Two-Tiered Transition of the North Atlantic Surface Hydrology during the Past 1.6 Ma: Multiproxy Evidence from Planktic Foraminifera

2021 ◽  
Vol 25 (4) ◽  
Author(s):  
Makoto Yamasaki ◽  
Chieko Shimada ◽  
Minoru Ikehara ◽  
Ralf Schiebel
Keyword(s):  
North Atlantic ◽  
Surface Hydrology ◽  
Planktic Foraminifera ◽  
The Past ◽  
The North ◽  
The North Atlantic

scholarly journals The Meridional Shift of the Midlatitude Westerlies over Arid Central Asia during the Past 21 000 Years Based on the TraCE-21ka Simulations

2020 ◽  
Vol 33 (17) ◽  
pp. 7455-7478
Author(s):  
Nanxuan Jiang ◽  
Qing Yan ◽  
Zhiqing Xu ◽  
Jian Shi ◽  
Ran Zhang
Keyword(s):  
Indian Ocean ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Last Deglaciation ◽  
The Past ◽  
The North ◽  
External Forcings ◽  
The Indian Ocean ◽  
The Last Deglaciation ◽  
The North Atlantic

AbstractTo advance our knowledge of the response of midlatitude westerlies to various external forcings, we investigate the meridional shift of midlatitude westerlies over arid central Asia (ACA) during the past 21 000 years, which experienced more varied forcings than the present day based on a set of transient simulations. Our results suggest that the evolution of midlatitude westerlies over ACA and driving factors vary with time and across seasons. In spring, the location of midlatitude westerlies over ACA oscillates largely during the last deglaciation, driven by meltwater fluxes and continental ice sheets, and then shows a long-term equatorward shift during the Holocene controlled by orbital insolation. In summer, orbital insolation dominates the meridional shift of midlatitude westerlies, with poleward and equatorward migration during the last deglaciation and the Holocene, respectively. From a thermodynamic perspective, variations in zonal winds are linked with the meridional temperature gradient based on the thermal wind relationship. From a dynamic perspective, variations in midlatitude westerlies are mainly induced by anomalous sea surface temperatures over the Indian Ocean through the Matsuno–Gill response and over the North Atlantic Ocean by the propagation of Rossby waves, or both, but their relative importance varies across forcings. Additionally, the modeled meridional shift of midlatitude westerlies is broadly consistent with geological evidence, although model–data discrepancies still exist. Overall, our study provides a possible scenario for a meridional shift of midlatitude westerlies over ACA in response to various external forcings during the past 21 000 years and highlights important roles of both the Indian Ocean and the North Atlantic Ocean in regulating Asian westerlies, which may shed light on the behavior of westerlies in the future.

scholarly journals Modeling the climatic implications of the Guliya δ<sup>18</sup>O record during the past 130 ka

2012 ◽  
Vol 8 (3) ◽  
pp. 1885-1914
Author(s):  
D. Xiao ◽  
P. Zhao ◽  
Y. Wang ◽  
X. Zhou
Keyword(s):  
North Atlantic ◽  
Climate Model ◽  
Surface Air Temperature ◽  
Late Summer ◽  
The Arctic ◽  
The Past ◽  
The North ◽  
Precession Cycle ◽  
The North Atlantic ◽  
Anomalous Pattern

Abstract. Using an intermediate-complexity UVic Earth System Climate Model (UVic Model), the geographical and seasonal implications and an indicative sense of the historical climate found in the δ18O record of the Guliya ice core (hereinafter, the Guliya δ18O) are investigated under time-dependent orbital forcing with an acceleration factor of 100 over the past 130 ka. The results reveal that the simulated late-summer (August–September) Guliya surface air temperature (SAT) reproduces the 23-ka precession and 43-ka obliquity cycles in the Guliya δ18O. Furthermore, the Guliya δ18O is significantly correlated with the SAT over the Northern Hemisphere (NH), which suggests the Guliya δ18O is an indicator of the late-summer SAT in the NH. Corresponding to the warm and cold phases of the precession cycle in the Guliya temperature, there are two anomalous patterns in the SAT and sea surface temperature (SST) fields. The first anomalous pattern shows an increase in the SAT (SST) toward the Arctic, possibly associated with the joint effect of the precession and obliquity cycles, and the second anomalous pattern shows an increase in the SAT (SST) toward the equator, possibly due to the influence of the precession cycle. Additionally, the summer (winter) Guliya and NH temperatures are higher (lower) in the warm phases of Guliya late-summer SAT than in the cold phases. Furthermore, the Guliya SAT is closely related to the North Atlantic SST, in which the Guliya precipitation may act as a "bridge" linking the Guliya SAT and the North Atlantic SST.

