Haflidi Haflidason

Paleoceanographic reconstructions of surface ocean conditions in the Greenland, Iceland and Norwegian seas through the last 14 ka based on diatoms

Prior reconstructions of the last glacial maximum and the Holocene did not include detailed paleoclimate data from the Greenland, Iceland and Norwegian (GIN) seas, which cover sensitive areas for oceanographic boundaries, sea ice distribution and deep water formation. In order to fill this gap, we studied nine well dated sediment cores from this area and reconstructed the paleoceanographic conditions of the surface GIN seas at 2000-year intervals since 13,400 BP based on the diatom record. Results show that a N.-S. extending sea-ice-free corridor had opened along Norway already at 13,400 BP, indicating a northward flow of a branch of the North Atlantic Drift, possibly caused by a change in the jet stream flow due to the decreased height of the North American ice sheet. A major change of climatic conditions occurred over the GIN seas as the insolation anomaly reached its maximum around 9000 BP, when the sea ice cover and the oceanic fronts retreated to a northwesterly position along Greenland, and the ocean temperatures rose. The first half of the Holocene is recorded as the warmest period during the last 13,400 BP in the GIN seas. The duration of this climatic optimum decreased both toward the north and toward the margins of the area. The second half of the Holocene is characterized by a cooling trend in step with the decreasing insolation. These results support the proposal of Imbrie et al. (1992) that the GIN seas region acts as an initial responder to insolation changes.

The tephrochronology of Iceland and the North Atlantic region during the Middle and Late Quaternary: a review

The tephrochronology of Iceland and the North Atlantic region is reviewed in order to construct a unified framework for the last 400 kyr BP. Nearly all of the tephra layers described are also characterised geochemically. A number of new tephra layers are analysed for the first time for their geochemical signature and a number of pre-Holocene tephra layers have been given an informal denotation. The tephrostratigraphy of Ash Zone II is highlighted. Where possible the rhyolitic tephra layers found outside Iceland have been correlated to known Icelandic tephra layers or to the volcanic source area. The application of tephra fallout in various depositional environments is described and discussed. Copyright

Quaternary seismic stratigraphy of the North Sea Fan: glacially-fed gravity flow aprons, hemipelagic sediments, and large submarine slides

Abstract Approximately 1000 km of high resolution sleeve-gun array transects on the North Sea Fan, located at the mouth of the Norwegian Channel, reveal three dominant styles of sedimentation within a thick (> 900 m) Quaternary sediment wedge comprising numerous sequences. These are interpreted as: terrigenous hemipelagic sedimentation, large scale translational slides, and aprons of glaciogenic debris flow deposits contributing to considerable fan construction. Four large, buried translational slides involved sediment volumes upwards of 3000 km 3 each and preceded the similarly dimensioned “first” Storegga Slide on the NE fan flank. Several thick (> 100 m) terrigenous hemipelagic deposits apparently represent long-lived (150–200 kyr) periods of sedimentation whose distribution indicates fan input via the Norwegian Channel. The upper sequences are each made upper sequences are each made up of one or several thick (> 100 m) aprons comprising stacked lensoid and/or lobate forms which range from 2 to 40 km in width and 15 to 60 m in thickness. They characterize debris flows attributed to periodic input from several phases of a Norwegian Channel ice stream reaching the shelf edge. Subsidence in the outer Norwegian Channel allowed preservation of several glaciation cycles represented by sheet erosion-bounded tills and progradational units. Much of the shelf/slope transition has been preserved, allowing a preliminary chronology of the fan sequences through correlation with borehole sediments in the Norwegian Channel. Debris flows, which signal the initial shelf-edge glaciation, are not recognized from the initial glaciation in the Channel (> 1.1 Myr) but are associated with a Middle Pleistocene and all following glacial erosion surfaces (GES) in the outer Norwegian Channel. This was followed by six further sequences, probably totalling over 13,000 km 3 of sediment. At least four of these were shelf-edge ice-maximum events the last of which was Late Weichselian age ( 14 C AMS). Considering earlier glaciation-related hemipelagic sedimentation, material since removed by the large slides, and extensive unmapped areas, total Quaternary fan sedimentation was in the vicinity of 20,000 km 3 .

