Coupled evolution of tectonic, ocean circulations, and depositional regime in the southeastern Amundsen Basin

2021 ◽  
Author(s):  
Estella Weigelt ◽  
Christoph Gaedicke ◽  
Wilfried Jokat
Keyword(s):  
Arctic Ocean ◽  
Ocean Circulation ◽  
North Atlantic ◽  
Middle Eocene ◽  
The Arctic ◽  
Circulation System ◽  
Time Interval ◽  
Fram Strait ◽  
Acoustic Basement ◽  
The Arctic Ocean

<p>The Lomonosov Ridge (LR) and Fram Strait (FR) represent prominent morphologic features in the Arctic Ocean. Their tectonic evolution control ocean circulation, sedimentation environment, glacial processes and ecosystem through time. We present findings of a 300 km long seismic transect from the Gakkel Deep through the southeastern Amundsen Basin (AB), and onto the LR. The data image an up to 3 km thick sedimentary sequence that can be subdivided into six major seismic units.</p><p>The two lower units AB-1 and AB-2 consist of syn-rift sediments of Paleocene to early Eocene age likely eroded off the Barents-Kara and Laptev Sea shelves, and the subsiding LR.</p><p>AB-2 includes the time interval of the “Azolla event,” which is regarded as an era of a warm Arctic Ocean punctuated by episodic incursions of fresh water. The connection to North Atlantic waters via the Fram Strait was not yet established, and anoxic conditions prevailed in the young, still isolated Eurasian Basin. Also, the LR still was above or close to sea level and posed an obstacle for water exchange between the Eurasian and Amerasian basins.</p><p>The top of AB-2 onlaps the acoustic basement at magnetic anomaly C21o (∼47.3 Ma). Its contact with unit AB-3 above is marked by a striking loss in reflection amplitudes. This prominent interface can be traced through the AB, indicating widespread changes in tectonic and deposition conditions in the Arctic Ocean since the middle Eocene. For younger crust the depth of acoustic basement rises significantly, as well as the deformation of the surface. Both are probably linked to a reorganization of tectonic plates accompanied by a significant decrease in spreading rates.</p><p>Units AB-3 and AB-4 indicate the accumulation of sediments between the middle Eocene and the earliest Miocene. Erosional, channel-like interruptions indicate these layers to reflect the stage when Fram Strait opened and continuously deepened. Incursions of water masses from the North Atlantic probably led to first bottom currents and produced erosion, slumping, and subsequent mixing of deposits.</p><p>The upper units AB-5 to AB-6 show reflection characteristics and thicknesses similar all over the Arctic Ocean indicating that basin-wide pelagic sedimentation prevailed at least since late Oligocene. Drift bodies, sediment waves, and erosional structures indicate the onset of a modern ocean circulation system and bottom current activity in the early Miocene in the Amundsen Basin. At that time, the FR was developed widely, and also the LR no longer posed an obstacle between the Amerasia and Eurasia Basins. Lastly, unit AB-6 indicates pronounced variations in the sedimentary layers, and is associated with the onset of glacio-marine deposition since the Pliocene (5.3 Ma).</p>

scholarly journals Opening of the Fram Strait led to the establishment of a modern-like three-layer stratification in the Arctic Ocean during the Miocene

arktos ◽  
2021 ◽  
Author(s):  
Akil Hossain ◽  
Gregor Knorr ◽  
Wilfried Jokat ◽  
Gerrit Lohmann
Keyword(s):  
Atlantic Ocean ◽  
Arctic Ocean ◽  
Ocean Circulation ◽  
Water Exchange ◽  
Current System ◽  
Early Miocene ◽  
The Arctic ◽  
Fram Strait ◽  
Exchange Flow ◽  
The Arctic Ocean

