  Onset of double-component convection due to different boundary conditions is
studied in a diversely oriented infinite slot with broken reflection symmetry
between the slot conditions for a component. Among other outcomes, the broken
symmetry results in small-amplitude viscous convection remaining of an
oscillatory nature for any slot orientation other than a horizontal one. Such a
universality also involves various abrupt changes in the marginal-stability
curves. In inviscid fluid, such changes emerge with zero instability
thresholds. Some of these abrupt changes give rise to new mechanisms for
three-dimensionality of the instability. One such a mechanism comes with
multiplicity and isolated existence of as well as hysteresis between solutions
of the linear stability equations. Both the hysteresis region and the other
abrupt 3D changes are described in terms of an analogy between the effect of a
ratio of the 2D and 3D wave numbers and that of a 2D ratio between two gravity
components. The mechanism of finite-amplitude steady convection in a horizontal
slot is also analyzed and its relevance to abrupt climate change is discussed.
(This is a substantially shortened Abstract. The full version of Abstract is on
the manuscript itself.)
