Gordon W. Tribble

Recurrent storm disturbance and recovery: a long-term study of coral communities in Hawaii

Damage caused by catastrophic storm waves and subsequent recovery was investigated with a series of 15 line transects on a reef off the west coast of Hawaii over a 20-year period (1973–1993). At the initiation of the study, four zones existed across the reef, each defined by a different dominant coral species. An intermediate intensity storm in 1974 caused a decrease in coral cover from 52% to 46% of bottom cover, while breakage and transport of fragments extended the depth of peak coral cover. In 1980, a “Kona” storm, which generated the largest storm surf on record, destroyed the coral zonation pattern almost entirely. Living coral was reduced from 46% to 10% of bottom cover, with greatest damage in the zones with highest cover. Twelve years later (1992), living coral cover increased to 15% of total bottom cover. Lack of significant correlation between increase of coral cover and initial cover indicated that recovery was from larval settlement, rather than regeneration of viable fragments. Extrapolation of recovery from 1980 to 1992 indicates that the pre-storm (1973) conditions would be reached in 40 years (exponential growth) to 70 years (linear growth). In 1993, following a hurricane and unusually large northwest swell, coral cover was once again reduced to 11%; recovery was set back to a level similar to that in 1980 following the Kona storm. In 1992 and 1993 no evidence of CaCO3 accretion was observed on the reef bench. Rubble fragments created by storm stress were deposited on the reef slope with little subsequent lithification. While hurricane force waves may occur very infrequently in Hawaii, this source of stress appears to effectively limit Holocene reef growth in all areas except sheltered embayments. The pattern of damage and recovery of this coral ecosystem conforms to the intermediate disturbance hypothesis, in which storms of intermediate intensity produce either an increase or decrease in diversity and cover, depending on the timing of severe storms. On a global scale, timescales of damage and recovery cycles vary substantially depending on the frequency of severe disturbances, and the adaptive capabilities of dominant species.

The influence of microclimates and fog on stable isotope signatures used in interpretation of regional hydrology: East Maui, Hawaii

Stable isotopes of precipitation, ground water and surface water measured on the windward side of East Maui from 0 to 3055 m altitude were used to determine recharge sources for stream flow and ground water. Correct interpretation of the hydrology using rainfall 18 O gradients with altitude required consideration of the influence of fog, as fog samples had isotopic signatures enriched by as much as 3‰ in 18 O and 21‰ in D compared to volume-weighted average precipitation at the same altitude. The isotopic analyses suggested that fog drip was a major component of stream flow and shallow ground water at higher altitudes in the watershed. Oxygen-18/altitude gradients in rainfall were comparable for similar microclimates on Maui (this study) and Hawaii Island (1990-95 study), however, East Maui 18 O values for rain in tradewind and high-altitude microclimates were enriched compared to those from Hawaii Island. Isotopes were used to interpret regional hydrology in this volcanic island aquifer system. In part of the study area, stable isotopes indicate discharge of ground water recharged at least 1000 m above the sample site. This deep-flowpath ground water was found in springs from sea level up to 240 m altitude, indicating saturation to altitudes much higher than a typical freshwater lens. These findings help in predicting the effects of ground water development on stream flow in the area.

Stoichiometric modeling of carbon diagenesis within a coral reef framework

Abstract Water sampled from the interior framework of Checker Reef, Oahu, Hawaii, indicates that the aerobic and anaerobic oxidation of organic matter dominates diagenesis within the reef framework. Reef interstitial water chemistry shows clear deviations from surface seawater: oxygen is depleted while dissolved inorganic carbon, H + , inorganic nutrients, sulfide and methane concentrations are elevated. Dissolved calcium is also elevated in most interstitial waters, indicating net dissolution of calcium carbonates. A mass-balance model used to determine the extent to which major biogeochemical reactions occur reveals that sulfate reduction is the predominant anaerobic process.

Christmas Island lagoonal lakes, models for the deposition of carbonate{evaporite{organic laminated sediments

