Water Depth Dependence of Long‐Range Correlation in Nontidal Variations in Seafloor Pressure.

Isolating the source of nontidal oceanographic noise in seafloor pressure data is critical for improving the use of these data for seafloor geodetic applications. Residuals between nearby bottom pressure records have typically been used to remove the nontidal components, as these are largely common‐mode. To evaluate the similarities between pairs of observed bottom pressure records at a range of water depths, we calculate the standard deviations of the time series of residuals between data from all site pairs, installed in the Hikurangi subduction zone offshore New Zealand. We find that the magnitude of the standard deviation depends more on relative water depth than the distance between sites. This confirms the result of previous studies from Cascadia that nontidal components are more similar along isobaths even if the distance between sites is large. Furthermore, in order to reduce noises, the required depth difference between site pairs also varies with site depths. Plain Language Summary: Coherent signals of ocean bottom pressure are observed along common water depths within an ocean bottom pressure array offshore New Zealand. We statistically evaluated the similarity of the seafloor pressure collected in 2014 offshore the North Island's east coast, where the Pacific Plate dives or "subducts" along the Hikurangi subduction zone beneath the North Island. This is important for removal of noise caused by oceanographic processes, which must be done to detect centimeter‐level vertical movement of the seafloor crust during slow slip events using seafloor pressure records. We measured the similarity of pairs of seafloor pressure records at a range of water depths. Similar to previous studies offshore the Cascadia subduction zone, our results confirm that seafloor pressure records from similar depths (but at large horizontal distances from each other) can be used effectively to reduce oceanographic noise in sea floor pressure data to reveal the seafloor crustal deformation. Key Points: The similarity of the nontidal components of bottom pressure varies with relative water depth, rather than distance between sitesBottom pressure data show that reference sites at similar depths will optimize oceanographic noise removal for seafloor geodetic studiesOceanographic models with baroclinicity represent the observed depth dependence of the nontidal variations better than barotropic models [ABSTRACT FROM AUTHOR]