Biological Pump Research Articles

Biochar as a green solution to drive the soil carbon pump

Biochar is a nature-based green solution to lift soil carbon storage and mitigate carbon release. Here, we propose a novel concept of biochar carbon pump (BCP) that bridges microbial carbon pump (MCP) and mineral carbon pump (MnCP), facilitating effective carbon sequestration. The BCP functions to promote carbon storage by introducing biochar-derived persistent C into soil, enhancing negative priming effects, altering soil microbial communities, and reinforcing organo-organic and organo-mineral interactions. Recognizing the value of BCP in bridging MCP and MnCP to facilitate diverse natural reactions for soil carbon sequestration is particularly significant in addressing climate change.

Indirect Impact of Eutrophication on Occurrence, Air-Water Exchange, and Vertical Sinking Fluxes of Antibiotics in a Subtropical River.

A significant challenge that warrants attention is the influence of eutrophication on the biogeochemical cycle of emerging contaminants (ECs) in aquatic environments. Antibiotics pollution in the eutrophic Pearl River in South China was examined to offer new insights into the effects of eutrophication on the occurrence, air-water exchange fluxes (Fair-water), and vertical sinking fluxes (Fsinking) of antibiotics. Antibiotics transferred to the atmosphere primarily through aerosolization controlled by phytoplankton biomass and significant spatiotemporal variations were observed in the Fair-water of individual antibiotics throughout all sites and seasons. The Fsinking of ∑AB14 (defined as a summary of 14 antibiotics) was 750.46 ± 283.19, 242.71 ± 122.87, and 346.74 ± 249.52 ng of m-2 d-1 in spring, summer, and winter seasons. Eutrophication indirectly led to an elevated pH, which reduced seasonal Fair-water of antibiotics, sediment aromaticity, and phytoplankton hydrophobicity, thereby decreasing antibiotic accumulation in sediments and phytoplankton. Negative correlations were further found between Fsinking and the water column daily loss of antibiotics with phytoplankton biomass. The novelty of this study is to provide new complementary knowledge for the regulation mechanisms of antibiotics by phytoplankton biological pump, offering novel perspectives and approaches to understanding the coupling between eutrophication and migration and fate of antibiotics in a subtropical eutrophic river.

The carbonate pump feedback on alkalinity and the carbon cycle in the 21st century and beyond

Abstract. Ocean acidification is likely to impact all stages of the ocean carbonate pump, i.e. the production, export, dissolution and burial of biogenic CaCO3. However, the associated feedback on anthropogenic carbon uptake and ocean acidification has received little attention. It has previously been shown that Earth system model (ESM) carbonate pump parameterizations can affect and drive biases in the representation of ocean alkalinity, which is critical to the uptake of atmospheric carbon and provides buffering capacity towards associated acidification. In the sixth phase of the Coupled Model Intercomparison Project (CMIP6), we show divergent responses of CaCO3 export at 100 m this century, with anomalies by 2100 ranging from −74 % to +23 % under a high-emission scenario. The greatest export declines are projected by ESMs that consider pelagic CaCO3 production to depend on the local calcite/aragonite saturation state. Despite the potential effects of other processes on alkalinity, there is a robust negative correlation between anomalies in CaCO3 export and salinity-normalized surface alkalinity across the CMIP6 ensemble. Motivated by this relationship and the uncertainty in CaCO3 export projections across ESMs, we perform idealized simulations with an ocean biogeochemical model and confirm a limited impact of carbonate pump anomalies on 21st century ocean carbon uptake and acidification. However, we highlight a potentially abrupt shift, between 2100 and 2300, in the dissolution of CaCO3 from deep to subsurface waters when the global-scale mean calcite saturation state reaches about 1.23 at 500 m (likely when atmospheric CO2 reaches 900–1100 ppm). During this shift, upper ocean acidification due to anthropogenic carbon uptake induces deep ocean acidification driven by a substantial reduction in CaCO3 deep dissolution following its decreased export at depth. Although the effect of a diminished carbonate pump on global ocean carbon uptake and surface ocean acidification remains limited until 2300, it can have a large impact on regional air–sea carbon fluxes, particularly in the Southern Ocean.