AbstractThe tectonic opening of the Fram Strait (FS) was critical to the water exchange between the Atlantic Ocean and the Arctic Ocean, and caused the transition from a restricted to a ventilated Arctic Ocean during early Miocene. If and how the water exchange between the Arctic Ocean and the North Atlantic influenced the global current system is still disputed. We apply a fully coupled atmosphere–ocean–sea-ice model to investigate stratification and ocean circulation in the Arctic Ocean in response to the opening of the FS during early-to-middle Miocene. Progressive widening of the FS gateway in our simulation causes a moderate warming, while salinity conditions in the Nordic Seas remain similar. On the contrary, with increasing FS width, Arctic temperatures remain unchanged and salinity changes appear to steadily become stronger. For a sill depth of ~ 1500 m, we achieve ventilation of the Arctic Ocean due to enhanced import of saline Atlantic water through an FS width of ~ 105 km. Moreover, at this width and depth, we detect a modern-like three-layer stratification in the Arctic Ocean. The exchange flow through FS is characterized by vertical separation of a low-salinity cold outflow from the Arctic Ocean confined to a thin upper layer, an intermediate saline inflow from the Atlantic Ocean below, and a cold bottom Arctic outflow. Using a significantly shallower and narrower FS during the early Miocene, our study suggests that the ventilation mechanisms and stratification in the Arctic Ocean are comparable to the present-day characteristics.

scholarly journals The Arctic and Subarctic Ocean Flux of Potential Vorticity and the Arctic Ocean Circulation*

2005 ◽  
Vol 35 (12) ◽  
pp. 2387-2407 ◽  
Author(s):  
Jiayan Yang
Keyword(s):  
Arctic Ocean ◽  
Ocean Circulation ◽  
Circulation Pattern ◽  
3D Models ◽  
Ocean Model ◽  
The Arctic ◽  
Fram Strait ◽  
The Arctic Ocean ◽  
Ocean Models ◽  
Arctic Ocean Circulation

Abstract According to observations, the Arctic Ocean circulation beneath a shallow thermocline can be schematized by cyclonic rim currents along shelves and over ridges. In each deep basin, the circulation is also believed to be cyclonic. This circulation pattern has been used as an important benchmark for validating Arctic Ocean models. However, modeling this grand circulation pattern with some of the most sophisticated ocean–ice models has been often difficult. The most puzzling and thus perhaps the most interesting finding from the Arctic Ocean Model Intercomparison Project (AOMIP), an international consortium that runs 14 Arctic Ocean models by using the identical forcing fields, is that its model results can be grouped into two nearly exact opposite patterns. While some models produce cyclonic circulation patterns similar to observations, others do the opposite. This study examines what could be possibly responsible for such strange inconsistency. It is found here that the flux of potential vorticity (PV) from the subarctic oceans strongly controls the circulation directions. For a semienclosed basin like the Arctic, the PV integral over the whole basin yields a balance between the net lateral PV inflow and the PV dissipation along the boundary. When an isopycnal layer receives a net positive PV through inflow/outflow, the circulation becomes cyclonic so that friction can generate a flux of negative PV to satisfy the integral balance. For simplicity, a barotropic ocean model is used in this paper but its application to the 3D models will be discussed. In the first set of experiments, the model with a realistic Arctic bathymetry is forced by observed inflows and outflows. In this case, there is a net positive PV inflow to the basin, due to the fact that inflow layer is thinner than that of outflow. The model produces a circulation field that is remarkably similar to the one from observations. In the second experiment, the model bathymetry at Fram Strait is modified so that the same inflows and outflows of water masses lead to a net negative PV flux into the Arctic. The circulation is reversed and becomes nearly the opposite of the first experiment. In the third experiment, the net PV flux is made to be zero by modifying again the sill depth at Fram Strait. The circulation becomes two gyres, a cyclonic one in the Eurasian Basin and an anticyclonic one in the Canada Basin. To elucidate the control of the PV integral, a second set of model experiments is conducted by using an idealized Arctic bathymetry so that the PV dynamics can be better explained without the complication of rough topography. The results from five additional experiments that used the idealized topography will be discussed. While the model used in this study is one layer, the same PV-integral constraint can be applied to any isopycnal layer in a three-dimensional model. Variables that affect the PV fluxes to this density layer at any inflow/outflow channel, such as layer thickness and water volume flux, can affect the circulation pattern. The relevance to 3D models is discussed in this paper.

scholarly journals Arctic Ocean circulation and variability – advection and external forcing encounter constraints and local processes

2011 ◽  
Vol 8 (6) ◽  
pp. 2313-2376 ◽  
Author(s):  
B. Rudels
Keyword(s):  
Sea Ice ◽  
Arctic Ocean ◽  
Ocean Circulation ◽  
Barents Sea ◽  
Atlantic Water ◽  
The Arctic ◽  
Fram Strait ◽  
Intermediate Layers ◽  
The Arctic Ocean ◽  
Almost All

