Unit 1: Introduction to Marine Geology/Geological Oceanography PDF

Unit 1. Introduction to Marine Geology/ Geological Oceanography Unit Outline ▪ Introduction of the course ▪ Definitions of Marine Geology, Geological Oceanography and Paleoceanography ▪ History of Geological Oceanography ▪ Tools of Geological Oceanography Learning Objec...

Unit 1. Introduction to Marine Geology/ Geological Oceanography Unit Outline ▪ Introduction of the course ▪ Definitions of Marine Geology, Geological Oceanography and Paleoceanography ▪ History of Geological Oceanography ▪ Tools of Geological Oceanography Learning Objectives to understand the scope of marine geology, geological oceanography and paleoceanography, to know their history and understand the tools used by them 1. Marine Geology and Geological Oceanography Science concerned with the character and history of the part of the Earth covered by seawater. From coastal (beach, lagoons, estuaries, salt marshes) to the depths (abyssal plains and trenches) Processes shaping ocean floor, water and climate  However, we don’t restrict ourselves to only what’s below the water: We also look at uplifted marine sediments, ophiolites, plate tectonics, paleoclimate – Kuenen, : “No Geology without Marine Geology” Think of an Ocean as a … punch bowl: In this course we will be looking both at: - Bowl = ocean basins shaped by the plate tectonics, and modified by weathering, erosion and deposition of sediments - Punch= water + dissolved and settling particles, the latter - non-living (e.g. a grain of silt) or living (a bacterium, or a whale)  Marine Geology vs. Geological Oceanography Often used interchangeably Other times – used to distinguish, depending on: 1. where you come from: ▪ geologists interested in oceans vs. oceanographers interested in geological processes 2. what are your interests: ▪ Marine geology: ocean as a place where geology happens: ▪ plate tectonics, volcanoes, earthquakes minerals, rocks, terrigenous sediments ▪ Geological oceanography: ocean as a place where oceanography happens: ▪ physical, chemical and biological processes = biogeochemistry, which affects geology (precipitation of minerals, sedimentation, diagenesis), and climate 3. What are the time-scales of interest: ▪ Geological oceanography is primarily interested in the present (+recent and near future) – modern sedimentation, coastal processes, biogeochemical cycles and climate ▪ Marine geology expands its grasp further back in time– oceanographic processes becoming old enough to become the domain of geologists, ▪ Even so, most marine geology limited to ages of less than ca. 175 mln yrs. Why? (see the next slide) Marine Geology vs. Land Geology Marine geologist are often looked down by land geologists because: - historically land is where most geology has beenk done (why? – think of the logistics of doing geology in both places …)mucheasyeronland - because there is very little seafloor in the ocean b older than the very end of Jurassic - why? Other differences of marine from land geologists: Different access => need for different tools: Marine geologists rely much more on: - less on direct sampling => much more difficult and expensive. - more on remote-sensing (air-gun arrays, multi- beam technology, satellite sensors and underwater vehicles: (towed, ROVs, AUVs, and submersibles)  Geological Oceanographers vs. other Oceanographers Geological oceanographers are looked down by other oceanographers too: at the bottom of the pecking order: physical oceanographers biological and chemical oceanographers geological oceanographers Consolation: that only holds for the present - for the past (and the future)- PALEOCEANOGRAPHY RULES!  Paleoceanography Paleoceanography: the study of the history of the oceans in the geologic past with regard to circulation, chemistry, biology, geology and patterns of sedimentation and biological productivity. Provides the (geological) time dimension to current physical, chemical and biological oceanography Critically important to climatology and prediction of the future climate – identifying important elements of the climate in the past (climate proxies in sediments and fossils!) allows to test the climate models of the future! 2. History of Geological Oceanography Herodotus’ map of the known world around 450 BCE—the Mediterranean Sea surrounded by the landmasses known as Europa, Asia, and Libya. Courtesy of MEER  Early exploration stage: 1. The circumnavigation by HMS Beagle (1831-1836) Charles Darwin © National Library of Medicine thewatersassuchmostlyused velutionDidntstudy sjustamodeotfravel 5Yeartrip Route of the HMS Beagle. 