Special delivery of proteinaceous matter to deep-sea microbes

Science Advances · 2025-03-19 · 11 citations

Earth's deep ocean holds a vast reservoir of dissolved organic carbon, traditionally considered old and resistant to microbial degradation. Radiocarbon analyses indicate the hidden occurrence of younger dissolved organic carbon components, assumed to be accessible to deep-sea microorganisms but not yet demonstrated. Using compound-class radiocarbon analysis, molecular characterization, and bioassay experiments, we provide direct evidence for rapid microbial utilization of young, labile, high-molecular weight proteinaceous material in bathypelagic waters. The abundance of labile proteinaceous material diminishes from epipelagic to mesopelagic waters but notably increases in bathypelagic waters, where it exhibits a short turnover time (days) and resembles surface plankton in molecular composition. This observation coincides with peak zooplankton biomass recorded over the year. The nonmonotonic depth trend suggests a deep-sea replenishment of organic particles from mesopelagic migrating zooplankton. Our results indicate the presence of labile organic molecules at bathypelagic depths and reveal a nonlinear supply of plankton-derived substrates that support microbial metabolism and carbon sequestration in the deep ocean.

Metre-scale vertical zonation of corals and sponges on a deep-marine cliff reflects trophic resource partitioning

Scientific Reports · 2025-02-25

Corals and sponges are considered foundational species and can create biodiversity hotspots in the deep sea, yet little is known of their competitive interactions, particularly with respect to resource partitioning among benthic fauna. Here we report on the feeding ecology of deep-water corals, sponges, ascidians, and anemones from a ~ 450 m deep submarine canyon wall off Nova Scotia, Canada. Analysis of bulk stable isotopes of carbon and nitrogen confirms isotopic niche partitioning between species despite their physical proximity. Compound-specific nitrogen isotopes of amino acids (δ15N-AA) separated the taxa along continua of trophic position and benthic-pelagic coupling and resolve the conspicuously enriched bulk nitrogen patterns commonly observed in sponges. Radiocarbon dating (as Δ14C) of tissue samples, particulate organic matter (POM) and dissolved inorganic carbon (DIC) from the Scotian Slope sheds light on food provenance and distinguishes diets dominated by older, recalcitrant forms of organic matter versus surface-derived POM. Our results reveal significant differences in resource utilisation among sympatric corals, sponges, ascidians, and anemones and highlight that organisms capable of feeding on more recalcitrant resources will likely play a greater role in supporting deep-water habitats where the quality and flux of fresh POM may be diminished.

Tracing Pan‐Canadian Arctic Water Masses and Dissolved Inorganic Carbon Cycling Using Stable and Radiocarbon Isotopes

Global Biogeochemical Cycles · 2025-03-27 · 2 citations

Abstract The Canadian Arctic is warming four times faster than the global average, yet the impact of this perturbation on the marine carbon cycle remains unknown. Dissolved inorganic carbon (DIC) stable isotope (δ 13 C) and radiocarbon (Δ 14 C) values are powerful tools for tracing water mass transport, residence times and carbon cycling. While the hydrography of the Canadian Arctic Archipelago (CAA) is well documented, few DIC δ 13 C and Δ 14 C values exist for the region. Here, we present new DIC δ 13 C and Δ 14 C depth profiles from 19 stations across the CAA sampled in 2021 and place them into the context of five recently published Baffin Bay values. CAA DIC δ 13 C and Δ 14 C values ranged from −0.68‰ to +1.86‰, and −90.7 to +49.5‰, respectively. Several negative DIC Δ 14 C values (−44.7‰ and −51.9‰) were observed near the Mackenzie River, indicating riverine permafrost carbon is actively incorporated into the nearshore DIC pool. “Bomb” DIC Δ 14 C values in the Kitikmeot Sea were attributed to enhanced tidal mixing and heterotrophy together with high regional water mass residence times. A comparison of historical DIC Δ 14 C depth profiles from 2009 to 2021 reveals significant dilution of “bomb” 14 C and minor contributions (2.1%–4.4%) of fossil anthropogenic CO 2 within Pacific Summer Water (PSW), Pacific Winter Water (PWW) and Atlantic Fram Strait Water (ATL FS ) in the Beaufort Sea. Finally, the contrast between deep Beaufort Sea and Baffin Bay DIC δ 13 C and Δ 14 C values reveal differences in residence time and carbon sources in the two regions.

