Despite the growing anthropogenic influence on marine atmospheric composition, aerosol characterization over marginal seas lags behind urban research due to logistical challenges. This study presents a ship-based characterization of springtime PM2.5 over the Yellow Sea and the East China Sea, integrating water-soluble ions, trace metals, iron speciation, and nitrate dual isotopes (δ15N and δ18O). Secondary inorganic ions dominated aerosol composition (85.87%), while over 60% of heavy metals showed anthropogenic enrichment. A moderate positive correlation between water-soluble iron (WS-Fe) and NO3- (R2 = 0.54) indicated that nitrate-related atmospheric processes may facilitate iron dissolution, or that NO3- and WS-Fe are co-transported within the same air masses. Bayesian isotope modeling identified vehicle emissions (31.0 ± 15.8%; 95% CI: 3.0%-62.5%) and ship emissions (18.2 ± 11.1%; 95% CI: 1.2%-41.8%) as dominant NOX sources. Nighttime pathways accounted for 52.5% of nitrate formation, nearly equal to daytime hydroxyl radical (·OH) oxidation (47.5%). This work extended compound-specific isotope analysis beyond traditional source apportionment by linking isotope-constrained NOX sources to aerosol iron solubility, thereby providing a uniquely integrated dataset for China's marginal seas. The results underscored the critical role of anthropogenic nitrogen emissions in modulating marine aerosol composition and acidity, carrying profound implications for iron bioavailability and toxic metal deposition in marginal sea ecosystems.

The Southern Ocean is one of the rapidly acidifying regions globally, yet direct observational constraints on its carbonate chemistry remain scarce. Here, we combine shipboard measurements of pH and aragonite saturation state (Omega(arag)) from the summer 2015 Chinese National Antarctic Research Expedition with reconstructed wintertime conditions to characterize acidification in Prydz Bay. We report the first observation-based occurrence of surface aragonite undersaturation (Omega(arag) < 1.0) in the northern basin-emerging nearly two decades earlier than model projections. Surface Omega(arag) undersaturation is primarily driven by accelerated uptake of anthropogenic CO2 and shoaling of the aragonite saturation horizon, fueled by persistent upwelling of CO2-rich Circumpolar Deep Water. In the ocean interior, organic matter remineralization, CaCO3 dissolution, and continued anthropogenic CO2 intrusion further lower pH and Omega(arag). Our results demonstrate that Prydz Bay is at the forefront of Southern Ocean acidification, highlighting the urgent need to incorporate both anthropogenic and natural biogeochemical feedbacks into high-resolution models to better predict future ecological impacts.

The global ocean is a major source of the climate-relevant atmospheric trace gas nitrous oxide(N2O).However,an accurate assessment of the global oceanic emissions of N2O is hampered by missing data on dissolved N2O from large regions such as the Southern Ocean.To address this deficit,N2O was measured in the Prydz Bay in February 2015 during the 31st Chinese National Antarctic Research Expedition.N2O concentrations(saturation)in the surface layer were generally low(undersaturation with respect to atmospheric equilibrium)and ranged from 13.3 nmol/L to 16.1 nmol/L(83%-102%)at the time of sampling.A comparison of our observations with archived data revealed that no discernible trend in N2O concentrations in the surface waters of Prydz Bay could be detected for the period between 2006 and 2015.Temperature and salinity changes driven by meltwater input were the predominant controls on N2O concentrations in surface waters.At depth,the distribution of N2O concentrations was dominated by production via nitrification in offshore deep waters and vertical convection in the shelf waters,where concentrations were lower and gradients were less steep.Our results suggest a rather unusual pattern of N2O distribution in the Prydz Bay(low N2O in shelf waters compared with the open ocean),providing important insights into the coastal dynamics of N2O in high-latitude polar regions.