Impact of Seasonality in the North Atlantic Jet Stream and Storm Migration on the Seasonality of Hurricane Translation Speed Changes

2021 ◽  
pp. 1-38
Author(s):  
Xi Guo ◽  
James P. Kossin ◽  
Zhe-Min Tan
Keyword(s):  
North Atlantic ◽  
Atlantic Coast ◽  
Jet Stream ◽  
Translation Speed ◽  
Multidecadal Variability ◽  
The Past ◽  
The North ◽  
Term Variation ◽  
The North Atlantic

AbstractTropical cyclone (TC) translation speed (TCTS) can affect the duration of TC-related disasters, which is critical to coastal and inland areas. The long-term variation of TCTS and their relationship to the variability of the mid-latitude jet stream and storm migration are discussed here for storms near the North Atlantic coast during 1948-2019. Our results reveal the prominent seasonality in the long-term variation of TCTS, which can be largely explained by the seasonality in the covariations of the mid-latitude jet stream and storm locations. Specifically, significant increases of TCTS occur in June and October during the past decades, which may result from the equatorward displacement of the jet stream and poleward migration of storm locations. Prominent slowdown of TCTS is found in August, which is related to the weakened jet strength and equatorward storm migration. In September, the effects of poleward displacement and weakening of the jet stream on TCTS are largely compensated by the poleward storm migration, therefore, no significant change in TCTS is observed. Meanwhile, the multidecadal variability of the Atlantic may contribute to the multidecadal variability of TCTS. Our findings emphasize the significance in taking a seasonality view in discussing the variability and trends of near-coast Atlantic TCTS under climate change.

Aeronautical Satellite Systems for Air Traffic Control and Communications in the European Environment

1969 ◽  
Vol 73 (700) ◽  
pp. 283-288
Author(s):  
H. G. Leysieffer
Keyword(s):  
North Atlantic ◽  
Traffic Control ◽  
Air Traffic ◽  
Traffic Surveillance ◽  
Satellite Systems ◽  
The Past ◽  
The North ◽  
The North Atlantic ◽  
Trade Route ◽  
North Atlantic Area

The North Atlantic is increasingly developing into the main trade route of the age. Shipping, the pioneer along this highway of commerce, in the past decade has been joined by air traffic displaying a striking growth rate. Not only is the number of aircraft simultaneously plying the Atlantic routes constantly on the increase, but also the volume of passengers and freight transported on each flight. The question, whether such flow of traffic in the air and on water could be dealt with in future with the safety to which it is entitled, has led to world-wide discussions over the past few years concerning the necessity for an air traffic surveillance system for the North Atlantic area. A further question, whether one should not include also sea traffic in such a system suggested itself. The initiative for holding such discussions naturally proceeded less from air and shipping undertakings, but rather from those committees who are entrusted in supervising the safety in the conduct of man and merchandise.

Deep water circulation patterns in the Atlantic during MISs 12-11

2020 ◽  
Author(s):  
Jasmin M. Link ◽  
Norbert Frank
Keyword(s):  
North Atlantic ◽  
Deep Water ◽  
Glacial Maximum ◽  
Water Circulation ◽  
Water Masses ◽  
Overturning Circulation ◽  
The Past ◽  
The North ◽  
Circulation Patterns ◽  
The North Atlantic

