Prokaryotes play a central role in marine biogeochemical cycles, yet quantifying their activity requires sensitive methods, particularly in the deep ocean where their biomass and metabolic rates are low. One widely used method to determine single-cell activity of prokaryotes is bioorthogonal non-canonical amino acid tagging (BONCAT), which offers a non-radioactive approach to measure protein synthesis. However, direct comparisons between BONCAT and radioisotope-based techniques across ocean depth gradients remain limited, particularly for low-activity prokaryotic communities. To address this knowledge gap, we applied BONCAT to quantify single-cell heterotrophic activity in prokaryotic communities from surface to bathypelagic depths (1000-4000 m) in the Southern Ocean near the Kerguelen Islands. Employing picolyl azide-based copper-catalysed click chemistry, we compared BONCAT (L-homopropargylglycine [HPG] incorporation) with microautoradiography (3H-methionine uptake). BONCAT consistently detected active cells throughout the water column, with HPG-derived total fluorescence intensity closely correlating with both microautoradiography (R2 = 0.91, P < .001) and bulk methionine incorporation (R2 = 0.94, P < .001). This strong relationship between BONCAT and microautoradiography was maintained into the upper bathypelagic depths, where detecting single-cell activity becomes challenging. Our results demonstrate that BONCAT provides estimates of single-cell heterotrophic activity consistent with microautoradiography in deep-ocean samples, supporting its application as a non-radioactive alternative in low-activity environments.

Trace metals are co-factors for enzymes that are essential for microbial metabolism and the cycling of major elements. Membrane transporters allow microbes to sense and react to trace elements in the environment and to balance their uptake and export for the regulation of intracellular metal homeostasis. The acquisition and efflux of trace metals could lead to reciprocal feedbacks between microbes and the surrounding environment. Whether these processes vary among trace metals and across habitats is presently not known. We used membrane transporters into and out of the cell as indicators for the uptake and efflux of trace metals and provide a detailed picture of the distribution of the respective genes in distinct provinces in surface waters and in subsurface water masses across a transect in the Southern Indian Ocean. We observed marked spatial and vertical patterns in normalized gene abundances of transporters of iron (Fe), manganese (Mn), nickel (Ni) and copper (Cu). Changes in gene abundances were specific to the type of transporter and trace metal, and pronounced differences between surface and specific water masses emerged. We found an enrichment in genes related to efflux and homeostasis of Fe, Ni and Cu in two water masses of the deep ocean that are North Atlantic Deep Water (NADW) and Lower Circumpolar Deep Water (LCDW). This pattern was observed on the community level and for metagenome-assembled genomes (MAGs) affiliated with Alteromonadaceae and Burkholderiaceae that were abundant in these two water masses. The enrichment in trace metal efflux and resistance genes points to microbially mediated processes, exerted by homeostasis, with potential influence on the trace metal speciation and distribution in specific water masses in the deep ocean. The gene repertoire and distinct distribution pattern of the taxa identified as potential key players could reflect an adaptation to these old water masses with trace metals acting as selective driver.

Prokaryotes play a central role in marine biogeochemical cycles, yet quantifying their activity requires sensitive methods due to low biomass and metabolic rates, particularly in the deep ocean. One recent method to determine single-cell activity of prokaryotes is bioorthogonal non-canonical amino acid tagging (BONCAT), which offers a non-radioactive approach to measure protein synthesis. However, direct comparisons between BONCAT and radioisotope-based techniques across ocean depth gradients remain limited, particularly for low-activity prokaryotic communities. To address this knowledge gap, we tested an optimised BONCAT protocol using picolyl azide fluorophores (BONCAT-pic) to assess single-cell heterotrophic activity in prokaryotic communities from surface to bathypelagic depths (1000–4000 m) in the Southern Ocean near the Kerguelen Islands. The method was first optimised using aged coastal and open-ocean seawater, and then compared to microautoradiography with 3H-methionine uptake. Statistical analysis shows that BONCAT-pic significantly improved detection sensitivity compared to standard azide reagents. BONCAT-pic consistently detected active cells in profiles over the open ocean water column, with cell proportions and fluorescence signals closely correlating with both microautoradiography (R2 = 0.9, p < 0.001) and bulk methionine incorporation (R2 = 0.6, p < 0.001). Our results demonstrate that BONCAT-pic is a reliable, fluorescence-based method for quantifying heterotrophic activity at the single-cell level, extending its applicability to prokaryotic communities in the deep ocean. ### Competing Interest Statement The authors have declared no competing interest.

