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

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.

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

Climate of the Past ◽

10.5194/cp-15-463-2019 ◽

2019 ◽

Vol 15 (2) ◽

pp. 463-475 ◽

Cited By ~ 9

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.

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

10.5194/egusphere-egu21-8650 ◽

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

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&#176;03&#8217; N, 5&#176;00&#8217; 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 210Pb 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-Ni&#241;o Southern Oscillation (ENSO), Innertropical Convergence Zone variability (ITCZ) and North Atlantic cold relapses (Bond events).

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Understanding Precipitation Changes in Iberia in Early Spring: Weather Typing and Storm-Tracking Approaches

Journal of Hydrometeorology ◽

10.1175/jhm472.1 ◽

2006 ◽

Vol 7 (1) ◽

pp. 101-113 ◽

Cited By ~ 153

Author(s):

Daniel Paredes ◽

Ricardo M. Trigo ◽

Ricardo Garcia-Herrera ◽

Isabel Franco Trigo

Keyword(s):

Iberian Peninsula ◽

North Atlantic ◽

Large Scale ◽

Western Mediterranean ◽

Early Spring ◽

The North ◽

Western Mediterranean Basin ◽

The North Atlantic ◽

Circulation Changes ◽

Precipitation Trends

Abstract March monthly accumulated precipitation in the central and western regions of the Iberian Peninsula presents a clear continuous decline of 50% during the 1960–97 period. A finer analysis using daily data reveals that this trend is exactly confined to the month of March. However, this is merely the most visible aspect of a larger phenomenon over the North Atlantic/European sector. The European precipitation trends in March for the period 1960–2000 show a clear distribution of increasing precipitation in the northern regions (the British Isles and parts of Scandinavia) together with decreasing trends throughout the western Mediterranean Basin. Relevant circulation changes over the North Atlantic and European sectors explain these precipitation trends. First, a regional Eulerian approach by means of a weather-type (WT) classification shows that the major rainfall contributors in March display significantly decreasing frequencies for the Iberian Peninsula, in contrast to the corresponding “wet” weather types for the U.K./Ireland sector, which display increasing frequencies. Within a larger context, a Lagrangian approach, based on the analysis of storm tracks over Europe and the North Atlantic region, reveals dramatic changes in the location of cyclones in the last four decades that coincide with the corresponding precipitation trends in Europe. The North Atlantic Oscillation is suggested to be the most important large-scale factor controlling both the circulation changes and the precipitation trends over the Euro–Atlantic area in March. Finally, the potential impact of reduced precipitation for rivers and water resources in the Iberian Peninsula is considered.

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Evidence for Two Distinct Modes of Large-Scale Ocean Circulation Changes over the Last Century

Journal of Climate ◽

10.1175/2009jcli2867.1 ◽

2010 ◽

Vol 23 (1) ◽

pp. 5-16 ◽

Cited By ~ 44

Author(s):

Mihai Dima ◽

Gerrit Lohmann

Keyword(s):

Ocean Circulation ◽

North Atlantic ◽

Large Scale ◽

Climate Changes ◽

Thermohaline Circulation ◽

Conveyor Belt ◽

The North ◽

Symmetric Pattern ◽

The North Atlantic ◽

Circulation Changes

Abstract Through its nonlinear dynamics and involvement in past abrupt climate shifts the thermohaline circulation (THC) represents a key element for the understanding of rapid climate changes. The expected THC weakening under global warming is characterized by large uncertainties, and it is therefore of significant importance to identify ocean circulation changes over the last century. By applying various statistical techniques on two global sea surface temperature datasets two THC-related modes are separated. The first one involves relatively slow adjustment of the whole conveyor belt circulation and has an interhemispherically symmetric pattern. The second mode is associated with the relatively fast adjustment of the North Atlantic overturning cell and has the seesaw structure. Based on the separation of these two patterns the authors show that the global conveyor has been weakening since the late 1930s and that the North Atlantic overturning cell suffered an abrupt shift around 1970. The distinction between the two modes provides also a new frame for interpreting past abrupt climate changes.