Overall ocean health depends critically on dissolved oxygen, which is increasingly impacted by global warming. The Arctic and subarctic regions are experiencing exceptionally rapid warming, known as Arctic amplification, yet its impact on oceanic oxygen remains poorly understood. Here we show that inflowing Atlantic Water (AW) drives deoxygenation in the upper eastern Arctic Ocean and the intermediate layers of the western Arctic Ocean at rates from -0.41 +/- 0.17 to -0.47 +/- 0.07 mu mol kg-1 yr-1, six times the global mean. Amplified Arctic warming is the primary driver, significantly reducing oxygen solubility in the Arctic gateway regions. Rapid subduction and circulation of AW further transmit the deoxygenation signal into Arctic deeper layers, greatly threatening marine ecosystems. Our findings highlight the dominant role of warming Atlantic inflow in shaping the Arctic Ocean oxygen dynamics, indicating that ongoing temperature increases will perpetuate deoxygenation trends and underscoring the need for widespread attention.

Macroalgae mariculture is promoted as a marine carbon dioxide removal (mCDR) strategy, particularly in East Asia. In practice, however, macroalgae is frequently co-cultured with fish and shellfish, complicating carbon budgets and potentially altering net carbon metabolism. While most work has emphasized organic carbon cycles, carbonate system responses under integrated aquaculture remain underexplored. In this study, we conducted seasonal surveys in Sansha Bay, one of the world' largest mariculture zones. Contrary to expectation, the bay persistently outgassed CO2 during winter (the seaweed growth peak season), spring, and fall. Sea surface CO2 partial pressure (pCO2) reached 500-1100 μatm with air-sea CO2 fluxes of 2.1-7.0 mmol m-2 d-1. Against an estimated natural background of 200 μatm (a strong sink), long-term effects of cultivation diverged by trophic group: seaweed cultivation lowered pCO2 by 42 ± 5 μatm, shellfish farming increased it by 36 ± 4 μatm, and fish farming raised it by 375 ± 18 μatm, elevating mean pCO2 to ∼567 ± 20 μatm and transforming the system from a CO2 sink to a source. In this semi-enclosed bay, dissolved inorganic carbon (DIC) generated from fish farming overwhelms algal uptake, driving increases in DIC and pCO2 and reducing the region's carbon sequestration capacity. Seasonal submarine groundwater discharge added ∼30-60 μatm to pCO2, and short-term mariculture activities could episodically elevate pCO2 up to 1100 μatm. Analysis of the dissolved inorganic carbon stable carbon isotope (δ13CDIC) indicates that seasonal increases in DIC and pCO2 in Sansha Bay are due to the decomposition of residual seaweed biomass in late spring and organic matter respiration from fish feed in fall. To achieve mCDR and protect coastal environments, it is essential to reduce formulated feed use or develop alternative environmentally friendly fish farming methods.