In the Mediterranean Sea, an accumulation of dissolved organic matter (DOM) is observed during the stratified summer period, which is decoupled from the spring phytoplankton maxima. This has been classically explained by nutrient limitation, that hampers prokaryotic DOM uptake of the labile DOM released by phytoplankton. However, relatively high heterotrophic prokaryotic activity in summer led us to hypothesize that the accumulated DOM might be recalcitrant and derived from these microorganisms. To test this, we tracked the seasonality of DOM molecular composition and chemical diversity using FT-ICR MS from 2019 to 2021 in the NW Mediterranean Sea, and framed it using a broad suite of environmental and biological parameters. Our results reveal a clear seasonal variation in DOM molecular composition and diversity in the surface mixed layer. Changes in composition reflected a higher proportion of molecular formulae containing CHO in spring and a higher proportion of molecular formulae containing CHOS and CHONS in summer. Proxies of DOM recalcitrance, such as aromaticity, unsaturation, and molecular size, were higher in summer, confirming our hypothesis of an accumulation of recalcitrant DOM in summer. In parallel, an increase in DOM diversity (as number of total molecular formulae, their relative intensity, their average distance (Dist) in the van Krevelen space and their functional diversity) was observed, suggesting that the accumulated DOM in summer is likely the result of the interplay between different processes including dissolved primary production, photodegradation and prokaryotic activity. Our results may have significant implications for carbon sequestration through the microbial carbon pump in the Mediterranean Sea as this DOM accumulated in the surface is likely to be stored once exported into deep layers.

The trace element iron (Fe) is a major constraint for microbially mediated processes in the Southern Ocean. The accelerated melting of glaciers could present a novel source of Fe, but whether glacial Fe is bioavailable to marine microbes is not known. We investigated the response of marine heterotrophic prokaryotes to Fe contained in colloids (20-200 nm) of glacial origin collected on Kerguelen Island (Southern Ocean). We followed prokaryotic growth in incubation experiments amended with colloids of either glacial or nonglacial origin and determined community composition and the abundance of genes involved in Fe-related processes in metagenomes and metagenome-assembled genomes (MAGs) at the final time point. Prokaryotic taxa belonging to Vibrionaceae and Pseudomonadaceae accounted together for 32% to 67% of the relative abundances in the glacial colloid-amended treatments, while Rhodobacteraceae, Flavobacteriaceae, and Alteromonadaceae were the dominant contributors to the communities in the incubations amended with nonglacial colloids. Metagenomic analysis revealed a higher abundance of genes involved in the biosynthesis of the siderophores pyoverdine and vibrioferrin as well as their respective transporters in the presence of glacial colloids compared to nonglacial colloids. Genes for the transport of both siderophores were present in diverse MAGs, while biosynthesis genes were detected in fewer MAGs. Our results suggest that the utilization of siderophores facilitates access to Fe from glacial colloids and points to the key role of specific prokaryotes in rendering this source of Fe available to Southern Ocean microbial communities.

The nitrogen cycle is crucial for aquatic systems, as it governs the availability of this essential nutrient and thereby supports the productivity of marine ecosystems. While most research in the oxygenated ocean has thus far focused on nitrogen fixation and nitrification, the potential role of dissimilatory processes remains poorly investigated. The objectives of the present study were to determine the spatial patterns of DNR processes [denitrification and dissimilatory nitrate reduction to ammonium], their associations with trace metals that are cofactors, and to identify the involved microbial taxa. We analyzed metagenomes collected along a latitudinal gradient and diverse water masses in the Indian sector of the Southern Ocean during the South West Indian GEOTRACERS section cruise. Genes involved in DNR dominated over those of other nitrogen-transforming processes across all water masses, with a notable preference for enzymes requiring copper over iron, indicating alternative trace metal adaptation. Metagenome-assembled genomes associated with DNR possessed inorganic carbon fixing pathways suggesting mixotrophic strategies. Our observations show the metagenomic potential of DNR as an alternative or additional source of energy for the microbial community in the carbon limited deep ocean.

