M.S. - Oceanography

Permanent URI for this collectionhttps://hdl.handle.net/10125/2125

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Contrasting metabolic responses to nutrient enrichment and thermal stress in Hawaiian corals
(University of Hawai'i at Manoa, 2025) Cranston, Shannon Keala Murphy; Jani, Andrea J.; Oceanography
Local-scale environmental factors on coral reefs, such as nutrient input, have varying effects on coral physiology and survivorship dependent upon sources, concentrations, and composition of enrichment. Anthropogenic inputs of excess nutrients, including effluent from sewage outfalls, promote algal dominance and are associated with coral reef decline. In contrast, natural nutrient enrichment from seabird guano has been argued to enhance coral growth rates and recovery from heat-induced coral bleaching. This study aimed to compare the effects of anthropogenic (primary-treated sewage effluent), seabird-derived (guano), and mineral (inorganic nitrogen salt) nutrient sources crossed with two weeks of 3ºC heat stress on the metabolism of two dominant coral species in Hawai‘i: Montipora capitata and Porites compressa. In M. capitata, guano enrichment increased productivity (net photosynthetic production, NPP, by 31% and gross photosynthetic production, GPP, by 26%) relative to unenriched controls with no changes to respiration rates under ambient temperature conditions. While heating depressed NPP by 48 and 66% for the inorganic nutrient-enriched and unenriched control M. capitata fragments, respectively, no equivalent thermal stress response was detected in effluent- and guano-enriched corals, suggesting these treatments dampened thermal stress. Four weeks after the heating event there was no detectable residual effect of prior heating on M. capitata metabolic rates: while the effluent- and guano-enriched corals maintained elevated photosynthetic rates, heated corals from each nutrient treatment had similar photosynthetic and respiration rates to their respective corals maintained at ambient temperatures. In contrast to M. capitata, P. compressa was initially unaffected by nutrient treatments alone, but was highly sensitive to heat stress, exhibiting 90-150% reductions in production and respiration rates across all nutrient treatments that lingered (3-39%) weeks after heating ended. During and following the heat stress, the nutrient enrichments generally manifested as decreased productivity relative to the controls, with no nutrient affects among thermally stressed corals, suggesting nutrient enrichment did not facilitate thermal recovery in Porites compressa. Our results highlight contrasting strategies of coral genera in utilizing organic and inorganic enrichment source compounds to influence primary production rates. The effects of guano, effluent, and inorganic nutrient sources in situ should be further contrasted before applying enrichment as a conservation method to promote thermal resilience
Turbulent kinetic energy dissipation rates at Station Aloha: Possible influences of eddies, wind, internal tides, and seasonality
(University of Hawai'i at Manoa, 2025) Adkison, Camille; Carter, Glenn; Oceanography
Turbulent kinetic energy (TKE) dissipation rates provide valuable insight into ocean mixing andits effect on biogeochemical processes, such as nutrient supply to the lower euphotic zone. This study investigates the conditions that lead to elevated TKE dissipation rates at Station ALOHA, focusing on the roles of mesoscale eddies, wind forcing, internal tides, and seasonal patterns. Using data from a lowered acoustic Doppler current profiler (LADCP), CTD casts, and shipboard ADCP (SADCP) collected during HOT cruises 299–328 (January 2018–March 2021), dissipation rates were calculated for each profile. Results show that dissipation rates are typically higher during winter months and lower in summer, suggesting seasonal influence. Elevated mixing frequently coincided with the presence of anticyclonic eddies, though a notable exception occurred during a cyclonic eddy event. These findings highlight the complex interplay of physical drivers influencing mixing, with implications for nutrient transport and the strength of the biological pump in the North Pacific Subtropical Gyre.
More realistic assessments of future exposure to high-tide flooding in American Samoa
(University of Hawai'i at Manoa, 2025) Baizeau, Carla; Thompson, Philip; Oceanography
American Samoa is experiencing the fastest rates of relative sea-level rise due post-seismic subsidence resulting from the 2009 earthquake. American Samoa is already undergoing severe flooding impacts and requires a planning tool to strategically adapt to future flooding conditions. Here, we propose a more realistic assessment of future exposure to high-tide flooding (HTF) compared to the already available sea-level rise viewers by including site-specific land subsidence projections (Han et al., 2019), several high-tide flooding frequencies, and an updated Digital Elevation Model (DEM). While land subsidence projections reduce the timing uncertainties of sea-level rise exposure, the DEM and HTF frequencies enhance the overall spatial extent of the exposed area. Choosing a less frequent HTF frequency, e.g., 50-days per year, provides a better representation of the useable area throughout the century. On the other hand, the majority of the more realistic subsidence impacts is felt within the next 50 years because of the trend of the projections. The American Samoa relative sea-level rise viewer publicly available on the PacIOOS website provides a risk/tolerance assessment of HTF exposure with a selection of sea-level rise scenarios, and HTF frequencies throughout the century. However, still water level, e.g., sea-level rise is not the only contributor to flooding. Total water level including still water level and the effects of waves can induce more damages on the coastline. The co-variability of wave power and sea-level was evaluated here, during the seasonal cycle and the dominant mode of Pacific tropical variability, i.e., El Niño Southern Oscillations (ENSO). Our analysis suggests that waves and sea-level can be treated independently in American Samoa.
