H1 (paleoclimate)

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H1 is the second Heinrich event of the last glacial period . It took place between 16,000 and 13,000 BC even before the beginning of the late glacial Meiendorf interstadial . Chr. Instead.

characterization

H1 is characterized by a decrease in the δ 18 O values from -40 to a minimum of -43 ‰ (determined using ice cores in Greenland ) and a decrease in the atmospheric δ 13 C values from -6.4 to -6.7 ‰ .

The concentrations of the greenhouse gases carbon dioxide and methane rose steadily during the H1 stage, as did the deuterium concentration (measured in the ice of the Antarctic ).

The H1-sedimentary layers are characterized by a very high proportion of from ice and icebergs verfrachteten components ( engl. Ice rafted detritus or abbreviated IRD ) from which up to 100% can make the sediment. The concentration of minerogenic fragments with a grain diameter of> 150 or 180 to 3000 μ (fine to coarse sand) can be up to 5500 grains / g. The proportion of fragments containing carbonate is also very high and can make up up to 25% of the sediment. Foraminifera show a clear minimum in H1 layers.

In the oceans of the southern hemisphere , the onset of H1 resulted in a significantly increased flow of opal , which indicates a surge of deep water.

Geographical distribution

The H1 sediment layer encountered in drill samples is arranged in the North Atlantic between Newfoundland and Ireland along an approximately 1500 km wide, west-eastern band that sweeps over at about 40 to 55 ° north latitude. Practical This distribution follows the course of the North Atlantic Current (Engl. North Atlantic Current or NAC ). Ruddiman (1977) referred to this belt as the IRD belt . Somewhat separately, the H1 location could also be found off southern Portugal , off Rockall and in the Hudson Strait .

The area of the H1 location is around 1 million square kilometers. The thickness of the H1 layer can vary between 2.5 and 32 centimeters, with the deposit maximum in the middle of the Atlantic at 45 ° north latitude and 32 ° west longitude. The sedimentation rates vary between 0.04 and 0.26 millimeters / year. Assuming an average layer thickness of 10 centimeters, 100,000 cubic kilometers of glacial sediment were entered in the North Atlantic, practically identical to the volume found for H3 . Events H2 and H4 were much more significant and about three times as severe.

Based on the introduced sediment volume, it is possible to indirectly infer the associated amount of meltwater. Dowdeswell et al. (1995) estimate 140,000 to 1.4 million cubic kilometers of meltwater that flowed into the North Atlantic over a period of 250 to 1250 years, causing the sea ​​level to rise by 0.39 to 3.9 meters.

stratigraphy

The H1 stage occurred towards the end of MIS 2 , a significant de-icing phase ( deglaciation ) of the last glacial period. This is immediately followed by the Dansgaard-Oeschger event DO1 , which leads to the Meiendorf interstadial of the late glacial.

Temporal position

Temporal classification of H1 during the last 47,500 years of geological history

The H1 stadial extends over the period 16,000 to 13,000 BC. Its temperature minimum was between 14,000 and 13,700 BC. Run through. Sidney Hemming (2004) settles the latter a little earlier at 14,800 BC. Chr. In the drill core V23-81, for example, the H1 layer covers the period 15,000 to 13,500 radiocarbon years or, calibrated with CalPal, 16,000 to 14,490 BC. The temperature minimum, characterized by a maximum input of almost 2000 grains / g, is in this case 14,200 radiocarbon years or 15,478 BC. In general, the dates made so far for the lower limit of H1 vary between 14,330 and 14,998 (15,555 and 16,299 BC) and for the upper limit between 13,190 and 13,860 radiocarbon years (14,171 and 15,146 BC). The duration of H1 measured in the drill cores can vary from 208 to 1370 years.

Explanation

As an explanation of the H1 stage, J. Alvarez-Solas et al. (2011) cite the following chain of events:

  • The Fennoscan Ice Sheet began from 18,000 BC. To melt away. Around 16,000 BC This had already been reduced to the highlands of the Scandinavian Caledonids and the British Ice Sheet was only present in the far north-east of Scotland .
  • Due to the melting of the ice sheets, an enormous amount of fresh water was released into the North Sea. This entry led to a sea level rise of around 2 meters over a period of 1000 years.
  • The formation of was the freshwater input North Atlantic Deep Water (Engl. North Atlantic Deep Water or NADW ) disturbed severe or reduced and also the meridional overturning circulation in the Atlantic (English. Atlantic meridional overturning circulation , or AMOC ) was overall weakened.
  • As a result, a clear halocline developed in the North Atlantic and the water masses below the surface (depth range 550 to 1050 meters) warmed up.
  • The Labrador ice shelf then began to break apart and sent an iceberg armada into the open sea. Furthermore, the elimination of the ice shelf belt, which had previously served as a back-up, now led to ice advances in the Laurentide Ice Sheet (English ice flow surges ) that calved in the Labrador Sea .

The sediment load of the ice shelf and the ice advances is ultimately responsible for the formation of the H1 layers. Geochemical analyzes of the rock fragments show a relatively narrowly defined area on the Hudson Strait (Labrador and Baffin Bay ) as the area of ​​origin. The renewed entry of meltwater also set in motion feedback to the NADW and AMOC.

Individual evidence

  1. ↑ Gwiazda, RH, SR Hemming and WS Broecker: Tracking the sources of icebergs with lead isotopes: The provenance of ice-rafted debris in Heinrich layer 2 . In: Paleoceanography . tape 11 , no. 1 , 1996, p. 77-93 .
  2. ↑ Broecker, W. et al .: Origin of the northern Atlantic's Heinrich events . In: Clim. Dyn. Band 6 , 1992, pp. 265-273 .
  3. ↑ Bond, GC et al .: The North Atlantic's 1 - 2 kyr climate rhythm: Relation to Heinrich events, Dansgaard / Oeschger cycles and the little ice age, in: Mechanisms of Global Climate Change at Millennial Time Scales . In: PU Clark, RS Webb and LD Keigwin (eds.): Geophys. Monogr. Ser. tape 112 . Washington DC 1999, p. 35-68, AGU .
  4. ↑ Ruddiman, WF: Late Quaternary deposition of ice-rafted sand in the subpolar North Atlantic (lat 40 to 65 ° N) . In: Geol. Soc. At the. Bull. Band 88 , 1977, pp. 1813-1827 .
  5. ↑ Dowdeswell, JA, MA Maslin, JT Andrews and IN McCave: Iceberg production, debris rafting, and the extent and thickness of Heinrich layers (H-1, H-2) in North Atlantic sediments . In: Geology . tape 23 , 1995, pp. 301-304 .
  6. ↑ a b Hemming, SR: Heinrich events: massive late Pleistocene detritus layers of the North Atlantic and their global climate imprint . In: Rev. Geophys. tape 42 , 2004, doi : 10.1029 / 2003RG000128 .
  7. ↑ Bond, G. et al .: Evidence for massive discharges of icebergs into the North Atlantic Ocean during the last glacial period . In: Nature . tape 360 , 1992, pp. 245-249 .
  8. ↑ Alvarez-Solas, J. et al .: Heinrich event 1: an example of dynamical ice-sheet reaction to oceanic changes . In: Climate of the Past . tape 7 , 2011, p. 1297-1306 .