AbstractInteractions between phytoplankton and heterotrophic bacteria significantly influence the cycling of organic carbon in the ocean, with many of these interactions occurring at the micrometer scale. We explored potential associations between specific phytoplankton and bacteria in two size fractions, 0.8–3 µm and larger than 3 µm, at three naturally iron‐fertilized stations and one high nutrient low chlorophyll station in the Southern Ocean. The composition of phytoplankton and bacterial communities was determined by sequencing the rbcL gene and 16S rRNA gene from DNA and RNA extracts, which represent presence and potential activity, respectively. Diatoms, particularly Thalassiosira, contributed significantly to the DNA sequences in the larger size fractions, while haptophytes were dominant in the smaller size fraction. Correlation analysis between the most abundant phytoplankton and bacterial operational taxonomic units revealed strong correlations between Phaeocystis and picoeukaryotes with SAR11, SAR116, Magnetospira, and Planktomarina. In contrast, most Thalassiosira operational taxonomic units showed the highest correlations with Polaribacter, Sulfitobacteria, Erythrobacter, and Sphingobium, while Fragilariopsis, Haslea, and Thalassionema were correlated with OM60, Fluviicola, and Ulvibacter. Our in‐situ observations suggest distinct associations between phytoplankton and bacterial taxa, which could play crucial roles in nutrient cycling in the Southern Ocean.

Marine microbes are strongly interrelated to trace metals in the ocean. How the availability of trace metals selects for prokaryotic taxa and the potential feedback of microbial processes on the trace metal distribution in the ocean remain poorly understood. We investigate here the potential reciprocal links between diverse prokaryotic taxa and iron (Fe), manganese (Mn), copper (Cu), and nickel (Ni) as well as apparent oxygen utilization (AOU) across 12 well-defined water masses in the Southern Indian Ocean (SWINGS-South West Indian Ocean GEOTRACES GS02 Section cruise). Applying partial least square regression (PLSR) analysis, we show that the water masses are associated with particular latent vectors that are a combination of the spatial distribution of prokaryotic taxa, trace elements, and AOU. This approach provides novel insights on the potential interactions between prokaryotic taxa and trace metals in relation to organic matter remineralization in distinct water masses of the ocean.

Trace metals are required as cofactors in metalloproteins that are essential in microbial metabolism and growth. The microbial requirements of diverse metals and the capabilities of prokaryotic taxa to acquire these metals remain poorly understood. We present here results from metagenomic observations over an entire productive season in the region off Kerguelen Island (Indian Sector of the Southern Ocean). We observed seasonal patterns in the abundance of prokaryotic transporters of seven trace elements (zinc [Zn], manganese [Mn], nickel [Ni], molybdenum [Mo], tungsten [W], copper [Cu] and cobalt [Co]) and the consecutive spring and summer phytoplankton blooms were strong drivers of these temporal trends. Taxonomic affiliation of the functional genes revealed that Rhodobacteraceae had a broad repertoire of trace metal transporters (Mn, Zn, Ni, W and Mo) and a more restricted set was observed for other prokaryotic groups, such as Flavobacteriaceae (Zn), Nitrincolaceae (Ni and W) and Thioglobaceae (Mo). The prevalence of trace metal transporters within a prokaryotic group, as determined on the family level, was overall confirmed in representative metagenome-assembled genomes. We discuss the potential involvement of prokaryotic groups in processes related to organic matter utilisation that require these metals and the consequences on carbon and trace metal cycling in surface waters of the Southern Ocean.

Biogeochemical cycles constitute Earth's life support system and distinguish our planet from others in this solar system. Microorganisms are the primary drivers of these cycles. Understanding the controls on marine microbial dynamics and how microbes will respond to environmental change is essential for building and assessing model -based forecasts and generating robust projections of climate change impacts on ocean productivity and biogeochemical cycles. An international community effort has been underway to create a global -scale marine microbial biogeochemistry research program to tackle gaps in this understanding. The BioGeoSCAPES: Ocean Metabolism and Nutrient Cycles on a Changing Planet program will identify and quantify how marine microbes adjust to a changing climate and assess the consequences for global biogeochemical cycles. This article summarizes the ongoing efforts to launch BioGeoSCAPES.

