Geology topics

Michael E. Field

Publications and source records attributed to Michael E. Field.

At least 19 recordsLinked to original sources

USGS2019

The major coral reefs of Maui Nui, Hawai‘i—distribution, physical characteristics, oceanographic controls, and environmental threats

Coral reefs are widely recognized as critical to Hawaiʻi’s economy, food resources, and protection from damaging storm waves. Yet overfishing, land-based pollution, and climate change are threatening the health and sustainability of those reefs, and accordingly, both the Federal and State governments have called for protection and effective management. In 2000, the U.S. Coral Reef Task Force stated that 20 percent of coral reefs should be protected by 2010. In 2016, the Governor of Hawaiʻi committed to effective management of 30 percent of Hawaiian coastal habitats by 2030 to protect coral reefs. At present, the amount of coral protected in the main Hawaiian Islands is less than 1 percent. Most of the large, highly diverse coral reef tracts in the main Hawaiian Islands surround the four islands of Maui, Molokaʻi, Lānaʻi, and Kahoʻolawe, collectively known as Maui Nui. This report provides fundamental information on the location, extent, coral cover, threats, and connectivity of these major coral reef tracts in Maui Nui essential for identifying areas for management and protection. By combining high-resolution bathymetric data with available maps, publications, and satellite and underwater images, nine major coral reef tracts are identified in the coastal waters of Maui Nui. Three very large reef tracts lie along the south side of Molokaʻi, two on the east side of Lānaʻi, and four off Maui. The factors that make these Maui Nui coral reef tracts a major and important resource for Hawaiʻi include their vast size and high coral cover (nearly 16,000 acres of reef, most of which has more than 50 percent live coral cover); diversity of shape, size, and location; and separation between reefs while retaining connectivity via currents. The decline in the health of these coral reefs over the past several decades has been slow but persistent. Punctuation of the decline by large-scale disturbance events, such as the thermal bleaching that occurred in 2015, is accelerating the loss of viable reef areas by an order of magnitude. The economic, cultural, and recreational value of these coral reef tracts highlights the importance of their long-term survival to the local communities and all of Hawaiʻi. There is scientific consensus that increasing pressures from climate change, overfishing, and land-based pollution will virtually assure the continued, and perhaps accelerating, decline of Hawaiʻi’s coral reefs unless action is taken. Information presented in this report, coupled with the results of numerous scientific studies, provides scientific underpinning to help establish a network of large-scale, connected Marine Protected Areas to meet the Federal and State governments’ call for effective management and protection of coral reefs in Maui Nui.

Hawaii↗

USGS2015

The Moloka‘i coral reef today, and alternatives for the future: Summary in The coral reef of south Moloka‘i, Hawai‘i—Portrait of a sediment-threatened fringing reef

From the contributions collected in this publication have emerged two important observations that have significance locally, nationally, and internationally. First, the fringing coral reef along the south coast of Moloka'i is one of the most extensive and luxuriant reefs in the eight main Hawaiian Islands. It is longer and more continuous and has denser coral cover than reefs at any of the other islands—this alone makes it a state and national treasure worthy of study and protection. The second observation is more sobering: sections of the south Moloka'i reef have been damaged in the past by sedimentation ultimately caused by human activities in adjacent watersheds. Although some of those activities are no longer taking place, their lingering effects are still being felt in the form of excess sediment runoff. We here review the basis for each of these observations, discuss how sedimentation affects the reef, and summarize the choices that are faced by the people of Moloka'i and the State of Hawai'i with regard to the reef’s future.

Hawai‘i↗

USGS2014

Response of reef corals on a fringing reef flat to elevated suspended-sediment concentrations: Moloka‘i, Hawai‘i

A long-term (10 month exposure) experiment on effects of suspended sediment on the mortality, growth, and recruitment of the reef corals Montipora capitata and Porites compressa was conducted on the shallow reef flat off south Molokaʻi, Hawaiʻi. Corals were grown on wire platforms with attached coral recruitment tiles along a suspended solid concentration (SSC) gradient that ranged from 37 mg l −1 (inshore) to 3 mg l −1 (offshore). Natural coral reef development on the reef flat is limited to areas with SSCs less than 10 mg l −1 as previously suggested in the scientific literature. However, the experimental corals held at much higher levels of turbidity showed surprisingly good survivorship and growth. High SSCs encountered on the reef flat reduced coral recruitment by one to three orders of magnitude compared to other sites throughout Hawaiʻi. There was a significant correlation between the biomass of macroalgae attached to the wire growth platforms at the end of the experiment and percentage of the corals showing mortality. We conclude that lack of suitable hard substrate, macroalgal competition, and blockage of recruitment on available substratum are major factors accounting for the low natural coral coverage in areas of high turbidity. The direct impact of high turbidity on growth and mortality is of lesser importance.

