Earth rotation changes since −500 CE driven by ice mass variations

• Ancient eclipse records constrain changes in Earth's rotation rate and clock error.
• There is a departure of the clock error from the predicted quadratic trend.
• 11 eclipse records drive the inferred millennial scale variability in clock error.
• Common Era ice mass flux can partially explain the deviation in the records since 700 CE.
• Ice mass flux cannot explain the variability in clock error prior to 700 CE.

We predict the perturbation to the Earth's length-of-day (LOD) over the Common Era using a recently derived estimate of global sea-level change for this time period. We use this estimate to derive a time series of “clock error”, defined as the difference in timing of two clocks, one based on a theoretically invariant time scale (terrestrial time) and one fixed to Earth rotation (universal time), and compare this time series to millennial scale variability in clock error inferred from ancient eclipse records. Under the assumption that global sea-level change over the Common Era is driven by ice mass flux alone, we find that this flux can reconcile a significant fraction of the discrepancies between clock error computed assuming constant slowing of Earth's rotation and that inferred from eclipse records since 700 CE. In contrast, ice mass flux cannot reconcile the temporal variability prior to 700 CE.