Iron (Fe) and manganese (Mn) are crucial micronutrients that limit oceanic primary productivity in the Southern Ocean. It has been recently suggested that hydrothermal activity may be an important source of oceanic dissolved iron, yet, this contribution is still not fully understood and only one active hydrothermal site has been reported on the Southwest Indian Ridge (SWIR), south of 40 degrees S. Using a multi-proxy approach, this study demonstrates the occurrence of hydrothermal venting on the SWIR in the near vicinity of the location 44 degrees 51.690 S, 36 degrees 10.460 E, which is likely to be a low or moderately high temperature fluid. Indeed, we report high values of dissolved methane to manganese ratios (up to 11.1 +/- 1.2 mol mol-1), low particulate iron (pFe) and manganese (pMn) concentrations (with maximum values of 0.7 nmol L-1 and 0.06 nmol L-1, respectively) associated with the presence of few oxyhydroxides, as well as high 223Radium (Ra) and 224Ra activities near the seafloor. The Fe and Mn data revealed a significant enrichment at depths influenced by hydrothermal circulation on the seafloor, within the Upper Circumpolar Deep Water. Dissolved Fe (dFe) and dissolved Mn (dMn) concentrations were enriched by 3- and 7-fold, respectively, and pFe and pMn by 2- and 1.5-fold, respectively, compared to a reference station located outside the SWIR. They were however lower than concentrations reported so far near high temperature vents, suggesting a weaker influence of this hydrothermal system on deep Fe and Mn reservoirs. We show that a large fraction of the dFe could be stabilized by organic complexation with humic substances (eHS, estimated 27-60% of dFe). High prokaryotic abundance related to the proximity of the hydrothermal vent suggests that other Fe-complexing ligands of biological origin might also stabilize Fe in its dissolved form. Collectively, these measurements integrated within the concept of a "multi-proxy approach", helped painting a more detailed picture of the complex interactions and processes in this region of the SWIR. Although the system is a source of both dFe and dMn to the deep ocean, the low current velocities and the bathymetry likely limit the fertilization of surface water by dFe and dMn along this section of the SWIR.

Heterotrophic prokaryotes (HP) contribute largely to dissolved organic matter (DOM) processing in the ocean, but they also release diverse organic substances. The bioavailability of DOM released by HP under varying environmental conditions has not been fully elucidated. In this study, we investigated the bioavailability of DOM released by a single bacterial strain (Sphingopyxis alaskensis) and 2 natural HP communities grown under P-replete and P-limited conditions. The released DOM (HP-DOM) was used as a substrate for natural HP communities at a coastal site in the Northwestern Mediterranean Sea. We followed changes in HP growth, enzymatic activity, diversity, and community composition together with the consumption of HP-DOM fluorescence (FDOM). HP-DOM produced under P-replete and P-limited conditions promoted significant growth in all incubations. No clear differences in HP-DOM lability released under P-repletion and P-limitation were evidenced based on the HP growth, and P-limitation was not demonstrated to decrease HP-DOM lability. However, HP-DOM supported the growth of diverse HP communities, and P-driven differences in HP-DOM quality were selected for different indicator taxa in the degrading communities. The humic-like fluorescence, commonly considered recalcitrant, was consumed during the incubations when this peak was initially dominating the FDOM pool, and this consumption coincided with higher alkaline phosphatase activity. Taken together, our findings emphasize that HP-DOM lability is dependent on both DOM quality, which is shaped by P availability, and the composition of the consumer community.

Heterotrophic microbes in the Southern Ocean are challenged by the double constraint of low concentrations of organic carbon (C) and iron (Fe). These essential elements are tightly coupled in cellular processes; however, the prokaryotic requirements of C and Fe under varying environmental settings remain poorly studied. Here, we used a combination of metatranscriptomics and metaproteomics to identify prokaryotic membrane transporters for organic substrates and Fe in naturally iron-fertilized and high-nutrient, low-chlorophyll waters of the Southern Ocean during spring and late summer. Pronounced differences in membrane transporter profiles between seasons were observed at both sites, both at the transcript and protein level. When specific compound classes were considered, the two approaches revealed different patterns. At the transcript level, seasonal patterns were only observed for subsets of genes belonging to each transporter category. At the protein level, membrane transporters of organic compounds were relatively more abundant in spring as compared to summer, while the opposite pattern was observed for Fe transporters. These observations suggest an enhanced requirement for organic C in early spring and for Fe in late summer. Mapping transcripts and proteins to 50 metagenomic-assembled genomes revealed distinct taxon-specific seasonal differences pointing to potentially opportunistic clades, such as Pseudomonadales and Nitrincolaceae, and groups with a more restricted repertoire of expressed transporters, such as Alphaproteobacteria and Flavobacteriaceae. The combined investigations of C and Fe membrane transporters suggest seasonal changes in the microbial requirements of these elements under different productivity regimes. The taxon-specific acquisition strategies of different forms of C and Fe illustrate how diverse microbes could shape transcript and protein expression profiles at the community level at different seasons. Our results on the C- and Fe-related metabolic capabilities of microbial taxa provide new insights into their potential role in the cycling of C and Fe under varying nutrient regimes in the Southern Ocean.

