Abstract
AbstractRecent studies have shown that stratigraphically disturbed meteoric ice bedded at Vostok Station between 3318 and 3539 m dates back to 1.2 Ma BP and possibly beyond. As part of the VOICE (Vostok Oldest Ice Challenge) initiative, a new deviation from parent hole 5G-1 was made at depths of 3270–3291 m in the 2018/19 austral season with the aim of obtaining a replicate core of the old ice. Sidetracking was initiated using the standard KEMS-132 electromechanical drill routinely employed for deep ice coring at Vostok, without significant changes to its initial design. Here we describe the method and operating procedures for replicate coring at a targeted depth in an existing slant hole, involving the use of a cable-suspended electromechanical drill. The design of the milling cutter head used for sidetracking is presented. The performance characteristics and the experience of drilling branch-hole 5G-5 at Vostok are described and discussed.
Highlights
The ice core recovered from the 5G-1 hole at Russia’s Vostok Station in Antarctica in the late 1990s provided a wealth of information about past climate and environmental changes through the last four glacial–interglacial cycles (Petit and others, 1999)
It has been argued (Lipenkov and Raynaud, 2015) that implementing a project focused on the old Vostok meteoric ice could shed light on how and to what extent the old Antarctic ice may help in deciphering the enigma of the Mid-Pleistocene climatic transition, the main scientific goal of the Oldest Ice Core project proposed by the planning group International Partnership in Ice Core Sciences
In 2013, in the course of re-drilling hole 5G-1, which had become filled with frozen sub-ice water after the first unsealing of Lake Vostok, the drill deviated from the parent hole and started the new 5G-3 branch hole at a depth of 3458 m, yielding a replicate core of old ice from the depth interval 3458–3539 m (Fig. 1)
Summary
The ice core recovered from the 5G-1 hole at Russia’s Vostok Station in Antarctica in the late 1990s provided a wealth of information about past climate and environmental changes through the last four glacial–interglacial cycles (Petit and others, 1999). A depth at which the sidetracking should be started was calculated taking into account (a) the request to obtain a full diameter core at a depth of 3311 m at a distance not exceeding 500 mm from the parent hole 5G-1, and (b) the minimum possible angle of the borehole curvature for a given length of the drill (10 m) (Vasilev and others, 2014, 2019).
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