scholarly journals The Late Quaternary Sedimentary Record of Reykjanes Ridge, North Atlantic

Radiocarbon ◽  
2001 ◽  
Vol 43 (2B) ◽  
pp. 939-947 ◽  
Author(s):  
M A Prins ◽  
S R Troelstra ◽  
R W Kruk ◽  
K van der Borg ◽  
A F M de Jong ◽  
...  
Keyword(s):  
Grain Size ◽  
Ocean Circulation ◽  
North Atlantic ◽  
Late Quaternary ◽  
Ice Cores ◽  
Deep Ocean ◽  
Reykjanes Ridge ◽  
The North ◽  
The North Atlantic ◽  
Deep Ocean Circulation

Variability in surface and deep ocean circulation in the North Atlantic is inferred from grain-size characteristics and the composition of terrigenous sediments from a deep-sea core taken on Reykjanes Ridge, south of Iceland. End-member modeling of grain size data shows that deep-ocean circulation in this area decreased significantly during periods of maximum iceberg discharge. The episodes of reduced circulation correlate with the cold and abrupt warming phases of the Dansgaard-Oeschger cycles as recognized in the Greenland ice cores.

Timing and duration of North American glacial lake discharges and the Younger Dryas climate reversal

2011 ◽  
Vol 75 (3) ◽  
pp. 541-551 ◽  
Author(s):  
John A. Rayburn ◽  
Thomas M. Cronin ◽  
David A. Franzi ◽  
Peter L.K. Knuepfer ◽  
Debra A. Willard
Keyword(s):  
Ocean Circulation ◽  
North Atlantic ◽  
North American ◽  
Younger Dryas ◽  
Ice Cores ◽  
Cold Event ◽  
Lawrence Estuary ◽  
The North ◽  
The North Atlantic ◽  
Proglacial Lake

AbstractRadiocarbon-dated sediment cores from the Champlain Valley (northeastern USA) contain stratigraphic and micropaleontologic evidence for multiple, high-magnitude, freshwater discharges from North American proglacial lakes to the North Atlantic. Of particular interest are two large, closely spaced outflows that entered the North Atlantic Ocean via the St. Lawrence estuary about 13,200–12,900 cal yr BP, near the beginning of the Younger Dryas cold event. We estimate from varve chronology, sedimentation rates and proglacial lake volumes that the duration of the first outflow was less than 1 yr and its discharge was approximately 0.1 Sv (1 Sverdrup = 106 m3 s−1). The second outflow lasted about a century with a sustained discharge sufficient to keep the Champlain Sea relatively fresh for its duration. According to climate models, both outflows may have had sufficient discharge, duration and timing to affect meridional ocean circulation and climate. In this report we compare the proglacial lake discharge record in the Champlain and St. Lawrence valleys to paleoclimate records from Greenland Ice cores and Cariaco Basin and discuss the two-step nature of the inception of the Younger Dryas.

scholarly journals Tracing the North Atlantic's Bottom Waters

Eos ◽  
2016 ◽  
Author(s):  
Terri Cook
Keyword(s):  
Ocean Circulation ◽  
North Atlantic ◽  
Deep Ocean ◽  
The North ◽  
Nuclear Fuel Reprocessing ◽  
Bottom Waters ◽  
European Nuclear ◽  
Deep Ocean Circulation ◽  
And Behavior ◽  
Fuel Reprocessing

Chemicals released by two European nuclear fuel reprocessing plants, along with certain chlorofluorocarbons, are helping to constrain the speed and behavior of North Atlantic deep-ocean circulation.

Assessing temperature fingerprints for the Atlantic overturning in the past two millennia

2020 ◽  
Author(s):  
Reyhan Shirin Ermis ◽  
Paola Moffa-Sánchez ◽  
Alexandra Jahn ◽  
Kira Rehfeld
Keyword(s):  
Time Scales ◽  
Ocean Circulation ◽  
North Atlantic ◽  
Time Scale ◽  
Deep Ocean ◽  
Meridional Overturning Circulation ◽  
The North ◽  
Surface Temperatures ◽  
Temperature Reconstructions ◽  
The North Atlantic

<p>The Atlantic Meridional Overturning Circulation (AMOC) is essential to maintain the temperate climates of Europe and North America. It redistributes heat from the tropics, and stores carbon in the deep ocean. Yet, its variability and evolution are largely unknown due to the lack of long-term direct circulation measurements. Previous studies suggest a connection between the variability of the AMOC strength and a temperature dipole in the North Atlantic. These results suggest a substantial decline in the strength of the overturning at the onset of the industrial era. </p><p>Here we compare temperature reconstructions from four sediment cores in the North Atlantic with model simulations of the Community Earth System Model (CESM1) as well as the Hadley Centre Coupled Model (HadCM3) over the Common Era. By examining the correlation between the surface temperatures in the North Atlantic and the strength of the overturning we test the robustness of previously used temperature fingerprints. Analysing variability in the surface and subsurface temperatures as well as the overturning strength in models we assess possible drivers of variability in ocean circulation. We compare the persistence times and the time scale dependent variability of the AMOC, the surface and ocean temperatures in the model with those in the temperature reconstructions. The sub-surface reconstructions match with the 200m ocean temperatures in persistence times but not with the AMOC in the models. The surface temperatures in the models show persistence times similar to those obtained for the AMOC. However, time scale dependent variabilities in the surface temperatures do not match those found the AMOC. Therefore, temperature fingerprints might not be a reliable basis to reconstruct the ocean overturning strength.</p><p>Due to the systematic comparison of two models on different time scales and an assessment of surface to sub-surface temperatures this study could provide new insights into the variability of Atlantic overturning on decadal time scales and beyond.</p>

