From this paper: "In particular, conditions favorable for B. braunii blooms are thought to occur during El Nin?o events in association with three distinct processes that promote olig- otrophic conditions and lake stratification. Firstly, the heavy rains associated with moderate-to-strong El Nin?o events are thought to dilute the nutrient pool and cause oligotrophic conditions. El Junco Lake is an endorheic lake (with the exception of occasional overflow conditions and possibly seepage) located within a caldera with a small catchment area consisting only of the narrow crater rim (Conroy et al., 2008). In such lakes the con- centration of nutrients tend to decrease as lake levels increase through dilution of the incoming nutrients (Smol et al., 2001; Magyari et al., 2009). Because monthly rainfall in this area can be an order of magnitude higher during strong El Nin?o events as com- pared to non-El Nin?o periods (cf., Fig. 4) and the lake has been re- ported to overflow during strong El Nin?o events, considerable dilu- tion and flushing of nutrients likely occur during these times. Sec- ondly, reduced nutrient input to the lake exacerbates oligotrophic conditions during strong El Nin?o events. A major source of nutri- ents to the lake is thought to be guano deposited directly into the lake by the large number of seabirds that frequent it (Colinvaux, 1968). Such a predominance of avian-derived nutrients has been documented in a number of lake systems (Manny et al., 1994; Marion et al., 1994). However, during strong El Nin?o events, this nutrient source is diminished as the Gala?pagos seabird population plummets in response to the massive fish die-offs associated with a deep thermocline and low ocean productivity in the EEP (Gibbs, 1987). Finally, El Nin?o events in the EEP are associated with con- ditions that increase water column stability and lake stratification, including warmer air temperatures, reduced cloud cover, and re- duced trade wind strength (Lewis Jr., 1983; O?Reilly et al., 2003; Ndebele-Murisa et al., 2010; Co?zar et al., 2012), conditions which have been shown to exacerbate nutrient depletion in the surface of oligotrophic lakes (O?Reilly et al., 2003). Increases in water column stability during El Nin?o events should further promote favorable conditions for the oil-rich, colony-forming B. braunii due to their buoyancy. In various lo- cations across the globe, B. braunii blooms have been strongly linked to increases in water column stability due to both their tolerance of oligotrophic conditions and their anti-sinking strategy (Kebede and Belay, 1994; Souza et al., 2008; Winder and Hunter, 2008). In particular, in a Columbian lake with conditions (including depth, pH, conductivity, and nutrient concentration) comparable to El Junco Lake, B. braunii blooms have been found to occur dur- ing the annual flood stage in association with nutrient flushing, oligotrophic conditions, and lake stratification (Pinilla, 2006), con- ditions that closely mimic moderate to strong El Nin?o events in El Junco Lake. These lines of evidence strongly suggest that conditions favor- able for B. braunii growth occur during moderate-to-strong El Nin?o events and thus that C34 botryococcene ?D records the hydrologic conditions of the lake during these events."