Some physical constants for the Marshall Islands area

Swartz, J. H.

doi:10.3133/pp260aa

Cited by 12 publications

(11 citation statements)

References 9 publications

(9 reference statements)

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“…Aquifer property values for groundwater flow and salt transport in SUTRA are shown in Table . The porosity of the Holocene and Pleistocene aquifers is 0.20 and 0.30, respectively (Swartz, ; Anthony, ), and longitudinal ( α L ) and transverse ( α T ) dispersivity, which control the dispersion of salinity in the aquifer, are given values of 6.0 and 0.05 m (Griggs and Peterson, ). Following the geology of Laura Island, Majuro Atoll in the Republic of Marshall Islands (Hamlin and Anthony, ), the Holocene aquifer extends to depths of 13 and 18 m below MSL on the ocean and lagoon sides of the island, respectively, with a sloping contact in between.…”

Section: Methodsmentioning

confidence: 99%

Quantifying transient post‐overwash aquifer recovery for atoll islands in the Western Pacific

Bailey

2015

Hydrological Processes

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Abstract:Marine overwash events for atoll islands in the Pacific and Indian Oceans, which cause salinization of fresh groundwater because of infiltrating seawater, pose a significant challenge for island community sustainability in regard to water supply. Understanding transient fresh groundwater development during a post-overwash period for a range of island sizes, geologic characteristics, and rainfall patterns is essential for water management. This paper presents a methodology for quantifying this development for an atoll nation, with methods applied to the 32 atolls of the Federated States of Micronesia (FSM) in the western Pacific. Using the numerical groundwater modelling code SUTRA, overwash events and post-overwash freshwater-seawater dynamics are simulated for the range of island widths (200 to 1100 m), geologic characteristics (hydraulic conductivity corresponding to leeward and windward islands), and rainfall patterns (western, central, and eastern regions) present in the FSM, thereby providing results for each atoll island. Results show that 10-17, 8-12, and 6-12 months are required to achieve 60% freshwater lens recovery for leeward islands in the western, central, and eastern FSM, respectively, with variation due to rainfall rate and island width. In contrast, 4-9 months is required for 60% recovery for windward islands. However, the natural thinness of the lend on windward islands typically precludes extensive use of groundwater under average rainfall conditions. Overwash characteristics (depth, duration, and seasonal timing) did not significantly affect recovery times. For the region of lowest rainfall (western FSM), 6-10 months is required to achieve potable groundwater at the typical depth of hand-dug wells. Results provide water resource managers and atoll island communities with important information regarding timing of potential fresh groundwater use following an overwash event.

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Section: Methodsmentioning

confidence: 99%

Quantifying transient post‐overwash aquifer recovery for atoll islands in the Western Pacific

Bailey

2015

Hydrological Processes

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“…For porosity of the Holocene deposits, we used Anthony’s (1987) value of 0.20 m 3 m −3 . For the Pleistocene limestone, we used Swartz’s (1962) value of 0.30 m 3 m −3 .…”

Section: Previous Workmentioning

confidence: 99%

Numerical Modeling of Atoll Island Hydrogeology

2009

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We implemented Ayers and Vachers' (1986) inclusive conceptual model for atoll island aquifers in a comprehensive numerical modeling study to evaluate the response of the fresh water lens to selected controlling climatic and geologic variables. Climatic factors include both constant and time-varying recharge rates, with particular attention paid to the effects of El Niño and the associated drought it brings to the western Pacific. Geologic factors include island width; hydraulic conductivity of the uppermost Holocene-age aquifer, which contains the fresh water lens; the depth to the contact with the underlying, and much more conductive, Pleistocene karst aquifer, which transmits tidal signals to the base of the lens; and the presence or absence of a semiconfining reef flat plate on the ocean side. Sensitivity analyses of steady-steady simulations show that lens thickness is most strongly sensitive to the depth to the Holocene-Pleistocene contact and to the hydraulic conductivity of the Holocene aquifer, respectively. Comparisons between modeling results and published observations of atoll island lens thicknesses suggest a hydraulic conductivity of approximately 50 m/d for leeward islands and approximately 400 m/d for windward islands. Results of transient simulations show that lens thickness fluctuations during average seasonal conditions and El Niño events are quite sensitive to island width, recharge rate, and hydraulic conductivity of the Holocene aquifer. In general, the depletion of the lens during drought conditions is most drastic for small, windward islands. Simulation results suggest that recovery from a 6-month drought requires about 1.5 years.