Hawaii↗

USGS2014

Island outlook: Warm and swampy

In his In Depth News story “Warming may not swamp islands” (1 August, p. 496 ), C. Pala argues that “coral reefs supporting sandy atoll islands will grow and rise in tandem with the sea,” based largely on studies that showed stable Pacific-island area over recent decades ( 1 – 4 ). He suggests that recent land losses are driven mostly by bad choices and that islanders are being affected “for the same reason as millions of people on the continents: because they live too close to shore.” We disagree with these conclusions.

Science↗

USGS2013

Rapid fluctuations in flow and water-column properties in Asan Bay, Guam: implications for selective resilience of coral reefs in warming seas

Hydrodynamics and water-column properties were investigated off west-central Guam from July 2007 through January 2008. Rapid fluctuations, on time scales of 10s of min, in currents, temperature, salinity, and acoustic backscatter were observed to occur on sub-diurnal frequencies along more than 2 km of the fore reef but not at the reef crest. During periods characterized by higher sea-surface temperatures (SSTs), weaker wind forcing, smaller ocean surface waves, and greater thermal stratification, rapid decreases in temperature and concurrent rapid increases in salinity and acoustic backscatter coincided with onshore-directed near-bed currents and offshore-directed near-surface currents. During the study, these cool-water events, on average, lasted 2.3 h and decreased the water temperature 0.57 °C, increased the salinity 0.25 PSU, and were two orders of magnitude more prevalent during the summer season than the winter. During the summer season when the average satellite-derived SST anomaly was +0.63 °C, these cooling events, on average, lowered the temperature 1.14 °C along the fore reef but only 0.11 °C along the reef crest. The rapid shifts appear to be the result of internal tidal bores pumping cooler, more saline, higher-backscatter oceanic water from depths >50 m over cross-shore distances of 100 s of m into the warmer, less saline waters at depths of 20 m and shallower. Such internal bores appear to have the potential to buffer shallow coral reefs from predicted increases in SSTs by bringing cool, offshore water to shallow coral environments. These cooling internal bores may also provide additional benefits to offset stress such as supplying food to thermally stressed corals, reducing stress due to ultraviolet radiation and/or low salinity, and delivering coral larvae from deeper reefs not impacted by surface thermal stress. Thus, the presence of internal bores might be an important factor locally in the resilience of select coral reefs facing increased thermal stress.

Coral Reefs↗

USGS2012

SedPods: a low-cost coral proxy for measuring net sedimentation

Sediment derived from impaired watersheds is a major stressor to adjacent coral reefs globally. To better understand stresses generated by specific processes and events, many coral reef scientists seek to collect physical samples of settling particles and obtain reproducible information about net rates of sediment accumulation on coral reefs. Yet, the tools most commonly used to gather this information, sediment tube traps, only provide information on the gross accumulation of sediment at a site, in that all particles are effectively trapped within the container, unlike what a coral surface experiences. To address the need for an improved measurement of net particle accumulation on coral surfaces, we propose using recoverable sediment pods (SedPods) that can be constructed from readily available materials for under US $20. These devices are inexpensive, easy to fabricate, and allow for capture of particles over a given time span. The particles can then be used for laboratory analysis and accurate calculation of net accumulation rates on a coral surface proxy. In an experiment in Hanalei Bay, HI, we found that net sediment accumulation on rectangular SedPods was an order of magnitude less than gross accumulation in nearby conventional tube traps.

Coral Reefs↗

USGS2012

Coastal circulation and sediment dynamics in Pelekane and Kawaihae Bays, Hawaii--measurements of waves, currents, temperature, salinity, turbidity, and geochronology: November 2010--March 2011

