Formation of bottom water and its variability in the northwestern part of the Sea of Japan

Abstract

The downslope descent of dense shelf water in the northwestern part of the Sea of Japan is investigated from a dynamical point of view, paying attention to the formation of bottom water in the winter of 2001. It is supposed that before 1980, the shelf water in Peter the Great Bay sometimes descended far down the continental slope, at least partly reaching depths in excess of 3000 m (the foot of the continental slope). After 1980, however, the shelf water did not descend as far; it either descended only moderately or not at all. In Winter 2001, however, the dense shelf water again descended to depths greater than 3000 m, resulting in the formation of bottom water. Descents of more than 3000 m are due to low temperatures coupled with high salinities, whereas the moderate descents of the late 20th century were purely related to the low temperature of the shelf water. It is estimated that over the continental slope, the shelf water becomes mixed with the ambient water in a ratio of about 1:9 for deep descents, whereas the ratio is about 1:5 for moderate descents. The formation of bottom water is greatly influenced by interannual atmospheric variability; thus in Winter 2001 a combination of the strengthened Siberian High (especially in its northern part) and the Aleutian Low advected very cold air into northeast Asia, producing dense shelf water and resulting in the formation of bottom water.

Distinct characteristics of the intermediate water observed off the east coast of Korea during two contrasting years

“…Isobe and Beardsley [] and Cui and Senjyu [] pointed out that the enhanced atmospheric disturbances in the positive AO phase lead to more intense cold‐air outbreaks, which cause the low SST in the northern EJS at decadal time scales. At interannual time scale, however, a high‐positive correlation (0.61) between the air temperature and the AO index (AOI) suggests that the water masses can be more easily formed under the condition of negative AO phase, as reported most recently [ Tanaka , ].…”

“…The northwestern EJS is known to the area where evidence of newly formed deep water is often observed [ Miyao et al ., ; Kim et al ., ; Talley et al ., ; Min and Kim , ; Tanaka , ]. In order to check whether the distinct properties of the intermediate water observed in 2001 and 2010 arise from the difference in wintertime water formation, we examined interannual variability in surface heat fluxes based on the MERRA data.…”

“…The bottom water formation with dense (very low temperature and high salinity) shelf water off the Russian coast descending to depths greater than 3000 m was observed and linked with severe atmospheric forcing in winter 2001 (late 2000 to early 2001) [ Kim et al ., ; Senjyu et al ., ; Tsunogai et al ., ; Talley et al ., ]. The local atmospheric condition and cold‐air outbreaks in that area are related to larger‐scale conditions proxied by the Arctic Oscillation (AO) and the Siberian High variability [ Talley et al ., ; Minobe et al ., ; Isobe and Beardsley , ; Tanaka , ]. Isobe and Beardsley [] and Cui and Senjyu [] pointed out that the enhanced atmospheric disturbances in the positive AO phase lead to more intense cold‐air outbreaks, which cause the low SST in the northern EJS at decadal time scales.…”

Re-initiation of bottom water formation in the East Sea (Japan Sea) in a warming world

“…Rate of CW (DW and BW) reduction increase (decrease) because of the decreasing (increasing) CW (DW and BW) formation. BW is known to be formed by the slope convection of highly dense surface water along the continental slope in the northern coast, e.g., off Peter the Great Bay 3 , 22 as observed during winter in 2000–2001 23 – 25 , whereas CW is considered to be formed by the open-ocean convection 3 of surface water with relatively lower density. Thus, more BW formation implies that winter sea surface density (SSD) in the northern ES (a purple box in Fig.…”

“…3a ). During the winter between 2000 and 2001, when the deep slope convection was observed 22 – 25 , both heat and fresh water flux anomalies were strongly positive (red star in Fig. 3a ).…”