J.B. Cowart’s research while affiliated with Florida State University and other places

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Publications (22)


Raised marine terraces along the Gulf of Aden coast of Somalia
  • Article

May 2013

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52 Reads

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7 Citations

Physical Geography

George A. Brook

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James B. Cowart

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Mapping in the Galweda-Elayu area of northern Somalia has revealed depositional and erosional marine terraces at elevations of approximately 16 m, 8 m, and 2 m. These terraces vary from 0–2300 m, 200–2200 m, and 0–800 m in width, respectively. Sediments exposed in stream-valley walls demonstrate that the two higher terraces were formed by marine transgressions followed later by regressions to below present sea level. Beach ridges on the terraced alluvial fan at the mouth of togga Galweda imply that sea level and/or land elevation varied by at least 6 m during the formation of the 16-m terrace and by at least 3 m during the formation of the 8-m terrace. 230Th/234U ages of corals suggest that the 8-m terrace was formed during deep-sea isotope substage 5c (105 kyr B.P.) and the 2-m terrace during substage 5a (80 kyr B.P.). A 7-kyr-old coral from above the present storm beach on the outer flanks of the 2-m terrace suggests that sea level in the Gulf of Aden was close to its present level by the middle Holocene. No material suitable for dating was recovered from the 16-m terrace, but on morphological grounds and based on marine-terrace elevations elsewhere in the Red Sea-Gulf of Aden rift zone, we believe that the 16-m terrace was formed during isotope substage 5e (132–120 kyr B.P.), when global sea level was about 6 m above present.


A 164 ka record of environmental change in the American Southwest from a Carlsbad Cavern speleothem

August 2006

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195 Reads

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42 Citations

Palaeogeography Palaeoclimatology Palaeoecology

A horizontal core 2.8 m in length drilled from the Georgia Giant column in Carlsbad Cavern provides climate information for the last 164 ka. Forty-six alpha spectrometric U-series ages determined at intervals of ∼ 7.6 cm along the core indicate five periods of deposition and five hiatuses, the longest from 136 to 110 ka. Variations in growth rate (0 to 70 mm/ka), in the abundance of aragonite, chalcedony, and Fe-bearing phases, and in ¹³C indicate that glacial intervals of the last 164 ka, OIS 6, 4, and 2, were much wetter than today, as were the colder substages 5d and 5b of OIS 5. By contrast, during the two warmest periods of the past 164 ka, namely OIS 5e and 1, there was no deposition on either side of the speleothem, suggesting conditions as dry or drier than today.



Water–Rock Geochemical Considerations for Aquifer Storage and Recovery: Florida Case Studies

January 2005

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64 Reads

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36 Citations

Developments in Water Science

Publisher Summary This chapter investigates the three aquifer storage and recovery (ASR) facilities in Southwest Florida to understand water–rock geochemical interactions during the ASR process. Mobilization of metals from the Floridan Aquifer System (FAS) matrix during ASR activities is apparent and is likely due to a complex interaction of geochemical processes. The chemically heterogeneous aquifer contains metal-rich phases in sufficient amounts to become mobilized by oxidation or other processes to yield concentrations in recovered waters that may exceed maximum contaminant levels (MCLs). Arsenian pyrite is among the sources of arsenic and other trace metals in the aquifer; however, preliminary sequential extraction studies and work by other researchers suggest that phases such as organics contain As and other metals. Moreover, organic material may contain uranium, which is also thought to be associated with carbonate minerals in the Suwannee Limestone. Water-quality data from more than 15 cycle tests from three ASR facilities in Southwestern Florida indicate significant mobilization of metals into stored and recovered water during ASR.


State Of Florida Department Of Environmental Protection

June 2004

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15 Reads

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9 Citations

David B. Struhs

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Edwin J. Conklin

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Division Director

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[...]

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Adel A. Dabous

This report includes results from Year Three of the study. Results from Years One and Two are presented in Williams and others (in review). Year Four of the project is underway. Water-quality variations and aquifer system characteristics (including three injection zones) at two ASR facilities, the Rome Avenue ASR (Hillsborough County) and the Punta Gorda ASR (Charlotte County), are the focus of the current study. Research presented herein confirms that understanding water-rock geochemical interactions is important to the continued success of ASR in Florida. Results of this investigation indicate the following: 1) chemical (including isotopic) variability exists within groundwaters and carbonates of the Floridan aquifer system; 2) this variability may result in site-specific geochemical processes affecting ASR well performance (e.g., plugging) and water quality; and 3) as oxygen-rich surface waters are injected into the Floridan aquifer system, trace metals such as arsenic (As), iron (Fe), manganese (Mn) and uranium (U) are mobilized (chemically leached) from the carbonate rocks and withdrawn during recovery. With regard to the third item, some of the periods of higher metals concentrations in recovered waters are shortlived, depending on the duration of the injection-storage-recovery cycle. It is significant that mobilization of U and As into recovered ASR waters has occurred within all three of the aquifer-storage zones investigated in this study. On the other hand, it is important to emphasize that only Fe and Mn concentrations (for relatively few samples) have exceeded secondary drinking water standards (i.e., maximum contaminant levels -- MCL). With the exception of one sample, As is not observed to have exceeded the MCL. iii The current MCL for As is 50 ug/l. The U...


