Mesoscale and high-frequency variability of macroscopic particles (> 100 μm) in the Ross Sea and its relevance for late-season particulate carbon export

Abstract

The Ross Sea plays a major role in the transfer of organic carbon from the surface into the deep sea due to the combination of high seasonal productivity and Antarctic bottom water formation. Here we present a particle inventory of the Ross Sea based on a combined deployment of a video particle profiler (VPP) and a high-resolution digital holographic microscope (DIHM). Longdistance (100s of kilometers) and short-distance (10s of kilometers) sections showed high variability of particle distributions that co-varied with the density structure of the water column. Particle export was apparent at sites of locally weakened pycnoclines, likely an indirect effect of nutrientmixing into the surface layer and local blooms that lead to export.Particle volume abundances at 200-300 m depth were highlycorrelated with particle volume abundances in the upper mixed layer (<60 m),consistent with particles at depth primarily the result of export rather than lateral advection.Phaeocystisantarctica(Haptophyta) colonies that were initially retained in the mixed layer sank below the euphotic zone within a period of two weeks. Fine-scale analysis at a resolution <1m revealed a significantly overdispersed (i.e., highly patchy) environment in all casts. Patchiness, as determined by the Lloyd index of patchiness and the Index of Aggregation, increased in and below the pycnocline presumably due to aggregation of particles while accumulating on density gradients. In contrast, particles in the upper mixed layer and in the nepheloid layers were more randomly distributed. In 40 of the 84 VPPdepth profiles, a

Distributions, sources, and transformations of dissolved and particulate iron on the Ross Sea continental shelf during summer

“…Conceivably, the cycling of Fe in the Ross Sea may instead be characterized by low “ f e” ratios, (uptake of new iron/uptake of new and regenerated iron), similar to values estimated for high nutrient low chlorophyll waters during the FeCycle study [ Boyd et al ., ]. In addition, the particulate material collected during PRISM likely undersampled the larger (>10 µm) sinking particles that represent the greatest fraction of pFe exported from Ross Sea surface waters [ Bochdansky et al ., ; Frew et al ., ; Smith et al ., ]; indirect evidence in support of this suggestion is described in section 4.3.2.…”

Globally Consistent Quantitative Observations of Planktonic Ecosystems

“…The systems are the LISST-HOLO (now in its 2nd version, Sequoia Sci., 4.4 µm pixel size, 1,600 × 1,200 pixel frames, 20 fps) and the HoloSea (4Deep, 1.5 µm pixel size, 2,048 × 2,048 pixel frames, 22 fps). Given their novelty, only a small number of publications have been produced using them or their prototype systems (Bochdansky et al, 2017;Davies and Nepstad, 2017). Automated image reconstruction and recognition requires significant computational power, an issue that is likely to be alleviated in the near future.…”

Estimating Carbon Flux From Optically Recording Total Particle Volume at Depths Below the Primary Pycnocline

“…The Video Particle Profiler (VPP) was previously described in Bochdansky et al (2017). Side lighting with two white highintensity LED lights [Fenix L2P, powered by a 2.4 V, 35 Ah FIGURE 1 | Stations occupied in the North Atlantic (June-July 2012) (A) and the Ross Sea (February-March 2013) (B).…”

“…Image data were aligned in Matlab with depth from the CTD using a common time stamp at 1 s (∼1 m) resolution. The projected area of the particle (sum of white and black pixels within the perimeter of the particle determined by eight-connectivity) was converted to a circle that was then converted to the volume of a sphere (Iversen et al, 2010;Bochdansky et al, 2017). To obtain total volumes (pixel 3 frame −1 ), volumes of particles were summed for each frame and the average total volume was calculated for each meter, and then again averaged over the depth ranges (50-60 or 200-300 m).…”

“…Depth intervals of 50-60 and 200-300 m were used previously in a comparison between upper and deeper water particle abundance across 77 stations visited during the Ross Sea cruise (Bochdansky et al, 2017). In our optical configuration the camera was exposed to ambient light that resulted in light contamination at the surface.…”