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This study presents in situ, high-resolution optical measurements of particle size distributions (PSD) within sediment plumes generated by a pre-prototype deep seabed nodule collector vehicle operating in the abyssal Pacific Ocean. These measurements were obtained using a cutting-edge instrument, the LISST-RTSSV sensor. The data collected in situ reveal marked differences compared to previously reported laboratory-based, ex situ measurements. The grain size and other key particle shape characteristics are found to be dependent on multiple factors, including the collector vehicle maneuvers, the time elapsed following sediment discharge, and the complex hydrodynamic processes that generate the sediment in suspension. Significantly, the PSD from a highly complex succession of straight-line maneuvers converges to that of the canonical case of a simple straight-line driving maneuver within a timescale of ten minutes. Our results underscore the importance of parameterizing sediment plume transport models based on well-informed, comprehensive PSDs of detrained suspended sediment measured in situ at adequate timescales and in regions no longer strongly influenced by active and complex hydrodynamic processes.

Optical sensors have distinct advantages when used in ocean observatories, autonomous platforms, and on vessels of opportunity, because of their high-frequency measurements, low power consumption, and the numerous established relationships between optical measurements and biogeochemical variables. However, the issues of biofouling and instrument stability over time remain complicating factors when optical instruments are used over periods longer than several days. Here, a method for obtaining calibration-independent measurements of spectral particle absorption and attenuation is presented. Flow-through optical instrumentation is routinely diverted through a large–surface area 0.2-μm cartridge filter, allowing for the calculation of particle optical properties by differencing temporally adjacent filtered and whole water samples. This approach yields measurements that are independent of drift in instrument calibration. The method has advantages not only for coastally moored deployments, but also for applications in optically clear waters where uncertainties in instrument calibration can be a significant part of the signal measured. The differencing technique is demonstrated using WET Labs (Philomath, Oregon) ac-9 and ac-s multi- and hyperspectral absorption and attenuation meters. For the ac-s sensor, a correction scheme is discussed that utilizes the spectral shape of water absorption in the near-infrared to improve the accuracy of temperature and scattering-corrected spectra. Flow-through particulate absorption measurements are compared with discrete filter-pad measurements and are found to agree well (R2 = 0.77; rmse = 0.0174 m−1).

While recent research has provided increasing insight into ocean ecosystem functions and rapidly improving predictive ability, it has become clear that for some key processes, including grazing by zooplankton, there simply is no currently available instrumentation to quantify relevant stocks and rates, remotely or in situ . When measurement capacity is lacking, collaborative research between instrument manufacturers and researchers can bring us closer to addressing key knowledge gaps. By necessity, this high risk, high rewards research will require iterative steps from best case scenarios under highly controlled and often artificial laboratory conditions to empirical verification in complex in situ conditions with diverse biota. To illustrate our point, we highlight the example of zooplankton grazing in marine planktonic food webs. Grazing by single-celled zooplankton accounts for the majority of organic carbon loss from marine primary production but is still measured with logistically demanding, point-sample incubation methods that result in reproducible results but at insufficient resolution to adequately describe temporal and spatial dynamics of grazer induced impacts on primary production, export production and the annual cycle of marine plankton. We advance a collaborative research and development agenda to eliminate this knowledge gap. Resolving primary production losses through grazing is fundamental to a predictive understanding of the transfer of matter and energy through marine ecosystems, major reservoirs of the global carbon cycle.

The ocean’s biological carbon pump (BCP) comprises a set of physical and biological processes that impact how carbon is exchanged between the atmosphere, the land, and the ocean. Sinking particles, such as “marine snow,” are a key mechanism of the BCP, where the depth of remineralization of carbon from these particles governs the extent to which carbon releases back into the atmosphere or sequesters in the deep ocean (Siegel et al., 2021). In addition, this sinking flux is a key energy source for deep water and benthic ecosystems. Studying these particles remains challenging, however, making it difficult to quantify carbon flux on a global scale. Global climate change further decreases the predictability of oceanic carbon flux due to the indirect changes induced by warming, ecosystem shifts, and acidification. Other human-induced alterations of the ocean’s carbon cycle, such as proposed marine carbon dioxide removal (mCDR) techniques like ocean alkalinity enhancement or nutrient fertilization, stand to further complicate carbon quantification and the ability to establish a carbon flux baseline from which future measurements can be compared and contextualized.

Suspended particle size and concentration are critical parameters necessary to understand water quality, sediment dynamics, carbon flux, and ecosystem dynamics among other ocean processes. In this study we detail the integration of a Sequoia Scientific, Inc., Laser In situ Scattering and Transmissometry (LISST) sensor into a Teledyne Webb Research Slocum autonomous underwater glider. These sensors are capable of measuring particle size, concentration, and beam attenuation by particles in size ranges from 1.00 to 500 μm at a resolution of 1 Hz. The combination of these two technologies provides the unique opportunity to measure particle characteristics persistently at specific locations, or survey regional domains from a single profiling sensor. In this study we present the sensor integration framework, detail quality assurance and control (QAQC) procedures, as well as provide a case study of storm driven sediment resuspension and transport. Specifically, Rutgers glider RU28 was deployed with an integrated LISST-Glider for 18 days in September of 2017. During this time period it sampled the nearshore environment off of coastal New Jersey, capturing full water column sediment resuspension during a coastal storm event. A novel method for in situ background corrections is demonstrated and used to mitigate long-term bio-fouling of the sensor windows. Additionally, we present a method for removing Schlieren contaminated time periods utilizing coincident conductivity temperature and depth, fluorometer, and optical backscatter data. The combination of LISST sensors and autonomous platforms has the potential to revolutionize our ability to capture suspended particle characteristics throughout the world’s oceans.

