Amresh Sinha

Precipitation in southwestern North America has exhibited significant natural variability over the past few thousand years. This variability has been attributed to sea surface temperature regimes in the Pacific and Atlantic oceans, and to the attendant shifts in atmospheric circulation patterns. In particular, decadal variability in the North Pacific has influenced precipitation in this region during the twentieth century, but links to earlier droughts and pluvials are unclear. Here we assess these links using δ 18 O data from a speleothem from southern California that spans AD 854-2007. We show that variations in the oxygen isotopes of the speleothem correlate to sea surface temperatures in the Kuroshio Extension region of the North Pacific, which affect the atmospheric trajectory and isotopic composition of moisture reaching the study site. Interpreting our speleothem data as a record of sea surface temperatures in the Kuroshio Extension, we find a strong 22-year periodicity, suggesting a persistent solar influence on North Pacific decadal variability. A comparison with tree-ring records of precipitation during the past millennium shows that some droughts occurred during periods of warmth in the Kuroshio Extension, similar to the instrumental record. However, other droughts did not and instead must have been influenced by other factors. Finally, we find a significant increase in sea surface temperature variability over the past 150 years, which may reflect an influence of greenhouse gas concentrations on variability in the North Pacific.

Let us begin with Lethe, a river in Hades whose waters caused forgetfulness to dead souls who drank from it. The daughter of Eris, Lethe was the sister of Thanatos , and with Zeus she bore the Graces/Charites. According to some myths, she was the mother of Dionysus. She was the goddess of oblivion and the river with the same name. When someone died and went to Hades, they had to drink from her water so they would forget their previous existence on earth. Once they had drunk from the waters of Lethe, they were left with nothing to reminisce about for eternity. If ever anybody was allowed back to life, again they had to drink from the river so they would not remember the afterlife. One of memory’s earliest myths proclaims that at the dawn of philosophy, at the oracle of Lebadeia, a descent into Hades required that the questor be first taken to Lethe, the spring of forgetfulness, and then to Mnemosyne, the mother of the Muses, the second spring, the spring of remembrance. Jean Pierre Vernant recounts the legend thus: Before venturing into the mouth of hell, the questor, who had already undergone rites of purification, was taken to two springs named respectively Lethe and Mnemosoune. He drank from the first and immediately forgot everything to do with his human life and, like a dead man, he entered the realm of Night. The water of the second spring was to enable him to remember all that he had seen and heard in the other world. When he returned he was no longer restricted to knowledge of the present moment: contact with the beyond had revealed both past and future to him. 2 Two questions that immediately come to mind are concerned with the anteriority of forgetting in relation to memory. Why was the initiate taken first to Lethe? What was the motivation behind this unusual ritual in the cavern of Trophonius in Boetia that demands forgetfulness as the first step? Secondly, why is the power of memory, which enables him to remember what “he had seen and heard in the other world,” constituted as the second step – though unmistakably a step, an unmistakable step – toward knowledge? The dip in the Lethe cleanses the initiate from the distracting and unmitigated sorrows of the past like a clean slate. It is well known that for the ancient Greeks, knowledge, a source of immortality, derived from memory. One could ask, is the knowledge that memory brings to us the knowledge that memory is the first presence of what was before it, namely forgetting?