Abstract. The first hydrographic data from the Arctic Ocean, the section from the Laptev Sea to the passage between Greenland and Svalbard obtained by Nansen on the drift by Fram 1893–1896, aptly illustrate the main features of Arctic Ocean oceanography and indicate possible processes active in transforming the water masses in the Arctic Ocean. Many, perhaps most, of these processes were identified already by Nansen, who put his mark on almost all subsequent research in the Arctic Ocean. Here we shall revisit some key questions and follow how our understanding has evolved from the early 20th century to present. What questions, if any, can now be regarded as solved and which remain still open? Five different but connected topics will be discussed: (1) The low salinity surface layer and the storage and export of freshwater. (2) The vertical heat transfer from the Atlantic water to sea ice and to the atmosphere. (3) The circulation and mixing of the two Atlantic inflow branches. (4) The formation and circulation of deep and bottom waters in the Arctic Ocean. (5) The exchanges through Fram Strait. Foci will be on the potential effects of increased freshwater input and reduced sea ice export on the freshwater storage and residence time in the Arctic Ocean, on the deep waters of the Makarov Basin and on the circulation and relative importance of the two inflows, over the Barents Sea and through Fram Strait, for the distribution of heat in the intermediate layers of the Arctic Ocean.

scholarly journals Arctic Ocean circulation and variability – advection and external forcing encounter constraints and local processes

Ocean Science ◽  
2012 ◽  
Vol 8 (2) ◽  
pp. 261-286 ◽  
Author(s):  
B. Rudels
Keyword(s):  
Sea Ice ◽  
Arctic Ocean ◽  
Ocean Circulation ◽  
Barents Sea ◽  
Atlantic Water ◽  
The Arctic ◽  
Fram Strait ◽  
Intermediate Layers ◽  
The Arctic Ocean ◽  
Almost All

Abstract. The first hydrographic data from the Arctic Ocean, the section from the Laptev Sea to the passage between Greenland and Svalbard obtained by Nansen on his drift with Fram 1893–1896, aptly illustrate the main features of Arctic Ocean oceanography and indicate possible processes active in transforming the water masses in the Arctic Ocean. Many, perhaps most, processes were identified already by Nansen, who put his mark on almost all subsequent research in the Arctic. Here we shall revisit some key questions and follow how our understanding has evolved from the early 20th century to present. What questions, if any, can now be regarded as solved and which remain still open? Five different but connected topics will be discussed: (1) The low salinity surface layer and the storage and export of freshwater. (2) The vertical heat transfer from the Atlantic water to sea ice and to the atmosphere. (3) The circulation and mixing of the two Atlantic inflow branches. (4) The formation and circulation of deep and bottom waters in the Arctic Ocean. (5) The exchanges through Fram Strait. Foci will be on the potential effects of increased freshwater input and reduced sea ice export on the freshwater storage and residence time in the Arctic Ocean, on the deep waters of the Makarov Basin, and on the circulation and relative importance of the two inflows, over the Barents Sea and through Fram Strait, for the distribution of heat in the intermediate layers of the Arctic Ocean.

scholarly journals The long-lived anthropogenic radionuclides I-129 and U-236 as tracers of water mass provenance, circulation timescales and mixing in the Arctic Ocean and Fram Strait

2020 ◽  
Author(s):  
Anne-Marie Wefing ◽  
Núria Casacuberta ◽  
Marcus Christl ◽  
John N. Smith ◽  
Paul A. Dodd ◽  
...  
Keyword(s):  
Arctic Ocean ◽  
Ocean Circulation ◽  
Water Mass ◽  
Atlantic Water ◽  
The Arctic ◽  
Fram Strait ◽  
Anthropogenic Radionuclides ◽  
Chemical Tracers ◽  
Pacific Waters ◽  
The Arctic Ocean

