Long-period (20-50 s) surface-gravity waves were recorded in the easte
rn Arctic (83 degrees N, 10 degrees E) using tiltmeters deployed on th
e ice and an acoustical current meter deployed a few meters below the
ice during the spring of 1989. The waves caused ice tilt of a few micr
oradians and horizontal velocity of the water just beneath the ice of
order 10(-4) m s(-1). The unprecedented sensitivity of the velocity me
asurements is the result of a path-averaging technique based on recipr
ocal transmission along 200-m horizontal paths. The measurements indic
ate that infragravity waves and low-frequency swell penetrate the Arct
ic Ocean through the Fram Strait and that they are freely propagating
and not tied to groups of short waves. It is suggested that these wave
s could provide a method to measure ice thickness distribution in the
Arctic Ocean.