Tropical Pacific temperature seasonality around Meltwater Pulse-1A from IODP Expedition 310 corals

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Seasonality plays a fundamental role in Earth’s climate, but the evolution of the annual cycle of temperature at Earth’s surface is not well constrained in the past - in particular for the tropical ocean, a key player in global climate dynamics. The amplitude of the temperature annual cycle is thought to be modulated by Earth’s orbital variations on longer timescales. Seasonality is of considerable importance to improved model projections of future climate change through retrospective simulations of past climates, but quantifiable evidence of the annual cycle of temperature from geological archives is sparse. Fossil shallow-water corals provide a unique but relatively rare archive of sea surface temperature seasonality for the tropical ocean and can be precisely dated by the U-series method. Emerging coral work from the Atlantic suggests that temperature seasonality of the tropical surface ocean is controlled mainly by orbital insolation changes during interglacials, even during periods of substantial climate perturbations and abrupt sea-level rise. However, comparable information for glacials and deglaciations is still lacking. Here we suggest reconstructing and quantifying tropical Pacific temperature seasonality during the last deglaciation with a specific focus on meltwater pulse (MWP) 1A (~14.5 kyr ago), by analysing geochemical proxies in the skeletons of fossil shallow-water corals (Porites) drilled by IODP Expedition 310 ’Tahiti Sea Level’. Supplemented by a new collection of modern Tahiti Porites corals recovered from the vicinity of the Expedition 310 drill sites serving as present-day benchmark to robustly assess the uncertainties in our reconstructions, we intend to test the hypotheses if tropical Pacific temperature seasonality is controlled mainly by orbital insolation changes during (1) the last deglaciation and, in particular, (2) during MWP-1A, a period characterized by abrupt sea-level rise and climate change and substantial climate perturbations. Our anticipated coral results will provide rare proxy data for comparisons with state-of-the-art climate model simulations, e.g., those of the German Climate Modeling Initiative PALMOD "From the Last Interglacial to the Anthropocene – Modeling a Complete Glacial Cycle", and will contribute to an improved understanding of the seasonal response of tropical Pacific climate variability to abrupt perturbations on glacial-interglacial timescales. This is of high relevance for improved projections of future tropical Pacific climate variability and its global teleconnections on society-relevant timescales.