The Indian Ocean climate response to volcanic eruptions remains poorly understood due to potential climate model biases and lack of validation from observations and subannual-resolution marine proxy records. We present monthly reconstructions of temperature and hydrology derived from Sr/Ca and oxygen isotopes in northeastern Indian Ocean corals back to 1774 CE. Our reconstructions from the southern Andaman Sea reveal an interval of pronounced cooling and freshening during the early 19^th century (~1809-1824), which we attribute to a cluster of tropical volcanic eruptions (including unidentified 1809, Tambora 1815). The regional cooling and freshening were unusually strong compared to the wider Indian Ocean. Using satellite and atmospheric and ocean reanalysis products (ERA5, ORAS5), we demonstrate coral records successfully document interannual changes in (1) northeastern Indian Ocean sea surface temperature, (2) Western Pacific Warm Pool sea surface salinity, (3) Andaman Sea subsurface temperature modulated by eastern Indian Ocean thermocline depth changes in response to the Indian Ocean Dipole (IOD), and (4) Andaman Sea hydrology linked to the atmospheric Walker Circulation of the tropical Pacific and Indian Ocean. Applying Superposed Epoch Analysis, we find early 19^th century eruptions forced negative IOD-like conditions in our reconstructions, followed by positive IOD-like conditions in subsequent years, regardless of eruption magnitude. From a northeastern Indian Ocean perspective, we propose that the cumulative effects of consecutive volcanic eruptions during the early 19^th century cluster may have forced positive IOD-like mean conditions, which manifested as pronounced cooling and freshening in the Andaman Sea as revealed by our coral reconstructions during ~1809-1824. Our results are consistent with historical reanalysis products (20CRv3) that point to positive IOD-like mean conditions during this interval, but with a different spatial expression in the eastern Indian Ocean compared to interannual IOD events of the modern era. Further, combining coral seawater oxygen isotope reconstruction with historical sea level pressure fields suggests the pronounced volcanic cooling and freshening in the northeastern Indian Ocean during the early 19^th century was associated with a major change in the tropical Pacific and Indian Ocean Walker Circulation. Our findings highlight the sensitivity of the northeastern Indian Ocean to external forcing and demonstrate that limited observations and proxy records to date have not captured the full range of regional climate variability. This complicates climate change projections for this highly populated region vulnerable to climate extremes. Ongoing work involves coral proxy-model comparisons using early 19^th century ensemble simulations with the MPI-ESM1.2 climate model to better constrain climatic variability across the region during this critical interval just prior to the start of instrumental observation.

暂无