Stable Isotopic (δ13C) Evidence for Global Microbial Sequestration of Refractory Dissolved Organic Matter

AbstractDissolved 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) δ13C values are 1.3 ± 0.6‰ lower than mean total DOC δ13C between depth ranges 0–200 m and 2–4 km on three GO‐SHIP Repeat Hydrography cruises. Lowest observed δ13C values correlate with low ∆14C 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 13C, highlighting the need for continued research on non‐retained DOC to predict mechanisms that drive ocean carbon storage.

Contribution of Smoke Aerosols From Wildfires in Indo‐China Peninsula to the Western Pacific Ocean Carbon Sink

AbstractSmoke aerosols from wildfires play a vital role in marine ecosystems and the ocean carbon cycle. This study analyzed a severe wildfires incident occurred in the Indo‐China Peninsula on 26 March 2019, and assessed its impact on ocean carbon sink. The satellite observations showed that the wildfires covered an area of about 56% of the entire peninsula, burning an area of 1.17 × 106 km2. Consequently, the wildfires discharged about 0.43 × 109 kg carbon. Moreover, a substantial amount of smoke released by severe wildfires was carried downstream by the wind and reached the western Pacific Ocean within 2 days. These smoke aerosols contribute to the ocean carbon sink through the mechanisms of the biological pump and their own carbon deposition. Model simulation results showed smoke aerosols contribute 6.44 × 104 kg black carbon to surface ocean by their own carbon deposition. Moreover, during the period of smoke aerosol's deposition, the flourishing growth of phytoplankton resulted in an increased carbon export of 0.25 ± 0.09 × 109 kg carbon (the biological pump mechanism), which represented approximately 57.97% ± 20.30% of the carbon emissions originating from the wildfire‐affected source region. Our research showed a positive impact of large wildfires on the ocean carbon sink, indicating the potential of smoke aerosols to alleviate the climate pressures resulting from carbon dioxide released by wildfires through improving the capacity of ocean carbon sink.

Aquatic photosynthetic carbon pump driven by periodic temperature variations affects dissolved inorganic carbon and hydrochemical characteristics in a groundwater-fed reservoir.

Under the influence of periodic temperature variations, biogeochemical cycling in water bodies is markedly affected by the periodic thermal stratification processes in subtropical reservoirs or lakes. In current studies, there is insufficient research on the influence and mechanism of dissolved inorganic carbon (DIC) distribution in karst carbon-rich groundwater-fed reservoirs under the coupled effects of thermal structure stratification and the biological carbon pump (BCP) effect. To address this issue, the Dalongdong (DLD) reservoir in the subtropical region of southern China was chosen as the site for long-term monitoring and research on relevant physicochemical parameters of water, DIC, and its stable carbon isotope (δ13CDIC), CO2 emission flux, as well as the reservoir's thermal stratification index. The results show that: (1) the DLD reservoir is a typical warm monomictic reservoir, which exhibits regular variations of mixing period-stratification period-mixing period on a yearly scale due to thermal structure changes; (2) DIC was consumed by aquatic photosynthetic organisms in the epilimnion during the stratification period, leading to a decrease in DIC concentration, partial pressure of CO2 (pCO2) and CO2 emission flux, and an increase in stable carbon isotope (δ13CDIC). During the mixing period, the trend was reversed; (3) During the thermal stratification, aquatic photosynthesis and water temperature were the primary factors controlling DIC variations in both the epilimnion and thermocline. Regarding the hypolimnion, calcite dissolution, organic matter decomposition, and water temperature were the dominant controlling factors. These results indicate that although carbon-rich karst groundwater provides a plentiful supply of DIC in the DLD reservoir, its availability is still influenced by variations in the reservoir's thermal structure and the metabolic processes of aquatic photosynthetic organisms. Therefore, to better estimate the regional carbon budget in a reservoir or lake, future studies should especially consider the combined effects of BCP and thermal structure variations on carbon variations.