Beam attenuation coefficient, c, provides an important optical index of plankton standing stocks, such as phytoplankton biomass and total particulate carbon concentration. Unfortunately, c has proven difficult to quantify through remote sensing. Here, we introduce an innovative approach for estimating c using lidar depolarization measurements and diffuse attenuation coefficients from ocean color products or lidar measurements of Brillouin scattering. The new approach is based on a theoretical formula established from Monte Carlo simulations that links the depolarization ratio of sea water to the ratio of diffuse attenuation Kd and beam attenuation C (i.e., a multiple scattering factor). On July 17, 2014, the CALIPSO satellite was tilted 30° off-nadir for one nighttime orbit in order to minimize ocean surface backscatter and demonstrate the lidar ocean subsurface measurement concept from space. Depolarization ratios of ocean subsurface backscatter are measured accurately. Beam attenuation coefficients computed from the depolarization ratio measurements compare well with empirical estimates from ocean color measurements. We further verify the beam attenuation coefficient retrievals using aircraft-based high spectral resolution lidar (HSRL) data that are collocated with in-water optical measurements.

Particulate matter in the ocean is ubiquitous, ranging in size from submicron colloids to large marine snow aggregates. Particle size and dynamics play major roles in—and are reflective of—many marine processes, ranging from ocean-basin scale phytoplankton blooms to sediment transport in coastal regions. The use of optical sensing techniques such as remote sensing or in situ scattering sensors affords examination of these dynamics across comparable, relevant, process scales. How the optical properties, especially backscattering, are dependent on the size, composition, and packaging of particulate matter remains an active area of research, using both modeling and empirical approaches. This dissertation advances new methods for making measurements of particle optical properties in the environment, and uses these methods for examining how the optical properties of particles depend on their size distribution and packaging into aggregates. Advances in methodology include the adaptation of an existing instrument for measurement of near-forward scattering, providing some of the first measurements of this important property in decades. The near-forward scattering is also related to particle dynamics in the bottom boundary layer. A method for measurement of optical properties that is resistant to bio-fouling is also described, and used over several years to build a dataset of particle size distribution and multi-spectral optical properties. The spectral shape of attenuated and backscattered light is shown to be related to the particulate size distribution in the highly-scattering bottom boundary layer. Finally, since a variety of dynamic processes act to change the particle size distribution in the environment, two experiments are described to isolate the effects of particle aggregation in order to link changes in particle packaging to optical properties.

With the significant development of exploratory deep-sea mining activities, the demand for routine environmental monitoring in the deep sea has become pressing. Today, no commercial instrumentation exists that can monitor the parameters of importance for regulators and operators. A collaboration led by Sequoia Scientific Inc., the Massachusetts Institute of Technology (MIT) and Scripps Institution of Oceanography (SIO) has been funded to develop a commercial instrument for deep-sea environmental monitoring of mining activity. The past decade has seen a substantial increase in activities surrounding the potential development of a global deep-sea mining industry, with numerous governments and private companies developing research and engineering programs. Besides the potential user base in the deep-sea mining industry, future users of the proposed new sensor could come from the ocean science, oil and gas, sediment transport, and coastal engineering sectors. An instrumentation package that can measure particle size, concentration and settling velocity in real time or near real time would be potentially attractive for scientists, managers and engineers in these sectors.

Beam attenuation coefficient, c, provides an important optical index of plankton standing stocks, such as phytoplankton biomass and total particulate carbon concentration. Unfortunately, c has proven difficult to quantify through remote sensing. Here, we introduce an innovative approach for estimating c using lidar depolarization measurements and diffuse attenuation coefficients from ocean color products or lidar measurements of Brillouin scattering. The new approach is based on a theoretical formula established from Monte Carlo simulations that links the depolarization ratio of sea water to the ratio of diffuse attenuation Kd and beam attenuation C (i.e., a multiple scattering factor). On July 17, 2014, the CALIPSO satellite was tilted 30Âdeg off-nadir for one nighttime orbit in order to minimize ocean surface backscatter and demonstrate the lidar ocean subsurface measurement concept from space. Depolarization ratios of ocean subsurface backscatter are measured accurately. Beam attenuation coefficients computed from the depolarization ratio measurements compare well with empirical estimates from ocean color measurements. We further verify the beam attenuation coefficient retrievals using aircraft-based high spectral resolution lidar (HSRL) data that are collocated with in-water optical measurements.