Testing the synchronicity of Pleistocene biostratigraphic events in the central Arctic – Do we have a consistent biostratigraphic framework?  

2021 ◽  
Author(s):  
Flor Vermassen ◽  
Helen K. Coxall ◽  
Gabriel West ◽  
Matt O'Regan
Keyword(s):  
Arctic Ocean ◽  
Sediment Cores ◽  
Age Determination ◽  
The Arctic ◽  
Calcareous Nannofossils ◽  
Central Arctic Ocean ◽  
Eurasian Basin ◽  
Future Work ◽  
Amerasian Basin

<p>Harsh environmental and taphonomic conditions in the central Arctic Ocean make age-modelling for Quaternary palaeoclimate reconstructions challenging. Pleistocene age models in the Arctic have relied heavily on cyclostratigraphy using lithologic variability tied to relatively poorly calibrated foraminifera biostratigraphic events. Recently, the identification of <em>Pseudoemiliania lacunosa</em> in a sediment core from the Lomonosov Ridge, a coccolithophore that went extinct during marine isotope stage (MIS) 12 (478-424 ka), has been used to delineate glacial-interglacial units back to MIS 14 (~500 ka BP). Here we present a comparative study on how this nannofossil biostratigraphy fits with existing foraminifer biohorizons that are recognised in central Arctic Ocean sediments. A new core from the Alpha Ridge is presented, together with its lithologic variability and down-core compositional changes in planktonic and benthic foraminifera. The core exhibits an interval dominated by <em>Turborotalita egelida</em>, a planktonic foraminifer that is increasingly being adopted as a marker for MIS11 in sediment cores from the Amerasian Basin of the Arctic Ocean. We show that the new age-constraints provided by calcareous nannofossils are difficult to reconcile with the proposed MIS 11 age for the <em>T. egelida</em> horizon. Instead, the emerging litho- and coccolith biostratigraphy implies that Amerasian Basin sediments predating MIS5 are older than the egelida-based age models suggest, i.e. that the <em>T. egelida</em> Zone is older than MIS11. These results expose uncertainties regarding the age determination of glacial-interglacial cycles in the Amerasian basin and point out that future work is required to reconcile the micro- and nannofossil biostratigraphy of the Amerasian and Eurasian basin.</p>

Sediment archives from the Arctic Ocean provide evidence for massive remobilization of permafrost carbon in Siberia during the last glacial termination

2020 ◽  
Author(s):  
Jannik Martens ◽  
Birgit Wild ◽  
Tommaso Tesi ◽  
Francesco Muschitiello ◽  
Matt O’Regan ◽  
...  
Keyword(s):  
Arctic Ocean ◽  
Large Scale ◽  
Sediment Cores ◽  
The Arctic ◽  
Last Deglaciation ◽  
Central Arctic Ocean ◽  
Last Glacial ◽  
The Arctic Ocean ◽  
Siberian Shelf ◽  
The Last Glacial

<p>Environmental archives and carbon cycle models suggest that climate warming during the last deglaciation (the transition from the last glacial to the Holocene) caused large-scale thaw of Arctic permafrost, followed by the release of previously freeze-locked carbon. In addition to changing oceanic circulation and outgassing of CO<sub>2 </sub>trapped in the deep glacial ocean, organic carbon (OC) release from thawing permafrost might have contributed to the rise in atmospheric CO<sub>2</sub> by 80 ppmv or ~200 Pg C between 17.5 and 11.7 kyr before present (BP). The few Arctic sediment cores to date, however, lack either temporal resolution or reflect only regional catchments, leaving most of the permafrost OC remobilization of the deglaciation unconstrained.</p><p>Our study explores the flux and fate of OC released from permafrost to the Siberian Arctic Seas during the last deglaciation. The Arctic Ocean is the main recipient of permafrost material delivered by river transport or collapse of coastal permafrost, providing an archive for current and past release of OC from thawing permafrost. We studied isotopes (Δ<sup>14</sup>C-OC, δ<sup>13</sup>C-OC) and terrestrial biomarkers (CuO-derived lignin phenols, <em>n</em>-alkanes, <em>n</em>-alkanoic acids) in a number of sediment cores from the Siberian Shelf and Central Arctic Ocean to reconstruct source and fate of OC previously locked in permafrost.</p><p>The composite record of three cores from the Laptev, East Siberian and Chukchi Seas suggest a combination of OC released by deepening of permafrost active layer in inland Siberia and by thermal collapse of coastal permafrost during the deglaciation. Coastal erosion of permafrost during the deglaciation suggests that sea-level rise and flooding of the Siberian shelf remobilized OC from permafrost deposits that covered the dry shelf areas during the last glacial. A sediment core from the Central Arctic Ocean demonstrates that this occurred in two major pulses; i) during the Bølling-Allerød (14.7-12.9 kyr BP), but most strongly ii) during the early Holocene (11-7.6 kyr BP). In the early Holocene, flooding of 80% of the Siberian shelf amplified permafrost OC release to the Arctic Ocean, with peak fluxes 10-9 kyr BP one order of magnitude higher than at other times in the Holocene.</p><p>It is likely that the remobilization of permafrost OC by flooding of the Siberian shelf released climate-significant amounts of dormant OC into active biogeochemical cycling and the atmosphere. Previous studies estimated that a pool of 300-600 Pg OC was held in permafrost covering Arctic Ocean shelves during the last glacial maximum; one can only speculate about its whereabouts after the deglaciation. Present und future reconstructions of historical remobilization of permafrost OC will help to understand how important permafrost thawing is to large-scale carbon cycling.</p>