Phylogenomic analysis expands the known repertoire of single-stranded DNA viruses in benthic zones of the South Indian Ocean

Phylogenomic analysis expands the known repertoire of single-stranded DNA viruses in benthic zones of the South Indian Ocean

Iron dissolution from Patagonian dust in the Southern Ocean: under present and future conditions

Although the input of desert dust as a key source of trace metals in the Southern Ocean (SO) has been previously studied, the dissolution process of metals in surface waters, particularly iron (Fe), remain poorly understood. Given the crucial role of Fe in primary production and the biological carbon pump in the SO, we focused on experimental estimations of Fe dissolution from Patagonian dust, the primary natural dust source in the SO. Our study considered both current and projected future conditions, encompassing sea-surface warming, acidification, increased photosynthetically active radiation, and doubled dust inputs. Through controlled laboratory experiments using filtered SO seawater, conducted over 7 days, we assessed changes in particulate Fe (pFe) concentrations, Fe redox speciation (Fe(II)/Fe(III)), and in the mineralogy of Fe-bearing dust in abiotic condition. The predominant minerals in the dust included quartz and aluminosilicates, with silicon (Si), aluminum (Al), and Fe as the major elements. No significant alterations in the mineralogy and the elemental composition of the dust were recorded during the dissolution experiments, neither under present nor under projected future conditions. The particulate Fe(II)/Fe(III) ratio remained consistently at 0.25 during the experiments, unaffected by changed conditions. Consequently, changes in environmental conditions in the SO would therefore not significantly alter the mineralogy and redox speciation of pFe in the Patagonian dust. On the contrary, pFe exhibited a dissolution rate of 3.8% and 1.6% per day under present and future conditions, respectively. The environmental changes anticipated for 2100 in the SO will likely to result in a decrease in the dissolution rate of pFe. Thus, even though a doubling of dust input by 2100 is anticipated, it will unlikely provide significantly more dissolved Fe (dFe) in seawater in the SO. Consequently, the future intensification of Patagonian dust inputs may not alleviate the Fe limitation in the SO.

Bacterial magnetofossil evidence for enhanced Pacific Ocean respired carbon storage during buildup of Antarctic glaciation

Global cooling with the onset of Antarctic glaciation ca. 34 Ma across the Eocene–Oligocene transition (EOT) terminated the early Cenozoic greenhouse climate state and marked the beginning of icehouse conditions. Although a pCO2 decline is considered to have been a major cause of this climate shift, the associated carbon-sequestration mechanism remains unclear. Here, we assessed ocean production and circulation changes across the EOT using numerical simulations combined with a novel proxy, namely, bacterial magnetofossils, the abundance and morphology of which are sensitive to sedimentary organic matter accumulation and oxygenation. We detected production and oxygenation declines in the equatorial Pacific Ocean coeval with increased biological production in the Southern Ocean after the EOT. Corroborated by simulation results and evidence from the Subantarctic region, we interpret this counterintuitive combination as a result of enhanced bottom-water formation and biological pump efficiency in the Southern Ocean due to Antarctic glacial buildup across the EOT. These results provide key evidence for deep Pacific Ocean deoxygenation and increased respired carbon concentrations, which amplified CO2 decline across the EOT.

Microbial interactions with microplastics: Insights into the plastic carbon cycle in the ocean

