Holocene relative sea-level history of Franz Josef Land, Russia

Abstract

One of the largest uncertainties in ice-volume changes during the late Quaternary Period is the extent of ice sheets over the Barents and Kara seas. Field research on central and eastern Franz Josef Land, Russia, provide new observations on postglacial emergence and deglaciation that further constrain the magnitude and timing of late Weichselian glaciations. Radiocarbon dating of driftage from raised-marine sequences place deglacial unloading prior to 9.4 ka. At a number of localities within 1 to 2 km of the present glacier margin, in situ shells from raised-marine sediments yield 14C ages between 9.7 and 8.4 yr B.P., evidence that outlet glaciers were at or behind present margins by the early Holocene Period. The altitude of the marine limit on Franz Josef Land ranges from 49 to 20 m above sea level (asl) and is low compared to eastern Svalbard (110 to 60 m asl). The age of the marine limit ranges from ≥10.4 ka to ca. 6.0 ka and exhibits greater diachrony where emergence is <35 m. A low initial rate of emergence reflects glacio-isostatic compensation offset by a eustatic rise in sea level, and perhaps an additional component from renewed water loading of the Barents Sea after deglaciation. The presence of raised beaches at 1 to 4 m asl that are 1 to 2 ka indicates that uplift is incomplete. An exponential extrapolation of uplift data for Franz Josef Land and eastern Svalbard yields current maximum uplift estimates of 0.7 to 1.6 mm/yr, an inferred <5.5 m of uplift remaining. These values are at least 50% to 80% lower than the inferred uplift residual for a modeled ice sheet in the Barents and Kara seas. The discrepancy indicates that further refinement is needed for this ice-sheet model. The compilation of emergence data from Franz Josef Land, Svalbard, and Novaya Zemlya confine maximum glacio-isostatic compensation to the Barents Sea; comparatively minor ice sheet loads were over Novaya Zemlya and the southeastern Barents Sea. Emergence isobases since 5 and 9 ka descend northward across Franz Josef Land, indicating a diminishing glacio-isostatic response into the Arctic Ocean.