Macroalgae culture-induced carbon sink in a large cultivation area of China.

Macroalgae culture-induced carbon sink in sediments has been little investigated. Here, total organic carbon (TOC), total nitrogen (TN), and δC were examined in sediments in a cultivation field of macroalgae (kelp and Gracilariopsis lemaneiformis) in Sansha Bay, Southeast China. Both proxies of C/N (TOC to TN ratio) and δC indicated a multisource of TOC.

Dynamics of particulate black carbon in the South China Sea: Magnitude, resident timescale, sinking speed, and flux.

The dynamics of particulate black carbon (PBC) in marine environments are poorly understood. Here, radioactive Th was used to constrain the resident timescale, settling speed, and sinking flux of PBC (soot) in the coastal Northeastern South China Sea (NSCS). The PBC concentration varied from 0.

Changes in the carbon source and storage in a cultivation area of macro-algae in Southeast China.

Macro-algae culture has recently attracted attention in China because of its capability to sequester carbon. Here, radionuclides, total organic carbon (TOC), and nitrogen (TN) were examined in a cultivation area of macro-algae in Southeast China. At the reference site, the ratio of TOC to TN (C/N, 8.

Carbon and Iron Uptake by Phytoplankton in the Amundsen Sea, Antarctica.

Freshwater components in the Southern Ocean, whether sea ice meltwater or meteoric water, influence the growth of phytoplankton by affecting water stability and supplying dissolved iron (DFe). In addition, melting sea ice stimulates phytoplankton blooms by providing ice algae. In this study, sea ice meltwater and meteoric water in the Amundsen Sea (AS) were differentiated by their stable oxygen isotopic compositions (δO), while the phytoplankton carbon fixation rate (CFR) and iron uptake rate (FeUR) values were determined using the C and Fe tracer assays, respectively.

The biological uptake of dissolved iron in the changing Daya Bay, South China Sea: Effect of pH and DO.

The oceanic acidification and coastal hypoxia have potential to enhance biological uptake of dissolved iron (Fe) by phytoplankton. In this study, the Fe uptake rate (FeUR) in Daya Bay was significantly negatively correlated with pH and dissolved oxygen (DO) (r = -0.81 and -0.

Semi-enclosed bays serve as hotspots for black carbon burial: A case study in Jiaozhou Bay, western Yellow Sea.

The provenance of black carbon (BC) and its role in affecting contaminant cycling in both the atmosphere and aquatic environments have been extensively studied. However, the fate and cycling dynamics of BC, particularly in marine environments, are poorly understood. Herein, soot BC was determined in the semi-enclosed Jiaozhou Bay to examine the seasonal variability, residence timescale in seawater, and settling flux to sediments, together with particle-reactive Th.

A persistent increase in primary productivity east off Hainan Island (northwestern South China Sea) over the last decades as inferred from sediment records.

Sediment cores were analyzed from the continental shelf of the northwestern South China Sea aiming to understand the change history of primary productivity and provide insights into key changes of environmental conditions in this region over the past ~100 years. Multiple proxies including stable carbon isotopic composition (δC) of sedimentary organic matter, diatom abundance and biogenic silica burial flux were applied along with Pb chronology. Notably, these independent evidences consistently point to a steady increase of primary production in this region only after ~1960s.

Responses of Two Coastal Algae (Skeletonema costatum and Chlorella vulgaris) to Changes in Light and Iron Levels.

Iron (Fe) is essential for phytoplankton growth and photosynthesis, and is proposed to be an important factor regulating algal blooms under replete major nutrients in coastal environments. Here, Skeletonema costatum, a typical red-tide diatom species, and Chlorella vulgaris, a widely distributed Chlorella, were chosen to examine carbon fixation and Fe uptake by coastal algae under dark and light conditions with different Fe levels. The cellular carbon fixation and intracellular Fe uptake were measured via C and Fe tracer assay, respectively.

N fixation impacted by carbon fixation via dissolved organic carbon in the changing Daya Bay, South China Sea.

We present the first concurrent measurements of N fixation rates (N uptake), primary production (C uptake), dissolved organic carbon (DOC) concentrations, and diazotrophic community composition derived from nitrogenase (nifH) abundance in the subtropical Daya Bay (DB) of the coastal northern South China Sea (NSCS) from 2015 to 2017. N fixation rates ranged from n.d.

Role of organic components in regulating denitrification in the coastal water of Daya Bay, southern China.

Both dissolved and particulate organic materials have been proposed to be important factors in regulating heterotrophic denitrification in various aquatic environments. However, the specific pathways and mechanisms remain elusive. In this study, water column samples were collected from Daya Bay, southern China, to examine the relationships between potential denitrification and different organic components in the water column.

Effects of particles on potential denitrification in the coastal waters of the Beibu Gulf in China.

Although the influence of suspended particulate matter (SPM) on denitrifying activity has been identified in river waters recently through metabolic incubations and community gene analysis, the regulations of SPM to denitrification in marine systems are still poorly understood. In the present study, the effects of suspended particle properties (including concentration, composition and size) on potential denitrification were explored in the coastal Beibu Gulf water columns based on a series of N-labeled incubations under artificial anaerobic condition. A gradient of oxygen (O) concentrations was also manipulated in the incubated seawaters to test the sensitivity of denitrification to O exposure.

Identification of the earlier human-induced sedimentation change in Daya Bay, northern South China Sea using Pb and Cs.

Over the past 30years, the rapid development of the Chinese economy resulted in environmental problems, especially in coastal areas. To discern the effects of anthropogenic activities, Pb and Cs were examined in the sediment from Daya Bay, northern South China Sea. The specific activity of Cs showed a clear maximum, corresponding to 1963.

A potential nitrogen sink discovered in the oxygenated Chukchi Shelf waters of the Arctic.

The western Arctic Shelf has long been considered as an important sink of nitrogen because high primary productivity of the shelf water fuels active denitrification within the sediments, which has been recognized to account for all the nitrogen (N) removal of the Pacific water inflow. However, potentially high denitrifying activity was discovered within the oxygenated Chukchi Shelf water during our summer expedition. Based on N-isotope pairing incubations, we estimated denitrification rates ranging from 1.

Abundance and sinking of particulate black carbon in the western Arctic and Subarctic Oceans.

The abundance and sinking of particulate black carbon (PBC) were examined for the first time in the western Arctic and Subarctic Oceans. In the central Arctic Ocean, high PBC concentrations with a mean of 0.021 ± 0.

Influence of a Decaying Cyclonic Eddy on Biogenic Silica and Particulate Organic Carbon in the Tropical South China Sea Based on 234Th-238U Disequilibrium.

Eddies play a critical role in regulating the biological pump by pumping new nutrients to the euphotic zone. However, the effects of cyclonic eddies on particle export are not well understood. Here, biogenic silica (BSi) and particulate organic carbon (POC) exports were examined inside and outside a decaying cyclonic eddy using 234Th-238U disequilibria in the tropical South China Sea.