Coral reef communities on the Island of Hawaii have been heavily affected by the construction of Kawaihae Harbor in the 1950s and by subsequent changes in land use in the adjacent watershed. Sedimentation and other forms of land-based pollution have led to declines in water quality and coral reef health over the past two decades (Tissot, 1998). Erosion mitigation efforts are underway on land, and there is a need to evaluate the impact of these actions on the adjacent coastal ecosystem. The Kohala Center and Kohala Watershed Partnership was awarded $2.69 million from the National Oceanographic and Atmospheric Administration’s (NOAA) Restoration Center as part of the American Recovery and Reinvestment Act of 2009 to stabilize soil and improve land-use practices in the Pelekane Bay watershed. The grant allowed the Kohala Watershed Partnership to implement various upland watershed management activities to reduce land-based sources of pollution into Pelekane Bay. However, a number of questions must be answered in order to: (1) evaluate the effectiveness of the terrestrial watershed remediation efforts; (2) understand the potential of the local marine ecosystem to recover; and (3) understand the potential threat that existing mud deposits in the bay pose to adjacent, relatively pristine coral reef ecosystems. The goal of this experiment was to help address these questions and establish a framework to evaluate the success of the Kohala Watershed Partnership restoration efforts. This research program will also provide resource managers with information relevant to other watershed restoration efforts currently being planned in neighboring watersheds. This project involved an interdisciplinary team of coral reef biologists from the University of Hawaii Coral Reef Assessment and Monitoring Program, who focused on the impact of sedimentation on the biota of Pelekane Bay, and a team of geologists and oceanographers from the U.S. Geological Survey (USGS), who focused on the circulation and sediment dynamics in Pelekane and Kawaihae Bays. The initial findings from the USGS research program are described in this report. These measurements support the ongoing studies being conducted as part of the USGS Coastal and Marine Geology Program’s Pacific Coral Reef Project to better understand the effect of geologic and oceanographic processes on coral reef systems.

Hawai'i↗

USGS2011

From ridge to reef—linking erosion and changing watersheds to impacts on the coral reef ecosystems of Hawai‘i and the Pacific Ocean

Coral reef ecosystems are threatened by unprecedented watershed changes in the United States and worldwide. These ecosystems sustain fishing and tourism industries essential to the economic survival of many communities. Sediment, nutrients, and pollutants from watersheds are increasingly transported to coastal waters, where these contaminants damage corals. Although pollution from watersheds is one of many factors threatening coral survival, it is one that local people can have a profound influence on. U.S. Geological Survey scientists are using mapping, monitoring, and computer modeling to better forecast the effects of watershed changes on reef health. Working with communities in Hawai‘i and on other U.S. islands in the Pacific, they are helping to provide the science needed to make informed decisions on watershed and coral reef management.

Hawai'i↗

USGS2011

The influence of sea-level rise on fringing reef sediment dynamics: field observations and numerical modeling

While most climate projections suggest that sea level may rise on the order of 0.5-1.0 m by 2100, it is not clear how fluid flow and sediment transport on fringing reefs might change in response to this rapid sea-level rise. Field observations and numerical modeling suggest that an increase in water depth on the order of 0.5-1.0 m on a fringing reef flat would result in larger significant wave heights and wave-driven shear stresses, which, in turn, would result in an increase in both the size and quantity of sediment that can be resuspended from the seabed or eroded from coastal plain deposits. Greater wave- and wind-driven currents would develop on the reef flat with increasing water depth, increasing the offshore flux of water and sediment from the inner reef flat to the outer reef flat and fore reef where coral growth is typically greatest.

Hawai'i↗

USGS2010

The morphology, processes, and evolution of Monterey Fan: a revisit

Long-range (GLORIA) and mid-range (TOBI) sidescan imagery and seismic-reflection profiles have revealed the surface morphology and architecture of the complete Monterey Fan. The fan has not developed a classic wedge shape because it has been blocked for much of its history by Morro Fracture Zone. The barrier has caused the fan to develop an upper-fan and lower-fan sequence that are distinctly different from one another. The upper-fan sequence is characterized by Monterey and Ascension Channels and associated Monterey Channel-levee system. The lower-fan sequence is characterized by depositional lobes of the Ascension, Monterey, and Sur-Parkington-Lucia systems, with the Monterey depositional lobe being the youngest. Presently, the Monterey depositional lobe is being downcut because the system has reached a new, lower base level in the Murray Fracture Zone. A five-step evolution of Monterey Fan is presented, starting with initial fan deposition in the Late Miocene, about 5.5 Ma. This first stage was one of filling bathymetric lows in the oceanic basement in what was to become the upper-fan segment. The second stage involved filling the bathymetric low on the north side of Morro Fracture Zone, and probably not much sediment was transported beyond the fracture zone. The third stage witnessed sediment being transported around both ends of Morro Fracture Zone and initial sedimentation on the lower-fan segment. During the fourth stage Ascension Channel was diverted into Monterey Channel, thereby cutting off sedimentation to the Ascension depositional lobe.