Modeled Impacts of Wave Extremes and Sea Level Rise at Puʻuhonua o Hōnaunau National Historical Park, HI: a Probabilistic Analysis
(University of Hawai'i at Manoa, 2024) Sanchez, Ashley Hiilani; Thompson, Philip; Oceanography
Damaging waves have previously impacted Puʻuhonua o Hōnaunau National HistoricalPark, HI, a site of immense cultural and historical significance. The ongoing threat of sea level rise has brought forth concerns among park staff and stakeholders regarding the longevity of the park and specific areas of importance, especially during times of increased wave activity. This study investigates the combined impacts of sea level rise and extreme wave events at the park. In-situ observations of water level data are collected in coastal waters surrounding the park; however, the in-situ observations did not effectively validate the wave model. The water level data are nevertheless used to demonstrate the wave transformation phenomenon. An extreme value analysis is performed on a hindcast dataset using the Peaks Over Threshold method wherein a number of extreme events are identified. Using a phase-resolving numerical model, SWASH, coupled with high-resolution topobathymetric data, coastal inundation is simulated under two sea level rise scenarios: 0.3 m and 1 m. Simulations are also run over three extreme wave return periods used by the extreme value analysis: 1 year, 10 years, and 50 years. The SWASH model analyses show that sea level rise amplifies the effects of wave-driven flooding, threatening low-lying cultural assets and natural features, such as Hale o Keawe and the Heleipālala anchialine ponds. Effective measures to mitigate the impact of sea level rise and extreme waves on the park must be explored in a timely manner.
Programmable flow injection for shipboard nutrient analysis: Method validation from the International Nutrient Intercomparison Voyage.
(University of Hawai'i at Manoa, 2024) Davis, Madeline Nicole; Hatta, Mariko; Measures, Christopher I.; Oceanography
Expanding nutrient data availability in remote locations and during small-scale events is most feasible through in-situ, autonomous sampling method. However, traditional flow-based analyzers, which are actively used in current oceanographic research cruises, face laminations, as they cannot be easily scaled down or made autonomous. Their large waste generation and dependency on user intervention present significant obstacles to technological advancement. The lack of alternative streamlined methods complicates sampling strategies and introduces logistical challenges. In these contexts, there is a pressing need for novel, yet straightforward instrumentation to gather data with reliably and at high frequencies. Programmable flow injection (pFI) represents a new generation of automated flow-based techniques aimed at improving the spatial-temporal distribution of nutrient data through rapid shipboard determinations. This work introduces innovations to the pFI method, including automated creation of a five-point standard curve using a single high concentrated standard solution, applying this to the oceanographic research cruises, including the International Nutrient Intercomparison Voyage (INIV) and the Hawaiian Ocean Time-series (HOT). These results yielded consistent and agreeable data with standard nutrient methods, indicating a promising outlook for integration of this new technology for regular nutrient measurements.
Evaluating species-specific naupliar recruitment during the winter-to-spring transition in the Northern Gulf of Alaska using molecular tools
(University of Hawai'i at Manoa, 2024) Block, Lauren Nicole; Lenz, Petra H.; Oceanography
The Gulf of Alaska is a highly seasonal environment that is characterized by an order-of-magnitude increase in copepod biomass in the photic zone between winter and spring. Copepod recruitment processes, including the location and timing of naupliar production, responsible for the transition from low-biomass winter conditions to the highly productive spring are not well characterized. The recruitment patterns of copepod nauplii were examined in Resurrection Bay, Alaska using biweekly sampling between January and March with zooplankton collected from three depth strata. Nauplii were identified using DNA metabarcoding and species-specific naupliar phenologies were contextualized with environmental data and copepodite and adult copepod population data. This study revealed that nauplii were abundant throughout the winter and were comprised of a diverse assemblage of species. The community composition changed over the course of the season, with different copepod species exhibiting three distinct naupliar phenologies. These include species with nauplii that were 1) present during the winter and absent during the spring, 2) absent during the winter and present during the spring, and 3) present during both winter and spring. Several closely related species were split across groups, revealing temporal niche partitioning of reproduction and naupliar phenologies. For most species in the third group, the presence of nauplii during the winter occurred despite the absence of ovigerous females. While ovigerous females may have been missed or the nauplii could have been sourced from reproductive populations outside of Resurrection Bay, it is also possible that some copepods overwinter as nauplii. Prior to the spring phytoplankton bloom, a moderate increase in chlorophyll α concentrations occurred during March, coinciding with a period of female maturation, an increase in naupliar abundances, and the appearance of later developmental stages. These observations suggest smaller increases in chlorophyll prior to the large spring bloom may be critically important to recruitment of copepod nauplii, their survival, and their growth.
