DOI: 10.5281/zenodo.6630862
title: Tidally modulated temperature observed atop a drillsite at the Noho hydrothermal site, mid-Okinawa Trough

description: These are the dataset used in a manuscript submitted to J. Geophys. Res. (AGU), entitled "Tidally modulated temperature observed atop a drillsite at the Noho hydrothermal site, mid-Okinawa Trough" by Kinoshita, M, K. Kitada and T. Nozaki. It is in revision as of June 10 2022. The authors of this dataset include those who organized or participated the expeditions and contributed to obtain the data shown here. <strong>Abstract</strong> We observed temperature variations over 10 months within a Kuroko ore (hydrothermal sulfide) cultivation apparatus installed atop a 50-m-deep borehole drilled in the Noho hydrothermal system in the mid-Okinawa Trough, southwestern Japan, for monitoring of hydrothermal fluids and in situ mineral precipitation experiments. Temperature and pressure in the apparatus fluctuated with the tidal period immediately after its installation. Initially, the average temperature was 75–76 °C and the amplitude of the semi-diurnal tidal temperature modulation was ~0.3 °C. Four months later, the amplitude of tidal temperature modulation had gradually increased to 4 °C in synchrony with an average temperature decrease to ~40 °C. Numerical modeling showed that both the increase in tidal amplitude and the decrease in average temperature were attributable to a gradual decrease in inflow to the apparatus, which promoted conductive cooling through the pipe wall. The reduced inflow was probably caused by clogging inside the apparatus, but we cannot rule out a natural cause, because the drilling would have significantly decreased the volume of hot fluid in the reservoir. The temperature fluctuation phase lagged the pressure fluctuation phase by ~150°. Assuming that the fluctuations originated from inflow from the reservoir, we conducted 2-D numerical hydrothermal modeling for a poroelastic medium. To generate the 150° phase lag, the permeability in the reservoir needed to exceed that in the ambient formation by ~3 orders of magnitude. The tidal variation phase can be a useful tool for assessing the hydrological state and response of a hydrothermal system. <strong>Key Points</strong> Temperature and pressure atop a borehole in the mid-Okinawa Trough hydrothermal system fluctuated with the tidal period during 10 months. The temperature tidal fluctuation phase lagged pressure by ~150° likely because of the poroelastic response of higher permeability sediment. A gradual temperature decrease and tidal amplitude increase were caused by reduced inflows that promoted conductive cooling. <strong>Explanation of the dataset</strong> *Fig.3_rawdata_C9017B_Long.txt:<br> *Fig.3_rawdata_C9017B_Short:<br> Temperature and pressure data recorded by the probes in the cell (Fig.3_rawdata_C9017B_Long) and the bottom inflow pipe (Fig.3_rawdata_C9017B_Short) during the whole observation period. All dates and times are Japanese Standard Time (JST: UTC+9). *Fig.5_Fig.8_Tidal-height_naotestj_C9017B_JST.txt: <br> Theoretical tidal height at the borehole C9017B, calculated using NAOTIDE program (Matsumoto, K., Takanezawa, T., & Ooe, M. (2000), Ocean tide models developed by assimilating TOPEX/POSEIDON altimeter data into hydrodynamical model: A global model and a regional model around Japan, J. Oceanography, 56, 567-581. https://doi.org/10.1023/A:1011157212596). *Fig.7_Flow-rate.txt: Flow velocity data and the sinusoidal fit during the period immediately after deployment of the apparatus, measured within the inflow pipe of the apparatus. <em><strong>Terms of use:</strong></em> These data are provided "as is", without any warranties of any kind. The data are provided under the Creative Commons Attribution 4.0 International license.
description: The exact location (longitude and latitude) for the Noho hydrothermal site is removed owing to limitations on the disclosure of information determined by the funding governmental agency (Council for Science, Technology and Innovation, Japanese Cabinet Office). Instead, we show the location in terms of the region as below: Latitude: 27-28N Longitude: 126deg30min - 127deg30min Water depth: 1550m