California↗

USGS2010

Turbidity on the shallow reef off Kaulana and Hakioawa watersheds, north coast of Kaho'olawe, Hawai'i: Measurements of turbidity and ancillary data on winds, waves, precipitation, and stream flow discharge, November 2005 to June 2008

The island of Kaho`olawe has particular cultural and religious significance for native Hawaiians. Once known as Kanaloa, the island was a center for native Hawaiian navigation. In the mid-20th century, the island was used as a bombing range by the U.S. Navy, and that practice, along with the foraging by feral goats, led to a near-complete decimation of vegetation. The loss of ground cover led to greatly increased erosion and run-off of sediment-laden water onto the island's adjacent coral reefs. Litigation in 1990 ended the U.S. Navy's use of the island as a bombing range, and in 1994 the island was transferred to the Kaho`olawe Island Reserve Commission (KIRC), http://kahoolawe.hawaii.gov/. As a result of the litigation, the U.S. Navy began a 10-year clean-up effort that was the foundation for the present restoration effort by KIRC (Slay, 2009). The restoration effort is centered on revegetating the island, reducing erosion, and limiting run-off onto adjacent reefs. Restoration efforts to mitigate sediment runoff to streams and gulches by restoring native vegetation and minimizing erosion have focused on two watersheds, Kaulana and Hakioawa, on the northeast and northwest sides of the island, respectively. Stream flow and sediment gages were installed by the U.S. Geological Survey Pacific Islands Water Science Center in each of the watersheds, and a weather station was established upland of the watersheds. For this study, turbidity monitors were installed on the insular shelf off the two watersheds to monitor the overall quality of reef waters and their changes in response to rain and stream flow discharge events.

Hawaii↗

USGS2010

Coastal circulation and sediment dynamics in Maunalua Bay, Oahu, Hawaii: Measurements of waves, currents, temperature, salinity, and turbidity: November 2008-February 2009

High-resolution measurements of waves, currents, water levels, temperature, salinity and turbidity were made in Maunalua Bay, southern Oahu, Hawaii, during the 2008–2009 winter to better understand coastal circulation, water-column properties, and sediment dynamics during a range of conditions (trade winds, kona storms, relaxation of trade winds, and south swells). A series of bottom-mounted instrument packages were deployed in water depths of 20 m or less to collect long-term, high-resolution measurements of waves, currents, water levels, temperature, salinity, and turbidity. These data were supplemented with a series of profiles through the water column to characterize the vertical and spatial variability in water-column properties within the bay. These measurements support the ongoing process studies being done as part of the U.S. Geological Survey (USGS) Coastal and Marine Geology Program’s Pacific Coral Reef Project; the ultimate goal of these studies is to better understand the transport mechanisms of sediment, larvae, pollutants, and other particles in coral reef settings. Project Objectives The objective of this study was to understand the temporal variations in currents, waves, tides, temperature, salinity and turbidity within a coral-lined embayment that receives periodic discharges of freshwater and sediment from multiple terrestrial sources in the Maunalua Bay. Instrument packages were deployed for a three-month period during the 2008–2009 winter and a series of vertical profiles were collected in November 2008, and again in February 2009, to characterize water-column properties within the bay. Measurements of flow and water-column properties in Maunalua Bay provided insight into the potential fate of terrestrial sediment, nutrient, or contaminant delivered to the marine environment and coral larval transport within the embayment. Such data are useful for providing baseline information for future watershed decisions and for establishing guidelines for the U.S. Coral Reef Task Force’s (USCRTF) Hawaiian Local Action Strategy to address Land-Based Pollution (LAS-LBP) threats to coral reefs adjacent to the urbanized watersheds of Manualua Bay. Study Area Maunalua Bay is on the south side of Oahu, Hawaii, and is approximately 10 km long and 3 km wide. The bay is flanked by two large, dormant craters: Koko Head to the east and Diamond Head to the west. Rainfall in the watersheds that drain into Maunalua Bay ranges from more than 200 cm/year at the top of the Ko‘olau Range that borders the northwestern part of the bay to less than 70 cm/year to the east at Koko Head. Seven major channels flow into the bay, and all but one have been altered by engineering structures.