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Younger Dryas research and its implications for understanding abrupt climatic change

Progress in Physical Geography Earth and Environment ◽

10.1177/030913339702100203 ◽

1997 ◽

Vol 21 (2) ◽

pp. 230-249 ◽

Cited By ~ 28

Author(s):

David E. Anderson

Keyword(s):

Climatic Change ◽

North Atlantic ◽

Large Scale ◽

Thermohaline Circulation ◽

Younger Dryas ◽

Theoretical Understanding ◽

The North ◽

Consequent Reduction ◽

The North Atlantic ◽

Abrupt Climatic Change

The Younger Dryas refers to the final phase of cold, glacial conditions preceding the abrupt climatic warming at the beginning of the Holocene. The existence of the Younger Dryas in Europe has been known for most of this century, although recent research suggests that the Younger Dryas cooling may have been global. Estimates of the timing of the event have also improved in recent years, showing that both the onset and termination of the Younger Dryas were abrupt, occurring within decades. The Younger Dryas has been linked with a large-scale shift of the North Atlantic thermohaline circulation (THC) to a near glacial mode with a consequent reduction in northward heat transport. This shift in the THC may have been triggered by a discharge of Laurentide ice, combined with meltwater inputs from several locations around the North Atlantic. Further study of the events leading up to the Younger Dryas is necessary for improving theoretical understanding of abrupt climatic change, and for evaluating GCM models which seek to simulate the response of the THC to freshwater forcing. With predicted increases in freshwater input to the North Atlantic resulting from increases in atmospheric CO2, a future shift in the THC is a possibility. Predicting the magnitude and climatic consequences of such an event depends upon further study of the Younger Dryas and of other abrupt palaeoclimatic changes which involved the THC.

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An n-alkane-based Holocene climate reconstruction in the Altai Mountains, northern Xinjiang, China

10.5194/egusphere-egu2020-3185 ◽

2020 ◽

Author(s):

Min Ran

Keyword(s):

North Atlantic ◽

Large Scale ◽

Time Lag ◽

Geographic Location ◽

Early Holocene ◽

Altai Mountains ◽

Temperature Changes ◽

The Holocene ◽

The North ◽

Highly Sensitive

The climate in the Altai Mountains is highly sensitive to large-scale forcing factors because of its special geographic location. Based on n-alkane data of 150 samples and with a chronologic support of 15 accelerator mass spectrometry (AMS) dates from a 600-cm core at GHZ Peat, the Holocene climatic changes in the Altai Mountains were reconstructed. The reconstruction revealed a warming and drying early Holocene (~10,750-~8500 cal. yr BP), a cooling and persistent dry middle Holocene (~8500-~4500 cal. yr BP), and a cooling and wetting late Holocene (~4500-~700 cal. yr BP). The Holocene temperature changes were primarily controlled by the summer solar radiation with a certain time lag in the early Holocene and also modulated by solar activity, and the time lag in the early Holocene was probably resulted from ice and permafrost melting. The Holocene moisture in the southern Altai Mountains was likely modulated by the North Atlantic Oscillations (NAO) or by the Atlantic Multi-centennial Oscillations (i.e., AMO-like) or by temperature, and or by any combination of the three (NAO, AMO-like, and temperature).

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A speleothem record from Portugal reveals phases of increased winter precipitation in western Iberia during the Holocene

The Holocene ◽

10.1177/09596836211011666 ◽

2021 ◽

pp. 095968362110116

Author(s):

Alexa Benson ◽

Dirk L Hoffmann ◽

Joan Daura ◽

Montserrat Sanz ◽

Filipa Rodrigues ◽

...

Keyword(s):

North Atlantic ◽

Atmospheric Pressure ◽

Western Europe ◽

Precipitation Amount ◽

Atlantic Multidecadal Oscillation ◽

Winter Precipitation ◽

Jet Stream ◽

The Holocene ◽

The North ◽

European Climate

The European climate during the Holocene period is characterised by frequent changes of temperature and precipitation. The North Atlantic plays a major role as a driver for European climate and is a dominant precipitation source, particularly for the western European and north African realm. Atmospheric pressure gradients over the Atlantic (North Atlantic Oscillation, NAO), Atlantic circulation patterns (Atlantic Multidecadal Oscillation, AMO) or positioning of the Atlantic jet stream have been suggested to be responsible for precipitation patterns across western Europe. However, proxy data provide an inconsistent picture on how precipitation responds to changes in the Atlantic realm such as changes of Atlantic temperature (IRD), atmospheric pressure (NAO), water circulation (AMO) or the jet stream. Here we present a record of speleothem-based winter precipitation amount from Portugal. The record covers most of the Holocene and demonstrates that wetter conditions were synchronous in western and southern Iberia during early and mid Holocene. The record also shows a correlation between increased winter precipitation amount in western Iberia and Atlantic cooling, evidenced by Bond events, between 10 and 4 ka.

