scholarly journals North Atlantic Ice‐Rafting, Ocean and Atmospheric Circulation During the Holocene: Insights From Western Mediterranean Speleothems

2019 ◽  
Vol 46 (13) ◽  
pp. 7614-7623 ◽  
Author(s):  
Y. Ait Brahim ◽  
J. A. Wassenburg ◽  
L. Sha ◽  
F. W. Cruz ◽  
M. Deininger ◽  
...  
Keyword(s):  
Atmospheric Circulation ◽  
North Atlantic ◽  
Western Mediterranean ◽  
The Holocene ◽  
Ice Rafting

Centennial to millennial-scale variability of Holocene climate and environmental dynamics in the western Mediterranean (Lake Sidi Ali, Middle Atlas, Morocco)

2021 ◽  
Author(s):  
Johannes Schmidt ◽  
Cathleen Kertscher ◽  
Markus Reichert ◽  
Helen Ballasus ◽  
Birgit Schneider ◽  
...  
Keyword(s):  
North Atlantic ◽  
Climate Changes ◽  
Western Mediterranean ◽  
Future Climate ◽  
Holocene Climate ◽  
The Holocene ◽  
The North ◽  
Middle Atlas ◽  
Environmental Responses

<p>The Western Mediterranean region including the North African desert margin is considered one of the most sensitive areas to future climate changes. In order to refine long-term scenarios for hydrological and environmental responses to future climate changes in this region, it is important to improve our knowledge about past environmental responses to climatic variability at centennial to millennial timescales. During the last two decades, the recovery and compilation of Holocene records from the subtropical North Atlantic and the Mediterranean Sea have improved our knowledge about millennial-scale variability of the Western Mediterranean palaeoclimate. The variabilities appear to affect regional precipitation patterns and environmental systems in the Western Mediterranean, but the timescales, magnitudes and forcing mechanisms remain poorly known. To compare the changes in Holocene climate variability and geomorphological processes across temporal scales, we analysed a 19.63-m long sediment record from Lake Sidi Ali (33°03’ N, 5°00’ W, 2080 m a.s.l.) in the sub-humid Middle Atlas that spans the last 12,000 years (23 pollen-based radiocarbon dates accompanied with <sup>210</sup>Pb results). We use calibrated XRF core scanning records with an annual to sub-decadal resolution to disentangle the complex interplay between climate changes and environmental dynamics during the Holocene. Data exploration techniques and time series analysis (Redfit, Wavelet) revealed long-term changes in lake behaviour. Three main proxy groups were identified (temperature proxies: 2ky, 1ky and 0.7ky cycles; sediment dynamic proxies: 3.5ky, 1.5ky cycles; hydrological proxies: 1.5ky, 1.2ky, 0.17ky cycles). For example, redox sensitive elements Fe and Mn show 1ky cycles and higher values in the Early Holocene and 1.5ky cycles and lower values in the Mid- to Late Holocene. All groups show specific periodicities throughout the Holocene, demonstrating their particular climatic and geomorphological dependencies. Furthermore, we discuss these periodicities relating to global and hemispheric drivers, such as the North Atlantic Oscillation (NAO), El-Niño Southern Oscillation (ENSO), Innertropical Convergence Zone variability (ITCZ) and North Atlantic cold relapses (Bond events).</p>

Sea surface temperatures and ice rafting in the Holocene North Atlantic: climate influences on northern Europe and Greenland

2004 ◽  
Vol 23 (20-22) ◽  
pp. 2113-2126 ◽  
Author(s):  
Matthias Moros ◽  
Kay Emeis ◽  
Bjørg Risebrobakken ◽  
Ian Snowball ◽  
Antoon Kuijpers ◽  
...  
Keyword(s):  
North Atlantic ◽  
Sea Surface ◽  
Northern Europe ◽  
Sea Surface Temperatures ◽  
The Holocene ◽  
Surface Temperatures ◽  
North Atlantic Climate ◽  
Climate Influences ◽  
Ice Rafting

scholarly journals Western Mediterranean hydro-climatic consequences of Holocene iceberg advances (Bond events)

2018 ◽  
Author(s):  
Christoph Zielhofer ◽  
Anne Köhler ◽  
Steffen Mischke ◽  
Abdelfattah Benkaddour ◽  
Abdeslam Mikdad ◽  
...  
Keyword(s):  
North Atlantic ◽  
Large Scale ◽  
Thermohaline Circulation ◽  
Winter Precipitation ◽  
Western Mediterranean ◽  
Coupled Processes ◽  
Opposite Pattern ◽  
The Holocene ◽  
The North ◽  
Winter Rain