The fate of microplastics (MPs) in the ocean is mostly driven by (i) photo-oxidation to smaller particles and dissolved constituents, which fuel the dissolved organic carbon pool (plastic-derived DOC, pDOC), and (ii) interactions with organic matter forming sinking aggregates (marine plastic snow). Two separate laboratory experiments were conducted to investigate the two pathways of MPs. In the first experiment, we measured potential rates of microbial pDOC utilization in bottle incubations over 15 days with microbial assemblages from coastal and offshore waters. Microbial utilization of pDOC was more efficient in the coastal (72% bioreactive pDOC) compared with the offshore experiment (32% bioreactive pDOC) 15 days. Changes in bacterial cell abundance and extracellular enzyme activities (glucosidase, peptidase, esterases) indicated that a fraction of pDOC was repackaged into microbial exopolymeric substances (EPS), stimulating growth of known EPS degrading bacteria within the phyla Verrucomicrobiota and Planctomycetota. Microbial EPS likely also played a key role in our second experiment that showed the formation of marine plastic snow in roller tanks with cultured cells of Emiliana huxleyi but not with cells of an Isocrysis sp. culture. Average sinking velocities of marine plastic snow were a factor of 1.2 lower compared with marine snow without MPs. Both aggregate types showed reduced sinking velocities in a density stratified sinking column. Our results from the two experiments on (i) microbial utilization of pDOC and (ii) the formation and sinking of marine plastic snow indicate potential effects of plastic-derived compounds on microbial elemental cycles (i.e., pDOC repackaged into EPS) with consequences for the efficiency of the biological carbon pump (i.e., marine plastic snow reduces carbon export) and the fate of plastic-derived compounds in the ocean.

Response of the calcareous nannofossils to the Cretaceous-Paleogene boundary event: A case study from Sinai, Egypt

A detailed study of calcareous nannofossils was conducted on a well-exposed succession encompassing the Cretaceous-Paleogene (K-Pg) boundary interval at Wadi Nukhul, Sinai, Egypt, as a part of the southern Tethyan margin. The nannofossil biostratigraphic data show that the Nukhul succession sustains a complete K-Pg boundary interval. The nannofossil assemblage indicates a shift from cool/oligo-mesotrophic conditions in the late Maastrichtian Micula murus Zone to warm/oligotrophic in the latest Maastrichtian M. prinsii Zone prior to the K-Pg boundary. At the K-Pg boundary, diversity, and total abundance of the calcareous nannofossils remarkably decreased signifying unstable marine conditions. The post-impact assemblage (lowermost part of NP1 Zone) was marked by acme of Cervisiella operculata indicating oligotrophic conditions in the photic zone related to the diminished of the marine primary producers in the lowermost Danian. At the upper portion of the NP1 Zone, the assemblage is still dominated by C. operculata, besides the successive occurrence of the small-sized incoming Paleocene taxa Biantholithus sparsus and Neobiscutum romeinii. This pattern was accompanied by increased frequencies of Zeugrhabdotus sigmoides indicating stressful cool/meso-eutrophic surface water conditions signify the initial recovery interval. Upward in the early Danian NP2-NP3 zones, the nannofossil species diversity and total abundance progressively increased. Also, the nannofossil assemblage characterized by the existence of the new Paleocene oligotrophic indicators like Cruciplacolithus primus, Coccolithus pelagicus, and Ericsonia subpertusa. This probably indicates a tendency toward rebuilding of the biological pump efficiency and, therefore, a full recovery phase was resumed.

A global dataset of carbon pumping by the world’s largest tropical rivers

The eco-morphodynamic activity of large tropical rivers interacts with riparian vegetation causing implications for the carbon cycle within inland waters. Through a multi-temporal analysis of satellite data spanning the years 2000–2019, we analyzed rivers exceeding 200 m in width across the tropical regions, revealing a Carbon Pump mechanism driving an annual mobilization of 12.45 million tons of organic carbon. The study identifies fluvial eco-morphological signatures as proxies for carbon mobilization, emphasizing the link between river migration and carbon dynamics. To enhance accessibility, our results are encapsulated in a visually compelling WebGIS application, offering a comprehensive understanding of the eco-geomorphological influences on the global carbon cycle within large tropical rivers. Our findings are instrumental in determining the carbon intensity of future hydropower dams, thereby contributing to informed decision-making in the realm of sustainable energy infrastructure. This study elucidates the intricate relationships that govern the nexus of tropical river dynamics, riparian ecosystems, and the global carbon cycle.