&lt;p&gt;Glacial Termination V is one of the most extreme glacial-interglacial transitions of the past 800 ka [1]. However, the changes in orbital forcing from Marine Isotope Stage (MIS) 12 to 11 are comparatively weak. In addition, MIS 11c is exceptionally distinct compared to other interglacials with for example a longer duration [2] and a higher-than-present sea level [3] despite a relative low incoming insolation. Therefore, the term &amp;#8220;MIS 11 paradox&amp;#8221; was coined [4]. However, only little is known about the Atlantic overturning circulation during this time interval [e.g. 5,6].&lt;/p&gt;&lt;p&gt;Here, we present Atlantic-wide deep water circulation patterns spanning the glacial maximum of MIS 12, Termination V, and MIS 11. Therefore, sediment cores throughout the Atlantic were analyzed regarding their Nd isotopic composition of authigenic coatings to reconstruct the provenance of the prevailing bottom water masses.&lt;/p&gt;&lt;p&gt;During the glacial maximum of MIS 12, the deep Atlantic Ocean was bathed with a higher amount of southern sourced water compared to the following interglacial. Termination V is represented by a sharp transition in the high-accumulating sites from the North Atlantic with a switch to northern sourced water masses. MIS 11 is characterized through an active deep water formation in the North Atlantic with active overflows from the Nordic Seas, only disrupted by a short deterioration. A strong export of northern sourced water masses to the South Atlantic points to an overall strong overturning circulation.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;[1] Lang and Wolff 2011, Climate of the Past 7: 361-380.&lt;/p&gt;&lt;p&gt;[2] Candy et al. 2014, Earth-Science Reviews 128: 18-51.&lt;/p&gt;&lt;p&gt;[3] Dutton et al. 2015, Science 349: aaa4019.&lt;/p&gt;&lt;p&gt;[4] Berger and Wefer 2003, Geophysical Monograph 137: 41-60.&lt;/p&gt;&lt;p&gt;[5] Dickson et al. 2009, Nature Geoscience 2: 428-433.&lt;/p&gt;&lt;p&gt;[6] V&amp;#225;zquez Riveiros et al. 2013, EPSL 371-372: 258-268.&lt;/p&gt;

Growing multicentennial-scale precipitation variability in Eastern Brazil during the late Holocene

2020 ◽  
Author(s):  
André Bahr ◽  
Stefanie Kaboth-Bahr ◽  
Andrea Jaeschke ◽  
Christiano Chiessi ◽  
Francisco Cruz ◽  
...  
Keyword(s):  
South America ◽  
North Atlantic ◽  
Precipitation Amount ◽  
Moisture Distribution ◽  
The South ◽  
The Past ◽  
The North ◽  
Eastern Brazil ◽  
Future Global Warming ◽  
The North Atlantic

&lt;p&gt;Eastern Brazil belongs to the ecologically most vulnerable regions on Earth due to its extreme intra- and inter-annual variability in precipitation amount. In order to constrain the driving forces behind this strong natural fluctuations we investigated a high-resolution sediment core taken off the Jequitinhonha river mouth in central E Brazil to reconstruct Holocene river run-off and moisture availability in the river&amp;#8217;s catchment. Modern day climate in the hinterland of the Jequitinhonha is influenced by the South American Summer Monsoon (SASM), in particular by the manifestation of the South Atlantic Convergence Zone (SACZ) during austral summer. Variations in the position and strength of the SACZ will have immediate impact on the moisture balance over the continent and hence influence sediment and water delivery. Our multi-proxy records, comprising XRF core-scanning, grain size, mineralogical (XRD), as well as organic biomarker analyses indicate abrupt centennial scale variations between dry and wet conditions throughout the past ~5 kyrs. Our results document a gradual weakening of the SASM over the past ~2,7 kyrs driven by changes in the intertropical heat distribution. This long-term trend is superposed by centennial to millennial-scale spatial shifts in moisture distribution that result from migrations of the SACZ. The combination of both processes caused increasingly pronounced aridity spells in eastern South America over the past 2 kyrs. As the spatial fluctuations were triggered by freshwater anomalies in the North Atlantic, we surmise that enhanced meltwater input into the North Atlantic due to future global warming might severely increase the risk for mega-droughts in tropical South America.&lt;/p&gt;

Sign in / Sign up

Export Citation Format

Share Document