A nearly 1.5 millennia long record of North Atlantic climatic forcing recorded in tree-ring growth records from Angstel/Vecht Delta, the Netherlands (1283 BCE-156 CE)

Michiel Arts , Jos Bazelmans

The impact of multi-annual to decadal climatic cycles on tree-ring growth remains understudied. Here, we analyse a nearly one-and-a-half-thousand-year-long tree-ring chronology (1283 BCE–156 CE) based on bog oaks from an alder carr environment in the Angstel-Vecht delta in the Netherlands to assess the influence of multi-year climatic oscillations on tree-ring growth and the origin of the identified cycles. Wavelet, crosswavelet, and bicoherence spectral analyses reveal significant cycles ranging from 2.2 to 100 years. To investigate the forcing mechanisms behind these cycles, we compare the tree-ring record with the Uamh an Tartair stalagmite record from northwestern Scotland, reflecting large-scale variability in North Atlantic precipitation. Cross-wavelet analysis reveals a quarter-cycle phase lag across multiple timescales, indicating a shared North Atlantic climatic driver, with the stalagmite responding almost instantaneously, whereas the Angstel/Vecht tree-ring record shows a delayed response. This delay is attributed to cumulative climate forcing mediated by groundwater changes and hydrological storage processes within the peatland system. The phase relationships suggest that, alongside flooding events, periods of increased regional rainfall elevate groundwater levels, suppressing oak growth in the Angstel/Vecht delta. The 100-, 60-, and 24-year cycles correspond to known climatic oscillations linked to North Atlantic climate modes such as the North Atlantic Oscillation (NAO) and the Atlantic Multidecadal Oscillation (AMO), or possibly solar cycles. Some cycles, such as the 40- and 15-year cycles, cannot be directly attributed to external forcing but instead appear to be nonlinear combination tones. These results indicate that cyclicity in tree-ring growth reflects non-linear interactions among multiple forcing mechanisms across timescales, and demonstrate that lowland wetland bog oak records provide sensitive archives of multiannual to multidecadal hydroclimatic variability in the North Atlantic region over long timescales.