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The 1257 CE eruption of Mt. Samalas in Indonesia is argued to be the largest of the last two millennia in terms of global volcanic aerosol forcing, with a reduction in insolation of more than 30 W/m2 (Sigl et al., 2015, Nature, 523). Large volcanic eruptions are tied to short-term climatic shifts, including changes to monsoon rainfall (Ridley et al., 2015, Nature Geoscience, 8). In order to investigate the impact of this eruption on the Indian summer monsoon in Nepal, we analyzed at ultra-high resolution the carbon and oxygen isotopes of a fast-growing, precisely-dated aragonite stalagmite from Siddha cave in the Pokhara Valley of central Nepal (28.0˚ N, 84.1˚ E; ~850 m.a.s.l.). We micromilled the stalagmite in ~40 µm-wide traverses during the interval through the Mt. Samalas eruption (a total of 261 analyses). Studies near Siddha cave and in Kathmandu, 130 km to the southeast, reveal that amount effects of oxygen isotopes in precipitation in this region are weak, and so we rely on carbon isotopes as a proxy for rainfall. Carbon isotopes define sinusoids that appear to represent annual cycles of rainfall associated with the summer monsoon and winter dry season. The average magnitude of these cycles is ~0.3 to 0.6‰. While some ambiguities exist, the number of seasonal cycles (18-21) is within error of the years of growth for this interval as determined by U/Th dating (26±8 years). To investigate the impact of the eruption on regional hydroclimate, we detrended the carbon isotope data and then calculated anomalies in the wet and dry seasons relative to the mean of those values. The most prominent feature of the time series is two large positive isotope anomalies separated by a moderate negative isotope anomaly. We interpret these to reflect disruptions to both the monsoon and dry season precipitation regimes by aerosol forcing from Mt. Samalas. If true, then these results reveal somewhat surprising an anomalously wet monsoon season in the first year after the eruption and that seasonal sinusoids return to their pre-eruption pattern after only two years following the eruption. In order to better understand these results, we investigate this interval using the Last Millennium Ensemble, a state-of-the-art suite of climate model simulations conducted by the National Center for Atmospheric Research with the Community Earth System Model. 

Abstract The Gulf of Maine, located in the western North Atlantic, has undergone recent, rapid ocean warming but the lack of long-term, instrumental records hampers the ability to put these significant hydrographic changes into context. Here we present multiple 300-year long geochemical records (oxygen, nitrogen, and previously published radiocarbon isotopes) measured in absolutely-datedArctica islandicashells from the western Gulf of Maine. These records, in combination with climate model simulations, suggest that the Gulf of Maine underwent a long-term cooling over most of the last 1000 years, driven primarily by volcanic forcing and North Atlantic ocean dynamics. This cooling trend was reversed by warming beginning in the late 1800s, likely due to increased atmospheric greenhouse gas concentrations and changes in western North Atlantic circulation. The climate model simulations suggest that the warming over the last century was more rapid than almost any other 100-year period in the last 1000 years in the region. 

Stalagmites and climate models reveal ITCZ shifts drove concurrent changes in Australian tropical cyclone and monsoon rainfall. 

Abstract Growth‐increment widths of Pacific geoduck (Panopea generosa), a long‐lived bivalve, are used to develop the first marine‐based, multicentennial, annually resolved, and exactly dated archive of Northeast Pacific sea surface temperatures (SST). The chronology is sampled from the Tree Nob Islands, British Columbia, Canada, continuously covers 1725–2008, and also contains nine older radiocarbon‐dated segments, which together span 58% of the last 1,500 years. Age‐related growth declines were removed by aligning all increments relative to age of increment formation and fitting with a single detrending curve to preserve low‐frequency signals. The geoduck chronology was used to reconstruct local SST variability across the seasonal window of April through November. The chronology at both the concurrent (lag‐0) and following (lag+1) year are both highly significant predictors of SST in a stepwise multiple linear regression, explaining 54% of the variance in the period of instrumental overlap (1940–2001), passing strict tests of calibration‐verification. Reconstructed SSTs contained significant spectral power at periods from 3 to 64 years, suggesting that 20th century variability in these periodicities is not unusual in the longer‐term context. The period of lowest growth coincided with the Dalton minimum, an episode of reduced solar irradiance from 1790–1830, as well as the 1809 Unknown eruption, suggesting that solar and volcanic signals are present in the SST history. The most conspicuous aspect of the reconstruction is the steady and unprecedented warming trend that began in the mid‐1800s and continues through present. The post‐1976 interval includes the two warmest decades of the reconstruction.