Oceanic N2O is a major source of atmospheric N2O gas and is involved in global warming and ozone depletion. It is thought to be mainly produced by nitrification, denitrification and nitrifier denitrification processes mediated by ammonia-oxidizing bacteria, ammonia-oxidizing archaea (AOA) and denitrifying bacteria. The Bering Sea, especially its continental shelf area, is considered a typical source of atmospheric N2O. During the 7th Chinese National Arctic Research Expedition (CHINARE2016), the distributions of N2O and ammonia-oxidizing microorganisms (AOOs) in the Bering Sea continental shelf and abyssal basin water were investigated. At a depth of 50 similar to 900 m within the abyssal basin, the in-situ ammonia oxidation process, particularly performed by AOA, exhibits considerable potential for the formation of supersaturated N2O. Meanwhile, beneath the oxygen minimum zone (depth range is approximately 800 similar to 1,000 m), supersaturated N2O is primarily driven by mixing processes, while the ammonia oxidation mediated by AOA also contributes to a certain extent. In addition, the N2O distribution characteristic exhibits a substantial disparity between the southern and northern Bering Sea shelves, with the former characterized as a mild sink and the latter as a weak source. The water column of the Bering Sea demonstrates a considerable potential for generating supersaturated N2O through ammonia oxidation, as corroborated by the current study. Nitrous oxide (N2O) is an important trace greenhouse gas that also acts as an ozone destroyer. The ocean is one of the main sources of N2O to the atmosphere. As a marginal sea of the Pacific Ocean with high productivity, the distribution mechanism of N2O is very complex affected by water masses mixing and intricate biogeochemical cycle processes. And the N2O flux of Bering Sea has distinct spatio-temporal variability. In this study, by incorporating previous research conclusions on the nitrogen cycle, we investigate the distribution mechanism of N2O and functional genes of ammonia oxidizing microorganisms in the Bering Sea to elucidate the potential contribution of individual nitrogen cycle processes to N2O supersaturation and which kinds of ammonia oxidation microorganisms are involved in this contribution, thus illustrating the distribution mechanisms of N2O in the northern Bering Sea. The flux of Bering Sea in summer was estimated based on the distribution mechanism of N2O. This findings were helpful to understand the mechanism of N2O metabolism in the Bering Sea and improve the accuracy of Marine N2O flux estimation. The source-sink characteristics of N2O in Bering Sea express obvious spatial and temporal variability Ammonia oxidation could potentially play a crucial role in the formation of N2O in the deep waters of the Bering Abyssal Basin The distribution mechanisms of N2O in the southern and northern shelves of the Bering Sea exhibit distinct characteristic

The Chukchi Sea shelf (CSS) is a highly productive region in the Arctic Ocean and it is highly efficient for absorbing atmospheric carbon dioxide and exporting and retaining carbon in the deep sea. However, with global warming, the carbon retention time in CSS may decrease, leading to less efficient carbon export. Here, we investigate the seasonal variability of carbonate chemistry in CSS using three sets of late- vs. early-summer reoccupations of the same transect. Our findings demonstrate substantially increased and rapid degradation of biologically produced organic matter and therefore acidification over time in the southern CSS due to earlier sea-ice retreat, resulting in significantly shorter carbon retention time. In sharp contrast, no increased degradation has been observed in the northern CSS where photosynthesis has just commenced. In the future, climate change would further diminish the carbon export capacity and exacerbate seasonal acidification not only within CSS but also across other polar coastal oceans.

Atmospheric particulate samples collected from Pingtan Island in Fujian province were analyzed for 20 organochlorine pesticides (OCPs) with the aims of elucidating the contamination levels and their influence factors, and providing more comprehensive and fundamental data for the risk assessment of OCPs in this coastal area. The concentration of total OCPs ranged from ND (not detected) to 27.25 pg m–3 (an average of 4.30 ± 4.07 pg m–3) and ND to 13.16 pg m–3 (an average of 3.11 ± 2.54 pg m–3) in 2006 and 2007 respectively, and the level are obviously lower than urban, industrial, suburban, and the similar research areas in the coastal areas of Europe. HCH (Hexachlorocyclohexane) and DDT (Dichlorodiphenyltrichloroethane) were the predominant contaminants, followed by Methoxychlor and Endrin, while the levels of Chlordane, Endosulfan, Aldrin and Dieldrin was relatively lower. Obvious seasonal variations in OCP levels correlate significantly with total particulate levels; higher concentrations of most OCP compounds appeared in winter, whereas lower concentrations appeared in summer. The distribution pattern of the level of most OCP compounds might be directly or indirectly influenced by meteorological conditions, and TOC (total organic carbon) is an important factor influencing the persistence of these OCPs in atmospheric particulates. The source of atmospheric particulates was traced by stable carbon isotopes, which indicate that the increased levels of OCPs in winter and spring influenced by the source of polluted air mass during the “heating season” of Northern China. The cancer risk probability was evaluated based on the residual levels of OCPs, and the results show that dermal contact was the primary pathway affecting human health, and the effect of OCP residuals in atmospheric particulates of the coastal area could not be neglected.

