Abstract In this study, we provide a method to quantify the uncertainty associated with sampling particle size distributions (PSD), using a global compilation of Underwater Vision Profiler observations (UVP, version 5). The UVP provides abundant in situ data of the marine PSD on global scales and has been used for a diversity of applications, but the uncertainty associated with its measurements has not been quantified, including how this uncertainty propagates into derived products of interest. We model UVP sampling uncertainty using Bayesian Poisson statistics and provide formulae for the uncertainty associated with a given sampling volume and observed particle count. We also model PSD observations using a truncated power law to better match the low concentration associated with rare large particles as seen by the UVP. We use the two shape parameters from this statistical model to describe changes in the PSD shape across latitude band, season, and depth. The UVP sampling uncertainty propagates into an uncertainty for modeled carbon flux exceeding 50%. The statistical model is used to extend the size interval used in a PSD‐derived carbon flux model, revealing a high sensitivity of the PSD‐derived flux model to the inclusion of small particles (80–128 μ m). We provide avenues to address additional uncertainties associated with UVP‐derived carbon flux calculations.
The spectral beam attenuation coefficient is an important optical property of natural water used to quantify light propagation and visibility in the aquatic media, and to study the concentration of the water constituents. Although beam attenuation in the ultraviolet spectral range may be particularly informative, to date, no transmissometer capable of measuring the beam attenuation in the ultraviolet is commercially available. The portable hyperspectral beam transmissometer developed in our lab is capable of measuring across a broad spectral range (300–750 nm) at 2 nm spectral resolution. The transmissometer exhibits a small acceptance angle (0.55 to 0.59° across the spectrum), a well collimated spectral light beam, and precision of ±0.012 m −1 . The attenuation of diverse water samples measured with our transmissometer was found to be significantly similar to that measured with a commercially available transmissometer. Moreover, the attenuation of filtered samples, measured with our transmissometer, was significantly similar to their absorption, measured with a bench‐top spectrometer. Testing the transmissometer in the field, the transmission of water samples collected in Lake Malawi, Africa, was measured on site. The magnitude and spectral shape of attenuation were in general agreement with previous reports. All assessment stages confirm the performance, accuracy, and applicability of our transmissometer. The extended spectral range and high spectral resolution of our portable transmissometer make it an excellent tool for studying the characteristics and distribution of dissolved and particulate matter in aquatic media and exploring the constraints imposed on the visibility and visual communication of aquatic organisms known to have ultraviolet photosensitivity.
Abstract Phytoplankton play a major role on Earth, impacting the global distribution and cycles of carbon, oxygen, nitrogen, sulfur, and other elements, and structuring marine food webs. One fundamental trait of phytoplankton with direct biogeochemical implications is their size, as it governs metabolic and sinking rates as well as prey–predator interactions. Phytoplankton size spans approximately 3.5 orders of magnitude (when expressed as an equivalent spherical diameter), and thus measuring the full range in size distribution of phytoplankton is challenging and rarely attempted. Here, we constructed phytoplankton size spectra by merging state‐of‐the‐art cytometry and imaging cytometry measurements that were collected in the western North Atlantic Ocean, along a latitudinal gradient (36°N to 55°N) and during different phases of the annual cycle of phytoplankton. The derived spectra show a seasonal pattern that parallels changes in phytoplankton biomass, and do not always follow a commonly assumed power‐law model. Shifts in size spectra were more pronounced in the sub‐Arctic and temperate subregions, compared to the subtropical region of the study area. We evaluated the relationships between different size groups and environmental parameters to derive ecologically meaningful size groups. Finally, to simulate Ocean Color remote‐sensing algorithms of phytoplankton size, we compared temporal variations in descriptors of the size spectra (median particle size, phytoplankton size distribution exponent) with optical size proxies derived from light absorption and attenuation; good agreement was observed in the northern sections of the study area where temporal changes in community size structure were more pronounced.
Microbes are dominant drivers of biogeochemical processes, yet drawing a global picture of functional diversity, microbial community structure, and their ecological determinants remains a grand challenge. We analyzed 7.2 terabases of metagenomic data from 243 Tara Oceans samples from 68 locations in epipelagic and mesopelagic waters across the globe to generate an ocean microbial reference gene catalog with >40 million nonredundant, mostly novel sequences from viruses, prokaryotes, and picoeukaryotes. Using 139 prokaryote-enriched samples, containing >35,000 species, we show vertical stratification with epipelagic community composition mostly driven by temperature rather than other environmental factors or geography. We identify ocean microbial core functionality and reveal that >73% of its abundance is shared with the human gut microbiome despite the physicochemical differences between these two ecosystems.
