Significance? 4/18/2017. Cause... Evidence. Significance? Sea Level changes; a variety of types

Transcription

1 Cause... Evidence. Significance? Relatively slow, long term changes with some exceptions 542my Present Significance? Some exceptions to the Relatively slow : The Mediterranean Sea The Messinian Event (~6 5.3my) & the Zanclean Flood Evidence, cause and significance? 1

2 The Messinian is the last Age of the late Miocene. It spans the time between 7.25 my my. A geologic Age is a subdivision of geologic time that divides an epoch into smaller parts. The Messian Event, aka the Messinian Salinity Crisis (MSC), was a geological event during which the Mediterranean Sea experienced partly or nearly complete desiccation/evaporation throughout the latter part of the Messinian age of the Miocene epoch, from ~5.96 to 5.33 my (million years ago), as a result of tectonic collision of Africa & Spain It took only ~2,000yrs to transform the sea into a desert! Mediterranean basin was approximately 1.5km - 2.7km (~5,000 9,000ft) beneath today's sea level. Distribution of Salts recovered by the Glomar Challenger in the 1970 s, and many others since The MSC ended with the Zanclean Flood, when the Atlantic reclaimed the basin. The Zanclean Flood marked the beginning of the Zanclean Age and the end of the Messinian, as water poured in from the Atlantic Ocean through the Strait of Gibraltar to deluge the Mediterranean Basin. Subsidence in the sea floor at the strait allowed water from the Atlantic to pour slowly into the Mediterranean basin for several thousand years, filling just 10%. However the Atlantic Ocean floodwaters filled 90% of the Mediterranean very rapidly likely in less than 2 yrs. SL Rise may have been > 10m/day at it s peak. Geologists call it an Instantaneous Flood. Catastrophic flooding 5.3my BP caused sea levels to rise in Mediterranean by ~10 meters a day, approx 1,000 Amazon rivers (209,000m 3 /sec X 1,000) Relatively slow, long term changes, with some exceptions 542my Present 2

3 Relatively fast, short term changes Milankovitch Cycles 100,000yrs 41,000yrs 26,000 yrs Height above or below present sea level (meters) Today s sea level Height below present sea level (feet) 250, , , ,000 50,000 0 Present Years before present Plateau Phase about 7 8 inches 3

4 Relatively fast, short term changes Relatively fast, short term changes If all ice melts (Greenland & Antarctica) SL rises 212 ft (65m). In last 20,000 yrs, SL has risen ~400ft. Add these together and you get a vertical possibility of 612 ft, equivalent to a 47 story building. From ~20,000 6,000 yrs BP, SL rose from 1 st floor to the 30 th floor. For the last 6,000 yrs, climate was stable, and stayed at the 30 th floor. A Plateau Phase. Recently the elevator started to rise. During last interglacial (the Eemian) the temp was 1 2 degrees C warmer than now, and SL was 6 to 9 m (20 to 30 feet) higher than today. On our current warming trend, all the glaciers and ice sheets will eventually melt, bringing us back to a planetary state that has not existed for 30 my. If this happens, we are heading to the 47 th floor. John Englander ,000 yrs BP, SL rose more than a foot per decade continuously for 4 centuries. Approximately 14,000 yrs BP global sea level rose ~20m, or ~66 feet in about years. Mean rates of sea level rise was ~53 mm/yr, or ~1.7 feet per decade, for 4 centuries. It has been 15 my since CO 2 levels were as high as they are today, just over 400ppm. As a result, global temperatures were ~ 6 degrees C (10 degrees F) warmer and SL was ~ 23-30m ( ft) higher than today. Global Climate Change? Observed and predicted sea level rise. There is a strong consensus that the 2007 IPCC estimates of sea level rise are far too low. Observations in the first 15 yrs of this century support that view. Some estimate by 2150 SL will be 6-12m (20-30ft) higher than today. Ninety-seven percent of climate scientists agree that climatewarming trends over the past century are due to human activities. (IPCC) 4