Abstract The acidification of coastal waters is distinguished from the open ocean because of much stronger synergistic effects between anthropogenic forcing and local biogeochemical processes. However, ocean acidification research is still rather limited in polar coastal oceans. Here, we present a 16 year (2002–2018) observational dataset in the Chukchi Sea during the rapid sea‐ice melting season to determine the long‐term changes in pH and aragonite saturation state (Ωarag). We found that pH and Ωarag significantly declined in the water column with average rates of −0.0095 ± 0.0027 years−1 and −0.0333 ± 0.0098 years−1, respectively, and are 4–6 times faster than those solely due to increasing atmospheric CO2. We attributed the rapid acidification to the increased dissolved inorganic carbon owing to a combination of ice melt‐induced increased atmospheric CO2 invasion and subsurface remineralization induced by a stronger surface biological production as a result of the increased inflow of the nutrient‐rich Pacific water.

The strong CO2 sink in Arctic Ocean plays a significant role in the global carbon budget. As a high-latitude oceanic ecosystem, the features of sea surface pCO2 and air-sea CO2 flux are significantly influenced by sea ice melt; however, our understanding of pCO2 evolution during sea ice melt remains limited. In this study, we investigate the dynamics of pCO2 during the progression of sea ice melt in the western Arctic Ocean based on data from two cruises conducted in 2010 and 2012. Our findings reveal substantial spatiotemporal variability in surface pCO2 on the Chukchi Sea shelf and Canada Basin, with a boundary along the shelf breaks at depths of 250-500 m isobaths. On the Chukchi Sea shelf, strong biological consumption dominates pCO2 variability. Moreover, in Canada Basin, the pCO2 dynamics are modulated by various processes. During the active sea ice melt stage before sea ice concentration decreases to 15%, biological production through photosynthetic processes and dilution of ice melt water lead to a reduction in DIC concentration and subsequent decline in pCO2. Further, these effects are counteracted by the air-sea CO2 exchange at the sea surface which tends to increase seawater DIC and subsequently elevate surface pCO2. Compared to the pCO2 reduction resulting from biological production and dilution effects, the contribution of air-sea CO2 exchange is significantly lower. The combined effects of these factors have a significant impact on reducing pCO2 during this stage. Conversely, during the post sea ice melt stage, an increase in pCO2 resulting from high temperatures and air-sea CO2 exchange outweighs its decrease caused by biological production. Their combined effects result in a prevailing increase in sea surface pCO2. We argue that enhanced air-sea CO2 uptake under high wind speeds also contributes to the high sea surface pCO2 observed in 2012, during both active sea ice melt stage and post sea ice melt stage. The present study reports, for the first time, the carbonate dynamics and pCO2 controlling processes during the active sea ice melt stage. These findings have implications for accurate estimation of air-sea CO2 fluxes and improved modeling simulations within the Arctic Ocean.

The Southern Ocean (SO) and Antarctica play important roles in the global climate. The new particle formation (NPF) alters the availability of cloud condensation nuclei (CCN), leading to impacts on the cloud reflectance and global radiative budget. In this review, we introduce the common instruments for measuring particle number concentration (PNC) and particle number size distribution (PNSD). Based on the observations over the Antarctic and some Antarctic research stations, we explored spatial and temporal characteristics of PNCs and PNSDs. From the SO to the interior of the Antarctic, the total PNCs show a decreasing trend, and the total PNCs present an obvious seasonal cycle, with the low concentration in winter (June–August) and the high concentration in summer (December–February). By summarizing the research progress over the SO and Antarctica, we discuss possible precursors of the NPF: sulfuric acid (H2SO4, SA), methanesulfonic acid (CH3S(O)2OH, MSA), dimethyl sulfide ((CH3)2S, DMS), iodic acid (HIO3, IA), iodous acid (HIO2), ammonia (NH3), dimethylamine ((CH3)2NH, DMA), highly oxygenated organic molecules (HOMs) and other organics with low vapor pressure. We also explore several possible nucleation mechanisms: ion-induced nucleation of H2SO4 and NH3, H2SO4-amines, H2SO4-DMA-H2O, H2SO4-MSA-DMA, IA-MSA, IA-DMA, heterogeneous IA-organics nucleation mechanisms and environmental conditions required for the NPF. NPF is one of the main sources of CCN in the remote marine boundary layer, such as the SO and Antarctica. Thus, we discuss the contribution of NPF to CCN and the indirect impacts of NPF on climate. Through this review, we could better understand the PNC and NPF over the SO and Antarctica and their impacts on the global climate.

