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
___ is among the most abundant elements in earth’s crust.
Does this element dissolve in oxygenated seawater? What happens to it?
Fe
nearly insoluble in oxygenated seawater
- the little dissolved Fe that is present is highly reactive, sticking to particles & sinking to bottom of water column
Describe the general pattern for biogeochemical cycling of trace metals
uptake & recycling in the sfc ocean & regeneration (sometimes over long time periods) at depth
T/F
Fe & other trace metals exist in many different forms, but we don’t know much about them
true
redfield ratio=
ratio of major elements observed in the tissues of algae when macro-nutrients are not liming productivity
C:N:P= 106:16:1
The redfield ratio is observed in _____ that feed on diatoms & most ocean water samples worldwide
zooplankton
In oceans, is N or P generally more limiting?
N more limiting
Limiting factor=
a physical or biological necessity whose presence in inappropriate amounts (too large or too small) limits the normal action of the organism
T/F
Any factor required for life can become a limiting factor
true
List some limiting factors that are typical in the oceans
light
temp
dissolved nutrients
salinity
dissolved gases
acid-base balance
hydrostatic pressure
Explain the dominant factor limiting diatom growth (equator to poles)
at equator: iron/ nitrogen
poles: light
Explain the dominant factor limiting diazotroph growth (equator to poles)
equator: Fe
poles: temp
High Nutrient Low Chlorophyll (HNLC) Regions=
Give 3 HNLC regions
some areas in the ocean where photosynthetic production is relatively low even though the [] of major nutrients is high
North Pacific
Equatorial pacific
southern ocean
What limits production in HNLC regions?
micronutrient (eg iron) limitation and grazing pressures
T/F
Most of the ocean doesn’t experience limiting in major nutrients
false
large regions of the ocean are limited in major nutrients, exceptions are regions of upwelling
The western continental margins are an example of high or low productivity area?
high
- upwelling site
__% of biomass from euphotic zone decomposes before descending
90%
Differences in regional productivity can be due to:
- uneven distribution of nutrients
- changes in availability of sunlight
Give the range in values for productivity in oceans.
Where is it lowest/ highest?
1-4000g C/m2/yr
lowest= open ocean
highest= estuaries & coral reef ecosystems
What is the ocean productivity like at the tropics?
Intense thermocline prevents nutrient-rich water from rising to the sfc and productivity is low throughout the year
What is the ocean productivity like at the N. Temperate oceans?
nutrients rising to the sfc combine with spring/ summer sunlight to stimulate a plankton bloom
What is the ocean productivity like at the polar ocean?
a high and thin productivity spike occurs when the sun reaches high enough above the horizon to allow light to penetrate the ocean sfc
In the arctic, diatoms bloom in ___ and then ____ productivity follows
May
zooplankton (mainly small crustaceans)
T/F
Arctic productivity is higher than Antarctic
false
Antarctic slightly more productive
T/F
- NADW downwells near Antarctica
- Antarctic experiences a slight productivity decrease from UV radiation (ozone hole)
- false: NADW upwells near Antarctica
- true
describe the polar ocean productivity in the summer
- isothermal & nutrient-rich waters
- plankton remain near sfc & zooplankton aggregate in large #s to feed
- whales then migrate to feed on zooplankton
What is evidence of large zooplankton biomass in the polar ocean summer
fast-growing whale calves
In the tropical oceans, a permanent ____ is a barrier to vertical mixing
thermocline
Overall, the tropical oceans have a low rate of primary productivity due to a lack of ______.
Give 3 exceptions
nutrients
- areas of equatorial upwelling
- areas of coastal upwelling
- coral reefs: symbiotic algae which recycle nutrients within the ecosystem
Temperate ocean productivity is limited by which 2 things?
- seasonal availability of sunlight
- seasonal availability of nutrients
Describe light/ nutrients at the following times in the temperate ocean:
- winter
- spring
- summer
- fall
- winter low: many nutrients, little sunlight
- spring high: spring bloom as light increases
- summer low: few nutrients, abundant sunlight
- fall high: fall bloom as nutrients increase again
Compare the productive times of the tropic, temperate, and polar ocean
Tropics: generally low year round
Temperate mid-lats: spring & fall blooms
Polar: spring-summer peak
Give 2 major reasons to care about ocean productivity
- fisheries
- biological C pump and atmospheric CO2 sequestration