scholarly journals On the 14C and 39Ar Distribution in the Central Arctic Ocean: Implications for Deep Water Formation

Radiocarbon ◽  
1994 ◽  
Vol 36 (3) ◽  
pp. 327-343 ◽  
Author(s):  
Peter Schlosser ◽  
Bernd Kromer ◽  
Gote Östlund ◽  
Brenda Ekwurzel ◽  
Gerhard Bönisch ◽  
...  
Keyword(s):  
Arctic Ocean ◽  
Deep Water ◽  
Atlantic Water ◽  
The Arctic ◽  
Central Arctic Ocean ◽  
Deep Waters ◽  
The Arctic Ocean ◽  
Bottom Waters ◽  
Eurasian Basin ◽  
Canadian Basin

We present ΔA14C and 39Ar data collected in the Nansen, Amundsen and Makarov basins during two expeditions to the central Arctic Ocean (RV Polarstern cruises ARK IV/3, 1987 and ARK VIII/3, 1991). The data are used, together with published Δ14C values, to describe the distribution of Δ14C in all major basins of the Arctic Ocean (Nansen, Amundsen, Makarov and Canada Basins), as well as the 39Ar distribution in the Nansen Basin and the deep waters of the Amundsen and Makarov Basins. From the combined Δ14C and 39Ar distributions, we derive information on the mean “isolation ages” of the deep and bottom waters of the Arctic Ocean. The data point toward mean ages of the bottom waters in the Eurasian Basin (Nansen and Amundsen Basins) of ca. 250-300 yr. The deep waters of the Amundsen Basin show slightly higher 3H concentrations than those in the Nansen Basin, indicating the addition of a higher fraction of water that has been at the sea surface during the past few decades. Correction for the bomb 14C added to the deep waters along with bomb 3H yields isolation ages for the bulk of the deep and bottom waters of the Amundsen Basin similar to those estimated for the Nansen Basin. This finding agrees well with the 39Ar data. Deep and bottom waters in the Canadian Basin (Makarov and Canada Basins) are very homogeneous, with an isolation age of ca. 450 yr. Δ14C and 39Ar data and a simple inverse model treating the Canadian Basin Deep Water (CBDW) as one well-mixed reservoir renewed by a mixture of Atlantic Water (29%), Eurasian Basin Deep Water (69%) and brine-enriched shelf water (2%) yield a mean residence time of CBDW of ca. 300 yr.

New paleomagnetic data on marine sediments from the Central Arctic Ocean

2020 ◽  
Author(s):  
Daria Elkina ◽  
Thomas Frederichs ◽  
Walter Geibert ◽  
Jens Matthiessen ◽  
Frank Niessen ◽  
...  
Keyword(s):  
Arctic Ocean ◽  
Marine Sediments ◽  
Sediment Cores ◽  
Environmental Research ◽  
The Arctic ◽  
Lomonosov Ridge ◽  
State University ◽  
Central Arctic Ocean ◽  
Great Debate ◽  
The Arctic Ocean

