scholarly journals Decade time scale variability of ventilation in the North Atlantic: High-precision measurements of bomb radiocarbon in banded corals

1989 ◽  
Vol 94 (C3) ◽  
pp. 3271 ◽  
Author(s):  
Ellen R. M. Druffel
Keyword(s):  
High Precision ◽  
North Atlantic ◽  
Time Scale ◽  
Precision Measurements ◽  
The North ◽  
Bomb Radiocarbon ◽  
The North Atlantic

scholarly journals Timing and structure of the Younger Dryas event and its underlying climate dynamics

2020 ◽  
Vol 117 (38) ◽  
pp. 23408-23417
Author(s):  
Hai Cheng ◽  
Haiwei Zhang ◽  
Christoph Spötl ◽  
Jonathan Baker ◽  
Ashish Sinha ◽  
...  
Keyword(s):  
Southern Hemisphere ◽  
North Atlantic ◽  
Time Scale ◽  
Asian Monsoon ◽  
Younger Dryas ◽  
Tropical Pacific ◽  
Last Glacial ◽  
The North ◽  
The North Atlantic ◽  
The Last Glacial

The Younger Dryas (YD), arguably the most widely studied millennial-scale extreme climate event, was characterized by diverse hydroclimate shifts globally and severe cooling at high northern latitudes that abruptly punctuated the warming trend from the last glacial to the present interglacial. To date, a precise understanding of its trigger, propagation, and termination remains elusive. Here, we present speleothem oxygen-isotope data that, in concert with other proxy records, allow us to quantify the timing of the YD onset and termination at an unprecedented subcentennial temporal precision across the North Atlantic, Asian Monsoon-Westerlies, and South American Monsoon regions. Our analysis suggests that the onsets of YD in the North Atlantic (12,870 ± 30 B.P.) and the Asian Monsoon-Westerlies region are essentially synchronous within a few decades and lead the onset in Antarctica, implying a north-to-south climate signal propagation via both atmospheric (decadal-time scale) and oceanic (centennial-time scale) processes, similar to the Dansgaard–Oeschger events during the last glacial period. In contrast, the YD termination may have started first in Antarctica at ∼11,900 B.P., or perhaps even earlier in the western tropical Pacific, followed by the North Atlantic between ∼11,700 ± 40 and 11,610 ± 40 B.P. These observations suggest that the initial YD termination might have originated in the Southern Hemisphere and/or the tropical Pacific, indicating a Southern Hemisphere/tropics to North Atlantic–Asian Monsoon-Westerlies directionality of climatic recovery.

Primary production in the North Atlantic: measurements, scaling, and optical determinants

1995 ◽  
Vol 348 (1324) ◽  
pp. 153-160 ◽  
Keyword(s):  
Optical Properties ◽  
Primary Production ◽  
North Atlantic ◽  
Time Scale ◽  
Biomass Yield ◽  
Particle Scattering ◽  
New Production ◽  
The North ◽  
The North Atlantic ◽  
Three Components

Productivity in the ocean is viewed from the perspective of its three components: biomass, yield (new production), and the rate of production. The three components are ordered along a time scale and a fundamental time scale is defined for the rate of production at the diel (24 h). Two optical properties, the absorption by phytoplankton and particle scattering, are presented and it is argued that they provide a means to unite the rate of production with biomass and yield at the diel scale.

scholarly journals Will Global Warming Suppress North Atlantic Tripole Decadal Variability?

2012 ◽  
Vol 25 (6) ◽  
pp. 2040-2055 ◽  
Author(s):  
Yun Yang ◽  
Lixin Wu ◽  
Changfang Fang
Keyword(s):  
Global Warming ◽  
North Atlantic ◽  
Time Scale ◽  
Decadal Variability ◽  
Buoyancy Frequency ◽  
The North ◽  
Ocean Atmosphere ◽  
The North Atlantic ◽  
Partial Blocking ◽  
Partial Coupling