Abstract. Gerald C. Bond established a Holocene series of North Atlantic ice rafted debris events based on quartz and hematite stained grains recovered from subpolar North Atlantic marine cores. These so-called ‘Bond events’ document nine large-scale and multi-centennial North-Atlantic cooling phases that might be linked to a reduced thermohaline circulation. Regardless of the high prominence of the Holocene North Atlantic ice rafted debris record, there are critical scientific comments on the study: the Holocene Bond curve has not yet been replicated in other marine archives of the North Atlantic and there exist only very few palaeo-climatic studies that indicate all individual Bond events in their own record. Therefore, evidence for consistent hydro-climatic teleconnections between the subpolar North Atlantic and distant regions is not clear. In this context, the Western Mediterranean region reveals key hydro-climatic sites for the reconstruction of a teleconnection with the subpolar North Atlantic. In particular, variability of Western Mediterranean winter precipitation might be the result of atmosphere-ocean coupled processes in the outer-tropical North Atlantic realm. Based on an improved Holocene δ18O record from Lake Sidi Ali (Middle Atlas, Morocco) we correlate Western Mediterranean precipitation anomalies with North Atlantic Bond events to identify a probable teleconnection between Western Mediterranean winter rains and subpolar North Atlantic cooling phases. Our data show a noticeable positive correlation between Western Mediterranean winter rain minima and Bond events during the Early Holocene and an opposite pattern during the Late Holocene. There is evidence for an enduring hydro-climatic change in the overall Atlantic atmosphere-ocean system and the response to external forcing during the Mid-Holocene. Regarding a potential climatic anomaly around 4.2 ka (Bond event 3) in the Western Mediterranean, a centennial-scale winter rain maximum is generally in phase with the overall pattern of alternating ‘wet and cool’ and ‘dry and warm’ intervals during the last 5,000 years.

scholarly journals Glaciers and Paleorecords Tell Us How Atmospheric Circulation Changes and Successive Cooling Periods Occurred in the Fennoscandia during the Holocene

2021 ◽  
Vol 9 (8) ◽  
pp. 832
Author(s):  
Jean-Louis Pinault
Keyword(s):  
Atmospheric Circulation ◽  
North Atlantic ◽  
Rossby Waves ◽  
Western Boundary Current ◽  
The Other ◽  
Western Boundary ◽  
Boundary Current ◽  
The Holocene ◽  
The North ◽  
The North Atlantic

Two major climatic phenomena that occurred during the Holocene are interpreted from the resonance in subharmonic modes of long-period Rossby waves winding around the North Atlantic gyre, the so-called gyral Rossby waves (GRWs). These are, on the one hand, the change in atmospheric circulation that occurred in the North Atlantic in the middle Holocene, and, on the other hand, the occurrence of abrupt cooling events more frequently than what is generally accepted. The amplitude of GRWs is deduced by filtering, within bands characteristic of various subharmonic modes, climate records from the Greenland ice sheet, pollen, and tree rings in northern Fennoscandia, and from two Norwegian glaciers in northern Folgefonna and on the Lyngen peninsula. While the subharmonic modes reflect the acceleration/deceleration phases of the western boundary current, an anharmonic mode is evidenced in the 400–450 year band. Abrupt cooling events of the climate are paced by this anharmonic mode while the western boundary current is decelerating, and the northward heat advection of air favors the melting of the pack ice. Then, the current of the northernmost part of the North Atlantic gyre cools before branching off to the north, which alters its buoyancy. On the other hand, according to high subharmonic modes, high-pressure systems prevailed over the North Atlantic in the first half of the Holocene while low-pressure systems resulted from baroclinic instabilities of the atmosphere dominate during the second half, favoring the growth of glaciers in Scandinavia by a better snowfall in winter and cooler summers.

scholarly journals The role of aerosol in altering North Atlantic atmospheric circulation in winter and its impact on air quality

2015 ◽  
Vol 15 (4) ◽  
pp. 1725-1743 ◽  
Author(s):  
F. S. R. Pausata ◽  
M. Gaetani ◽  
G. Messori ◽  
S. Kloster ◽  
F. J. Dentener
Keyword(s):  
Air Pollution ◽  
Air Quality ◽  
Atmospheric Circulation ◽  
North Atlantic ◽  
Western Mediterranean ◽  
Radiation Budget ◽  
Atlantic Sector ◽  
Pollution Mitigation ◽  
Future Air Pollution

