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BIO262 - oceanography > nutrients > Flashcards

nutrients Flashcards

1
Q

2 things that limit phytoplankton growth

A
  • nutrients
  • light
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2
Q

what is usually the growth-limiting nutrient for phytoplankton

A

nitrogen
- But Si, P and Fe can also be limiting

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3
Q

what does N exist as in marine environments

A

Nitrate (NO3-), nitrite (NO2-) or ammonium (NH4+)

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4
Q

what must be recycled within the system to sustain primary production

A

nutrients - can be done through multiple processes and pools

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5
Q

top 3 most concentrated element / nutrients in seawater

A

silicon (Si)
nitrogen (N)
phosphorus (P)
SiNP

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6
Q

examples of Macronutrients + Micronutrients in seawater

A

Macronutrients:
- Nitrogen - NO3- and NH4+
- Phosphorus - PO43-
Micronutrients:
- iron - required for photosynthesis - very abundant on land, not in seawater

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7
Q

what’s the Redfield ratio

A

the ratio that the average elemental composition of phytoplankton follow (general guideline) - means phytoplankton need nutrients in specific proportions for optimal growth
- 106 C: 16 N: 1 P
- 106 C: 15 Si: 16 N: 1 P (for diatoms)
- Species that live in the water collum have evolved to these ratios
- Many phytoplankton species do exhibit flexible internal elemental composition

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8
Q

what does the oxidation number of nitrogen tell us

A

we can determine whether it is an oxidation (number goes up -) reaction or a reduction (number goes down +) reaction
- if oxygen was taken away from a nitrate ion, the nitrogen would have a charge of +5 aka missing 5 electrons

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9
Q

what is Nitrification and what does it require

A

Converting ammonium -> nitrite -> nitrate (Both sensitive to light)
- bacteria Nitrosomonas and Nitrobacter
- oxygen

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10
Q

what is Denitrification and what does it require

A

Converting nitrate -> nitrogen gas
- denitrifiers bacteria - break down the nitrate present in the water collum and use it to power their respiration
- low oxygen
- energy

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11
Q

is energy required or released when oxidation number of N increases

A

released

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12
Q

is energy required or released when oxidation number of N decreases

A

required

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13
Q

what is Nitrogen fixation and what does it require

A

Converting nitrogen gas -> ammonium (something that is biologically available)
- microorganisms called diazotrophs e.g Trichodesmium - prevents o2 getting in to give an anoxic environment
- enzyme nitrogenase - very sensitive to oxygen
- anoxic environment

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14
Q

why is Nitrification important

A

For primary production (photosynthesis) to happen, need inorganic form of nitrogen

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15
Q

what equation looks at the rate of phyto nutrient uptake (V)

A

Ks + S
- Ks = half-saturation constant
- S = concentration of dissolved inorganic nitrogen

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16
Q

what do the differences in Ks and Vmax lead to as for light

A

species successions

17
Q

how will Changes through the year (therefore different nutrient concs) mean we are going to get a change in the species present

A

different species are able to make use of the different nutrients

18
Q

what’s the F-ratio look at

A

Looks at where the nitrogen is coming from – ratio of the uptake of nitrate relative to the total uptake (nitrate + ammonium)

19
Q

f-ratio equation

A

(Vnitrate + Vammonium)

20
Q

what’s New production

A

phyto growth fuelled by new N, usually NO3- -> high f-ratio
- NO3- enters SML from rivers, run off or below thermocline

21
Q

what’s recycled production

A

phyto growth fuelled by NH4+ -> low f-ratio
- NH4+ is remineralized within the SML by zooplankton

22
Q

explain Thermohaline circulation

A

circulation that is not driven by wind but density gradients from temperature + salinity variations instead
- Drives a lot of the water around the world
- During sea ice formation, salt is expelled (brine rejection) so sea ice is mostly fresh, and the surrounding water gains additional salt - increases density
- The cold water that forms in north sinks down (as dense as water gets)
- Cold water gets pushed south + upwards as its warming
- Other water has to move to make way for the cold water + the surface water that has sank has to get replaced – global pump
- Very slow water movement; average time to complete one cycle ~1,000 years
- Global redistribution of large amount of heat; important for long-term regulation planet’s climate
- Global warming decreases sea ice formation, hence disrupts THC