Abstract In this paper, the modulations of the North Atlantic tripole (NAT) decadal variability from global warming are studied by conducting a series of coupled ocean–atmosphere experiments using the Fast Ocean Atmosphere Model (FOAM). The model reasonably captures the observed NAT decadal variability with a preferred time scale of about 11 years. With the aid of partial-blocking and partial-coupling experiments, it is found that the NAT decadal cycle can be attributed to oceanic planetary wave adjustment in the subtropical basin and ocean–atmosphere coupling over the North Atlantic. In a doubled CO2 experiment, the spatial pattern of the NAT is preserved; however, the decadal cycle is significantly suppressed. This suppression appears to be associated with the acceleration of oceanic planetary waves due to an increase of buoyancy frequency in global warming. This shortens the time from a decadal to an interannual time scale for the first-mode baroclinic Rossby waves to cross the subtropical North Atlantic basin, the primary memory for the NAT decadal variability in the model. The modeling study also found that the global warming does not modulate the North Atlantic air–sea coupling significantly, but it may be model dependent.

scholarly journals The Tertiary opening of the North Atlantic: DLC investigations along the east coast of Greenland

1995 ◽  
Vol 165 ◽  
pp. 106-115
Author(s):  
H.C Larsen ◽  
C.K Brooks ◽  
J.R Hopper ◽  
T Dahl-Jensen ◽  
A.K Pedersen ◽  
...  
Keyword(s):  
North Atlantic ◽  
Time Scale ◽  
Tectonic Evolution ◽  
East Coast ◽  
Thermal State ◽  
The North ◽  
Rifted Margins ◽  
The North Atlantic ◽  
Break Up

Work along the east coast of Greenland in the summer of 1994 represents the initiation of the Danish Lithosphere Centre (DLC) investigations into the magmatic and tectonic evolution accompanying initial break-up of the North Atlantic in this area. As described by Larsen (this report), the aims of DLC are the understanding of the composition and thermal state of the asthenosphere and the deformation of the lithosphere during continental break-up and formation of volcanic rifted margins. Furthermore, the time scale of these events is crucial to any model of break-up.

scholarly journals Impact of the oceanic geothermal heat flux on a glacial ocean state

2015 ◽  
Vol 11 (4) ◽  
pp. 3597-3624 ◽  
Author(s):  
M. Ballarotta ◽  
F. Roquet ◽  
S. Falahat ◽  
Q. Zhang ◽  
G. Madec
Keyword(s):  
Ocean Circulation ◽  
North Atlantic ◽  
Time Scale ◽  
Ekman Transport ◽  
Western Boundary ◽  
Characteristic Time Scale ◽  
Boundary Current ◽  
Geothermal Heating ◽  
The North ◽  
The North Atlantic

Abstract. The oceanic geothermal heating (OGH) has a significant impact on the present-day ocean state, but its role during glacial periods, when the ocean circulation and stratification were different from those of today, remains poorly known. In the present study, we analyzed the response of the glacial ocean to OGH, by comparing ocean simulations of the Last Glacial Maximum (LGM, ∼ 21 ka ago) including or not geothermal heating. We found that applying the OGH warmed the Antarctic Bottom Waters (AABW) by ∼ 0.4 °C and increased the abyssal circulation by 15 to 30 % north of 30° S in the deep Pacific and Atlantic basins. The geothermally heated deep waters were then advected toward the Southern Ocean where they upwelled to the surface due to the Ekman transport. The extra heat transport towards Antarctica acted to reduce the amount of sea ice contributing to the freshening of the whole AABW overturning cell. The global amount of salt being conserved, this bottom freshening induced a salinification of the North Atlantic and North Pacific surface and intermediate waters, contributing to the deepening of the North Atlantic Deep Water. This indirect mechanism is responsible for the largest observed warming, found in the North Atlantic deep western boundary current between 2000 and 3000 m (up to 2 °C). The characteristic time scale of the ocean response to the OGH corresponds to an advective time scale (associated with the overturning of the AABW cell) rather than a diffusive time scale. The OGH might facilitate the transition from a glacial to an inter-glacial state but its effect on the deep stratification seems insufficient to drive alone an abrupt climate change.

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>

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