Quaternary environmental change in the Western Desert of Egypt: Evidence from cave speleothems, spring tufas, and playa sediments

January 2003

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129 Reads

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35 Citations

U-series ages for speleothems in Djara Cave, and spring tufas along the eastern scarp of the Kharga Oasis, suggest humid intervals during marine isotope stages (MIS) 5, 7, 9 and 13 and possibly also during warm interstadials of MIS 6 and 8, when sapropels formed in the eastern Mediterranean. Based on TL analysis, eroded playa sediments in the Farafra, Kharga and Dakhla Oasis are Holocene. The absence of speleothem and tufa of MIS 1 age indicates drier conditions than during earlier interglacials. If meteoric water with the same δ 18O as deep Nubian aquifer groundwater deposited the Djara Cave speleothems, and if they were deposited in isotopic equilibrium with these waters, then mean annual temperatures in the Western Desert at times of speleothem deposition were at least as warm as today. Published δ 13C of bicarbonate in Nubian aquifer groundwaters in the Kharga, Dakhla, Farafra and Bahariya oases indicates recharge in an area of C 3 vegetation probably in southwest Egypt and northwest Sudan with subsequent artesian flow to the northeast. δ 13C of cave speleothem and tufa resulted from local recharge through a vegetation cover with at least 50% C 4 plants. This suggests a north-to-south increase in rainfall at the time of speleothem and tufa deposition. Greater rainfall during pre-Holocene interglacials may be a response to higher summer solar radiation and increased monsoonal activity, and to lower winter radiation and a more southerly position for the winter westerlies.



Djara Cave in the Western Desert of Egypt: Morphology and evidence of Quaternary climatic change

January 2002

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742 Reads

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37 Citations

Cave and Karst Science

With stalactites, columns, stalagmites and flowstones up to 6m high and 1.5m in diameter, Djara Cave in the Western Desert is one of very few well-decorated caves in Egypt. U-series ages for four speleothems (140 ± 16, 201 ± 2/233 ± 24, 221 ± 34, and 283 ± 56ka) suggest humid intervals during marine isotope stages 5 and 7, and possibly also during stage 9. Importantly, none of the secondary carbonates date to the Holocene, despite archaeological evidence both in the cave, and on the ground surface above it, of visits to the site by ancient peoples, and of a more humid period of climate from about 11.5 to 6.5ka. δ18O of speleothem carbonate averaged -12.1‰ PDB, indicating deposition by meteoric waters significantly depleted in 18O. Using 18O PDB of speleothem carbonate, and 18O SMOW of ancient groundwater in the Nubian aquifer, the mean annual temperature at the time of speleothem deposition is estimated to have been 23.1°C, which is 1°C above the present mean annual temperature at the Farafra and Baharya oases. In Israel and Oman, modern speleothem carbonate is less depleted in 18O than Holocene-age material, and this in turn is less depleted than carbonate deposited during isotope stage 5. This suggests that in these areas the Holocene was wetter than the present but not as wet as during marine isotope stage 5. At Djara Cave, the absence of speleothem deposits of Holocene age also suggests that this period was not as wet as during earlier interglacials. The 18O-depleted waters from which the Djara speleothems were deposited appear to have originated in air masses that crossed North Africa from west to east at a time when there was a more southerly westerly airflow than now.


U-Series Nuclides as Tracers in Groundwater Hydrology

January 2000

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42 Reads

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53 Citations

The occurrence of the heavy radionuclides in the hydrosphere has become increasingly important in the context of today’s emphasis on the measurement of quality and quantity of water resources. The study of the natural aqueous behaviour of uranium, radium, and the shorter-lived daughters serves both as a background for radioactivity pollution studies, and also as a widely applicable method of tracing movements of the groundwater itself.


