There are two forms of production in marine ecosystems. The more widely used and important is photosynthesis, which we all know, is the metabolic pathway that converts light energy into chemical energy. Phytoplankton, the main focus of my EOSC 470 course (the one that this test is for) mostly use photosynthesis as a way of feeding themselves, earning themselves the name photoautotrophs. Another mode of primary production is chemosynthesis. Chemosynthesis is the conversion of carbon molecules and nutrients into organic matter to form energy by way of oxidation of inorganic molecules such as hydrogen gas or hydrogen sulphide or methane.
There are some hydrothermal vent communities that live in absolute darkness and live by converting molecules into energy. It's very warm close to these vents compared to the surrounding ocean - about 23 or 24 degrees. The primary element for these organisms is sulphur and the main precipitate of hydrogen sulphide is fine black powder. Makes the vents look like black smoke chimneys underwater!
The equation for photosynthesis (simplified) is as follows: 6 CO2 + 6 H2O + photons → C6H12O6 + 6 O2 + 6 H2O
carbon dioxide + water + light energy → glucose + oxygen + water Photosynthesis has two stages, one light dependent and the other light independent.
Some organisms are anoxygenic in that they don't produce oxygen with photosynthesis. Some purple and green bacteria are examples of organisms that don't.
Light is probably the most important parts of a marine system. Light drives primary production in the layers of the ocean where light reaches. Sunlight is the energy that drives photosynthetic reactions. In light reactions, water is split and this produces protons, electrons and water. These electrons are used in the electron transport chain in photophosphorylation of photosynthesis. Photophosphorylation is the process that produces ATP using light energy, a fundamental energy unit. All organisms use ATP, it is the energy currency of life.
Water splitting is also know as evolution of oxygen. Water splitting is the only reason we have oxygen in the atmosphere.
Cyanobacteria are the only bacteria that produce oxygen during photosynthesis. The Earth’s primordial atmosphere was anoxic. Organisms like cyanobacteria produced our present-day oxygen containing atmosphere.
The most ancient form of photosynthesis contained photosystem I only. There was no evolution of oxygen. Water splitting came with photosystem II. H20 is endlessly abundant and therefore, there was an abundant supply of electrons to fuel ATP production and photophosphorylation after the evolution of photosystem II.
Phytoplankton are also a link between atmospheric and geologic carbon (C) as they transport it to the sea floor when they move through the water column (sinking ie: carking it). The ocean floor has a lot of carbon, around 38,000 Pg of it. Although this isn't comparable to the amount of inorganic carbon and organic carbon in continental crust, it is still a lot higher than the estimated 700 Pg of C in surface waters and the 600 Pg of CO2 in the atmosphere.
Ocean ecosystem are formed by the interaction of chemical, biological and chemical interactions. There is the physical forcing element (solar input) which controls heat, wind, evaporation/precipitation and light; this interacts with both Ocean ecosystems (biomass productivity and species composition) and the chemical environment (salinity, nutrients and gases).
Ocean temperature is regulated by incoming solar radiation and can vary seasonally. In general, areas with relatively cooler temperatures are areas of upwelling. Coastal upwelling is the best known as it supports some of the worlds most productive fisheries. Areas of coastal upwelling include western South Africa, off the coast of Peru, the Arabian sea and eastern New Zealand.
Other types of upwelling are equatorial upwelling and southern ocean upwelling.
In the case of equatorial upwelling: nutrient rich water is upwelled from below and causes a band of nutrient rich water and consequently, a band of phytoplankton abundance. Water wells up at the equator because of diverging surface waters due to ekman transport (coriolis effect) and diverging wind currents and surface ocean currents. The water from down below wells up to replace the water at the surface resulting in a band of cool, nutrient rich water. Waters with low nutrient levels and correspondingly low phytoplankton biomass are the location of large, open ocean gyres.
Southern ocean upwelling: upwelling around Antarctica due to strong westerly winds. The water that wells up is extremely old and nutrient rich.
This brings me onto thermoclines, haloclines and pycnoclines.
Oooh yeah.
First up, thermoclines in different latitudes. Because this midterm is likely to ask me to compare different oceanic regions. We've done a lot of pacific vs artic or arabian vs equatorial pacific work, not necessarily just for thermoclines and the like but also for other things such as PAR depth profiles (looking for the depth that photosynthetically active radiation goes to and how it varies with depth) and irradience at surface and in deep water yadayada. It's all very interesting but so hard to remember!