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“…Coralline algae have only 5-6 mol.% MgCO 3 indicating that they lost much of their Mg. No cement was observed. Measured porosity is approximately 50% (Swartz, 1962). 3.5.3 | E-1 well upper Eocene Core 2 Core 2 of the E-1 well (854-856 m deep) is in the uppermost part of the Upper Eocene (Figure 12B) and shows diagenetic textures similar to those observed in Pleistocene strata of the Enewetak Atoll.…”

Section: Plio-pleistocene Stratamentioning

confidence: 77%

Deep marine diagenesis, offshore Hawaii and Enewetak, with implications for older carbonates

Saller¹,

Winterbottom²

2022

The Depositional Record

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Cenozoic limestones from Hawaii and Enewetak were studied to characterise diagenesis in deep sea water. Hawaii samples were from subsea outcrops of drowned Pleistocene reefs 150-1,505 m deep (maximum age 550-600 ka). Most samples had early fibrous aragonite and high-magnesium calcite cements precipitated in shallow sea water. Partial dissolution of aragonite (including coral) and highmagnesium calcite were significant at 412 m and increased to 1,505 m. Crusts of 'stubby' sparry calcite cement (2-8 mol.% MgCO 3 ; 'lower Mg calcite') precipitated on early aragonite and high-magnesium calcite cements at 473-1,358 m. Dissolution of aragonite and high-magnesium calcite was incomplete. Aragonite and high-magnesium calcite were not neomorphosed to low-magnesium calcite ( <5 mol.% MgCO 3 ). Enewetak well samples came from 3 to 1,400 m (Holocene to Upper Eocene). Lower Miocene to Upper Eocene carbonates at 380-1,380 m near the atoll margin showed pervasive dissolution of aragonite and conversion of high-magnesium calcite fossils to low-magnesium calcite. Their lower-Mg calcite cements (380-820 m; mainly radiaxial) were associated with aragonite dissolution. The lower-Mg calcite cements and bulk limestones below 500 m had geochemistry indicating precipitation or stabilisation in sea water at 10-27°C. Data indicate Enewetak dolomitisation (1,250-1,320 m) in cold sea water during burial >1,000 m. Coralline algae showed little petrographic alteration, but Mg decreased downward from 15 to 1.5 mol.% MgCO 3 . In both areas, aragonite dissolution, alteration of high-magnesium calcite, and precipitation of lower-Mg calcite cements occurred in deep sea water (>300 m) undersaturated for aragonite, but supersaturated for low-magnesium calcite. Original high-magnesium calcite was partially dissolved in Hawaii samples, but converted to low-magnesium calcite in deep Enewetak cores, possibly due to gradual deepening at Enewetak. Dolomitisation and low-magnesium calcite dissolution occurred below the calcite saturation depth (approximately 1,000 m) in Enewetak, but not deep Hawaii samples, possibly because dolomitisation is slower. Temporal variations in carbonate saturation, especially related to pCO 2 , are interpreted as the main control on mineralogy during marine diagenesis now and in many ancient oceans.

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Some physical constants for the Marshall Islands area

Cited by 12 publications

References 9 publications

Quantifying transient post‐overwash aquifer recovery for atoll islands in the Western Pacific

Quantifying transient post‐overwash aquifer recovery for atoll islands in the Western Pacific

Numerical Modeling of Atoll Island Hydrogeology

Deep marine diagenesis, offshore Hawaii and Enewetak, with implications for older carbonates

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