Radium in the Suwannee River and Estuary

July 1999

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11 Reads

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37 Citations

Biodegradation

A two-year study of radium in the Suwannee River has shown that groundwater discharge, via springs, is a very important source of radium both to the river and to offshore Gulf of Mexico waters. Dissolved radium is maintained within relatively narrow limits in the river by uptake into suspended particles. In the estuary, dissolved radium versus salinity profiles show distinctive nonconservative behavior with radium in significant excess of its linear mixing value at mid-salinities. Unlike the situation in many other estuaries, however, desorption of radium from particles cannot account for most of the observed excess. Thus, the anomalously high radium characteristic of much of the west Florida shelf apparently does not have a riverine source. Direct effusion of high-radium groundwater into these coastal waters is thought to be the major supplier of radium, and perhaps other elements as well.


Citations (21)


... A first wetter interval at ~140 to 120 ka is seen in the northern subregion, when diverse isolated basins became interconnected in megalake Makgadikgadi reflecting changed hydroclimatic conditions in humid Angola (Burrough et al., 2009b). Speleothem growth reflects instead more localised climate conditions (133 ± 27 ka; Brook et al., 1998). In the southern sub-region, presence of palygorskite suggests semi-arid climate from 156 ± 11 to 121 ± 6 ka (Lukich et al., 2019(Lukich et al., , 2020. ...

Reference:

Reply to the discussion of Moustafa (2021) on Sayed et al. (2020) (Marine and Petroleum Geology, 17, 2020-104401)
Comparison of Quaternary environmental change in eastern and southern Africa using cave speleothem, tufa and rock shelter sediment data
  • Citing Article

... There are, however, also ecological grounds for considering them together as the distribution of these biomes was in flux from MIS 6-2 due to fluctuations in moisture balance. During drier climatic episodes a range of evidence suggests the rainforests fragmented into isolated refugia interspersed with open-canopy woodlands and grass savannas, with periods of enhanced moisture promoting widespread forest re-expansion (e.g., Van Noten 1982;Brook et al. 1990;Maley 1996;Jahns et al. 1998;Dupont et al. 2000;Runge 2000Runge , 2001aBonnefille 2011). During the LGM, for example, it is estimated the African rainforests were *15-30% of their current size, as compared to *50% for those of the Amazon Basin (Anhuf 2000;Anhuf et al. 2006). ...

Paleoenvironmental data for Ituri, Zaire, from sediments in Matupi Cave, Mt. Hoyo
  • Citing Article
  • January 1990

... Huq et al. (2018) found that As in sediments was mainly adsorbed on Fe(III) minerals when studying the characteristics of iron-bearing minerals in high-arsenic aquifer sediments. According to research by Arthur et al. (2005), the source of arsenic and other trace metals in aquifers is arsenopyrite, and the chemically heterogeneous aquifers have enough levels of metal-rich phases to be enriched by oxidation or other means. Sulfate in the Ganges River Basin was reduced to create arsenic-bearing pyrite under early reducing circumstances, according to research by Chowdhury et al. on groundwater in Bangladesh (Acharyya et al. 1999), West Bengal, and India. ...

Water-rock geochemical considerations for aquifer storage and recovery: Florida case studies southwest Florida
  • Citing Article
  • January 2005

... Pyrite reactivity may decrease after repeated ASR cycles or continuous injection due to depletion of a significant fraction of reactive pyrite 43,108 and/or surface passivation limiting the rate of oxidation. 70,109 Following oxidative dissolution of pyrite, ferrous iron quickly oxidizes to form poorly crystalline Fe (oxyhydr)oxides (e.g., ferrihydrite), which have a strong sorption affinity for oxyanions including those of As, Mo, and V. Dissolved contaminant concentrations generally remain low in the presence of stable surface complexes. ...

Water–Rock Geochemical Considerations for Aquifer Storage and Recovery: Florida Case Studies
  • Citing Chapter
  • January 2005

Developments in Water Science

... Their networks could be controlled by tectonic elements (Robinson, 2002). These humid conditions were favorable for the formation of terrestrial carbonates (Nicoll et al., 1999;Brook et al., 2003;Smith et al., 2004;Skinner et al., 2013;Nicoll and Sallam, 2017;Sallam et al., 2018;Kele et al., 2021;Mousa et al., 2023), whereas playas and dunes reflect aridification and establishment of hyper-arid conditions, respectively (Mousa et al., 2023(Mousa et al., , 2024. Tufa deposits with a thickness up to 35 m formed along the retreated scarps of the depression where groundwater were discharged from shallow perched aquifers during the relatively wet phases; widely-distributed Cenozoic limestones served as a source for carbonate material dissolved in groundwater. ...

