| 1. |
- Kirchner, N., et al.
(författare)
-
Capabilities and limitations of numerical ice sheet models : a discussion for Earth-scientists and modelers
- 2011
-
Ingår i: Quaternary Science Reviews. - : Elsevier. - 0277-3791 .- 1873-457X. ; 30:25-26, s. 3691-3704
-
Tidskriftsartikel (refereegranskat)abstract
- The simulation of dynamically coupled ice sheet, ice stream, and ice shelf-systems poses a challenge to most numerical ice sheet models. Here we review present ice sheet model limitations targeting a broader audience within Earth Sciences, also those with no specific background in numerical modeling, in order to facilitate cross-disciplinary communication between especially paleoglaciologists, marine and terrestrial geologists, and numerical modelers. The ‘zero order’(Shallow Ice Approximation, SIA)-,‘higher order’-, and‘full Stokes’ice sheet models are described conceptually and complemented by an outline of their derivations. We demonstrate that higher order models are required to simulate coupled ice sheetice shelf and ice sheet-ice stream systems, in particular if the results are aimed to complement spatial ice flow reconstructions based on higher resolution geological and geophysical data. The zero order SIA model limitations in capturing ice stream behavior are here illustrated by conceptual simulations of a glaciation on Svalbard. The limitations are obvious from the equations comprising a zero order model. However, under certain circumstances, simulation results may falsely give the impression that ice streams indeed are simulated with a zero order SIA model.
|
|
| 2. |
- O'Regan, Matt, et al.
(författare)
-
Stratigraphic Occurrences of Sub-Polar Planktic Foraminifera in Pleistocene Sediments on the Lomonosov Ridge, Arctic Ocean
- 2019
-
Ingår i: Frontiers in Earth Science. - : FRONTIERS MEDIA SA. - 2296-6463. ; 7
-
Tidskriftsartikel (refereegranskat)abstract
- Turborotalita quinqueloba is a species of planktic foraminifera commonly found in the sub-polar North Atlantic along the pathway of Atlantic waters in the Nordic seas and sometimes even in the Arctic Ocean, although its occurrence there remains poorly understood. Existing data show that T. quinqueloba is scarce in Holocene sediments from the central Arctic but abundance levels increase in sediments from the last interglacial period [Marine isotope stage (MIS) 5, 71-120 ka] in cores off the northern coast of Greenland and the southern Mendeleev Ridge. Turborotalita also occurs in earlier Pleistocene interglacials in these regions, with a unique and widespread occurrence of the less known Turborotalita egelida morphotype, proposed as a biostratigraphic marker for MIS 11 (474-374 ka). Here we present results from six new sediment cores, extending from the central to western Lomonosov Ridge, that show a consistent Pleistocene stratigraphy over 575 km. Preliminary semi-quantitative assessments of planktic foraminifer abundance and assemblage composition in two of these records (LOMROG12-7PC and AO16-5PC) reveal two distinct stratigraphic horizons containing Turborotalita in MIS 5. Earlier occurrences in Pleistocene interglacials are recognized, but contain significantly fewer specimens and do not appear to be stratigraphically coeval in the studied sequences. In all instances, the Turborotalita specimens resemble the typical T. quinqueloba morphotype but are smaller (63-125 mu m), smooth-walled and lack the final thickened calcite layer common to adults of the species. These results extend the geographical range for T. quinqueloba in MIS 5 sediments of the Arctic Ocean and provide compelling evidence for recurrent invasions during Pleistocene interglacials.
|
|
| 3. |
- Stranne, Christian, 1979, et al.
