Marine heatwaves modulate food webs and carbon transport processes

The impact of marine heatwaves (MHWs) on ecosystem functions and services remains poorly constrained due in part to the limited availability of time-resolved datasets integrating physical, chemical and biological parameters at relevant operating scales. Here we paired over a decade of autonomous Biogeochemical (BGC)-Argo profiling float data with water column plankton community composition profiles to investigate the impacts of MHWs on carbon cycling dynamics in the Northeastern subarctic Pacific Ocean (NESAP), resolving temperature-induced changes in production and transport of particulate organic carbon (POC) within the water column. POC concentrations were extremely high during MHWs in Spring 2015 and 2019, associated with detritus enhancement and changes in plankton community structure. Instead of sinking, particles

Export of particulate organic carbon by the mountainous tropical rivers of Western Ghats, India: Variations and controls

Source, transport and fluxes of Amazon River particulate organic carbon: Insights from river sediment depth-profiles

Spatial patterns and environmental controls of particulate organic carbon in surface waters in the conterminous United States

Determining true particulate organic carbon: bottles, pumps and methodologies

Biogeochemical response of Emiliania huxleyi (PML B92/11) to elevated CO 2 and temperature under phosphorous limitation: A chemostat study

The transport of particulate organic carbon (POC) from land to deep-sea sediments is a key component of the global carbon cycle. However, the magnitude and mechanisms of terrestrial POC transport on continental shelves remain poorly understood due to the complexity of these systems. In this study, we investigated the vertical fluxes and fates of terrestrial versus marine POC using stable carbon isotope ratios (δ13C) and 234Th tracers in the southern coastal region of Korea. The total suspended matter concentrations were highest in the bottom layer, while the POC concentrations were higher in both the surface and bottom layers. Based on δ13C values, terrestrial POC accounted for 29 ± 24% of the total POC, with higher contributions at the innermost stations and in the bottom layer, while the contributions of marine POC were only higher in the surface layer. Based on 234Th-238U disequilibria, residence times of particulate 234Th (10 ± 6 days) were calculated to be significantly longer than those of dissolved 234Th (3.8 ± 2.3 days). Much higher vertical fluxes of terrestrial POC in the deeper layers than in the upper layers suggest that terrestrial POC undergoes multiple cycles of turnover through resuspension before burial, while marine POC undergoes preferential degradation during sinking. Our findings highlight that resuspension processes in coastal margins and the refractory nature of terrestrial POC likely facilitate its long-range transport (> 200 km) to the deep Ulleung Basin of the East/Japan Sea.

In this study, particulate organic carbon (POC) contents and their distribution pattern in surficial sediments of the Baltic Sea are presented for 1,471 sampling stations. POC contents range from approx. 0.1% in shallow sandy areas up to 16% in deep muddy basins (e.g. Gotland Basin). Some novel relationships were identified between sediment mass physical properties (dry bulk density (DBD), grain size) and POC levels. Notably, the highest POC concentrations (about 10–17 mg cm–3) occur in sandy mud to mud (60–100% mud content) with intermediate POC contents of about 3–7% and DBDs of 0.1–0.4 g cm–3. Areas with this range in values seem to represent the optimum conditions for POC accumulation in the Baltic Sea. The maximum POC contents (8–16%) are found in fluid mud of the central Baltic Sea characterized by extremely low DBDs (<0.1 g cm–3) and moderate POC concentrations (4–7 mg cm–3). Furthermore, sediment mass accumulation rates (MAR), based on 210Pb and 137Cs measurements and available for 303 sites of the Baltic Sea, were used for assessing the spatial distribution of POC burial rates. Overall, these vary between 14 and 35 g m–2 year–1 in the mud depositional areas and, in total, at least 3.5 (±2.9) Mt POC are buried annually. Distribution patterns of POC contents and burial rates are not identical for the central Baltic Sea because of the low MAR in this area. The presented data characterize Baltic Sea sediments as an important sink for organic carbon. Regional differences in organic carbon deposition can be explained by the origin and transport pathways of POC, as well as the environmental conditions prevailing at the seafloor (morphology, currents, redox conditions). These findings can serve to improve budget calculations and modelling of the carbon cycle in this large brackish-water marginal sea.

Carbon transported by rivers is an important component of the global carbon cycle. Here, we report on organic carbon transport along the third largest river in China, the Songhua River, and its major tributaries. Water samples were collected seasonally or more frequently to determine dissolved organic carbon (DOC) and particulate organic carbon (POC) concentrations and C/N and stable carbon isotopic ratios. Principal component analysis and multiple regression analysis of these data, in combination with hydrological records for the past 50 years, were used to determine the major factors influencing the riverine carbon fluxes. Results indicate that the organic carbon in the Songhua River basin is derived mainly from terrestrial sources. In the 2008–2009 hydrological year, the mean concentrations of DOC and POC were 5.87 and 2.36 mg/L, and the estimated fluxes of the DOC and POC were 0.30 and 0.14 t·km−2·year−1, respectively. The riverine POC and DOC concentrations were higher in subcatchments with more cropland, but the area-specific fluxes were lower, owing to decreased discharge. We found that hydrological characteristics and land-use type (whether forest or cropland) were the most important factors influencing carbon transport in this system. Agricultural activity, particularly irrigation, is the principal cause of changes in water discharge and carbon export. Over the last 50 years, the conversion of forest to cropland has reduced riverine carbon exports mainly through an associated decrease in discharge following increased extraction of water for irrigation.

