Search

Coastal and ocean acidification can alter ocean biogeochemistry, with ecological consequences that may result in economic and cultural losses. Yet few time series and high resolution spatial and temporal measurements exist to track the existence and movement of water low in pH and/or carbonate saturation. Past acidification monitoring efforts have either low spatial resolution (mooring) or high cost and low temporal and spatial resolution (research cruises). We developed the first integrated glider platform and sensor system for sampling pH throughout the water column of the coastal ocean. A deep ISFET (Ion Sensitive Field Effect Transistor)-based pH sensor system was modified and integrated into a Slocum glider, tank tested in natural seawater to determine sensor conditioning time under different scenarios, and validated in situ during deployments in the U.S. Northeast Shelf (NES). Comparative results between glider pH and pH measured spectrophotometrically from discrete seawater samples indicate that the glider pH sensor is capable of accuracy of 0.011 pH units or better for several weeks throughout the water column in the coastal ocean, with a precision of 0.005 pH units or better. Furthermore, simultaneous measurements from multiple sensors on the same glider enabled salinity-based estimates of total alkalinity (AT) and aragonite saturation state (ΩArag). During the Spring 2018 Mid-Atlantic deployment, glider pH and derived AT/ ΩArag data along the cross-shelf transect revealed higher pH and ΩArag associated with the depth of chlorophyll and oxygen maxima and a warmer, saltier water mass. Lowest pH and ΩArag occurred in bottom waters of the middle shelf and slope, and nearshore following a period of heavy precipitation. Biofouling was revealed to be the primary limitation of this sensor during a summer deployment, whereby offsets in pH and AT increased dramatically. Advances in anti-fouling coatings and the ability to routinely clean and swap out sensors can address this challenge. The data presented here demonstrate the ability for gliders to routinely provide high resolution water column data on regional scales that can be applied to acidification monitoring efforts in other coastal regions.

Coastal and ocean acidification can alter ocean biogeochemistry, with ecological consequences that may result in economic and cultural losses. Yet few time series and high-resolution measurements exist to track the existence and movement of water low in pH and/or carbonate saturation. Past acidification monitoring efforts have either low spatial resolution (mooring) or high cost and low temporal and spatial resolution (research cruises). Therefore, there is a critical need to deploy new, cost-effective technologies that can routinely provide high resolution water column data on regional scales in our coastal ocean. We developed the first integrated glider platform and sensor system for sampling pH in the water column of the coastal ocean. A Deep-Sea ISFET (Ion Sensitive Field Effect Transistor) pH sensor system was modified and integrated into a Slocum G2 glider and tested during a deployment in the Mid-Atlantic Bight. Measurements of pH exhibited a time lag that shifted during the deployment, but shifts were applied to correct pH. Glider pH and spectrophotometric pH measured in discrete water samples were in good agreement for some comparisons but not others, and those offsets were likely the result of delayed or incomplete conditioning (at deployment start) or mismatches due to water sampling techniques. Glider pH data along the cross-shelf transect revealed higher pH associated with the depth of chlorophyll and oxygen maximums and a warmer, saltier water mass. Lower pH occurred in bottom waters of the middle shelf and slope, and nearshore following a period of heavy precipitation. These results demonstrate the application of glider-based acidification monitoring in other coastal regions, providing the foundation of what could become a national acidification monitoring network.

The pigment absorption peak in the red waveband observed in phytoplankton and particulate absorption spectra is primarily associated with chlorophyll- a and exhibits much lower pigment packaging compared to the blue peak. The minor contributions to the signature by accessory pigments can be largely removed by computing the line height absorption at 676 nm above a linear background between approximately 650 nm and 715 nm. The line height determination is also effective in removing the contributions to total or particulate absorption by colored dissolved organic matter and non-algal particles, and is relatively independent of the effects of biofouling. The line height absorption is shown to be significantly related to the extracted chlorophyll concentration over a large range of natural optical regimes and diverse phytoplankton cultures. Unlike the in situ fluorometric method for estimating chlorophyll, the absorption line height is not sensitive to incident irradiance, in particular non-photochemical quenching. The combination of the two methods provides a combination of robust phytoplankton biomass estimates, pigment based taxonomic information and a means to estimate the photosynthetic parameter, E K , the irradiance at which photosynthesis transitions from light limitation to light saturation.

The biological and physical processes contributing to planktonic thin layer dynamics were examined in a multidisciplinary study conducted in East Sound, Washington, USA between June 10 and June 25, 1998. The temporal and spatial scales characteristic of thin layers were determined using a nested sampling strategy utilizing 4 major types of platforms: (1) an array of 3 moored acoustical instrument packages and 2 moored optical instrument packages that recorded distributions and inten- sities of thin layers; (2) additional stationary instrumentation deployed outside the array comprised of meteorological stations, wave-tide gauges, and thermistor chains; (3) a research vessel anchored 150 m outside the western edge of the array; (4) 2 mobile vessels performing basin-wide surveys to define the spatial extent of thin layers and the physical hydrography of the Sound. We observed numerous occur- rences of thin layers that contained locally enhanced concentrations of material; many of the layers per- sisted for intervals of several hours to a few days. More than one persistent thin layer may be present at any one time, and these spatially distinct thin layers often contain distinct plankton assemblages. The results suggest that the species or populations comprising each distinct thin layer have responded to different sets of biological and/or physical processes. The existence and persistence of planktonic thin layers generates extensive biological heterogeneity in the water column and may be important in maintaining species diversity and overall community structure.

