Atmospheric gaseous elemental mercury (GEM) concentrations in the Arctic exhibit a clear summertime maximum, while the origin of this peak is still a matter of debate in the community. Based on summertime observations during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition and a modeling approach, we further investigate the sources of atmospheric Hg in the central Arctic. Simulations with a generalized additive model (GAM) show that long-range transport of anthropogenic and terrestrial Hg from lower latitudes is a minor contribution (~2%), and more than 50% of the explained GEM variability is caused by oceanic evasion. A potential source contribution function (PSCF) analysis further shows that oceanic evasion is not significant throughout the ice-covered central Arctic Ocean but mainly occurs in the Marginal Ice Zone (MIZ) due to the specific environmental conditions in that region. Our results suggest that this regional process could be the leading contributor to the observed summertime GEM maximum. In the context of rapid Arctic warming and the observed increase in width of the MIZ, oceanic Hg evasion may become more significant and strengthen the role of the central Arctic Ocean as a summertime source of atmospheric Hg.

The nitrous oxide (N₂O) distributions in a shelf‐slope‐basin section from the Chukchi Sea shelf to the Chukchi Abyssal Plain (CAP) in the western Arctic Ocean were observed for the first time during the fourth Chinese National Arctic Research Expedition (4th CHINARE) in late August 2010. The N₂O concentrations were 11.4–16.9 nmol L⁻¹, corresponding to saturation values of 92–118% in the surface water. In the surface, biological factor was negligible to N₂O production, and physical process dominated the surface N₂O distribution. The N₂O undersaturation may be the result of dilution by sea ice meltwater. The oversaturation may be caused by the diffusing of N₂O‐rich shelf bottom water. Below the surface, N₂O concentrations ranged from 11.4 to 21.4 nmol L⁻¹. On the Chukchi Sea shelf, N₂O concentrations increased from the surface to the near‐bottom water, indicating sediment N₂O produced by nitrification or denitrification emission may be a significant source. The subsurface maxima in the upper halocline layer (UHL) may receive partial contribution from nitrification production but was primarily caused by the spreading of shelf water.

Nitrous oxide in the surface water was measured using an automatic underway system, along with measurements of surface water pCO₂, dissolved oxygen, salinity, temperature, and sea ice coverage, along a cruise track through the Bering Sea and Chukchi Sea to the Canadian Basin during the 7^th Chinese National Arctic Research Expedition. The results show that, overall, the regions along the cruise track are net sources of N₂O to the atmosphere. Several N₂O oversaturation maxima were observed along the cruise track, with an absolute maximum of approximately 60%. According to the hydrographic setting and the distribution patterns of pCO₂, dissolved oxygen, and sea ice coverage in the study area, it was concluded that the N₂O oversaturation maxima may result from hydrographic processes, such as mixing of different water masses, upwelling or convection, and possible production beneath the sea ice. Additionally, the lowest value of approximately 90% may result from dilution related to the melting of sea ice. An evaluation of the air–sea flux along the cruise track shows that the continental shelf and upwelling region are N₂O sources, whereas the study area in the open Arctic Ocean does not show obvious source or sink characteristics.

The ocean, particularly the Southern Ocean, is considered a significant source of atmospheric N₂O, which is an ozone‐depleting greenhouse gas. However, there are limited data available supporting this conclusion. Thus, this study sampled and analyzed the oceanic N₂O in Prydz Bay. The results demonstrated that the distribution of N₂O in this embayment differed between the north and south sides of the Antarctic Slope Front (ASF), corresponding to the different hydrographic characteristics on each side. Although the air to sea N₂O flux north of the shelf break is ∼−1.20 ± 0.44 μmol m⁻² d⁻¹, the source sink characteristics need to be further constrained because the Circumpolar Deep Water (CDW) may occasionally outcrop over the surface layer. The water masses over the continental shelf south of the shelf break may be a temporary or even a permanent N₂O sink when sea ice is absent. The air to sea flux south of the shelf break is ∼−3.65 ± 0.95 μmol m⁻² d⁻¹, and the water column is undersaturated with N₂O, which may result from the deep convection of N₂O‐undersaturated surface water during the winter. Evidence also suggests that the formation of Antarctic Bottom Water (AABW) may provide a pathway for N₂O removal from the upper layer at high latitudes.