from a sediment core retrieved from a deep basin on the western side of the Antarctic Peninsula that reveals a dramatic perspective on paleoclimatic changes over the past 3700 yr. Analyses completed include measurement of magnetic susceptibility and granulometry, bed thickness, particle size, percent organic carbon, bulk density, and microscopic evaluation of diatom and benthic foraminiferal assemblages and abundances. Downcore variability of these parameters demonstrates the significance of both short-term cycles, which recur approximately every 200 yr, and longer term events (≈2500 yr cycles) that are most likely related to global climatic fluctuations.

Geological Society of America Bulletin↗
USGS1996

Expanded record of Quaternary oceanographic change: Amerasian Arctic Ocean

Four sediment cores collected from the Northwind and Mendeleyev ridges, Arctic Ocean, from 1089 m to 1909 m water depth, provide an oceanographic record extending back into the Matuyama reversed polarity chron. Benthic foraminiferal analyses show four prominent assemblage zones: Bolivina arctica , Cassidulina teretis , Bulimina aculeata , and Oridorsalis tener from the upper Matuyama reversed polarity chronozone through the Brunhes normal polarity chronozone. These assemblage zones represent depth-dependent benthic foraminiferal biofacies changes associated with oceanographic events that occurred in the Amerasian basin at ∼780 and 300 ka, and indicate oceanographic influence from the North Atlantic. Recognition of these benthic assemblage zones in Arctic cores from the Alpha Ridge indicates that the benthic foraminiferal zonations in intermediate to deep water (>1000 m) Arctic cores may be more useful than preexisting lithostratigraphic zonations and should provide important information pertaining to the Quaternary paleoceanographic evolution of the Arctic Ocean.

Geology↗
USGS1996

Modern benthic foraminifer distribution in the Amerasian Basin, Arctic Ocean

A total of 38 box cores were collected from the Amerasian Basin, Arctic Ocean during the U.S. Geological Survey 1992 (PI92-AR) and 1993 (PI93-AR) Arctic Cruises aboard the U.S. Coast Guard Icebreaker Polar Star. In addition, the cruises collected geophysical data, piston cores and hydrographic data to address the geologic and oceanographic history of the western Arctic Ocean. This paper reports the results of the quantitative analyses of benthic foraminifer distribution data of the total (live + dead) assemblages derived from 22 box core-top samples. The results show that a distinct depth distribution of three dominant benthic foraminifer assemblages, the Textularia spp. - Spiroplectammina biformis, Cassidulina teretis and Oridorsalis tener - Eponides tumidulus Biofacies are strongly controlled by the dominant water masses within the Canada Basin: the Arctic Surface Water, Arctic Intermediate Water and Canada Basin Deep Water. The faunal distributions and their oceanographic associations in the Canada Basin are consistent with observations of benthic foraminifer distributions from other regions within the Arctic Ocean.

Micropaleontology↗