Abstract. Numerical model scenarios of future climate depict a global increase in temperatures and changing precipitation patterns, primarily driven by increasing greenhouse gas (GHG) concentrations. Aerosol particles also play an important role by altering the Earth's radiation budget and consequently surface temperature. Here, we use the general circulation aerosol model ECHAM5-HAM, coupled to a mixed layer ocean model, to investigate the impacts of future air pollution mitigation strategies in Europe on winter atmospheric circulation over the North Atlantic. We analyse the extreme case of a maximum feasible end-of-pipe reduction of aerosols in the near future (2030), in combination with increasing GHG concentrations. Our results show a more positive North Atlantic Oscillation (NAO) mean state by 2030, together with a significant eastward shift of the southern centre of action of sea-level pressure (SLP). Moreover, we show a significantly increased blocking frequency over the western Mediterranean. By separating the impacts of aerosols and GHGs, our study suggests that future aerosol abatement may be the primary driver of both the eastward shift in the southern SLP centre of action and the increased blocking frequency over the western Mediterranean. These concomitant modifications of the atmospheric circulation over the Euro-Atlantic sector lead to more stagnant weather conditions that favour air pollutant accumulation, especially in the western Mediterranean sector. Changes in atmospheric circulation should therefore be included in future air pollution mitigation assessments. The indicator-based evaluation of atmospheric circulation changes presented in this work will allow an objective first-order assessment of the role of changes in wintertime circulation on future air quality in other climate model simulations.

The spatiotemporal pattern of the Bond 4 event (5.2 ka) : a global data-based review

2021 ◽  
Author(s):  
Bassem Jalali ◽  
Marie-Alexandrine Sicre
Keyword(s):  
North Atlantic ◽  
High Latitude ◽  
Eastern Mediterranean ◽  
Western Mediterranean ◽  
Ice Age ◽  
Spatiotemporal Pattern ◽  
Climate Conditions ◽  
The Holocene ◽  
The North ◽  
The North Atlantic

<p>The Bond 4 event starting at 7000 yr BP and culminating around 5200 yr BP corresponds to the largest (in magnitude and duration) invasion of drifting ice across the subpolar North Atlantic during the Holocene (Bond et al., 2001). While several studies have focused on other events of the Holocene, such as the 8.2 ka, the 4.2 ka and the Little Ice Age, little is known about the mid-Holocene 5.2 ka event. Here we present a global compilation of carefully selected high-resolution time series of sea surface temperature (SST; N=58) and humidity/precipitation (N=35) to characterize in space and time the 5.2 ka event pattern.</p><p>The SST records show the occurrence of cold conditions in the North Atlantic, western Mediterranean as well as in the western Pacific Ocean. However, they indicate warming in the high latitude North Atlantic, the southeastern Atlantic, the eastern Mediterranean and the Arabian and Red seas. Humidity/precipitation data (mainly based on oxygen  isotope records in speleothems) indicate dry conditions in the northern hemisphere subtropical and mid latitude regions of all continents. Based on these data and others from marine and lacustrine records in tropical regions, we suggest a possible weakening of monsoon systems, i.e. in Africa, North America, southwest Asia as well as East Asia. Precipitation reduced as well in most regions of the Mediterranean (i.e. except Iberian Peninsula). All together these data indicate severe climate conditions during the 5.2 ka event.</p><p>Based on the recent compilation of sortable silt from the high latitude North Atlantic of McCave and Andrews (2019), the 5.2 ka event coincides with a decrease of the main Shallow and bottom ocean flows (i.e. North Iceland Irminger Current, East Greenland Current, Iceland-Scotland overflow) probably reflecting a weakening of the North Atlantic Deep Water formation. This event also corresponds to the occurrence of several solar minima as well as several tropical volcanic mega-eruptions that could have triggered a global colder and drier climate (Steinhilber et al., 2012; Kobashi et al., 2017). </p>

scholarly journals Western Mediterranean hydro-climatic consequences of Holocene ice-rafted debris (Bond) events

2019 ◽  
Vol 15 (2) ◽  
pp. 463-475 ◽  
Author(s):  
Christoph Zielhofer ◽  
Anne Köhler ◽  
Steffen Mischke ◽  
Abdelfattah Benkaddour ◽  
Abdeslam Mikdad ◽  
...  
Keyword(s):  
North Atlantic ◽  
Large Scale ◽  
Thermohaline Circulation ◽  
Winter Precipitation ◽  
Western Mediterranean ◽  
Coupled Processes ◽  
Opposite Pattern ◽  
The Holocene ◽  
The North ◽  
Winter Rain

