19. Marine Biogeochemical Cycles 2 Flashcards
Where is the oxygen minimum layer? Describe it
Usually around ~1000m depth
- oxygen decreases throughout first 1000m as it’s consumed by heterotrophic organisms (mixing at sfc)
- the oxygen min layer coincides with a nutrient maximum
The growth of the oxygen minimum zone outer layer is due to what?
- What will therefore likely happen to the OML in the future?
- due to weakened ocean circulation, which slows oxygen replenishment
- Will likely expand toward the surface by 5 to 50m
What might be the affect of an expanding OML on fishing?
May lead to more overfishing b/c low oxygen zones will likely expand upward toward the sfc, compacting O2-rich regions where the fish live
–> neg impact on the fishery industry
____ is a critical component of proteins, chlorophyll, and nucleic acids
nitrogen
T/F
Dissolves N2 (gas) is abundant in seawater
true
Can most organisms use the free N2 from atmosphere/ oceans directly?
no
Nitrogen must be “fixed” to be usable by most organisms
- “Fixed” N is bound with ____ and ____
- What performs N fixation?
O and H
specialized bacteria/ cyanobacteria
T/F
Oceanic regions are often N-limited
Why are coastal regions often more productive than the open ocean?
True
Coastal areas experience less N-limitation because of nitrate runoff from land, so more ability to be productive
Give the 3 main forms of N available for uptake by living organisms
Ammonium (NH4+)
Nitrate (NO3-)
Nitrite (NO2-)
In the deep ocean, most N is in which form?
NO3- (nitrate)
At upwelling regions, ___ is brought up, yielding higher production
NO3-
Give 2 ways N is lost from the ocean
- In anoxic sediments and low O2 regions of the ocean where denitrifying bacteria respire nitrate to N2 (lost to atmosphere)
- Where N-containing organisms and debris are buried in ocean sediments
Which ocean (pacific/ atlantic) has more dissolved oxygen? Nitrate?
Atlantic= more oxygen
Pacific= more nitrate
Phosphorus is used by all organisms to do what?
Link the parts of nucleic acids and in molecules that carry energy within the cell
Calcium phosphate is used in the formation of:
bones, teeth, & some shells
Silica (silicon dioxide) is used by several marine organism groups (list 3). Used for what?
- diatoms
- coccolithophores
- radiolarians
used to make their skeletons
How do phosphorus and silica enter the oceans? Where are they used by organisms?
Enter ocean in rivers and precipitation after weathering out of rocks
- used by organisms at ocean sfc
P is released in which form when organisms die?
- Decomposers convert it back to:
it can then be reused by phytoplankton/ bacteria
organic
inorganic form (phosphate)
Silica in shells is released when organisms die and is available to be reused as which form?
ionized, dissolved form, silicate
T/F
Phosphorus & silica have water column profiles similar to nitrogen
Describe it
True
- [low] at very surface, increases rapidly
- slowly decreases/ stabilizes with depth
Both phosphorus and silica cycles operate in 3 loops. Describe the 3
- rapid recycling occurs in daily feeding, death, and decay of sfc organisms
- slower loop occurs as bodies fall below the pycnocline and P & S escape downward into deep-ocean circulation
- may not be upwelled again for a 100s of yrs - Longest loop begins with P or S locked into rocks/ shells that become marine sediments –> sediment is subducted –> P and S re-enter system through volcanoes (could take millions of yrs)
Iron is used in very small quantities for what?
in reactions of photosynthesis, certain enzymes crucial to N fixation, & in proteins
Give 3 trace metals (other than iron) that are used by organisms in small quantities (mainly in enzymes)
zinc, copper, manganese
T/F
Organisms don’t need much Fe, so it’s rarely a limiting nutrient in the ocean (for phytoplankton growth)
false
organisms don’t need much Fe, but its [] in the ocean compared to N and P can sometimes be so low that phytoplankton growth is limited by Fe availability