2. Polar research: Ships “Erebus” and “Terror”: did well under James Ross in Antarctica - depth soundings along the way max.”14,450 feet” Later, under Franklin, looking for the North-West Passage - not so well …  3. The first oceanographic expedition Challenger: 1872-76 Courtesy of Steve Nicklas, NOS, NGS/NOAA Sir John Murray – “father of marine geology”: - Recognized major types of sediments, deep-sea oozes formation, plankton assemblages - But didn’t dispel the myth of the deep ocean as a tranquil place with uninterrupted sedimentation  Then … not much happened in the next 70 years: - Wegener (continental drift) was laughed out - oceans were left to the biologists... - oceanography was (and still is) prohibitively expensive - So where to find the money? Well, link the research to national interests or national pride (a precursor of the space race in the 1960ties …) Restoring the German pride (after the Great War defeat): a lot of quality acoustic profiling in the Atlantic: c ofthereloseinthewartobouncebacktheystartedoceanresurch sentoutintotheocean therate eaauencyswere theywouldcomebackwouldgiveusapictureoftheoceanfloorsonar Morphological West-to-East Profile of the North Atlantic Ocean. Source: Deutsche Atlantische Expedition auf dem Forschungs- und Vermessungsschiff "Meteor", Vol. 2: Hans Maurer, Die Echolotungen des "Meteor", Berlin/Leipzig, de Gruyter 1933, supplement  Then: WWII happened: Whentravelingthroughwatersboatswoulduse odetectsubmarinesbelow  Echosounders ! greatly improved, to detect those guys: submarines …. but after the war - used in topographic mapping A similar thing happened again during the Cold War – looking for hiding places for the Soviet subs gave us great maps of the ocean bottom morphology off the coast of US and Canada Gravity measurements -> found large negative anomalies (weaker gravitational pull over ocean trenches) why there? In other areas (e.g. sediments) - not much progress …  1950s -1960s 1. Marine explosion-seismology (lots of explosives left after WWII...) -> settinginthemoffwouldsentoff thebottom shapes frequencies tounderstand allowingus studying sediments; later replaced by air-guns forreasuratheywillcause frequencys thesemethodshelpedusdiscover discovery of fracture zones! 2. Use of isotopes => e.g. paleotemperature, by Cesare Emiliani – father of paleoceanography.  1970s -current Exam tellus somethingfromthecurre Explain 1. Deep ocean drilling samplesfromoceanbottens abilitytoget 2. Submarine technology Underwaterveicals 3. Satellites (GPS and platforms for instruments) 4. Many centres of marine geology research Universitys 5. Large international multi-year programs diffrentExpositions 6. Increased use of computers for modeling complex ocean processes (local and OGCMs)  Deep Ocean Drilling In 1968: Deep Ocean Drilling Project (DOCP) The Glomar Challenger, a unique The Joides Resolution can handle drilling vessel 122 meters long, over 9.1 kilometers of drill pipe could manage about 7.6 kilometers and operate safely in heavier seas of drill pipe. Provided, among and winds than the Glomar others: dating basal sediments on Challenger could: 2000 deep-sea transects away from the Mid- cores from major geological Atlantic Ridge. features; total of 322 km of cores: jump-started paleoceanography! From 2013: International Ocean Discovery Program (IODP) using the Joides Resolution and the Chikyu (drilled 7.7km below the sea level) 16-9-8 Modern oceanographic research includes: 1. More international efforts because of the cost and scale of research. 2. Modern tools: Underwater vehicles (submersibles, ROV, AUV) for deep ocean exploration. Remote sensing from satellite platforms for large-scale, wide- area investigations. Supporting technologies  1. Collecting samples of the sea floor Started in XIX century with 1. Bottom dredges scrape the sediment and collect material in a wire or canvas bag. collects Rocks Shells somesedimentsthat are stickey 2. Grab samplers take a “bite” out of the sediment covering the bottom. What can they sample and what they can’t? Goodforsediments butnotasgoodforrock Rockmaystick theclawopenloosingeverything 3. Gravity corers use a heavy weight to drive a core barrel into a soft bottom - You use the winch to lower the corer on cable line - You place it one the bottom - When cable line relaxes, the heavy weight drives the core barrel into the sediment. - Enough to get ca. 1.5-2 m deep core - What do we need if we want to sample deeper? Youwouldneed a pistoncorer  4. Piston corers: mgy or on a gym how it works Able to take a much longer core than a gravity corer: the stackline is in controle When the pilot corer touches the bottom, it releases the slack line This makes the weighted barrel to free-fall, and drive itself deep into the sediment with much more momentum therefore: deeper, than a gravity corer “piston” is not the reason for the deep sampling, but helps to preserve the sediment layering in the long tube The longer the corer tube – the deeper into sediments it can penetrate: That’s why Woods Hole has one that takes – 50 m long cores! Note: in the deep ocean, the sedimentation rates are typically 30m/mln yrs, so 50 m would get you >1.5 mln years But there are places where sedim. rates as low as 0.1m/mln years… => which extends the time-line much more…  If want even LONGER sediment cores, and/or to drill into the crust: Deep ocean drilling! The ship has to be in one place - GPS + powerful horizontal thrusters – still drilling activities are limited when the weather is bad …  Submersibles, ROVs Submersibles – here: Alvin ROVs Can’t core sediments, but may have manipulators for collecting rocks and organisms, May have also suction to collect surface sediments Pros and cons of submersibles vs. ROVs ?  