Quaternary environmental change in the Western Desert of Egypt: Evidence from cave speleothems, spring tufas, and playa sediments
  • Citing Article
  • January 2003

... Stable oxygen values for tufa and speleothem carbonates for Wadi Dabsa tufa this study (bar with horizontal hatching), and a range of other sites, arranged by (A) longitude and (B) latitude (blue bars are speleothem carbonate, and dashed dark blue lines are fluid inclusion data for the speleothems where this is available, the grouped Negev Caves record is in a darker blue, to be distinguished from Soreq Cave (Sq) and Peqin Cave (Pq) at the same longitude on plot (A), white boxes with black outlines are tufa carbonate samples. From south to north, plot (B), these are Mukalla Cave Nicholson et al., 2020); Wadi Dabsa (this study); Hoti Cave Nicholson et al., 2020); Dungul and Dinegel Oases (Kele et al., 2021); Kurkur Oases (Crombie et al., 1997); Tadrart Acacus (Cremaschi et al., 2010); Djara Cave (Brook et al., 2002); Wadi Sunnur Cave (El-Shenawy et al., 2018); Soreq Cave (Ayalon et al., 2002;Bar-Matthews et al., 1997, 2003Bar-Matthews and Ayalon, 2004); Negev desert caves from a range of locations (Vaks et al., 2006(Vaks et al., , 2010(Vaks et al., , 2013; Peqin Cave (Ayalon et al., 2002;Bar-Matthews et al., 1997, 2003Bar-Matthews and Ayalon, 2004) and Susah Cave (Rogerson et al., 2019). derived CO 2 to vadose water during recharge (Andrews et al., 1997). ...

Djara Cave in the Western Desert of Egypt: Morphology and evidence of Quaternary climatic change
  • Citing Article
  • January 2002

Cave and Karst Science

... The carbonate minerals within subsurface vadose zones and aquifers can act as good scavengers of contaminants and as a source of contaminants; while calcite can incorporate many elements into the structure, carbonate cycling, or rapid or gradual changes in aquifer geochemistry may promote carbonate dissolution, resulting in the release of structural elements of concern (such as Sr, Se, As, Cd and others) (Arthur et al., 2002;Kawano and Maeda, 2020;Kirsch et al., 2014;Lazareva et al., 2015;Lu et al., 2010a), although each element may behave differently. Taking As as an example, studies have shown that while As(III) adsorption to calcite was negligible, As(V) sorbed well to calcite (Martin et al., 2014), suggesting greater As mobility under reducing conditions (So et al., 2008). ...

Mobilization of arsenic and other trace elements during aquifer storage and recovery, southwest Florida
  • Citing Article
  • January 2002

... 200 ka, and more humid periods were rather exceptional (e.g. Brook et al., 1996;Burrough et al., 2009;Blome et al., 2012). A predominately arid climate concurs with special adaptations of Khoisan-speaking people, including traits which are absent in other human groups such as the ability to store water and lipid metabolites in body tissues (Schuster et al., 2010). ...

Wet and dry periods in the southern African summer rainfall zone during the last 330 kyr from speleothem, tufa and sand dune age data
  • Citing Article
  • January 1996

... In the relatively dry western and central parts of southern Africa, lake and speleothem records are commonly discontinuous (e.g. Brook et al., 1999;Hipondoka et al., 2014) or located in regions fed by large catchments draining the tropics (e.g. palaeolake Makgadikgadi; Burrough et al., 2009), and elemental and dendrochronological records are scarce (Humphries, 2021). ...

Evidence of wetter and drier conditions in Namibia from tufas and submerged speleothems
  • Citing Article
  • Full-text available
  • January 1999

... The hypotheses for the drivers of wetter phases on the western coast of Namibia include: (i) tropical African summer rain belt expansions during global interglacials, compared to glacials (Collins et al., 2011(Collins et al., , 2013; (ii) expanded summer rainbelt with monsoonal precipitation originating from the Indian Ocean (Brook et al., 1997), with a precessional forcing; or (iii) a mechanism relating to conditions in the southern Atlantic connected (in-phase) to hydroclimatic conditions in the Northern Hemisphere, so that wetter conditions in the Namib Desert occurred at the same time as wetter conditions in the Northern Hemisphere tropics (Chase et al., 2019). Our Narabeb record is not continuous enough to assess conditions through full glacial-interglacial cycles, however, the ages at transitions suggest these were times with increased moisture availability (and possibly with fluctuations). ...

Quaternary climatic change in southern and eastern Africa during the last 300 ka: The evidence from caves in Somalia and the Transvaal region of South Africa
  • Citing Article
  • January 1997