Abstract. Gerard C. Bond established a Holocene series of North Atlantic ice-rafted debris events based on quartz and haematite-stained grains recovered from subpolar North Atlantic marine cores. These so-called “Bond events” document nine large-scale and multi-centennial North Atlantic cooling phases that might be linked to a reduced thermohaline circulation. Regardless of the high prominence of the Holocene North Atlantic ice-rafted debris record, there are critical scientific comments on the study: the Holocene Bond curve has not yet been replicated in other marine archives of the North Atlantic and there exist only very few palaeoclimatic studies that indicate all individual Bond events in their own record. Therefore, evidence of consistent hydro-climatic teleconnections between the subpolar North Atlantic and distant regions is not clear. In this context, the Western Mediterranean region presents key hydro-climatic sites for the reconstruction of a teleconnection with the subpolar North Atlantic. In particular, variability in Western Mediterranean winter precipitation might be the result of atmosphere–ocean coupled processes in the outer-tropical North Atlantic realm. Based on an improved Holocene δ18O record from Lake Sidi Ali (Middle Atlas, Morocco), we correlate Western Mediterranean precipitation anomalies with North Atlantic Bond events to identify a probable teleconnection between Western Mediterranean winter rains and subpolar North Atlantic cooling phases. Our data show a noticeable similarity between Western Mediterranean winter rain minima and Bond events during the Early Holocene and an opposite pattern during the Late Holocene. There is evidence of an enduring hydro-climatic change in the overall Atlantic atmosphere–ocean system and the response to external forcing during the Middle Holocene. Regarding a potential climatic anomaly around 4.2 ka (Bond event 3) in the Western Mediterranean, a centennial-scale winter rain maximum is generally in-phase with the overall pattern of alternating “wet and cool” and “dry and warm” intervals during the last 5000 years.

scholarly journals Holocene hydrography evolution in the Alboran Sea: a multi-record and multi-proxy comparison

2019 ◽  
Vol 15 (3) ◽  
pp. 927-942 ◽  
Author(s):  
Albert Català ◽  
Isabel Cacho ◽  
Jaime Frigola ◽  
Leopoldo D. Pena ◽  
Fabrizio Lirer
Keyword(s):  
North Atlantic ◽  
Climatic Variability ◽  
Planktonic Foraminifera ◽  
Warming Trend ◽  
Western Mediterranean ◽  
Alboran Sea ◽  
The Holocene ◽  
Sst Variability ◽  
Peak Structure ◽  
Alborán Sea

Abstract. A new high-resolution deglacial and Holocene sea surface temperature (SST) reconstruction is presented for the Alboran Sea (western Mediterranean), based on Mg∕Ca ratios measured in the planktonic foraminifera Globigerina bulloides. This new record is evaluated by comparison with other Mg∕Ca SST records and previously published alkenone SST reconstructions from the same region for both the Holocene and glacial periods. In all cases there is a high degree of coherence between the different Mg∕Ca SST records but strong discrepancies when compared to the alkenone SST records. We argue that these discrepancies are due to differences in the proxy response during deglaciation which we hypothesize to reflect a resilience strategy of G. bulloides, changing its main growth season, and consequently Mg∕Ca records a shorter deglacial warming than alkenones. In contrast, short-term Holocene SST variability is larger in the Mg∕Ca SST than in the alkenone SST records. We propose that the larger Mg∕Ca SST variability is a result of spring temperatures variability, while the smoothed alkenone SST variability represents averaged annual temperatures. The Mg∕Ca SST record differentiates the Holocene into three periods: (1) the warmest SST values occurred during the Early Holocene (11.7–9 cal. kyr BP), (2) a continuous cooling trend occurred during the Middle Holocene that culminated in the coldest Holocene SST having a double cold peak structure centred at around 4.2 cal. kyr BP, and (3) the Late Holocene (4.2 cal. kyr BP to present) did not follow any clear cooling/warming trend although millennial-scale oscillations were enhanced. This SST evolution is discussed in the context of the changing properties in the Atlantic inflow water associated with North Atlantic circulation conditions and also with local hydrographical and atmospheric changes. We propose that a tight link between North Atlantic circulation patterns and the inflow of surface waters into the Mediterranean played a major role in controlling Holocene climatic variability of this region.

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