<p>Accurate dating of marine sediments from the Arctic Ocean remains a subject of great debate over the last decades. Due to the lack of adequate materials for biostratigraphy and stable isotope analyses, paleomagnetic reconstructions came into play here but though yielded ambiguous interpretations. Moreover, sedimentation rates in the Quaternary, determined for isolated morphological features in the Arctic Ocean, are often applied to the entire Arctic Ocean realm resulting in an inappropriate oversimplification of probably diverging regional depositional regimes.</p><p>Paleomagnetic studies on four long sediment cores, collected from the Mendeleev Ridge and the Lomonosov Ridge, complemented by the results from one core from the Podvodnikov Basin, have provided an opportunity to compare the sedimentation history of these profound structures in the Arctic Ocean. Cores PS72/396-5 and PS72/410-3 (Mendeleev Ridge), PS87/023-1, PS87/030-1 (Lomonosov Ridge) and PS87/074-3 (Podvodnikov Basin) were retrieved during expeditions of RV Polarstern in 2008, and 2014. Paleomagnetic, rock magnetic and physical properties measurements were carried out at the Center for Geo-Environmental Research and Modeling (GEOMODEL) of the Research Park in St. Petersburg State University, at the University of Bremen, and the Alfred Wegener Institute.</p><p>According to the results on the Mendeleev Ridge’s cores, complemented with 230Th excess study on core PS72/396-5, the Brunhes Matuyama boundary (0.78 Ma) is observed at the first meters below the seafloor. That, together with the Matuyama Gauss transition (2.58 Ma) recorded in both cores, implies the mean sedimentation rate in this area to be in the order of mm/kyr.</p><p>In contrast to the Mendeleev Ridge, the cores from the Lomonosov Ridge and the Podvodnikov Basin have shown a more complex paleomagnetic record with a relevant shift to negative inclinations significantly deeper downcore. This could signify a relevant difference in the sedimentation regimes between both ridges during the Quaternary.    </p>

scholarly journals Calcareous nannofossils anchor chronologies for Arctic Ocean sediments back to 500 ka

Geology ◽  
2020 ◽  
Vol 48 (11) ◽  
pp. 1115-1119
Author(s):  
Matt O’Regan ◽  
Jan Backman ◽  
Eliana Fornaciari ◽  
Martin Jakobsson ◽  
Gabriel West
Keyword(s):  
Arctic Ocean ◽  
Marine Sediments ◽  
Magnetic Polarity ◽  
The Arctic ◽  
Calcareous Nannofossils ◽  
Central Arctic Ocean ◽  
Considerable Uncertainty ◽  
Key Species ◽  
First Time ◽  
Age Constraints

Abstract Poor age control in Pleistocene sediments of the central Arctic Ocean generates considerable uncertainty in paleoceanographic reconstructions. This problem is rooted in the perplexing magnetic polarity patterns recorded in Arctic marine sediments and the paucity of microfossils capable of providing calibrated biostratigraphic biohorizons or continuous oxygen isotope stratigraphies. Here, we document the occurrence of two key species of calcareous nannofossils in a single marine sediment core from the central Arctic Ocean that provide robust, globally calibrated age constraints for sediments younger than 500 ka. The key species are the coccolithophores Pseudoemiliania lacunosa, which went extinct during marine isotope stage (MIS) 12 (478–424 ka), and Emiliania huxleyi, which evolved during MIS 8 (300–243 ka). This is the first time that P. lacunosa has been described in sediments of the central Arctic Ocean. The sedimentary horizons containing these age-diagnostic species can be traced, through lithostratigraphic correlation, across more than 450 km of the inner Arctic Ocean. They provide the first unequivocal support for proposed Pleistocene chronologies of sediment from this sector of the Arctic, and they constitute a foundation for developing and testing other geochronological tools for dating Arctic marine sediments.

scholarly journals Arctic Ocean Warming Contributes to Reduced Polar Ice Cap

2010 ◽  
Vol 40 (12) ◽  
pp. 2743-2756 ◽  
Author(s):  
Igor V. Polyakov ◽  
Leonid A. Timokhov ◽  
Vladimir A. Alexeev ◽  
Sheldon Bacon ◽  
Igor A. Dmitrenko ◽  
...  
Keyword(s):  
Arctic Ocean ◽  
Atlantic Water ◽  
Ocean Model ◽  
The Arctic ◽  
Ice Thickness ◽  
Polar Ice ◽  
Central Arctic Ocean ◽  
Ice Cap ◽  
1D Model ◽  
Eurasian Basin

Abstract Analysis of modern and historical observations demonstrates that the temperature of the intermediate-depth (150–900 m) Atlantic water (AW) of the Arctic Ocean has increased in recent decades. The AW warming has been uneven in time; a local ∼1°C maximum was observed in the mid-1990s, followed by an intervening minimum and an additional warming that culminated in 2007 with temperatures higher than in the 1990s by 0.24°C. Relative to climatology from all data prior to 1999, the most extreme 2007 temperature anomalies of up to 1°C and higher were observed in the Eurasian and Makarov Basins. The AW warming was associated with a substantial (up to 75–90 m) shoaling of the upper AW boundary in the central Arctic Ocean and weakening of the Eurasian Basin upper-ocean stratification. Taken together, these observations suggest that the changes in the Eurasian Basin facilitated greater upward transfer of AW heat to the ocean surface layer. Available limited observations and results from a 1D ocean column model support this surmised upward spread of AW heat through the Eurasian Basin halocline. Experiments with a 3D coupled ice–ocean model in turn suggest a loss of 28–35 cm of ice thickness after ∼50 yr in response to the 0.5 W m−2 increase in AW ocean heat flux suggested by the 1D model. This amount of thinning is comparable to the 29 cm of ice thickness loss due to local atmospheric thermodynamic forcing estimated from observations of fast-ice thickness decline. The implication is that AW warming helped precondition the polar ice cap for the extreme ice loss observed in recent years.

