Self-Building Landscapes: Sand Seas Grow by Steering Climate

It is widely recognized that landform influence s flow at the local scale, for example channels erode to accommodate flow, and bedform amplitude saturates . With some notable exceptions, however, we generally regard climate as a boundary condition that is imposed upon a landform by the Earth system. Here we identify a case where land form controls the generative fluid well beyond its own scale, and as this coupled system evolves, climate is altered. Deserts experience large diurnal cycles in temperature, which gives rise to strong non-equilibrium dynamics in atmospheric flow. Aeolian dune fields are domains of low thermal inertia that enhance these effects, resulting in strong convection and atmospheric mixing that produces larger-than-expected surface winds. These winds can enhance the expansion of dune fields leading to a positive land-climate feedback, where the coupling strengthens as sand seas grow. We motivate this global result with explicit and detailed in situ measurements from White Sands Dune Field, New Mexico. We demonstrate th e coupling by constructing an exhaustive dataset of the climate, form, age, size and sediment of Earth's sand seas using remote sensin g (ASTER, CALIPSO, LANDSAT), reanalysis (ERA-5) and previous literature (Global Dune Atlas). By comparing climatologies and dunes of over 40 sand seas, we show that larger and more mature of these geomorphic systems have stronger control over their generative geophysical fluid flows, but how that controls the size of their largest dunes remains illusive.