Arctic Ocean properties and processes are highly relevant to the regional and global coupled climate system, yet still scarcely observed, especially in winter. Team OCEAN conducted a full year of physical oceanography observations as part of the Multidisciplinary drifting Observatory for the Study of the Arctic Climate (MOSAiC), a drift with the Arctic sea ice from October 2019 to September 2020. An international team designed and implemented the program to characterize the Arctic Ocean system in unprecedented detail, from the seafloor to the air-sea ice-ocean interface, from sub-mesoscales to pan-Arctic. The oceanographic measurements were coordinated with the other teams to explore the ocean physics and linkages to the climate and ecosystem. This paper introduces the major components of the physical oceanography program and complements the other team overviews of the MOSAiC observational program. Team OCEAN’s sampling strategy was designed around hydrographic ship-, ice- and autonomous platform-based measurements to improve the understanding of regional circulation and mixing processes. Measurements were carried out both routinely, with a regular schedule, and in response to storms or opening leads. Here we present along-drift time series of hydrographic properties, allowing insights into the seasonal and regional evolution of the water column from winter in the Laptev Sea to early summer in Fram Strait: freshening of the surface, deepening of the mixed layer, increase in temperature and salinity of the Atlantic Water. We also highlight the presence of Canada Basin deep water intrusions and a surface meltwater layer in leads. MOSAiC most likely was the most comprehensive program ever conducted over the ice-covered Arctic Ocean. While data analysis and interpretation are ongoing, the acquired datasets will support a wide range of physical oceanography and multi-disciplinary research. They will provide a significant foundation for assessing and advancing modeling capabilities in the Arctic Ocean.

Sixteen years of data on typhoons in the South China Sea (SCS) are used to investigate their impacts on sea surface temperature (SST) and chlorophyll‐a (Chl‐a). The time series of SST and Chl‐a before and after typhoons are composited for all typhoon locations to assess their responses. Decreases in SST and increases in Chl‐a occur after 73% and 70% of the typhoons, respectively, with overall averaged changes equal to −0.42 ± 0.015°C and 0.056 ± 0.003 log₁₀ mg/m³, respectively. The largest responses are found near the typhoon center, and the extent of changes in these parameters decreases linearly with distance. The SST responds rapidly, starting to drop 2 days ahead of the typhoon passage and continuing to drop until 2 days after its passage. On the other hand, the Chl‐a increases after the typhoon passage, remaining high for 5 days before beginning to return to the initial conditions. Large (weak) changes are associated with typhoons that have high (low) wind speeds and slow (fast) translation speeds. This is especially true for SST, whereas some typhoons with slow translation speeds are characterized by increases in Chl‐a, mostly occurring near the coast. The largest SST and Chl‐a changes induced by a single typhoon are found in the upwelling region off Vietnam. The study offers a comprehensive quantitative analysis that describes the general pattern of SST and Chl‐a responses to typhoons in the SCS.