Central Arctic Ocean Response to Pleistocene Earth-Orbital Variations

1984 ◽  
Vol 22 (1) ◽  
pp. 121-128 ◽  
Author(s):  
Robin F. Boyd ◽  
David L. Clark ◽  
Glenn Jones ◽  
W.F. Ruddiman ◽  
A. McIntyre ◽  
...  
Keyword(s):  
Arctic Ocean ◽  
Sediment Cores ◽  
The Arctic ◽  
Lower Latitude ◽  
Sedimentation Rates ◽  
Orbital Forcing ◽  
Central Arctic Ocean ◽  
The Third ◽  
Ocean Response ◽  
Ocean Sediment

Three central Arctic Ocean sediment cores were sampled for percentage carbonate, number of foraminifera, and texture. These three parameters were used in spectral analyses to test the idea that the ice-covered Arctic Ocean may respond to orbital forcing in a different manner than has been indicated for lower latitude ice-free oceans. The record for two of the cores represents approximately 1 my, and the record for the third, approximately 400,000 yr. The 100,000-yr frequency is well represented in all of the cores. A 40,000-yr frequency may be present, as well. An unexpected 70,000-yr frequency occurs in most of the spectra and may reflect nonlinear sedimentation rates or the combined effect of obliquity and eccentricity. The strong 100,000-yr signal confirms that, in spite of ice feedback, the Arctic Ocean has responded to orbital forcing in much the same manner as have ice-free oceans.

scholarly journals Arctic Ocean stratification set by sea level and freshwater inputs since the last ice age

2021 ◽  
Author(s):  
Jesse R. Farmer ◽  
Daniel M. Sigman ◽  
Julie Granger ◽  
Ona M. Underwood ◽  
François Fripiat ◽  
...  
Keyword(s):  
Arctic Ocean ◽  
Surface Waters ◽  
Ice Age ◽  
The Arctic ◽  
Bering Strait ◽  
Central Arctic Ocean ◽  
Phytoplankton Productivity ◽  
Nitrate Consumption ◽  
Western Arctic ◽  
Last Ice Age

AbstractSalinity-driven density stratification of the upper Arctic Ocean isolates sea-ice cover and cold, nutrient-poor surface waters from underlying warmer, nutrient-rich waters. Recently, stratification has strengthened in the western Arctic but has weakened in the eastern Arctic; it is unknown if these trends will continue. Here we present foraminifera-bound nitrogen isotopes from Arctic Ocean sediments since 35,000 years ago to reconstruct past changes in nutrient sources and the degree of nutrient consumption in surface waters, the latter reflecting stratification. During the last ice age and early deglaciation, the Arctic was dominated by Atlantic-sourced nitrate and incomplete nitrate consumption, indicating weaker stratification. Starting at 11,000 years ago in the western Arctic, there is a clear isotopic signal of Pacific-sourced nitrate and complete nitrate consumption associated with the flooding of the Bering Strait. These changes reveal that the strong stratification of the western Arctic relies on low-salinity inflow through the Bering Strait. In the central Arctic, nitrate consumption was complete during the early Holocene, then declined after 5,000 years ago as summer insolation decreased. This sequence suggests that precipitation and riverine freshwater fluxes control the stratification of the central Arctic Ocean. Based on these findings, ongoing warming will cause strong stratification to expand into the central Arctic, slowing the nutrient supply to surface waters and thus limiting future phytoplankton productivity.

