Contrasting Community Assembly Mechanisms Underlie Similar Biogeographic Patterns of Surface Microbiota in the Tropical North Pacific Ocean

Bacteria and microeukaryotes are extremely diverse groups in the ocean, where they regulate elemental cycling and energy flow. Studies of marine microbial ecology have benefited greatly from the rapid progress that has been made in genomic sequencing and theoretical microbial ecology.

Deep Water Pathways In The North Pacific Ocean Revealed By Lagrangian Particle Tracking

Lagrangian particle tracking experiments are conducted to investigate the pathways of deep water in the North Pacific Ocean. The flow field is taken from a state-of-the-art deep circulation simulation. An unprecedented number of particles are tracked to quantify the volume transport and residence time. Half of the North Pacific deep water returns to the Southern Ocean, and its principal pathway is along the western boundary current in the Southwest Pacific Basin in the deep layer. About 30 % is exported to the Indian Ocean after upwelling to the shallow layer in the western North Pacific Ocean. The rest is transported to the Arctic Ocean through the Bering Strait or evaporates within the Pacific Ocean. Upwelling of deep water is confined in the western North Pacific Ocean owing to the strong vertical mixing. The mean residence time of deep water in the North Pacific Ocean is estimated to be several hundred years, which is considerably shorter than the conventional understandings of the deep Pacific Ocean circulation.

Knowledge on the Biological and Fisheries Aspects of the Japanese Sardine, Sardinops melanostictus (Schlegel, 1846)

Japanese sardine (Sardinops melanostictus) is a significant small pelagic fish and a valuable resource that plays an essential ecological role in the marine ecosystem. It is present in the far Eastern Asian maritime waters, including the Pacific Ocean, Sea of Japan, and the East China Sea. Encircling nets, particularly purse seines, are the most used fishing equipment to catch this species. Their fishing grounds are located entirely in coastal areas. Japanese sardine catches have shown varying trends over the last five decades, with a high frequency of captures occurring in the 1980s before collapsing in the early 1990s. The economic and ecological importance of this species has prompted much research, which provided additional information about their spawning migration, distribution, fisheries, and biology. This research was mostly undertaken in the Sea of Japan and its adjacent waters spanning in the north Pacific Ocean. Despite all this research and the importance of this species in its habitats and in commercial fisheries, there is a lack of a recent review presenting the status of global fisheries and biological information for this species. This paper summarizes and updates information on the global geographical distribution, biological aspects, trends in catches, stock fluctuations and assessment, and management measures of the Japanese sardine population. This paper also summarizes information related to the influence of environmental factors on the occurrence of this species and also identifies information gaps. Further research directions are also discussed in this work, which may help improve the knowledge of Japanese sardine and establish rational management measures for their conservation.

210Po-210Pb Disequilibrium in the Western North Pacific Ocean: Particle Cycling and POC Export

Estimating the particulate organic carbon (POC) export flux from the upper ocean is fundamental for understanding the efficiency of the biological carbon pump driven by sinking particles in the oceans. The downward POC flux from the surface ocean based on 210Po-210Pb disequilibria in seawater samples from the western North Pacific Ocean (w-NPO) was measured in the early summer (May-June) of 2018. All the profiles showed a large 210Po deficiency relative to 210Pb in the euphotic zone (0–150 m), while this 210Po deficiency vanished below ∼500 m (with 210Po/210Pb ∼1 or > 1). A one-dimensional steady-state irreversible scavenging model was used to quantify the scavenging and removal fluxes of 210Po and 210Pb in the euphotic zone of the w-NPO. In the upper ocean (0–150 m), dissolved 210Po (D-Po) was scavenged into particles with a residence time of 0.6–5.5 year, and the 210Po export flux out of the euphotic zone was estimated as (0.33–3.49) × 104 dpm/m2/year, resulting in a wide range of particulate 210Po (P-Po) residence times (83–921 days). However, in the deep ocean (150–1,000 m), 210Po was transferred from the particulate phase to the dissolved phase. Using an integrated POC inventory and the P-Po residence times (Eppley model) in the w-NPO euphotic zone, the POC export fluxes (mmol C/m2/d) varied from 0.6 ± 0.2 to 8.8 ± 0.4. In comparison, applying the POC/210Po ratio of all (>0.45 μm) particles to 210Po export flux (Buesseler model), the obtained POC export fluxes (mmol C/m2/d) ranged from 0.7 ± 0.1 to 8.6 ± 0.8. Both Buesseler and Eppley methods showed enhanced POC export fluxes at stations near the continental shelf (i.e., Luzon Strait and the Oyashio-Kuroshio mixing region). The Eppley model-based 210Po-derived POC fluxes agreed well with the Buesseler model-based fluxes, indicating that both models are suitable for assessing POC fluxes in the w-NPO. The POC export efficiency was < 15%, suggesting a moderate biological carbon pump efficiency in the w-NPO. These low export efficiencies may be associated with the dominance of smaller particles and the processes of degradation and subsequent remineralization of these small particles in the euphotic zone of oligotrophic regions in the w-NPO.

Changing of surface thermal parameters in the Northern Pacific and some possible climatic affects

В работе на основе базы данных температуры поверхности воды в северной части Тихого океана на климатическом масштабе 1980 - 2019 годы с временным шагом один год исследована зависимость скорости изменения температуры от широты. В летний (август) период отмечается устойчивая зависимость темпов роста средней зональной температуры поверхности в направлении от тропиков к субарктике. Характерная скорость роста температуры в тропических широтах 0,011 0C/год, в субтропиках 0,021 0C/год, в субарктических акваториях выше 400N имеем 0,027 0C/год. В зимний сезон (февраль) такой тенденции не наблюдается. Представлены количественные оценки возможного влияния температурных трендов на глобальную циркуляцию. Рост поверхностной температуры увеличивает вертикальную стратификацию и уменьшает вертикальный обмен вод, относительное ослабление вертикальной скорости не превышает 0,01 % за десятилетие, что представляет незначительным. Представлена количественная оценка уменьшения геострофической составляющей горизонтальной скорости течения продолжения Куросио на восток вследствие климатического сглаживания перепада температуры воды южнее и севернее струи. The change of sea surface temperature (SST) in the North Pacific Ocean on the climatic scale 1980 - 2019 is considered. The rate of temperature change as a function of latitude with the one year time step and the 10 degrees spatial step is investigated. The latitudinal time series for summer and winter are separated. The summer (August) period has the climatic stable dependence of the surface temperature growth rate in the direction from the tropics to the subarctic area. The characteristic rate of temperature rise in tropical latitudes is 0.011 0C / year; in the subtropics is 0.021 0C / year; in subarctic waters above 40 0N this is 0.027 0C / year. The winter season (February) does not have this tendency. The quantitative estimates of the temperature trends influence on global circulation are presented. The SST growth enhances vertical stratification and decreases the vertical water exchange. The estimation of the relative vertical speed decrease is not more than 0.01% / decade. The quantitative assessment of the weakening of the geostrophic horizontal velocity in the Kuroshio extension due to the climatic smoothing of the SST south - north gradient is presented.