Flow of dense shelf water provide an efficient mechanism for pumping CO2 to the deep ocean along the continental shelf slope, particularly around the Antarctic bottom water (AABW) formation areas where much of the global bottom water is formed. However, the contribution of the formation of AABW to sequestering anthropogenic carbon (C-ant) and its consequences remain unclear. Here, we show prominent transport of C-ant (25.0 +/- 4.7 Tg C yr(-1)) into the deep ocean (>2,000 m) in four AABW formation regions around Antarctica based on an integrated observational data set (1974-2018). This maintains a lower C-ant in the upper waters than that of other open oceans to sustain a stronger CO2 uptake capacity (16.9 +/- 3.8 Tg C yr(-1)). Nevertheless, the accumulation of C-ant can further trigger acidification of AABW at a rate of -0.0006 +/- 0.0001 pH unit yr(-1). Our findings elucidate the prominent role of AABW in controlling the Southern Ocean carbon uptake and storage to mitigate climate change, whereas its side effects (e.g., acidification) could also spread to other ocean basins via the global ocean conveyor belt.

Regulated by the rapid changes in temperature, mixing, and biological production during warm seasons, the surface carbonate system in the Bering Sea is subject to significant spatial-temporal variability. However, the seasonal evolution of the carbon cycle and its controls are less clear due to the lack of observations. Here, we present the carbonate data collected during a forward voyage in July and a return voyage in September 2018 across the Bering Sea. For both voyages, we show distinct dissolved inorganic carbon versus total alkalinity (DIC-TA) relationships and partial pressure of CO 2 ( p CO 2 ) distribution patterns in the Southern Basin (54-57°N), the Northern Basin (57-59°N), the Slope (59-61°N), the Shelf (61-64°N), and the Bering Strait (>64°N). In the Southern Basin, the Northern Basin, and the Slope, surface water was a two end-member mixing of Rainwater and Bering Summer Water (BSW) during the forward voyage and a two end-member mixing of North Pacific Surface Water (NPSW) and BSW during the return voyage. As a result, the observed DIC was almost consistent with the conservative mixing line, with a slight DIC addition/removal of -8.6~5.8 µmol kg -1 , suggesting low biological production/respiration during both voyages. Seasonally, the higher factions of NPSW featuring low p CO 2 during the return voyage dominated the p CO 2 drawdown from July to September in the Southern Basin and the Slope. On the Shelf, the surface water was a two end-member mixing of plume water from the Anadyr River and BSW during both voyages, but the decreased DIC consumption via biological production from 59.9 ± 25.8 µmol kg -1 to 34.8 ± 14.0 µmol kg -1 contributed to the p CO 2 increase from July to September. In the Bering Strait, the coastal area was characterized by the influence of plume water from the Anadyr River in July and the coastal upwelling in September. The high biological production in plume water made a strong CO 2 sink during the forward voyage, while the upwelling of carbon-enriched subsurface water with minor DIC consumption made the coastal ecosystem a strong CO 2 source during the return voyage. In different geographical regions, the observed seawater p CO 2 was much lower than the overlying atmospheric CO 2 , resulting in a net CO 2 sink with fluxes of -2.1~-14.0 mmol m -2 d -1 and -2.5~-11.6 mmol m -2 d -1 , respectively, during the forward and return voyages.