The atoll of Christmas Island (now known as Kiritimati) in the Kiribati Republic (Central Pacific) lies at about 28N in the intertropical convergence zone. Much of the surface area of the atoll (ca. 360 km 2 ) is occupied by numerous lakes in which carbonate, evaporite (calcium sulfate, halite) and organic layers are deposited. Observations suggest that deposition of these different laminae is controlled by climatic and biologic factors. It is thought that periodic climatic variations, such as El Nino- Southern Oscillations (ENSO) events which bring heavy rainfall to the atoll, result in the succession of the precipitation of carbonate minerals (during periods after dilution of hypersaline waters by heavy rains), followed by evaporitic minerals (carbonate, calcium sulfate, halite) when salinity increases through evaporation. Thick (up to 5 cm) microbial (essentially cyanobacterial) mats develop continuously on the lake bottom surfaces providing the sediment with an important (total organic carbon 2-5%) organic contribution in the form of an internal, geometrically structured, network in which the authigenic minerals precipitate. The high bioproductivity of these microbial populations is reflected in low d 13 C values of sedimentary organic carbon (214 to 217‰), interpreted as being the result of high atmospheric CO2 demand (Geochim. Cosmochim. Acta, 56 (1992) 335). The well-laminated organic layers present in the sediment profile result from the death and burial of microbial populations at the time of severe climatic events (storms, heavy rainfall). These lagoonal lakes provide a model for the deposition of carbonate and organic matter in an evaporitic environment. The high ratio of deposited carbonate vs. sulfate 1 chloride, when compared to low ratio in evaporitic salinas, results from both a lack of limitation of calcium, magnesium and carbonate ions (in a carbonate reef environment) and active processes of high-Mg calcite precipitation (organomineralization). q 2001 Elsevier Science B.V. All rights reserved.

Underwater observations of active lava flows from Kilauea volcano, Hawaii

Underwater observation of active submarine lava flows from Kilauea volcano, Hawaii, in March-June 1989 revealed both pillow lava and highly channelized lava streams flowing down a steep and unconsolidated lava delta. The channelized streams were 0.7-1.5 m across and moved at rates of 1-3 m/s. The estimated flux of a stream was 0.7 m 3 /s. Jets of hydrothermal water and gas bubbles were associated with the volcanic activity. The rapidly moving channelized lava streams represent a previously undescribed aspect of submarine volcanism.

Organic matter oxidation and aragonite diagenesis in a coral reef

ABSTRACT A combination of field and theoretical work is used to study controls on the saturation state of aragonite inside a coral-reef framework. A closed-system ion-speciation model is used to evaluate the effect of organic-matter oxidation on the saturation state of aragonite. The aragonite saturation state initially drops below 1 but becomes oversaturated during sulfate reduction. The C:N ratio of the organic matter affects the degree of oversaturation, with N-poor organic material resulting in a system more corrosive to aragonite. Precipitation of sulfide as FeS strongly affects the aragonite saturation state, and systems with much FeS formation will have a stronger tendency to become oversaturated with respect to aragonite. Both precipitation and dissolution of aragonite are predicted at different stages of the organic reaction pathway if the model system is maintained at aragonite saturation. Field data from a coral-reef framework indicate that the system maintains itself at aragonite saturation, and model-predicted changes in dissolved calcium follow those observed in the interstitial waters of the reef. Aragonite probably acts as a solid-phase buffer in regulating the pH of interstitial waters. Because interstitial water in the reef has a short residence time, the observed equilibration suggests rapid kinetics.

Lava‐seawater interactions at shallow‐water submarine lava flows

Hydrothermal plumes associated with nearshore lava flows from Kilauea Volcano, Hawaii were studied on five occasions during 1989–1990 to address the current lack of data on direct lava-seawater interactions. The following enrichments were found in the sea-surface hydrothermal plumes above the active underwater lava flows: H2, 15,000x ambient seawater concentrations; Mn, 250x; and Si, 20x. Water temperatures reached 46°C. Lower concentrations and temperatures were observed in the plumes with increasing distance from shore, with H2, Si, and Mn concentrations linearly related to seawater temperature. Unlike deep sea spreading center hydrothermal plumes, no CH4 enrichment was observed. The elevated H2 is likely to be from water-rock reactions, rather than from the release of magmatic gas. The plume mass/heat ratios presented here suggest that submarine flood basalts, although aerially large, should be relatively small immediate contributors to oceanic geochemical cycles compared to hydrothermal circulation through the crust.

Well-point sampling of reef interstitial water

A technique is described for collecting reef interstitial water using manually-driven well points. This method does not require the use of hydraulic drills, and eliminates the problems associated with the casing of boreholes. The technique allows collection of samples from discrete depths within reef frameworks, and produces samples unaffected by atmospheric or surface seawater contamination. Data from Checker Reef, Oahu, Hawaii illustrate the utility of this approach.

A description of the high-latitude shallow water coral communities of Miyake-jima, Japan

The corals growing on the shoal-water slopes of Miyake-jima, Japan, form one of the higher latitude (34°05′N) coral communities in the Indo-Pacific province. It also appears to be the highest latitude where development of a coral reef framework has occurred. In 1979 a collection of 263 coral specimens representing 80 hermatypic and 11 ahermatypic species was made. The coral communities in one bay were analyzed at nine different localities along 98 transects. From the coral collections and transect investigations a physiographic description of the reef habitats, the general distribution pattern of the corals, and a species checklist are given. A detailed analysis of the coral community is presented for the transect localities. Variables reported include: surface coverage, predominant species colony size and density, and species richness, evenness and diversity. Although coral coverage was not high, species diversity values were comparable with more tropically-situated areas.