wili,
In my earlier post I had meant to say that areas of downwelling can temporarily sequester some CO2 into the deep ocean water (just like upwelling cold water can vent CO2); however, I don't think that I actually said that in my earlier post, and I am too distracted to find my old post to correct what I actual said (if you tell me the reply # I will go back and correct what I actually said).
werther,
Continuing my disjointed points about changing ENSO patterns and also Global ENSO interactions:
(A) The following reference indicates that the ENSO dynamics since the 1970's cannot be explained by simple extrapolations of past frequencies and amplitudes. This supports the idea that changes in the Earth System as a whole (eg the Southern Ocean/Atmospheric system was seriously effected by the formation of an ozone hole over Antarctica in the 1970's, and increasing GHG concentrations worldwide are contributing directly to this trend of changes in the ENSO dynamics):
http://onlinelibrary.wiley.com/doi/10.1002/grl.50264/abstractThe 1970's shift in ENSO dynamics: A linear inverse model perspective; Christopher M. Aiken, Agus Santoso, Shayne McGregor, & Matthew H. England; Geophysical Research Letters; Volume 40, Issue 8, pages 1612–1617, 28 April 2013; DOI: 10.1002/grl.50264
Abstract:
"Inverse methods are used to investigate whether the observed changes in El Niño–Southern Oscillation (ENSO) character since the 1970's climate shift are consistent with a change in the linear ENSO dynamics. Linear Inverse Models (LIMs) are constructed from tropical sea surface temperature (SST), thermocline depth, and zonal wind stress anomalies from the periods 1958–1977 and 1978–1997. Each LIM possesses a single eigenmode that strongly resembles the observed ENSO in frequency and phase propagation character over the respective periods. Extended stochastically forced simulations using these and the LIM from the combined period are then used to test the hypothesis that differences in observed ENSO character can be reproduced without changes in the linear ENSO dynamics. The frequency and amplitude variations of ENSO seen in each period can be reproduced by any of the three LIMs. However, changes in the direction of zonal SST anomaly propagation in the equatorial Pacific cannot be explained within the paradigm of a single autonomous stochastically forced linear system. This result is suggestive of a possible fundamental change in the dynamical operator governing ENSO and supports the utility of zonal phase propagation, rather than ENSO frequency or amplitude, for diagnosing changes in ENSO dynamics."
(B) The following linked reference makes it clear that the Antarctic Circumpolar Wave, ACW, and the global ENSO wave, GEW, reinforce each other by positive feedback mechanisms:
White, W. B., S.-C. Chen, R. J. Allan, and R. C. Stone, Positive feedbacks between the Antarctic Circumpolar Wave and the global El Niño–Southern Oscillation Wave, J. Geophys. Res., 107(C10), 3165, doi:10.1029/2000JC000581, 2002.
http://onlinelibrary.wiley.com/doi/10.1029/2000JC000581/abstractAbstract
"Atmospheric and oceanic teleconnections link the Antarctic Circumpolar Wave (ACW) in the Southern Ocean [White and Peterson, 1996] and the global El Niño-Southern Oscillation (ENSO) wave (GEW) in the tropical Indo-Pacific Ocean [White and Cayan, 2000], both signals characterized by eastward phase propagation and 3- to 5-year- period variability. We extend the tropical standing mode of ENSO into the extratropics by regressing the Niño-3 sea surface temperature (SST) index against sea level pressure (SLP) anomalies over the globe, finding the Pacific-South America (PSA) pattern in SLP anomaly [Cai and Baines, 2001] straddling Drake Passage in the Southern Ocean. The amplitude of this PSA pattern is ∼1/3 that of the ACW in this domain and thus cannot be considered its principal driver. On the other hand, suppressing the tropical standing mode of ENSO in interannual ST (surface temperature) and SLP anomalies over the globe allows the GEW to be observed much more readily, whereupon its eastward phase propagation across the Warm Pool is found to remotely force the ACW in the eastern Pacific and western Atlantic sectors of the Southern Ocean through atmospheric teleconnections [Sardeshmukh and Hoskins, 1988] which propagate along with it. Subsequently, the ACW propagates this imposed GEW signal throughout the remainder of the Southern Ocean as a coupled wave in covarying ST and SLP anomalies, whereupon entering the Indian sector 1.5 to 2.5 years later it spawns a northern branch which takes another 1.5 to 2.5 years to propagate the ACW signal equatorward into the Warm Pool south of Indonesia. There it interferes constructively with the GEW. Thus the two forms of teleconnection, one fast and directed from the tropics to the high southern latitudes via the atmosphere and the other slow and directed from the high southern latitudes to the tropics via the ocean, complete a global circuit of 3- to 5-year duration that reinforces both the ACW and GEW and influences the tropical standing mode of ENSO."