Applications of the Underwater Vision Profiler for Particle Annotation in the Oligotrophic North Pacific Subtropical Gyre
(University of Hawai'i at Manoa, 2024) James, Reece Charles; White, Angelicque; Oceanography
Machine learning algorithms (MLAs) are increasingly applied to optical imaging datasets of oceanic plankton and marine aggregates to obtain improved image annotation efficiency while preserving high annotation consistency. However, this process relies on an ever-decreasing number of expert morphological taxonomists to annotate training sets and validate MLA outputs. While recent attention has focused on training annotators on how to use machine learning algorithms, there has been limited effort to educate new annotators on how to annotate the datasets needed to train and verify such algorithms. By teaching new annotators how to create regionally-relevant and accurate training sets for MLAs, one could better utilize instruments, such as the Underwater Vision Profiler 5 HD (UVP), that are the basis for growing databases of images collected over an expanding set of temporal and regional studies. The UVP is a high resolution in situ camera-based instrument that samples particles above 0.064 mm up to ~54 mm, producing images for those particles that are > 0.5 mm. The UVP images a size fraction of fragile plankton and marine aggregates known to play an important role in the Biological Carbon Pump (BCP) and can quantify their vertical distribution, changing morphological characteristics, and visual interactions from the sea surface to ~6000 db. In this study, the UVP has been used to assess particle distributions on 14 Hawaiʻi Ocean Time-series (HOT) cruises between 2020 to 2023 at Station ALOHA (22.750N, 158.00 0W). Significant findings from this initial effort include - (1) seasonal changes in the slope of particle size distributions evidence summer (June – August) increases in the abundance of large particles, (2) subsurface peaks of large particles were frequently observed at the base of the euphotic zone between 100 to 150 db which we interpret to be the accumulation of sinking particles along isopycnals, and (3) in moving towards assessing organismal abundance, it became apparent that an annotation guide for the UVP was not available to the user community. To facilitate further research, we identified key classifiers for our region including 13 categories of organismal and detrital UVP images, including the genus Trichodesmium, Rhizaria, and marine aggregates. We then outlined a method and standards for development of a cooperatively annotated dataset with intra-annotator self-consistency. Individual annotations were made by two annotators and then compared to a cooperatively annotated dataset, displaying 87.6% and 88.1% agreement. Comparing the annotations made between annotator’s individual datasets, the agreement was 85.2%. In comparison, predictions by a machine learning algorithm tailored to the UVP, the EcoTaxa random forest, had only 31% precision. With this manually annotated dataset, the temporal and spatial patterns of aggregates and organisms were then assessed. One pronounced pattern observed was that marine aggregates were found in concentrations more than double that of organismal categories with peaks in concentration at the mixed layer boundary. Further research will investigate co-occurrence patterns and potential relationships with regional hydrodynamics and climate indices as the time-series of UVP data lengthens. Importantly, the standardized UVP annotation schema developed herein will allow increasingly large optical datasets collected by the HOT program to be annotated by multiple annotators. This will reduce the overall time spent manually annotating images and facilitate consistency across datasets. The classification guide and annotation pipeline described here maximizes the potential research questions that can be addressed with the large datasets generated by the UVP and outlines a path for new users in different regions to generate their own classification guides and annotation pipelines.
ADAPTATION OF AUTONOMOUS SENSORS TO EVALUATE A MESOCOSM SETUP FOR EXAMINING HAWAIIAN CORALS UNDER VARIOUS CHEMICAL PERTERBATIONS
(University of Hawai'i at Manoa, 2024) Morris, Ally; Sabine, Christopher L.; Oceanography
Marine ecosystems, such as coral reefs, are sustained by positive net community calcification, but calcification is impeded by Ocean Acidification (OA), which alters ocean chemistry and disrupts the ability of calcifying organisms to maintain their calcium carbonate skeletons. Mesocosm experiments were performed at the Hawai’i Institute of Marine Biology in Kāneʻohe Bay, Oʻahu to investigate if calcification is limited by carbonate ions or waste protons from calcification. These studies often involve labor-intensive discrete measurements, which can be limited in sample number and often require a long bench time to analyze (15 - 30 minutes). In response to this challenge, two low-cost waterproof housings of the autonomous Honeywell Durafet® pH sensor were created and deployed in mesocosm tanks from June to August of 2023 to (1) quantify spatial variability of pH in tanks under OA simulated and ambient conditions, and (2) to evaluate predictors of Net Community Calcification (Gnet) in tanks under three different OA scenario treatments, coupling elevated pCO2 with high, low or ambient Total Alkalinity (AT). To evaluate spatial variability in the tanks, high frequency pH measurements (~20 sec) were made every 17.78 centimeters (seven inches) around the tank perimeter at top, middle and bottom depths. Spatial measurements showed that tanks were not chemically homogenous as pH and corals were driving benthic patterns in the tank. Furthermore, autonomous measurements and discrete samples (taken via an automatic sampler) of bulk mesocosm seawater showed that major independent predictors of Gnet in treatments of high and low AT and high pCO2 were the aragonite saturation state (Ωa) and Net Community Production (Pnet). The work presented here provides detailed information about mesocosm tank dynamics and coral response that will be useful for future mesocosm experiments.
