Laminated Holocene lacustrine sediment records of ENSO and PDO-scale climate variability from the Pacific Basin

The Pacific Ocean is a dominant driver of global climate variability on interannual to multidecadal timescales. The El Niño Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) are large-scale ocean-atmospheric patterns which influence hydroclimate anomalies and correspondingly influence the structure and condition of terrestrial ecosystems. Here, laminated lacustrine sediments from the Ecuadorian Andes and Pacific Northwest of North America are used to reconstruct the long-term variability of these relatively high-frequency (interannual-decadal) climatic phenomena. Flood deposits from Laguna Pallcacocha, Cajas Parque Nacional, Ecuador, have previously been used to quantify the frequency of El Niño events over the Holocene (11,700 BP-present). Here, I employ sedimentary sequences from three lakes, each of which displays different sensitivities to El Niño-driven flood events in an effort to reconstruct changes in both the frequency and amplitude of ENSO. An XRF-based flood reconstruction from the well-studied Laguna Pallcacocha sedimentary record supports an emerging consensus among proxies indicating 10-20 year flood return intervals during the early Holocene (11,700-7,500 BP), >20 year El Niño return intervals during the middle Holocene (7,500-4,000 BP) and 2-10 year El Niño frequency from 4,000 to present. The Little Ice Age (LIA: 1450-1850 CE) experienced infrequent, high-intensity El Niño’s compared to the preceding Medieval Climate Anomaly (MCA: 950-1250 CE) which experienced the opposite pattern. Given the global recognition and significance of ENSO, a significant body of paleoclimate literature is devoted to elucidating its past dynamics. The relatively recent discovery of multidecadal phenomena, difficult to detect given the relatively short timespan of instrumental observations, has led to a relative paucity in high-resolution climate records sensitive to long-term changes in PDO-like phenomena. Oxygen isotope reconstructions of precipitation-evaporation balance from Castor and Round Lake, Washington help reveal long-term links between the tropics and northern hemisphere mid-latitudes. At both sites, the MCA was marked by relatively stable and moist conditions, while the LIA was marked by intense oscillations between drought and pluvial cycles, leading to enhanced fire activity. Over the course of the Holocene, long-term changes in orbital configuration, interannual to multidecadal forcing associated with ENSO and PDO, and abrupt landscape disturbances such as volcanic tephra deposits have left profound impacts on terrestrial ecosystems. These findings demonstrate that climate phenomena which operate on timescales relevant to human society have exhibited wide ranges of variability over the Holocene