<p>Anthropogenic chemical tracers are powerful tools to study ocean circulation timescales, water mass provenance and mixing regimes. In the Arctic Ocean, the releases of artificial radionuclides from European nuclear reprocessing plants (RPs) act as valuable transient tracers as they label the inflowing Atlantic Waters with a distinct anthropogenic signal. In recent years, the combination of the two long-lived radionuclides <sup>129</sup>I and <sup>236</sup>U has emerged as a new tracer pair and several studies have shown their potential to track pathways and timescales of Atlantic Water circulation in the Arctic Ocean and Fram Strait.</p><p>The circulation times of Atlantic-origin waters in the Arctic Ocean that were inferred using this tracer pair (in combination with the naturally occurring <sup>238</sup>U) agree to those obtained by means of other transient tracers. Moreover, the combination of <sup>129</sup>I and <sup>236</sup>U promises to be a useful marker of water mass mixing regimes both in the surface waters and the subsurface Atlantic layer. In particular, the interface between Atlantic and Pacific Waters in the polar surface layer of the Arctic Ocean can be easily identified as these two water masses are labelled by very different <sup>129</sup>I/<sup>236</sup>U and <sup>236</sup>U/<sup>238</sup>U atom ratios.</p><p>Here we present a compilation of <sup>129</sup>I and <sup>236</sup>U in a quasi-synoptic pan-arctic section including the Fram Strait and we show how this data can be used to gain information about circulation patterns. We discuss timescales and transport characteristics of Atlantic Water flow, the position and variability of the front between Atlantic and Pacific Waters and the temporal variability of Pacific Waters in the Fram Strait.</p>

scholarly journals Unprecedented decline of Arctic sea ice outflow in 2018

2021 ◽  
Author(s):  
Hiroshi Sumata ◽  
Laura de Steur ◽  
Sebastian Gerland ◽  
Dmitry Divine ◽  
Olga Pavlova
Keyword(s):  
Atlantic Ocean ◽  
Sea Ice ◽  
Arctic Ocean ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Fram Strait ◽  
Atlantic Sector ◽  
The Arctic Ocean

Abstract Fram Strait is the major gateway connecting the Arctic Ocean and North Atlantic Ocean, where nearly 90% of the sea ice export from the Arctic Ocean takes place. The exported sea ice is a large source of freshwater to the Nordic Seas and Subpolar North Atlantic, thereby preconditioning European climate and deep water formation in the downstream North Atlantic Ocean. Here we show that in 2018, the ice export through Fram Strait showed an unprecedented decline since the early 1990s. The 2018 ice export was reduced to less than 40% relative to that between 2000 and 2017, and amounted to just 25% of the 1990s. The minimum export was attributed to regional sea ice-ocean processes driven by an anomalous atmospheric circulation over the Atlantic sector of the Arctic. The anomalous circulation caused a stagnation of southward sea ice drift, causing a sudden drop of sea ice thickness north of the Fram Strait due to local heat supply from the ocean. The result indicates that a drastic change of the freshwater cycle and its environmental consequences happen not only through ongoing Arctic-wide ice thinning, but also by regional scale atmospheric anomalies in the Atlantic sector on annual timescales.

scholarly journals Seasonal patterns in Arctic planktonic metabolism (Fram Strait – Svalbard region)

2013 ◽  
Vol 10 (3) ◽  
pp. 1451-1469 ◽  
Author(s):  
R. Vaquer-Sunyer ◽  
C. M. Duarte ◽  
J. Holding ◽  
A. Regaudie-de-Gioux ◽  
L. S. García-Corral ◽  
...  
Keyword(s):  
Arctic Ocean ◽  
Early Spring ◽  
The Arctic ◽  
Fram Strait ◽  
Metabolic Rates ◽  
Net Community Production ◽  
Western Sector ◽  
The Arctic Ocean ◽  
European Arctic ◽  
Community Production

Abstract. The metabolism of the Arctic Ocean is marked by extremely pronounced seasonality and spatial heterogeneity associated with light conditions, ice cover, water masses and nutrient availability. Here we report the marine planktonic metabolic rates (net community production, gross primary production and community respiration) along three different seasons of the year, for a total of eight cruises along the western sector of the European Arctic (Fram Strait – Svalbard region) in the Arctic Ocean margin: one at the end of 2006 (fall/winter), two in 2007 (early spring and summer), two in 2008 (early spring and summer), one in 2009 (late spring–early summer), one in 2010 (spring) and one in 2011 (spring). The results show that the metabolism of the western sector of the European Arctic varies throughout the year, depending mostly on the stage of bloom and water temperature. Here we report metabolic rates for the different periods, including the spring bloom, summer and the dark period, increasing considerably the empirical basis of metabolic rates in the Arctic Ocean, and especially in the European Arctic corridor. Additionally, a rough annual metabolic estimate for this area of the Arctic Ocean was calculated, resulting in a net community production of 108 g C m−2 yr−1.

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.

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