Unraveling coral nutrition strategies in response to nuisance macroalgae: insights from amino acid isotopic analysis in the Northwestern Hawaiian Islands
(University of Hawai'i at Manoa, 2024) Kaluhiokalani, Mario; Popp, Brian; Oceanography
Coral reef ecosystems are under increasing threat from local and global stressors, including the introduction and proliferation of invasive species. Understanding coral nutrition strategies in response to environmental stress is crucial for predicting reef resilience. This study investigates the impact of macroalgal cover, specifically the nuisance red alga Chondria tumulosa, on nutritional strategies of two corals (Montipora capitata, Pocillopora spp.) in the Northwestern Hawaiian Islands (NWHI). Coral samples were collected pre- and post-invasion of C. tumulosa, with bulk tissue and compound-specific isotopic analysis of amino acids (CSIA-AA) employed to assess coral nutrition. Bulk carbon and nitrogen stable isotopic compositions (δ13C, δ15N) revealed coupled nutritional reliance between coral host and symbiont with a consistent δ13C decrease with depth. CSIA-AA demonstrated significant separation in essential amino acid δ13C fingerprints between coral hosts, symbionts, plankton, and C. tumulosa relating to autotrophic fidelity in M. capitata and trophic plasticity in Pocillopora consistent with previous work. Trophic position (TPGlx-Phe) of plankton was 2.3±0.6, consistent with primary consumers, while coral TPGlx-Phe indicate high reliance on autotrophy in M. capitata (TPGlx-Phe: 1.1±0.2) and greater heterotrophic feeding on plankton in Pocillopora spp. (TPGlx-Phe: 1.6±0.4). A higher-than-expected TPGlx-Phe was found in C. tumulosa (1.5±0.1), suggesting inclusion of heterotrophic bacteria living on or among the macroalgae. It is unlikely that Pocillopora spp. obtained nutrition directly from C. tumulosa, however, our work suggests that essential amino acid δ13C values can be used to identify organisms that prey on C. tumulosa. These findings underscore the importance of understanding coral-algal interactions in the face of environmental change and highlight the utility of CSIA-AA in elucidating complex trophic dynamics within coral reef ecosystems.
Scale Separation of the Mechanism of Wind Response to Sea SurfaceTemperature in the Northern Equatorial Pacific
(University of Hawai'i at Manoa, 2024) Naeemullah, Stacey; Schneider, Niklas; Oceanography
The dynamics of air-sea interaction in the mesoscale have a two-fold scale separation. In physical space, basin scale and mesoscale winds have opposing responses to SST: negative correlation on the basin scale and positive correlation in the mesoscale. In wavenumber space, there is a further scale separation delineated by Rossby number, $R_0=\frac{U}{fL}$. At $R_0 \geq +1$, turbulent mixing processes, spatially in phase with SST, govern the dynamics; at $R_0 \ll 1$ pressure gradient responses, spatially phase shifted from SST, predominate. Spectral transfer functions can be used to elucidate these dynamics using the regression coefficient between SST and wind response in wavenumber space. Similar to prior research in the low and mid-latitudes, transfer functions for the Eastern Equatorial Pacific about tropical instability waves show distinct scale separation with increasing wind speeds. Impulse response functions show the hypothesized dynamics based on the scale-dependent signals in the transfer functions. When winds are reconstructed using impulse response functions for $R_0\ll1$ and $R_0\geq1$, the results are consistent with expected dynamics for pressure gradient response and vertical mixing response, respectively. $f$-scaling shows similar rotation dependent dynamics, supporting the conclusion of $R_0$ scale separation of the dynamics of wind response to SST.
