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.
Enhanced ventilation in the Okhotsk Sea through tidal mixing at the Kuril Straits
Abstract The role played by tide-induced diapycnal mixing at the Kuril Straits in the formation of the Okhotsk Sea water is examined using an ocean general circulation model. The result shows that tidal mixing causes a freshening of intermediate water down to ∼ 27.6 σ θ . This implies an enhancement of ventilation by tidal mixing, since a freshening flux can come only from above in the Okhotsk Sea. In fact, when compared with the case without tidal mixing, the production rate of Dense Shelf Water (DSW) increases from 0.01 to 0.13 Sv ( 10 6 m 3 s - 1 ) with maximum DSW density increased from 26.6 to 26.8 σ θ . This enhanced production of DSW allows us to successfully reproduce a layer of local potential vorticity minimum in the Okhotsk Sea, which characterizes the Okhotsk Sea Mode Water. The analysis reveals that tidal mixing at the Kuril Straits has two roles in enhancing ventilation. First, it preconditions the water properties of the DSW because tidal mixing at the Kuril Straits induces an upward salt flux from the saltier lower layer. The subsequent transport of the saline water from the Straits to regions of sea-ice generation increases the density of subducting water, resulting in more realistic densities and production rates of DSW. Second, tidal mixing directly modifies water properties throughout the water column. The ventilation due to this mechanical mixing further enhances the intermediate layer ventilation, and is dominant in the Kuril Straits and in the layer denser than the DSW. Although the effect of double diffusion on ventilation in the Okhotsk Sea is also examined, it is much less effective than the tidal mixing. Since the Okhotsk Sea is a key location for the ventilation of the North Pacific intermediate layer, the important implication here is that tidal mixing at the Kuril Straits enhances the meridional overturning in the entire North Pacific Ocean.
BIOSYNTHESIS OF DAUNORUBICIN GLYCOSIDES: ANALYSIS WITH BLOCKED MUTANTS
ABSTRACT Daunorubicin (daunomycin; NSC 82151) is an anthracycline antibiotic that is useful in the treatment of human leukemias. Several Streptomyces species accumulate higher glycosides of daunorubicin, which can be converted to daunorubicin by simple hydrolysis. We isolated a number of mutants of a daunorubicin glycoside-producing streptomycete, and found that some were deficient in accumulation of daunorubicin glycosides. One such mutant accumulated no detectable anthracyclines, while other mutants accumulated anthracyclines or aglycones that have not been reported before or have been described as co-metabolites of daunorubicin glycosides. Some of these anthracyclines and aglycones were purified and used as substrates in bioconversion experiments with various mutants. The results allowed us to construct a proposed pathway for the biosynthesis of daunorubicin glycosides by this streptomycete. KEYWORDS Anthracycline; daunorubicin; biosynthesis; blocked mutants; biotransformation.