在全球海洋中,人为二氧化碳(CO2)吸收导致了海水酸碱度pH和文石饱和度(Ωarag)的持续下降,这一过程被称为海洋酸化[1](Ocean Acidifi-cation).在部分中低纬度大洋海盆和南大洋中已观察到了气候变化驱动所导致的大范围、大规模的年代际海洋酸化,其酸化速率通常与增强的大气中CO2浓度强迫所驱动的速率一致[2-3].在北极,由于水温低,表层海水相较世界其他海域更容易吸收CO2,而基于观测数据的表层海水pH和Ωarag年代际尺度的变化特征及其驱动机制的研究仍存在大量空白.

Oceanic uptake of anthropogenic CO2 causes a decrease in seawater pH and aragonite saturation state (Ωarag), a process known as ocean acidification (OA). The western North Pacific is a hotspot for anthropogenic CO2 sinks; however, the spatiotemporal variability of pH and Ωarag and their controlling mechanisms remain unexplored. In this study, we provide high-frequency and high-precision underway measurements of sea surface pCO2 and pH to investigate the distribution and drivers of OA metrics across different hydrochemical gradients in the western North Pacific in late spring 2018, a season with the highest primary production in the year. Our results show that the surface pH reached near air-sea equilibrium in the subtropical zone but gradually increased northward across the Kuroshio Recirculation (KR) zone and peaked in the Kuroshio Extension (KE) zone. We found that sea surface temperature played the most prominent role in regulating pH, which was also counteracted by the effects of air–sea gas exchange and vertical mixing. In contrast, the distribution of Ωarag largely mirrored the pH and was governed by air–sea gas exchange and vertical mixing, the effects of which on Ωarag were enhanced by temperature. Biological activity thrived in the KE zone to increase both pH and Ωarag, which further reinforced the latitudinal pattern of pH, but weakened that of Ωarag. These findings are based on direct in situ measurements of pH and improve our understanding of the spatiotemporal variability of OA metrics in the western North Pacific region.

The composition of marine aerosol is quite complex, and its sources are diverse. Across the East China Sea (ECS) and the Yellow Sea (YS), multi-dimensional analysis of marine aerosols was conducted. The characteristics of carbonaceous aerosols and gaseous pollutants were explored through in situ ship-based observation, MERRA-2 reanalysis datasets and TROPOMI data from Sentinel-5P satellite. Black carbon (BC)’s average concentration is 1.35 ± 0.78 μg/m3, with high-value BC observed during the cruise. Through HYSPLIT trajectory analysis, sources of BC were from the northern Eurasian continent, the Shandong Peninsula, the ECS and Northwest Pacific Ocean (NWPO). The transport of marine sources like ship emissions cannot be ignored. According to the absorption Angstrom exponent (AAE), BC originates from biomass burning (BB) in the shortwave band (~370 nm) and from fossil fuel combustion in the longwave band (~660 nm). Organic carbon (OC), sulfate (SO42−) and BC report higher Angstrom exponent (AE) while dust and sea salt reveal lower AE, which can be utilized to classify the aerosols as being fine- or coarse-mode, respectively. OC has the highest AE (ECS: 1.98, YS: 2.01), indicating that anthropogenic activities could be a significant source. The process of biomass burning aerosol (BBA) mixed with sea salt could contribute to the decline in BBA’s AE. Ship emissions may affect the distribution of tropospheric nitrogen dioxide (NO2) in the ECS, especially during the COVID-19 pandemic. Tropospheric NO2 over the YS has the highest value (up to 12 × 1015 molec/cm2). Stratospheric NO2 has a ladder-like distribution from north to south, and the variation gradient was lower than that in the troposphere. Carbon monoxide (CO) accumulates in the south and east of the ECS and the east of the YS, while the variation over the eastern YS is relatively frequent. Seas near the Korean Peninsula have extremely high CO concentration (up to 1.35 × 1017 molec/cm2).