2. Remote sensing a) From satellites and other flying platforms (planes, helicopters) Most important geological (and physical) oceanography instrument: The TOPEX/Poseidon i. Altimeter: satellite launched by Tocating attitude NASA in 1992 has provided detailed, - Name: “measuring altitude”– how the satellite accurate data on the level above the sea surface of the sea surface. Courtesy NASA/JPL-Caltech - Able to measure to within a few cms (!) vearyaccurate - Information on marine geology and physical oceanography  How is this Bottom topography from a satellite possible ? bSencing c of Remote This is how: - A seamount attract the water haveapileofless o ence creating the local ifYou sea surface mound less dencesaycrustwenifit was less the wouldbemorelocalized dence effect then if it wascrust - A trench or I depression -> local depression If rocks BELOW the seafloor are denser or less dense than surrounding rock they would a (wider) mound or depression So the measured height of the sea at a given location depends on: 1. Gravimetric anomalies (sub seafloor structure) 2. Bottom topography 3. Physical oceanography (ocean currents, waves, winds, tides) How can we separate these signals? “1” from “2” – spatially: the influence of “1” spreads wider “1” and “2” - from “3” – temporarily: physics drivers fluctuate over time, so when you take the long term average – they mostly cancel themselves out – so what’s left – is the unchanging geological signal What’s for one oceanographer: “noise”, for another is a “signal” …  ii. Optical sensors Measures lightreflected fromsurface Could use the whole spectrum of light => photography WillIdentify - coastlines - suspended sediments - Very shallow water bottom topography (if more than few (Landsat, Mississippi Delta) 10s deep – you can’t see the bottom) -Or record only a few wavelengths: SeaWifs, CZCS etc… Measure the ratio of these wavelengths, since different wavelengths are differently absorbed by what’s in the water: - Concentration of suspended sediments - Concentration of dissolved matter (Gelbstoff = “yellow stuff”) bythecoasttheyaremoredominatedbysediments usually stuffbiological Yellow matter -Conc. of chlorophyll: proportional to algal concentration -> source of organic sediments b) Sounding equipment (to study the surface of the bottom) Deployed from ships, towed or mounted on AUVs A number of acoustic instruments to measure the morphology of the bottom 1. Single beam echo sounding 2. Side-scan sonar (forward looking) 3. Synthetic aperture sonar (SAR) 4. Multi-beam echo sounders (MBES) 1. Single Beam Echo Sounding signal sent willbounce off seabed show data structural Result – a line along the path of the instrument the lighterthecolorthe moredence 2. Side-scan sonar: no longer a line but one or two swaths thesignalcreates theshadow thesignalcan'tgothrough theobject making ashade 3. Synthetic Aperture Sonar illuminating the same spot on the sea floor with several pings from different positions as the sonar moves 16-9-8 thesynthesisedviewofwhatitlookslike  get Why the name? “Aperture” in photography refers to the opening of a lens's diaphragm; here: used to describe the area of a sensor collecting the signal By hitting the same target from several angles => it is as if it was a stationary sonar with a much larger aperture 4. Multi-beam echo sounders (MBES) - more than 100 beams - each ~1° wide or less - wide swath (angular sector ~120 ° or more) Examples of Multi Beam images: c) Sounding equipment - looking beneath the seafloor: Seismic surveys sound source - typically: air-guns air guns are loud (up to 255 dB) and have low frequency (0- 200 Hz) – the best penetration of the bottom sensors: aligned into 2-5 km long (streamers) What is Seismic Surveying? higherfrequencywilltravelless distancebut more Peroice Lowfrequencywill travelfarther butlessPersica “TWT” = The elapsed time for a seismic wave to travel from its source to a given reflector and return to a receiver at the Earth's surface e.g. looking for places where the oil may get trapped e.g. salt domes 3. Supporting technologies - GPS! Position - Computers (modelling, analysis of the seismic signals) - Isotopic analysis Pateoclimet - Sediment traps - Buoys to helpwith Physics Some Bio - Etc.