scholarly journals Evolution of <sup>231</sup>Pa and <sup>230</sup>Th in overflow waters of the North Atlantic

2018 ◽  
Vol 15 (23) ◽  
pp. 7299-7313 ◽  
Author(s):  
Feifei Deng ◽  
Gideon M. Henderson ◽  
Maxi Castrillejo ◽  
Fiz F. Perez ◽  
Reiner Steinfeldt
Keyword(s):  
Water Column ◽  
Ocean Circulation ◽  
North Atlantic ◽  
Water Mass ◽  
Deep Ocean ◽  
Water Age ◽  
Meridional Transport ◽  
The North ◽  
Basin Scale ◽  
The North Atlantic

Abstract. Many palaeoceanographic studies have sought to use the 231Pa∕230Th ratio as a proxy for deep ocean circulation rates in the North Atlantic. As of yet, however, no study has fully assessed the concentration of, or controls on, 230Th and 231Pa in waters immediately following ventilation at the start of Atlantic meridional overturning. To that end, full water-column 231Pa and 230Th concentrations were measured along the GEOVIDE section, sampling a range of young North Atlantic deep waters. 230Th and 231Pa concentrations in the water column are lower than those observed further south in the Atlantic, ranging between 0.06 and 12.01 µBq kg−1 and between 0.37 and 4.80 µBq kg−1, respectively. Both 230Th and 231Pa profiles generally increase with water depth from surface to deep water, followed by decrease near the seafloor, with this feature most pronounced in the Labrador Sea (LA Sea) and Irminger Sea (IR Sea). Assessing this dataset using extended optimum multi-parameter (eOMP) analysis and CFC-based water mass age indicates that the low values of 230Th and 231Pa in water near the seafloor of the LA Sea and IR Sea are related to the young waters present in those regions. The importance of water age is confirmed for 230Th by a strong correlation between 230Th and water mass age (though this relationship with age is less clear for 231Pa and the 231Pa∕230Th ratio). Scavenged 231Pa and 230Th were estimated and compared to their potential concentrations in the water column due to ingrowth. This calculation indicates that more 230Th is scavenged (∼80 %) than 231Pa (∼40 %), consistent with the relatively higher particle reactivity of 230Th. Enhanced scavenging for both nuclides is demonstrated near the seafloor in young overflow waters. Calculation of the meridional transport of 230Th and 231Pa with this new GEOVIDE dataset enables a complete budget for 230Th and 231Pa for the North Atlantic. Results suggest that net transport southward of 230Th and 231Pa across GEOVIDE is smaller than transport further south in the Atlantic, and indicate that the flux to sediment in the North Atlantic is equivalent to 96 % of the production of 230Th and 74 % of the production for 231Pa. This result confirms a significantly higher advective loss of 231Pa to the south relative to 230Th and supports the use of 231Pa∕230Th to assess meridional transport at a basin scale.

scholarly journals Evolution of <sup>231</sup>Pa and <sup>230</sup>Th in overflow waters of the North Atlantic

2018 ◽  
Author(s):  
Feifei Deng ◽  
Gideon M. Henderson ◽  
Maxi Castrillejo ◽  
Fiz F. Perez
Keyword(s):  
Water Column ◽  
Ocean Circulation ◽  
North Atlantic ◽  
Water Mass ◽  
Deep Ocean ◽  
Water Age ◽  
Meridional Transport ◽  
The North ◽  
Basin Scale ◽  
The North Atlantic

