A sensitivity study of the dense shelf water formation in the Okhotsk Sea
[1] Sensitivity of Dense Shelf Water (DSW) formation to tidal mixing around the Kuril Straits, wind stress, and river runoff in the Okhotsk Sea is examined by an ice-ocean coupled model. Horizontal resolution of the model is set to 3–8 km in the northern Okhotsk Sea for well resolving the coastal polynyas which is believed to be the principal region of DSW formation. The model shows a good performance in terms of sea ice production and the consequent DSW formation. DSW is also found to be formed in the offshore region apart from the coastal polynya. DSW is defined independently for each experiment such that it identifies the water influenced by brine. By introducing such definition the sensitivity of the DSW formation is assessed separately for change of density and that of formation rate. The density of DSW exhibits high sensitivity to all the elements considered herein, while its formation rate is sensitive only to winds. Winds affect the DSW formation rate mainly by influencing that occurs in the offshore region.
Long-term variation in sea ice production and its relation to the intermediate water in the Sea of Okhotsk
Abstract Overturning in the North Pacific extending to the intermediate layer (about 200–800 m depth) originates from the sinking of dense shelf water (DSW) formed by sea ice production in the Okhotsk coastal polynyas. It has been suggested that this overturning has weakened during the past 50 years. The purpose of this study is to clarify the long-term variability of sea ice production in the polynyas and to discuss its linkage with DSW formation and the overturning. First, we have developed a thin ice thickness retrieval algorithm using Special Sensor Microwave/Imager (SSM/I) data for the Sea of Okhotsk, and have estimated the ice production for 21 years (1988–2008) by calculating heat flux from SSM/I-derived ice thickness. From a comparison with atmospheric variables, it is suggested that interannual variability of sea ice production in the polynyas can be explained mainly by three atmospheric parameters: autumn air temperature northwest of the sea, winter air temperature north of the sea, and late winter offshoreward wind speed north of the sea. By using these parameters from atmospheric reanalysis data, the annual ice production for the 34 years period from 1974 to 2008 is reconstructed from a multiple regression coefficient analysis. The reconstructed ice production shows a significant decreasing trend of ∼11.4% over 34 years, which is mainly explained by the warming of autumn air temperature. It is also found that the variation in the annual total ice production corresponds well with the potential temperature variation in Okhotsk Sea Intermediate Water (OSIW). This first observational evidence of a linkage between the annual total ice production and OSIW supports a hypothesis that decreasing ice production in the Okhotsk coastal polynyas, at least in part, has led to weakening of the overturning in the North Pacific.
The Inca Occupation of the South Coast of Peru
like the others, however; it forks into several nearly parallel ravines of which the largest are Huayuri, Rio Grande-Palpa, Ingenio (called Collao in ancient times), Nasca proper (the ancient Caxamarca), Taruga, and Poroma. Due to peculiarities of the local topography, the irrigated areas in Ica and the ravines of Nasca are located inland, at the foot of the mountains, rather than at the mouths of the rivers as is more usual in Peruvian coastal valleys. No sharp natural or cultural boundary separates the valley of Chincha from the valleys of Cafiete (ancient Huarco and Runahuana), Asia, and Mala, the next valleys going up the coast to the northwest. At the other end of the area we are considering, however, there is a sharp break; beyond Yauca the Andean foothills reach out to the sea, natural conditions are quite different, and there are important differences in the archaeological picture as well. The historical sources which mention the south coast are not particularly helpful, except in so far as they provide us with a few dates. To begin with, no chronicler gives an explicit account of the political organization of the south coast at the time it came into contact with the Incas. It can, perhaps, be inferred from Cabello Balboa's statements about common policy toward the Inca invaders that there was some sort of political connection between the valleys of Mala, Cafiete, and Chincha, but the connection need have been no more than a temporary military alliance. Cabello makes no mention at all of Pisco. The valleys of Ica, Nasca, and 125