NUMERICAL SENSITIVITY EVALUATION OF THE PHASE-RESOLVING WAVE MODEL SWASH AND ITS APPLICABILITY IN AN OPERATIONAL FORECAST ENVIRONMENT FOR REEF-LINED COASTS
(University of Hawai'i at Manoa, 2024) Gibbs, Jatasey Alexander; Thompson, Philip PT; Oceanography
An evaluation of the Simulating WAves till SHore (SWASH, Zijlema, 2011) spectral wave-flow model on the north shore of Oahu, Hawaii, was conducted to determine sensitivity to various numerical settings and grid configurations. It also aimed to assess what could be achievable in an operational forecasting environment, such as NOAA’s National Weather Service Forecast Offices, with regard to computational expenses involved. Spatial resolution, water level, boundary conditions, friction, and the computational time window were analyzed and compared across a two-dimensional (2D) grid and along a one-dimensional transect. Water elevations derived from these tests were evaluated at a nearshore point that remained wet throughout the simulations and used to compare bulk-averaged output parameters that included: sea and swell height, wave setup, infragravity wave height, and the two-percent exceedance wave height. The sensitivity of these bulk quantities to model framework decisions that impact computational expense pose immense challenges for implementation in an operational forecast environment. We present results demonstrating how forecast sites can balance operational feasibility and accuracy.
O KE KAHUA MA MUA, MA HOPE O KE KŪKULU: IMPACTS OF A DECADE OF BIOCULTURAL RESTORATION ON AQUATIC BIOGEOCHEMISTRY AND DIATOM COMMUNITY ABUNDANCE IN HEʻEIA FISHPOND
(University of Hawai'i at Manoa, 2023) Beebe, Charles Albert Kaiaka; Alegado, Rosanna A.; Oceanography
Biocultural restoration and Indigenous resource management that benefit coupled natural-human ecosystems has recently gained attention as an alternative to nature-only based approaches. In Hawaiʻi, Native Hawaiian stewardship of ʻāina has also regained traction; yet, few large-scale efforts have evaluated the ecosystem shifts that result from biocultural restoration. In this contribution, we assess shifts in physical and biogeochemical conditions concomitant with over a decade of biocultural restoration at Heʻeia Fishpond, a traditional Hawaiian mariculture system built in an estuary of Koʻolaupoko, Oʻahu. Using discrete sampling of nutrients and quantification of diatom abundance, we further link customary management practices with potential for primary production in this estuarine system. We hypothesized that biocultural restoration, including but not limited to the removal of invasive vegetation and rebuilding of traditional fishpond structures, engendered environmental conditions that increased the potential ecological capacity for efficient food web dynamics required for production of target fish species. We found that restoration increased freshwater input, particularly during the wet season, associated with increased diatom abundance. Furthermore, these infrastructure changes increased the horizontal spatial homogeneity of water quality conditions, allowing increased access to freshwater and nutrients throughout the fishpond with positive implications for resource management. These data parameterize the results of biocultural restoration into metrics that can be applied to other coastal ecosystems undergoing restoration, providing a model for increasing ecosystem resilience in the face of climate change.
Satellite-based Assessments Of Ocean Acidification For The Hawaiian Islands Region
(University of Hawaii at Manoa, 2023) Jackson, Caroline; Sabine, Christopher L.; Oceanography
Ocean acidification (OA) is a growing global environmental concern with impacts affecting regions all over the world, including remote areas such as Hawai‘i. OA is gaining worldwide attention due to environmental impacts including the detrimental effects of OA on coral reefs. Increased anthropogenic release of CO2 into the atmosphere will result in increased absorption by the world oceans. There is a general lack of information regarding small-scale spatiotemporal variations in surface ocean carbon parameters, however satellites and other remote sensing platforms are becoming increasingly utilized for Earth system observations and can be used to help evaluate OA patterns around Hawai‘i. With the use of empirical algorithms, remote measurements of sea surface temperature (SST) and sea surface salinity (SSS) can be used to assess OA patterns in coastal and open-ocean waters around the state. For the purposes of this study, in situ data collected from mooring buoys and ship studies are used to develop empirical algorithms that relate satellite observations to OA conditions for the Hawaiian Islands region (HIR).
Controls On Isotopic And Elemental Incorporation Of Lithium In Inorganic Calcium Carbonates
(University of Hawaii at Manoa, 2023) Hite, Corinne; Uchikawa, Joji; Oceanography
There is increasing interest in using the δ7Li value of marine biogenic CaCO3 (i.e., foraminifera tests) as a tracer for secular changes in silicate weathering, an important process in sequestering atmospheric CO2. However, culture studies have suggested the possibility of additional controls on Li incorporation in foraminiferal CaCO3, indicating a need to better understand the physical and chemical controls on Li incorporation in inorganic CaCO3 without the complications of vital effects from a biological system. To this end, the present study conducted inorganic calcite and aragonite precipitation experiments with systematic manipulations of solution chemistry parameters (pH, [DIC], and [Ca2+]) using a pH-stat system. Both calcite and aragonite samples had lower δ7Li values than the δ7Li value of dissolved Li in the experimental solution, indicating preferential uptake of the lighter isotope (6Li) in carbonate minerals. This is presumably due to the tetrahedral coordination of Li bound with water molecules in solution resulting in the strongest bonds. Aragonite consistently had δ7Li values lower than calcite, likely due to differences in Li coordination within the crystal lattice and the resulting bond strength. There was an observed effect on the Li isotopic fractionation in aragonite samples with changes in pH, [DIC], and [Ca2+]. Additionally, a significant relationship was found between the Li isotopic fractionation in calcite samples and pH. Despite being statistically significant, these relationships were weak and resulted in a minimal overall effect on fractionation compared to the experimental uncertainty. There was no clear relationship observed between precipitation rate and fractionation, suggesting fractionation is dominated by equilibrium effects rather than kinetic effects. Overall, the present study has implications for the use of Li in carbonate minerals as a proxy tool for silicate weathering. In particular, while precipitation rate and solution chemistry may not dramatically influence Li isotope fractionation in inorganic calcite, biological vital effects may play a significant role and should be further evaluated in order to confidently use Li isotopes for silicate weathering reconstructions.
