Constraints on sea-level rise during meltwater pulse 1B from the Great Barrier Reef.

The timing, rate, and magnitude of rapid sea-level rise during Meltwater Pulse 1B (MWP-1B, ~11.45-11.1 ka) remain controversial. Robust constraints on past MWPs are crucial to future predictions of global ice sheet instability. Using 154 new and existing U/Th and calibrated C-AMS dates from coral, algae, and microbialites recovered during Integrated Ocean Drilling Program Expedition 325, this study reconstructs reef development and relative sea-level (RSL) rise on the Great Barrier Reef (GBR). We identify 107 in situ RSL index points while refining estimates of vertical accretion and paleowater depth. Results show RSL rise during MWP-1B did not exceed 10.2-7.7 m or rates of 30-23 mm/yr, and was likely less. The GBR did not drown, indicating resilience to MWP-1B. These findings are more consistent with Tahiti and other Pacific records and do not support the Barbados record of MWP-1B as an abrupt step in global sea level, with a magnitude > 11 m.