Late-glacial and Holocene palaeoceanography of the North Icelandic shelf

High-resolution gravity cores and box cores from the North Icelandic shelf have been studied for palaeoceanographic history based on lithological and biostratigraphical foramin- iferal data. Results from two outer shelf cores covering the last 13.6 k 14 C yr BP are presented in this paper. The sediments accumulated in north-south trending basins on each side of the Kolbeinsey Ridge at water depths of ca. 400 m. Sedimentation rates up to 1.5 m kyr -1 are observed during the Late-glacial and Holocene. The Vedde and Saksunarvatn tephras are present in the cores as well as the Hekla 1104. A new tephra, KOL-GS-2, has been identified and dated to 13.4 k 14 C yr BP, and another tephra, geochemically identical to the Borrobol Tephra, has been found at the same level. At present, the oceanographic Polar Front is located on the North Icelandic shelf, which experiences sharp oceanographic surface boundaries between the cold East Icelandic Current and the warmer Irminger Current. Past changes in sedimentological and biological processes in the study area are assumed to be related to fluctuations of the Polar Front. The area was deglaciated before ca. 14 kyr BP, but there is evidence of ice rafting up to the end of the GS-1 (Greenland Stadial 1, Younger Dryas) period, increasing again towards the end of the Holocene. Foraminiferal studies show a relatively strong GS-2 (pre-13 kyr BP) palaeo-Irminger Current, followed by severe cooling and then by unstable conditions during the remainder of the GI-1 (Greenland Interstadial 1, Bolling-Allerod) and GS-1 (Younger Dryas). Another cooling event occurred during the Preboreal before the Holocene current system was established at about 9 kyr BP. After a climatic optimum between 9 and 6 kyr BP the climate began to deteriorate and fluctuate. Copyright

Coupled response of the late glacial climatic shifts of northwest Europe reflected in Greenland ice cores: Evidence from the northern North Sea

The climatic regimes of the land areas adjacent to the North Sea are controlled by the influx of Atlantic water north of the British Isles and into the North Sea. A high-resolution record from the Norwegian Channel off western Norway covering the past 15 ka ( 14 C) shows that prior to the Younger Dryas, there were three periods of sea-surface conditions there similar to those of the present, interspersed with arctic conditions. These changes, corresponding to an increase of (Approx.)5 °C in summer sea-surface temperatures, took place on the scale of

Configuration, history and impact of the Norwegian Channel Ice Stream

The Norwegian Channel between Skagerrak, in the southeast, and the continental margin of the northern North Sea, in the northwest, is the result of processes related to repeated ice stream activity through the last 1.1 m yr. In such periods the Skagerrak Trough (700 m deep) has acted as a confluence area for glacial ice from southeastern Norway, southern Sweden and parts of the Baltic. Possibly related to the threshold in the Norwegian Channel off Jaeren (250 m deep), the ice stream, on a number of occasions over the last 400 ka, inundated the coastal lowlands and left an imprint of NW-oriented ice directional features (drumlins, stone orientations in tills and striations). Marine interstadial sediments found up to 200 m a.s.l. on Jaeren have been suggested to reflect glacial isostasy related to the Norwegian Channel Ice Stream (NCIS). In the channel itself, the ice stream activity is evidenced by mega-scale glacial lineations on till surfaces. As a result of subsidence, the most complete sedimentary records of early phases of the NCIS are preserved close to the continental margin in the North Sea Fan region. The strongest evidence for ice stream erosion during the last glacial phase is found in the Skagerrak. On the continental slope the ice stream activity is evidenced by the large North Sea Fan, which is mainly a result of deposition of glacial-fed debris flows. Northwards of the North Sea Fan, rapid deposition of meltwater plume deposits, possibly related to the NCIS, is detected as far north as the Voring Plateau. The NCIS system offers a unique possibility to study ice stream related processes and the impact the ice stream development had on open ocean sedimentation and circulation.

