Early Holocene Establishment of the Barents Sea Arctic Front

A main feature of the Barents Sea oceanography is the Arctic front. The Arctic front marks the transition between the dominating water masses of the Barents Sea: Atlantic Water in the south and Arctic Water in the north. Presently, the Barents Sea Arctic front is directed by the topography of the Bear Island Trough and to some degree the location of the sea ice boundary. During the last glacial maximum, the Svalbard-Barents Sea and Scandinavian Ice Sheets covered the Barents Sea. Hence, no water entered the Barents Sea, neither from the south nor from the north. Following the deglaciation of the Barents Sea, the present-day ocean circulation developed. The evolution of how the present location of the Barents Sea Arctic front established during the early Holocene is documented by foraminiferal relative assemblage data from six core sites along the western Barents Sea margin and opening. The relative abundance of Arctic front indicator Turborotalita quinqueloba, in combination with the cold, polar Neogloboquadrina pachyderma and warm, Atlantic Neogloboquadrina incompta, are used to infer the location of the Barents Sea Arctic front relative to the individual core sites. Until ca. 11 ka BP, the Barents Sea Arctic front followed the western margin of the Barents Sea. All sites along the Barents Sea margin where still dominated by Arctic Water between ca. 11 and 10.2 ka BP, however, the Barents Sea Arctic front turned eastwards into the southwestern Barents Sea. From ca. 10.2 to 8.8 ka BP, the Barents Sea Arctic front moved eastward and was located right above most sites as it followed the Barents Sea margin. The northwestern Barents Sea Arctic front was close to the present location from ca. 8.8 to 7.4 ka BP, however, it was still confined to the southwestern Barents Sea. From ca. 7.4 ka BP, the Barents Sea Arctic front has been located close to the present position, along the margin southwards from Svalbard, turning eastwards along and beyond the northern Bear Island Trough margin

Insolation and gacial meltwater influence on sea‐ice and circulation variability in the Northeastern Labrador Sea during the last glacial period

The variable amounts of ice rafted debris (IRD) and foraminifers in North Atlantic sediments are related to the abrupt, millennial-scale alteration from Greenland stadials to interstadials during the last glacial period and indicate past ice sheet instabilities, changes in sea-ice cover and productivity. In the Norwegian Sea, Greenland stadials were likely characterized by an extensive, near-perennial sea-ice cover whereas Greenland interstadials were seasonally ice-free. The variability in other areas, such as the Labrador Sea, remains, however, obscure. We therefore investigated deep-sea sediment core GS16-204-22CC retrieved south of Greenland. Using a multiproxy approach, we distinguish two sediment regimes and hence different environmental conditions between ca. 65 and 25 ka b2k. Regime 1 (similar to 65-49 ka b2k) is characterized by the dominance of planktic foraminifers in the sediments. During late MIS4 and early MIS3, the site was covered by near-perennial sea-ice with occasional periods of iceberg discharge. During the younger part of regime 1 the northeastern Labrador Sea was seasonally ice-free with hardly any icebergs melting near the site and long-term environmental conditions were less variable. Regime 2 (similar to 49-25 ka b2k) is characterized by pronounced stadial-interstadial variability of foraminifer and IRD fluxes, suggesting an extensive sea-ice cover during most Greenland stadials and seasonally ice-free conditions during most Greenland interstadials. During MIS2 environmental conditions were very similar to those of the younger part of regime 1. While all Heinrich (H) related Greenland stadials are marked by depleted oxygen isotope values at our core site, only H4 and H3 are associated with pronounced IRD peaks. Plain Language Summary North Atlantic sediments contain variable amounts of sand-sized mineral grains and microorganism shells. Mineral grains indicate iceberg transport from continental ice sheets, like the Greenland ice sheet (more icebergs/melting sea-ice, more grains). If the sea-ice cover is too thick, no light can penetrate and fewer microorganisms live in the water beneath the ice. Using these indicators, we investigated ocean sediments from south of Greenland covering the time period between ca. 65 and 25 thousand years ago. This time period was characterized by several abrupt changes between cold and warm climates on millennial timescales. We find that the ocean south of Greenland was sea-ice covered for most of the year with occasional time periods of iceberg discharge between 65 to 56 thousand years ago. From 56 to 49 thousand years ago the ice-free season was extended and hardly any icebergs melted near the site. From 49 thousand years ago our study area was covered by sea-ice year-round during cold time intervals whereas warm time intervals were only seasonally sea-ice covered. Continental ice sheets were growing during this time interval and we observed two major calving events related to two of the four very cold climate intervals recorded in the analyzed sediment.Fundacao de a Ciencia e a Tecnologia IF/01500/2014 UID/Multi/04326/2019info:eu-repo/semantics/publishedVersio

A first chronology for the East Greenland Ice-core Project (EGRIP) over the Holocene and last glacial termination

