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Climate changes are multivariate in nature, and disentangling the proximal drivers of biotic responses to paleoclimate events requires time series of multiple environmental proxies. We reconstruct a multivariate time series of local environmental change for the early Miocene Newport Member of the Astoria Formation (20.26–18 Ma), using proxies for temperature (δ18O), productivity (δ13C), organic carbon flux (Δδ13C), oxygenation (δ15N), and sedimentary grain size (% mud). Our data suggest increases in productivity and declines in oxygenation on the Oregon shelf during this interval of global warming. We evaluate the association of individual environmental factors, and combinations of factors, with changes in faunal composition observed in benthic foraminiferal and molluscan communities collected from the exact same sediments as the environmental data. The δ15N values are the most parsimonious correlates with major changes in foraminiferal composition, whereas molluscan composition is most closely related to δ13C values, suggesting that different components of the environment are influencing each group. When the proxies that have the best supported relationships with the faunal gradients are removed from the analyses to simulate the absence of those proxy data, significant relationships between the faunal gradients and the remaining environmental proxies can still be found. This suggests that environmental drivers can be incorrectly attributed to faunal changes when key proxy data are missing. Paleoecological studies of biotic response that test multiple environmental drivers for multiple taxonomic groups are powerful tools for identifying the ecological consequences of past warming events and the regional drivers of ecological changes.

Explanations for the genesis and propagation of recurrent cholera pandemics since 1817 have remained elusive. Evolutionary change of the pathogen is presumed to have been a dominant factor behind the 7th El Tor pandemic, but little is known to support this hypothesis for preceding pandemics. We investigate the concomitant roles of climate and putative strain variation for the 6th cholera pandemic (1899-1923; the one with the highest ever associated mortality in India), using newly assembled historical records for climate variables and cholera deaths for Bengal, Assam, Bihar and Bombay provinces in former British India. We compare this historical pandemic with the 7th (El Tor) one and with the temporary emergence of the O139 strain in Bangladesh and globally. Finally, we ran multi-model climate simulations to infer past and future long-term means of rainfall distributions on the basis of 39 models for 1861-2100, and for different periods of 50 years (1875-1925; 1975-2025 and 2050-2100). The 6th cholera pandemic featured a large scale synchronisation with a delay of a few years in both seasonal and interannual cholera variability over the endemic Bengal region during the El Nino event of 1904-07. Additional evidence supporting the establishment of a new strain includes a shift of cholera incidence to older age groups, an increase in the case fatality rate and the suppression of the spring cholera peak. The 6th cholera pandemic of Indian origin was associated with a novel and particularly invasive strain of new territory, and also with some delay, of endemic parts of India that act as a genetic regional reservoir of the disease. Climate anomalies appear to have played an important role in facilitating the establishment of this invasive strain, with environmental conditions similar to those underlying strain changes associated with ENSO in today Bangladesh. The evolutionary change of pathogens can act synergistically with climatic conditions in the replacement and propagation of emerging strains, as was the case in cholera 7th pandemic. Increased climate variability and extremes under global warming would thus provide windows of opportunity for emerging new pathogens.

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