Geomagnetic field inclinations for the past 400 kyr from the 1‐km core of the Hawaii Scientific Drilling Project

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Abstract
A volcanic record of geomagnetic field inclination for the past ∼400 kyr at Hilo, Hawaii, has been obtained from the 941.5 m of core recovered by the Hawaii Scientific Drilling Project. The analysis of 195 lava flows reveals six instances of near‐zero inclination and two instances of fully negative inclination (reverse polarity) within an otherwise normal‐polarity core. In particular, flow unit 23 (∼178 m depth) records a horizontal inclination and may be associated with the Laschamp event; flow units 40 and 42 (∼260 m depth) record negative inclinations and are close in age to the Blake event; and flow unit 55 (∼320 m depth) records a negative inclination with a relative declination change of ∼75° with respect to the overlying flow and is probably the Jamaica/Biwa I/Pringle Falls event. The five instances of shallow inclination found below 400 m depth appear to have resulted from long‐term secular variation as they are part of inclination swings between ∼0° and ∼60° with a periodicity of ∼10–50 kyr. In contrast, the inclination shifts at ∼178 m and ∼320 m depths significantly deviate from long‐term trends, suggesting the existence of at least two independent processes producing time variations of the geomagnetic field. The secular variation has a mean of 30.9° (α95 = 2.27°), which is significantly shallower than the expected dipole mean of 36°. The dispersion (σ = 12.5°) agrees with global paleosecular variation data for 0–5 Ma and secular variation models.