Chlorophyll Bloom Dynamics and Associations with Mesoscale and Submesoscale Features in the North Pacific Subtropical Gyre
(University of Hawaii at Manoa, 2023) Ash, James Patrick; White, Angelicque; Oceanography
Large summer chlorophyll blooms spanning hundreds of square kilometers and persisting for weeks-months, are consistently observed in satellite records of the Northeast Pacific Subtropical Gyre (NPSG), at an approximate latitude of ~30°N. These blooms occur at a near annual rate, and uniquely within the late summer months of June-October. Understanding the potential impacts and biophysical drivers of these chlorophyll anomalies is both ecologically and climatologically important. These large-scale blooms can export carbon from the upper ocean to the deep ocean and fuel the productive fisheries found in the ecologically important transition zone between the North Pacific Subtropical Gyre and the subpolar gyre. The purpose of this project is to characterize chlorophyll blooms in the NE Pacific Gyre, as well as describe their association with submesoscale and mesoscale features to identify potential physical drivers. First, an analysis of the merged satellite CHL product is done to characterize the magnitude, frequency, and geographic location of chlorophyll blooms in the NPSG. Then the sea level anomaly (SLA) and finite sized Lyapunov exponents (FSLE) were used to identify sub-mesoscale and mesoscale features i.e. fronts, anti-cyclonic eddies, and cyclonic eddies. Through this process, we provide a quantitative characterization of chlorophyll anomalies in the NPSG. Further analyses present a case-study time-series of the 2018 bloom in order to better understand the time resolved change in phytoplankton biomass and how it relates to physical drivers of biomass growth and accumulation. To achieve this, a generalized additive model (GAM) is used to determine the effects of SLA and SSTA on the CHL anomaly signal of the 2018 plankton bloom.
Wave Energy Transformations In A Complex Reef Environment; Observations, Modeling And Applications
(University of Hawaii at Manoa, 2023) Tognacchini, Camilla; Luther, Douglas S.; Oceanography
Wave-driven runup events are severely impacting West Maui’s (WM) coastline with episodic inundation and chronic erosion. A combination of background sea level, tides and wave driven components, such as setup and infragravity (IG) wave energy, contribute to the level of runup experienced at the shore. The setup, swash and IG wave responses under different sea and swell forcing conditions are highly variable along the WM coastline, due to complex nearshore bathymetry. Simulating the setup, swash, and IG wave energy responses to large swell events at different locations along the WM coast is necessary for accurate calculation of runup, enabling forecasting of, and community preparation for, these coastal inundation events. The PacIOOS Coastal Hazards Group has implemented a two-dimensional, fully-nonlinear and weakly dispersive, phase resolving numerical wave model (Boussinesq Ocean and Surf Zone; Roeber and Cheung, 2012), using high resolution bathymetry and topography of WM. The model simulates the cross- and along-shore transformations of gravity and IG wave energy for simulation of runup. The main objective of this study is to validate the model for the WM domain against observations of swell events. Nearshore sea level observations are derived from bottom water pressure records collected at different depths (1-13 meters) and locations along the West Maui coastline, from November 2018 - June 2020. Comparisons between in situ observations and co-located virtual stations within the model reveal a high degree of agreement in both the sea and swell and IG period bands, between 8 seconds and up to 10 minutes. Spectral analysis is used in the comparisons to investigate the spatial variability of the wave energy. A series of sensitivity tests using variable model resolutions shows that the choice of a 5 x 5 meter grid is optimal for this domain. Observations and model comparisons are discussed for both a North swell and a South swell event at six different locations along the WM coastline, including two relatively compact arrays. The simulation for the North swell is in better agreement with observations on the northern coast of WM (at Oneloa, Nāpili and Kahana). Similarly, the simulation for the South swell is in better agreement with observations in the southern area of WM (at Puamana and Olowalu). The comparisons reveal the high IG amplitude variability alongshore resulting from complicated IG wave patterns, which are generally well simulated in the model. At both arrays the comparisons of coherence phase and amplitude of the observations and model reveal the model is simulating well the frequency-dependent, spatial variability of the nearshore wave-driven phenomena that contribute to runup. The few occasions where the simulation is unimpressive suggest that ways to improve the model methodology should be investigated.