Iron (Fe) governs the cycling of organic carbon in large parts of the Southern Ocean. The strategies of diverse microbes to acquire the different chemical forms of Fe under seasonally changing organic carbon regimes remain, however, poorly understood. Here, we report high-resolution seasonal metagenomic observations from the region off Kerguelen Island (Indian Sector of the Southern Ocean) where natural Fe-fertilization induces consecutive spring and summer phytoplankton blooms. Our data illustrate pronounced, but distinct seasonal patterns in the abundance of genes implicated in the transport of different forms of Fe and organic substrates, of siderophore biosynthesis and carbohydrate-active enzymes. The seasonal dynamics suggest a temporal decoupling in the prokaryotic requirements of Fe and organic carbon during the spring phytoplankton bloom and a concerted access to these resources after the summer bloom. Taxonomic assignments revealed differences in the prokaryotic groups harbouring genes of a given Fe-related category and pronounced seasonal successions were observed. Using MAGs we could decipher the respective Fe- and organic substrate-related genes of individual taxa assigned to abundant groups. The ecological strategies related to Fe-acquisition provide insights on how this element could shape microbial community composition with potential implications on organic matter transformations in the Southern Ocean.

We determined phosphorus (P) limitation effect on the quantity and quality of dissolved organic matter (DOM) released by heterotrophic prokaryotes (HP). We grew two single-bacterial strains from different lifestyles, the copiotrophic Photobacterium angustum and the oligotrophic Sphingopyxis alaskensis, and natural HP communities collected in fall and spring from the Mediterranean Sea, on glucose under two treatments: P-replete versus P-limiting. DOM release by HP comprised up to 30% of the initial carbon provided for growth. P-availability influenced carbon allocation to different cellular processes (respiration vs. growth), but did not significantly affect the net quantity of DOM released by HP. However, using fluorescence spectroscopy, we demonstrated an effect of P-limitation on DOM quality, with a predominance of humic-like compounds under P-limitation but protein-like compounds under P-repletion. Our results suggest that P-limitation could determine the fate of HP-derived DOM in the ocean, thus affecting the microbial carbon pump.

The sea surface microlayer (SSML) is critical to air-sea exchanges of gases and primary aerosols. However, despite the extent of this boundary layer, little is known about its specific bacterial community (bacterioneuston) and how it may affect ocean-atmosphere exchanges. Here, we studied the bacterial community composition in the surface waters of three different basins of the Western Mediterranean Sea and assessed the selective air-sea transfer of marine bacteria through experimental nascent sea spray aerosol production in a 10 L tank with plunging jets. In situ, the bacterioneuston harbored basin-specific enriched taxa and followed a similar spatial pattern as the underlying bacterioplankton community. Aerosolization potential showed that sea spray taxa might be recruited from both the underlying water and the SSML, and that taxa enriched in the bacterioneuston were not always aerosolized. Our results suggest that the Mediterranean nutrient gradient, as well as pulse events such as dust deposition, affect the distribution of the bacterial community at the ocean-atmosphere interface, which may impact biogeochemical processes, climate regulation and bacterial dispersal through aerosolization.

Coastal ecosystems deteriorate globally due to human-induced stress factors, like nutrient loading and pollution. Bacteria are critical to marine ecosystems, e.g., by regulating nutrient cycles, synthesizing vitamins, or degrading pollutants, thereby providing essential ecosystem services ultimately affecting economic activities. Yet, until now bacteria are overlooked both as mediators and indicators of ecosystem health, mainly due to methodological limitations in assessing bacterial ecosystem functions. However, these limitations are largely overcome by the advances in molecular biology and bioinformatics methods for characterizing the genetics that underlie functional traits of key bacterial populations – “key” in providing important ecosystem services, being abundant, or by possessing high metabolic rates. It is therefore timely to analyze and define the functional responses of bacteria to human-induced effects on coastal ecosystem health. We posit that categorizing the responses of key marine bacterial populations to changes in environmental conditions through modern microbial oceanography methods will allow establishing the nascent field of genetic counselling for our coastal waters. This requires systematic field studies of linkages between functional traits of key bacterial populations and their ecosystem functions in coastal seas, complemented with systematic experimental analyses of the responses to different stressors. Research and training in environmental management along with dissemination of results and dialogue with societal actors are equally important to ensure the role of bacteria is understood as fundamentally important for coastal ecosystems. Using the responses of microorganisms as a tool to develop genetic counselling for coastal ecosystems can ultimately allow for integrating bacteria as indicators of environmental change.