So thermoclines.
Surface currents move water in the uppermost layer of the oceans. Over most of the oceans (except at high latitudes), a thin layer of warm surface waters overlies the much colder deep waters. The zone of abrupt temperature decrease, as we pass from surface to deep water, is called the
There is little variation in the thermocline at high latitudes and the thermoclines at mid and low latitudes usually look that same in terms of change, except for the starting surface temperatures.
In some areas, there is seasonality in the structure of the thermocline. At high latitudes, there is low to no seasonality because of not much variation in surface ocean currents. A seasonal thermocline develops at the approach of summer in mid latitudes as surface waters warm up. It affects depth as well as starting temperature.
On to salinity, yay! A halocline is a measure of salinity in a water column, a strong vertical salinity gradient. The upper layer of water, the surface waters, again usually has a uniform salinity profile because of mixing from surface currents and wind currents. Salinity also relates to density as the more salty water gets, the more dense it is. Depending on the latitude, the halocline either increases or decreses.
In low latitudes (ie nearer to the equator) there is a decreasing halocline because of excess evaporation at the surface meaning there is more salt in the mixed surface layer than in the layers below.
At high latitudes, the halocline increases with depth.
Now for density: Density is inversely proportional to temperature and propotional to salinity. The densest water is cold and salty, the least dense water is light and fresh. The ocean is separated into layers by density. And this stratification of density limits vertical exchange in water columns between surface waters and deep ocean. This also is related to the amount of nutrients at the surface. As a general rule, there are few nutrients in surface waters because of phytoplankton using it up and more nutrients in deeper ocean waters. Where there are high nutrient concentrations in surface waters, these waters are generally cold with deep water transport to the surface (upwelling) and surface currents. Increasing stratification affects the transport of nutrients from deep water to the surface. Phytoplankton use up all the nutrients at the surface and the limited availability of nutrients at the surface drive ecological succession. Who can persist at the lowest nutrient levels?
At high latitudes: the density follows the halocline. There is weak stratificatin at high latitudes.
At low latitudes, it's the same story. The density follows the halocline: (strong stratification). The lightest, low density water floats above the higher density water.
At high latitudes: the density follows the halocline. There is weak stratificatin at high latitudes.
And now for something completely different!
Going on from the discussion of nutrient levels, diatoms are the first contributers to what is know as the north atlantic bloom. Diatoms thrive in regions with high nutrients but the ultimate phytoplankton is the prokaryote, the cyanobacterium. Cyanobacteria can persist in low nutrient levels. In subtropical regions where there are low nutrient levels (and high stratification limiting transport between layers), there will be high levels of cyanobacteria.
The type of phytoplankton in the surface few layers of the ocean, where phytoplankton are making the best use of light, dictate the composition of the sediments in the ocean floor below. Diatoms, for example, are make out of silica and there is often a high % of sedimentary opal beneath regions with high numbers of diatoms.
Diatoms are crafty buggers. Even though they can only really thrive in high nutrient waters, there is a global trend that means the oceans favour diatoms. Plankton abundance has been changed and one theory says it has happened by the following steps:
There is increased oceanic turbulence. The ocean is shifting towards diatom dominance
1) Significant global cooling 60 million years ago and formation of ice caps
2) Because of this, latituditional temperature gradients were increased. From ice caps - extremely cold, to tropics/equator - very warm.
3) this in turn increased wind speeds and convection
4) This in turn increased turbulence which
5) increases nutrient abundance in the upper layers of the ocean - nutrients from the bottom of the ocean and getting to the surface
6) the locking up of water in ice caps decreased sea levels so coasts were exposed and caused erosion of surfaces and the increased introduction of material to the water
7) this increased nutrient delivery to oceans
8) higher nutrient levels favour diatom growth.
That's just one theory though!
Something new again: The coriolis affect!
The apparent deflection of water and air masses travelling across the rotating earth. The deflection occurs to the right in the northern hemisphere and to the left in the southern hemisphere. Coriolis deflection also affects moving water. The net transport of water is about a 90 degree offset from the prevailing wind direction.