Hawaii↗

USGS2009

Coral proxy record of decadal-scale reduction in base flow from Moloka'i, Hawaii

Groundwater is a major resource in Hawaii and is the principal source of water for municipal, agricultural, and industrial use. With a growing population, a long-term downward trend in rainfall, and the need for proper groundwater management, a better understanding of the hydroclimatological system is essential. Proxy records from corals can supplement long-term observational networks, offering an accessible source of hydrologic and climate information. To develop a qualitative proxy for historic groundwater discharge to coastal waters, a suite of rare earth elements and yttrium (REYs) were analyzed from coral cores collected along the south shore of Moloka'i, Hawaii. The coral REY to calcium (Ca) ratios were evaluated against hydrological parameters, yielding the strongest relationship to base flow. Dissolution of REYs from labradorite and olivine in the basaltic rock aquifers is likely the primary source of coastal ocean REYs. There was a statistically significant downward trend (−40%) in subannually resolved REY/Ca ratios over the last century. This is consistent with long-term records of stream discharge from Moloka'i, which imply a downward trend in base flow since 1913. A decrease in base flow is observed statewide, consistent with the long-term downward trend in annual rainfall over much of the state. With greater demands on freshwater resources, it is appropriate for withdrawal scenarios to consider long-term trends and short-term climate variability. It is possible that coral paleohydrological records can be used to conduct model-data comparisons in groundwater flow models used to simulate changes in groundwater level and coastal discharge.

Hawai'i↗

USGS2008

Winds, Waves, Tides, and the Resulting Flow Patterns and Fluxes of Water, Sediment, and Coral Larvae off West Maui, Hawaii

A series of recent studies has focused on the flow patterns and particle fluxes along the coast of West Maui, Hawaii, USA, from Honolua south to Puumana. From those studies a relatively good understanding has emerged of the physical processes that influence the relative amount of suspended sediment in nearshore waters and the circulation patterns that transport sediment and coral larvae along the coast and between islands. This report is a synthesis of our existing knowledge on the nature of flow and transport off West Maui.

Open-File Report↗

USGS2007

Sedimentary properties of shallow marine cores collected in June and September 2006, Hanalei Bay, Kaua'i, Hawai'i

Sedimentary facies, short-lived isotopes 7 Be, 137 Cs, and 210 Pb, and magnetic properties of sediment cores in Hanalei Bay, Kaua‘i, Hawai‘i, were used to assess sediment sources and patterns of deposition associated with seasonal flooding of the Hanalei River. Sediment cores were collected from the seafloor in June and September of 2006 to supplement similar data collected during the summer of 2005. The youngest and thickest terrigenous sediment was observed on the east side of the bay: near the Hanalei River mouth and in a bathymetric depression, known locally as the Black Hole, that acts as a temporary sediment sink. Deposits from floods that occurred between February and April 2006 left flood deposits in the eastern bay that, by June of 2006, were on the order of 10 cm thick. A flood occurred on August 7, 2006, that was smaller than floods that occurred the previous winter but was a substantial discharge event for the summer season. Deposits from the winter 2006 floods continued to dominate the sedimentary record in the eastern bay through early fall, even after the addition of newer sediment during the August 7 flood; this is consistent with the much higher sediment input of the winter floods compared with the August 7 flood. Broad variations in magnetic grain size and relative magnetite-hematite abundance in several sediment cores indicate many sources of upland terrigenous sediment. As a group, recent flood deposits show much less variation in these properties compared with older deposits, implying either that the 2006 winter–spring flood sediment originated from one or more distinct upland settings, or that substantial mixing of sediment from multiple sources occurred during transport. Sediment is most readily remobilized and advected out of the bay during winter, when oceanic conditions are energetic. In summer, wave and current measurements made concurrently with this study showed weak currents and little wave energy, indicating that sediment delivered during summer floods most likely remains in the bay until winter storms can remove it. Increased turbidity and sedimentation on corals resulting from floods of the Hanalei River could affect the sustainability of coral reefs and their many associated species. This possibility is of particular concern during summer months when wave energy is low and sediment is not readily remobilized and transported out of the bay. The timing (seasonality) and magnitude of sediment input to the coastal ocean relative to seasonal variations in wave and current energy could have significant ecological consequences for coral-reef communities in the Hawaiian Islands.

