Significant finding: Study shows why Europe’s climate varied over the past 3000 years

From CARDIFF UNIVERSITY and the “motion from the ocean makes or breaks English vineyards” department.

Ocean floor mud reveals secrets of past European climate
Samples of sediment taken from the ocean floor of the North Atlantic Ocean have given researchers an unprecedented insight into the reasons why Europe’s climate has changed over the past 3000 years.

In this 1677 painting by Abraham Hondius, ‘The Frozen Thames, looking Eastwards towards Old London Bridge’, people are shown enjoying themselves on the ice during a “frost fair”.

From the warmer climates of Roman times when vineyards flourished in England and Wales to the colder conditions that led to crop failure, famine and pandemics in early medieval times, Europe’s climate has varied over the past three millennia.

For the first time, researchers have been able to pinpoint why this occurs, and the answer lies far out at sea in the North Atlantic Ocean.

Scientists from Cardiff University have studied fossil remains of shell-bearing plankton and grains buried in sediments from the North Atlantic to determine what conditions were like in the ocean on timescales of 10-20 years over a 3000-year period.

Writing in the journal Nature Communications, the researchers found that during cold periods, icy-cold waters from the Arctic would flow south into the Labrador Sea in the North Atlantic, altering the ocean circulation patterns and potentially slowing down the currents that transport heat to Europe.

Sediment core location and regional ocean circulation. Red arrows indicate the warm and salty waters originating from the North Atlantic Current (NAC) flowing west as the Irminger Current (IC). Cold and fresh polar waters from the East Greenland Current (EGC) are indicated by the dark blue arrows, the dotted blue arrow indicates the West Greenland Current. The locus of Labrador Sea Water (LSW) formation is indicated by the blue spiral and the white arrows indicate the spreading of LSW through intermediate depths to the Irminger and Iceland Basins and to the lower latitudes. New reconstructions used in this study are shown in black and location of published proxy records presented in Figs. 2 and 3 are colour-coded and labelled in grey. Unlabelled red diamonds show the locations of the deep sea corals from ref. 42. Bathymetric basemap made using ODV (Schlitzer, R., Ocean Data View, https://odv.awi.de, 2015)

“Seawater can hold more heat than the air, so it can act like a large storage heater. As such, the oceans can store and transport vast amounts of heat and are hence key for modulating our climate. Interestingly, we find changes in the circulation and distribution of waters in the North Atlantic which would have impacted the transport of heat to Europe,” explains Dr Paola Moffa-Sanchez, from Cardiff University’s School of Earth and Ocean Sciences who led the study.

Using the data contained in tiny marine fossil plankton shells and sediment grains, the researchers were able to build a record of past ocean conditions and link this with key historical records where the European climate was known to have been, on average, colder or warmer.

Microfossils from marine sediments Credit: Hannes Grobe/AWI

For example, the researchers were able to link a slowing down of the North Atlantic currents with a notorious cold period, often called the Little Ice Age, which ensconced Europe between 1300 to about 1850. Extensive cold winters were depicted in European paintings at the time, such as the famous ice skaters on the Thames in London.

Similarly, the researchers identified another slowing down of the North Atlantic currents at the same time as an extreme cold period in the 6th century, which led to widespread crop failures and famines worldwide. It is also believed that the consequences of this cold period perhaps contributed to the spreading of the Plague of Justinian — one of the deadliest pandemics in human history that took the lives of an estimated 25 to 50 million people across the world.

“Our study shows the importance of the ocean on our climate and how this has naturally varied in the past when ocean measurements were not available. We’ve been able to link our results to historical records and provide an explanation behind some of the significant effects that the climate has had on the European population,” explains Professor Ian Hall.

Schematic timeline highlighting historic records of climate variability in Europe. Red and blue lines denote the time-span for the evidence for warm and cold periods, respectively. Ages are in years BP (black) and years CE/BCE (grey). This information has been extracted from several publications indicated by the superscript in the annotations: 1. ref. 68 and references herein; 2. ref. 69; 3. ref. 70 and references herein; 4. ref. 71 ; 5. ref. 72; 6. ref. 73; 7. ref. 74 The cold and warm periods established through the glacier advances and retreats used as a framework for the study of these centennial events49 are found within the axis of the timeline and highlighted by the vertical grey bars (consistent with Figs. 2 and 3). The marine paleoceanographic reconstructions for the LSW and Subpolar Gyre (SPG) presented in Fig. 3 are represented in blue and pink horizontal bars indicating time intervals below and above average values of the records for the last 3000 years for weaker and stronger LSW/SPG, respectively. For more information on the agreement with terrestrial proxy records and historical events see Supplementary Fig. 4

“Recently, because of our human influenced warmer climate, the Atlantic is receiving more freshwater from melting Arctic ice, which is in turn affecting the movement of the waters in the North Atlantic. Future changes in ocean circulation are likely to be felt within the pattern of climate change in Europe.”

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The paper: http://ift.tt/2iJCaJh (open access)

North Atlantic variability and its links to European climate over the last 3000 years

Abstract

The subpolar North Atlantic is a key location for the Earth’s climate system. In the Labrador Sea, intense winter air–sea heat exchange drives the formation of deep waters and the surface circulation of warm waters around the subpolar gyre. This process therefore has the ability to modulate the oceanic northward heat transport. Recent studies reveal decadal variability in the formation of Labrador Sea Water. Yet, crucially, its longer-term history and links with European climate remain limited. Here we present new decadally resolved marine proxy reconstructions, which suggest weakened Labrador Sea Water formation and gyre strength with similar timing to the centennial cold periods recorded in terrestrial climate archives and historical records over the last 3000 years. These new data support that subpolar North Atlantic circulation changes, likely forced by increased southward flow of Arctic waters, contributed to modulating the climate of Europe with important societal impacts as revealed in European history.

Data availability

The data sets generated during the current study are available through the NOAA climate data centre (http://ift.tt/2A8PT5Q) and available from the corresponding author.

via Watts Up With That?

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November 27, 2017 at 06:53AM

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