Meltwater pulse 1A (MWP1a) is the name used by

Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million year ...

geologist A geologist is a scientist who studies the solid, liquid, and gaseous matter that constitutes Earth and other terrestrial planets, as well as the processes that shape them. Geologists usually study geology, earth science, or geophysics, althou ...

paleoclimatologist Paleoclimatology ( British spelling, palaeoclimatology) is the study of climates for which direct measurements were not taken. As instrumental records only span a tiny part of Earth's history, the reconstruction of ancient climate is important t ...

s, and

oceanographer Oceanography (), also known as oceanology and ocean science, is the scientific study of the oceans. It is an Earth science, which covers a wide range of topics, including ecosystem dynamics; ocean currents, waves, and geophysical fluid dynamic ...

s for a period of rapid

post-glacial The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togethe ...

sea level rise Globally, sea levels are rising due to human-caused climate change. Between 1901 and 2018, the globally averaged sea level rose by , or 1–2 mm per year on average.IPCC, 2019Summary for Policymakers InIPCC Special Report on the Ocean and Cr ...

, between 13,500 and 14,700 calendar years ago, during which global

sea level Mean sea level (MSL, often shortened to sea level) is an average surface level of one or more among Earth's coastal bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical datuma standardis ...

rose between and in about 400–500 years, giving mean rates of roughly /yr. Meltwater pulse 1A is also known as catastrophic rise event 1 (CRE1) in the Caribbean Sea.Blanchon, P., and J. Shaw (1995) ''Reef drowning during the last deglaciation: Evidence for catastrophic sea-level rise and ice-sheet collapse.'' Geology. 23(1):4-8. The rates of sea level rise associated with meltwater pulse 1A are the highest known rates of post-glacial,

eustatic sea level The eustatic sea level is the distance from the center of the earth to the sea surface. An increase of the eustatic sea level can be generated by decreasing glaciation, increasing spreading rates of the mid-ocean ridges or more mid-oceanic ridges. ...

rise. Meltwater pulse 1A is also the most widely recognized and least disputed of the named, postglacial meltwater pulses. Other named, postglacial meltwater pulses are known most commonly as ''meltwater pulse 1A0'' (''meltwater pulse 19ka''), '' meltwater pulse 1B'', ''

meltwater pulse 1C The early Holocene sea level rise (EHSLR) was a significant jump in sea level by about during the early Holocene, between about 12,000 and 7,000 years ago, spanning the Eurasian Mesolithic. The rapid rise in sea level and associated climate ...

'', ''meltwater pulse 1D'', and ''meltwater pulse 2''. It and these other periods of rapid sea level rise are known as ''meltwater pulses'' because the inferred cause of them was the rapid release of

meltwater Meltwater is water released by the melting of snow or ice, including glacial ice, tabular icebergs and ice shelves over oceans. Meltwater is often found in the ablation zone of glaciers, where the rate of snow cover is reducing. Meltwater ca ...

into the oceans from the collapse of continental

ice sheet In glaciology, an ice sheet, also known as a continental glacier, is a mass of glacial ice that covers surrounding terrain and is greater than . The only current ice sheets are in Antarctica and Greenland; during the Last Glacial Period at La ...

Sea level and timing

Postglacial Sea level Rise Curve and Meltwater Pulses (MWP)

Meltwater pulse 1A occurred in a period of rising sea level and rapid climate change, known as '' Termination I'', when the retreat of continental ice sheets was going on during the end of the last

ice age An ice age is a long period of reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages and gre ...

. Several researchers have narrowed the period of the pulse to between 13,500 and 14,700 calendar years ago with its peak at about 13,800 calendar years ago. The start of this

event coincides with or closely follows the abrupt onset of the Bølling-Allerød (B-A)

interstadial Stadials and interstadials are phases dividing the Quaternary period, or the last 2.6 million years. Stadials are periods of colder climate while interstadials are periods of warmer climate. Each Quaternary climate phase is associated with a Ma ...

and warming in the NorthGRIP ice core in

Greenland Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an island country in North America that is part of the Kingdom of Denmark. It is located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland ...

at 14,600 calendar years ago.Blanchon, P. (2011) ''Meltwater Pulses.'' In: Hopley, D. ed., pp. 683-690, ''Encyclopedia of Modern Coral Reefs: Structure, form and process.'' Springer-Verlag Earth Science Series, Springer Science, New York. During meltwater pulse 1A, sea level is estimated to have risen at a rate of /yr. This rate of sea level rise was much larger than the rate of

current sea level rise Globally, sea levels are rising due to human-caused climate change. Between 1901 and 2018, the globally averaged sea level rose by , or 1–2 mm per year on average.IPCC, 2019Summary for Policymakers InIPCC Special Report on the Ocean and Cryo ...