This paper provides the first chronology for the deep ice core from the East Greenland Ice-core Project (EGRIP) over the Holocene and the late last glacial period. We rely mainly on volcanic events and common peak patterns recorded by dielectric profiling (DEP) and electrical conductivity measurement (ECM) for the synchronization between the EGRIP, North Greenland Eemian Ice Drilling (NEEM) and North Greenland Ice Core Project (NGRIP) ice cores in Greenland. We transfer the annual-layer-counted Greenland Ice Core Chronology 2005 (GICC05) from the NGRIP core to the EGRIP ice core by means of 381 match points, typically spaced less than 50 years apart. The NEEM ice core has previously been dated in a similar way and is only included to support the match-point identification. We name our EGRIP timescale GICC05-EGRIP-1. Over the uppermost 1383.84 m, we establish a depth–age relationship dating back to 14 967 years b2k (years before the year 2000 CE). Tephra horizons provide an independent validation of our match points. In addition, we compare the ratio of the annual layer thickness between ice cores in between the match points to assess our results in view of the different ice-flow patterns and accumulation regimes of the different periods and geographical regions. For the next years, this initial timescale will be the basis for climatic reconstructions from EGRIP high-resolution proxy data sets, e.g. stable water isotopes, chemical impurity or dust records

Secondary standard for determining geochemical composition of tephra layers from deep sediment core GS16-204-22CC

We investigated marine sediment core GS16-204-22CC for increased tephra occurrences and geochemically analysed the major element composition of tephra shards to identify their source volcano(es). In total we observed eight tephra zones of which five concentration peaks show isochronous features that can be used as independent tie-points in future studies. To ensure analytical precision, secondary standards (BCR2g (Basalt) and Lipari Obsidian (Rhyolitic)) were measured at the start and end of each run. Reference values are listed below and in the dataset comment. Standard SiO2 TiO2 Al2O3 FeO MnO MgO CaO Na2O K2O P2O5 Total Beam Size Date Comment BCR2g 54.1 2.26 13.5 12.42 - 3.59 7.12 3.16 1.79 0.35 98.49 Wilson (1997) "Wilson S.A. 1997 The collection preparation and testing of USGS reference material BCR-2 Columbia River Basalt: U.S. Geological Survey Open-File Report " std 0.8 0.05 0.2 0.2 - 0.05 0.11 0.11 0.05 0.02 Lipari 74.03 0.02 12.72 1.75 0.08 0 0.72 4.06 5.18 - 98.62 Sparks (1990) "Sparks R.S.J. 1990. – written communication to University of Edinburgh" Lipari 73.72 - 13.04 1.76 - 0.03 0.76 4.06 5.06 - 98.43 Hunt and Hill (1996) "Hunt J.B. Hill P.G. 1996. An inter-laboratory comparison of the electron probe microanalysis of glass geochemistry. Quaternary International 34-36 229-241.

Surface water properties and sea ice distribution proxies from sediment core JM09-KA11-GC, western Barents Sea

A marine sediment core (JM09-KA11-GC) from the Kveithola Trough at the western Barents Sea margin has been investigated in order to reconstruct sub-surface temperatures and sea ice distribution at a sub-centennial resolution throughout the Holocene. The relationship between past variability of Atlantic water inflow and sea ice distribution has been established by measurement of planktic foraminifera, stable isotopes and biomarkers from sea ice diatoms and phytoplankton. Throughout the early Holocene (11 900–7300 cal yr BP), the foraminiferal fauna is dominated by the polar species Neogloboquadrina pachyderma (sinistral) and the biomarkers show an influence of seasonal sea ice. Between 10 900 and 10 700 cal yr BP, a clear cooling is shown both by fauna and stable isotope data corresponding to the so-called Preboreal Oscillation. After 7300 cal yr BP, the sub-polar Turborotalita quinqueloba becomes the most frequent species, reflecting a stable Atlantic water inflow. Sub-surface temperatures reach 6 °C and biomarker data indicate mainly ice-free conditions. During the last 1100 cal yr BP, biomarker abundances and distributions show the reappearance of low-frequency seasonal sea ice and the planktic fauna show a reduced salinity in the sub-surface water. No apparent temperature decrease is observed during this interval, but the rapidly fluctuating fauna and biomarker distributions indicate more unstable conditions

Geochemical composition of tephra layers from deep sediment core GS16-204-22CC-A,eastern Labrador Sea, south of Greenland

This dataset contains major element oxide data of tephra layers from marine sediment core GS16-204-22CC-A , located in the eastern Labrador Sea, south of Greenland. The core is investigated for increased tephra occurrences and geochemically analysed for the major element composition of tephra shards to identify their source volcano(es

Geochemical composition of tephra layers from deep sediment core GS16-204-22CC-A, eastern Labrador Sea, south of Greenland

This dataset contains major element oxide data of tephra layers from marine sediment core GS16-204-22CC. The core has been investigated for increased tephra occurrences and geochemically analysed for the major element composition of tephra shards to identify their source volcano(es). In total we observed eight tephra zones of which five concentration peaks show isochronous features that can be used as independent tie-points in future studies