Distribution and community structure of deep-sea demersal fish assemblages across the central Pacific Ocean using ROV data
(University of Hawaii at Manoa, 2023) Selig, Gina Morgan; Drazen, Jeffrey C.; Oceanography
Four Marine National Monuments exist within the Pacific Islands region including the Papahānaumokuākea Marine National Monument, the Marianas Trench, Pacific Remote Islands, and Rose Atoll Marine National Monuments. Together these make up an area of 3,063,223 square kilometers; however significant knowledge gaps remain regarding the distribution and community composition of fishes, especially deeper than 500 meters. With the additional threats of global change, fishing, and deep-sea mining, there is a need to characterize these communities for conservation and management purposes. The remoteness of deep-sea habitats has resulted in deep-sea fishes being poorly sampled globally, with most descriptions of demersal fish communities focused along temperate continental margins. Demersal deep-sea fish communities from islands and seamounts are poorly described, even in the Hawaiian archipelago. Knowledge across all depths, in similar settings, is even more sparse for other archipelagos in the central Pacific. However, recent remotely operated vehicle (ROV) explorations of the central Pacific and archived video from submersible dives conducted by the Hawai`i Undersea Research Laboratory (HURL) provide an opportunity to explore the structure of these communities. Here we describe demersal fish communities from archipelagos across the tropical Pacific, including in multiple Marine National Monuments, and examine the relationship of the assemblages to depth and environmental conditions. We used data collected from 227 dives conducted by underwater vehicles resulting in the identification of 24,837 individuals belonging to 89 families and 175 genera across regions for depths ranging from 250-3000 m. The most frequently occurring genera between 250-500 m were Epigonus, Setarches, Polymixia, and Antigonia, between 500- 1000 m were Chlorophthalmus, Aldrovandia, and Neocyttus, and between 1000-3000 m were Synaphobranchus, Kumba, Halosaurus, Ilyophis, and Ipnops. There are strong changes in the fish communities with depth, and communities become more similar between regions with greater depth. Depth explained the most variance in community composition followed by water mass distributions, seafloor particulate organic carbon flux (a food supply proxy), concentrations of dissolved oxygen, and salinity. The Line Islands and Tokelau Ridge had the highest values of seafloor particulate organic carbon flux for all depth zones investigated (250-3000 m) and the highest abundance of fishes at 250-500 m and 500-1000 m, respectively. Accumulation curves indicated that diversity at the genus level within all regions and depth bins (except 1000-2000 m and 2000-3000 m) had not been reached with the existing sampling effort. However, when combining samples from all regions, diversity generally appeared to decrease with depth. Overall, this study demonstrates that there are significant regional differences in the composition of the deep-sea fish fauna as well as differences across depth. Such distribution patterns suggest that existing Marine National Monuments are not replicates of diversity, but complementary components of the regional diversity. The effectiveness of the Monuments in protecting deep-sea fish communities will depend on the spatial distribution and depths of human-caused disturbances such as climate change and deep-sea mining, therefore we suggest further sampling in the regions to fully characterize the communities and better define boundaries and gradients of faunal change.
Spatial and Temporal Variability in the Carbon and Oxygen Systems in an Indigenous Aquaculture System: Heʻeia Fishpond, Oʻahu, Hawaiʻi
(University of Hawaii at Manoa, 2022) Lechner, Evan; Sabine, Christopher L.; Oceanography
Carbon and oxygen are integral components in a range of organic and inorganic coastal processes. Variability in carbon and oxygen systems can be driven by a range of temporal and spatial factors. The following report is composed from the results of a 12-month study assessing the magnitude of spatial and temporal variability in the carbon and oxygen systems within an Indigenous Hawaiian aquaculture system at Heʻeia Fishpond, located on the western edge of Kāneʻohe Bay. We observe patterns in the spatial variability of both DIC and % O2 saturation between north and south mixing regions within the pond. An analysis of the ΔTA/ΔDIC relationship of the observed spatial variability revealed that aerobic respiration was the dominate metabolic pathway, particularly in the south of the pond. The respiration signal was identified across the 12-month field campaign, in addition to tidal and diel temporal cycles. During neap tide sampling the respiration signal was typically measured as a drawdown of oxygen and an increase in dissolved inorganic carbon originating in the benthos. However, both diel field measurements and carbon parameter analysis suggest that the spatial signal in DIC and % O2 includes both respiration and production in comparable measure. Given the observation of in-situ regimes of significant respiration and production, the typically observed respiration signal must be driven by the benthic metabolism of autochthonous organic matter. Likewise, while the spatial respiration signal in carbon and oxygen was observed throughout the field campaign, it was observed to weaken during the spring tide. The variability in the strength of the respiration signal caused by tidal flux, particularly from Heʻeia Stream, suggests that the physical dynamics of flow direction and residence time within the pond are sensitive to both tidal flushing and elevated streamflow. Taken together, the spatial and temporal variability observed in this project demonstrate the potential for sheltered estuarine ecosystems to develop microenvironments of biogeochemical change. At Heʻeia we observed that such microenvironments seemed to be connected to both the flow of water from Heʻeia stream and the location of invasive mangroves and algae. Both the enhancement of streamflow and invasive species removal are targets of the ongoing restoration work at Heʻeia. Our data suggests that continued progress towards these goals is likely to reduce the significance of low % O2 saturation and elevated DIC associated with the respiration signal we observed by equalizing residence time across the fishpond and removing the benthic algae that may be one of the drivers of the signal.