First characterization of the marine ecosystem of Archer Fiord in the Lasting Ice Area of the High Arctic: a productivity paradox

Arctic Science · 2025-11-03

The Lasting Ice Area along the northern coastline of Ellesmere Island and Greenland will be the region where Arctic multiyear sea ice will persist the longest in a warming climate, making this area critical for ice-dependent species. In 2019, the Tuvaijuittuq Marine Protected Area was established for the interim protection of the waters off northern Ellesmere Island. We present the first comprehensive study of the Archer Fiord–Lady Franklin Bay system located at the northern end of Nares Strait, in the Tuvaijuittuq area. Data on the hydrography, biogeochemical cycles, pelagic and benthic productivity, and seabed sediment were collected along a nearshore-offshore transect. The region is influenced by meteoric waters as well as Pacific and Atlantic-derived waters, and likely acts as a strong seasonal CO 2 sink. Despite fall-bloom conditions, low primary, secondary, and benthic productivity contrasted with the relatively high abundance of marine mammals. This productivity paradox either suggests (1) that organic matter and detritus deposited and accumulated over long periods prior to our survey sustain the benthic community on which marine mammals depend for foraging; (2) local productivity hotspots in areas outside the sampled stations; or (3) a highly efficient system with minor production surpluses. Solving this paradox will require further surveys in the area.

Picky Eaters: Carbon isotopic evidence for the uniform bioavailability of riverine dissolved organic matter to a model marine microorganism

2024-03-25

Dissolved organic matter (DOM) is a key component of the global carbon cycle, with rivers delivering significant amounts of DOM to oceans. Urbanization and agricultural land-use alter the age and chemical composition of riverine DOM, which likely impact the downstream bioavailability of riverine DOM. Here, we use bioreactor incubations of a marine bacterium (Pseudoalteromonas sp. 3D05) to investigate DOM bioavailability from two distinct rivers: the Suwannee River (natural, non-urbanized), and the Upper Mississippi River Basin (anthropogenically influenced). We measured rates of microbial CO2 production and radiocarbon ages (as Δ14C) to assess bioavailable DOM remineralization. We observed nearly identical cell densities and degradation patterns for both riverine DOM incubations. Respired DOM Δ14C values were also similar and decreased over time indicative of preferential utilization of recently synthesized “modern” substrates. These findings reveal unexpected similarities in riverine DOM bioavailability, indicating similar short term biological reactivity despite large DOM compositional differences.

Stable Isotopic (<i>δ</i>¹³C) Evidence for Global Microbial Sequestration of Refractory Dissolved Organic Matter

Geophysical Research Letters · 2024-05-03 · 7 citations

Abstract Dissolved organic carbon (DOC) in the global oceans is an important long‐term carbon sink. Connections between molecular size, reactivity, and isotopic characteristics show that DOC exists on a continuum from biologically reactive to recalcitrant. The driving mechanisms behind the creation and persistence of recalcitrant DOC remain unknown. We show mean recalcitrant DOC (isolated via solid‐phase extraction; SPE‐DOC) δ 13 C values are 1.3 ± 0.6‰ lower than mean total DOC δ 13 C between depth ranges 0–200 m and 2–4 km on three GO‐SHIP Repeat Hydrography cruises. Lowest observed δ 13 C values correlate with low ∆ 14 C and proximity to deep ocean hydrothermal systems. These data support the hypothesis that reworking of DOC through the microbial carbon pump is a key driver of the ocean's long‐term carbon sink. Mass‐balance modeling shows deep‐ocean DOC not captured by SPE is enriched in 13 C , highlighting the need for continued research on non‐retained DOC to predict mechanisms that drive ocean carbon storage.