(författare)
-
Arctic Ocean perennial sea ice breakdown during the Early Holocene Insolation Maximum
- 2014
-
Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 92, s. 123-132
-
Tidskriftsartikel (refereegranskat)abstract
- Arctic Ocean sea ice proxies generally suggest a reduction in sea ice during parts of the early and middle Holocene (similar to 6000-10,000 years BP) compared to present day conditions. This sea ice minimum has been attributed to the northern hemisphere Early Holocene Insolation Maximum (EHIM) associated with Earth's orbital cycles. Here we investigate the transient effect of insolation variations during the final part of the last glaciation and the Holocene by means of continuous climate simulations with the coupled atmosphere sea ice ocean column model CCAM. We show that the increased insolation during EHIM has the potential to push the Arctic Ocean sea ice cover into a regime dominated by seasonal ice, i.e. ice free summers. The strong sea ice thickness response is caused by the positive sea ice albedo feedback. Studies of the GRIP ice cores and high latitude North Atlantic sediment cores show that the Bolling Allerod period (c. 12,700-14,700 years BP) was a climatically unstable period in the northern high latitudes and we speculate that this instability may be linked to dual stability modes of the Arctic sea ice cover characterized by e.g. transitions between periods with and without perennial sea ice cover.
|
|
| 4. |
- West, Gabriel, et al.
(författare)
-
Late Holocene Paleomagnetic Secular Variation in the Chukchi Sea, Arctic Ocean
- 2022
-
Ingår i: Geochemistry Geophysics Geosystems. - : American Geophysical Union (AGU). - 1525-2027. ; 23:5
-
Tidskriftsartikel (refereegranskat)abstract
- The geomagnetic field behavior in polar regions remains poorly understood and documented. Although a number of Late Holocene paleomagnetic secular variation (PSV) records exist from marginal settings of the Amerasian Basin in the Arctic Ocean, their age control often relies on a handful of radiocarbon dates to constrain ages over the past 4,200 years. Here we present well-dated Late Holocene PSV records from two sediment cores recovered from the Chukchi Sea, Arctic Ocean. The records are dated using 26 C-14 measurements, with local marine reservoir corrections calibrated using tephra layers from the 3.6 cal ka BP Aniakchak eruption in Northern Alaska. These C-14-based chronologies are extended into the post-bomb era using caesium-137 dating, and mercury isochrons. Paleomagnetic measurements and rock magnetic analyses reveal stable characteristic remanent magnetization directions, and a magnetic mineralogy dominated by low-coercivity minerals. The PSV records conform well to global spherical harmonic field model outputs. Centennial to millennial scale directional features are synchronous between the cores and other Western Arctic records from the area. Due to the robust chronology, these new high-resolution PSV records provide a valuable contribution to the characterization of geomagnetic field behavior in the Arctic over the past few thousand years, and can aid in developing age models for suitable sediments found in this region.
|
|
| 5. |
- Snoeijs-Leijonmalm, Pauline, et al.
(författare)
-
A deep scattering layer under the North Pole pack ice
- 2021
-
Ingår i: Progress in Oceanography. - : Elsevier BV. - 0079-6611 .- 1873-4472. ; 194
-
Tidskriftsartikel (refereegranskat)abstract
- The 3.3 million km marine ecosystem around the North Pole, defined as the Central Arctic Ocean (CAO), is a blind spot on the map of the world's fish stocks. The CAO essentially comprises the permanently ice-covered deep basins and ridges outside the continental shelves, and is only accessible by ice-breakers. Traditional trawling for assessing fish stocks is impossible under the thick pack ice, and coherent hydroacoustic surveys are unachievable due to ice-breaking noise. Consequently, nothing is known about the existence of any pelagic fish stocks in the CAO, although juveniles of Boreogadus saida richly occur at the surface associated with the sea ice and ice-associated Arctogadus glacialis has been reported as well. We here present a first indication of a possible mesopelagic fish stock in the CAO. We had the opportunity to analyse a geophysical hydroacoustic data set with 13 time windows of usable acoustic data over a transect from 84.4 °N in the Nansen Basin, across the North Pole (90.0 °N), to 82.4 °N in the Canada Basin. We discovered a deep scattering layer (DSL), suggesting the presence of zooplankton and fish, at 300–600 m of depth in the Atlantic water layer of the CAO. Maximum possible fish abundance and biomass was very low; values of ca. 2,000 individuals km and ca. 50 kg km were calculated for the DSL in the North-Pole area according to a model assuming that all acoustic backscatter represents 15-cm long B. saida and/or A. glacialis. The true abundance and biomass of fish is even lower than this, but cannot be quantified from this dataset due to possible backscatter originating from pneumatophores of physonect siphonophores that are known to occur in the area. Further studies on the DSL of the CAO should include sampling and identification of the backscattering organisms. From our study we can conclude that if the central Arctic DSL contains fish, their biomass is currently too low for any sustainable fishery.