Reflections on Arctic Maritime Delimitations: A Comparative Analysis between the Case Law and State Practice

2011 ◽  
Vol 80 (4) ◽  
pp. 459-484
Author(s):  
Yoshifumi Tanaka
Keyword(s):  
Comparative Analysis ◽  
Arctic Ocean ◽  
Case Law ◽  
The Arctic ◽  
Coastal State ◽  
Ocean Governance ◽  
State Practice ◽  
The Arctic Ocean

AbstractThe determination of spatial ambit of the coastal State jurisdiction is fundamental for ocean governance and the same applies to the Arctic Ocean. In this regard, a question arises how it is possible to delimit marine spaces where the jurisdiction of two or more coastal States overlaps. Without rules on maritime delimitation in marine spaces where the jurisdiction of coastal States overlaps, the legal uses of these spaces cannot be enjoyed effectively. In this sense, maritime delimitation is of paramount importance in the Arctic Ocean governance. Thus, this study will examine Arctic maritime delimitations by comparing them to the case law concerning maritime delimitation. In so doing, this study seeks to clarify features of Arctic maritime delimitations.

scholarly journals Recent Sea Ice Decline Did Not Significantly Increase the Total Liquid Freshwater Content of the Arctic Ocean

2018 ◽  
Vol 32 (1) ◽  
pp. 15-32 ◽  
Author(s):  
Qiang Wang ◽  
Claudia Wekerle ◽  
Sergey Danilov ◽  
Dmitry Sidorenko ◽  
Nikolay Koldunov ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Sea Ice ◽  
Arctic Ocean ◽  
Ocean Circulation ◽  
General Circulation ◽  
The Arctic ◽  
Sea Ice Decline ◽  
The Arctic Ocean ◽  
Eurasian Basin ◽  
The Impact

Abstract The freshwater stored in the Arctic Ocean is an important component of the global climate system. Currently the Arctic liquid freshwater content (FWC) has reached a record high since the beginning of the last century. In this study we use numerical simulations to investigate the impact of sea ice decline on the Arctic liquid FWC and its spatial distribution. The global unstructured-mesh ocean general circulation model Finite Element Sea Ice–Ocean Model (FESOM) with 4.5-km horizontal resolution in the Arctic region is applied. The simulations show that sea ice decline increases the FWC by freshening the ocean through sea ice meltwater and modifies upper ocean circulation at the same time. The two effects together significantly increase the freshwater stored in the Amerasian basin and reduce its amount in the Eurasian basin. The salinification of the upper Eurasian basin is mainly caused by the reduction in the proportion of Pacific Water and the increase in that of Atlantic Water (AW). Consequently, the sea ice decline did not significantly contribute to the observed rapid increase in the Arctic total liquid FWC. However, the changes in the Arctic freshwater spatial distribution indicate that the influence of sea ice decline on the ocean environment is remarkable. Sea ice decline increases the amount of Barents Sea branch AW in the upper Arctic Ocean, thus reducing its supply to the deeper Arctic layers. This study suggests that all the dynamical processes sensitive to sea ice decline should be taken into account when understanding and predicting Arctic changes.

scholarly journals Eastern Arctic Ocean Diapycnal Heat Fluxes through Large Double-Diffusive Steps

2019 ◽  
Vol 49 (1) ◽  
pp. 227-246 ◽  
Author(s):  
Igor V. Polyakov ◽  
Laurie Padman ◽  
Y.-D. Lenn ◽  
Andrey Pnyushkov ◽  
Robert Rember ◽  
...  
Keyword(s):  
Arctic Ocean ◽  
Dissipation Rate ◽  
Critical Role ◽  
Density Ratio ◽  
Atlantic Water ◽  
Heat Fluxes ◽  
The Arctic ◽  
Eurasian Basin ◽  
Average Flux ◽  
Double Diffusive

AbstractThe diffusive layering (DL) form of double-diffusive convection cools the Atlantic Water (AW) as it circulates around the Arctic Ocean. Large DL steps, with heights of homogeneous layers often greater than 10 m, have been found above the AW core in the Eurasian Basin (EB) of the eastern Arctic. Within these DL staircases, heat and salt fluxes are determined by the mechanisms for vertical transport through the high-gradient regions (HGRs) between the homogeneous layers. These HGRs can be thick (up to 5 m and more) and are frequently complex, being composed of multiple small steps or continuous stratification. Microstructure data collected in the EB in 2007 and 2008 are used to estimate heat fluxes through large steps in three ways: using the measured dissipation rate in the large homogeneous layers; utilizing empirical flux laws based on the density ratio and temperature step across HGRs after scaling to account for the presence of multiple small DL interfaces within each HGR; and averaging estimates of heat fluxes computed separately for individual small interfaces (as laminar conductive fluxes), small convective layers (via dissipation rates within small DL layers), and turbulent patches (using dissipation rate and buoyancy) within each HGR. Diapycnal heat fluxes through HGRs evaluated by each method agree with each other and range from ~2 to ~8 W m−2, with an average flux of ~3–4 W m−2. These large fluxes confirm a critical role for the DL instability in cooling and thickening the AW layer as it circulates around the eastern Arctic Ocean.

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