Strong and efficient summertime carbon export driven by aggregation processes in a subarctic coastal ecosystem

AbstractSinking marine particles, one pathway of the biological carbon pump, transports carbon to the deep ocean from the surface, thereby modulating atmospheric carbon dioxide and supplying benthic food. Few in situ measurements exist of sinking particles in the Northern Gulf of Alaska; therefore, regional carbon flux prediction is poorly constrained. In this study, we (1) characterize the strength and efficiency of the biological carbon pump and (2) identify drivers of carbon flux in the Northern Gulf of Alaska. We deployed up to five inline drifting sediment traps in the upper 150 m to simultaneously collect bulk carbon and intact sinking particles in polyacrylamide gels and measured net primary productivity from deck‐board incubations during the summer of 2019. We found high carbon flux magnitude, low attenuation with depth, and high export efficiency. We quantitatively attributed carbon flux between 10 particle types, including various fecal pellet categories, dense detritus, and aggregates using polyacrylamide gels. The contribution of aggregates to total carbon flux (41–93%) and total carbon flux variability (95%) suggest that aggregation processes, not zooplankton repackaging, played a dominant role in carbon export. Furthermore, export efficiency correlated significantly with the proportion of chlorophyll a in the large size fraction (> 20 μm), total aggregate carbon flux, and contribution of aggregates to total carbon flux. These results suggest that this stratified, small‐cell‐dominated ecosystem can have sufficient aggregation to allow for a strong and efficient biological carbon pump. This is the first integrative description of the biological carbon pump in this region.

Temporal and vertical variations in carbon flux and export of zooplankton fecal pellets in the western South China Sea

The enhancement of particulate organic carbon transfer to the deep sea by zooplankton fecal pellets constitutes a crucial component of the marine biological carbon pump. Here, we investigated time-series variations in characteristic and flux of zooplankton fecal pellets at different water depths of two sediment-trap mooring stations from May 2021 to May 2022 in the western South China Sea. The results show that numerical fluxes of fecal pellets were 0.75 ± 0.60 × 104, 0.63 ± 0.63 × 104, and 0.38 ± 0.29 × 104 pellets m−2 d−1 at 500 m, 1170 m, and 1380 m water depth, respectively, corresponding to their carbon fluxes of 0.10 ± 0.06, 0.09 ± 0.04, and 0.10 ± 0.04 mg C m−2 d−1. Both numerical and carbon fluxes of fecal pellets exhibited clear seasonal variations, with two peaks occurred in August and early November at all water depths. The fecal pellets have distinct morphological types (spherical, cylindrical, and ellipsoidal) and their contributions to the numerical and carbon fluxes were different. At all water depths, ellipsoidal and spherical pellets accounted for 96.0% of the numerical flux and 72.1% of the carbon flux. Cylindrical pellets were rare in quantity, accounting for 4.0% of numerical flux, but their carbon contribution accounted for 27.9% of the total fecal pellet carbon flux. The proportional fractions of zooplankton fecal pellets contributed to the overall particulate organic carbon from 0.7% to 28.2% in the western South China Sea, and fell in a reasonable range around the world. Multiple mechanisms, including East Asian monsoon climate and zooplankton community structure may be responsible for the production and fate of fecal pellets as well as their contribution to the settling particulate organic carbon.

Fabrication of a hybrid device for the integration of light-triggered proton pumps

Biological ion pumps, such as bacteriorhodopsin (bR), utilize photons to move ions against concentration gradients, offering energy harvesting and spatiotemporal control of chemical gradients. This capability goes far beyond the capabilities of today's synthetic devices, suggesting a hybrid approach to embed bRs in synthetic devices in order to direct the proton flow towards useful system applications. In this study, a hybrid silicon-based nanochannel network with integrated purple membranes (PM) containing bR was fabricated. The fabrication method combines thermal scanning probe lithography, etching techniques, atomic layer deposition, plasma-enhanced chemical vapor deposition, and photolithography to create devices with buried nanochannels on silicon substrates. PM patches were deposited onto specified sites by a tunable nanofluidic confinement apparatus. The resulting device holds the potential for locally controlling directed ion transport in micrometer scale devices, a first step towards applications, such as locally affected proton catalyzed chemical reaction networks. Furthermore, this fabrication strategy, employing a maskless overlay, is a tool for constructing intricate nanofluidic network designs which are mechanically robust and straightforward to fabricate.

