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Multibeam bathymetry and 3.5-kHz sub-bottom profiler data collected from the US icebreaker Healy in 2003 provide convincing evidence for grounded ice on the Chukchi Borderland off the northern Alaskan margin, Arctic Ocean. The data show parallel, glacially induced seafloor scours, or grooves, and intervening ridges that reach widths of 1000 m (rim to rim) and as much as 40 m relief. Following previous authors, we refer to these features as “megascale glacial lineations (MSGLs).” Additional support for ice grounding is apparent from stratigraphic unconformities, interpreted to have been caused by ice-induced erosion. Most likely, the observed sea-floor features represent evidence for massive ice-shelf grounding. The general ESE/WNW direction of the MSGLs, together with sediment, evidently bulldozed off the Chukchi Plateau, that is mapped on the western (Siberian) side of the plateau, suggests ice flow from the Canada Basin side of Chukchi Borderland. Two separate generations of glacially derived MSGLs are identified on the Chukchi Borderland from the Healy geophysical data. The deepest and oldest extensive MSGLs appear to be draped by sediments less than 5 m thick, whereas no sediment drape can be distinguished within the resolution of the sub-bottom profiles on the younger generation.

FIGURE 1. Multi-beam echo sound survey of the site and location relative to the island of Kauai (inset). FIGURE 2. Equipment lay down for KauaiEx. The principal sound source located at the southern end (left) broadcast to VLA' s distributed along the track. Acoustic sensors were interleaved with environmental sensors including thermistor strings along the entire propagation path. FIGURE 4. Deployment of the telesonar testbed (left). Track of the towed transmitter (T1) relative to the receiver testbed (T3) (right). FIGURE 5. Matched-filter response or replica correlogram showing the impulse response of the channel in 3 separate frequency bands.

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