Oceans and Climate Change

• 50% of the human population lives within tens of kilometers from the oceans.
• The theme exemplifies the interdisciplinary nature of ocean sciences when considering the most important scientific questions facing contemporary human society.
• Environmental problems include:
  • Global climate change due to the greenhouse effect.
  • Acidification of the oceans.
  • Deoxygenation of the oceans.
• These problems are largely caused by the release of CO₂ into the atmosphere, mainly from burning fossil fuels.
• Gases like CO₂, CH4, and CFC in the atmosphere function like greenhouse glass.

Concentrations and Climate Change

• Since the Industrial Revolution, CO₂ concentration has steadily increased because of the burning of fossil fuels.
• In May 2023, the CO₂ concentration reached 423.3 ppm, over 50% above the pre-industrial level of about 280 ppm.
• The curve measuring CO₂ fluctuations showed annual oscillations measured directly in Mauna Loa, Hawaii.
• From 1960, data showed a long-term upward trend, increasing by about 3 ppm per year and expected to increase more.
• Average temperature of lower atmosphere is estimated to increase 1-2 degrees Celsius, with additional degrees in coming decades.
• Climate change may devastate:
  • Agriculture, causing less food.
  • The environment causing species extinctions.
  • Civilization.
• Sea level will rise from thermal expansion and melting ice which will inundate coastal lands.
• Some island chains may disappear.

Ocean Acidification

• Oceans absorb much of the CO₂ released by fossil fuel burning.
• This CO₂ forms a weak acid, increasing ocean acidity even though ocean waters are weakly alkaline.
• The rate of acidification is much faster than in Earth's past.
• Many species won't adapt to greater acidity.
• Ocean acidification may cause marine species extinction and marine ecosystem alteration.
• Species creating hard parts like skeletons and shells of CaCO3, like shellfish and pteropods, are at risk.
• Increasing coastal waters acidity in Pacific Northwest impact oyster larvae growth, affecting the oyster industry.
• Bering Sea pH decreased to 7.7, due to Alaska having cold water and high biological productivity, making it the most acidic part of the world ocean.
• Alaska king crab and pteropod populations are collapsing, impacting the food source for Bering Sea fishes like salmon.
• Acidification will cause major changes to the marine ecosystems.

Ocean Deoxygenation

• Widespread deoxygenation of the oceans is a recently recognized threat, caused by climate change and civilization.
• Civilization releases nitrogen and phosphorus, mostly from agriculture and sewage, into the oceans.
• Deoxygenating involves complex physical, chemical, and biological processes.
• There are 3 main layers of the ocean:
  • Surface layer of less than 200 m.
  • Pycnocline between 200 and 800 m where density changes rapidly; Pycnocline = Thermocline = Halocline.
  • Deep zone beyond 800 m.
• The surface layer is well mixed and exchanges gases with the atmosphere, determining its oxygen concentration.
• Deep-water layers are colder and mix slowly.
• Respiration by living organisms in deep-water removes water's oxygen and adds CO₂.
• Oxygen-rich surface water sinks at high, cool latitudes.
• This water moves slowly, losing oxygen and gaining carbon dioxide.
• Oxygen concentrations are high in the surface layer, while the oxygen minimum is just below the pycnocline zone between 200 and 1000m.

Climate Change Impacts

• Climate warming will reduce oxygen concentrations in surface layers, because less oxygen can dissolve at higher temps.
• Warming of ocean surface enhances temp differences between deep/surface layers:
  • Inhibiting vertical mixing between deep and surface layers.
  • Reducing cold surface waters sinking.
• There is prolonged time without atmospheric contact before surface layers can exchange gases.
• Warming ocean increases food production by phototrophy and supply of detritus to the deep, increasing oxygen consumption.

Oceanic Ecosystems

• Dead zones are caused by anthropogenic nutrients, from nitrogen and phosphorus.
• Dead zones reduce the amount of available oxygen in coastal and estuarine areas like Chesapeake Bay and the Gulf of Mexico.
• In dead zones, living organisms that cannot swim away die when these areas lose their oxygen.
• Oceans capture, store, and redistribute solar heat energy, integral to weather and climate.
• Oceans and the atmosphere act as a complex system that regulates climate and CO₂ concentrations .

Oceans and Origins of Life

• In early conditions with ultraviolet radiation and lightning, organic compounds were created from CO2, CH4, NH3, H2, and H₂O.
• Such compounds included amino acids that are the important building blocks for the complex molecules needed for life to exist.
• There are 3 ways these compounds could have been created:
  • On the surface of solid particles.
  • Deep within the Earth.
  • At hydrothermal vents.
• The compounds may have first reached the Earth in meteorites.
• All known organisms transport chemical substances dissolved in water.
• Water is essential to life.

Early Earth

• The earliest organisms were similar to chemosynthetic microbes from hydrothermal vents, deep within the Earth’s crust, characterized by temperature and pressure.
• At first, oceans were formed about 4 billion years ago.
• The atmosphere consisted mostly of N, smaller amounts of CO2 and CH4, and no O2.
• Later, photosynthetic microorganisms developed and split water molecules to build chemical compounds, releasing oxygen.
• Between 1 and 2 billion years ago, photosynthetic organisms changed the composition of Earth's atmosphere.
• Oxygen stabilized at 20%. Marine invertebrates appeared 700 million years ago, with hominids arriving 4 million years ago.
• The oceans and atmosphere reached approximately the same chemical compositions that they have today.
• Oceans played a major role in nurturing the development of life on Earth.

Earth History & Ocean Data

• Earth formed about 4.6 billion years ago.
• Animals existed on Earth for an extremely brief period and Homo sapiens existed for only a short time.
• Ocean and atmosphere reached dynamic steady state 1000 million years ago.
• Ocean sciences require data representation in a geographic context using maps or charts, graphs, and diagrams.
• To understand a graph, look at shape of line, curve and axes.
• Contour plots describe distributions of variables on flat surface.
• Plotted variables may measure sea level, height, and/or depth through topographic/bathymetric maps.
• Contours must connect themselves in a closed loop.
• Red means highest value while violet means lowest value in filled contour plots.
• Profiles use vertical exaggeration because ocean depth is 11 km and their widths are several 1,000 km; most profiles have exaggerations greater than 100 to 1.
• Latitude and longitude identify points on Earth. 0 longitude runs through Greenwich London, confirmed in 1851 and measured by time. Longitude couldn’t accurately be measured until the invention of the chronometer in the 1760s.
• The latitude and longitude can be used to draw maps.
• No projection preserves all characteristics and different projections are used for different purposes.
• The Mercator projection is widely used and preserves directions.
• The Goode's interrupted and Robinson projections are good at preserving relative distances and areas.
• MYA means millions of years ago.
• 5•10⁹ years is the age of the universe equivalent to 5 to the power of positive 9 factors of 10.
• Scientists use the International System of Units (SI).
• 7 base units:
  • Length (m)
  • Mass (kg)
  • Time (s)
  • Electric current (A)
  • Thermodynamic temperature (K)
  • Amount of a substance (mol)
  • Luminous intensity (cd)