Variable aging and storage of dissolved black carbon in the ocean

Proceedings of the National Academy of Sciences · 2024-03-22 · 21 citations

During wildfires and fossil fuel combustion, biomass is converted to black carbon (BC) via incomplete combustion. BC enters the ocean by rivers and atmospheric deposition contributing to the marine dissolved organic carbon (DOC) pool. The fate of BC is considered to reside in the marine DOC pool, where the oldest BC 14 C ages have been measured (&gt;20,000 14 C y), implying long-term storage. DOC is the largest exchangeable pool of organic carbon in the oceans, yet most DOC (&gt;80%) remains molecularly uncharacterized. Here, we report 14 C measurements on size-fractionated dissolved BC (DBC) obtained using benzene polycarboxylic acids as molecular tracers to constrain the sources and cycling of DBC and its contributions to refractory DOC (RDOC) in a site in the North Pacific Ocean. Our results reveal that the cycling of DBC is more dynamic and heterogeneous than previously believed though it does not comprise a single, uniformly “old” 14 C age. Instead, both semilabile and refractory DBC components are distributed among size fractions of DOC. We report that DBC cycles within DOC as a component of RDOC, exhibiting turnover in the ocean on millennia timescales. DBC within the low-molecular-weight DOC pool is large, environmentally persistent and constitutes the size fraction that is responsible for long-term DBC storage. We speculate that sea surface processes, including bacterial remineralization (via the coupling of photooxidation of surface DBC and bacterial co-metabolism), sorption onto sinking particles and surface photochemical oxidation, modify DBC composition and turnover, ultimately controlling the fate of DBC and RDOC in the ocean.

Picky Eaters: Carbon Isotopic Evidence for the Uniform Bioavailability of Riverine Dissolved Organic Matter to a Model Marine Microorganism

Geophysical Research Letters · 2024-07-03

Abstract Dissolved organic matter (DOM) is a key component of the global carbon cycle, with rivers delivering significant amounts of DOM to oceans. Urbanization and agricultural land‐use alter the age and chemical composition of riverine DOM, which likely impact the downstream bioavailability of riverine DOM. Here, we use bioreactor incubations of a marine bacterium ( Pseudoalteromonas sp. 3D05) to investigate DOM bioavailability from two distinct rivers: the Suwannee River (natural, non‐urbanized), and the Upper Mississippi River Basin (anthropogenically influenced). We measured rates of microbial CO 2 production and radiocarbon ages (as Δ 14 C) to assess DOM remineralization. We observed nearly identical cell densities and degradation patterns for both riverine DOM incubations. Respired DOM Δ 14 C values were also similar and decreased over time indicative of preferential utilization of recently synthesized “modern” substrates. These findings reveal unexpected similarities in riverine DOM bioavailability, indicating similar short term biological reactivity despite large DOM compositional differences.

Cycling of labile and recalcitrant carboxyl-rich alicyclic molecules and carbohydrates in Baffin Bay

Nature Communications · 2024-10-09 · 9 citations

Abstract Marine dissolved organic matter (DOM) is an important, actively cycling carbon reservoir (662 GtC). However, the chemical structure and cycling of DOM within rapidly warming, polar environments remains largely unconstrained. Previous studies have shown rapid surface cycling of carbohydrates as biologically-labile DOM (LDOM). Conversely, carboxyl-rich alicyclic molecules (CRAM) are often used as examples of biologically-recalcitrant DOM (RDOM). Traditional DOM isolation methods (e.g., ultrafiltration (10–30% of DOM) and solid-phase extraction (40–60% of DOM) induce chemical-, size- and compositional-bias – complicating inferences to total DOM cycling. Here, we use a total DOM proton ( 1 H) nuclear magnetic resonance (NMR) spectroscopy method to show carbohydrates and CRAM have high concentrations in the surface ocean and low concentrations at depth in Baffin Bay. Between 21–43% of surface CRAM is removed at depth. These results suggest both CRAM and carbohydrates are major LDOM constituents – contradicting the existing CRAM cycling paradigm and further constraining the long-term persistence of deep ocean DOM.

Dissolved Organic Radiocarbon in the West Indian Ocean

Geophysical Research Letters · 2023 · 4 citations

• Oceanography
• Geology
• Environmental science

Abstract We report marine dissolved organic carbon (DOC) concentrations, and DOC Δ 14 C and δ 13 C in seawater collected from the West Indian Ocean during the GO‐SHIP I07N cruise in 2018. We find bomb 14 C in DOC from the upper 1,000 m of the water column. There is no significant change in ∆ 14 C of DOC in deep water northward, unlike that of dissolved inorganic carbon (DIC), suggesting that transport of deep water northward is not controlling the 14 C age of DOC. Variability of DOC ∆ 14 C, including high values in the deep waters, is more pronounced than in other oceans, suggesting that dissolution of surface derived particulate organic carbon is a source of modern carbon to deep DOC in the West Indian Ocean. Low δ 13 C are present at two of the five stations studied, suggesting a source of low δ 13 C DOC, or additional microbial utilization of deep DOC.