Distribution and formation of the mesothermal structure (temperature inversions) in the North Pacific subarctic region

Abstract

Abstract. The distribution and formation of mesothermal structure (temperature inversions) in the North Pacific subarctic region are investigated through analysis of climatological hydrographic data. It is suggested that the heat and salt that maintain the mesothermal water and thus the halocline in the density range of 26.7-27.2cr0 are transported as a crossgyre flow from the transition domain just east of Japan, where the waters are influenced by the subtropical gyre water mass, to the eastern subarctic region. Along the transport route the isopycnal potential temperature and thus salinity are well conserved. In the western subarctic gyre, the Bering Sea, and the northern Gulf of Alaska, the temperature reaches its minimum at the surface in winter and the areal coverage agrees well with the distribution of the mesothermal structure. In the southeastern part of the zonally distributed mesothermal structure in the area of 170øE -150øW and 45ø-50øN, where the winter sea surface temperature is higher than that in the deeper layer, dichothermal water is formed by subsurface intrusion of the low-temperature and low-•alinity water that outcropped in the previous winter over the warm and saline water transported from the transition domain. The type 1 formation process should be further classified into two types. One is a pure seasonal cycle as in the Gulf of Alaska (Figure 3a). In spring and summer, mesothermal water exists at around 100 m, while in fall, at the end of the heating period, it vanishes. In the other type as observed in the Okhotsk Sea, the Bering Sea, and the western subarctic gyre (Figure3b), the mesothermal structure exists throughout the year. This type cannot be explained by verti-16,885

East-west differences in population structure and vertical distribution of copepods along 47^|^deg;N in the subarctic Pacific in June 2009

“…In addition, relatively strong temperature inversions (>0.5°C) were observed between 160°E and 174°E. Temperature inversions are often apparent in the subarctic North Pacific (Ueno & Yasuda 2000, supporting the conclusion that the stations between 160°E and 174°E were located in the subarctic region. The present results revealed that in the surface layer, temperature was higher and chl.…”

Oceanic fronts and jets around Japan: a review

“…In the northern part of the KOC region, the 4 °C isotherm at 100 m depth (Favorite et al 1976) traces the southern boundary of the SAC well in the western and central portions of the North Pacific. This isotherm is the formal proxy of the southern limit of the "pure" subarctic stratification with a subsurface temperature minimum underlain by a temperature maximum (Belkin et al 2002), which is termed as the Subarctic Front (SAF) by Ueno and Yasuda (2000) and Yasuda (2003). 4 Further, recent studies based on satellite observations have identified two remarkable quasi-stationary jets in the SAFZ immediately south of the SAC [Isoguchi et al 2006;J1 and J2 in Figs.…”

“…SAB is the subarctic boundary. The front associated with the SAC is indicated as SAF here based on Ueno and Yasuda (2000) and Yasuda (2003) gradient, along-front flow speed, volume transport, frontal depth from the surface, and eddy kinetic energy (EKE) at the surface. These metrics provide the information on the momentum field associated with fronts.…”

Ocean acidification from 1997 to 2011 in the subarctic western North Pacific Ocean

“…We obtained a decadal time series by combining data from the two stations, because the duration of sampling at each individual station data was not sufficient. Typically, in this region the minimum temperature (T min ) in the water column is associated with the remnant of the mixed layer water in the preceding winter and occurs at about 26.5σ θ (∼ 100 m), and the maximum temperature occurs at about 27.1σ θ (∼ 370 m) (e.g., Ueno and Yasuda, 2000;Osafune and Yasuda, 2006). Each year, the surface mixed layer reached its maximum depth from mid-March to early April (Fig.…”

“…1), so occasionally no T min water is observed because of the northward migration of subtropical water (Tsurushima et al, 2002). Because this migrated subtropical water enters the south edge of western subarctic gyre and passes eastward (Ueno and Yasuda, 2000), we did not use observation data if no T min layer could be identified. This indicates the combined K2 and KNOT data in this study does not include the subtropical water and is not obviously different in hydrography.…”