Technical note: A comparison of methods for estimating coccolith mass

Abstract. The fossil record of coccolithophores dates back approximately 225 million years, and the production of their calcite platelets (coccoliths) contributes to the global carbon cycle over short and geological timescales. Variations in coccolithophore parameters (e.g. community composition, morphology, size and coccolith mass) are a key factor for ocean biogeochemical dynamics (e.g. biological carbon pump) and have been used as a palaeoproxy to understand past oceanographic conditions. Coccolith mass has been frequently estimated with different methods with electron microscopy being the most applied. Here, we compared the electron microscopy (EM) method with the Coulter multisizer (CM) (i.e. electric field disturbance) and bidirectional circular polarization (BCP) methods to estimate coccolith masses (pg CaCO3) in controlled laboratory experiments with two ecotypes of Emiliania huxleyi. Average coccolith mass estimates were in good agreement with literature data. However, mass estimates from the CM were slightly overestimated compared to EM and BCP estimates, and a correction factor (cf=0.8) is suggested to compensate for this discrepancy. The relative change in coccolith mass triggered by morphotype-specific structures and environmental parameters (i.e. seawater carbonate chemistry) was suitably captured by each of the three techniques.

Variability in the relationship between light scattering and chlorophyll a concentration in oligotrophic tropical regions of the Western Pacific Ocean.

It is important to determine the relationship between the concentration of chlorophyll a (Chla) and the inherent optical properties (IOPs) of ocean water to develop optical models and algorithms that characterize the biogeochemical properties and estimate biological pumping and carbon flux in this environment. However, previous studies reported relatively large variations in the particulate backscattering coefficient (bbp(λ)) and Chla from more eutrophic high-latitude waters to clear oligotrophic waters, especially in oligotrophic oceanic areas where these two variables have little covariation. In this study, we examined the variability of bbp(λ) and Chla in the euphotic layer in oligotrophic areas of the tropical Western Pacific Ocean and determined the sources of these variations by reassessment of in-situ measurements and the biogeochemical-argo (BGC-Argo) database. Our findings identified covariation of bbp(λ) and Chla in the water column below the deep Chla maximum (DCM) layer, and indicated that there was no significant correlation relationship between bbp(λ) and Chla in the upper layer of the DCM. Particles smaller than 3.2 µm that were in the water column above the DCM layer had a large effect on the bbp(λ) in the vertical profile, but particles larger than 3.2 µm and smaller than 10 µm had the largest effect on the bbp(λ) in the water column below the DCM layer. The contribution of non-algal particles (NAPs) to backscattering is up to 50%, which occurs in the water depth of 50 m and not consistent with the distribution of Chla. Phytoplankton and NAPs were modeled as coated spheres and homogeneous spherical particles to simulate the bbp(λ) of the vertical profile by Aden-Kerker method and Mie theory, and the results also indicated that the backscattering caused by particles less than 20 µm were closer to the measured data when they were below and above the DCM layer, respectively. This relationship also reflects the bbp(λ) of particles in the upper water was significantly affected particle size, but bbp(λ) in the lower water was significantly affected by Chla concentration. This effect may have relationship with phytoplankton photoacclimation and the relationship of a phytoplankton biomass maximum with particle size distribution in the water column according to the previous relevant studies. These characteristics also had spatial and seasonal variations due to changes of Chla concentration at the surface and at different depths. There was mostly a linear relationship between Chla and bbp(700) during winter. During other seasons, the relationship between these two variables was better characterized by a power function (or a logarithmic function) in the lower layer of the DCM. The spatial and vertical relationships between the bbp(λ) and Chla and the corresponding variations in the types of particles described in this study provide parameters that can be used for accurate estimation of regional geochemical processes.