In the oligotrophic waters of the Mediterranean Sea, during the stratification period, the microbial loop relies on pulsed inputs of nutrients through the atmospheric deposition of aerosols from both natural (e.g., Saharan dust), anthropogenic, or mixed origins. While the influence of dust deposition on microbial processes and community composition is still not fully constrained, the extent to which future environmental conditions will affect dust inputs and the microbial response is not known. The impact of atmospheric wet dust deposition was studied both under present and future environmental conditions (+3 ∘C warming and acidification of −0.3 pH units), through experiments in 300 L climate reactors. In total, three Saharan dust addition experiments were performed with surface seawater collected from the Tyrrhenian Sea, Ionian Sea, and Algerian basin in the western Mediterranean Sea during the PEACETIME (ProcEss studies at the Air–sEa Interface after dust deposition in the MEditerranean sea) cruise in May–June 2017. Top-down controls on bacteria, viral processes, and community, as well as microbial community structure (16S and 18S rDNA amplicon sequencing), were followed over the 3–4 d experiments. Different microbial and viral responses to dust were observed rapidly after addition and were, most of the time, more pronounced when combined with future environmental conditions. The dust input of nutrients and trace metals changed the microbial ecosystem from a bottom-up limited to a top-down controlled bacterial community, likely from grazing and induced lysogeny. The relative abundance of mixotrophic microeukaryotes and phototrophic prokaryotes also increased. Overall, these results suggest that the effect of dust deposition on the microbial loop is dependent on the initial microbial assemblage and metabolic state of the tested water and that predicted warming and acidification will intensify these responses, affecting food web processes and biogeochemical cycles.

The Green Edge project was designed to investigate the onset, life, and fate of a phytoplankton spring bloom (PSB) in the Arctic Ocean. The lengthening of the ice-free period and the warming of seawater, amongst other factors, have induced major changes in Arctic Ocean biology over the last decades. Because the PSB is at the base of the Arctic Ocean food chain, it is crucial to understand how changes in the Arctic environment will affect it. Green Edge was a large multidisciplinary, collaborative project bringing researchers and technicians from 28 different institutions in seven countries together, aiming at understanding these changes and their impacts on the future. The fieldwork for the Green Edge project took place over two years (2015 and 2016) and was carried out from both an ice camp and a research vessel in Baffin Bay, in the Canadian Arctic. This paper describes the sampling strategy and the dataset obtained from the research cruise, which took place aboard the Canadian Coast Guard ship (CCGS) Amundsen in late spring and early summer 2016. The sampling strategy was designed around the repetitive, perpendicular crossing of the marginal ice zone (MIZ), using not only ship-based station discrete sampling but also high-resolution measurements from autonomous platforms (Gliders, BGC-Argo floats …) and under-way monitoring systems. The dataset is available at https://doi.org/10.17882/86417 (Bruyant et al., 2022).

Trace elements (TE) are tracers of multiple biotic and abiotic processes in the ocean and some of them are essential for marine life. Vertical export by particles is a major removal process of a large fraction of TE from the surface ocean. However, the seasonal export dynamics and its controlling factors, critical for the understanding of the internal TE cycling, remain poorly constrained. Here, we report and discuss the seasonal export of 15 TE in sinking particles collected by a sediment trap deployed in a highly productive region of the Southern Ocean. Basalt material was the main carrier phase for the export flux of 9 TE, and its dynamic was characterized by a strong decrease over time. TE export driven by biological carriers such as diatom spores and vegetative cells added pulsed seasonal dynamics to the lithogenic signal, while the contribution of fecal pellets was less variable over the season. For each TE, we were able to decipher the biological carrier phases that represent the most dominant export pathway. We discuss this partitioning with regards to the known metabolic functions of the different trace metals or TE of biological interest.