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Evidence of a dynamic Holocene glacial history is preserved in the terrestrial and marine archives of St. Jonsfjorden, a small fjord-system on the west coast of Spitsbergen, Svalbard. High-resolution, remotely sensed imagery from marine and terrestrial environmentswas used to construct geomorphological maps that highlight an intricate glacial historyof the entire fjord-system. The geomorphology and stratigraphy indicate an early Holocene local glacier advance constrained to the Lateglacial-early Holocene transition. Identification and 14 C dating of the thermophilous bivalve mollusc Modiolus modiolus to 10.0AE0.12 cal. ka BP suggest a rapid northward migration of the species shortly after deglaciation. Further evidence enhances the understanding of the onset and subsequent climax of the Neoglacial-Little Ice Age in inner St. Jonsfjorden. The present-day terminus of Osbornebreen, the dominating glacier system in St. Jonsfjorden, is located over 8.5 km up-fjord from its Neoglacial maximum extent. Cross-cutting relationships suggest subsequent advances of all the smaller glaciers in the area following the break-up of Osbornebreen. Glacial deposits, landforms and their cross-cutting relationships observed in both terrestrial and marine settings imply a complex and highly dynamic environment through the later part of the Holocene.

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Despite warming regional conditions and our general understanding of the deglaciation, a variety of data suggest glaciers re-advanced on Svalbard during the Lateglacial-early Holocene (LGEH). We present the first well-dated end moraine formed during the LGEH in De Geerbukta, NE Spitsbergen. This landform was deposited by an outlet glacier re-advancing into a fjord extending 4.4 km beyond the late Holocene (LH) maximum. Comparing the timing of the De Geerbukta glacier re-advance to a synthesis of existing data including four palaeoclimate records and 15 other proposed glacier advances from Svalbard does not suggest any clear synchronicity in glacial and climatic events. Furthermore, we introduce six additional locations where glacier moraines have been wave-washed or cut by postglacial raised marine shorelines, suggesting the landforms were deposited before or during high relative sea-level stands, thus exhibiting a similar LGEH age. Contrary to current understanding, our new evidence suggests that the LGEH glaciers were more dynamic, exhibited re-advances and extended well beyond the extensively studied LH glacial expansion. Given the widespread occurrence of the LGEH glacier deposits on Svalbard, we suggest that the culmination of the Neoglacial advances during the Little Ice Age does not mark the maximum extent of most Svalbard glaciers since deglaciation; it is just the most studied and most visible in the geological record.