Collapse of the Icelandic ice sheet controlled by sea-level rise?

The Skagafjörður fjord in northern Iceland is located between the Tröllaskagi Peninsula in the east and the Skagi Peninsula in the west. The tributary valleys of the fjord originate in the highland area about 15 km north of the Hofsjökull icecap. The results of this work improve the knowledge of the deglaciation pattern in Skagafjörður and explore the adequacy of the 36Cl cosmic ray exposure dating method in an Icelandic environment, where this method has rarely been applied to deglaciated surfaces. The 36Cl dating method was applied to 13 rock samples taken on a transect from the coastal areas towards the highlands. All samples were obtained from rock outcrops with glacier‐polished surfaces from the Last Glaciation and from one of the few well‐preserved erratic boulders. The cosmogenic results, combined with previous radiocarbon results, indicate that the ice margin was situated in the outermost sector of Skagafjörður at approximately 17–15 ka BP. Subsequently, it retreated and occupied the central part of the fjord between 15 and 12 ka BP and then the innermost sector of the fjord about 11 ka BP. The samples collected between this position and the highlands show an average age of approximately 11 ka, indicating rapid deglaciation after the early Preboreal. These results agree with earlier studies of the deglaciation history of northern Iceland, reinforce previous deglaciation models in the area and enable a better understanding of glacial evolution in the North Atlantic from the Late Pleistocene to Holocene transition.

Section: Discussionmentioning

confidence: 99%

The rapid deglaciation of the Skagafjörður fjord, northern Iceland

Andrés

Palacios

Sæmundsson

et al. 2018

“…In spite of improved knowledge of the Late Weichselian deglaciation history of Iceland in recent decades the records are still sporadic and often poorly constrained in time (Geirsdóttir et al . ; Norðdahl & Ingólfsson ). This hampers correlation between glacial and climate records and therefore our ability to understand the relationships between glacier dynamics and climate/oceanographic changes.…”

mentioning

confidence: 99%

Refining the history of Younger Dryas and Early Holocene glacier oscillations in the Borgarfjörður region, western Iceland

Sigfúsdóttir

Benediktsson

2019

The lower Borgarfjörður region, western Iceland, has been central to the reconstructions of the dynamics and collapse of the Icelandic Ice Sheet during the deglaciation. Here, extensive stratigraphical sections and landforms provide a rare opportunity to study past glacier dynamics in this part of Iceland. Previous studies reveal that a large outlet glacier in Borgarfjörður advanced during the Late Weichselian resulting in large‐scale deformation of glaciomarine sediments and the formation of a series of ice‐marginal moraines. However, the events recorded by these sediments and landforms are poorly constrained in time. We present and discuss 22 new radiocarbon dates in the context of recent reconstructions of the regional glacier dynamics in order to constrain the timing of the glacier oscillations. The results show that a dynamic, marine‐terminating glacier advanced out of Borgarfjörður sometime after c. 13.0 cal. ka BP, resulting in the formation of an extensive moraine complex. The timing indicates that the advance occurred during climate cooling and widespread glacier expansions within the Younger Dryas. Followed by the first initial advance, the glacier exhibited at least five re‐advances punctuated by phases of retreat. Each re‐advance terminated proximal (within 5 km) to the outermost moraine complex although the extent of periodic retreat and the exact timing of these oscillations are unknown. All these phases of re‐advance occurred prior to the onset of the Holocene (around 11.7 cal. ka BP), during which marine fauna re‐colonized the area and the Borgarfjörður glacier retreated from the moraines. During the Early Holocene (sometime after c. 11.3 cal. ka BP), the Borgarfjörður glacier re‐advanced to a position within ~5 km of the YD ice limit. This is the first recorded Early Holocene large‐scale glacier advance in western Iceland and suggests that glacier expansion in this region coincided with widespread advances elsewhere in Iceland.

“…A general deglaciation following the LGM extent of the IIS was greatly enhanced during the Bølling climatic amelioration, and the Úthérað area and thereafter the Lögurinn basin may have sometimes been ice‐free between about 14.7 and 13.2 cal. ka BP (Norðdahl & Ingólfsson ; Pétursson et al . ; Patton et al .…”

Section: Discussionmentioning

confidence: 99%

“…After a rapid retreat or collapse of the IIS (Norðdahl & Ingólfsson ), enhanced by the Bølling climatic amelioration (Rasmussen et al . ; Deschamps et al .…”

Section: Discussionmentioning

confidence: 99%

“…The high rate of glacio‐isostatic uplift in Iceland was driven by rapid unloading of the crust (rate of deglaciation) and moderated by properties of the lithosphere and asthenosphere below the uplifted area (for references see Norðdahl & Ingólfsson ). The progress and eventual cessation of glacio‐isostatic uplift has been described as an exponential function over time (e.g.…”

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

Glacio‐isostatic age modelling and Late Weichselian deglaciation of the Lögurinn basin, East Iceland

Norðdahl

Inǵólfsson

Vogler

et al. 2018

Self Cite

Knowledge of the glaciation of central East Iceland between 15 and 9 cal. ka BP is important for the understanding of the extent, retreat and dynamics of the Icelandic Ice Sheet. Crucially, it is not known if the key area of Fljótsdalur‐Úthérað carried a fast‐flowing ice stream during the Last Glacial Maximum; the timing and mode of deglaciation is unclear; and the history and ages of successive lake‐phases in the Lögurinn basin are uncertain. We use the distribution of glacial and fluvioglacial deposits and gradients of former lake shorelines to reconstruct the glaciation and deglaciation history, and to constrain glacio‐isostatic age modelling. We conclude that during the Last Glacial Maximum, Fljótsdalur‐Úthérað was covered by a fast‐flowing ice stream, and that the Lögurinn basin was deglaciated between 14.7 and 13.2 cal. ka BP at the earliest. The Fljótsdalur outlet glacier re‐advanced and reached a temporary maximum extent on two separate occasions, during the Younger Dryas and the Preboreal. In the Younger Dryas, about 12.1 cal. ka BP, the outlet glacier reached the Tjarnarland terminal zone, and filled the Lögurinn basin. During deglaciation, a proglacial lake formed in the Lögurinn basin. Through time, gradients of ice‐lake shorelines increased as a result of continuous but non‐uniform glacio‐isostatic uplift as the Fljótsdalur outlet glacier retreated across the Valþjófsstaður terminal zone. Changes in shoreline gradients are defined as a function of time, expressed with an exponential equation that is used to model ages of individual shorelines. A glaciolacustrine phase of Lake Lögurinn existed between 12.1 and 9.1 cal. ka BP; as the ice retreated from the basin catchment, a wholly lacustrine phase of Lake Lögurinn commenced and lasted until about 4.2 cal. ka BP when neoglacial ice expansion started the current glaciolacustrine phase of the lake.