5 CLIMATE CHANGE: HOW DO WE KNOW? Global sea level rose about 17 centimeters (8 inches) since The rate in the last decade, is nearly double that of the last century. Global surface temperature reconstructions show that the Earth has warmed since Most of this warming has occurred from 1970s, to present, with the 20 warmest years having occurred since 1981 and with all 10 of the warmest years occurring in the past 12 years. Even though the 2000s witnessed a solar output decline resulting in an unusually deep solar minimum in , surface temperatures continue to increase The oceans have absorbed much of this increased heat, with the top 700 meters ( ~2,300 feet) warming ~0.302 degrees Fahrenheit since The Greenland and Antarctic ice sheets have decreased in mass. Between : Greenland lost 150 to 250 cubic kilometers (36 to 60 cubic miles) of ice/year and Antarctica lost about 152 cubic kilometers (36 cubic miles) of ice/yr. Glaciers are retreating almost everywhere around the world including in the Alps, Himalayas, Andes, Rockies, Alaska and Africa. Losing ~2.2mile 3 /yr, 2X as much as 50 yrs ago. Since 1950, the number of record high temperature events in the United States has been increasing, while the number of record low temperature events has been decreasing. Since the Industrial Revolution, the acidity of surface ocean waters has increased by ~30%. The increase is the result of humans emitting more carbon dioxide into the atmosphere and hence more being absorbed into the oceans. The amount of carbon dioxide absorbed by the upper layer of the oceans is increasing by ~2 billion tons per year. Satellite observations reveal that the amount of spring snow cover in the Northern Hemisphere has decreased over the past five decades and that the snow is melting earlier. Ref: IPCC, NOAA, National Research Council (NRC) NASA, National Snow and Ice Data Center, World Glacier Monitoring Service Cities that would be severely effected by a 0.5 meter (or 1.6ft) rise in seal level by 2070 Calcutta, India: 14 million people, $2.0 trillion in assets Guangzhou, China: 10 million people, $3.4 trillion in assets Mumbai, India: 11 million people, $1.6 trillion in assets Miami, Florida: 4.8 million, $3.5 trillion in assets Shanghai, China: 5.5 million people, $1.7 trillion in assets Bangkok, Thailand: 5.1 million people, $1.1 trillion in assets Tianjin, China: 3.8 million people, $1.2 trillion in assets New York, NY: 2.9 million people and $2.1 trillion in assets Ho Chi Minh City, Vietnam: 9.2 million people, $650 billion in assets Dhaka, Bangladesh: 11 million people, $540 billion in assets Ningbo, China: 3.3 million people, $1.1 trillion in assets Tokyo, Japan: 2.5 million people, $1.2 trillion in assets Alexandria, Egypt: 4.4 million people, $650 billion in assets Haiphong, Vietnam:: 4.7million people, $330 billion in assets Amsterdam, Netherlands: 1.4 million people, $843 billion in assets New Jersey Shoreline October

6 The Black Sea, another exception to relatively fast. An extremely rapid shoreline change Present-day Black Sea, a salt water inland sea Black Sea The Bosporus Straight is up to 2 miles wide Sea of Marmara Bathymetry: deep basin in the south, very shallow shelves in the north. The shallow shelves that surround the deeper basin are ~155,000Km 2 Black Sea today (light blue) and 7,600 BP (dark blue) Light blue area is ~155,000 kilometers 2 Source: William Ryan and Walter Pitman,

7 What is 155,000Km 2? Georgia = ~154,000 km 2 Population >10 million The Spread of Humanity ~8,000 yrs BP the planet s population was only ~ 5 million; it s estimated 500,000-1 million lived in the region adjacent to the fresh water lake. The Black Sea was a fresh water lake for much of it s history, over 100,000 yrs. ~8000 BP evaporation caused it to be smaller (Approx ft lower than today). Surrounded by large fertile valleys and floodplains Meanwhile, global sea level was rising. About 7600 years BP (or ~5600BC), the ocean overtopped the ridge at the Bosphorus, and ~60,000 meters 3 /sec of water rushed in at 60mph, 200X Niagara Falls 7

8 A major flood occurred; lake size increased by 30% and rose in height by ~500 feet, lasting <100 days! 60,000 miles 2 or 155,000 kilometers 2 were covered, at a rate of ~1/2 mile/day. People could outrun it, but they couldn t bring all their possessions Evidence: Many salt water marine species of mollusks found directly over fresh water deposits, all ~7,600 yrs old. Immigrants from the Mediterranean. The salt water mollusks on top of fresh water subaerial bottom show an abrupt transition. Mud cracks; some with fill from sand storms with deep sea mud on top of them Fossil plants with deep sea mud on top of them Gravel and sands from river deltas with deep sea mud on top of them Preservation of landforms; sand dunes with perfect morphological shape, found ancient shorelines at 90, 110 & 156 meters (~512 ft) Robert Ballard discovered remains of an ancient structure in Sept 2000 Eventually stories of the flood reached the entire world. Found in writings of Sumerians (Epic of Gilgamesh), Romans, Greeks, Babylonians, Mexicans, Persians, Ireland. Sea Level Changes Why Important? SL Rise: South Florida Case Study In Summary: Sea level changes have been happening throughout geologic time, and will continue to do so. There are several different types, causes and time orders The more we know about all of them, the better off we are Currently most places in the world are experiencing a relatively rapid rise in sea level, and human infrastructure is in the way. The currently rise in sea level is mostly likely related to human activities We need to start planning and preparing for the inevitable, there are no signs that the current rise in sea level is going to stop. 8

9 Review Questions How do scientists know that sea level was at times meters higher than today? What is the evidence and when did this happen? A major drop in global sea level is associated with mass extinction in the geologic past. How did scientists figure out that the Mediterranean Sea dried out and turned into a desert in the Messinian Age? How long did this take? What is the Zanclean Flood? Approximately 90% of the Mediterranean Sea filled up very rapidly ~5.33MY BP. How long do scientists estimate this took? What are Milankovictch Cycles and what are the significance of them? If global sea level rises by 0.5 meters in the next 70 years, in general who would be effected? List several things that we can measure that strongly indicate we are experiencing global climate change. Describe what happened in the Black Sea approximately 7,000 YR BP. What is the evidence for this? 9