Biology subjects

Romanelli, E.

Publications and source records attributed to Romanelli, E..

3 recordsLinked to original sources

bioRxiv2026

Differences between suspended and sinking particles regulate carbon flux in the upper mesopelagic during a Phaeocystis Bloom

Despite decades of research, the factors determining the sinking velocity of marine biogenic particles remain poorly constrained, and growing evidence suggests that particle composition and morphology are as important as size in determining particle fate. We compared characteristics of suspended and sinking particles at three depths below the mixed layer and within the layer of maximal flux attenuation during the decline of a Phaeocystis pouchetii bloom in the Labrador Sea using marine snow catchers. Biochemical and morphological characteristics of suspended and sinking particles always differed, with differences depending primarily on bloom stage, and depth accounting for comparatively less variation. Exopolymer particles played a key role, with the relative concentrations of transparent exopolymer particles consistently higher in the suspended than in the sinking particle fraction. In contrast, the partitioning of coomassie-stainable particles changed with the bloom stage, as a function of the Phaeocystis life cycle. Ballast minerals played a negligible role during the late-bloom and bloom-decline stages, and their relative importance increased during the non-bloom stage. The C:N ratio was lower in suspended than sinking particles, with differences in morphological measures depending on bloom stage. Our findings emphasize that export potential is driven not only by particle size, but also by bloom stage, which is closely linked to plankton community composition and plays a key role in the timing and magnitude of carbon flux in the upper mesopelagic. Further, this work highlights the important and diverse roles of exopolymers in regulating carbon flux.

systems biology↗

bioRxiv2026

Particle lability drives degradation dynamics and bacterial community assembly during a Phaeocystis bloom decline

Microbial degradation of suspended and sinking organic carbon regulates long-term oceanic carbon storage by controlling the efficiency of the biological pump. Yet microbial controls on carbon export and remineralization remain poorly constrained, limiting predictions of how ocean carbon cycling will respond to climate change. Here, we combined in situ sampling with ship-based incubations to quantify prokaryote-driven removal rates of suspended and sinking total organic carbon (TOC). Samples were collected below the mixed layer during three stages of a spring Phaeocystis pouchetii bloom in the Labrador Sea. Phaeocystis blooms can dominate regional phytoplankton biomass and are expected to increase under future climate. Removal rates were used as a proxy for carbon lability and combined with 16S rRNA metabarcoding and carbon composition analyses to link microbial community structure with substrate characteristics. Removal rates of sinking particles (0.02-0.06 d-1) were an order of magnitude higher than those of suspended TOC (0.002 d-1) during bloom-decline and non-bloom. In contrast, during late-bloom, suspended carbon exhibited rates of 0.01 d-1, comparable to sinking particles, and was enriched in exopolymer-rich colonies. Prokaryotic community composition varied primarily among bloom stages rather than carbon fractions, indicating that bloom stage-- and thus particle origin and composition--was the dominant control on bacterial degradation and assembly. Bacterial diversity peaked where carbon was refractory and originated from mixed phytoplankton. Together, these results demonstrate that suspended Phaeocystis-derived carbon can be rapidly remineralized when blooms produce exopolymer-rich colonies and highlight bloom stage as key regulator of microbial carbon processing and biological pump efficiency.

microbiology↗

bioRxiv2024

Intense storms affect sinking particle fluxes after the North Atlantic diatom spring bloom

The sinking of large particles (i.e., marine snow) has long been recognized as a key pathway for efficient particulate organic carbon (POC) export to the ocean interior during the decline of spring diatom blooms. Recent work has suggested that particles smaller than marine snow can also substantially contribute to POC export. However, a detailed characterization of small and large sinking particles at the end of blooms is missing. Here, we separately collected suspended and small and large sinking particles using Marine Snow Catchers and assessed their biogeochemical composition after the North Atlantic spring bloom in May 2021. During the three weeks of sampling, when four intense storms (maximum wind speeds 37 - 50 kts) created high turbulent energy dissipation rates and deepened the mixed layer, we observed two distinct sedimentation episodes. During the storm periods, sinking particles were dominated by small (diameter < 0.1 mm), slow-sinking (~18 m d-1), silica-rich particles that carried a moderate POC flux (< 6 mmol C m-2 d-1) to 500 m depth. Once the storms ceased, the volume of large (diameter > 0.1 mm), fast-sinking (> 75 m d-1), carbon-rich marine snow aggregates (not fecal pellets) increased exponentially and POC fluxes at 100 m depth were more than fourfold greater (30{+/-}12 mmol C m-2 d-1) than those during the previous event. The aggregates consisted of a mixed post-bloom plankton community. Our data suggest that the intense storms determined the timing, type, and magnitude of POC flux at the end of a spring phytoplankton bloom.

biochemistry↗