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.

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.

6. Climate surprises

2021 ◽  
pp. 90-105
Author(s):  
Mark Maslin
Keyword(s):  
Ocean Circulation ◽  
Deep Ocean ◽  
Climate System ◽  
Delayed Response ◽  
Tipping Points ◽  
Threshold Response ◽  
Slowing Down ◽  
The North ◽  
Deep Ocean Circulation ◽  
Different Parts

‘Climate surprises’ assesses the possibility that there are thresholds or tipping points in the climate system that may occur as we warm the planet. Scientists have been concerned about these tipping points over the last three decades. One can examine the way different parts of the climate system respond to climate change with four scenarios. These include linear but delayed response; muted or limited response; delayed and non-linear response; and threshold response. It is worth considering here the melting of the Greenland and/or Western Antarctic ice sheet; the slowing down of the North Atlantic deep ocean circulation; the potential massive release of methane from melting gas hydrates; and the possibility of the Amazon rainforest dieback.

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 Regional and global signals in seawater δ18O records across the mid-Pleistocene transition

Geology ◽  
2019 ◽  
Vol 48 (2) ◽  
pp. 113-117 ◽  
Author(s):  
Heather L. Ford ◽  
Maureen E. Raymo
Keyword(s):  
Ocean Circulation ◽  
North Pacific Ocean ◽  
Deep Ocean ◽  
Ocean Drilling Program ◽  
Ocean Drilling ◽  
Ice Volume ◽  
The North ◽  
Global Ice Volume ◽  
Deep Ocean Water ◽  
Deep Ocean Circulation

Abstract High-resolution seawater δ18O records, derived from coupled Mg/Ca and benthic δ18O analyses, can be used to evaluate how global ice volume changed during the mid-Pleistocene transition (MPT, ca. 1250–600 ka). However, such seawater δ18O records are also influenced by regional hydrographic signals (i.e., salinity) and changes in deep-ocean circulation across the MPT, making it difficult to isolate the timing and magnitude of the global ice volume change. To explore regional and global patterns in seawater δ18O records, we reconstruct seawater δ18O from coupled Mg/Ca and δ18O analyses of Uvigerina spp. at Ocean Drilling Program Site 1208 in the North Pacific Ocean. Comparison of individual seawater δ18O records suggests that deep-ocean circulation reorganized and the formation properties (i.e., salinity) of deep-ocean water masses changed at ca. 900 ka, likely related to the transition to marine-based ice sheets in Antarctica. We also find that an increase in ice volume likely accompanied the shift in glacial-interglacial periodicity observed in benthic carbonate δ18O across the MPT, with increases in ice volume observed during Marine Isotope Stages 22 and 16.

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.

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