Biologically mediated particulate organic and inorganic carbon (POC and PIC) export from surface waters is the principal determinant of the vertical oceanic distribution of pH and dissolved inorganic carbon and thus sets the conditions for air-sea exchange of CO2; exported organic matter also provides the energy fueling communities in the mesopelagic zone. However, observations are temporally and spatially sparse. Here we report the first hourly-resolved optically quantified POC and PIC sedimentation rate time series from an autonomous Lagrangian Carbon Flux Explorer (CFE), which monitored particle flux using an imaging optical sedimentation recorder (OSR) at depths below 140m in the Santa Cruz Basin, CA, in May 2012, and in January and March 2013. Highest POC vertical flux (∼ 100-240mmolCm-2d-1) occurred in January, when most settling material was millimeter- to centimeter-sized aggregates but when surface biomass was low; fluxes were ∼ 18 and ∼ 6mmolCm-2d-1, respectively, in March and May, under high surface biomass conditions. An unexpected discovery was that January 2013 fluxes measured by CFE were 20 times higher than that measured by simultaneously deployed surface-tethered OSR; multiple lines of evidence indicate strong undersampling of aggregates larger than 1mm in the latter case. Furthermore, the January 2013 CFE fluxes were about 10 times higher than observed during multiyear sediment trap observations in the nearby Santa Barbara and San Pedro basins. The strength of carbon export in biologically dynamic California coastal waters is likely underestimated by at least a factor of 3 and at times by a factor of 20.

Abstract. The magnitude and controls of particulate carbon exported from surface waters and its remineralization at depth are poorly known. The Carbon Flux Explorer (CFE), a Lagrangian float-deployed imaging sediment trap, has been designed to optically measure the hourly variations of particle flux to kilometer depths for months to seasons while relaying data in near-real time to shore via satellite without attending ships. The main optical proxy of particle load recorded by the CFE, volume-attenuance (VA; units of mATN-cm2), while rigorously defined and highly precise, has not been robustly calibrated in terms of particulate organic carbon (POC), nitrogen (PN), and phosphorus (PP). In this study, a novel 3D printed particle sampler using cutting edge additive manufacturing was developed and integrated with the CFE. Two such modified floats (CFE-Cals) were deployed a total of 15 times for 18-24-hour periods to gain calibration imagery and samples at depths near 150 meters in four contrasting productivity environments during the June 2017 California Current Ecosystem – Long Term Ecological Research (LTER) process study. Regression slopes for VA : POC and VA : PN (units mATN-cm2 : mmol; R2 in parentheses) were 10.07 × 103 (0.86), 10.05 × 104 (0.87) respectively and was not sensitive to environment or classes of particles sampled. PP was not strongly correlated with VA.

The magnitude and controls of particulate carbon exported from surface waters and its remineralization at depth are poorly constrained. The Carbon Flux Explorer (CFE), a Lagrangian float-deployed imaging sediment trap, has been designed to optically measure the hourly variations of particle flux to kilometer depths for months to seasons while relaying data in near-real time to shore via satellite without attending ships. The main optical proxy for particle load recorded by the CFE, volume attenuance (VA; units of mATN cm2), while rigorously defined and highly precise, has not been robustly calibrated in terms of particulate organic carbon (POC), nitrogen (PN) and phosphorus (PP). In this study, a novel 3-D-printed particle sampler using cutting edge additive manufacturing was developed and integrated with the CFE. Two such modified floats (CFE-Cals) were deployed a total of 15 times for 18-24 h periods to gain calibration imagery and samples at depths near 150m in four contrasting productivity environments during the June 2017 California Current Ecosystem Long-Term Ecological Research (LTER) process study. Regression slopes for VA: POC and VA: PN (units mATN cm2: mmol; R2, n, p value in parentheses) were 1.01×104 (0.86, 12, < 0.001) and 1:01×105 (0.86, 15, < 0.001), respectively, and were not sensitive to particle size classes or the contrasting environments encountered. PP was not well correlated with VA, reflecting the high lability of P relative to C and N. The volume attenuance flux (VAF) to POC flux calibration is compared to previous estimates.

To understand the vertical variations in carbon fluxes in biologically productive waters, four autonomous carbon flux explorers (CFEs), ship-lowered CTD-interfaced particle-sensitive transmissometer and scattering sensors, and surface-drogued sediment traps were deployed in a filament of offshore flowing, recently upwelled water, during the June 2017 California Current Ecosystem-Long Term Ecological Research process study. The Lagrangian CFEs operating at depths from 100-500 m yielded carbon flux and its partitioning with size from 30 μ m-1 cm at three intensive study locations within the filament and in waters outside the filament. Size analysis codes intended to enable long-term CFE operations independent of ships are described. Different particle classes (anchovy pellets, copepod pellets, and > 1000 μ m aggregates) dominated the 100-150 m fluxes during successive stages of the filament evolution as it progressed offshore. Fluxes were very high at all locations in the filament; below 150 m, flux was invariant or increased with depth at the two locations closer to the coast. Martin curve bfactors (± denotes 95 % confidence intervals) for total particulate carbon flux were + 0.37 ± 0.59, + 0.85 ± 0.31,-0.24 ± 0.68, and-0.45 ± 0.70 at the three successively occupied locations within the plume, and in transitional waters. Interestingly, the flux profiles for all particles < 400 μ m were a much closer fit to the canonical Martin profile (b-0.86); however, most (typically > 90 %) of the particle flux was carried by > 1000 μ m sized aggregates which increased with depth. Mechanisms to explain the factor of 3 flux increase between 150 and 500 m at the mid-plume location are investigated.

Seismic velocities and elastic moduli of rocks are known to vary significantly with applied stress, which indicates that these materials exhibit nonlinear elasticity. Monochromatic waves in nonlinear elastic media are known to generate higher harmonics and combinational frequencies. Such effects have the potential to be used for broadening the frequency band of seismic sources, characterization of the subsurface, and safety monitoring of civil engineering infrastructure. However, knowledge on nonlinear seismic effects is still scarce, which impedes the development of their practical applications. To explore the potential of nonlinear seismology, we performed three experiments: two in the field and one in the laboratory. The first field experiment used two vibroseis sources generating signals with two different monochromatic frequencies. The second field experiment used a surface orbital vibrator with two eccentric motors working at different frequencies. In both experiments, the generated wavefield was recorded in a borehole using a fiber-optic distributed acoustic sensing cable. Both experiments showed combinational frequencies, harmonics, and other intermodulation products of the fundamental frequencies both on the surface and at depth. Laboratory experiments replicated the setup of the field test with vibroseis sources and showed similar nonlinear combinations of fundamental frequencies. Amplitudes of the nonlinear signals observed in the laboratory showed variation with the saturating fluid. These results confirm that nonlinear components of the wavefield propagate as body waves, are likely to generate within rock formations, and can be potentially used for reservoir fluid characterization.