, which has been estimated to be in the region of /yr.

Source(s) of meltwater pulse 1A

The source of meltwaters for meltwater pulse 1A and the path they took remains a matter of continuing controversy. The technique of ''sea-level fingerprinting'' has been used to argue that major contribution to this meltwater pulse came from Antarctica.Bassett, S.E., Milne, G.A., Mitrovica, J.X., Clark, P.U., 2005. ''Ice sheet and solid Earth influences on far-field sea-level histories.'' Science 309:925–928.Deschamps, P., N. Durand, E. Bard, B. Hamelin, G. Camoin, A.L. Thomas, G.M. Henderson, J. Okuno, and Y. Yokoyama, Yusuke (2012) ''Ice-sheet collapse and sea-level rise at the Bolling warming.'' Nature. 483(7391):559-564. On the other hand, other studies have argued for the

Laurentide Ice Sheet The Laurentide Ice Sheet was a massive sheet of ice that covered millions of square miles, including most of Canada and a large portion of the Northern United States, multiple times during the Quaternary glacial epochs, from 2.58 million year ...

in North America being the dominant source of this meltwater pulse.Tarasov, L., and W.R. Peltier (2006) ''A calibrated deglacial drainage chronology for the North American continent: evidence of an Arctic trigger for the Younger Dryas.'' Quaternary Science Reviews. 25:659–688.Bentley, M.J., C.J. Fogwill, A.M. Le Brocq, A.L. Hubbard, D.E. Sugden, T.J. Dunai, and S.P.H.T. Freeman (2010) ''Deglacial history of the West Antarctic Ice Sheet in the Weddell Sea embayment: constraints on past ice volume change.'' Geology. 38(5):411-414. The magnitude of eustatic sea level rise during meltwater pulse 1A is a significant indicator of its sources. A eustatic sea level rise around could plausibly be solely explained by a North American source. On the other hand, if the eustatic sea level rise was larger and closer to , a significant fraction of the meltwater that caused it likely came from the Antarctic Ice Sheet.Clark, P.U., R.B. Alley, L.D. Keigwin, J.M. Licciardi, S. Johnsen, and H. Wang (1996) ''Origin of the first global meltwater pulse following the last glacial maximum.'' Paleoceanography. 11(5):563-577.Carlson, A.E., D.J. Ullman, F.S. Anslow, S. Faron, F. He, P.U. Clark, Z. Liu, and B.L. Otto-Bliesner (2012) ''Modeling the surface mass-balance response of the Laurentide ice sheet to Bolling warming and its contribution to Meltwater Pulse 1A.'' Earth and Planetary Science Letters. 315-316:24-29. Ice sheet modelling work suggests that the abrupt onset of the Bølling-Allerød (B-A) may have triggered the separation of the Cordilleran ice sheet and

(and the opening of the

ice-free corridor The settlement of the Americas began when Paleolithic hunter-gatherers entered North America from the North Asian Mammoth steppe via the Beringia land bridge, which had formed between northeastern Siberia and western Alaska due to the lowering of ...

) producing a major contribution to meltwater pulse 1A from the North American ice sheet. A contribution of around in 350 years to meltwater pulse 1A from the

Antarctic Ice Sheet The Antarctic ice sheet is one of the two polar ice caps of Earth. It covers about 98% of the Antarctic continent and is the largest single mass of ice on Earth, with an average thickness of over 2 kilometers. It covers an area of almost and ...

could have been caused by

Southern Ocean The Southern Ocean, also known as the Antarctic Ocean, comprises the southernmost waters of the World Ocean, generally taken to be south of 60° S latitude and encircling Antarctica. With a size of , it is regarded as the second-smal ...

warming. Besides the North American and Antarctic Ice Sheet, the Fennoscandian and Barents Sea Ice Sheet could also have contributed to meltwater pulse 1A.

Mississippi River meltwater flood events

In the case of the

Mississippi River The Mississippi River is the List of longest rivers of the United States (by main stem), second-longest river and chief river of the second-largest Drainage system (geomorphology), drainage system in North America, second only to the Hudson B ...