In 1998–1999, beam attenuation coefficient (bac) profiles, suspended particulate matter (SPM) and particulate organic carbon (POC) concentrations were assessed during five cruises in the Saronikos Gulf, eastern Mediterranean, Greece. SPM and POC concentrations (0.05–1.84 mg l−1 and 10.2–468.6 μg l−1, respectively) exhibited strong spatial and temporal variations, related to the different environmental characteristics of various sectors of the gulf, including wind regime and biological productivity. The Elefsis and Keratsini bays, as well as the area around Psyttaleia Island, showed the highest POC concentrations. The vertical distribution of POC at stations in the western basin, as well as in the inner and outer Saronikos Gulf is characterised by higher POC concentrations in surface waters, associated with higher biological activity. The wastewater treatment plant effluents discharged south of the Psyttaleia Island are a major source of organic particles which directly influence the intermediate water layers, at least during the stratification period. Assessments of relationships between bac and SPM or POC concentrations revealed a relatively strong correlation between bac and POC. An equation converting bac readings to POC concentration was established which can be applied to historical and/or future bac measurements, independently of season. POC concentrations estimated from calibrated continuous transmissometer readings were used to estimate the standing stock of POC in the Saronikos Gulf, which varied between 6,110×106 and 13,450×106 g C during the period June 1998 to February 1999.

This study was designed to determine the amount of particulate organic carbon (POC) introduced to the Gulf of Mexico by the Mississippi River and assess the influence of POC inputs on the development of hypoxia and burial of organic carbon on the Louisiana continental shelf. Samples of suspended sediment and supporting hydrographic data were collected from the river and >50 sites on the adjacent shelf. Suspended particles collected in the river averaged 1.8±0.3% organic carbon. Because of this uniformity, POC values (in μmol l−1) correlated well with concentrations of total suspended matter. Net transport of total organic carbon by the Mississippi-Atchafalaya River system averaged 0.48×1012 moles y−1 with 66% of the total organic carbon carried as POC. Concentrations of POC decreased from as high as 600 μmol l−1 in the river to 35% along the shelf at ≥10 km from the river mouth. River flow was a dominant factor in controlling particle and POC distributions; however, time-series data showed that tides and weather fronts can influence particle movement and POC concentrations. Values for apparent oxygen utilization (AOU) increased from ∼60 μmol l−1 to >200 μmol l−1 along the shelf on approach to the region of chronic hypoxia. Short-term increases in AOU were related to transport of more particle-rich waters. Sediments buried on the shelf contained less organic carbon than incoming river particles. Orgamic carbon and δ13C values for shelf sediments indicated 3 that large amounts of both terrigenous and marine organic carbon are being decomposed in shelf waters and sediments to fuel observed hypoxia.

The transport of particulate organic carbon (POC) from land to deep‐sea sediments is a critical component of the global carbon cycle. However, the transport processes of terrestrial POC across continental shelves remain poorly understood due to the complexity of these systems. In this study, we investigated the vertical fluxes and fates of terrestrial vs. marine POC using stable carbon isotope ratios (δ13C) and 234Th tracers along two transects in the southern coastal region of Korea. The POC concentrations were highest in the surface layer and decreased with depth, with a slight increase near the seafloor. The δ13C values revealed that terrestrial POC contributed 29% ± 24% of the total POC, with higher contributions at the innermost stations and in the bottom layer. Based on 234Th–238U disequilibria, the residence times of particulate 234Th (8.1 ± 3.6 d) were significantly longer than those of dissolved 234Th (3.7 ± 2.2 d). The much higher vertical fluxes of terrestrial POC in the deeper layer relative to the upper layer suggest that terrestrial POC undergoes multiple turnover cycles through sediment resuspension before burial, while marine POC degrades preferentially in the course of settling. These findings highlight that effective sediment resuspension and the refractory nature of terrestrial POC allow for its long‐range transport (&gt; 200 km) to the deep Ulleung Basin in the East Sea (Japan Sea). This study sheds new light on the mechanisms driving the transport of terrestrial POC from coastal regions to the deep ocean.

Design and application of a semi-automated filtration system to study the distribution of particulate organic carbon in the water column of a coastal upwelling system

Human activities changed organic carbon transport in Chinese rivers during 2004-2018

Spatiotemporal variability of organic carbon in streams and rivers of the Northern Hemisphere cryosphere