Hawai'i↗

USGS2006

usSEABED: Pacific Coast (California, Oregon, Washington) Offshore Surficial-Sediment Data Release, version 1

Over the past 50 years there has been an explosion in scientific interest, research effort, and information gathered on the geologic sedimentary character of the continental margin of the United States. Data and information from thousands of publications have greatly increased our scientific understanding of the geologic origins of the margin surface but rarely have those data been combined and integrated. This publication is the first release of the Pacific coast data from the usSEABED database. The report contains a compilation of published and unpublished sediment texture and other geologic data about the sea floor from diverse sources. usSEABED is an innovative database system developed to unify assorted data, with the data processed by the dbSEABED system. Examples of maps displaying attributes such as grain size and sediment color are included. This database contains information that is a scientific foundation for the U.S. Geological Survey (USGS) Sea floor Mapping and Benthic Habitats project and the Marine Aggregate Resources and Processes assessment project, and will be useful to the marine science community for other studies of the Pacific coast continental margin. The publication is divided into 10 sections: Home, Introduction, Content, usSEABED (data), dbSEABED (processing), Data Catalog, References, Contacts, Acknowledgments, and Frequently Asked Questions. Use the navigation bar on the left to navigate to specific sections of this report. Underlined topics throughout the publication are links to more information. Links to specific and detailed information on processing and to those to pages outside this report will open in a new browser window.

California, Oregon, Washington↗

USGS2006

Coastal circulation and sediment dynamics in Hanalei Bay, Kauai, Part I, Measurements of waves, currents, temperature, salinity and turbidity; June–August, 2005

High-resolution measurements of waves, currents, water levels, temperature, salinity and turbidity were made in Hanalei Bay, northern Kauai, Hawaii, during the summer of 2005 to better understand coastal circulation and sediment dynamics in coral reef habitats. A series of bottom-mounted instrument packages were deployed in water depths of 10 m or less to collect long-term, high-resolution measurements of waves, currents, water levels, temperature, salinity and turbidity. These data were supplemented with a series of vertical instrument casts to characterize the vertical and spatial variability in water column properties within the bay. The purpose of these measurements was to collect hydrographic data to learn how waves, currents and water column properties vary spatially and temporally in an embayment that hosts a nearshore coral reef ecosystem adjacent to a major river drainage. These measurements support the ongoing process studies being conducted as part of the U.S. Geological Survey (USGS) Coastal and Marine Geology Program's Coral Reef Project; the ultimate goal is to better understand the transport mechanisms of sediment, larvae, pollutants and other particles in coral reef settings. This report, the first part in a series, describes data acquisition, processing and analysis.

Hawaii↗

USGS2006

Coastal circulation and sediment dynamics in Hanalei Bay, Kaua'i, Hawaii: Part II: Tracking recent fluvial sedimentation: Isotope stratigraphy obtained in Summer 2005

Delivery and dispersal of fluvial sediment in Hanalei Bay, Kaua’i, Hawaii, have important implications for the health of local coral reefs. The reef community in Hanalei Bay represents a relatively healthy ecosystem. However, the reefs are periodically stressed by storm waves, and increases in sediment and dissolved substances from the Hanalei River have the potential to cause additional stress. Increased turbidity and sedimentation on corals during Hanalei River floods that occur in seasons of low wave energy, when sediment would not be readily remobilized and advected out of the bay, could affect the health and sustainability of coral reefs and the many associated species. Measurements of short-lived isotopes 7 Be and 137 Cs in sediment cores have been used to trace the thickness and distribution of terrestrial sediment in Hanalei Bay, in order to assess spatial and temporal patterns of sediment deposition and remobilization relative to coral-reef locations. A third isotope, 210 Pb, derived primarily from seawater, provides additional information about recent sedimentary history. Isotope profiles and observations of sedimentary facies from cores collected at multiple locations in June 2005, and again in August 2005, indicate the presence of recent fluvial sediment and organic debris in the east part of the bay near the mouth of the Hanalei River. Away from the immediate vicinity of the river mouth, sediment in the uppermost 1 m below the sea floor had not retained a significant quantity of fluvial sediment within the eight months prior to either sampling effort. During the study interval in summer 2005 the Hanalei River had no major floods and there was relatively little sediment input to the bay. Sediment away from the river mouth was dominated by carbonate sand, although some terrestrial sediment was present in sub-sea-floor horizons. Sedimentary facies and isotope inventories throughout the bay showed substantial spatial heterogeneity. Sediment cores will be collected again at the same sites discussed here during early and late summer 2006. If possible, additional sites will be sampled in the Black Hole depocenter near the river mouth. Major floods in winter and spring 2006 are expected to leave a significant new sediment signal in the bay that should be detected in summer 2006.

Hawaii↗