, the sediments of the Louisiana continental shelf and slope, including the Orca Basin, within the

Gulf of Mexico The Gulf of Mexico ( es, Golfo de México) is an ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of the United ...

preserve a variety of paleoclimate and paleohydrologic proxies.Biller, N.B. (2012
''Evidence for Meltwater Pulse 1a in the Gulf of Mexico based on radiogenic isotopes of leachates.''
Undergraduate Thesis, Department of Geological Sciences University of Florida, Tallahassee, Florida. 39 pp.Meckler, A.N., C.J. Schubert, P.A. Hochuli, B. Plessen, D. Birgel, B.P. Flower, K.-U. Hinrichs, and G.H. Haug (2008
''Glacial to Holocene terrigenous organic matter input to sediments from Orca Basin, Gulf of Mexico.''
Earth and Planetary Science Letters 272 (2008) 251–263.Marchitto, T.M. K.-Y. Wei (1995
''History of Laurentide meltwater flow to the Gulf of Mexico during the last deglaciation, as revealed by reworked calcareous nannofossils''
Geology. 23(9):779-782. They have been used to reconstruct both the duration and discharge of Mississippi River meltwater events and superfloods for the Late glacial and postglacial periods, including the time of meltwater pulse 1A.Kennett, P., K. Elmstrom, and N. Penrose (1985) ''The last deglaciation in orca basin, gulf of Mexico: High-resolution planktonic foraminiferal changes.'' Palaeogeography, Palaeoclimatology, Palaeoecology. 50(1):189-216.Aharon, P. (2003) ''Meltwater Flooding Events in the Gulf of Mexico Revisited: Implications for Rapid Climate Changes During the Last Deglaciation. Paleoceanography.'' 18(4):3-1 to 3-13.Aharon, P. (2006) ''Entrainment of meltwaters in hyperpycnal flows during deglaciation superfloods in the Gulf of Mexico.'' Earth and Planetary Science Letters. 241:260–270. The chronology of flooding events found by the study of numerous cores on the Louisiana continental shelf and slope are in agreement that the timing of meltwater pulses. For example, meltwater pulse 1A in the Barbados coral record matches quite well with a group of two Mississippi River meltwater flood events, MWF-3 (12,600 radiocarbon years ago); and MWF-4 (11,900 radiocarbon years ago). In addition, meltwater pulse 1B in the Barbados coral record matches a cluster of four Mississippi River superflood events, MWF-5, that occurred between 9,900 and 9,100 radiocarbon years ago. The discharge of water coursing down the Mississippi River during meltwater flood MWF-4 is estimated to have been 0.15 sverdrups (million cubic meters per second). This discharge is roughly equivalent to 50% of the global discharge during meltwater pulse 1A. This research also shows that the Mississippi meltwater flood MWF-4 occurred during the

Allerød oscillation The Allerød oscillation ( da, Allerødtiden) was a warm and moist global interstadial that occurred c.13,900 to 12,900 BP, nearly at the end of the Last Glacial Period. It raised temperatures in the northern Atlantic region to almost present-da ...

and had largely stopped before the beginning of the

Younger Dryas The Younger Dryas (c. 12,900 to 11,700 years BP) was a return to glacial conditions which temporarily reversed the gradual climatic warming after the Last Glacial Maximum (LGM, c. 27,000 to 20,000 years BP). The Younger Dryas was the last stag ...

stadial. The same research found an absence of meltwater floods discharging into the Gulf of Mexico from the Mississippi River for a period of time following meltwater flood MWF-4, known as the ''cessation event'', that corresponds with the Younger Dryas stadial. Prior to Mississippi River meltwater flood MWF-3, two other Mississippi River meltwater floods, MWF-2 and MWF-1, have been recognized. The first of these, MWF-1, consists of three separate, but closely spaced events that occurred between 16,000 and 15,450 (MWF-1a); 15,000 and 14,700 (MWF-1b); and 14,460 and 14,000 (MWF-1c) radiocarbon years ago. Each of these flood events had a discharge of about 0.08 to 0.09 sverdrups (million cubic meters per second). Collectively, they appear to be associated with meltwater pulse 1A0. Later, one of the largest of the Mississippi River meltwater floods, MWF-2, occurred between 13,600 and 13,200 radiocarbon years ago. During its 400 radiocarbon year duration, the maximum discharge of Mississippi River meltwater flood MWF-2 is estimated to have been between 0.15 and 0.19 sverdrups. Despite the large size of Mississippi River meltwater flood MWF-2, it is not known to be associated with an identifiable meltwater pulse in any sea level record.

Antarctica iceberg discharge events

With respect to the Antarctic Ice Sheet, research by Weber and others constructed a well-dated, high-resolution record of the discharge of icebergs from various parts of the Antarctic Ice Sheet for the past 20,000 calendar years, They constructed this record from variations in the amount of iceberg-rafted debris versus time and other environmental proxies in two cores taken from the ocean bottom within Iceberg Alley of the

Weddell Sea The Weddell Sea is part of the Southern Ocean and contains the Weddell Gyre. Its land boundaries are defined by the bay formed from the coasts of Coats Land and the Antarctic Peninsula. The easternmost point is Cape Norvegia at Princess Martha ...

