Spatial Variability in the Deep Marine Response to Astronomical Forcing

Abstract:

Much of our understanding of past climate change and its connection to astronomical forcing relies on high-resolution measurements of deep marine sedimentary records. These records have revealed that carbon cycle dynamics and climate are often intimately connected on astronomical timescales, although the causal relationships and prevailing feedbacks at play are difficult to disentangle. The amplitude, spectral power, and relative phasing between environmental proxies such as δ¹⁸O, δ¹³C, and wt% CaCO₃ or Fe content measured in deep sea records provide valuable information required to evaluate the mechanisms and associated timescales that drove astronomically forced environmental changes. However, a comprehensive evaluation of how astronomical signals are transferred spatially, between proxies, and within Earth surface reservoirs is missing.

Here, we use a spatially resolved ocean-coupled Earth system model (cGENIE) to simulate the direct impact of astronomical forcing on the marine environment by changing the amount and distribution of incoming solar radiation in a time-dependent manner. We evaluate the oscillations generated in the ocean temperature, δ¹³C, and sedimentary calcium carbonate preservation and find noteworthy spatial heterogeneity. Amplitudes, spectral power, and phase relations between environmental variables simulated by the model vary from site to site, mainly depending on seafloor sediment depth and ocean circulation patterns. In some extreme cases, the phasing between two variables in parts of the basin containing newly formed deep waters may be completely reversed from the phasing recorded in regions where the oldest water masses accumulate. A better understanding of the propagation of astronomical cycles through the Earth system is essential to the interpretation of paleoclimate records.