|
|
| 6. |
- Swärd, Henrik, 1975-
(författare)
-
In the wake of deglaciation - sedimentary signatures of ice-sheet decay and sea-level change : Studies from south-central Sweden and the western Arctic Ocean
- 2018
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lacustrine and marine sedimentary archives help unravel details concerning the withdrawal of large ice sheets and resulting sea-level changes during the last deglaciation (22 -11 kyr). In a series of four manuscripts, this PhD thesis investigates the sedimentological signatures from deglacial processes at three key locations in the northern hemisphere: (i) Lake Vättern (LV) in south-central Sweden, (ii) Herald Canyon (HC) in the western Chukchi Sea, and (iii) Mackenzie Trough (MT) on the westernmost edge of the Canadian Beaufort Shelf. One lacustrine (LV) and two marine (HC and MT) sediment cores were analyzed using a broad range of methods to describe the physical, chemical, mineralogical and biological characteristics, and used to construct paleoenvironmental interpretations.Constituting the westernmost part of the Baltic Sea during parts of the last deglaciation, LV has long been envisaged as a key region for deglacial studies in southern Scandinavia. Sediments in LV highlight four major lake development stages following the withdrawal of the Fennoscandian Ice Sheet. These include the Baltic Ice Lake, the Yoldia Sea, the Ancylus Lake and the ultimate isolated lake stage. New radiocarbon dates indicate that the lake became isolated at 9530±50 cal. yr BP. A sharp transition from a varved clay unit to a partly sulfide laminated clay unit marks the final drainage of the Baltic Ice Lake, dated to 11 650±280 cal. yr BP. However, an earlier peak in pore water chlorinity identified in the sediment provides the most compelling evidence to date for an initial drainage of the Baltic Ice Lake (~12.8 cal. kyr BP) near the onset of the Younger Dryas cold event.Located downstream from where Pacific water flows into the Arctic, HC is a key location for understanding the details of the early Holocene (~11 cal. yr BP) flooding of the Bering Strait, and investigating sedimentological proxies for Pacific water in Arctic Ocean sediment cores. The deglacial transgression of the shelf and opening of the Bering Strait is reflected in the grain size and biogenic silica content from the HC sediment core. However, a clear Pacific water signature is not seen in the clay mineralogy which exhibits increased variability after the opening of the Bering Strait. This is interpreted as a combination of Pacific and East Siberian sources for bottom waters in HC. The absence of a clear Pacific water signature in the clay mineralogy highlights potential limitations to using this proxy in other records from the western Arctic.Far field studies from the Arctic Ocean have argued that Mackenzie River sediments in Younger Dryas age sediments can be recognized by a unique mineral and isotopic composition, but no detailed proximal study of Mackenzie River sediments exists to support this assertion. The mineral and isotopic (Sr and Nd) studies presented in this thesis from the third of the key regions, the MT, fills this gap. The results show that the mineral assemblage and ɛNd of fine fraction material remained relatively stable during the decay of the Laurentide Ice Sheet. An exception to this exists in a transitional sedimentary unit, deposited immediately after transgression at the site, and might be related to meltwater pulses associated with the drainage of the Lake Agassiz. The results suggest that the modern mineral and isotopic signature of Mackenzie River sediments may not be a suitable proxy for deglacial meltwater events in far field sedimentary records.
|
|
| 7. |
- Löwemark, Ludvig, et al.