. The sediments within Iceberg Alley provide a spatially integrated signal of the variability of the discharge of icebergs into the marine waters by the Antarctic Ice Sheet because it is a confluence zone in which icebergs calved from the entire Antarctic Ice Sheet drift along currents, converge, and exit the Weddell Sea to the north into the

Scotia Sea The Scotia Sea is a sea located at the northern edge of the Southern Ocean at its boundary with the South Atlantic Ocean. It is bounded on the west by the Drake Passage and on the north, east, and south by the Scotia Arc, an undersea ridge and ...

.Weber, M.E., P.U. Clark, G. Kuhn, A. Timmermann, D. Sprenk, R. Gladstone, X. Zhang, G. Lohmann, L. Menviel, M.O. Chikamoto, T. Friedrich, and C. Ohlwein (2014) ''Millennial-scale variability in Antarctic ice-sheet discharge during the last deglaciation.'' Nature. 510(7503):134–138. Between 20,000 and 9,000 calendar years ago, this study documented eight well-defined periods of increased iceberg

Ice calving Ice calving, also known as glacier calving or iceberg calving, is the breaking of ice chunks from the edge of a glacier.Essentials of Geology, 3rd edition, Stephen Marshak It is a form of ice ablation or ice disruption. It is the sudden release ...

and discharge from various parts of the Antarctic Ice Sheet. The highest period of discharge of icebergs recorded in both cores is known as AID6 (Antarctic Iceberg Discharge event 6). AID6 has a relatively abrupt onset at about 15,000 calendar years ago. The peak interval of greatest iceberg discharge and flux from the Antarctic Ice sheet for AID6 is between about 14,800 and 14,400 calendar years ago. The peak discharge is followed by gradual decline in flux until 13,900 calendar years ago, when it abruptly ends. The peak period of iceberg discharge for AID6 is synchronous with the onset of the Bølling interstadial in the Northern Hemisphere meltwater pulse 1A. Weber and others estimated that the flux of icebergs from Antarctica during AID6 contributed a substantial (at least 50%) to the global mean sea-level rise that occurred during meltwater pulse 1A.Clark, P.U., J.X. Mitrovica,, G.A. Milne, and M.E. Tamisiea (2002) ''Sea-level fingerprintingas a direct test for the source of global meltwater pulse IA.'' Science 295, 2438–2441. These icebergs came from the widespread retreat of the Antarctic Ice Sheet at this time, including from the Mac Robertson Land region of the

East Antarctic Ice Sheet The East Antarctic Ice Sheet (EAIS) is one of two large ice sheets in Antarctica, and the largest on the entire planet. The EAIS lies between 45° west and 168° east longitudinally. The EAIS holds enough ice to raise global sea levels by and ...

; the

Ross Sea The Ross Sea is a deep bay of the Southern Ocean in Antarctica, between Victoria Land and Marie Byrd Land and within the Ross Embayment, and is the southernmost sea on Earth. It derives its name from the British explorer James Clark Ross who ...

sector of the

West Antarctic Ice Sheet The Western Antarctic Ice Sheet (WAIS) is the segment of the continental ice sheet that covers West Antarctica, the portion of Antarctica on the side of the Transantarctic Mountains that lies in the Western Hemisphere. The WAIS is classified as ...

; and the

Antarctic Peninsula The Antarctic Peninsula, known as O'Higgins Land in Chile and Tierra de San Martín in Argentina, and originally as Graham Land in the United Kingdom and the Palmer Peninsula in the United States, is the northernmost part of mainland Antarctic ...

Ice Sheet.Deschamp, P., N. Durand, E. Bard, B. Hamelin, G. Camoin, A.L. Thomas, G. M. Henderson, J. Okuno, and Y. Yokoyama (2012) ''Ice-sheet collapse and sea-level rise at the Bølling warming 14,600 years ago.'' Nature. 483(7391):559-64.

References

External links

* Gornitz, V. (2007
Sea Level Rise, After the Ice Melted and Today
Science Briefs, NASA's Goddard Space Flight Center. (January 2007) * Gornitz, V. (2012
The Great Ice Meltdown and Rising Seas: Lessons for Tomorrow
Science Briefs, NASA's Goddard Space Flight Center. (June 2012) * Liu, J.P. (2004
Western Pacific Postglacial Sea-level History.River, Delta, Sea Level Change, and Ocean Margin Research Center
Marine, Earth and Atmospheric Sciences, North Carolina State University, Raleigh, NC. * Usai, Luigi (2021-03-18).

' (in Italian). {{ISBN, 979-8-7238-5624-0. Glaciology Oceanography Paleoclimatology Sea level