Quantifying the Mesoscale Rectification of Latent Heat Flux
(University of Hawaii at Manoa, 2022) Donaldson, Bailey Carole-Levien; Schneider, Niklas; Oceanography
Ocean mesoscale fronts and eddies can impact large scale features due to nonlinear rectification. This project quantifies the rectification of ocean mesoscale sea surface temperature, wind speed, and specific humidity to the large-scale latent heat flux. We quantified nonlinearities caused by (1) the Clausius Clapeyron relation, (2) the positive correlation of sea surface temperatures and wind speed at the mesoscale, and (3) the covariability of wind speed and specific humidity. A Taylor Expansion to the second order of the latent heat flux around the large-scale wind speed, sea surface temperature, and specific humidity is used to estimate the nonlinear rectification of the three nonlinearities for the Gulf Stream, Kuroshio Extension, and Agulhas Return Current. We conducted two trials. Trial 1 utilized satellite observations of wind speed, sea surface temperature, and an estimated specific humidity to calculate nonlinearity (1) and (2). Trial 2 utilized ERA5 reanalysis of wind speed, sea surface temperature, and specific humidity to calculate all three nonlinearities. The average of the rectification terms are small for each trial, and generally range from -0.5 to 1.8 W/m^2 with some regional exceptions. Results indicate that in Trial 1, the rectification from Clausius Clapeyron ranges from 0.09 to 3.85 W/m^2 and the rectification from the sea surface temperature-wind covariability ranges from -4.06 to 4.39 W/m^2 depending on the region. In Trial 2, the rectification from Clausius Clapeyron ranges from 0.05 to 3.74 W/m^2, the sea surface temperature-wind covariability ranges from -14.92 to 14.19 W/m^2, and the wind-specific humidity covariability ranges from -9.30 to 7.91 W/m^2. Results find that the Clausius Clapeyron term exhibits a dependence on background wind speed and both covariability terms exhibit a dependence on wind direction. All rectification terms exhibit a strong dependence on filter size and humidity. The Taylor Expansion in Trial 1 had a low error, however, the results from Trial 2 were highly variable and exhibited a large error that is directly related to the Clausius Clapeyron term. On large spatial and temporal averages, the rectification is modest but can be important at times over strong mesoscale sea surface temperature variance and under particular background wind conditions.
Effects of nutrient supply on metabolic rates in the oligotrophic ocean: Insights from a long-term and large-scale incubation experiment
(University of Hawaii at Manoa, 2022) Salazar Estrada, Andrés Esteban; Ferrón, Sara; Oceanography
Phytoplankton in the surface ocean account for nearly half of all the primary production on Earth, while accounting for less than 1% of terrestrial plant biomass. This outsized importance makes determining the rates at which organic matter is produced and consumed in the surface ocean paramount to constraining the global carbon cycle. To understand the effects of nutrient supply and nutrient supply ratio on oligotrophic microbial communities, a collaborative, long-term (30 days) manipulation experiment was undertaken in Honolulu, Hawai‘i. Between August and September of 2021, 24 large scale (~120 L) incubators were provided with 7 daily nutrient addition treatments, plus a control, in triplicate, while monitoring the rates of gross oxygen production (GOP), daytime respiration in the light (LR), daytime respiration in the dark (DR), and net oxygen change (NOC). Our results show significant increases in GOP (9 to 14-fold) for the treatments provided with inorganic nitrogen, as well as a shift to more autotrophic conditions. The addition of inorganic phosphorus had a much smaller but noticeable effect in GOP during the experiment, suggesting the possible enhancement of photosynthesis by N2-fixation. The addition of iron did not show any significant effect on metabolic rates. LR was estimated to be on average 30% greater than DR measurements throughout the experiment—with the difference between the two increasing with GOP. The difference between both estimates of respiration could be indicative of diel variations in community respiration, which has implications for properly constraining the carbon cycle in aquatic ecosystems.

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