23
Q

Two of the major water masses in Thermohaline circulation (THC)

A
  • North Atlantic Deep Water (NADW)
  • Antarctic Bottom Water (AABW)
24
Q

what happens to oxygen and nutrient conc in deep water mass flow pattern at a depth of 4000 m

A
  • Oxygen concentration decreases as the water mass travels due to oxygen consumption for remineralisation (Note: The deep ocean is cut off from the atmosphere)
  • Nutrient concentration increases as the water mass travels due to nutrient release from remineralisation
25
Q

what’s the dominant form of phosphorus used by phytoplankton and where does it come from

A

Inorganic form (PO43-)
- Comes from terrestrial systems
- Don’t get as much recycling as nitrates

26
Q

Silicon characteristics

A
  • Less reactive – tends to sit in water collum for long time
  • Needed by diatoms and other organisms with siliceous components
  • After death the biogenic silica sink to the deep ocean
  • Because of slow dissolution, biogenic silica may become part of opal in sediment
27
Q

why are micro nutrients “Micro”

A

because they are needed in only a small amount - but when their concentrations are below what is needed, they can be the limiting factor

28
Q

what are High Nutrient Low Chlorophyll regions and what do they suggest

A

In some parts of the ocean nitrate concentration is high but chlorophyll is lower than expected
- suggests phytoplankton are under-utilizing the available nitrate

29
Q

examples of High Nutrient Low Chlorophyll (HNLC) regions

A

Subarctic Pacific
Equatorial Pacific
Southern Ocean

30
Q

Possible explanations for HNLC

A
  • Grazing keeps the standing stock low
  • Phytoplankton growth is limited by something else
31
Q

what does John Martin’s iron hypothesis suggest

A

Suggests phytoplankton growth in the HNLC regions is limited by the supply of iron
- Martin’s famous quote: “Give me a half tanker of iron and I will give you another ice age”
- Increase iron supply will stimulate phytoplankton bloom
- Increased photosynthesis will draw down extra atmospheric CO2
- Upon bloom termination phytoplankton carbon will sink to the deep ocean
- Slow thermohaline circulation means that the carbon will be kept out of atmospheric circulation for a very long time
- If enough CO2 is removed, we may reverse the global warming trend

32
Q

explain IronEx II experiment

A
  • Got a large vessel and filled it with shipping containers full of SF6 + iron sulphate (biologically available iron)
  • Drove boat to high nutrient, low chlorophyll area and offloaded this off the boat and repeated over a course of a few weeks
33
Q

what were the results of the IronEx II experiment

A
  • Shift in phyto composition: start = Prochlorococcus & Synechococcus (tiny bacteria – best at making use of a limiting nutrient), end = diatoms
  • Photosynthetic competence increased Fv/Fm
  • Depleted surface waters of NO3- (macronutrients)
34
Q

what can we conclude from the IronEx II experiment

A
  • Iron limits phytoplankton growth in the Equatorial Pacific
  • Explains HNLC
35
Q

how does iron enter the oceans

A

naturally gets from the land to open ocean via dessert – dust that contains loads of iron gets blown from land to sea

36
Q

what is Eutrophication

A

Excessive nutrient input into waters leads to environmental problems

37
Q

Hypoxia meaning

A

a condition when oxygen concentrations fall below the level necessary to sustain most animal life (ca. 2 mg O2 l-1)

38
Q

how do Nutrients + pollutants get into coastal waters and cause eutrophication

A

from anthropogenic activity - land run-off (agriculture), industrial waste, Burning organic fuels e.g. car use releases nitrogen compounds into atmos where it dissolves into clouds and rains down
- Areas of high populations are associated with high nitrate + nitrite introductions to these environments

BIO262 - oceanography (13 decks)

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