(författare)
-
Arctic Ocean manganese contents and sediment colour cycles
- 2008
-
Ingår i: Polar Research. - : Norwegian Polar Institute. - 0800-0395 .- 1751-8369. ; 27:2, s. 105-113
-
Tidskriftsartikel (refereegranskat)abstract
- Cyclical variations in colour and Mn content in sediments from the central Arctic Ocean have been interpreted to represent climatically controlled changes in the input of Mn from the Siberian hinterland and/or variations in the intermediate and deep water ventilation of the Arctic basins, although a diagenetic origin has not been excluded. A reinvestigation of core 96/12-1pc using an Itrax XRF core scanner confirms that these colour cycles are indeed controlled by variations in Mn content, although changes in the source region of the sediment may override the Mn-colour signal in certain intervals. The prominent Mn cycles show no correspondence to any of the other measured elements. This decoupling of the Mn and the bulk chemistry of the sediment is taken to indicate that the cycles observed are caused by variations in water column ventilation and riverine input rather than variations in sediment source or diagenesis. We therefore conclude that the Mn cycles do represent warm phases with increased ventilation and/or riverine input, and that they therefore could be used for chronostratigraphic correlation between cores from the central Arctic Ocean where traditional isotope stratigraphy is difficult or impossible to establish due to the lack of calcareous microfossils.
|
|
| 8. |
- Kaufman, Darrell S., et al.
(författare)
-
Amino acid racemization in mono-specific foraminifera from Quaternary deep-sea sediments
- 2013
-
Ingår i: Quaternary Geochronology. - : Elsevier BV. - 1871-1014 .- 1878-0350. ; 16:SI, s. 50-61
-
Tidskriftsartikel (refereegranskat)abstract
- The deep-sea environment is among the most stable on Earth, making it well suited for amino acid geochronology. Foraminifera with calcareous tests are distributed across the World Ocean and are often recovered in sufficient abundance from sediment cores to derive robust mean amino acid D/L values of multiple replicates from each stratigraphic level. The extent of racemization (D/L) can be compared with independent age control, which in most cases is based on correlation with global marine oxygen-isotope stages and radiocarbon ages from the same stratigraphic levels. In this study, we report the results of amino acid racemization analysis of multiple foraminifera species from well-dated sediment cores taken from the Pacific, Atlantic, and Arctic oceans. The composite of results analyzed to date (179 samples, each composed of an average of 8.6 subsamples = 1531 analyses) show that D/L values generally increase systematically down core, and are similar for samples of comparable ages from different deep-sea sites. Previously published equations that relate D/L values of aspartic and glutamic acids to post-depositional temperature and sample age for Pulleniatina obliquiloculata generally conform to the D/L trends for species analyzed in this study. Laboratory heating experiments were used to quantify the difference in the rate of racemization between P. obliquiloculata and other taxa. For example, aspartic acid in P. obliquiloculata racemizes an average of 12-16% faster than in the common high-latitude species, Neogloboquadrina pachyderma (s). Apparently, the unexpectedly high D/L values previously reported for N. pachyderma (s) older than 35 lea from the Arctic Ocean cannot be attributed to taxonomic effects.
|
|
| 9. |
|
|
| 10. |
- Polyak, Leonid, et al.
(författare)
-
Quaternary sedimentation in the Arctic Ocean : Recent advances and further challenges
- 2011
-
Ingår i: Oceanography. - : The Oceanography Society. - 1042-8275. ; 24:3, s. 52-64
-
Tidskriftsartikel (refereegranskat)abstract
- This paper reviews current knowledge of sedimentation patterns in the Arctic Ocean during the pronounced climatic cycles of the last several hundred thousand years, an especially relevant time period that provides long-term context for present climate change. The review is largely based on data collected during recent research icebreaker cruises to the Arctic Ocean, with a focus on the 2005 Healy-Oden TransArctic Expedition (HOTRAX) and 2007 Lomonosov Ridge Off Greenland (LOMROG) expedition. The sediment cores and geophysical seafloor mapping data collected enable reconstruction of past oceanic environments. Evaluation of these data suggests that the two major Arctic Ocean circulation systems, the Trans-Polar Drift and the Beaufort Gyre, persisted throughout most of the Late to Middle Quaternary, approximately the last 0.5 to 0.7 million years. Extreme conditions, nonanalogous to modern environments, also occurred in the past, especially during Pleistocene glacial intervals. Some of these intervals likely featured much thickened and/or concentrated sea ice and incursions of ice shelves and armadas of megasized icebergs from the margins to the center of the Arctic Ocean. In contrast, much warmer conditions with reduced sea ice extent existed during interglacial periods. Characterization of ice conditions during these intervals is critical for evaluating the present and projected future reduction of Arctic sea ice.
|
|