A model based on Mie theory is described that estimates bulk participate refractive index n¯p from in situ optical measurements alone. Bulk refractive index is described in terms of the backscattering ratio and the hyperbolic slope of the particle size distribution (PSD). The PSD slope ξ is estimated from the hyperbolic slope of the particulate attenuation spectrum γ according to the relationship γ ≈ ξ − 3, verified with Mie theory. Thus the required in situ measurements are the particulate backscattering coefficient, the total particulate scattering coefficient, and the particulate attenuation coefficient. These parameters can be measured with commercially available instrumentation with rapid sampling rates and real-time data return. Application of the model to data from the Gulf of California yielded results that agreed with expectations, e.g., predicted n¯p was 1.04–1.05 in the chlorophyll maximum and 1.14–1.18 near sediments. Below the chlorophyll maximum in case I type waters, predicted n¯p values were between 1.10 and 1.12, suggesting the presence of a significant inorganic mineral component in the background or detrital organic particles with low water content.

Spectral attenuation and absorption coefficients of particulate matter and colocated hydrographic measurements were obtained in the Mid-Atlantic Bight during the fall of 1996 and the spring of 1997 as part of the Coastal Mixing and Optics experiment. Within the bottom boundary layer (BBL) the magnitude of the beam attenuation decreased and its spectral shape became steeper with distance from the bottom. Concurrently, the slope of the particulate size distribution (PSD) was found to increase with distance from the bottom. Changes in the PSD shape and the magnitude of the beam attenuation as functions of distance from the bottom in the BBL are consistent with particle resuspension and settling in the BBL, two processes that are dependent on particle size and density. For particles of similar density, resuspension and settling would result in a flattening of the PSD and an increase in the beam attenuation toward the bottom. In both fall and spring the magnitude of the particle attenuation coefficient correlates with its spectral shape, with a flatter shape associated with higher values of the attenuation. This observation is consistent with idealized optical theory for polydispersed nonabsorbing spheres. According to this theory, changes in the steepness of the particle size distribution (particle concentration as a function of size) will be associated with changes in the steepness of the attenuation spectra as a function of wavelength; a flatter particle size distribution will be associated with a flatter attenuation spectrum. In addition, the observed ranges of the beam attenuation spectral slope and the PSD exponent are found to be consistent with this theory.

Optical properties of dissolved (colored dissolved organic material (CDOM)) and particulate matter and hydrographic measurements were obtained at the Mid-Atlantic Bight during the fall of 1996 and the spring of 1997 as part of the Coastal Mixing and Optics experiment. To assess the temporal and spatial variability, time series were obtained at one location and cross-shelf transects were carried out. On short timescales, variability in the vertical distribution of the dissolved fraction was mostly due to high- frequency internal waves. This variability was conservative, resulting in no changes on isopycnals. Over longer periods and episodically, CDOM variability was dominated by storms. The storms were associated with sediment resuspension events and were accompanied by an increase in the absorption by the dissolved materials. Data from spatial transects show that near the bottom, over the shelf, and in both spring and fall, increased particulate absorption and increased CDOM absorption co-occur. These data support the hypothesis that bottom sediments can act as a source of dissolved organic carbon during sediment resuspension events.

We have collected data during eight separate research cruises from open ocean to estuarine oceanic environments. Inherent optical property data collected during these cruises were incorporated into a large database totaling 1914 vertical samples. The range of each inherent optical property within this database spans over 2 orders of magnitude. Using this database, we examine the spectral relationships of each of the inherent optical properties based on the measurements made at 488 nm. The results of this study show that there are dependencies in the individual inherent optical properties (IOP) spectra that are linearly related. The information from the regression models is used to explain the linear dependencies observed in the global data set. A separate data set collected from a recent cruise is used to compare regional relationships with the global. The implication of this research is that over a diversity of oceanic regimes, there are fundamental, first-order relationships in the individual IOP spectra. These relationships can provide an estimate of the individual IOP spectral relationships when no information about the IOP is available, as is often the case in ocean color remote sensing. More detailed models, however, may be necessary in order to more accurately predict the IOP spectral relationships on regional scales where the expected range of variability is small.

Coastal waters represent the commingling of offshore marine and terrestrial surface source waters and therefore are naturally complex and variable. Our long term goal is to establish observational and modeling approaches to predict sources and scales of variability in the source waters, particularly those related to land use activities in upstream watersheds, from observations and measurements in the coastal waters. Hydrologic optics provides an approach to characterizing physical and biogeochemical processes in aquatic systems over a range of time and space scales. The linkage between observations of the inherent optical properties (IOPs; absorption, scattering and fluorescence) and the geophysical properties lie in the establishment of robust optical proxies and the quantification of the temporal and spatial scales over which these proxies remain conservative in their properties. Our objectives are to identify and quantify specific optical and chemical characteristics of the colored particulate and dissolved fractions originating in the Penobscot River system that are associated with defined land use activities (land use proxies), and to determine the scales of variability over which these proxies can be detected both temporally (i.e. seasonal and episodic events) and spatially (from the source into coastal waters).

Coastal waters represent the commingling of offshore marine and terrestrial surface source waters and therefore are naturally complex and variable. Our long term goal is to establish observational and modeling approaches to predict sources and scales of variability in the source waters, particularly those related to land use activities in upstream watersheds, from observations and measurements in the coastal waters. Hydrologic optics provides an approach to characterizing physical and biogeochemical processes in aquatic systems over a range of time and space scales. The linkage between observations of the inherent optical properties (IOPs; absorption, scattering and fluorescence) and the geophysical properties lie in the establishment of robust optical proxies and the quantification of the temporal and spatial scales over which these proxies remain conservative in their properties. Our objectives are to identify and quantify specific optical and chemical characteristics of the colored particulate and dissolved fractions originating in the Penobscot River system that are associated with defined land use activities (land use proxies), and to determine the scales of variability over which these proxies can be detected both temporally (i.e. seasonal and episodic events) and spatially (from the source into coastal waters).