This is known as Eckman transport of surface waters, booyah! Transport of water occurs perpendicular to prevailing winds.
Because of this deflection, oceanic gyres (big mounds of water and the flow around them), are clockwise in the northern hemisphere and anticlockwise in the southern hemisphere.
A quick note about light - in the open ocean, there is more blue-green light available. So open ocean phytoplankton species are going to be more adjusted to blue-green light than coastal species. Coastal waters are where blue light is strongly absorbed and green light is more readily available. This gives rise to the different colours in ocean waters. The light that is being reflected is the spectrum that is more readily available. Coastal waters are greeny and open ocean waters are bluey.
This stresses the importance of light quality. While quantity is important for growth, quality is as well. Some phytoplankton species can only use certain parts of the light spectrum.
Water molecules are the culprits for the lack of red light, they strongly absorb red light.
For my reference (in hopes I will remember later on this morning:
550s - 600s = longer wavelengths, red type pigment (absorbs red light)
low 400s = shortwave lengths, blue type pigment (absorbs blue light)
There is a lot more to be studied but I think I will have to stop there for this post, it's getting heaps long! So much more to add yet so little time to write and remember it!
Hope that was as exciting for you as it was for me :p
Going on from the discussion of nutrient levels, diatoms are the first contributers to what is know as the north atlantic bloom. Diatoms thrive in regions with high nutrients but the ultimate phytoplankton is the prokaryote, the cyanobacterium. Cyanobacteria can persist in low nutrient levels. In subtropical regions where there are low nutrient levels (and high stratification limiting transport between layers), there will be high levels of cyanobacteria.
The type of phytoplankton in the surface few layers of the ocean, where phytoplankton are making the best use of light, dictate the composition of the sediments in the ocean floor below. Diatoms, for example, are make out of silica and there is often a high % of sedimentary opal beneath regions with high numbers of diatoms.
Diatoms are crafty buggers. Even though they can only really thrive in high nutrient waters, there is a global trend that means the oceans favour diatoms. Plankton abundance has been changed and one theory says it has happened by the following steps:
There is increased oceanic turbulence. The ocean is shifting towards diatom dominance
1) Significant global cooling 60 million years ago and formation of ice caps
2) Because of this, latituditional temperature gradients were increased. From ice caps - extremely cold, to tropics/equator - very warm.
3) this in turn increased wind speeds and convection
4) This in turn increased turbulence which
5) increases nutrient abundance in the upper layers of the ocean - nutrients from the bottom of the ocean and getting to the surface
6) the locking up of water in ice caps decreased sea levels so coasts were exposed and caused erosion of surfaces and the increased introduction of material to the water
7) this increased nutrient delivery to oceans
8) higher nutrient levels favour diatom growth.
That's just one theory though!
Something new again: The coriolis affect!
The apparent deflection of water and air masses travelling across the rotating earth. The deflection occurs to the right in the northern hemisphere and to the left in the southern hemisphere. Coriolis deflection also affects moving water. The net transport of water is about a 90 degree offset from the prevailing wind direction.
This is known as Eckman transport of surface waters, booyah! Transport of water occurs perpendicular to prevailing winds.
Because of this deflection, oceanic gyres (big mounds of water and the flow around them), are clockwise in the northern hemisphere and anticlockwise in the southern hemisphere.
A quick note about light - in the open ocean, there is more blue-green light available. So open ocean phytoplankton species are going to be more adjusted to blue-green light than coastal species. Coastal waters are where blue light is strongly absorbed and green light is more readily available. This gives rise to the different colours in ocean waters. The light that is being reflected is the spectrum that is more readily available. Coastal waters are greeny and open ocean waters are bluey.
This stresses the importance of light quality. While quantity is important for growth, quality is as well. Some phytoplankton species can only use certain parts of the light spectrum.
Water molecules are the culprits for the lack of red light, they strongly absorb red light.
For my reference (in hopes I will remember later on this morning:
550s - 600s = longer wavelengths, red type pigment (absorbs red light)
low 400s = shortwave lengths, blue type pigment (absorbs blue light)
There is a lot more to be studied but I think I will have to stop there for this post, it's getting heaps long! So much more to add yet so little time to write and remember it!
Hope that was as exciting for you as it was for me :p
.jpg)