Abstract. Many paleoceanographic studies have sought to use the 231Pa / 230Th ratio as a proxy for deep ocean circulation rates in the North Atlantic. As yet, however, no study has fully assessed the concentration of, or controls on, 230Th and 231Pa in waters immediately following ventilation at the start of Atlantic meridional overturning. To that end, full water-column 231Pa and 230Th concentrations were measured along the GEOVIDE section, sampling a range of young North Atlantic deep waters. Th-230 and 231Pa concentrations in the water column are lower than those observed further south in the Atlantic, ranging between 0.004 and 0.738 dpm/1000l, and between 0.023 and 0.295 dpm/1000l, respectively. Both 230Th and 231Pa profiles generally increase with water depth from surface to deep water, followed by decrease near the seafloor, with this feature most pronounced in the Labrador Sea (LA Sea) and Irminger Sea (IR Sea). Analyzing this dataset with Extended Optimum Multi-Parameter (eOMP) Analysis and CFC-based water mass age indicates that the low values of 230Th and 231Pa in water near the seafloor of the LA Sea and IR Sea are related to the young waters present in those regions. This importance of water age is confirmed for 230Th by a strong correlation between 230Th and water mass age (though this relationship is less clear, for 231Pa and 231Pa / 230Th ratio). Scavenged 231Pa and 230Th were estimated and compared to their Potential Total concentrations in the water column. The result shows that more 230Th is scavenged (~ 80 %) relative to 231Pa (~ 40 %), consistent with the relatively higher particle-reactivity of 230Th. Enhanced scavenging for both nuclides is demonstrated near the seafloor in young overflow waters. Calculation of meridional transport of 230Th and 231Pa with this new GEOVIDE dataset enables a complete budget for 230Th and 231Pa for the North Atlantic. Results suggest that net transport southward of 230Th and 231Pa across GEOVIDE is smaller than transport further south in the Atlantic, and indicates that the flux to sediment in the North Atlantic is equivalent to 96 % of the production of 230Th, and 77 % of the production for 231Pa. This result confirms a significantly higher advective loss of 231Pa to the south relative to 230Th and supports the use of 231Pa / 230Th to assess meridional transport at a basin scale.

scholarly journals Surface and deep water circulation in late Cretaceous North Atlantic greenhouse ocean

2009 ◽  
Author(s):  
◽  
Carolina Isaza Londoño
Keyword(s):  
Ocean Circulation ◽  
Late Cretaceous ◽  
North Atlantic ◽  
Deep Water ◽  
Water Mass ◽  
Deep Ocean ◽  
Water Circulation ◽  
Regional Warming ◽  
The North ◽  
The North Atlantic

This research provides the first of its kind empirical data regarding the evolution of Maastrichtian surface to deep ocean circulation in the North Atlantic. Differences in foraminiferal abundances and oxygen and carbon isotopic ratios of bulk carbonate and foraminifera between two Ocean Drilling Program Sites in the subtropical North Atlantic indicate a sharp water mass boundary was a relatively stable and persistent feature of the Maastrichtian North Atlantic despite significant regional warming across the interval. Neodymium isotopes of fish debris, on the other hand, indicate significant changes in intermediate and deep water circulation through the Late Cretaceous and especially during the Maastrichtian. During the Cenomanian-Campanian interval at least three different deep water masses were active in the North Atlantic including one formed by downwelling of warm saline waters in the Demerara Rise region. During the Campanian-Maastrichtian, low-latitude-sourced waters seem to have reached abyssal depths, but from the mid-Maastrichtian on, this water mass seems to have declined in importance. From the mid-Danian on, we found evidence for only one water mass (plausibly sourced in the northern North Atlantic, as it is today) at bathyal and abyssal depths in the North Atlantic. Our data demonstrate that surface and, especially, intermediate and deep water circulation patterns are an important (and measurable) variable that helps determine greenhouse temperature distributions on regional and global scales.

The Role of Oscillating Southern Hemisphere Westerly Winds: Global Ocean Circulation

2020 ◽  
Vol 33 (6) ◽  
pp. 2111-2130
Author(s):  
Woo Geun Cheon ◽  
Jong-Seong Kug
Keyword(s):  
Ocean Circulation ◽  
North Atlantic ◽  
North Pacific ◽  
Global Ocean ◽  
The North ◽  
Westerly Winds ◽  
The North Atlantic ◽  
Global Ocean Circulation ◽  
The Antarctic ◽  
The North Pacific

AbstractIn the framework of a sea ice–ocean general circulation model coupled to an energy balance atmospheric model, an intensity oscillation of Southern Hemisphere (SH) westerly winds affects the global ocean circulation via not only the buoyancy-driven teleconnection (BDT) mode but also the Ekman-driven teleconnection (EDT) mode. The BDT mode is activated by the SH air–sea ice–ocean interactions such as polynyas and oceanic convection. The ensuing variation in the Antarctic meridional overturning circulation (MOC) that is indicative of the Antarctic Bottom Water (AABW) formation exerts a significant influence on the abyssal circulation of the globe, particularly the Pacific. This controls the bipolar seesaw balance between deep and bottom waters at the equator. The EDT mode controlled by northward Ekman transport under the oscillating SH westerly winds generates a signal that propagates northward along the upper ocean and passes through the equator. The variation in the western boundary current (WBC) is much stronger in the North Atlantic than in the North Pacific, which appears to be associated with the relatively strong and persistent Mindanao Current (i.e., the southward flowing WBC of the North Pacific tropical gyre). The North Atlantic Deep Water (NADW) formation is controlled by salt advected northward by the North Atlantic WBC.

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