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

10.5194/egusphere-egu21-15576 ◽

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

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.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&#160; 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.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 &#64258;ows (i.e. North Iceland Irminger Current, East Greenland Current, Iceland-Scotland over&#64258;ow) 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).&#160;

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Biogeography of acoustic biodiversity of NW Mediterranean coralligenous reefs

Scientific Reports ◽

10.1038/s41598-021-96378-5 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Lucia Di Iorio ◽

Manon Audax ◽

Julie Deter ◽

Florian Holon ◽

Julie Lossent ◽

...

Keyword(s):

Large Scale ◽

Spatial Scales ◽

Western Mediterranean ◽

Ecosystem Functions ◽

Marine Biodiversity ◽

Predator Species ◽

The North ◽

Mediterranean Habitats ◽

Geographical Regions ◽

Nw Mediterranean

AbstractMonitoring the biodiversity of key habitats and understanding the drivers across spatial scales is essential for preserving ecosystem functions and associated services. Coralligenous reefs are threatened marine biodiversity hotspots that are challenging to monitor. As fish sounds reflect biodiversity in other habitats, we unveiled the biogeography of coralligenous reef sounds across the north-western Mediterranean using data from 27 sites covering 2000 km and 3 regions over a 3-year period. We assessed how acoustic biodiversity is related to habitat parameters and environmental status. We identified 28 putative fish sound types, which is up to four times as many as recorded in other Mediterranean habitats. 40% of these sounds are not found in other coastal habitats, thus strongly related to coralligenous reefs. Acoustic diversity differed between geographical regions. Ubiquitous sound types were identified, including sounds from top-predator species and others that were more specifically related to the presence of ecosystem engineers (red coral, gorgonians), which are key players in maintaining habitat function. The main determinants of acoustic community composition were depth and percentage coverage of coralligenous outcrops, suggesting that fish-related acoustic communities exhibit bathymetric stratification and are related to benthic reef assemblages. Multivariate analysis also revealed that acoustic communities can reflect different environmental states. This study presents the first large-scale map of acoustic fish biodiversity providing insights into the ichthyofauna that is otherwise difficult to assess because of reduced diving times. It also highlights the potential of passive acoustics in providing new aspects of the correlates of biogeographical patterns of this emblematic habitat relevant for monitoring and conservation.

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Seasonal Predictability of Wintertime mid-latitude Cyclonic Activity over the North Atlantic and Europe

10.5194/egusphere-egu21-11134 ◽

2021 ◽

Author(s):

Alvise Aranyossy ◽

Sebastian Brune ◽

Lara Hellmich ◽

Johanna Baehr

Keyword(s):

North Atlantic ◽

Large Scale ◽

Jet Stream ◽

Cyclonic Activity ◽

Max Planck ◽

Pressure System ◽

Wind Speeds ◽

Average Lifespan ◽

The North ◽

The North Atlantic

We analyse the connections between the wintertime North Atlantic Oscillation (NAO), the eddy-driven jet stream with the mid-latitude cyclonic activity over the North Atlantic and Europe. We investigate, through the comparison against ECMWF ERA5 and hindcast simulations from the Max Planck Institute Earth System Model (MPI-ESM), the potential for enhancement of the seasonal prediction skill of the Eddy Kinetic Energy (EKE) by accounting for the connections between large-scale climate and the regional cyclonic activity. Our analysis focuses on the wintertime months (December-March) in the 1979-2019 period, with seasonal predictions initialized every November 1st. We calculate EKE from wind speeds at 250 hPa, which we use as a proxy for cyclonic activity. The zonal and meridional wind speeds are bandpass filtered with a cut-off at 3-10 days to fit with the average lifespan of mid-latitude cyclones.&#160;Preliminary results suggest that in ERA5, major positive anomalies in EKE, both in quantity and duration, are correlated with a northern position of the jet stream and a positive phase of the NAO. Apparently, a deepened Icelandic low-pressure system offers favourable conditions for mid-latitude cyclones in terms of growth and average lifespan. In contrast, negative anomalies in EKE over the North Atlantic and Central Europe are associated with a more equatorward jet stream, these are also linked to a negative phase of the NAO.&#160; Thus, in ERA5, the eddy-driven jet stream and the NAO play a significant role in the spatial and temporal distribution of wintertime mid-latitude cyclonic activity over the North Atlantic and Europe. We extend this connection to the MPI-ESM hindcast simulations and present an analysis of their predictive skill of EKE for wintertime months.

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