Geology topics

N.G. Prouty

Publications and source records attributed to N.G. Prouty.

5 recordsLinked to original sources

USGS2016

Observations of nearshore groundwater discharge: Kahekili Beach Park submarine springs, Maui, Hawaii

Study region The study region encompasses the nearshore, coastal waters off west Maui, Hawaii. Here abundant groundwater—that carries with it a strong land-based fingerprint—discharges into the coastal waters and over a coral reef. Study focus Coastal groundwater discharge is a ubiquitous hydrologic feature that has been shown to impact nearshore ecosystems and material budgets. A unique combined geochemical tracer and oceanographic time-series study addressed rates and oceanic forcings of submarine groundwater discharge at a submarine spring site off west Maui, Hawaii. New hydrological insights for the region Estimates of submarine groundwater discharge were derived for a primary vent site and surrounding coastal waters off west Maui, Hawaii using an excess 222 Rn ( t 1/2 = 3.8 d) mass balance model. Such estimates were complemented with a novel thoron ( 220 Rn, t 1/2 = 56 s) groundwater discharge tracer application, as well as oceanographic time series and thermal infrared imagery analyses. In combination, this suite of techniques provides new insight into the connectivity of the coastal aquifer with the near-shore ocean and examines the physical drivers of submarine groundwater discharge. Lastly, submarine groundwater discharge derived constituent concentrations were tabulated and compared to surrounding seawater concentrations. Such work has implications for the management of coastal aquifers and downstream nearshore ecosystems that respond to sustained constituent loadings via this submarine route.

Hawaii↗

USGS2013

Environmental assessment of metal exposure to corals living in Castle Harbour, Bermuda

Environmental contamination in Castle Harbour, Bermuda, has been linked to the dissolution and leaching of contaminants from the adjacent marine landfill. This study expands the evidence for environmental impact of leachate from the landfill by quantitatively demonstrating elevated metal uptake over the last 30 years in corals growing in Castle Harbour. Coral Pb/Ca, Zn/Ca and Mn/Ca ratios and total Hg concentrations are elevated relative to an adjacent control site in John Smith's Bay. The temporal variability in the Castle Harbour coral records suggests that while the landfill has increased in size over the last 35 years, the dominant input of metals is through periodic leaching of contaminants from the municipal landfill and surrounding sediment. Elevated contaminants in the surrounding sediment suggest that resuspension is an important transport medium for transferring heavy metals to corals. Increased winds, particularly during the 1990s, were accompanied by higher coral metal composition at Castle Harbour. Coupled with wind-induced resuspension, interannual changes in sea level within the Harbour can lead to increased bioavailability of sediment-bound metals and subsequent coral metal assimilation. At John Smith's Bay, large scale convective mixing may be driving interannual metal variability in the coral record rather than impacts from land-based activities. Results from this study provide important insights into the coupling of natural variability and anthropogenic input of contaminants to the nearshore environment.

Castle Harbour↗

USGS2011

Growth rate and age distribution of deep-sea black corals in the Gulf of Mexico

Black corals (order Antipatharia) are important long-lived, habitat-forming, sessile, benthic suspension feeders that are found in all oceans and are usually found in water depths greater than 30 m. Deep-water black corals are some of the slowest-growing, longest-lived deep-sea corals known. Previous age dating of a limited number of black coral samples in the Gulf of Mexico focused on extrapolated ages and growth rates based on skeletal 210 Pb dating. Our results greatly expand the age and growth rate data of black corals from the Gulf of Mexico. Radiocarbon analysis of the oldest Leiopathes sp. specimen from the upper De Soto Slope at 300 m water depth indicates that these animals have been growing continuously for at least the last 2 millennia, with growth rates ranging from 8 to 22 µm yr –1 . Visual growth ring counts based on scanning electron microscopy images were in good agreement with the 14 C-derived ages, suggestive of annual ring formation. The presence of bomb-derived 14 C in the outermost samples confirms sinking particulate organic matter as the dominant carbon source and suggests a link between the deep-sea and surface ocean. There was a high degree of reproducibility found between multiple discs cut from the base of each specimen, as well as within duplicate subsamples. Robust 14 C-derived chronologies and known surface ocean 14 C reservoir age constraints in the Gulf of Mexico provided reliable calendar ages with future application to the development of proxy records.

Marine Ecology Progress Series↗

USGS2010

Coral Ba/Ca records of sediment input to the fringing reef of the southshore of Moloka'i, Hawai'i over the last several decades

The fringing reef of southern Moloka’i is perceived to be in decline because of land-based pollution. In the absence of historical records of sediment pollution, ratios of coral Ba/Ca were used to test the hypothesis that sedimentation has increased over time. Baseline Ba/Ca ratios co-vary with the abundance of red, terrigenous sediment visible in recent imagery. The highest values at One Ali’i are near one of the muddiest parts of the reef. This co-varies with the lowest growth rate of all the sites, perhaps because the upstream Kawela watershed was historically leveed all the way to the nearshore, providing a fast-path for sediment delivery. Sites adjacent to small, steep watersheds have ∼decadal periodicities whereas sites adjacent to mangrove forests have shorter-period fluctuations that correspond to the periodicity of sediment transport in the nearshore, rather than the watershed. All four sites show a statistically significant upward trend in Ba/Ca.

Hawai'i↗

USGS2008

Geochemical signature of land-based activities in Caribbean coral surface samples

Anthropogenic threats, such as increased sedimentation, agrochemical run-off, coastal development, tourism, and overfishing, are of great concern to the Mesoamerican Caribbean Reef System (MACR). Trace metals in corals can be used to quantify and monitor the impact of these land-based activities. Surface coral samples from the MACR were investigated for trace metal signatures resulting from relative differences in water quality. Samples were analyzed at three spatial scales (colony, reef, and regional) as part of a hierarchical multi-scale survey. A primary goal of the paper is to elucidate the extrapolation of information between fine-scale variation at the colony or reef scale and broad-scale patterns at the regional scale. Of the 18 metals measured, five yielded statistical differences at the colony and/or reef scale, suggesting fine-scale spatial heterogeneity not conducive to regional interpretation. Five metals yielded a statistical difference at the regional scale with an absence of a statistical difference at either the colony or reef scale. These metals are barium (Ba), manganese (Mn), chromium (Cr), copper (Cu), and antimony (Sb). The most robust geochemical indicators of land-based activities are coral Ba and Mn concentrations, which are elevated in samples from the southern region of the Gulf of Honduras relative to those from the Turneffe Islands. These findings are consistent with the occurrence of the most significant watersheds in the MACR from southern Belize to Honduras, which contribute sediment-laden freshwater to the coastal zone primarily as a result of human alteration to the landscape (e.g., deforestation and agricultural practices). Elevated levels of Cu and Sb were found in samples from Honduras and may be linked to industrial shipping activities where copper-antimony additives are commonly used in antifouling paints. Results from this study strongly demonstrate the impact of terrestrial runoff and anthropogenic activities on coastal water quality in the MACR. ?? 2008 Springer-Verlag.

Coral Reefs↗