Chronology of late Holocene climatic events in the northern North Atlantic based on AMS14C dates and tephra markers from the volcano Hekla, Iceland

A combination of AMS14C dating and tephrochronology has been used to date late Holocene oceanographic events in a 335 cm marine record, covering about 4600 cal. yr with sedimentation rates exceeding 80 cm 1000 yr−1. The core site is located 50 km offshore on the northern Icelandic shelf. Tephra markers from Iceland serve to correlate the marine and terrestrial records. Especially notable is the presence of three geochemically correlated tephra markers from the Icelandic volcano Hekla (Hekla 4, Hekla 3 and Hekla 1104). Benthic and planktonic foraminiferal abundance and distribution as well as the petrography of the sand fraction of the muddy shelf sediments are used as palaeoceanographic proxies. The foraminiferal assemblages reflect a general cooling trend during the last 4600 yr. A marked drop in sea-surface temperatures is registered at about 3000 cal. yr BP, corresponding to the level of the Hekla 3 tephra. There is faunal indication of temperature amelioration during the Medieval Warm Period and a cooling again during the Little Ice Age. Periods of ice rafting events are indicated by ice rafted debris (IRD) concentrations, e.g. at around 3000 cal. yr BP and during the Little Ice Age. The former event occurred just prior to the deposition of the Hekla 3 tephra marker, the largest Holocene Hekla eruption. A correlation with terrestrial climatic events in Iceland is presented. A standard marine reservoir correction of 400 14C yr appears to be reasonable, at least during periods with high influence of water masses from the Irminger Current on the northern Icelandic shelf. An increase to ca. 530 14C yr may have occurred, however, when water masses derived from the East Greenland Current were dominant in the area. Copyright

The last 18 kyr fluctuations in Norwegian sea surface conditions and implications for the magnitude of climatic change: Evidence from the North Sea

A combined record of three cores spanning the last 18 kyr from the northern North Sea is investigated for content of benthic and planktonic foraminifera and stable oxygen isotopes. The paleoenvironmental development through this time period shows an early deglaciation (18–14.4 ka) and the Younger Dryas (12.7–11.5 ka) characterized by arctic/polar conditions and increased ice rafting in the Norwegian Channel. During the Bolling-Allerod period, warm sea surface temperature (9°C) conditions similar to present conditions are inferred, while bottom waters stayed cold (0–1°C) with normal salinity. The Bolling-Allerod period is interrupted twice at 13.9–13.6 ka (Older Dryas) and at 13.0–12.8 ka (Inter-Allerod Cooling Period) by reductions in sea surface temperatures and increased sea ice cover. The beginning of the Holocene period is marked by increases in surface and bottom water temperature. Superimposed on the broad climatic changes through the Holocene, a series of short-lived oscillations in the ocean circulation are recorded. The amplitude of these Holocene events appears larger in the early Holocene (prior to 8 ka) than compared with the remaining part of the Holocene. This amplification can possibly be attributed to a general increased freshwater budget in the North Atlantic at this time during the final stages of the deglaciation of the Laurentide and Scandinavian ice sheets.

Extreme sediment and ice discharge from marine-based ice streams: New evidence from the North Sea

A major problem for understanding the dynamics of ice streams has been a lack of precise data on ice streaming longevity and sediment transport efficacy. Here we present the first well-constrained data on sediment flux from a paleoice stream. This has been achieved by computing the volume of sediment deposited as debris flows on the fan located at the outlet of the Norwegian Channel ice stream, and converting to a flux measurement by accounting for the duration of streaming in this episode (between 20 and 19 ka during the last glacial stage). In this period the ice stream delivered an average 1.1 Gt of sediment per year, equivalent to 8000 m 3 yr −1 per meter width of ice stream front. The calculated flux is an order of magnitude higher than most previous estimates for other paleoice streams and is comparable to the present sediment flux from the world9s largest rivers. The short period of debris-flow deposition suggests that the Norwegian Channel ice stream underwent rapid on-off switching, with punctuated iceberg delivery to the North Atlantic as a consequence.

The Storegga Slide Complex; Repeated Large Scale Sliding in Response to Climatic Cyclicity

The Holocene Storegga Slide is the last of a series of slides occurring in the same area during the last 500ky. The objectives of the present paper are to present the current understanding of the trigger mechanisms and development of the Storegga Slide, and to show the link between the sliding and Pleistocene climatic fluctuations in the area. Instability is created by the rapid loading of fine-grained hemipelagic deposits and oozes by rapid glacial deposition during peak glaciations. Postglacial earthquake activity was the most likely trigger. Although slide development is complicated and involves a number of slide mechanisms and processes, the overall development is retrogressive, starting at the mid- to lower slope. Sliding stops when the headwall reaches the flat lying, overconsolidated glacial deposits of the shelf.