Organic matter accumulation as a convergence response to astronomical forcing: Insights from Milankovitch periods and sea-level fluctuations during the early Cambrian

The accumulation of organic matter (OM) in marine sediments is a vital part of the global carbon cycle today and on ancient Earth, and is driven by a cumulative shift of organic carbon flux through oceans to marine sediments. This shift is a complicated process that is known to be influenced by the biological pump, diagenesis, and thermal alteration, so is affected by oceanic conditions and palaeo-climate, but less attention has been paid to the triggers of OM accumulation. Here, a set of marine sedimentary rocks from the early Cambrian in the southwestern part of the Yangtze Platform in China was used to search for clues to the triggers of OM accumulation. The effect of astronomical forcing, which potentially is a major control on Earth's oceanic conditions, was assessed via frequency analysis based on a high-resolution log dataset from a borehole in Yunnan Province. An astronomical time scale was constructed based on a 405,000 year-tuned filter. Palaeo-oceanic sedimentary conditions and palaeo-climate, which were recorded in the sedimentary rocks, were determined through geochemical analyses of major, trace, and rare earth elements. The mutual influence of astronomical forcing and the early Earth oceanic sedimentary conditions and paleoclimate were examined though Pearson Correlation analyses to provide evidence for the intensity of alteration of sedimentary conditions and the forces impacting the shift of organic carbon in the marine ecosystem. The results show that two convergence responses of OM accumulation were associated with ca. 1.5 and 2.4 million year (Myr) Milankovitch cycles. Fluctuations in sea level establish a connection between Milankovitch forcings and changes in sedimentary conditions, thereby providing evidence for the triggering of a cumulative shift of OM flux to sediments, and the effect of astronomical forcing on the organic carbon cycle.

Effect of hydrodynamic and ecosystem conditions on persistent organic pollutant temporal-spatial variations in the Yellow Sea

Coastal seas are important pools of persistent organic pollutants (POPs) discharged from land. Considering the complex conditions in coastal seas and various biochemical features of POPs, special temporal-spatial variations in POPs have been reported. To understand these variations, we developed a three-dimensional hydrodynamic–ecosystem–POP coupled model and applied it to the Yellow Sea. We selected two POP species (polychlorinated biphenyl congener 153 (PCB-153) and decabromodiphenyl ether (BDE-209)), which have different biochemical properties, as target materials. The dissolved PCB-153 simulated concentration was high in late spring and low in autumn, whereas that of BDE-209 was high in summer and low in winter. Both PCB-153 and BDE-209 showed high particle-bound concentrations in early spring. In summer, dissolved PCB-153 accumulated at the sea bottom, whereas dissolved BDE-209 accumulated at the sea surface. Seasonal and spatial variation differences in the two POPs are likely caused by greater Henry’s Law Constant (H′) and bioconcentration factor (BCF) of PCB-153 than that of BDE-209, which leads to higher volatilization and stronger absorption by the particles for PCB-153 than BDE-209. As a component of such differences, the “biological pump” of PCB-153 in the central Yellow Sea is more apparent than that of BDE-209.

The microbial carbon pump and climate change.

The ocean has been a regulator of climate change throughout the history of Earth. One key mechanism is the mediation of the carbon reservoir by refractory dissolved organic carbon (RDOC), which can either be stored in the water column for centuries or released back into the atmosphere as CO2 depending on the conditions. The RDOC is produced through a myriad of microbial metabolic and ecological processes known as the microbial carbon pump (MCP). Here, we review recent research advances in processes related to the MCP, including the distribution patterns and molecular composition of RDOC, links between the complexity of RDOC compounds and microbial diversity, MCP-driven carbon cycles across time and space, and responses of the MCP to a changing climate. We identify knowledge gaps and future research directions in the role of the MCP, particularly as a key component in integrated approaches combining the mechanisms of the biological and abiotic carbon pumps for ocean negative carbon emissions.