Rapid warming and loss of sea ice in the Arctic Ocean could play an important role in the dissolution and emission of greenhouse gas nitrous oxide (N2O). We investigated dissolved N2O in spatiotemporal distribution on the northeastern Bering Sea shelf (NEBS) in the summer of 2012. The results showed that N2O concentrations were higher in the Chirikov Basin (mean ± SD, 14.8 ± 2.4 nmol/L) than in the south of St. Lawrence Island (mean ± SD, 17.7 ± 2.3 nmol/L). In the Chirikov Basin, N2O displayed a decreasing distribution pattern from west (~20.4 nmol/L) to east (~12.9 nmol/L). In the area south of St. Lawrence Island, N2O almost presented a two-layer structure, although it showed a vertically homogeneous distribution in the inner shelf. In the cold bottom water, the N2O was affected mainly by in situ production or sediment emission. Longer resident time may cause N2O accumulation in the cold bottom water. The calculated sea–air flux (−1.6~36.2 μmol/(m2·d)) indicates that the NEBS is an important potential source of atmospheric N2O and could play an important role in global oceanic N2O emission with intensifying global issues.

The Arctic Ocean has turned from a perennial ice‐covered ocean into a seasonally ice‐free ocean in recent decades. Such a shift in the air‐ice‐sea interface has resulted in substantial changes in the Arctic carbon cycle and related biogeochemical processes. To quantitatively evaluate how the oceanic CO2 sink responds to rapid sea ice loss and to provide a mechanistic explanation, here we examined the air‐sea CO2 flux and the regional CO2 sink in the western Arctic Ocean from 1994 to 2019 by two complementary approaches: observation‐based estimation and a data‐driven box model evaluation. The pCO2 observations and model results showed that summer CO2 uptake significantly increased by about 1.4 ± 0.6 Tg C decade−1 in the Chukchi Sea, primarily due to a longer ice‐free period, a larger open area, and an increased primary production. However, no statistically significant increase in CO2 sink was found in the Canada Basin and the Beaufort Sea based on both observations and modeled results. The reduced sea ice coverage in summer in the Canada Basin and the enhanced wind speed in the Beaufort Sea potentially promoted CO2 uptake, which was, however, counteracted by a rapidly decreased air‐sea pCO2 gradient therein. Therefore, the current and future Arctic Ocean CO2 uptake trends cannot be sufficiently reflected by the air‐sea pCO2 gradient alone because of the sea ice variations and other environmental factors.

Nitrous oxide (N2O) is the third most important greenhouse gas in the atmosphere, and the ocean is an important source of N2O. As the Arctic Ocean is strongly affected by global warming, rapid ice melting can have a significant impact on the N2O pattern in the Arctic environment. To better understand this impact, N2O concentration in ice core and underlying seawater (USW) was measured during the seventh Chinese National Arctic Research Expedition (CHINARE2016). The results showed that the average N2O concentration in first-year ice (FYI) was 4.5 ± 1.0 nmol kg−1, and that in multi-year ice (MYI) was 4.8 ± 1.9 nmol kg−1. Under the influence of exchange among atmosphere-sea ice-seawater systems, brine dynamics and possible N2O generation processes at the bottom of sea ice, the FYI showed higher N2O concentrations at the bottom and surface, while lower N2O concentrations were seen inside sea ice. Due to the melting of sea ice and biogeochemical processes, USW presented as the sink of N2O, and the saturation varied from 47.2% to 102.2%. However, the observed N2O concentrations in USW were higher than that of T-N2OUSW due to the sea–air exchange, diffusion process, possible N2O generation mechanism, and the influence of precipitation, and a more detailed mechanism is needed to understand this process in the Arctic Ocean.