Marine Nutrient Cycles

Question 1

Ratio of nutrients in the ocean

Answer 1

C:N:P
106:16:1

Question 1

carbon dominatesocean diversity

Answer 1

98% carbon in ocean is in oxidised form co2
Photoautotrophs (phytoplank) are hence responsible for producing most of the organic carbon

Question 2

Nutrients cycle

Answer 2

Oxygen and nutrient distributions are closely linked to photosynthetic activity in the surface ocean. Primary surface carbon production happens mainly in coastal zones due to upwelling and mixing

Question 3

What are examples of Seafloor carbon stocks

Answer 3

Transitional vegetated zones, Non vegetated sea floor, vegetated sea floor, salt marsh, bare sediment, maerl beds, kelp forests

Question 4

How do vegetated marine habitats play major roles in nutrient cycling

Answer 4

These habitats generate biomass by photosynthesis, this enters the sediment below when it dies. They also trap loads of sediment and organic matter floating in water column as they collide with their 3D structures and settle.
50% of organic matter (OM) buried in seagrass beds is from external sources (dead plankton, algal material and detritus).
The 3D structure and density of these environments plays a key role in their contribution to nutrient cycle

Question 5

how are estuaries key in marie nutrient distribution

Answer 5

Source of nutrients such as
Nitrogen and Phosphorus to the oceans so the
waters are rich in both.
Combination of sediment
runoff, material produced by plants and that produced by phytoplankton creates a diverse ‘soup’ of Organic Matter

Question 6

Organic matter production in the oceans

Answer 6

Fertility of the sea differs greatly depending on season and location.
Estimates place costal season par with forests and upwelling zones/deep estuaries equal to that of rainforests.
Physically, wide continental shelves over which the waters are shallow are hotspots for production (wake action is also key).

Question 7

What are the two major disruptions to ocean nutrient cycles

Answer 7

Ocean acidification
Excessive nutrient addition

Question 8

What is ocean acidification

Answer 8

CO2 dissolves readily at the air-water interface of oceans to become part of total Dissolved inorganic carbon (DIC). This DIC exists in 3 forms: Carbonate ion (CO3-), bicarbonate ion (HCO3-) and aqueous CO2 (CO2[aq]), which includes Carbonic Acid (H2CO3).
Currently, CaCO3 sat in ocean horizons is buffering ocean CO2 uptake and encouraging shell formation. Equatorial seas being richest in Aragonite.
Predictions suggest that at 560-900 ppmv, large areas of the Southern Ocean will be undersaturated

Question 9

What is excessive nutrient addition

Answer 9

Excessive nutrient addition can result in hypoxic zones (Ocean Hypoxia is the third threat to global oceans). Along with Sea surface temperature (SST) increases and Ocean acidification, hypoxia is becoming an increasing threat to ocean functioning
* Coastal hypoxia is triggered by nutrient addition
* Open-ocean hypoxia can be triggered by shifts to currents, SST increases and hence, increased stratification. These two are also intrinsically linked because coastal seas fuel deep ocean microbial communities.